THE TENTH EUROPEAN REGIONAL ASTRONOMY MEETING of the SAU Prague Czechoslovakia 24

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THE TENTH EUROPEAN REGIONAL ASTRONOMY MEETING OF THE SAU

Prague Czechoslovakia

24- 29 August 1987 THE TENTH EUROPEAN REGIONAL ASTRONOMY MEETING OF THE IAU

24- 29 August 1987 FOREWORD

This brochure includes abstracts of papers presented at the Tenth Euro- pean Regional Astronomy Meeting. The sequence of abstracts is alphabetical of the name of the first author within each Session or Workshop. The booklet is printed in offset, hence its quality depends on the quality of the typescripts submitted by the authors. Abstract received later than 20 May 1987 are not included in this brochure. They will be available under the title LATE ABSTRACT in the Registration Office. CONTENTS

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PS 1-3 Plenary Sessions 1 TS 1 Development of Solar Active Regions 3 TS 2 The Complex of Interplanetary Bodies 22 TS 3 Resonances in the Solar System 39 SW 1 Structure of Galaxies and Star Formation 47 SW 2 Rapid Variability of Single, Binary and Multiple Stars 74 CP 1 Ultraviolet Stellar Spectra 82 CP 2 Cosmology and Formation of Galaxies 85 CP 3 Modern Astrometry 88 CP Halley's Comet (Merged with TS 2) CP 5 High-Energy Astrophysics 90 CP 6 Active Extragalactic Objects 91 CP 7 Binary Stars 9* CP 8 The Sun (Merged with TS 1)

MAGNETIC FIELDS OF THE SUN AND STARS

V. Bumba

Astronomical Institute of the Czechoslovak Academy of Sciences 251 65 Ondfejov, Czechoslovakia

We summarize the main results obtained by the joint effort of solar and stellar physicists through the investigation of solar and solar type activities on the low- -mass main sequence stars. We demonstrate the basic role of magnetic field in this activity and the importance of its interaction with the convection and differential rotation of each star. We compile data obtained by ground-based optical, radio and space observations of these stars giving us ideas about the physical conditions in the stellar photospheres, chromospheres and coronae, their activity periodicities and relations of this activity to other stellar parameters. We discuss the possible depth of the dynamo action in the Sun and stars in its relation to the convective zone. We present some results of the method of direct stellar magnetic field measurements in comparison with various indirect evidences about the action of stellar magnetic fields. We show also some observed differences both between the sun- and star-spots, and plages, and we bring information concerning the stellar flares. Finally, to compare the main behaviour of magnetic fields on the Sun and stars and the characteristics of the solar and stellar activities, we bring some of our new observational results concerning the mutual relation of magnetic and other activities with differential rotation on the Sun. We also try to indicate the location and manifestation of solar dynamo action and the influence of convective motions on the development of solar activity from the distribution of solar magnetic fields.

Hipparcos - High Precision Astroaetric Data From Space M.A.C. Ferryman Astrophysics Division, European Space Agency ESTEC, Noordvijk, The Netherlands

The goal of the Hipparcos mission is an ambitious one - the creation of an astroaetric catalogue of some 120 000 stars, vith an unprecedented precision on each of the five astronetrie parameters of each star: the tvo positional components, the tvo proper Motion components and, the key to estimating distances within our Galaxy, the parallax. Vith the availability of these data, the astronomical community will be provided vith fresh and dramatic insights into many aspects of this fundamental branch of science. Astrometrists vill have at their disposal a vast quantity of accurate and homogeneous data which can be used to improve upon the present knowledge of the optical reference frame, and which vill provide a dense reference system for past and future ground-based observations. Astrophysicists vill be provided vith parallaxes and proper motions of not only a highly accurate but also a remarkably homogeneous nature. Less-veil appreciated by-products of the astroaetric measurements vill be a systematic search for and measurements of binary and multiple star systems, and about 100 high-precision photometric measurenents for each star distributed over the 2.5-year mission lifetime. The satellite construction is on schedule for launch by Ariane in July 1988. The payload has been fully manufactured, and laboratory tests indicate that in all key areas the technical specifications have been achieved, and that the predicted accuracy of about 2 milli-arcsec for each of the astroaetric parameters vill be met. The scientific consortium INCA has completed, on schedule, the construction of the part of the Input Catalogue necessary for satellite operations. Containing the list of all objects to be observed, this catalogue represents the high-priority scientific targets for observation, contains detailed data for each star contained in the catalogue (cross-identifications, astroaetric and photometric data, etc), and vill be of great value in its own right as a research tool. The other institutes collaborating vith ESA in the project, and responsible for the preparation of the entire data treatment, have operational simulations for all parts of the data analysis, and expect to be ready to treat the satellite data as it arrives from the satellite. The presentation and the full text of the paper vill provide an overviev of the scientific motivations for the project, an outline of the principals of the satellite operation, the satellite and predicted accuracy status, and a summary of the steps constituting the data reduction.

- 1 - REVIEW OF RESULTS ON HALtEY'S COMET

Jurgen Rahe

Since its recovery in 1982, Comet Halley was the focus of an unparalleled global scientific effort of exploration. Remote and in-situ measurements were conducted from the ground, from Earth orbit, from Venus orbit, from interplanetary space, and from within the comet itself. Many discoveries, such as the presence of an unexpectedly large nucleus or the abundance of organic material, have led to major changes in our ideas about the general nature of comets. In this report the results of the-various studies will be summarized.

THE PHOBOS MISSION Boris Valnfcek Astronomical Institute of the Czechoslovak Academy of Sciences 251 65 Ondfejov

The complex space experiment Phobos will consist of two space probes carrying more than twenty experiments each. The primary purpose of the mission, launched in June 1988, is the exploration of the Mars satellite Phobos and of the planet itself. Various methods are used, including landing on the satellite and activation of its surface minerals by laser beam. During orbiting around Mars, the atmosphere of the planet will be studied. The secondary purpose is to study solar activity during the flight from Earth to Mars, gathering informations on solar wind, interplanetary shock waves, and gamma bursts. Solar X-ray activity will be monitored and solar corona observed in X-rays; stereoscopic studies of the Sun will be made. The coordinator of the experiment is the Space Research Institute of the Academy of Sciences of the USSR, the other participants are from Austria, Bulgaria, Czechoslovakia, Finland, German Democratic Republic, German Federal Republic, Hungary, Poland, Sweden, Switzerland and ESA.

_ o _ TS 1 DEVELOPMENT OF SOLAR ACTIVE REGIONS

Microwave Emission Associated with a Moving Sunspot 12 3 C. E. Alissandrakis, F. Chiuderi-Drago and M. J. Hagyard 1. Section of Astrophysics, Astronomy and Mechanics, Department of Physics, University of Athens, GR 157 83, Athens, Greece. 2. Observatoire de Paris, Meudon, France and University of Florence, Italy. 3. NASA/MSFC, Ala. 35812, U.S.A.

High resolution microwave observations provide important diagnostics for the physical conditions and the magnetic field in the chromosphere-corona transition region and the low corona (Alissandrakis et dl, 1980). He have used force-free extrapolations of photospheric magnetic field observat? s from Marshall Space Flight Center to compute the total intensity and circular polarization of suns t associated emission from active region 2502 in the period June 13 to June 15, 1980. The computed emission was compared to high resolution observations of the same active region at 6.16 cm obtained with the Westerbork Synthesis Radio Telescope (Shibasaki et al, 1983). The most interesting aspect of this active region was the developement of a new spot between the preceeding and the following spots on June 14, which subsequently merged with the preceeding spot. The new spot was associated with enhanced emission, with peak brightness temperature in excess of 4X10 K. Our model computations are in satisfactory agreement with the observations of June 13. How- ever, they fail to reproduce the enhanced emission associated with the new spot on June 14, although they reproduce the observed structure of the circular polarization map. This indicates that the discrepancy is due to the physical conditions assumed, rather than due to the extrapolated magnetic field. We show that unrealistic values of the conductive flux are required to reproduce the observed total intensity. We suggest that the enhanced emission is of non-thermal nature, due to mildly relativistic particles accelerated in the process of sunspot motion.

References

Alissandrakis, C. E., Kundu, M. R. and Lantos, P. : 1980, Astron. Astrophys. 82, 30. Shibasaki, K., Chiuderi-Drago, F., Melozzi, M., Slottje, C. and Antonucci, E. : 1982, Solar Phys. 89, 307.

THE EVEPSHEO FLOW IN THE SOLRR PHOTOSPHERE, CHROMOSPHERE RNO CHROHOSPHERE-CORONR TRRNSITION REGION. 1 2 3 3 3 C.E. Rlissandrakis , D. Dialetis , P. Mein , B. Schaieder , and G. Siaon . 1 Section of Flstrophysics, Rstronoay and Mechanics, Departeaent of Physics, University of Rthens, Panepistimiopolis, Rthens 15783, Greece. 2 Rstronomical Institute, National Observatory of Rthens, P.O.Box 20048, Rthens 11010, Greece. 3 Observatoire de Meudon, D.H.5.O.P., L.R. 326, F-92190 Meudon, France.

Me have studied the height and time dependent characteristics of the Evershed flou in the photosphere, chromosphere and chroaosphere-corona transition region. Ha have used the Multichannel Subtractive Double Pass Spectrograph (MSDP) to obtain line of sight velocity aaps in H-alpha, the Heudon aagnetograph for aapping the photospheric velocity and magnetic field and observations obtained by the Ultraviolet Spectroaeter and Polariaeter (UV5P) on the Solar Maximum Mission CSMM> spacecraft to obtain line of sight velocities in C IV in sunspot regions. The observations arm practically simultaneous in the three atmospheric levels and cover three consecutive days (Sept. 28, 29 and 30, 1980>. Our emphasis uas on the large scale, quasi-stationary characteristics of the flow. The photospheric and chroaospheric aaps shou the uell known radial structure of the velocity field. In the photosphere the velocity is low above the umbra and shows a maximum above the penumbra. In addition to the reversal of the flow in the chromosphere both the characteristic scale of the flou and the velocity arc larger; the velocity maximum is locate outside the photospheric penumbra. In the chroaosphere-corona transition region there is a clear tendency for a chroaospheric-type Evershed effect. The flou is predominantly horizontal but a substantial upflow was observed above the central part of the umbra. The velocity is 5-10 tiaes greater than in the chromosphere, but the characteristic scale of the flow seeas the saae. The observations arm interpreted in teras of siphon flow.

- 3 - Intensity profiles in fluxtubes

J. Sanchez Almeida*1*, S. Solanki*2',-M, Collados'1', J.C. del Toro Iniesta1 '.

(1) Instituto de Astroflsica de Canarias (2) Institute of Astronomy ETH-Zentrum

The network and faculae are thought to be made of magnetic zones, with small filling factor, surrounded by the quiet photosphere (as reviewed by Stenflo, 1984). These "magnetic elements" cannot be observed directly with spectroscopic tools, because of their small sizes (less than O."2 if one associates them with faculae bright points; Mehltretter, 1974). We wish to present a method for reconstructing the intensity profile (I) form in the magnetic zone. It follows the same line as in Solanki and Stenflo (1984). As a starting point we use I and V (fourth stokes parameter, which comes only from magnetic places) of the whole facula and the I observed in the quiet sun. Filling factors, magnetic field strength and continuum ratio between magnetic and non-aagnetic photosphere are obtained indirectly. We need the Unno equations triplet Zeeman pattern, longitudinal field and two component model.

The method has been applied to some FTS data (Stenflo et al., 1984) with promising results. As the intensity contrast is unknown, which makes filling factor and continuum contrast imprecise, only the normalised I profile is obtained. The derivation of these profiles is the first step towards the modelling of a "magnetic element" atmosphere, fitting the "observed" I to a synthetic one.

References

Mehltretter, J.P.: 1974, Solar Phys. 3jS, 43. Solanki, S., and Stenflo, J.O.: 1984, Astron.'Astrophys. 140. 185. Stenflo, J.O.: 1984, Adv. Space Res. 4., 8. Stenflo, J.O., Harvey, J.W., Brault, j.w., and Solanki, S.: 1984, Astron. Astrophys. 131. 333. Unno, W.i 1956, Pub. Ast. Soc. Japan 8, 108.

CONNECTION OF THE LARGE-SCALE SOLAR MAGNETIC AND VELOCITY FIELDS WITH THE SOLAR ACTIVE PHENOMENA P. Ambroz

Astronomical Institute of the Czechoslovak Academy of Sciences, Ondfejov, Czechoslovakia

The paper characterizes the evolution, structure and areal distribution of the large-scale background magnetic fields in the solar photosphere. The direction of the horizontal streaming of the solar photospheric plasma was found. Active regions are formed mainly in places where the global circulation displays maximum vorticity. Fi- laments occur in the areas with a high value of velocity gradient perpendicular to the filament axis. Evolutionary characteristics of the selected active regions are described and the relationship between the weak background and the strong local magnetic fields is documented.

DOES THE LOCAL DYNAMO ACT IN SUNSPOT GROUPS?

V. Bumba

Astronomical Institute of the Czechoslovak Academy of Sciences, 251 65 Ondfejov, Chechoslovakia

On a series of magnetic maps showing the local magnetic field developments we demonstrate that their sunspot groups developing to reach higher types C, D, E etc., continue their magnetic development during the period of new magnetic flux addition' immediately after the first magnetically bipolar balanced stage. It is probably a magnetohydrodynamical process of magnetic field strengthening or a new magnetic flux generation. It is closely related to a specific singularity in the local magnetic field topology at the inner field boundary not far from the centre of the group, where the gulf of one polarity is compressed in-between the boundary curvature of the field of opposite polarity and where large radial velocities may be observed. This is the region, where new peaks of both the leading and the following polarities in a special orthogonal relation of the new to the old tubes of lines of force develop, where the greatest field gradients are formed. The flare frequencies and their significance correlate well with the degree of complexity of magnetic field topoloqv in this situation.

- 4 - HIGH FLARE ACTIVITY AND REDISTRIBUTION OF SOLAR GLOBAL MAGNETIC FIELDS

V. Bumba11, L. Hejna1^, L. Gesztelyi2^ 1) Astron. lnst. of the Czechosl. Acad. of Sci., 251 65 Ondfejov, Czechoslovakia Heliophys. Obs. of the Hungarian Acad. of Scie., H-4010 Debrecen, Hungary

We demonstrate that both in the global and in the scale of large and complex active region the high frequency of large solar flares is closely connected with the redistribution of the whole background magnetic field patterns. We compared the time coincidence of the structural disturbances of the Magnetic Active Longitudes (MALs) with the changes of flare numbers per Carrington's rotations during the years 1965-1980. We found that the disturbances of the normal course of the MALs correlated with the maxima and the mode of their distribution with the mean level of solar flare numbers. In the case of the last submaximum of the 21st cycle of solar activity, the second peak of which was represented by the white-light flare region of April 1984 /NOAA 4474/, we showed that its development was a part of a global process ip the solar atmosphere. It was accompanied by a complete reorganization of the MALs patterns and of the background field sector structure related to them. Even the restructurali- zation of coronal holes took place around the time of the maximum stage of the region's formation. In both cases, in the global just as in the local scales, we might follow the geophysical consequences of the entire reconstruction of global solar field amplified by the occurrence of many large flares.

ON THE COMBINED EFFECTS OF FLUID VISCOSITY AND ELECTRICAL RESISTANCE ON ATMOSPHERIC ALFVFlN WAVES L.M.B.C. Campos Instituto Superior T6cnico, 1D96 Lisboa, Portugal

We consider Alfv6n waves propagating obliquely in an atmosphere, subject to an uniform magnetic field of arbitrary direction, in the presence of viscous stresses and electrical resistance. The wave equation is solved exactly in the case of an isothermal atmosphere, for which the Alfv6n speed increases exponentially on twice the scale height and the dynamic viscosity increases exponentially on the scale height; the rate of ionization is assumed uniform, leading to a constant electrical dif f usiv.ity. The exact solution includes, as particular cases, those obtained before for Alfv6n waves in an isothermal atmosphere, in the non-dissipative case with vertical and oblique magnetic field, and in the case of resistive dissipation alone. The wave fields are expressed at all altitudes in terms of hypergeometric functions, which are used to plot the amplitudes and phases, for several combinations of wave frequency, horizontal wavenumber, inclination of the magnetic field to the vertical, and viscous and resistive diffusivities. It is shown that, for certain ranges of values of the parameters, intense localized dissipation of waves can occur. The present theory is compared vith the RLC-analogy, the resonance model and the phase mixing approximation.

VARIATION OF THE GRANULATION WITH THE SOLAR LATITUDE M. Collados, I. Rodriguez Hidalgo, M. Vazquez Instituto de Astroffsica de Canarias, Spain

It has been known, for a considerable time, th3t the C-shape of the bisectors of photospheric spectral lines and the position of their minimum, depend markedly upon the heliocentric angle of the observed region. Moreover, this dependence has proved to be different for the equatorial and polar diameters. Explanations such as the variation with the latitude of the granular characteristics or the existence of meridional flows are the most probable to give account of this assymetry. Thus, it becomes essential to analyse the properties of the granulation at different latitudes in order to select one of these alternatives. Bearing this purpose in mind, observations were carried out during the summers of 1985 and 1986, at the Observatorio del Teide (Tenerife), using the 40 cm. Vakuum Newton Telescope. We took photographs of the granulation in the continuum (with a filter centered at 550 nm. and FWHM 18 nm.), at different heliocentric angles along the rotation axis (N-S) and equator (E-W). Here we present the preliminary results of the possible latitudinal variation of granulation properties.

- 5 - Photometry of sunspots M. Collados, I. Rodriguez, B. Ruiz, M. Vazquez Instituto de Astrofisica de Canarias

Photoelectric measurements of sunspot and pore intensities were carried out during 1986 at the Observatorio del Teide using the 40 cm Newtonian Reflector and the KIS photometer. Quasi-simultaneously aureolae and high resolution photographs were obained. The following points are considered in this contribution. (A) Correction of the data for stray light effects. (B) Comparison of photoelectric and photographic measurments, making special emphasis on the influence of umbral dots. (C) Existence of a dependence size-intensity for small sunspots and pores.

PROPER MOTIONS OF NOAA REGIONS 3885 AND 3886 Jl-10 SEPTEMBER 1982/ G. Csepura and I. Nagy Heliophyiical Observatory of the Hwigarian Academy of Sciences, H-4010 Debrecen, Bwigary

Between 1-10 September 1982 there were two active regions on the north hemisphere of the Sun: the NOAA regions 3885 and 3886 in the vicinity of each other. They rotated onto the disc as developed sunspot groups. The first one /NOAA rgn. 3885/ was a return of the preceeding part of the Mt. W. group 18511. The rotational motion of the old, fragmented umbra was studied. The other sunspot group /NOAA rgn. 3886/ was a younger one, which showed a high flare activity. The connection between the proper motions of the sunspots and the flare occurrences were investigated.

FAR-INFRARED SOLAR IMAGES TAKEN FROM A BALLOON-BORNE PLATFORM C. Degiacotni*. F.K. Kneubuhl* and D. Huguenin** •Infrared Physics Laboratory, ETH, CH-8093 Zurich, Switzerland **Geneva Observatory, CH-1290 Sauverny, Switzerland

A review on far-infrared brightness-temperature maps of the solar atmosphere is presented. They have been taken with the aid of a 60 cm-diameter balloon-borne telescope at a height of 39 km in France. Three bandpass filters at the wavelengths 50 |tm, 80 |im and 200 |im of 6 to 10 >i bandwidth have been applied. The filters as well as the Au-doped Ge bolometer were cooled by liquid He. An observation on 30.4.83 represents the active sun, while one on 28.9.84 shows the quiet sun. The observations at the three wavelengths correspond to three different heights in the solar atmosphere at the transition of the photosphere and chromosphere. Over active regions, average temperature enhancements of 75 K to 250 K are observed relative to the inactive regions depending of the height in the solar atmosphere.

- 6 - MAGNETIC EDDY DIFFUSION AND THE PROBLEM OF SURGE FORMATION V. N. Oermendjiev Department of Astronomy and NAO Bulgarian Academy of Sciences, 72 Lenin Blvd., Sofia 1784, Bulgaria

The process of solar surge formation is studied by means of computer simulations on the base of a two-dimensional MHO model. It is assumed in the model that a small-scale magnetic field is penetrating as an eddy in a compressible initial plasma media with physical parameters near to those of the lower chromosphere. Com- puter simulations show that nonlinear effects lead to the formation of relatively denser and hotter "island structures". This phenomenon is discussed as a unifying link in magnetic and thermal mechanisms of surge formation proposed by different authors.

DEVELOPMENT OF SUNSTOT GROUPS RELATED TO THE SOLAR DIFFERENTIAL ROTATION DURING THE EARLY PERIOD OF A NEW SOLAR CYCLE L. Dezso and Agnes Kovacs Heliophysical Observatory, Hungarian Academy of Sciences, H-4O1O Debrecen, Hungary

The 'Debrecen Photoheliographic Results' beginning with the year 1977 (available from 1987) gives various kinds of position and area data of sunspots daily for a single moment, including all spot groups visible at least on two days. In addition, this catalogue also indicates the magnetic spot polarities and for each sunspot, wherever reasonable, a special number as a mark of identification. By these means, on the basis of about 1OO spot groups between 15 and 4O heliographic latitudes, special features of the spot activity have been studied. So, on the one hand, the diverse distributions of spot areas (separately for both the N and S polarity spots), on the other hand, the principal spot motions within the groups, as well as the local solar rotation in the regions of spot groups by means of tracers of spot positions have been determined. The most important new characteristics found are presented.

ON THE LONG-LIVED PHOTOSPHERIC GRRNULES. D. Oialetis, Th. Prokakis, E. Sarris and G. Tsiropoula. Rstronomical Institute, National Observatory of Rthens P.O. Box 20048, Rthens 11810, Greece.

He have studied the spatial distribution of the long-lived granules froa a population of 346 granules located in a photospheric region 37"x37". Our study is based on an exceptional sequence of photos taken by R. duller at the Pic du Midi Observatory on Hay 16, 1979. The high spatial resolution (better- than 0.4") and the long duration of the observational sequence (56 sin) in combination with the method used perait the accurate determination of the granule lifetiee and confira the validity of the obtained results. He have determined the lifetiae of all the granules situated in this rectangular photospheric region. For the determination of the eean lifetiae (13.5 ain) we have used a aethod recently developed < Rlissandrakis et al., 1987), that permits to define accurately the aean lifetiae froa photographic observations by using the survival function of the population under study. He coapare this result with previous •easureaents (Oialetis et al., 1986) in order to test the suggested relation between the granule mman lifetiae and the solar cycle. He conclude that there is no evident relation between the aean lifetiae and the solar cycle. Finally we have studied the spatial distribution of the long-lived granules. Rs long-lived granules we consider all the granules with lifetiae greater than the aean lifetiae of the population. He found that the long-lived granules arm not randomly distributed in the arma under study, but they arm located in well defined regions with aean length 8"-I0" and mman width 2"-4". This result seems to confirm our suggestion CDialetis et al., 1986) that there arm at least two families of granules as for as their lifetiae is concerned. He discuss the possible causes of the existence of regions characterized by slower evolutionary process.

References.

Rlissandrakis C.E., Oialetis 0., and Tsiropoula G.: 1987, flstron. flstrophys. 174, 279. Dialetis D., Maoris C, Prokakis Th., and Sarris E.: 1986, Rstron. Rstrophys. 169, 33C-

- 7 - LINEAR POLARIZATION OF RESONANCE LINES IN THE ABSENCE OF MAGNETIC FIELDS M. Faurobert Nice Observatory, B.P. 139, 06003 Nice Cedex, France

The linear polarization of spectral lines in the absence of magnetic fields, also called "resonance polarization", is observed in the solar spectrum. It is doe to the coherent scattering by the atoms of an anisotropic radiation field. This mechanism is the quantum counterpart of the Rayleigh scattering. The largest polarization rates (a few percent) are observed for the strong resonance lines, such as Cal (4227 A), Call H and K, NaOj (5890 A). The interpretation of those observations may provide information on the processes which take place in the non-LTE formation of the solar lines (coupling between atomic levels, partial frequency redistrjbotion) and it will be the basis for the determination of weak magnetic fields in the solar chromosphere by means of the Hanle effect. For strong resonance lines partial frequency redistribution effects are known to play a crucial role but, in polarization calculations, they had always been treated with approximations such as Kneer's approximation. I have developed a full treatment of the effects of multiple scattering on the linear resonance polarization taking into account the exact form of the frequency redistribution function. The results show the importance of a rigorous treatment of the redistribution in frequency when the optical thickness of the line is larger than 10. I have also studied the sensitivity of the polarization to the probability of collisional destructions of the photons, to the continuous absorption and to the optical thickness of the chromosphere.

A MODEL FOR THE PENETRATION OF LYMANot- IN THE SOLAR CHROMOSPHERE M. Faurobert^, H. Frisch^2), A. Skumanich^ (1) High Altitude Observatory, National Center for Atmospheric Research , P.O. box 3000, Boulder, CO. 80307, U.S.A. (2) Observatoire de Nice, B.P. 139, 06003 Nice Cedex, France

A multi-level calculation of the hydrogen spectrum by Skumanich and Lites, followed by a two-level representation of each transition, shows that all the solar Ly- manob photons are created in the high chromosphere, above *i««10^ ( To denotes the optical depth at the center of the line). Below this depth the Lyman

- 8 - FRAGMENTS IN SUNSPOTS J.I. Garcia de la Rosa Institute de Astrofisica de Canarias, 38200 La Laguna, Tenerife, Spain

High resolution white light and H-alpha observations, carried out in IzafTa (Te- nerife) at the 40 cm Vacuum Telescope of the Kiepenheuer Institute (FRG), allow us to study the processes taking place during the emergence of some 20 large active regions (flux larger than 5xl02l Mx). In the present work, emphasis is made on the study of the fragments which coa- lesce to form the spots, trying to answer the following question: do the fragments keep their identity until the sunspot decay?. This question is relevant for the suggested connection between some umbral dots and the interstices between fragments. Several examples are presented to illustrate the following conclusions of the work: Ci) Fragments do keep their identity during the lifetime of the spot, showing, however, some changes in morphology and location. (ii) Fragments fit like pieces of a jigsaw puzzle, as is evidenced by their penumbrae only appearing in the side which is finally going to belong to the external pe- rimeter of the spot. This is a proof against any sort of random process during the coalescense of the fragments. (iii) The base of the Arch Filamentary Systems observed in H-alpha, seem to be associated to the fragments, enabling the study of their development and mutual inclination (twists in the flux rope). 21 (iv) The typical magnetic flux content of a fragment is around 10 Mx.

Detailed processes accoapanyina the decay of an act: re region

Garcia de la Rosa J.I., Collados H.

Instituto de Astrofisica de Canarias

High resolution (better than 1") magnetograms are used to study the decay of the small active region NOAA - 4588. The observations were carried out in 1984 at the Vacuum Tower Telescope of the Sacramento Peak Observatory. A modified set up of the Universal Birefringent filter, tunned at the 6120 A magnetic line, produces two simultaneous 1/2 (I±V) images which can be added (for the I picture) or substracted to obtain the magnetogram (V), without noise due to seeing differences. This procedure allows the direct superposition of the I and V pictures to study the interactions between granulation and magnetic concentrations.

Some of the processes observed are:

(i) The granulation continously massages and deforms the magnetic concentrations, contributing to their fragmentation, (ii) Fragments, generally smaller than the resolution limit, are transported by the supergranulation and re-concentrated at the enhanced network. (iii) Only a small percentage of the flux is able to reconnect at the neutral line, (iv) At least an example is shown where two opposite polarity magnetic features move towards each other over a long distance, finally disappearing when they meet. This observation suggests that subphotospherically controlled sinking is taking place. SUNSPOT GROUPS AS TRACERS OF SOLAR DIFFERENTIAL ROTATION Lidia Gesztelyi and Judit Pap

* Heliophys-i-cal Observatory of the Hungarian Academy of Sciences, H—4010 Debrecen, Hungary ** Department of Astronomy, Lovdnd EOtvSs University, H-1083 Budapest, Kun B6la t4v 2, Hungary

Measurements of the proper motions of young bipolar sunspot groups show that these groups rotate faster than the surrounding photosphere. The results of the time series analysis carried out on the irradiance records of the SMM/ACRIM radiometer and on the projected areas of the young as well as the active sunspot groups show a period near 23-24 days at the time of the solar maximum year. The main period in the case of the projected areas of the old sunspot groups was 28 days. This later period can be due to the photospheric rotation. The 23-24 days periodicity in the irradiance records observed by the SMM/ACRIM radiometer indicates that the decreases of the solar constant may be in connection with the effect of young sunspot groups. The 23-24 days period in the power spectra of the young and active spots areas as well as the faster proper motion of the young sunspots could indicate that these young sunspots are connected to the deeper layers of the Sun. In such way the sunspot groups in the early stage of their life would be an indicator of rotation of the deeper layers of the Sun. According to our working hypothesis these deeper layers could rotate faster than the photosphere with a period around 23-24 days.

VELOCITY FIELD AND SOME ASPECTS OP SOLAR ACTIVITY S.I.Gopasyuk Crimean Astrophysical Observatory, p/o Nauchny, Crimea, 334413, USSR

Abstract - Some general characteristics of the observed plasma motions in the active region are described. The data concerning the birth and evolution of sunspots, intrinsic internal motions, the balance of plasma fluxes in individual sunspots and in the active region as a whole are presented. Special attention is paid to plasma motion in aunspots and toraional oscillations in the spots. The importance of toraional oscillations in sunspots has been determined for the study of the magnetic field structure and plasma convection in subphotospherio layers of the Sun.

PHYSICAL CONDITIONS IN COOL FLARE LOOPS P. Heinzel Astronomical Institute of the Czechoslovak Academy of Sciences, 251 65 Ondfejov, Czechoslovakia

Large two-ribbon flares are frequently accompanied by a system of (post)-flare loops, cooler structures being visible in several optical and UV lines. We investigate the non-LTE formation of hydrogen lines in stationary loop structures, taking into account the influence of turbulent motions and macroscopic velocity flows along the loop. We demonstrate some diagnostically important effects on hydrogen HeO line and identify them using narrow-band Hoi/ filtergrams of different events. This diagnostics, together with analysis of other spectral features like hydrogen L»£- line or Lyman continuum, provides us with a reasonable description of physical conditions prevailing in the cool flare loops. However, we finally stress the importance of even more complex (and difficult) radiation-hydrodynamical approach.

- 10 GENERATION AND SPATIAL DISTRIBUTION OF THE ELECTRIC CURRENTS IN B. FLRRING ACTIVITY COMPLEX

J.C.HEHOUX* and B.V.SOMOV*

lQbservatoire de Paris,92195 Heudon Principal Cedex,France. zLebedev Physical Institute,Leninakii Prospekt 53,Moscow 117924,USSR

Assuming the existence of organised photospheric velocitiy fields in active regions,we study the creation of photospheric and coronal D.C. currents by vortex and radial motions. Vortex motions leading to opposite temporal evolutions of the magnetic flux in old and new active regions create two systems of coronal currents flowing along the lines of force that connect the old to the new active region. The magnetic energy stored in these currents is higher than the energy of the biggest flares. The effect of radial photospheric motions is also discussed.

The two systems of coronal currents are inside two different magnetic cells. They interact along the separator that is the intersection of the magnetic lines surfaces which separate the magnetic cells produced by the photospheric magnetic sources. Due to source motions and electric current evolution,the separator may be the location of the reconnection of the total magnetic field . This reconnection would affect the magnetic field of the various j,oops of the two current systems and could lead to an interruption of the currents that would fast release the stored magnetic energy. The separator being perpendicular to the two current systems,these instabilities could affect all the loops and produce ribbon flares.

ELECTRIC CURRENT DENSITY IN THE SUNSPOT PHOTOSPHERE DERIVED PROM VECTOR MAGNET0GRAM5 A. Hofmann and J. Staude Central Institute of Astrophysics, Observatory Einsteinturm, DDR-1560 Potsdam

We present observational results from which we can determine azimuthal currents flowing across the magnetic field. Making use of the relation between electric current and the rotation of the field we derive the vertical component of the current density from measurements of the photospheric vector magnetic field. Around a flux bundle the distribution of the vertical current densities is dominated by azimuthal currents if: (i) the bundle is strongly inclined against the line-of-sight, (ii) the bundle is sufficiently separated, (iii) the field-aligned currents producing the torsion of the bundle do not distinctly exceed the aaimuthal currents producing its concentration. Then we observe two separated current density contours of opposite sign located symmetrically on both sides of the bundle's axis. Simple relations between the observed current densities and the inclinations of the field are used to separate from each other the field-aligned component and the azimuthal component. The values of the densities or current strengths of the azimuthal currents fall within limits of (0,5...1,2) 10~2 A m-2 or (0,5...2,0) 10in A, respectively. The relative errors amount to values between 20 and 45 percent.

- 11 - PHYSICAL STRUCTURE OP THE CORONAL PART OP SOLAR ACTIVE REGIONS AS IHPERBED PBDM X-RAY AND EDY OBSERVATIONS (Review Pamper)

J. Jakimieo Astronomical Institute, Wroclaw University, Kopernika 11, Wroclaw, Poland

X-ray and EUV observations provide two kinds of important information about solar active regions* 1. X-ray and EUV images show the spatial distribution of hot plasma, which, in turn, gives very important information about the structure of the magnetic field in the coronal part of the active regions. Best data of this kind were provided by the SKYLAB orbital observatory. Some important points resulting from the observations will be briefly aiscussed in the review. 2. Investigation of the X-ray and BUT epectra of solar motive regions provides an important diagnostic tool of thermodynamic aad kinematio parameters of the hot plasma in the regions (determination of tke temperature, density, velocities e*o.)and allows to investigate their spatial and time variations* thia will be the main topic of the review. Results of temperature and density diagnostics from various observations will be presented and critically discussed* Main sources of such speetrocoopio data are the instruments aboard the Solar Hajdjmim Mission satellite (XRP, HUS, UVSP). The improved temperature and density diagnostics opens a possibility to test more comprehensively existing theories of the plasma heating and cooling in the coronal parts of active regions. Some attention will also be paid to the intercomparlson of the structures seen in the soft X-rays and those seen in centimeter radio waves.

MAGNETIC FIELD LINE RECONNECTION BY LOCALIZED ENHANCEMENT OP RESISTIVITY AND ITS INTERRUPTION M. Karlicky Astronomical Institute, Ondfejov Observatory, Czechoslovakia

The nonlinear development of magnetic reconnection in a current-sheet system is studied numerically. The reconnection process, developing from an initial localized enhancement of electrical resistivity, is at some moments inter- rupted by a sharp decrease in electrical resistivity. The development of this process is studied and the results discussed in the frame of solar flare theory.

RADIO WAVE DIAGNOSTICS OF SOLAR ACTIVE REGIONS (INVITED REVIEW) PART I - MM-C&fr-BANDS, PART II - DJfr-M-BANDS M. Karlicky8, A. Krugerb a - Astronomical Institute, Ondfejov Observatory, Czechoslovakia b - Zentralinstitut fur Astrophysik, AdW der DDR, Potsdam, GDR

Part I of this review considers the outcome of different methods of observations of active regions at mm- and cm-waves exploring the source structures and source heights in the chromosphere and corona. Different features of the S-component radiation above sunspots, plage regions and from coronal loops connecting different magnetic polarity ere discussed. Diagnostic capacities of different kinds of microwave bursts are briefly taken into account. Calculations of emission models of bremsstrahlung and gyromagnetic radiation are summarized covering a great variety of plasma parameters. The results of the diagnostics by different methods accomplish a composed picture of the mean distribution of physical parameters and their scatter ranges in the source regions of solar microwave emission. Part II of this review considers the dm- and m-radio spectral observations as diagnostic tool for determination of plasma parameters in the coronal parts of solar active regions. The main attention is devoted to the radio diagnostics of solar flares. The most important types of dm- and m-radio bursts are presented, the latest theoretical and observational results summarized, and their diagnostic aspects briefly discussed.

- 12 - ON THE ORIGIN OF GIANT HXIS ARCHES R.A. Kopp, LflNL, Los Alamos, NM 87545 G. Poletto, Osservatorio Astrofisico di Arcetri, Firenze, Italy

During SMM operation in 1980 the HXIS instrument detected several giant coronal arches extending to high altitudes (E 105 km) and with widely separated footpoints. These gigantic structures, whose X-ray emission could be observed for several hours, always appear in association with two-ribbon (2-R) flares, suggesting that their origin is related to the basic flare mechanism.

It is generally accepted that the continued energy release during the decay phase of 2-R flares can be explained in terms of magnetic reconnection, which allows an open field configuration to relax back to a lower energy state. The growing post-flare loop system is the visible manifestation of this process, tracing the rise with time of the neutral point.

In the present paper we examine two possibilities for the mechanism of formation of giant post- flare arches. The first of these is that, analogous to the post-flare loops seen at lower altitudes, an arch originates after the flare as a result of magnetic reconnection high in the corona. This reconnection process, however, may be topologically quite distinct from that which produces the post- flare loops, as the field lines involved do not represent a direct linkage across the photospheric neutral line. The arch in this case would bear no special temporal relationship to the post-flare loop system. For the HXIS arch seen after the 21 May 1980 flare, the reconnection mechanism is supported by a quantitative comparison of the magnetic energy released with the observed thermal energy content of the arch.

The second possibility is that the arch is a pre-existing coronal flux tube which, at the time of the flare, simply becomes filled with hot plasma as a result of intense chromospheric r-'aporation at the flare-associated footpoint. The entire structure remains intact and, in fact, sir . i exhibit only minor motions during the flare process. Some observational evidence exists to favor ..nis flux tube - filling hypothesis for the arches of 6-7 November 1980, in the form of the relative timing of the footpoint brightening as seen in H3.

LONG-LASTING X-RAY EMISSION FROM THE ACTIVE REGION L. Kfivsky, F. Farnfk, 0. Sudova , B. Valnicek

Astronomical Institute of the Czechoslovak Academy of Sciences, 251 65 Ondfejbv, Czechoslovakia

Using the GOES 2 and PROGNOZ 8 satellites data we describe the X-ray emission on 25 January 1981, which lasted for at least 10 hours. We suppose the source of that emission was in an extremely active region on the east limb (S 15, E 90). The increase was very pronounced mainly in the soft channels (2-8 keV). where the basic (pre-event) level increased by about 1 order of magnitude (to 10'^Wm"^), and many brightenings and flares were superimposed on that long-time increase. During two flares hard X-ray emission was recorded. The radio bursts are also very frequent and intensive (mostly types III and V). The biggest flare of that period was observed in Hot by the coronograph on Lomnicky Stit starting at 0B 50 UT (L. Kfivsky, L. Scheirich, 1984). This flare was in the shape of rising flare-loops channel, as well as mass ejections on side of the channel was observed. These ejections were directed into the corona, and some of them returned to the solar disc. In the time interval 08 48 - 09 25 a type IV and in f)8 56 - 09 16 a type II radio emission was observed. Charged particles may also have been emitted, but near the Earth they were not registered. The acceleration phase could be observed between 09 DO - 09 15, according the X-ray and radio bursts. The studied event belong to the interval of Solar Maximum Year.

- 13 - EXAMINATION OF SOLAR RADIO BIMOT O113ETS IN VIEW OP DIFFfiR/iNT FLARE SCENARIOS AND PRE-FLARE STRUCTURES A. Kriiger, H. Aurafl, and B. Kliem Zentralinstitut fur Astrophysik der Akademie der Wissenschaften der DDR, Potsdam, G.D.R.

The time profiles of the solar- microwave emission exhibit various phenomena reflecting the evolution of magnetic flux tubes before and during +he onset of flare events. Different scen.irioa are possible to describe the processes of energy release in a flux tube ;-id the interaction of a number of tubes during the pre-flare stage and the early flare development. :iulti-peak structures at quite different time 3cales displa-id by flux records at mm-, cm-, and dm-waves are examined; they rise the question how to distinguish between repeated energy release at one site and the pro )agatirn of the flare disturbances over an extended source area. A discussion of observational results in the frame of some scenarios serves to find out favoured assumptions for the construction of models of both, the pre-flare state and the development of the impulsive phase.

ON MOIWL CALCULATIONS OF THiS S-C0I.1P0NEM INS I Oil AND OUTSIDE OP SUNSPOTS A. Kriiger, J. Hildebrandt Zentralinstitut flir Astrophy,>ik der Akademie der Wieaenachaften der DDR, Potsdam, G.D.R.

This paper reports on aome consequences of a comparison between model calculations of the S-componem nolar radio emission and observations of active regions at different wavelenghts in the nun- and cm-range. Computations of the transfer of the 3-component emission Terr, carried out on the base of horizontally averaged semi-empirical models of the solar atmosphere above sunspots and plage regions consistent with optical and dUV observations and account for Coulomb bremsstrahlung and gyromugnetic radiation in dipole-like or force-free extrapolated magnetic field configurations. While the mean characteristics are quite in accordance, discrepancies between observations and calculation arise mainly with respect to fine structures. Con- sidering such discrepancies, (i) possible reasons for an obvious lack of observed ring structures of S-component sources above sunspots are discussed, (ii) Sub- telescopic fine structures in plage regions are predicted whereas bright plage elements are assumed to be embedded in a quasi-quiet background, (iii) The difficulty of recognition of non-impulsive burst emissions is considered which may cause strange cases of long-enduring "hot" loop emission.

LONG-PERIOD COMPONENTS IN SOLAR WIND VELOCITIES L. Kulcar 1/, V.. Letfus 2/ 1/ Astronomical Institute of the Slovak Academy of Sciences, 059 60 Tatr. Lomnica 2/ Astronomical Institute of the Czechoslovak Academy of Sciences,251 65 Ondrejov

In the present contribution we applied several methods of spectral-statistical analysis /in particular fast Fourier analysis, maximum entropy spectral analysis, periodogram etc./ to the time series of the solar wind velocity data for searching hidden periodicities. The original solar wind data we analysed were obtained on probes at the distance 1 AU from the Sun and stretched over the 17 year interval from 1963 to 1980. Because of investigating long-period components /on time scales of 0.5 to 15 years/ in variations, we proceeded daily solar wind velocity values averaged over each Bartels rotation Nos. 1784-2006 /i.e. 223 input data/. The spectra showed the peaks at periods of 14.9-13-7, 7.2-7.1, 4.8-4t5, 3.6-3.1, 2.8-2,6, 2.1-2.0, 1.7-1.4, 1.3, 1.1, 1.0, 0.8, 0.7 and 0.6-0.5 years. The found solar wind velocity periods were compared with the ones found in various solar and geomagnetic activity indices.

- 14 - Physical ttractare aad diagacstics of solar active regioas ttedace froai optical .visible aad UV, observations. P.Lemaire LPSP - BP n° 10 - 91371 -Verrieres le buisson Cedex-France

Abstract. Since the 1978-79 Skylab Workshop on Solar Active Regions ,significant progress has been made in the diagnostic and modeling of active solar structures.This paper review the status of our knowledge of the physical properties of active regions in the photosphere.chromosphere and transition zone ,as inferred from observations. Plages are the main active region which we study.A comparison with quiet sun and some other solar structures is made in order to emphasize the specificity of plages properties. To conclude we present some requirements for new observations and theoretical developments to improve our understanding of the physical structure of solar active regions.

EXTREME SOLAR ACTIVITY OP EARLY FEBRUARY 1986 AND ITS GEOPHYSICAL CONSEQUENCES E. Markova1^, L. Pastorek , F. Zloeh^, J. Lagtovicka , P. Perglerova , J. Py-

Observatory tfpiee, 542 32 Upice; 2'SUAA Hurbanovo, 947 01 Hurbanovo; Astronomi- cal Institute, Czech.Acad.Sci., 251 65 Ondfejov; Geophysical Institute, Czech. Aoad.Sci., Bocni II, 141 31 Prague 4; Czechoslovakia During the solar cycle minimum period, a period of a suddenly enhanced solar activity occurred in early February 1986. Two proton flares were observed during this period after a long period of a totally quiet solar activity (R » 0 in most days in the second half of December and in January). Other flares, various phenomena accom- panying proton flares, like type II and type IV radio bursts and a large Forbush decrease of cosmic ray intensity were observed, as well as an extremely severe geomagnetic storm (Kp =9) and strong disturbances in the Earth s ionosphere (SIDs and ionospheric storm). Czechoslovak solar and geophysical observations for this period are presented and interpreted with the use of other observations. A special attention is given to the flares of February 4 (start 0732 and 1025 UT) and February 5 (start 0934 UT), because spectroheliograms from the Hurbanovo observatory are available for these events.

SOME EVOLUTIONARY ASPECTS OF SOLAR ACTIVE REGIONS M.J. Martres Observatoire de Paris, Section d Astrophysique, 92195 Meudon, France

The appearance of isolated sunspot groups as well as their clustering in large active regions depend on a complex dynamo process. Signatures of this dynamo process may be deduced from three different outstanding researches. a) The emergence of new fluxes (spots or flares) is preceded by local cyclonic motions observed at the photospheric level, in regions of weak magnetic fields such as polarity inversion line, gaps between magnetic hills or borders of the facula. This velocity structure is a short scale in time and space response to a local sub- photospheric perturbation and thus create currents and new magnetic flux. b) Magnetic tracers such as long lived Hoc filaments and sunspots show that the regions of emergence of new flux (family of sunspots groups, eruptive sites or para- sitic polarities) are related to the existence of limited areas rotating rigidly; these "pivot points" which do not follow the differential rotation could be anchored more deeply than the active centers themselves. c) A large scale circulation, tied to the global rotation reflects the motions of the underlying fluid (frozen field). Recent results show the existence of azimutal .rolls which bring up the deep magnetic field. They move slowly toward the poles. They seem to govern the cyclicity and modulate the observed solar rotation. All these observational results should be taken in account for understanding the production and the development of active regions.

- 15 - FINE STRUCTURE OF ACTIVE REGIONS ft. Muller Pic du Midi and Toulouse Observatories, France

The structure of active regions will be described as it appears from the best resolved observations. At the photospheric level, an active region is a mixture of magnetic fields and convective elements interacting each others, resulting in sunspots of different sizes and shapes, facula and granules; the structure is changing along the active regions evolution. Properties of umbral dots and penumbral filaments will be described as well as those of facular points and granules in the photosphere surrounding sunspots. Emphasis will be put on the difference from network bright points and gianules in the quiet photosphere. Chromospheric and transition zone phenomena related to these features will also be described. Current physical interpretations of the observed features will be discussed.

MOTIONS AROUND A DECAYING SUNSPOT R. Muller, B. Mena Pic du Midi and Toulouse Observatories, France

The motion of facular points and granules have been measured in the same region near a decaying sunspot. It is found that both features move away across the moat surrounding in the sunspot. The mean speed of facular points is larger than that of granules: 0.65 km s~l and 0.45 km s~* respectively. These results are consistent with previous measurements of the speed of bright network features and moving magnetic fields, as well as of non-magnetic photospheric material. They support models in which a decaying sunspot is at the center of a supergranule, whose horizontal motions sweep out granules and magnetic flux tubes associated to the facular points.

DYNAMICS OF THE SOLAR GRANULATION R. Muller^1), Th. Roudier(1\ J.M. Malherbe(2), P. Mein('2) (1) Pic du Midi and Toulouse Observatories, France (2) Observatoire de Paris, Section d'Astrophysique, 92195 Meudon, France

High resolution (0V5) two-dimensional spectra of the solar granulation (line Na D2 ), performed at the Pic du Midi Observatory with the DPMS spectrograph, have been analysed. Velocity power spectra have a slope of - 1.6, close to the - 5/3 value expected for a turbulent atmosphere, in the range 3" - D'.'5. This means that the turbulent cascade occur? in this range (the inertial subrange). It thus appears that granules are of turbulent rather than of convective origin. The convective energy is injected at scales larger than 3".

SEMIEMPIRICAL MODELS OF QUIESCENT PROMINENCES D. Novocky1 and P. Heinzel2 1 Astronomical Institute of the Slovak Academy of Sciences, Tatranska Lomnica 2 Astronomical Institute of the Czechoslovak Academy of Sciences, Ondfejov

Simultaneous high-dispersion Call H and K, Ha , Hg , and D, emission line profiles of quiescent prominences have been recorded in Stara' Lesna Observatory. After data reduction, a full set of calibrated profiles is used to construct semiempirical non-LTE prominence models. From the best fit to observed emission lines we derive the depth-dependent physical parameters of the prominence plasma and discuss the condition of energy balance inside the prominence.

- 16 - SEARCH FOR SOLAR g MODES P.L. Palle(1), T. Roca Cortes(i:) G.R. Isaak (2) H.B. van der Raay^2-' (1) Instituto de Astrofisica de Canarias, La Laguna, Tenerife, Spain (2) Physics Department, University of Birmingham, Birmingham, U. K.

Accurate measurements of solar acoustic oscillation ( p modes) frequencies have already provided important new data, enabling the diagnosis of the Internal Struc- ture of the Sun. On the other hand, theory predicts the existence of solar gravity oscillations C g modes) whose detection is still marginal. The main reasons are their frequencies, y-^0.2 mHz. , and amplitudes of less than 15 cm/s. However, because these modes are extremly sensitive to the physical conditions in the very deep sun, they can give us detailed information on the physics of the core. Using a resonant scattering spectropho+ometer we measured the radial velocity of the Sun at the KI 7699 h line with very high resolution and temporal stability. The observations carried out at Izana (Tenerife) continuously for the last three years, have been used to search for solar g modes. Analysis of the whole lot of data as one single time series provide us with a spectral resolution of ~ 12 nHz., and the amplitudes of g modes appears above noise level, ~ 1 cm/s. The signature of g modes is found in the signal and the parameter T , related with conditions at the bottom and below the convection zone, and related with the rotation rate of the very deep layers ( r < 0.2Ro ), are found.

SOLAR 530.3 nm CORDNA IRRADIANCE VARIATIONS IN THE CYCLE 21 M. Rybansky, V. Rusin, E. Ozifcakova Astronomical Institute, Slovak Academy of Sciences, 059 60 Tatranska Lomnica, Czechoslovakia

It is generally known that intensity of the 530.3 nm coronal line depends on the solar activity. A mechanism for such variability, connected with a magnetic fields, as well as temporal and spatial variabilities of this line is not completely understood because of a gap of observations. The coronal index (CI ) which represents the 530.3 nm line irradiance (mean daily values in W/sr x 10l6) derived from daily measured intensities around the whole corona as seen from the Earth, was used for a study of this variability in the cycle 21. Ground-based observations have verified the reality of 530.3 nm coronal irradiance variations over time scales of about 27 days, and several months, connected with the rotation and evolution of active regions. Maximum values of the CI were observed in the second half of 1981 year just before a deep decrease in the Wolf's number. Monthly average values of the CI vary in the range from 1.64 to 18.93 x 1016 W sr"1. Amplitude of the daily values of CI from their average monthly values is varied from 8% to 44%. Briefly comparison the CI with similar indeces in the UV emissions shows relative a good agreement. It suggests on their conncection to solar magnetic activity.

SURGES AS TRACERS OF MAGNETIC FIELD LINES B. Schmieder, P. Mein, G. Simnett, Tandberg-Hanssen E.,M.J.Martres Observatoire de Paris, Section d Astrophysique, 92195 Meudon, France

During the maximum activity year 1980, chromospheric mass ejections were observed with the Multichannel Subtractive Double Pass Spectrograph operating at Meudon (MSOP), while the UV and X ray emissions were observed respectively with Ultra Violet Spectrograph (UVSP) and the HXIS instrument on board the SMM satellite. These ejections are not related directly to flares but are located in active regions near sunspots. As the magnetic field is frozen in the matter, the study of the dynamics leads to the geometry of the magnetic structures and to the temporal evolution of the magnetic field lines. Ejections of matter recur often with a period of 10 to 20 minutes. In CIV, the bright loops coincide with the H-alpha surge but are more extended. Associated with the events are either X ray emission or type III burst. We in- terprete these signatures by invoking, respectively closed or open structures. The estimate of the energy involved gives constraints on the mechanism responsible for the surge.

- 17 - ON THE ONSET OF ERUPTIVE PROMINENCES AND CORONAL TRANSIENTS

G. Simon*, N. Mein*, B. Schmieder*, E. Tandberg-Hanssen**, S.T. Wu***. * Observatoire de Paris, Section de Meudon, 92195 MEUDON PRINCIPAL, FRANCE ** Space Science Laboratory, Marshall Space Flight Center, Huntsville, U.S.A. *** University of Alabama, Huntsville, U.S.A.

During the Maximum Year, preflare and preeruptive phenomena have been observed which give a new idea on the association of eruptive prominences and coronal transients. The propagation of a C TV brightenning through a prominence is related to the onset of a MHD wave. It is followed by the activation of the prominence and.its eruption some two hours later. A coronal transient is observed above 1.6 Ro. It is argued that the eruption of the prominence is the result of perturbations in the magnetic field configuration initiated by the MHD waves. The consequence would be that more generally the primary initiation of the eruption may happen up to several hours before the rise of the prominence.

SPECTROSCOPIC INVESTIGATION OP TWO-COMPOTJEWT UMBRAL STRUCTURE

M. Sobotka

Astronomioal Institute of the Czechoslovak Academy of Sciences, 25165 Qndrejov

The complex internal structure of umbrae (dark cores, bright dots etc.) is often described by means of two-component semiempirical models. We have investigated the dependence of such models on the umbral radius rn. For this purpose we used the speotroscopio observations of 11 umbrae differing in size (2" * ru ^ 8") in the lines Fe I 543.5 nm and Na I D2, obtained in the years 1982-1983 from the horizontal telescope/spectrograph in Ondfejov. A simple grid of two-component models defined by only 3 parameters (filling factor of the bright component and temperature scaling factors of the bright and dark components) was generated and by comparison of computed and observed (corrected for stray light) line profiles the corresponding models were selected. The results are aa follows: 1. Th<- large umbrae (ru > 4") differ in brightness mainly due to fluctuations in temperature of the dark component. The filling factor is practically constant and does not exceed 5 %. 2. The small umbrae (ru< 3") differ in brightness due to both the fluctuations in temperature of the dark component and the considerable changes in the filling factor (from 5 % to 30 %). 3. The bright aomponent is cooler then the quiet photosphere and in most cases it may be described by the temperature down-scaling factor A© = 0.10 . 4. No correlation among the filling factor and the temperature scaling factors was found.

MAGNETIC FIELDS: OBSERVATIONS AND THEORY S.K. Solanki Institut fur Astronomie, ETH-Zentrum, CH-B092 Zurich, Switzerland

Theoretical model calculations of magnetic elements in the photospheric layers of solar active regions are compared with the results of observations. We shall concentrate mainly on small scale magnetic elemants and shall attempt to give an over- view of the contributions that theory and observations can make to answering the following questions: What is the field strength and the magnetic field structure of a magnetic element? Are magnetic elements inclined with respect to the vertical? Do magnetic canopies exist and how can they be explained? What are the diameters of magnetic elements? What kinds of mass motions are present in magnetic flux concentrations and what role do they play for their structure, stability and energetics? How high is the temperature in magnetic elements and what are the underlying heating mechanisms? How does the concentrated magnetic field interact with its non-magnetic surroundings? What do these surroundings look like?

- 18 - OSCILLATIONS AND WAVES IN SONSPOOS (Invited paper) J. Staude (a), Y.D. Zhugzhda (b), and V. Locans (c) (a) Central Institute of Astrophysics, Observatory 'SinstainturmJ DDR-1560 Potsdam (b) IZMIRAN, SU-142O92 Troitsk; (c) Radioastrophysical Observatory, SU-226524 Riga

Magneto-atmospheric waves are likely candidates for energy transport and heating in stellar atmospheres. Sunspots provide a unique example of a magnetized atmosphere where up-to-date observations can resolve many details of such, periodic disturbances and of the atmospheric structure as well, thus models of both waves and atmospheres can be tested. Therefore we focus our interest on sunspots. We review the basic features of oscillations observed at different height levels in the sunspot atmosphere, moreover, various possibilities for a theoretical interpretation are discussed. In the umbra oscillation power is concentrated in several period bands (3 min., 5 min., and 5620 min.) which on their part are composed of closely packed p9aks. The observed amplitudes and phases of velocity and of intensity oscillations depend in a characteristic way on the period «"fl on the height. These features are used to look for the most probable physical mechanisms which could produce the different modes: At subpfaotospheric depths two independent resonators are acting. A resonator for slow, quasi-transverse waves can explain the lifetimes of umbral dots ( £20 min.), while a resonator for fast (acoustic), quasi-longitudinal waves could result in the umbral 5-min. oscillations. The acoustic resonator strongly couples with the slow-mode longitudinal resonator at photospheric and chromospheric heights, the latter produces the resonance peaks in the 3-min. band. Running penumbral waves can be explained by the transformation of 5-sniii' waves from the convective zone in the almost horizontal magnetic field. The interpretation of oscillations provides a new method of probing subphoto- spheric, but also atmospheric layers of suaspots (e.g., of determining temperature gradients), thus completing customary spectroscopic diagnostics.

EVOLUTIONARY ASPECTS OP THE SOLAR ACTIVE REGIONS 1 2 N.JT.Stepanyan , A. Antalova 1 Crimean Astrophysical Observatory, 334413 Nauchny, Crimea, USSR. 2Astron. Institute, Slovak Academy of Sciences, 05960 Tatr. Lomnica, Czechoslovakia

Some aspects of the evolutionary activity of the active regions are considered, connected namely with the changes of the physical conditions in active regions and flare appearance. Spectral observations of plages and sunspots permitted us to determine the changes of temperature and density distribution with height in regions in question. The investigation of spectra obtained at different stages of evolution of active regions allows to reproduce a picture of changes of physical parameters with plage evolution. The upward cooling in sunspots (from the depth of about 400 km) at a rate of 15 m/s has been determined by spectral observations of sunspots during the first hours of their lifetime. The study of sunepot magnetic fields in the vicinity of flares leads to a conclusion, that the flares affect the changes of height distribution of the magnetic field, inclination of the magnetic tubes, as well aa the correlation between hot and cool components of sunspots. The occurence of the IDE flares in active regions, aa a function of their magnetic type and age is considered.

- 19 - LiiBAII Diagnostic for Basic Flaring Loop Parameters L. Sylwester , J. Sylwester , J.Jakimiec , A.Fludra , G.Peres , 1 - Space Research Center, Polish Academy of Sciences, V/rociaw, Poland 2 - Astronomical Institute, iVrociaw University, Wroclaw, Poland 3 - Astronomical Observatory, Palermo, Italy We have analysed the relations between basic physical parameters in the flaring loops. Eased on the results of the "Palermo Code" hydrodynamic flare modelling, we have checked that even for transient energy input, the energy deposition rate can be adequately expressed in terms of the actual maximum temperature of the plasma in the loop. Taking this into account, we have used a simple equation governing the energy balance in the flaring loop. This equation relates the basic characteristics such as: the maximum temperature, the mean temperature and the eEiisuion measure with the loop's length and cross-section as the parameters, lixcept the geometry parameters the other characteristics can be determined based on the soft X-ray spectral analysis. In the paper, we describe the diagnostic procedure called L^'BAK which may be helpful in deriving basic geometrical loop parameters. Palermo model calculations have been used to test reliability of the procedure.

CONTINUUM INTENSITY AND MAGNETIC FLUX OF SOLAR FLUXTUBES J.C. del Toro Iniesta(1), M. Semel(2-\ M. Collados(1), 3. Sanchez Almeida ' (1) Instituto de Astrofisica de Canarias, 38200 La Laguna, Tenerife, Spain (2) 0.A.S.O.P. Observatoire de Meudon, 92195 Meudon, France

The importance of the continuum intensity contrast between the solar fluxtubes and their neighbourhood has been reported by Schussler (1987). This is one of the key-magnitudes in order to understand the nature of fluxtubes and their role in Solar Activity. Up till now, have only been made photometric determinations of the contrast between photospheric bright points (assumed to be coincident with fluxtubes) and the quiet photosphere giving values between 1.3 and 1.5. On the other hand, del Toro Iniesta et al. (19B7) showed that some fluxtube properties vary in a single facula. Thus, the evaluation of the magnetic flux seems to be very important in order to determine whether or not it shows such kind of local variations. We present determinations of the continuum intensity contrast between the solar fluxtubes and their surrounding background, and the magnetic flux of these unresolved magnetic concentrations. The measurements are based on high-resolution (1") spectro- polarimetric observations, obtained simultaneously at several points of a solar facula. As far as we know, this is the first time that such a determination has been made with this type of observations.

SIMULTANEOUS MEASUREMENTS OF CHROHOSPHERIC LINES IN SUNSPOT OMBIA AN FENOMBSA J.-C. VIAL et A- BELLOUT L.F.S.P., B.P. 10, 91371 VERRIERES LE BUISSOH CEDES, FRANCE

We report on simultaneous profiles measurements obtained in the La, LB, Mgll and Call lines in a sunspot unbra and penumbra, performed with the L.P.S.P. Instrument on 0S0 8. Although the statistics does not allow for a full time coverage In all lines, we are able to analyze Call H and K shifts and Intensity variations, along with calibrated aTerage profile* in other lines. Jesuit* are compared with predictions of the model where resonant transmission of acoustic wares takes place between the temperature minimum and the transition region (see Zugzda et al.. Solar Phya. 82, 369 and Gunian and Lelbacher, 1984, Ap. J., J83, 859).

- 20 - MODELLING SOLAR ACTIVE REGIONS FROM OBSERVATIONAL DATA

E. Wiehr

Universitats-Sternwarte, D-3400 Gbttingen, B.R.D.

Empirical atmosphere models for sunspots and plages are discussed. Particular interest is given to the influence of fine structures such as umbral dots, penumbral filaments and filigree. The role of magnetic and velocity fields is considered inclusive oscillatory velocities. An outline is given for needs and limits of future observations at significant higher spatial resolution.

BRIGHT FACUIAR POINTS ( FILIGREE ) IN ACTIVE REGIONS

TH. G. Zachariadis

Research Center for Astronomy and Applied Mathematics, Academy of Athens, 14, Anagnostopou-lou str., 10673.Athens, Greece.

High resolution observations of the MacMath 16315 active center near the center of the disk were analysed in order to study the bright points both below an Arch Filament System (AFS) and in two neighbouring regions covered by pianettes. The observations were taken in the wings of Ha ( Ha - 1.0 A and Ha - 0.75 A ) at the observatory of Pic du Midi in September 26,1979 and had a duration of 80 min. The measurements of the time evolution were carried out for a region under an AFS while for the other characteristic selected pictures of the same region as well as of neighbouring regions covered by plagettes were used. The bright points of one of the plagettes seem to extend under the AFS forming the well-known filigree pattern in the same reciion where we also observe Ellerman bombs. The average value of the relative intensity of the bright points with respect to the background in the plagette regions as well as under the AFS was 1.13 ±0.033. This value was the same for Ha - 1.0 A* as well as for Ha - 0.75 A. The lifetime of bright points under the AFS ranqes from 3 to 18 min with an average value of 10 min.The time evolution of the intensity of bright points under the AFS is different from that of the Ellerman bombs under the same AFS : The relative intensity of bright points rises to the maximum value within 1 min and remain's constant during the rest of its lifetime while the Ellerman bombs show intensity variations during their lifetime between 1.11 and 1.48. (Zachariadis et al, 1987 ). The average size of bright points at Ha -1.0& was found smaller than that at Ha -0.75 X. References Zachariadis , G.Tfl., Alissandrakis E.C. and Banos G. :1987, Solar Physics in press.

- 21 - TS 2 THE COMPLEX OF INTERPLANETARY BODIES

CHEMICAL ANALYSIS OF INTERPLANETARY DUST PARTICLES WITH SYNCHROTRON RADIATION. Ch. Antz1, M. Bavdaz2, E.K. Jessberger1, A. Knochel2, R. Wallenwein1 ^ax-Planck-Institut fur Kernphysik, P.O.Box 103980, 6900 Heidelberg, FRG 2Universitat Hamburg, Institut fur Anorgan. u. Angew. Chemie, Martin-Luther-King-Platz 6, 2000 Hamburg 13, FRG

Two 10-um interplanetary dust particles (IDP's), collected in the stratosphere by plane, have been analyzed with X-ray fluorescence excited by white synchrotron radiation (SYXFA) at the HASYLAB (DESY) in Hamburg. The measured abundances of the minor and trace elements with 12 < Z < 37 basically are in agreement with results from PIXE determinations [1] of the same particles. It was even possible to obtain an estimate of the abundance of Sn (Z=50) of which only about 2x10 i4 g is present in one of these small IDPs. The results verify the expectation that SYXFA is a very promising analytical tool and probably one of the most powerful non destructive techniques for chemical analysis of micron-sized samples. Moreover, we find that the combined application of two such techniques, SYXFA and PIXE [1], to the same valuable particle lends high credibility to the results. [1] R. Wallenwein, et al., this conference

PHOTOGRAPHIC DATA OF EXTREME PRECISION EVALUATED BY EXACT SINGLE-BOD/ SOLUTION OF METEOR PHYSICS

P. B. Babadzhanov and z. Ceplecha 1/ Institute of Astrophysics, Dushanbe, 734870, USSR 2/ Astronomical Institute of, the CSAV, 251 65 Ortdrejov Observatory, CSSR

The exact solution of the single-body motion and ablation of a meteoroid in the atmosphere /Pecina and Ceplecha, Bull. Astron. Inst. Czechosl. 34, 102 and 35, 120> I = I/t/, where I is the distance along the meteoroid trajectory as function of time, t/is applied to one of the most precise double-station records of a fireball photographed from Dushanbe Oct 30, 1962- The entire trajectory of 5.2 seconds duration from 77 km to 36 'xm of height with 258 time marks corresponds to a single value of the ablation coefficient, tf = 0.0275^ 0.0003 sz/kmZ derived for CIRA 72 November 'atmosphere at Dushanbe. The resulting standard deviation in I of - 15 m is close to the geometric precision of the observed distances. Among all 258 time marks, only 4 values of computed I deviate slightly more than 3 standard deviations, while about one such value is expected for the normal distribution. Two succeeding values greater than 3 standard deviations at 4.33 seconds may represent some breakage of the body. If CIRA 72 October atmosphere for Dushanbe is used the ablation coefficient becomes 6 = 0.0300* 0.0003 sz/km2. The value of k>£T/3 for this fireball resulted in 0.185 cnr/g /k is the shape-density coefficient and m«, is the initial mass before ablation/. The initial velocity, vw, was de- teruined as v— = 13.6340 - 0.0009 km/s /CIRA 72 November/ or v«, = 13.6303 2 ±0.0009 km/s /CIRA 72 October/. The velocity changes during the entire trajectory from 13.61 to 5.85 km/s.. The deceleration changes from -0.0 35 km /s2 lit the beginning point to -4.08 km /s£ at tfce aaximum deceleration point ft = 4.73 s at a height of 38.4 kmj and -3.65 kn' /s^ at the terminal point.

- 22 - ON THE LIGHT PULSATION OF TWO BRIGHT GEMINIDS ACCORDING TO PHOTOGRAPHIC DATA

P.B. Babadshanov and N.A. Konovalovt. Institute of Astrophysics, Dushanbe, 734670, USSR

Thejfiotometric light curves of two bright Geminids are investigated in the paper. The analysis of the light curves reveals a peculiar nature of meteor luminousity with rapid flickering and snail brightness fluctuations. This peculiarity of the luminousity of the bright Geminids points to a certain ablation process of these meteoroids in the Earth s atmosphere. The autofluctuating nature of evaporation has been used to explain the observed rapid flickering. Using the heat-conductivity equation the heat transfer coefficient .4 versus the atmospheric densityp was obtained. The calculations were done for stone and iron meteomids. As is turned out in the both cases A decreases mo- notony when a meteoroid penetrates into the atmosphere. The energy of ablation Q. for the both meteoroids was found using the obtained value? of-A . According to estimates of <3 a conclusion was made that the both investigated Geminid meteoroids were ablated in the atmosphere by the melting and cvcl'C ejection of the surface-layer of meteoric matter.

EVOLUTION OF METEOR STREAMS

P.3. Babadzhanov and Yu. V. Obrubov Institute of Astrophysics, Dushanbe, 734670, USSR

A meteor stress is gone rail/ considered to be as an elliptical ring of relatively sirall thickness. Such shape is mostly attributable for meteor streams in an early stage of their evolution. Differences in planetary perturbations influenced on me- meteor particles i-jected from the parent body from various points at different velocities and time t.ai lead to a significant thickening of the stream. Our recent studies on the evolution of the Geminid and Quadrantid meteor streams have shown that these streams can produce sev/eial couples of showers active in different seasons of tie /ear. As for the Geminid stream it may produce two couples of showers /in December and September/ and three showers have been actually observed. Theoreti- cally the Quadrartid stream are assumed to have six showers and the activities of the five has been proved by observations. The nual itative study of the evolution of 30 short period meteor streams has shown that some meteor streams could produce up to eight showers. Delta-Draconids, Kap- pa-Cygnids and probably Tau-HercuIids can belong to such streams. More often mete- or 'treain? can produce four showers each. The orbits of the stream particles, producing these showers have about the sane eccentricities, inclinations, longitudes of perihelions and clo^e semimajor axes. But argument of perihelions are assumed to be W-, 2 = * w° and w, u = 180° - W°, whereW is an argument of perihelion of *ome stream particle orBft crossing the Earth's orbit. Peliable e«tabli?hed interrelations of meteor streams with comets and asteroids are much le«=* than the showers observed. Parent bodies of many meteor streams are unknown, ihi* fact probably proves that the smae parent body may be responsible for several meteor showers. In addition to the original results a review of recent papers on the evolution of meteor streams and theirs interrelations with comets and asteroids is given.

Evolution of the Interplanetary Dust

M. Banaszkiewicz, I. Kapisinski Space Research Centre, ul. Bartycka 18, 00-716 Warsaw. Poland Astronomical Institute, Slovak Academy of Sciences, 842 28 Bratislava, Czechoslov

The existing models of the interplanetary dust mass distribution and density /fan model, cosine model/ are taken as the initial conditions for the evolutionary studies. The dynamics of the dust is determined by gravitational attraction of the Sun with perturbing radiative forces and rare collisions which redistribute the mass and change the orbital elements of fragments. Erosive collisions and sputtering are taken into account in addition to catastrophic collisions. The effect of planetary perturbations is c'icu»a«d.

- 23 - LONG-TERM DYNAMICS OF HALLEY-TYPE COMETS A. Carusi/1/, L- Kresak /2/, E. Perozzi /1/, 6.B. Valsecchi/1/

/1/ IAS - Reparto di Planetologia, Rone, Italy 121 SAV - Astronomical Institute, Bratislava, Czechoslovakia

The integration of motion of Halley-type comets carried out in the framework of the Long-Terro Evolution Project has shown some interesting features of the dynamics of these comets. Similarly to long-period comets, these objects move essentially on barycentric elliptical orbits except for the fraction of period spent within the orbit of Jupiter. Indirect planetary perturbations experienced within this region may allow, on a short time-scale, the trapping of some Halley-type comets in resonances with Jupiter of the form n:1. , Integrations of motion of these comets, over periods of time of more than 10 years, have therefore been performed, in order to investigate this phenomenon on time scales comparable to the presumed lifetime of Halley-type comets as active objects.

DYNAMICAL EVOLUTION OF SHORT-PERIOD COMETS

A. carusi and G.B. Valsecchi

IAS - Reparto di Planetologia, Rome, Italy

The dynamical evolution of short-period comets, and in particular of those belonging to the so-called "Jupiter family"/ is reviewed. Encounters with Jupiter play a dominant role in determining the dynamical fate of these objects, atthough, in some peculiar cases, also interactions with other planets can be important. Integrations of motion of observed comets, over a time span comparable with their lifetimes as active object*, are compared with previous Monte Carlo studies, to get insight into tne non observed phases of the dynamical evolution of these objects.

EFFECTS OF NO-TRIAXIAL SHAPE ON THE ASTEROIDS SPIN AXIS DIRECTION DETERMINATION 8Y MEANS OF THE AMPLITUDE-MAGNITUDE METHOD

A. Cellino, V. zappala, M. Di Martino

Osservatorio Astronomico di Torino, Strada Osservatorio 20, 10025 Pino Torinese /TO/, Italy

The amplitude-magnitude /AM/ method is at present largely applied for determining the rotation axis direction of asteroids; such a method gives reliable results which in general are in good agreement with the ones obtained by means of essentially different methods, like the so-called photometric astrometry. One of the critical assumtions of the AM model, however, is that asteroids are triaxial ellipsoids with semiaxes a b c. Although such hypothesis appears now very reasonable on the basis of physical considerations about the expected equilibrium shapes of asteroids, we are interested in studying the influence that significant deviations from a purely triaxia l-el lipsoid shape can have on the derived spin axis direction. To do this, a numerical program has been developed in order to compute the lightcurves of irregularly-shaped objects at given aspect angles. This paper presents rge results obtained concerning the uncertainty on the rotation axis direction of asteroids when a possible no-triaxial-shape is taken into account.

- 24 - NUMBERS AND MASSES OF DIFFERENT POPULATIONS OF SPORADIC METEOROIDS FROM PHOTOGRAPHIC AND TELEVISION RECORDS Zdenfk Ceplecha

Astronomical Institute of the Czechoslovak Academy of Sciences, 251 65 Ondfejov Observatory, Czechoslovakia

Double- and multistation data on meteors from photographic and television records are used toderive relative and absolute numbers of sporadic meteoroids coming to the Earth's vicinity and their mass accession. Seven different meteoroid populations are dealt with separately inside a mass interval of 6x10 g to 2x10~5 g and their cumulative numbers determined. The maximum mass influx for the entire Earth's surface of 3x1O9 g per year per unit logarithmic interval of mass fg/y/1/Ef belongs to the upper boundary of this investigated mass interval with indication of some further increase to greater masses. A local maximum of 10s fg/y/1/E| takes place at 0.3 g, preceded by a minimum of 3x10'lg/y/1/EI at 5 g. The most numerous population proved to be the A-group; only at 10""'* g the new revealed population C3 of short-period radonly-inclined orbits takes over toward smaller masses. The population index of cumulative numbers is mostly lower than 1 except the interval from 3 g to 0.3 g, where it reaches 2. The relative mass scale of photographic and television meteors is based on integration of the whole light curve /in contrast to visual observations, where only the maximum brightness defines mass; more popu- lated smaller bodies of high velocities are then added to few bigger bodies of low velocities at the same maximum brightness, unresolved; this makes the cumulative slope seemingly steeper/. The calibration to absolute scales was possible using a recent work of Halliday, Blackwell and Griffin /Science 223, 1405/. The total influx of sporadic meteoroids in the above given mass interval of 11 orders resulted in 5x109 g per year for the entire Earth's surface.

SHOULD WE BELIEVE EXISTING ESTIMATES OF COMETARY MASS LOSS RATE? LESSONS FROM THIS VISIT OF COMET P/HALLEV

J.F. Crifo L.P.S.P., B.P. 10, 91371 Verrieres le Buisson Cedex, France

The recent visit of Comet P/Halley has opened the unprecedented possibility of comparing estimates of its dust mass loss rate based on remote optical sensing with in-situ sampling of this dust. As a consequence, P/Halley dust mass loss rate is found to be nearby 2.5 times greater than its gas mass loss. This number is about an order of magnitude above predictions based on remote sensing only. Nonetheless, it docs not seem to result from unusual properties of this comet. More likely, this result points out that overcon- fidence has been placed in the capability of remote sensing observations to provide reliable estimates of cometary dust mass losses. Some imlications of this result are discussed.

THE SYMMETRY PLANE OF THE ZODIACAL CLOUD RETRIEVED FROM IRAS DATA

R. Dunont1, A.C. Levasseur-Regourd2 'Observatoire de Bordeaux, B.P. 21, F-33270 Floirac, France 2Service d'ASronomie C.N.R.S., B.P. 3, F-91371 VerriSres-le-Buisson, France

The annual oscillations of the brightnesses observed at 12 and 25 \im by IRAS near the ecliptic poles are mainly due to the inclination of the Symmetry plane (SP) of the interplanetary dust cloud upon the ecliptic, but also, secondarily, to the eccentricity of the earth's orbit.

Comparing the brightnesses at the poles and in the ecliptic (near 90° elongation) allows a retrieval of the inclination i and ascending node SI SP/ecliptic through an inversion technique, with very little model-dependence. The results (i « 1.5°, Si « 90°) conflict with some of those previously obtained from the same observations by more model-dependent approaches, but they agree with former optical determinations from D2A satellite and from Tenerife ground-based data.

- 25 - SPATIAL DISTRIBUTION OF NEUTRAL AND IONIZED GAS IN THE HALLEY COMET COMA AFTER THE PERIHELIUM

R. Falciani , M. Festou , L.A. Smaldone and G.P. Tozzi

: Osservatorio Astrofisico di Arcetri - L. E. Fermi 5 - 1-50125 Firenze - Italy I Observatoire de Besangon - 41 b. Av. del 1'Observatoire - F-2500 Besancon - France Dip. di Fisica dell'Universita - Pad. 19/20 - Mostra d'Oltreniare - 1-80125 Napoli - Italy

Long slit spectra of Halley comet obtained at E.S.O. between March 20.3 - 23.3 have been analyzed. •The spectra, obtained with a Boiler & Chivens spectrograph feeded by the 1.52 ESO telescope, equipped with an image intensifier tube detector, covered the 3650-6300 X spectral range. The slit, the height of which corresponded to about 8 arcmin on the sky (and to 270000 Km on the comet), was put parallel and perpendicular to the sunward direction. Column densities have been deduced for the + most prominent neutral (CN, C2, NH2, etc) and ionized (H20 ) species, as a function of nuclear distances. These profiles have been interpreted using the vectorial model to obtain the production rate:; of these species and their possible variation with time. These results have been compared with corresponding data obtained during the pre-perihelium phase.

PHYSICAL PROPERTIES OF ASTEROIDS

P. Farinella

Dipartimento di Matematica, University di Pisa, Via F. Buonarroti 2, 1-56100 Pisa, Italy

In the last few decades new observational techniques have provided a wealth of physical information on several hundreds of asteroids, out of the more than 3000 whose orbits are known. These objects are no longer seen as pointlike bodies mainly interesting as a 'dynamics] zoo', but have become small 'worlds' with known sizes, gross shapes, surface compositions, rotational properties and collisional histories. The diversity of these 'worlds' is astonishing: thcry range in size fn a about. 1 to 1000 km, in spin period from i few hours to several days, in shape from nearly E;phericM tc very olor.gated and/or irregular, in surface reflecitivity from 0.02 to 0.4, in composition from metal-rich and silicate rocks to volatile-rich carbonaceous assemblages. Of course there are many peculiar objects: asteroids with variegated surfaces and patches of different brightness and colour; asteroids which have suffered internal heating and have developed a core-mantle-crust structure; bodies converted by catastrophic impacts into piles of rubble held together only by gravity; objects with triaxial equilibrium figures or with a binary nature; outer-belt asteroids whose spectrophotometric properties are very much alike those of comet nuclei. These data are currently being interpreted in the frame of complex theoretical models for the formation of asteroids and their subsequent evolution, comparing the astronomical evidence with the results of meteoritic studies and with laboratory simulations and impact experiments. However, many basic uncertainties and open problems exist which cannot be solved by earth-bound observations and studies but need close-up investigations carried out by dedicated space missions. For instance in situ density and composition determinations as well as high resolution imaging for just a few (suitably selected) asteroids would be exceedingly valuable. Since space missions have investigated to date (or will in a few years) all the major planets, their satellites and ring systems ind also some comets, asteroids are the next obvious target to be considered with a high priority.

ON THE SOURCE AND STRUCTURE OF INTERPLANETARY DUST PARTICLES H. Fechtig Max-Planck-Institut fur Kernphysik, 6900 Heidelberg, FRG

The current view is that interplanetary dust particles stem mainly from comets. A considerable fraction nay be particles from long period comets as indicated by the Pioneer 10/11 dust experiments. The densities of Halley dust grains vary between 0.1 and 4 g/cW3 and are therefore comparable with the densities of the Brownlee particles. Taking into account the similarities in elemental compositions of cometary grains and Brownlee particles, possible mechanisms are discussed which alter cometary grains into Brownlee particles.

- 26 - RESONANCE INTERMETTANCE CAUSES THE GRAVITATIONAL SPLITTING OF METEOR STREAMS C. Froeschle, H. SchoLL Observatoire de Nice, B.P. 139, F-O6OO3 Nice CEDEX, France

The frequency distribution of,semimajor axes of meteor streams shows deep minima at mean motion resonances with Jupiter Like in the case of asteroids. Hence, the dynamical evolution of meteor stream particles in resonance appears to be affected by the same resonance mechanisms as the dynamical evolution of resonant asteroids. In the latter case, a simple model, the planar circular restricted averaged Sun-Jupite-asteroid model, reveals the main features of the topological structure of mean motion resonances: a separatrix divides a suitably defined phase space in three regions: inner circulator, outer circulator and Hbrator. Crossing of the separatrix and, hence, arising of stochasticity may occur in elliptic models including Jupiter's eccentricity. According to our numerical experiments, the instant of crossing the separatrix is a function of the particle's so-called critical argument which is determined basically by the angle between the particle's and Jupiter s position. Hence, for a young resonant meteor stream the following scenario may occur: particles of different portions of the stream cross tfie separatrix at different instant of time. Due to the particular dependence of the crossing time of a particle's position with respect to Jupiter's position, a stream may break up into arcs separating from each other. Because of the stochastic nature of this process, the arcs will disappear, of course. Investigating the orbital evolution of known resonant meteor streams and of model streams, we found examples for such a transitory arc formation. The orbital inclination of a meteor stream appears to be a critical parameter for arc formation.

THE DISTRIBUTION OF INTERPLANETARY DUST

Richard H. Giese and Bernhard Kneifiel Ruhr-Univesitat Bochum, Bereich Extraterrestrische Physik 4630 Bochum, FRG.

The three dimensional distribution of interplanetary dust in the solar system can be derived from optical observations of the surface brightness over the sky. There are, however, ambiguities due to the integration over the line of sight, which lad to different types of proposed 3D-distributions such aa "fan models", "ellipsoid models", "lobe models" etc. Infrared data of the zodiacal emission from rocket (ZIP) and satellite (IRAS) experiments brought independent information due to the different physical mechanism producing the observed radiation (thermal emission vs scattering). First combined interpretation of optical and infrared observations with respect to special problems such as spatial changes of the dust albedo or variation of number densities with solar distance yielded interesting results (eg. Dumont and Levasseur-Regourd, Hong) which make it necessary to review the present status of modelling of particle numbers and physical dust properties taking synoptically into account optical and infrared results.

DYNAMICS OF INTERPLANETARY DUST

E. Griin

Max-Planck-Institut fur Kernphysik, 6900 Heidelberg, FRG

In situ measurements by spaceprobes, microcrater distributions and remote observations both in the IR and visible wavelength range have established the mass frequency and spatial distribution of dust particles in interplanetary space. Consequences of the Poynting-Robertson effect and collisions on these distributions and the contributions of various sources (interstellar dust, asteroids and comets) are discussed. It is shown that the contribution from a distributed source of large particles in the inner solar system is most important. At the present time the Poynting-Robertson effect can transport into the inner solar system less than 10% of the material required to replenish collisional losses.

- 27 - DUST PRODUCTION OP COMET HALLE? WITH ACCOUNT OP LARGE PARTICLES CONTRTBTJTIOir A. Hajduk Astronomical Institute, Slovak Academy of Sciences 84228 Bratislava, Czechoslovakia

Critical analysis of the results of apace experiments, taking into account the contribution of large particles to the total mass production of comet Halley leads to much higher values of the dust production rate than those derived from the first analysis of space measurements. As a consequence it seems necessary to correct the gas to dust ratio of the mass production by a factor of 5, at least, from 0.2 to 1.0 or more. The corrected values of dust production rate are in much better agreement both with the current concepts of the comet's history and with the evolution of its meteor stream.

PARTICLE DENSITY VARIATIONS ALONG THE ORBIT OP THE HALLET HETBOR STREAM •. Hajdakova* Department of Astronomy, Comenius University 84215 Bratislava, Czechoslovakia

Mechanisms leading to higher particle concentrations in several places along the meteor stream associated with comet Halley are discussed. The positions of the mass concentrations represented by the mean anomaly of the stream's orbit, as determined from long series of observations of the Orionids and Eta Aquarids, are correlated with the deviations in the semimaior axis and argument of perihelion of the evolving orbit of the comet. It is shown that random deviations in the orbital elements of the comet may be responsible for the nonstable mass concentrations in the stream.

LABORATORY INVESTIGATION OP THERMAL CONDUCTIVITY OP DUST CRUST MODELS ON THE ICE COUBT NUCLEI SURFACES Kh. I. Ibadinov, A.A. Rahmonov Institute of Astrophysics Tadjik Academy of Sciences,73467O,Dushanbe,USSR

The exsistence of dust crust (matrix) on the surzaoe of ice comet nuclei •has got direct conformation during VEGA -1,2 and Giotto missions to Halley's comet. There are no reliable data on the thermophysical propertis of this crust now, but it is known that this dust crust plays an importent role In the nuclei evolution and other comet phenomena. In the purposes of investigation of thermal conductivity of comet ioe nucleus dust crust we carried out the laboratory experiments with oomet nuclei models under the conditions similar to natural ones at the heliocentrical distances 1-3 A.U. The HpO ice with dust particles of quartz, graphite and nickel was studied. The dust matrices 5-15 mm in thickness were formed in sublimation process of dust ice irradiated with a light beam. In most oases the effective thermal conductivity of dust matrices with sublimation products diffusing through them, are at temperatures 160-270 K as high as 0.1-0.3 W. nrT . K-1 . Keywords : dust crust, thermal conductivity, ice nucleus, laboratory modelling

- 28 - ON THE PHENOMENON OF ANOMALOUS DISTRIBUTION OF METAL ATOM EMISSION IN COMETARY HEADS

S. Ibadov

Institute of Astrophysics, Dushanbe, 734670, USSR

The possibility is considered of arising of free metal atoms, particularly that of sodium, in the circumnuclear region of cometary atmospheres due to evaporation of dust particles outflowing from the nucleus. Investigation of the nonstationary energy balance equation including the account of cooling the dust particles not only by a proper radiation, but also by a criogenic gas flow from the nucleus, leads to the conclusion about the existence in the comas of bright comets of two zones: depression and vacuum ones. In the depression zone the temperature of dust particles T is mainly determined by gas temperature, i.e. T is essentially lower than the temperature, corresponding to the vacuum regime usually accepted. The cometocentric coordinate is found from such consideration of the zone of the maximal releasing and, correspondingly, of the maximal radiat- ing of metal atoms in the cometary heads. This is in accordance with the displacement of the Na I line intensity maximum from the nucleus toward the Sun observed in the head.of Comet Mrkos 1957 d. The result obtained indicates the universal character of the phenomenon of anomalous distribution of metal atom emissions, including the Na I lines, in the heads of bright comets.

ELIMINATION OF THE ASTEROID SHORT-PERIODIC PERTURBATIONS: THEORY AND ACCURACY Z. Knezevic and B. Jovanovic

Astrononska opservatorija, Beograd, Yugoslavia

The discussion is presented of the results of elimination of the short-periodic perturbations of asteroid motions by means of the fourth degree analytical theory. The obtained "mean" elements were compared with corresponding numerically derived ones and the accuracy of results has been evaluated. Special attention has been paid to the high eccentricity and high inclination objects, as well as to the nearly commensurable ones. THE CONTRIBUTION OF PERIODIC COMETS TO THE ZODIACAL CLOUD L. Kresak and M. Kresakova Astronomical Institute, Slovak Academy of Sciences, 84228 Bratislava, Czechoslovakia

In our previous paper (ESA Symposium on the Diversity and Similarity of Comets, Brussels 1987), the mass loss rates of all the known periodic comets during the last two centuries were computed using backward integrations of their orbits and a uniform calibration referred to their variable absolute total magnitudes. In the present paper, the comets passing within 1 AU of the Sun are examined in more detail. The amount of dust injected into orbits crossing or approaching that of the earth; its fraction staying at a given time within it; and the ecliptical flattening of the produced dust cloud are estimated. It is shown that, at any time, a major contribution is due to a very limited number of parent otjects. The current influx appears too small to maintain the zodiacal cloud in equilibrium. While the Poynting-Robertson effect tends to displace individual particles into inner orbits, the critical period of their stay therr constitutes only a small fraction of the lifetimes of inspiralling particles. This fact poses serious problems for the interpretation of the origin of the zodiacal cloud. Alternative sources of replenishmant are required : time—limited contribution, by exceptionally large and active comets; continuing decay of extinct cometary nuclei and their fragments moving in short-period orbits; or ai> effective disintegration process of larger dust particles limited to the vicinity of the Sun.

IAU METEOR DATA CENTER B.A. Lindblad Lund Observatory, Box 43, S-221 00 Lund, Sweden

The purpose of the IAU Meteor Data Center is to retrieve and distribute data regarding the orbital and physical properties of meteoroids. The data files include photographic and radio determined meteoroid orbits, but no orbit determinations based on visual observations. The number of two-station photographic meteoroid orbits available at the data center is about 4 300 of which about 2 500 have been precisely reduced, and 1790 have been reduced by a graphical procedure. The number of meteoroid orbits available for study is thus comparable to the number of asteroid orbits. Most of the photographic orbits have been previously published in the literature, but some unpublished material is included. The total number of multi-station radio orbits available is of the order of 64 000, comprising about 40 000 orbits from the Harvard Radio Meteor Project, about 4 000 orbits from two Australian surveys by Nilsson and Gartrell, and about 20 000 orbits from three different USSR surveys carried out at Obninsk, Kharkov and Mogadisho. Most of these (.ata have not been available to researchers before. Some errors in the published lists have been corrected after correspondence with the original investigators. Various checks are presently being devised in order ro detect further typing or punching errors.

SPECTRAL OBSERVATIONS OF HALLEY'S COMET AT DUSHANBE

0. M. Mamadov

Institute of Astrophysics, 734670 Dushanbe, USSR

During October 1985-May 1986 about 50 spectrograms of Halley s Comet were taken with the 70-cm reflecting telescope and the grating spectrograph SPM-1 of the institute of Astrophysics Hissar astronomical observatory. A two cascade image intensifier with fiber optics was used. The spectra covered the region 6000-9000 A, their reciprocal dispersion was equal to 160 X/mm. Bands of CN /red system/, C2 /Phillips system/, H20, CO, NH2, H2 and to the first time, that of N2 /I positive system/ were identified.

- 30 - IMAGE PROCESSING OF VEGA-TV OBSERVATIONS D. MBhlmann, G. Elter, B. Rubbert, H. Danz, T. Manfloldt, U. Ueidtich Institut ftlr Kosraosforschung der AdW der DDR, Berliij, DDR H. Lorenz, G. Richter Zentralinstitut fUr Astrophysik der AdW der DDR, Potsdam-Babelsberg, DDR

Different algorithms, used to identify real structures in the near-nucleus TV-images of the VEGA-spacecrafts are described. They refer mainly to imagerestau- rations, noise-reduction and different methods of textura analysis. The resulting images, showing first indications for structures of the surface of P/Hallev- are discussed shortly. 7

The Origin and Evolution of the Port Cloud

W.M. Napier

Royal Observatory, Blackford Hill, Edinburgh, Scotland, UK.

The Oort comet cloud is situated close to the dynamical interface between the Solar System and the Galaxy. Its long-term behaviour is affected not simply by stellar encounters, but also by interactions with massive nebulae, and by galactic tides. It now appears that, because of encounters with molecular clouds, the dynamical lifetime of the long-period comet system is much less than the age of the Solar System, and that the comets must be replenished from some massive reservoir. The location of this source is a controversial topic which bears directly -in the question of comet cosmogony. Suggested reservoirs are a dense inner Oort cloud, or the molecular cloud system itself.

The various galactic interactions also throw comets towards the inner planetary system; terrestrial encounters with the debris from very large comets in particular are expected. These episodes generate climatic and biological trauma on the Earth, and fundamental galactic periodicities are expected to occur in such phenomena as geomagnetic reversals and the evolution of life. Conversely the terrestrial record provides severe new constraints on the structure and past evolution of the Oort cloud. In particular the concepts of a 'dense inner cloud' or a 'solar companion star' are difficult to reconcile with the record of past impact cratering. Thus the recognition of the Oort cloud as a dynamically active system has raised many new questions, which are here reviewed.

METEOROID STREAMS ASSOCIATED WITH APOLLO ASTEROIDS : EVIDENCE FROM THE ADELAIDE RADAR ORBIT SURVEYS

Duncan Olsson-Steel Lund Observatory, Box 43, S-22100 Lund, Sweden; and The University of Adelaide, Australia.

Since the discovery of 3200 Phaethon (the 'Geminid' asteroid) in 1983 there has been renewed interest in the association of meteor showers with Earth-approaching asteroids. In the past the existence of several streams associated with different asteroids (in particular Adonis, Apollo, Hermes and Oljato) has been suggested but not proven. In the present search the 3759 meteor orbits determined at Adelaide in the 1960's (the only surveys yet conducted from the southern hemisphere) have been compared to the orbits of all Aten-Apollo-Amor asteroids discovered to 1986 November. Strong evidence is found for streams contiected with Apollo- type asteroids 1566 Icarus, 1937 UB Hermes, 2101 Adonis, 2201 Oljato, 2212 Hephiistos, 5025 P-L, 1982 TA, and 1984 KB. The final five in this list may be members of the Taurid-Arietid complex, with Jupiter-crosser 5025 P-L being particularly noteworthy; also possibly connected with this complex is long-period comet 1967 II Rudnicki. No stream associated with 1862 Apollo was identified, but this may be due to the lack of observations at the appropriate solar longitude. No streams associated with any Aten or Amor asteroid were found: this may be due to the limited detectability of their meteors, if they exist, because of their low geocentric velocities. In general streams were discovered for all asteroids coming within 0.1 AU of the Earth having radiants accessible from Adelaide and having geocentric velocities above about 22 km/sec : this suggests that meteoroid streams are a general feature of Earth-approaching asteroids. These streams may have originated in collisions with smaller bodies, or may be remnant tails from epochs in which the asteroids were active comets.

- 31 - THE DISPERSAL OF METEOROID STREAMS BY RADIATIVE EFFECTS Duncan Olsson-Steel Lund Observatory, Box 43, S-22100 Lund, Sweden; and The University of Adelaide, Australia.

For some years a major problem in meteor astronomy has been an explanation of the dispersion of the orbits of meteoroids within particular streams. For streams with aphelia well within Jupiter's orbit (such as the Geminids) planetary perturbations are insufficient to explain the dispersion although they can accommodate the required movement of the heliocentric distance of the node so as to explain why this shower was not observed prior to the 1860's. The width of the stream (duration of the shower) requires unreasonably large ejection velocities from the parent body for this to be "a viable explanation. By numerically integrating the orbits of meteoroids with identical physical properties but differing spin directions, and allowing for perturbations due to the solar radiation field (radiation pressure, Poynting-Robertson effect, Yarkovsky-Radzievskii effect), the main observed characteristics of the Geminid shower are explicable: these characteristics include the shower duration at different magnitudes, the skew rate profile, and the changes in the mass distribution and the radiant diffuse- ness as the shower progresses. The necessary spin rates are about 3000 rev/sec for 1 mm radius meteoroids (i.e. radar meteors) and 1000 rev/sec for 1 cm meteoroids (i.e. visual meteors). These spin rates would be attained within a thousand years of release of the meteoroids by the parent body, with the spin-up being dominated by the solar radiation pressure imposing a torque on the non- uniform meteoroids. Such spin rates can also explain various anomalous effects observed in meteors, such as fragmentation in visual meteors and the variation of the initial width of radar meteor trains. It therefore appears that the Yarkbvsky-Radzievskii effect is an important source of dispersion within meteoroid streams which has been largely neglected until now, but should be incorporated into future models. Reference: D.Olsson-Steel, 'The dispersal of the Geminid meteoroid stream by radiative effects', Mon. Not. R. astr. Soc, (in press).

THE TRUE HEIGHT DISTRIBUTION AND FLUX OF RADAR METEORS

Duncan Olsson-Steel1'2 and W.G.Elford2 1) Lund Observatory, Box 43, S-22100 Lund, Sweden. 2) The University of Adelaide, South Australia.

When compared to satellite detector measurements for dust particles of mass < 10~6g and optical meteor observations for mass > 10~2g, the flux at interstitial masses as measured by radar meteor techniques is discrepant: the radars render fluxes which are too small by a factor of about 20 to 30. This has most often been explained as being due to the majority of the flux being held in low-velocity meteoroids which produce little ionization and hence have limited radar detectabilities. We have proposed an alternative explanation whereby the discrepancy is caused by the wavelength- dependent underdense echo ceiling of meteor radars, which mostly operate at frequencies above 20 MHz (Elford, IAU Symp. No. 90, p.101, 1979), and have suggested that such radars, which exhibit height distributions peaking at about 95 km with few meteors above 105 km, detect only the few percent of underdense meteors which give lower altitude trains (cf. Greenhow, Smithson.Contrib.Astrophys., 7, 5, 1963). To test this hypothesis we have determined the height distribution of metecs with radars operating at 2 and 6 MHz, for which the echo ceilings are at about 140 and 120 km respectively. These distributions show peaks above 105 km, with most meteors occurring above this height. A comparison with standard echo attenuation theory indicates that the true influx maximizes above 110 km with many meteors occurring right up to 140 km. Additional observations using the powerful Jindalee over-the-horizon radar in central Australia have confirmed these results, and shown that the cumulative flux of particles of mass > 10~6g is 9 x 10" m~ sec"1; this is consistent with satellite observations and is over an order of magnitude higher than derived from previous radar meteor observations (Thomas, Whitham and Elford, Proc.Astron. Soc.Aust., b, 303, 1986). This solves many problems of atmospheric physics and chemistry, but raises questions regarding the supply of meteoroidal matter from comets.

- 32 - PLANETARY ORIGIN OF FIREBALLS AND COMETS

V. Padevet Astronomical Institute, Czechoslovak Academy of Sciences, Ondrejov

The four-degree fireball classification based on their end heights has proved to be an outstending criterion for distinguishing the quality of the material of meteoroids /Ceplecha and McCrosky, 1976/. But only the theory of end heights can quantitatively determine the previously ascertained structural differences /Padsvet, 1987/. The theory of the fireballs' end heights forecast the existence ot two main type of fireballs. The first type of undercriticaI bodies can reach the Earth's surface /meteorities/ whereas the second type of overcritical bodies cannot reach it. At the end point of overcritical fireball, there takes place a total disintegration of the meteoroid's structure due an excessive pressure. These properties of the theory of end heights enable us to discover unknown material structure of Large meteoroids. So far we assumed that meteorites may originate only from the deep entering fireballs of Groups I, II. However, also the high ending fireballs of Group III A, III B are due to the known types of meteorites, chiefly carbonaceous C2, C1 ones. As all meteorites including the carbonaceous meteorites underwent a development in the bodies of the planetary type /Jakes', 1978/, then planetary origin of fireballs is possible. As approximately 30 % of the fireballs posses cometary orbits and for some fireballs we can even find their parental comets /Ceplecha, 1977, 1983/, comets may posses not primordial but probably planetary origin. Although most authors support the primordial hypothesis, it is in fact very difficult to prove the existence of the remains of the primordial sub- stance in the solar system. The origin of comets may be looked for in the disintegration of one or more bodies of the planetary type within Jupiter's orbit /Van Flandern, 1978/. The early evolution of planet might represent an explosion of a hot massive nucleus whose unrestricted expansion is hindered by gravitation.

COLLISIONAL FRAGMENTATION PROCESSES: EXPERIMENTS AND ATTEMPTS FOR A THEORY P. Psolicchi Istituto di A«;trortomia, <}n. of Pisa, Piazza Torricelli 2, 1-56100 Pisa, Italy

Collisional fragmentation processes play a key role in the evolution of astero- idc, as well as of satellite systems. The physical problem is not well understood, involving various and complex properties of solid bodies. The experiments give us some useful informations, but a more systematical exploration of the input parameters /specific impact energy, velocity of impact, angle of impact, physical properties of the material and so on/ is required. Moreover, the problem of scaling from centimeter sized laboratory targets to hundred kilometer sized astronomical "targets" has to be studied; in particular the self-gravitation can affect strongly both the fragmentation process and the final fate of the outcomes. In this context, a semiempirical approach has been developped, with the purpose of a simple /and rough/ modelling of the process, to be used for the interpretation of laboratory experiments, to clarify its scaling properties and, finally, to attempt some kind of fit with the observations.

- 33 - HETEOROID DECELERATION AND THE FRESNEl CHARACTERISTICS

P. Pecina

Astronomical Institute, Czechoslovak Academy of Sciences, 251 65 Ondfejov, Czechoslovakia

The work describes briefly the application of the complete soLution of the basic equations of meteoric physics, found in connection with solving the problems of photographic meteor theory, to the construction of theoretical Fresnel characteristics. It is shown know the meteoroid deceleration can be incorporated into concepts of radar physics. The corresponding radar equation is derived and the possibility of using the- ss Fresnel characteristics for the evolution of the ablation parameter^ and the pre- at-ospheric velocity v=- from the registered amplitudes is discussed.

POST-PERIHELIOH METEOR COMPLEX 0? P/EtfCKE V. Porubcan and J. Stohl Astronomical Institute SAV, 84-228 Bratislava, Czechoslovakia

The Taurid meteor complex associated with P/Encke is studied on the basis of relevant radar observations of the Beta Taurids and other daytime meteor showers at the post-perihelion encounter of the complex with the Earth. Orbital characteristics, radiants and width of the post-perihelion complex are derived from the observations, and compared with corresponding theoretical values derived from the pre-perihelion observations of the Taurids and other associated showers. Reality of the associations and the structure of the whole complex al>e evaluated and discussed.

ON THE INTERACTION METEOR COMPLEX. J.Rajchl Astronomical Institute,Czechoslovak Academy of Sciences 25165 Ondrejov,Czechoslovakia

An approach to the problem of a meteoric complex called the Interaction Meteor Co plex /IMC/ is applied and discussed,where author s former idea of the interaction layer /Rajchl 1969/ is generalized.Instead of atmospheric particles as projectiles and meteor bodies as a target,the role of an extended interaction of meteoroid* is emphasized,both with planet surfaces and/or their satellites-called "hard" or local interaction- and with planet atmospheres /"soft or non-local interaction/,elasio or inelastic in form.The dissipation and related formative aspects are joined in one complex of compact topological nature.Examples of all the above mentioned types of interaction/e.g.superrotavxon of the Earth atmosphere,planetary rings,noctilucent clouds,enhanced airglow/ are presented.In more detail the inelastic soft interaction of whole "spectrum" from faint meteors,detected by TV technique to Fireball Network bolids with the Earth atmosphere is considered.First results in the form of a T or three-phase structure and cross-complementarity are reported.Possibility of existence of an other,one-phase structure as a real alternative for the outer planets of the Solar Planetary System is from the topological compactness inference deduced and by results of Levin and Simonenko /I982/ supported.

- 34 - PHYSICAL EVOLUTION OF COMETS

Hans Rickman

Astronomiska Observatoriet, Box 515, S-75120 Uppsala, Sweden

What is the mechanism by which long-period comets fade during repeated passages upon arrival fpom the Oort cloud? What thermal evolution should be expected from a cometary nucleus? What observational evidences bear upon the estimate of a typical lifetime for short-period comets? What is the controlling physical mechanism? What evidence do we have for the build-up of refractory mantles on comet nuclei? Do we see evolutionary trends in comet magnitudes and nongravitational effects? Do comets evolve into asteroidal bodies - permanently or temporarily? How are the physical and dynamical evolutions of comets interrelated? All these problems will be dealt with in an attempt at assembling a coherent picture out of all available evidence. As a basis for the discussion, emphasis will be placed upon recent progress in the understanding of cometary origins and the structure of cometary nuclei partly resulting from the exploration of Halley's comet.

POSITIONAL REDUCTION OF PHOTOGRAPHS TAKEN BY FISH-EYE OBJECTIVES

P, Spumy Astronomical Institute of the Czechoslovak Academy of Sciences, 251 65 Ondfejov, Czechoslovakia

The cameras with Fish-Eye Zeiss Distagon objectives fOpton-Distagon, focal distance 30 mm, field of view 180°, focal ratio 1/3.51 have been used with a great success in the Czech part of the European Network for fireballs already more then ten years. In this work the method used up to now for a positional reductions of the photographs is compared with other reductional formulas. It was found that the reduction formula presently used fnr determination of the zenith distance is suitable, however the formula for determination of the azimuth can be replaced by a new expression, which essentially improves the total positional reduction.

PRODUCTION RATES OF GASES AND SOLIDS IN COMET P/HALLEY DURING THE 1986 APPARITION B. Stecklum, W. Pfau

University Observatory, DDR-6900 Jena, German Democratic Republic

From photoelectic photometry at our 90-cm telescope we derived continuum and emission band fluxes within the bandpasses of the standard IHW filters. These data were converted to give production rates for CN, C3, C2, and solids. The observations cover the range of pre-perihelion distances from 2.1 AU to 1.1 AU and include one post-perihelion measurement at 1.7 AU. The production rates of the gaseous components show a strong dependence on heliocentric distance. This result is compared with behaviour of other comets and theoretical considerations. The dependence is less steep for the solids. This may be due to relatively pronounced backscattering properties of the grains. During one pre-perihelion night /r = 1.15 AU/ intensity profiles along three sections through the coma of P/Halley were measured. Compared with the Haser model the profiles show a global anisotropy of the coma and possibly local structure.

- 35 - PHOTOMETRY OF COMET HALLEY AT THE SKALNATE PLESO OBSERVATORY 2. PRE-PERIHELION OBSERVATIONS IN EMISSION BANDS CO+, C- AND IN CONTINUUM J. Svoren Astronomical Institute of the Slovak Academy of Sciences, Skalnate Pleso Observatory, 059 60 Tatranska lomnica, Czechos Lovakia A second part of the pre-perihelion photoelectric measurements of P/Halley obtained at the Skalnate PLeso Observatory is presented. The observations cover 9 nights from November 8, 1985 to January 5, 1986. A set of focal diaphragms of the following diameters was used: 29.53", 48.98", 81.08", 137.34" and 220.53". Results of this paper are magnitudes in focal diaphragms in the standard IHW + system reffering to Co and C2 emissions and to Cont, 3650 and Cont. 4845. The dependences of the magnitudes upon the diameters of focal diaphragms, coma diameters, total brightness and fluxes in emission bands are also determined.

MASS DISTRIBUTION OP UliDEKDENSE METE0E ECHOES: SELECTION OF BASIC DATA M. Simek Astronomical Institute, Czechoslovak Academy of Sciences, 251 65 Ondrejov, Czechoslovakia

Volume of recorded underdense meteor echoes is determined by the transmitted power, treshold sensitivity of the receiver, antenna gain including its directivi- ty and Ly the range of reflecting point on meteor trail. These parameters must be considered when the mass-distribution index s is evaluated.

HALLEY DUST COMPOSITION M. Sole, P. Hsiung, E.K. Jessberger, J. Kissel Progress is reported in evaluating mass spectra of cometary dust grains that have been obtained by particulate impact analyzers flown onboard the Vega and Giotto spacecraft. Statistical analysis and intercomparison of mass spectra transferred in less and more compressed models /mode 1 to 3/ shows the elemental and isotropic composition of about 3000 grains. The study demonstrates that - the mean elemental abundances are similar to abundances of chondrites c 1 with the exception of H, C, N, 0 elements, - the occurence of natural isotopes matches well the terrestrial values, - about five various classes of spectra can be found: 1 with dominant Mg-Si element group, 2 spectra dominated by CON elements, 3 spectra with both groups of elements, 4 spectra rich in carbon and 5 spectra with strong iron line. Classification of particle types, deviations from it and time and local variations of prevailing particle types in coma are discussed.

ON APPLICABILITY OP METEOR STREAM MEMBERSHIP CRITERIA J. Stohl and V. Porubcan Astronomical Institute SAV, 84228 Bratislava, Czechoslovakia

Various meteor stream membership criteria (especially the D-eriterion and X-criterion) used in evaluating potential associations of individual meteor orbits with a mean orbit are analysed on the basis of precise photographic orbits of chosen meteor showersfthe- Taurids , Orionids, Perseids and Geminids). On some false associations of meteors with a particular shower is infered fron the analysis of the distributions of various orbital elements. Applicability of the criteria to the determination of the stream memberehip for individual meteors is discussed and suggestions on relevant use of the criteria are presented*

- 36 - CHARGING OF DUST PARTICLES BY ELETRONS ANO IONS

l.J. Svestka, 2.E. GrUn, S. Pinter, S. Schumacher

I.Prague Observatory,Prague Czechoslovakia,2.Max-Planck-Institut fUr Kernphysik, Heidelberg,Germany

Dust particles of sizes between 1 and 100 mikrometers from various materials have been suspended with help of quadrupole field in vacuum chamber at pressures from 10 to ID mbar and charged by Ar+ ions of energies up to ID keV as well as by electrons of energies up to 25 keV. For damping of particles motion at pressures below lo mbar the damping system with photomultipliers and feeback curcuits was developed. By charging with Ar ions charge-to-mass ratios up to 4 C.kg were measured and various phenomena observed. Study of parameters of secondary electron emission and other physical properties of small particles by charging at different chamber pressure was proposed and measurements were started.

TAIL LENGTHS OF COMET HALLEY FROM HISTORICAL DATA

G. A. Tammann, F. Esin /Yilmaz/, F. Limboz

In this paper a test for the presence or absence of secular changes in comet HaUey is derived from historical data on the tail length. The linear lengths of comet tail are calculated for almost 2000 years with the heLp of visueL estimates of the tail lengths collected from various sources. A plot of linear lengths against time before and after perihelion defines quite well an upper envelope and shows no indication that HaLley's taiL has faded during the last two millenia.

PROTON MICROPROBE ANALYSIS OF INTERPLANETARY DUST PARTICLES

R. Wallenwein, Ch. Antz, E.K. Jessberger, K. Traxel

Max-Planck-Institut fur Kernphysik, P.O.Box 103980, 6900 Heidelberg, FRG

Interplanetary dust particles (IDP'S) which can be collected non-destructively in the stratosphere contain valuable information on small cosmic bodies like comets. Strato- spheric IDP'3 are small - typical 1-10 inn diameter with a mass of less than 10~8 g - and thus they are difficult to analyze. As many as possible different and consequently non-destructive analytical methods should be applied because of the individual structure and composition and hence history of each IDP. Therefore we used both, a proton-microprobe and synchrotron radiation x-ray fluorescence [1], for the analysis of these snail objects.

This is a report on the results obtained with the proton-microprobe. First feasibil- ity tests had previously been performed with two IDP's, Zodiac and Bounce [2]. Almost aLl elements in the range of 13 < Z < 30 have been quantitatively determined. Further analysis with improved experimental conditions and two different IDP's have been performed recently. Most elements in the range of 12 < Z < 35 and some additional trace elements have been detected. The quantitative results of these analyses will be presented.

[1] Chr. Antz et al. this conference [2] E.K. Jessberger, R. Wallenwein (1986), PIXE-characterization of stratospheric micrometeorites. Adv. Space Res., COSPAR Toulouse, in Press

- 37 - EVOLUTION OF ASTEROIDS AND ASTEROID FAMILIES

V. Zappala Osservatorio Astronomico di Torino, 1-10025 Pino Torinese, Italy

Large scale collisions are presently thought to be the major process causing the evolution of asteroids since their relative velocities were increased to about 5 km/s, presumably by encounters with Jupiter-scattered planetesimals and/or by sweeping resonances. Simple statistical computations show that all asteroids have been impacted by bodies up to 1/10 of their size during the solar system lifetime. The outcomes of these impacts depend crucially on target size; while for bodies less than about 100 km across catastrophic fragmentation occurs, with the fragments ejected into independent heliocentric orbits, for larger asteroids the most dis- ruptive impact could shatter the body yet not impart sufficient velocity to most of the fragments to cause permanent dispersal. Under these conditions, gravity causes much of the debris to reassemble, forming brecciated rubble piles with quasi- equilibrium shapes depending on their angular momentum of rotation. This latter quantity is itself determined to a large extent by the collisional process, so that only the few largest asteroids probably "remember" their primordial spin rate. When fragments are dispersed, an asteroid family arises, namely a group of asteroids for which a suitably chosen set of orbital parameters show a significant clustering about the values of their parent body /though the procedure needed to filter out planetary perturbations on the orbits and to evidence the clusters is complex and introduces severe uncertainties/. Collisions also caused a gradual comminution of asteroids, probably reducing the total mass of the belt by a factor of the order of 5; however, a large fraction of the original solid material present in the belt was probably ejected by the same primordial process which stirred up the orbital motions. Evidence supporting the above scenario is provided by data on the size distribution, the rotational properties and the shapes of asteroids, as well as by analyses of families /compared with the outcomes of laboratory impact experiments/ and by meteoritic studies.

UNUSUAL MOTION OF AMOR

K. Ziolkowski Space Research Centre, Warsaw, Poland

Precise analysis of the orbit of minor planet /1221/ Amor, based on all observations made in 1932-1980, shows that in 1956 there was an unexplained event in the motion of the asteroid. Possible interpretations of that fact as well as discussions of peculiarities in the long-term mot a on of Amor in 1650-2150 will be presented.

PLASMA TAIL OF COMET BENNETT 1970 II

J. Zvolankova, 0. Kubafek, and E. M. Pittich

Astronomical Institute, Slovak Academy of Sciences 842 28 Bratislava, Czechoslovakia

A set for fourteen large-scale phenomena exposures of comet Bennett 1970 II between 1970 April 27 and 30 is investigated. Clearly visible kink* of the plasma tail enabled us to determine their mean radial velocities relative to the nucleus. No expressive disconnection event was observed within this period.

Keywords: Comet Bennett 1970 II, Plasma tail. Disconnection event.

- 38 - TS 3 RESONANCE IN THE SOLAR SYSTEM

RESONANT MOTIONS OF RIGID BODIES IN THE SOLAR SYSTEM Yu. V. Barkin Higher Technical School, Department of Theoretical Mechanics 2nd Baumanskaya Street, 5, Moscow, USSR

Resonant motions of the systems of mutually gravitating rigid bodies are studied using periodic and conditionally periodic solutions of non-linear multifrequency oscillating systems containing a small parameter. Conditions for existence of periodic solutions of these systems in the general cases and some degenerate cases were obtained. Along with the selection of initial conditions, the problem parameters are selected as holomorphic functions of the small parameter. The existence of periodic solution of three kinds in the general problem of three rigid bodies with quasi-concentric density distribution is demonstrated. One of the possible explanations of the observed resonance in the motion of Venus is given by means of the periodic solution of the first kind for the problem. Periodic solutions in the planet version of the problem od n rigid bodies are found. These solutions generalize the corresponding periodic solutions of the problem of n point bodies. The bodies of the system are assumed to be of small size and with quasiconcentric density distributions. A constructive method of obtaining conditionally periodic solutions of multifrequency oscillating system in the neighbourhood of periodic solutions for the corresponding unperturbed system is worked out. Using this method, analytical theory of the rotatiaon of the Moon is worked out and new resonant effects in the motion of the Moon are described. It was shown that the mean vector of sideric angular velocity of the rotation of the Moon does not coincide with its polar axis of inertia and has definite numerical value. The mean resonant motion of the Moon around its center of mass makes more precise and supplements classical Cassini's laws. The results are obtained taking into account the influence of higher-order harmonics of the Moon-Earth system force function, the influence of the gravitational attraction of the Sun and the planets, the influence of the ecliptic evolution.

QUASI RESONANT TERMS IN SECULAR VARIATIONS PLANETARY THEORIES

P. Bretagnon

Bureau des Longitudes, 77 avenue Denfert-Rochereau, 75014 Paris, France

Secular variations planetary theories constructed at the Bureau des Longitudes use either order by order methods (with respect to the masses) or iterative methods. In all cases, the convergence of the solutions with respect to the masses is slackened by the upcoming of quasi resonant terms giving smaller and smaller divisors. This shows how difficult it is to get very precise solutions over long time spans such as several thousands of years. On another hand, if we locally develop the quasi resonant terms with respect to time, we can get very precise analytical solutions over reduced time spans. We have therefore undertaken an analytical solution for the t.'me span 1950-2050, aiming at a 30 meter precision on the position pf the Earth with respect to the barycenter of the solar system. This precision is in fact needed for the comparison to the millisecond pulsar data. •

AN ANALYTICAL APPROACH TO THE TIME TRANSFORMATION TDB-TDT.

L. Fairhead

Bureau des Longitudes, 77 avenue Denfert-Rochereau, 75014 Paris, France

An analytical formula for the time transformation TDB-TDT valid over a few thousand years around J2000 has been computed with an accuracy at the 1 ns level. This computation was carried out by integrating the differential equation derived from the general PPN metric given by Brumberg in Astrometric Techniques, IAU Symposium 109, (1986). The transformation TDB-TDT is independent of the PPN parameters introduced by Brumberg and of the 3 most commonly-used coordinate systems, at least at the 1 ns level. The analytical theories bodies. We scales, cannot I to calculate this transformation yield different results to our own procedure. These differences are due to the averaging out, in the numerical procedures, of long-period terms in the planetary theories used in the calculation. Resonances in the Solar System are at the source of these terms and, we feel, are thus not properly represented in the numerical procedures. '

- 39 - ORBITAL RESONANCES AMONGST PLANETARY SATELLITES

S. Ferraz-Mello

Universidade de Sao Paulo, Instituto Astronomico e Geofisico, Sao Paulo, Brazil

Orbit-orbit resonances are a common feature amongst planetary satellites. 12 Saturnian satellites (out of 17) are involved in 8 pairs of resonant interaction: i\ pairs in co-orbital motion (Oanus- -Epimetheus, Tethys-Telesto, Tethys-Calypso and Dione-Dione B), 3 couples in (p+l):p resonances (Mimas-Tethys, Enceladus-Dione and Titan-Hyperion) and one couple in secular resonance (Rhea- -Titar). Some satellites of Jupiter and Uranus also present resonances; these resonances involve three orbits (instead of two as for the mentioned Saturnian satellites) and follows the model first studied by Laplace. They are the three inner Galilean satellites of Jupiter (Io, Europa and Ganymede) and three Uranian satellites (Miranda, Ariel and Umbriel). Resonant satellite orbits are the realm of analytical studies. Indeed, for most of them, their fast motion (periods of the order of some days) prohibites, the use of numerical integration of the equations of motion, even for the sake of producing ephemerides for relatively short intervals. This lecture does not intend to be a review of the extensive literature on satellite resonances but rather presentation of some today's main problems and some of the proposed solutions.

ON THE ORIGIN OF GAPS IN THE DISTRIBUTION OF MINOR PLANETS

S. Ferraz-Mello

Universidade de Sao Paulo, Instituto Astronomico e Geofisico, Sao Paulo, Brazil

An analytical averaging theory founded on the restricted elliptic three-body problem and valid for motions around high-eccentricity libration centers has been constructed. It reveals that for some commensurabilities there are forbidden intervals in the distribution of the values of the semi-major axis around which the actual values oscillate. These intervals coincide with gaps in the distribution of actual minor planets. The results already obtained for the 2:1 resonance show that the 2:1 gap may be completely explained by the existence of a forbidden regions. Additional hypothesis as collisions or extraordinary forces are not needed.

CHAOTIC BEHAVIOUR OF RESONANT MOTIONS

C. Froeschl^

Observatoire de Nice, B.P. 139, F-06003 Nice Cedex

After a long period of gestation, chaotic orbits and Spins have arised in the solar system in close connection with resonances. Methods and models already used either in stellar dynamic or by plasma physicists like surfaces of section, Lyapunov characteristic exponents, mapping technique... have been applied successfully. Very often the introduction of action-angle variables allow to reduce a resonant problem to a problem with one degree of freedom. The removal of high frequency terms lead to hamiltonian systems which after some simplifications appear as hamiltonians of either the perturbed pendulum (the first fundamental model for resonance) or the so called second fundamental model which seems be closer to a large class of orbit and spin orbit resonance problem. The onset of stochasticity is predicted using the Chirikov overlap criterion or the crossing of the separatrix. Semi analytical perturbation theories allow good interpretations of the numerical results and even more give some limits to the validity of mappings models. Finally a third source of chaotic motion associated with an interplay between two degrees of freedom has been identified and baptized Super Resonance.

- 40 - CHAOTIC MOTION IN SECULAR RESONANCES Ch. Froeschle, H. Scholl Observatoire de Nice, B.P. 139, F-06003 Nice Cedex

Regions of chaotic motion appear at mean motion resonances as it was shown for the Sun-Jupiter and for the Saturn-Enceladus system. We aim to find also regions of chaotic motion at a different kind of resonances, namely at the so-called secular resonances. While at mean motion resonances, the forcing frequency is given by the revolutionary frequency of a perturbing body, in the secular resonance case the forcing frequencies are caused by the precessional motion of planetary nodal and/or apsidal lines. . In particular, we investigated the possibility of chaotic motion at the secular resonances \>r, v,, \> by integrating numerically the Sun-Jupiter-Saturn-asteroid model over ~ 10 years. At tne secular resonance v., we found, indeed, a fictituous asteroid alternating between libration and outer circulation as well as a fictituous case alternating between libration and inner circulation. Both kinds of alternation were related to chaotic motion at mean motion resonances. Hence, in analogy, we conjecture to have found regions of chaotic motion for the v secular resonance. On the other hand, the asteroid (2335) James known as a v resonance case does not show chaotic motion over 10 years. At the secular resonances v and -J, we found librators and outer circulations but no alternators. An extension of the integration period will probably yield alternators also for these two secular resonances. According to our model calculations, the v resonant case (2368) Beltovata will be ejected from the respective resonance by close approaches to Jupiter which indicates chaotic motion. The remaining 15 asteroids located in and near these two secular resonances did not reveal chaotic motion in our model. The next step will be to answer the following question: to what extent chaotic motion may play a role for the depletion of secular resonances and for the delivery of Appollo- -Armor asteroids?

RESONANCES IN THE SOLAR SYSTEM: MATHEMATICAL THEORY John D. Hadjidemetriou University of Thessaloniki, Thessaloniki, Greece

Many configurations in the Solar System consist of a massive body (Sun or a major planet) and a set of smaller bodies (planets or satellites, respectively) moving under their mutual gravitational attraction. Such a system can be considered as a set of perturbed two-body subsystems (Sun-planet of planet-satellite), the perturbation being due to the gravitational coupling between the above subsystems, thus making the system nonintegrable. Evidently, the unperturbed motion is orbitally stable, but the coupling may destroy the stability. We study the mechanism by which instability is generated through the above mentioned coupling and its relation to the ratio n,:n?;n3:... of the frequencies of the two-body subsystems. Qualitative difference appear when the number of planets (or satellites) is increased from two to three or more. In the case of circular motion of two planets around the Sun, instability is generated only at the resonances (2n+l):(2n-l), i.e. 3:1, 5:3,... In the case of elliptic orbits both stable and unstable motion exists at the resonances 2:1, 3:2, 3:1, 5:2, 7:3. Similar results, but less important hold for higher order resonances. These results are also true for the motion of an asteroid, considered massless, under the perturbation from Jupiter. The unperturbed (i.e. uncoupled) motion of three or more planets around the Sun is critical, which means that a small Hamiltonian perturbation always exists, which generates instability. However stable planetary systems with more than two planets in circular orbit exist. The same is true for elliptic motion. In fact, the increase of the mass of at least one planet plays a stabilizing role, so that it is more likely to find in nature such solar systems (as our own!). Chaotic motion exists above an energy level and this may be related to the trapping of asteroids near a resonance , resulting to a group, or to the avoidance of a resonance, resulting to a gap. Perhaps additional perturbations, though small, play an important role in the distribution of asteroids . Finally, the stability of a solar system with two Suns and two or more planets is studied, in connection to the existing resonances in the system.

- 41 - EFFICIENCY OF VARIOUS METHODS OF THE SEARCH FOR PERIODIC ORBITS P. Hadrava and 3. Kadrnoska Astronomical Institute of the Czechoslovak Academy of Sciences, Ondrejov

The periodic orbits in circular restricted 3-body problem are calculated by different numerical as well as analytical methods. The efficiency of methods of both kinds are compared in this contribution. The improvement of analytical methods can be achieved by an artificial splitting of perturbation term. The analytical approximations are thus sufficiently accurate even for large values of mass ratio \i . The use of these approximations as zero order approximation in numerical codes for search for periodic orbits improves their efficiency also.

SLOW DYNAMICAL CHAOS IN PERTURBED RESONANCE PROBLEM Jacques Henrard Facultes Universitaires Notre-Dame de la Paix, Namur

Orbit-Orbit resonance problems are usually modelized by one degree of freedom systems, the phase space of which contains two homoclinic orbits like the well known "pendulum phase space". This one degree of freedom model is usually obtained by averaging over the frequencies of other degrees of freedom assumed to be much faster than the resonance frequency. It may happen that combination of these other frequencies is also slow (double resonance problems). In some of these cases, the problem can be modelized by a "pendulum phase space" the dynamics of which changes slowly and periodically with time. This slow change forces the homoclinic orbits, to sweep periodically an area of the phase space. The motion in this area can be described as a chaotic motion with a long diffusion time. We shall review the recent progresses in describing this situation with help of the Adiabatic Invariant Theory. We shall apply this description to the problem of the slow dynamical chaos found numerically by Wisdom in the Kirkwood Gaps of the Asteorid Belt.

RESONANCES IN THE ORBITAL MOTION OF ARTIFICIAL SATELLITES A. H. Jupp Dept. of Applied Maths, and Theoretical Physics, Liverpool Univ., PO Box 147 Liverpool L69 3BX England '

- 42 - ORBITAL ANALYSES OF INTERCOSMOS SATELLITES AND THE EARTH GRAVITY FIELD MODELLING

Jaroslav KlokoCnik Astronomical Institute of the Czechoslovak Academy of Sciences CS - 251 65 Ondfejov, Czechoslovakia

Orbital inclinations of INTERCOSMOS 3, 5, 9, 10 and 11 satellites have been analysed as passing through A/oC - orbital resonances and the values of the lumped geopotential coefficients of the 14th, 15th, 29th and 30th orders have been computed. Thesi* results have been used as a part of the input data for adjustments of the values of the individual harmonic coefficients of the relevant orders, as constraints for the comprehensive Earth gravity models GRIM 3, 3B, 3L1, for the accuracy calibration of older Goddard Earth Models, and for various inter-comparisons of the Earth gravity models.

A SIMPLIFIED MODEL OF THE LUNAR SPIN-ORBITAL RESONANCE COUPLING FOR NUMERICAL INTEGRATION G. Krasinsky

Institute of Theoretical Astronomy, USSR Academy of Sciences, 10 Kutuzov Quay, 192187 Leningrad

A method taking into account resonance effects in lunar orbital motion is developed. The method makes it possible to avoid numerical integrations of the equations for lunar rotation. The absence of the spurious secular effects (which arise in standard nonselfconsistent methods) is guaranteed.

Evolution of HIP 8 plauetn of the Solar Syntem over 10 million years and more. Secular resonances among the inner planets. J. l.askar Bureau drs Longitudes. 77 avenue Denfcrt-Rorheroau, 75014 Paris, France

This work on the long term evolution of the whole Solar system was started about 4 years ago, in the following of the previous works of Brtimberg and Duriez. In a first paper (Laskar, 1985) the construction of an analytic secular system of second order for the 8 main planets was presented. In (Laskar, 1986) the accuracy of the system was analysed through numerical integration over 10 000 years and directly compared to the results of the numerical ephemeris DE102 and to the semi-analytical ephemeris VSOP82 . Our secular system contain about 150 000 monomial terms, but its simple organisation allowed an efficient vectorisation of its numerical integration on a CRAY1 computer. Tjis numerical integration has been performed over 30 millions years. The output is then Fourier analysed in order to obtain a representation of the solution similar to the results of a completely analytical solution like (Bretagnon, 1974) for the 8 planets or (Duriez, 1979) for the outer planets. The solutions obtained for the outer planets is very similar to what was obtained by Duriei or to the results of the recent long term numerical integrations over 100 millions of years of Applegate et al. and Carpino et al., which suggest a good stability of this system. On the contrary, numerous secular resonances appear in the first terms of the solutions for the inner planets. The last developements of this current analysis will be presented.

- 43 - SECULAR VARIATIONS OF THE SEMIMAJOR AXES OF THE OUTER PLANETS A. Milani Instituto di matematica, Via Buonarroti 2, 1-56100 Pisa, Italy

Long term numerical integrations of the orbits of the outer planets within the Long- stop research project allow to investigate the secular dynamical behaviour of the system. A digital filter is applied (on line with the numerical integration) in order to cut off the short periodic terms (p minor 10 000 years) which would otherwise maskthe smaller long term variations. After the numerical integration is completed the filtered output is Fourier analyzed and a synthetic secular perturbation theory is constructed to be compared with the available analytic secular perturbation theories. The secular variations of the major semiaxes of the outer planets have been detected for the first time from the filtered output of the Longstop la 9.3 myr numerical integration, they have never been computed analytically. The most interesting feature is an oscillation, in antiphase, of the semimajor axes of Uranus and Neptune revealing an almost exact exchange of energy of the two planets with one another. The relative energy exchange has a period of 1 119 416 yr and an amplitude of the order of 10" while the expected amplitude was several orders of magnitude smaller. An analytic computation of this effect based on Lie series transformations shows that the variation detected in the numerical output is actually correct: the large amplitude is due to a small devisor involving the quasi-resonance in mean motion between Uranus and Neptune.

A 31 MYR PERIOD EFFECT IN THE ORBITS OF THE OUTER PLANETS A. M. Nobili Instituto di matematica, Via Buonarroti 2, 1-56100 Pisa, Italy

The Fourier analysis of the filtered output of the Longstop lb lOOmyr numerical integration of the orbits of the outer planets reveals the presence of a spectral line with period 31 myr. The corresponding critical argument involves the pericentres of Jupiter and Uranus and the nodes of Uranus and Neptune, it does circulate, completing three revolutions in the timespan of the numerical integration. The frequency Resolution and the possibility to compute the period in two different ways do indicate that the effect is real. The value of the detected period depends also on the accuracy of the model used for the inner planets. The presence of a long period does also mean the presence of a small devisor, and small devisors are related to non-convergence of the pertuibative series, hence to the solution not being quasi- periodic. In the construction of a synthetic secular perturbation theory from the Longstop lb numerical integration it is found that together with discrete regions of the secular spectrum, where the detected lines can be identified with theoretically predicted lines, there are indeed regions where many lines of comparable amplitude are packed together. An unsuccessful attempt to identify them with theoretical lines reveals that they must come from higher order terms of the Hamiltonian. Nevertheless their amplitude is large, and this might be due to the small devisor.

- 44 - A NOTE ON LEMAITRE'S MODEL FOR THIRD ORDER RESONANCE

Th. Pauwels Koninklijke Sterrenwacht van Belgie

In recent papers Henrard and Lemattre have studied what they call "The Second Fundamental Model For Resonance" and higher-order generalization of it. By a more analytic approach to Lemaltre's model for third order resonance, some new features were found,which could not be seen on Lemaitre's plots.

A NUMERICAL STUDY OF RESONANCES IN COLLISIDNAL DISKS

Bruno Sicardy

Observatoire de Meudon et Universite Paris 7

Many recent observations^have shown that resonances have a wide variety of effects in planetary rings: spiral waves, gaps, confinment, sharp edges, arcs. While resonances are known to be associated with such structures, the role of inter-particle collisions is still poorly understood, although necessary to explain the long term evolution of rings. Since collisions are difficult to handle in a mathematical framework, numerical studies may be useful. We present here a 3-D numerical model which describes the evolution of 100 massless particles orbiting a planet. Inelastic collisions between particles are taken into account, together with the gravitational perturbations of one or two satellites. We study the exchange of energy and angular momentum between the ring and the satellites around the Lindblad resonances M:M-1. A repulsive torque between the disk and the satellites is observed. The magnitude of this torque agrees well with the values derived in other contexts when studying viscous accretion disks or spiral density waves in Saturn's rings. This result shows that the torque exerted at Lindblad resonances appears for quite general physical conditions. We also investigated the combined effect of corotation and Lindblad resonances in the stability of planetary arcs. We have verified that inelastic collisions destroy an arc of particles placed at the L4 or L5 Lagrange points of a given satellite. A second satellite can however replenish the energy lost by collision and thus stabilize the arc via a Lindblad resonance. Stable arcs have also been numerically obtained with only one satellite of eccentric orbit. The same satellite then creates the corotation and Lindblad resonances necessary to stabilize the arc. These results are compared with current analytical models of Neptune arcs. Also, the role of initial conditions is discussed in view of studying the origin of the Trojan asteroids.

COMPARISON OF PERTURBATION AND WISDOM METHODS FOR 5/2 RESONANCE

M. Sidlichovsky

Astronomical Institute of Czechoslovak Academy of Sciences, BudeBskiS 6, 120 23 Praha 2, Czechoslovakia

Some preliminary results of perturbation method applied to 5/2 asteroidal resonance with Jupiter are presented. Results are compared with tho^ obtained bv the author with the Wisdom method previously applied to this resonance by Sidlic.ov- sky and Melendo. Inferences for the origin of the Kirkwood gaps are drawn. SECULAR AND MEAN MOTION RESONANCES IN THE ASTEROIOAL BELT

H. Scholl

Observatoire de Nice, B.P. 139, F-06003 Nice Cedex

The physics of the two types of resonances characterizing the dynamical structure of the asteroidal belt are presented. In the case of mean motion resonances, the frequency of Jupiter's rotation about the Sun determines the various resonance frequencies. For secular resonances, the resonance frequencies correspond to eigen- frequencies of the system of differential equations describing the motions of nodal and apsidal lines of planetary orbits. Both types of resonances are related to gaps in the asteroidal belt. The Kirkwood gaps are well known examples at mean motion resonances. The competing theories for the formation of these gaps are reviewed. Solely chaotic motion at resonances does not appear to explain gap formation. The search for additional mechanisms is continuing. The secular resonances gained considerable interest because of their alleged role as sources of Earth-crossing objects like Apollo asteroids and meteorites. Recent numerical model calculations on secular resonances are reviewed under this aspect.

SEMIANALYTICAL THEORY FOR RESONANT SATELLITES IN NONSINGULAR ELEMENTS

I.V. Tupikova

Institute for Theoretical Astronomy, Kutuzov quay, 10, 191187 Leningrad, USSR

The third-order semianalytical theory for the motion of the resonant satellites under the influence of the Earth's gravitational potential and the gravitational attractions of the Sun and the Moon is derived; the effects of the precession and nutation are also taken into account. The disturbing functions are averaged with respect to the mean anomaly of the satellite by the Lie transforms method; the explicit expressions for the different mixed perturbations are obtained. The system of nonsingular variables allows to avoid the singularities at' E=o and/or I=o. SW 1 STRUCTURE OF GALAXIES AND STAR FORMATION

The apiral-rortex •truoture of flat galaxies (prediction, theory, laboratory and numerical experiments, observations} Y.l.Afanaaiev, P.Baev, A.M.Tridman, I.H.Ivchenko, Yu.ff.Maxov, A.G.Horosov, X.V.Ieslin, I.I.Paaha, V.L.Polyachenko, A.Yu.Rylov, B.I.Snezhkin, Tu.T.Torgaahin,

Astronomical Council of the Acad. Sci. USSR, 48 Pjatnitskaya str. Moscow, USSR

Recent observations show a dip on the rotation curve for most of spiral galaxies. Theoretically, it implies that spiral density waves must be induced by shear instabilities. Calculations prove that the observed amount of gas in galactic disks (10% for the Galaxy) is sufficient to develop the hydrodynamlcal instability in gas subsystems. As surface density perturbations of shallow water and galactic gas disks are described by the same equations, experiments with shallow water rotating similar to galactic disks have been made. In stationary stages of rotation stationary spiral patterns occur. The number of arms depends on the profile of rotation curve, in agreement with theoretical results. Different rotation parameters lead to different structures: the circular mode, one-, two- eight-armed spirals. Branching of the spirals is observed when rotation parameters change,which suggests that the spiral branching in several galaxies comes from their non-stationary rotation. Anticyolonic vortices are observed between the arms. Aximuthal averaging of the surface density, C(r)» gives a good fit for the Galaxy* i1n1 iw of 6 before the molecular ring. Por realistic profiles of shallow water rotation the spirals are trailing. But they happen to lead for opposite directions of rotation of inner and outer regions. It may explain the leading spirals in galaxies whose spin is opposite either to that of close companions or to the vector of orbital momentum of the pairs. lumerical computations confirm the theoretical and experimental results. Preliminary observational data agree with these results.

FLAT DISK MODELS, ROTATION CURVES A HEW MODEL POR MILKY WAY M. U n a 1 AKYOL Selc.uk Univ. Pac. of Education, 42090-Konya-Turkey

Abstract. Flat disk models for galaxies are studied on the basis of oscillation of distributed mass around equilibrium configuration. Convincing perspectives to existing galaxy types are available. Several types of galactic orbits are possible with peculiar rotation curves. Supersonic and very high velocities seems likely. Conventional rotation curve breaks into two sections inner to the Solar circle and spiral arms. A new model for our galaxy is proposed.

- 47 - AGES OF GLOBULAR CLUSTERS DERIVED FROM BVRI CCD PHOTOMETRY

GONZALO ALCAINO AND WILLIAM LILLER

Instituto Isaac Newton, Ministerio de Educaci6n de Chile Santiago, Chile.

ABSTRACT

The modern generation of electronic detectors, such as the CCD, have made improved photometry possible, especially at magnitudes near photographic plate limits and at wavelengths extending to the near infrared. Vigorous efforts should now be made to extend measurements to longer wavelenghts, since VandenBerg and Bell (1985) have recently calculated BVRI synthetic isochrones. Consequently, we have embar- ked on a program of CCD BVRI photometry for determining the aqes of globular clusters. From BVRI CCD frames obtained with the 1.54 Danish telescope at ESO-La Silla we have at this moment completed the reductions of the following 5 globular clusters: NGC 104 (47 Tuc), NGC 2298, NGC 5139 (u Cen) NGC 6121 (M4) and NGC 6362. For these clusters, we have derived ages all close to 17xl09y, providing strong evidence that the globular cluster system is coeval, and that the epoch of the galactic contraction was short.

THE EXISTENCE AND SHAPE OF DUST LANES IN BARS

E. ATHANASSOULA

Observatoire de Marseille 2, Place Le Verrier, 13248 Marseille Cedex 04, France

ABSTRACT I study the flow of gas and the major families of periodic orbits in and around the bars or ovals of model barred galaxies. I show that the locll of the shocks depend on a number of parameters character- ising the bar and disk potentials. Thus a comparison to the dust lanes observed in real galaxies gives Indications on the underlying potentials and corresponding stellar density distributions. In particular the existence of an inner Llndblad resonance Is absolutely necessary for the formation of shocks at the regions where the dust lanes along the bars are observed. The extent of the x2 and x3 families as well as the location of the ultra harmonic resonance greatly influence the existence and shape of the shocks.

A SPATIAL DISTRIBUTIOH OP THE YOUHG POPULATIONS OP VARIOUS AGE GROUPS IS THB SGR- CAR ARM V.S.Avedisova Astronomical Council USSR Acad.Sci. 48 Pjatnitskaya str., Moscow, 109017 USSR

The spatial distribution of the young objects of various age groups in the Sgr-Car arm in the longitude range 1- 280° - 360°- 20° is inrestigated. 99 open clusters from Lynga1.? catalogue are divided into three age groups :1.lgt« 7.0, 2. 7.0luminosities. Both transrerse and longitudinal age gradients have been found in the arm. Two giant star formation complexes with size of about 1 kpc at 1 » 285°-300° and at 1 • 34O°-2O° have been found to exist. Each of them contains extremely young clusters (lgt<7.5), four to five giant molecular clouds (GMC) and several H11gi«nt regions. Between these complexes we have found an elder one of the same sice but without any signs of active star formation region, young cluster and GMC. This complex contains twenty four (5-6)•10 years old open clusters and a small number of faint H11 regions. Assuming that it is a remnant of-a giant star formation complex the upper limit of GMC lifetime is (5-6).10 years. The sizes of these large complexes are in a good agreement with those found by Elmegreen for gas superclouds that are forming in the result of gravitational instability in the Galaxy disk. The estimation of spiral ana location for the objects of various age groups is derived. The distance of the arm from the galactic center grows with object age from 7.0kpc to 7.4kpc for lgt - 7.0 to 7.7 (R « 8.5 kpc). The pinch-angle also shows some age trend (from 15° to 18° within the standaxvt deviation). Spiral pattern velocity is estimated. The problem of star formation efficiency is discussed. - 48 - Observations of young cometary nebulae with the IRflM 30-m telescope

Rafael BACHILLER1, José CERNICHARO2'3 and Jesus MARTIN-PINTADO1'4

(1) Centro Astronömico de Yebes (OAN,IGN) . Apartado 148. 19080 Guadalajara. Spain (2) IRAM. Voie 10. Domaine Universitaire. 38406 St. Martin d'Hëres Cedex. France (3) Observatoire de Grenoble. USMG. CEBMD. BP 68. 38402 St. Martin d'HSres Cedex. Franœ (4) IRAM. Av. Divina Pastora, 7. Nöcleo Central. 18012 Granada. Spain

The two prototypical young cometary nebulae around R Mon and PV Cep have been extensi^ vely observed with~20 arcsec resolution in the J = 1-0 line of CO and CO using the IRAM 30-m telescope (located on the Pico Veleta, near Granada, Spain).

The molecular line maps, when compared to optical observations, give us detailed information on the nature of cometary nebulae as well as on the kinematical structure of the gas in these regions.

Our observations suggest that the cometary nebulae R Mon and PV Cep are actually the brightest fans of bipolar nebulae. Furthermore, it appears that optical cometary nebulae are hollow cones which have been emptied by the action of winds from the star located at the tip of the nebula. High velocity CO is flowing along the cone walls and is accelerated in the flow direction. Around the positions of stars R Mon and PV Cep we observe molecular maxima which could be due to residual material originated during the collapse process that led to the formation of these stars. SOLVING ASYMMETRIES IN THE HVC'S DISTRIBUTION

E. Bajaja', R. Morras2 and V.G.I. Pdppel-2

^Max-Planck-Institut far Radioastronomie, Auf dem Httgel 69, D-5300 Bonn I, Federal Republic of Germany ^nstituto Argentino de Radloastronomia. C.C. 6, Villa Ellsa (1894), Argentine

The IAR survey of high velocity HI In the southern hemisphere (Bajaja et al., 1985) has been used together with other surveys, to produce a whole sky sample of HCVs. All detections apparently associated with a fealaxy, Including the Milky Way, and the Magellanic Stream, were subtracted in order to have a sample of "genuine HCVs". The VLSR - galactic longitude correlation shows several asymmetries in both axes which have been noticed before (cf. van Woerden et al., 1985). We apply a simple kinematical model on a regular distribution of points, which reproduces the asymmetries for the high velocity subcomponent and also the distribution on a VLSR - galactic latitude diagram. The model implies the existence of an approximately constant central infall velocity component in the clouds and a relative motion of the LSR, towards * = l]0-*5\ b = 1O'*5-, with a velocity of 385*5 km/s. These values approximate those generally accepted for the motion of the LSR with respect to the Local Group of galaxies. This suggests that the high velocity subcomponent of the HCV's could be associated with this Group and in that case the motion of the galaxy within it would be of 200 km/s towards • = 133-.5, b = I9-.5, i.e. about 43* from M31. The mass of this subcomponent, assuming a distance of 1 Mpc and a uniform distribution, has been estimated, by extrapolation of the IAR data, as 1.3 1O10 solar masses.

OBSERVATIONS OF BIPOLAR OUTFLOWS

John Bally

AT&T Bell Laboratories, Crawford Hill Holmdel, New Jersey USA

Energetic outflows, often collimated into two oppositely directed jets, are frequently found to be associated with new-born stars still buried in their parent molecular clouds. Millimeter wavelength observations of molecular transitions of species such as CO have shown that the cold molecular component of l the outflows has velocities up to 60 km s~ with a total mass ranging between 0.01 MQ for low mass stellar sources to over 100 M0 for flows having several massive stars at their core. Optical and near infra-red observations reveal a hot (over 103 Kelvin) flow component exhibiting velocities in excess of 300 km s"1. Although some jets associated with low luminosity sources, such as HH-34, exhibit a very high degree of collimation, the structure of most massive outflows is complicated, appearing "bipolar" only in low angular resolution observations. At high resolution, many sources exhibit lumps, oscillations, or flow in more than just two directions. In this talk I will review millimeter-wave as well as some near-infrared and optical observations of this important phase of stellar birth.

MORPHOLOGY AND EVOLUTION OF SPIRAL STRUCTURE G. Bertin * and C. C. Lin 2

1 Scuola Normale Superiore, Pi»» 56100 I, Italy 2 Massachusetts Institute of Technology, Cambridge, MA 02139 USA

Quasi Stationary Spiral Structure is the natural interpretation for grand design spiral galaxies. The best theoretical tool to describe QSSS morphologies is the study of spiral modes. Modal studies are characterized by two distinct stages. At the dynamical level, one wishes to compute spiral modes efficiently on a variety of equilibrium models and to master the relation between the properties of the basic states and the properties of the relevant spiral modes. At the astrophysics! level, realistic basic states are identified by discussing the processes of evolution and self-regulation; in particular, we identify some basic states consistent with QSSS grand designs and others where more flocculent spiral structure is expected to occur. For this second stage it is crucial to have a proper interpretation of the results obtained from one-component models in view of the multiple component astrophysical systems to be described (which include stars, Population I objects, and cold gas). Following this outline, under the guidance of a simple analytic (asymptotic) theory, a very large set of galaxy models has been studied numerically. This is essentially a three dimensional survey within a flexible class of models, where one parameter measures the amount of participating disk mass, a second parameter determines the hotnees of the disk and the third is a scale length which combines properties of the size of the nuclear bulge and the distribution of the cold gas component. AU the essential morphological types found in the Hubble diagram have been reproduced; in particular, parameter regimes are identified for SA and SB galaxies and specifically for SB0, SB(r) and SB(s) objects. Distinction is made between systems where gas is expected to play an active or a passive role.

- 50 - THE LOCAL INTERSTELLAR MEDIUM

Leo Blitz University of Maryland

The structure of the interstellar medium within 200 pc of the Sun as deduced from observations at all wavelengths will be reviewed. Special attention will be given to the most recent results from the analysis of IRAS data on the " Infrared Cirrus " and the high latitude molecular clouds. In particular it w'll be shown that a large fraction of the infrared, molecular and atomic gas in the local interstellar medium originates in loops and filaments. The energy in these loops and filaments is considerably smaller than that resulting from supernova explosions, and several classes of progenitors will be examined. Such an origin will be shown to be consistent with youth, chemical composition and unboudedness exhibited by the molecular cores of the cirrus.

HALO PARAMETERS IN SPIRAL GALAXIES

A. Bosma, E. Athanassoula Observatoire de Marseille 2, Place Le Verrier, 1J248 Marseille Cedex 04, France

We are currently analyzing rotation curve data of a large number of spiral galaxies using composite disk/halo models constrained by stability considerations. In a first paper (flthanassoula et al. 1987, accepted for publication) we presented models for a large number of galaxies using data in the literature. Here we show the results for a few galaxies for which additional data on the velocity dispersions are available, as well as for several galaxies with abnormally low surface brightness disks.

Chemo-Dynamical Evolution of Galaxies

A. Burkert and G. Hensler

Universitats-Sternwarte Hiinchen, Scheinerstr. 1, D-8000 Hunchen 80

Up to now, the evolution of galaxies has been studied using either dynamical or chemical models.

However, since Larson's first pioneering works, no further extensive calculations, including the dynamical as well as the chemical aspects of galaxy evolution have been made.

In this paper we therefore want to present calculations, which consider chemical and dynamical evolution of galaxies simultaneously. The interstellar medium (ISM) is treated as a multi-component medium, following the picture of HcKee and Ostriker. Heating of the ISM by supernovae, stellar winds and molecular outflows is taken into account. Yields by supernova-ejecta increase the metallicity of the ISM, by this changing the cooling rate.

The dynamics of the gaseous components is described by means of the isotropic Eulerian equation. However we allow for an anisotropic velocity distribution among the stars, which form from the cool, cloudy gaseous component, assuming a constant Salpeter initial mass function.

- 51 - A CATALOGUE OF ECLIPSING BINARIES IN FIELDS OF OPEN CLUSTERS J.V. Clausen and A. Gim^nez

Copenhagen University Observatory, BrorJEelde, Denmark Institutes de Astroflsica de Andalucia, Granada, Spain

A catalogue of optical coincidences of eclipsing binary systems with galactic clusters is presented. A detailed comparison of available catalogues of clusters and binaries has been performed with particular attention to get accurate positions and the detection of identification errors in the source catalogues. Only those open clusters with angular diameters assigned in a homogeneous way by Lyngaa have been considered. About 300 binary systems in about 140 open clusters have been identified as candidates in this survey. For most of these binaries, the only available information is approximate magnitudes, spectral types and orbital periods. Only 80 of the 3500 eclipsing binaries catalogued in "A finding list for observers of interacting binary stars" are mentioned as possible or certain cluster members. Individual discussion on membership is currently being made. A few well studied eclipsing binaries are known members of open clusters and association, e.g. GL Car, BF Cen, V346 Cen a..d CW Cep included in an observing project of uvby photometry already in operation since some years ago. The purpose of these studies is the comparison of independent information about distances, age and chemical composition as well as the discovery of clusters members among specific groups of eclipsing binaries.

SPIRAL STRUCTURE AND STAR FORMATION

B. G. Elmegreen

IBM Watson Research Center, New York, USA

Star formation in spiral galaxies usually occurs in giant molecular and atomic complexes that contain 10 M . These complexes are often located in the spiral arms of grand design galaxies, bu? they also appear to be present in galaxies with no regular spiral structure, distributed throughout the disk. Because the overall star formation rate and molecular abundance is the same in galaxies with and without prominent density waves, such waves are apparently not necessary to form the complexes directly from the ambient gas. Gravitational instabilities probably form the complexes, and they do this whether or not a density wave is present. Color composite photographs of /«50 galaxies, which have been computer processed to remove the average radial profiles of the light, clearly show the distribution and ubiquity of giant star formation sites in galaxies with various spiral arm types.

THE FINE STRUCTURE OF GALACTIC SPIRAL ARMS J. V. Feitzinger Observatory of the City of Bochum, Castroperstr. 67 463o Bochum, FRG and Astronomical Instltut, Ruhr-University Bochuro

Th» crinkly structure of the HI centroid distribution of tha galactic spiral arms was investigated and hints of azimuthal corrugations along most of tha galactic spiral arms wore found. Threa distinct corrugation scalas saaro to axist. Tha scala lsngth within each class doas not dapand on the radial distance in tha Galaxy, wharaas tha corrugation amplitude does. These corrugations where also found in tha distribution of O and B-stars, stellar associations and HII regions. There is also slight evidence for a meandering of HI spiral arm centroids in the galactic plane. The socalled rolling notion phenomenon occurs in localized portions of spiral arms, which are characterized by pronounced vertical velocity gradients. We call them velocity active regions (VARs). The VARs are shown to be correlated with deviations in the arms' radial velocity, high vertical extensions of spiral arms and star forming- regions. A galactic fountain model with rising and falling HI gas is able to explain tha observed vertical gas velocities in VARs. In the context of the stochastic selfpropagating star formation theory these phenomena can be interpreted. Furthermore, if the underlying geometry of the spiral arms taken from the density wave theory is also used in the case of a selfpropagatlng star formation wave (detonation wave), the global large scale velocity field Is nearly the same as In the case of the ordered density wave streaming motion. The kinematic differences between a density wave and a detonation wave of selfpropagating star formation processes are diminishing. The introduction of turbulence via the stochastic star formation processes shows that the small scale (2oo pc) streaming structure is completely irregular and unpredlot- able .

- 52 - A new method of reduction of dimensionality in discriminant analysis: Application to the membership problem in open clusters J. CABRERA-CANO (1), J. MUNOZ (2), E. J. ALFARO (3)

(1) Dpto. de Optica, Facultad de FIsicas, Universidad de Sevilla. (2) Dpto. Estadlstica Matemâtica Facultad de Matematicas, Universidad de Sevilla. (3) Instituto de Astroflsica de Andalucla, CSIC, GRANADA, Apdo. 2144, Spain

The problem to establish a membership probability for the stars in the vicinity of an open cluster is of great interest in order to clarify some related topics concerning the evolution and dynamics of these objects.

Up to date, the most reliable criterium to discriminate between field and cluster stars is provided by the analysis of relative proper motions and radial velocities. Unfortunately the cluster sample available with these data is far to be complete. Thus, a question arises. Is it possible to ex- tract this information from the more abundant photometric data?.With this aim we have developed a method of reduction of dimensionality in discriminant analysis. The method has been specially designed for the case of separation between two populations and it is based on the heterocedasticity of both groups. For this reason, it is of interest for the case of zero mean difference vector. An example of application using the uvby and Hp photometry of the open cluster IC 4996 is presented.

NEAR-INFRARED MORPHOLOGY OF M32 J. Cepa, M. Prieto, J.E. Beekman. Instituto de Astroflsica de Canarias 38200-La Laguna, Tenerife, Spain

We present near-infrared photometric observations in filters J and K of M32. Isophotal naps with an angular resolution of 89 pc are presented and radial J, K, and J-K averaged profiles are derived. The isophotal maps show a major-axis angular displacement of 70' with respect to the position angle inferred by previous authors fron visible band observations. From the radial averaged profiles, characteristic surface brightness and effective radius are obtained. A search for radial colour index trends with the relative position of H31 is also made.

EARLY STAGES OF STAR FORMATION

Rolf Chini

Max-Planck-Institut für Radioastronomie, Auf dem Hügel 00, 6300 Bonn 1, F.R.C.

Tha process of star formation, starting from molecular clouds, their fragmentation into high density cores and the birth of a star out of an ultra-compact substructure within a cloud core seems to be a fairly well understood phenomenon In stellar evolution. In fact most of the expected stages during the creation of a star could be confirmed observationally: radio molecular line spectroscopy revealed the existence of nolecular clouds with clumps of MH ~ 1E3-1E4MQ and densities nu » 3E2 cm"'. Certain molecules even trace fragments of considerably higher density, npj » 1E4 cm"'. On the other hand 1R astronomy has made the approach from the short wavelength range and detected young dust embedded stars and cocoon stars, which are still surrounded by remnants of their protostellar dust cloud. Nevertheless a protostar, i.e. an object with densities 1E6-1E11 cm"3, lifetimes of some 1ES yrs and with at best a low luminosity stellar core which accretes via central collapse or a massive disk, has so far not been observed. At present It seems that only submm observations of cold dust might have a chance to discover this last unobserved stage of early stellar evolution. The present paper reports on subnun observations of different star forming regions: Several molecular clouds near bright HII regions have been mapped at 350 and 1300pm. A number of previously unknown high density condensations (ty - 1E9 cm'1) of cold gas and dust (- 10-60MQ) could be detected; it is suggested that these condensations are Isothermal protostars In their earliest contraction stages. Observations of compact HII regions from 1 to 1300pm give new Insight into the formation of younp, massive stars and their dusty environment. Dark clouds and globules have been studied at 360 and 1300jim to investigate the formation of low mass stars. All these observations suggest that I) dust grain properties may change drastically in cold and dense regions and well knowns relations derived from the diffuse interstellar medium cannot be applied for star forming regions, II) molecules are condensed onto the grain surfaces and thus are no longer good indicators for physical conditions in the cold, high density medium.

- 53 - A MODEL FOR GALACTIC EVOLUTION. Federico FERRINI Istituto di Astronomia Universita di Pisa Pisa Italy

The feedback and self-regulated models are gaining a large credibility in the understanding of the evolution of galaxies. Our group (S.N.Shore, F.Marchesoni, F.Palla, D.Galli and the present author) has developed since 1981 a series of nonlinear models, to describe the history of spiral galaxies. In particular, the halo plus disk model allows to determine the star forma_ tion rate and the chemical evolution, as well as the dark remnant content and the connection of these quantities with the galactic morphology. The complex dynamics of the galactic phases are well described by the proposed system of equations, which allow to discuss in the same scenario the smooth histories of isolated objects and the bursting behaviour of perturbed galaxies.

DUST GRAINS IN GALACTIC HALOS.

Federico FERRINI

Istituto di Astronomia Universita di Pisa Pisa Italy In a series of papers by the present author, B.Barsella, J.M.Greenberg and S. Aiello, the forces on dust grains out cf the disk of a typical spiral galaxy are cal_ culated. The contribution of the various massive and luminous components of the gala_ xy (bulge, disk and halo) is considered. Our analysis was limited to grains forwhich -he optical properties can be calculated easily, that is graphite and 'astronomical' silicate. The main results are, first, that a selective expulsion is active on the grair.t according to their nature and radii and luminosity characteristics of the gala_ xy, second, a confinement of grains is possible in a region high on the galactic disk. The presence of dust above the disk might be important to test the presence of mass in the halo, independently of the dynamical properties of disks.

2.2 •icron stellar counts at the Galactic Plane

Francisco Garzon

Instituto de Astroflsica de Canarias 38200 La Laguna, Tenerife, Spain

We present 2.2 micron maps of selected areas of the Galactic Plane, taken with the 1.5 m. Sanchez-Magro telescope on the island of Tenerife. A model of the galactic stellar distribution has been developed and the derived stellar surface densities are compared with the observations. The results are in good agreement with the experimental data and suggest remarkable differences between the luminosity functions for the disk and the spheroid components. The extinction toward the galactic centre shows an abrupt increase when compared with other galactic directions. We note also that a better fit is obtained when the 5 Kpc ring is included in the model but cannot infer from our data the existence of a thick disk. OPTICAL AND RADIO PROPERTIES OF SPIRALS IN THE VIRGO CLUSTER

G. Giuricin1, F. Mardirossian1, M. Mezzetti1, M. Ramella3

department of Astronomy. Via G.B. Tiepolo 11. 34131 Trieste, Italy *Osservatorio Astronomlco, Via G.B. Tiepolo 11, 34131 Trieste, Italy

Improving previous studies based on galaxies belonging to various aggregations, our examination of the radio and optical properties of Virgo spirals indicates that the ratio of the radio continuum-to-optical luminosity of spirals is linked to their T colour indices (u-B)o and to their H« emission strengths. Furthermore, our study clarifies that HI deficient spirals tend also to be weaker radio continuum emitters.

INFRARED OBSERVATIONS OF THE INTERSTELLAR MEDIUM

Harm J. Habing Sterrewacht Leiden

Thin interstellar clouds, called cirrus, have attracted attention by their infrared emission discovered by IRAS. However, the objects can also be seen on photographic plates, in HI and in CO. Emission line stars, probably TTau like, have been discovered. The clouds offer many good possibilities to study their physical and chemical properties.

— 55 ~ Je number in light liluc pencil INFRARED EMISSION PROM OOCOOH STARS IN STAR-FORMING RSGIOHS Th. Henning and W. Pfau Universitats-Sternwarte, SchillergHPchen 2 DDR-6900 Jena

All well-investigated very young and massive stars with optically thick ciroumstel- lar dust shells IBH-like objects) show the silicate feature at about 9.5 /an. The only BH object where a second silicate band at 18 jam was detected in the pre-IRAS era was the BECKLIH-HEUGKBAUER object in Orion itself. We found in the IRAS LRS Ca- taloK two objects which show the second silicate absorvtion band, too. These are GL 2591 and S 140-IRS. In addition, the IR point source GL 961 waB classified by the IRAS scheme as an object with a red spectrum and no 10-^im band (IRAS class 5n). No typical objects are given in the IRAS Explanatory Supplement for this clasB. But radiative transfer models for GL 961 and similar objects show that this source has a typical self-absorption profile in the 10-^nn region with an optical depth in the band centre of about 2.5. Furthermore, we looked through the IRAS Survey Point Source Catalog for BH-like objects. We found eight sources with good flux quality and no confusion,hy extended sources. The IRAS telescope was incapable to spatially resolve star-forminR regions as S 140-IRS or the binary system GL 961. But we know from other observations that S 14O-IRS1 and GL 961E dominate the FIR spectra. The energy distributions of all objects show a steep increase from 12 to 100 pm. The colour indices as defined by Ry *1OK(»IS.-/»;S; ) ti=»ui2;um; i-2:25 jum; i*3»60/um» 1-4:100 jum) are in the ranges 0.0*R«.*1.0, 0.0£Ru*0.5f and -0.24R,, So.2. R«and Rsvare similar to the indices derived from the IRAS data of IR objects with HjO masers in the Orion and Cepheus regions, whereas for Bo the range occupied by BH-like objects is defini- tely narrower. Radiative transfer calculations show that the flux below 25 pm can be produced by a compact clrcumstellar dust shell. The IRAS observations for a> 25 jam call for a second more extended cold envelope, which should not gravely affect the near IR spectra.

PHOTOMETRY AND SPECTROSCOPY OF THE YOUNG STELLAR CLUSTER NGC 2244

H. Hensberge1, W. Verschueren2, C. de Loore2

1 Sterrewacht Leiden, (fassenaarse Meg 78, 2300 RA Leiden, The Netherlands 2 University of Antwerp (RUCA), Theoretical Mechanics and Astrophysics, Groenenborgerlaan 171, 2020 Antwerpen, Belgium

The final dynamical evolution of a cluster is strongly influenced by the removal of the parent gas cloud after the star fornation process in the region has stopped. The knowledge of a number of essential physical parameters of young open clusters and associations, such as the mass and velocity distribution of the stars and the gas as a function of position in the cluster, is of vital importance for the construction of detailed dynamical models of these regions. In this context, NGC 2244, the young stellar cluster in the Rosette Nebula, has been selected for an observational study. In December 1986 and January 1987, we obtained high precision echelle spectra (CASPEC at the 3.6 • at E.S.O., II stars) for radial velocity determinations, nulti-colour photometry (Walraven photometry at the 90 en at E.S.O., 60 probable members) and CCD spectra at 260 A/nm (CARELEC at the 193 ca at O.H.P., SO stars + standards) for classification purposes. This contribution describes our first results, based on the Walraven and CARELEC data, in terns of cluster distance, spectral types, stellar Basses, Membership and reddening, and discusses our future empirical and theoretical plans.

- 56 - A 13C0 SURVEY IN THE GALACTIC PLANE FROM 1=38° TO 1=67.5° : CLOUDS AND ARMS T. Jacq, D. Despois, A. Baudry

Observatoire de 1'University de Bordeaux 1 B.P. 21 - 33270 Floirac France

The distribution and kinematics of molecular gas in the Milky Way and in outer galaxies is of major importance to modern astrophysics. To trace the molecular gas, we have used the J=1-0 transition of the '^CO isotope of carbon monoxyde, as H2 cannot be directly detected and I^CO lines are strongly saturated. Unlike HI whose distribution in the Galaxy is more or less continuous, the molecular gas presents a markedly clumpy structure. Our 13C0 survey extends the 13C0 survey of Liszt, Xiang and Burton (1981, 1984) ; it clearly appears that the molecular material becomes less dense for galactic longitudes beyond 40°. From our 1-V map, an automatic procedure extracted 181 "LV CLOUDS" using criteria on the brightness and the number of connected pixels. The heliocentric distances of the clouds were determined from the rotation curve of Gordon and Burton (1978) and the distance ambiguity was tentatively removed from a critical use of the similar works of Dame et al (1986) and Myers et a! (1986). Criteria on the shape (Al/Av) of the LV CLOUDS, and Ab information from the 12C0 data of Sanders et 41 (1986) were also used. This enables us to map directly the clouds in a R-e (or log R, e) diagram and to search for logarithmic spiral arms. This method is better than the usual method where one fits arms in the 1-v diagram. We propose to match our data with three spiral arms : i) the more firmly established is the Per arm (pitch angle 12-13°) which we trace in a longitude range where its detection is difficult, due to the small number of clouds. ii) a spiral feature with a 22° pitch angle, "P22", which can be seen as a spur branched on the Sag arm. This feature is very well constrained by our data. iii) the Sag arm, which accounts for a large part of the matter below its tangent point at 1=50°. This arm is the less clear feature in our data ; it appears as an extension of the Car arm if most part of a big region, formed of 4 Giant Molecular Clouds is placed at the near distance, in contradiction with other distance indicators and the work of Dame et al (1986) ; this implies that a better distance information is crucial for these clouds.

RADIAL VARIATION OF SPECTRAL TYPES IN THE VERY YOUNG LMC CLUSTERS NGC 2098 and SL 666 E. Kontizas1, E. Xiradaki2 and M. Kontizas2

1) Astronomical Institute National Observatory of Athens .) University of Athena, Laboratory of Astrophysics

Spectral classification of stars, at magnitude range -6^My^-i in the very young LMC clusters NGC 2098 and SL 666 was carried out in order to study the variation of spectral types with distance from the cluster centre. In both objects it is found that the early type stars (B+A) spectral types are accumulated in the inner regions of the clusters whereas the late type stars (K+M) are almost negligeable in the centre and rather equally distributed in the outer areas. This phenomenon seems to be prominent for the faint stars of the studied range. Star counts of stars on photographic plates with different exposure time for these two clusters has shown additional evidence that the bright stars are segregated in the central regions. Consequently, the essential observational results on star formation obtained in this work is in agreement with the actual theoretical conjectures on the fragmentation of proto-cluster clouds, and also with other observational results on very young stellar groups. Density Profiles of Star Clusters in the Magellanic Clouds

M. Kontizas( , M. Metaxa(1), M. Chrysovergis(1) and E. Kontizas(2) (1) Laboratory of Astrophysics, University of Athens, Panepistimiopolis, Athens. (2) Astronomical Institute, National Observatory of Athens, P.O. BOX 20048-Thission, GR-118 10, GREECE.

A large number of star clusters in the Magellanic Clouds are found to be of intermediate age, showing a variety of density profiles. Most of the profiles resemble theoretical models assuming tidal truncation. A few of them give strong evidence for mass seggregation whereas in some cases collapse can be suggested. Although the relaxation mechanism by stellar encounters would explain the shape of the profiles, the stellar evolutionary age of these clusters is too short to explain the dynamical evolution of these clusters. So the observed profiles may be attributed to the initial relaxat ion. A number of clusters were found with an unexpected distortion in the outer areas of their density profiles at systematically constant distances to their centres. It is propable that an halo is formed around these clusters giving evidence that the morphology of the MCS may favorite the occurence of such effects.

A Hi«h Besolution Study of Diffuse Interstellar Bands

J. KreiowsKi1) and B.E. Westerlund2'

J> Institute of Astronomy, N. Copernicus University, Chopma 12/16, Pl-67-lOO Toruil, Poland £> Astronomical Observatory, Box 515, S-75120 Uppsala, Sweden

Abstract We are carrying out an extensive investigation of tne unidentified diffuse interstellar bands (DIBs) in the spectral range 5770 - 6700 A In the directions of nearby ana distant stellar associations. The observational material consists of high resolution (R=100,000) spectra obtained with the ESO Coude1 Echelle Spectrograph fed by the 1.4m Coude1 Auxiliary- Telescope on La Silla. The spectra of the reciprocal dispersion 1.7 K/mm were recorded with the aid of 1672 element Retlcon array with the sampling 0.025 A per diode. The signal-to-noise ratio exceeds 100 in every case. The programme was focused on the comparison of the diffuse spectra derived from stars of nearby, Sco OB£ association, with those of distant, Car-Cru OB complex. We show that the profiles of diffuse interstellar bands derived from spectra of nearby stars are formed in single clouds only. The observed ratios of DIBs allow to divide the clouds Into 3 categories differing in optical properties - one of them does not produce DIBs in spite of quite substantial reddening; other ones form diffuse spectra with evidently different DIB ratios. We prove that distant stars are very UKely to be obscured by combinations of all 3 categories of interstellar clouds. Thus DIB ratios are usually observed somewhere in between of the extreme cases found for single clouds. Moreover the observed profiles are seriously modified by Doppler splitting, as the intervening clouds differ usually also in radial velocities. These facts make a discussion of low-to-moderate resolution DIB shapes practically meaningless as the observed profiles are ill-defined averages over intrinsically different clouds modified additionally by Doppler shifts. It is liRely that the components of DIBs are formed in the clouds defined by the sodium line velocities; the strengths of bands do not necessarily correspond to the strengths of the sodium line components. The DIB profiles derived from the spectra of nearby stars, containing single sodium lines, are recommended for comparison with theoretical or laboratory results. Other profiles reflect the complicated, cloudy structure of the interstellar medium.

- 58 - SECONDARY STAR FORMATION IN IC 1396

M. Kun and L. G. Balazs Konkoly Observatory, H-1525 Budapest, P.O. Box 67, Hungary

The possible formation of a new stellar generation can be seen in the bright rimmed dark clouds that surround the giant HII region IC 1396. A well-defined ring of IRAS point sources is projected on the dark clouds surrounding the ionized region. The 127 infrared sources that outline the ring can be selected from other IRAS-sources of the region on the basis of their infrared brightnesses and colours. All they are brighter at 25 microns than at 12 microns and they emit most of their energy at 100 microns. Most of them are not identified with optical objects in the IRAS Point Source Catalog, but some of them apparently coincide with visible dark globules. We suggest that they probably are density enhancements in the shocked neutral gas layer preceding the ionization front. The fact that they are point-like at least in one IRAS-band suggests that their sizes are smaller than the spatial resolution of the IRAS survey. At the distance of IC 1396 they should be smaller than 0.1 pc. At least some of them may eventually become stars due to the convergent shock driven into the density inhomogeneities by the propagating ionization front. Here we are probably witnessing a situation in which the high mass stars of a young open cluster trigger star formation in the adjacent dark clouds.

HIGH VELOCITY HERBIG-HARO OBJECTS NEAR CEP A Rainer Lenzen Max-Planck-Institut fur Astronomie D-6900 Heidelberg Federal Republic of Germany

Deep H,*-, fsil] - and J pm CCD images are presented which have been taken at the prime focus of the 3,5 m telescope of Calar Alto in Spain. Two arctnin northeast of the well known region of star formation Cep A a new Herbig-Haro Object is found. High proper motions of this object and of various H«. knots in GGD37, the Herbig-Haro Object west of Cep A, are deduced by comparing our Ha images to the corresponding Palomar red glas copy. For a distance of 725 pc, tangential velocities of 200 to 250 km/s are derived which all have their common origin near the cluster of compact HII radio regions found by Hughes and Wouterloot (1982). The resulting kinematic age is 1800*400 years. A long slit spectrum of the new eastern Herbig-Haro Object has been taken. The observed line ratios are typical for shock excitation. No radial velocities exceeding 60 km/s could be found there, while in GGD37 radial velocities of more than 400 km/s have been observed. We conclude that all the observed activities like Co-mass outflow, IR-reflection nebulae and the excitation of Herbig-Haro Objects are powered by the same source or cluster of sources near the H20-maser positions.

LARGE SCALE GALACTIC SHOCKS IN BASKED GALAXIES

P.O. Lindblad, S. jersHter Stockholm Observatory SaltsJSbaden. Sweden

Recent observations of the kinematics of the barred galaxy NGC 1365 is discussed with emphasis on very sharp velocity gradients occurlng In the system.

- 59 - OPEN CLUSTERS AND ASSOCIATIONS

G. LyngS

Lund Observatory

Observations of photometric and spectroscopic data for open clusters and associations has been intensive during the latest few years. .Incentives are many:

- each cluster is an object for which the state of evolution and other characteristics can be studied much better than for individual stars

- the systems of open clusters and associations in our own and other galaxies give information about the recent evolution of the galaxies themselves

- the clusters and associations are sensors of the conditions in interstellar space

Collections of observed data have been made by Alter, Balasz and Vanysek in the comprehensive Prague-Budapest card catalogues. My own efforts in this directions have resulted in computer readable catalogue of open cluster data, of which the 5th edition has appeared recently. In collaboration with K. Janes and C. Tilley of Boston University, I have now entered weight classes. The purpose of these is to monitor the reliability of conclusions based on cluster data. It appears that physical systems of 10-1000 stars can be divided into three different categories: - associations and unbound open clusters - bound open clusters in the disk - old open clusters Properties such as ages, linear diameters and abundances will be discussed for these categories on the basis of the data contained in the 5th edition of the Lund catalogue. The galactic distribution of your, clusters and associations shows the existence of complexes inside the disk. The system of old clusters seem to back up the concept of a thick disk.

THE IMF OF STARBURST CLUSTERS

Jorge Melnick

European Southern Observatory, Karl-Schwarzschild-Str. 2, D-8046 Garching bei Munchea, Federal Republic of Germany

The stellar initial mass function can only be directly observed, and indeed is only well defined, in very young and massive star clusters. Elsewhere, richness and stochastic effects m..kt it impossible to reconstruct the initial mass spectrum from present day luminosity functions even if one could have complete samples of stars for entire galaxies.

In this contribution the IMP' of siarburst clutters is investigated on Lhe basis of integrated observations of HII galaxies (dwarf galaxies with giant MI region spectra) and population synthesis models. It is found that th-' IMF changes systematically with oxygen abundance and tli.it I'lis change consists either of abundance dependent bimudality, where bol.i the upper an_d I lie lenvi-r m?s 1ira.ii.' simultaneously change with abundance, or c;f a decrease in the slope as the metal 1 ic-.ity deru.asrs. The continuity of the properties of LMC globmar .-lusters of ages; ranging from less than 10' y\ ••• ic i Hubble time strongly suggests the latter as the. correct interpretation.

The consequence of a variable IMF for the problem of the missing mass in dwarf galaxies is discussed.

- 60 - STAR FORMATION RATES IN GALAXIES

Peter G. Mezger

Max-Planek-Institut fur Radloastronomie, Auf dem Hiigel 69, 6300 Bonn 1, F.R.G.

0 stars ionize the surrounding gas, OB stars heat the surrounding dust to temperatures » 30K The Lyman continuum photon production rate NLac can be estimated from observations of radio free-free emission, the luminosity of OB stars L""« can be estimated from FIR continuum observation*. N,uc and • v.Ca^ " t0 deHve the formatlon rate of massive stars. The total star formation rate la obtained with the Ini'ial Mass Function IMF. It is shown that for our Galaxy only a "bimodar IMF can reconcile present-day O-star formations rates with the distribution of mass permanently locked up low-mass and u63u stsrs. Submm continuum observations yield the flux density of cold dust which is associated with the bulk of interstellar gas in external galaxies, IRAS observations yield the warm dust luminosities A linear relationship between Saubmm and L"" suggests that massive star formation rates are usually proportional to the gas content of galaxies.

THE 4V (four vectors) MODEL OF THE RADIO EMISSION Jelena Milogradov-Turln Institute of Astronomy, Faculty of Sciences, University of Beograd, Studentski trg 16, p.f. 550, 11 000 Beograd, Yugoslavia

The study of the T-T graphs plotted for radio spurs in the frequency range between 10 MHz and 1420 MHz and the total spectral indices survey between 38 and 408 MHz has shown that their properties can be explained by the 4v model of the radio emission. Two out of four vectors belong to the background radiation and two to a spur itself. The background components are:the isotropic extragalactic radiation of a high spectral index and the radiation of the galactic disc of "a moderate spectral index, which depends on the galactic latitude. The spur components aret the basic spur component of a rather low spectral index and a steep spectral index component present on the outer side of the spur, where the temperature gradient Is steep. Such a 4v model explains all the basic properties of the T-T graphs as the fork-like splitting and the "curvature rule".

A NEW BIPOLAR NEBULA HARBOURING A TRAPEZIUM SYSTEM AT ITS CENTRE Th. Neckel, H.J. Staude and K. Meisenheimer Max-Planck-Institut fur Astronomie 6900 Heidelberq-Kbnigstuhl (FRG)

CCD imaging in R, I and Gunn z of the well defined bipolar nebula No. 14 in the list of Neckel and Staude (Astron. Astrophys. 131, 200 t1984J ) revealed that it contains a Trapezium system as central source (dimension: 3.5 arcsec at d - 1.5 kpc; earliest spectral type: BO.5). The extinction rises form Ay = 8 mag in front of the outer two stars to 15 mag in front of the two stars adjacent to the equatorial dust lane. This implies a high and sharply confined dust concentration in the system. CCD polarimetry shows that the four stars are polarized in the same way as the surrounding field stars. Thus in this case the magnetic field apparently does not play a crucial role in determining the bipolar morphology.

- 61 - The catalog of chemically peculiar stars In open clusters Andrzej NlediielsKl, Marek Muciek Institute of Astronomy, N.Copernicus University, Choplna 12/18, PL-87-100 Torun, Poland

Abstract

A catalog of all known Ap and Am stars in open clusters is compiled. It contains identification, membership (if available), V, B-V, U-B, spectral type, peculiarity type and references.

DYNAMICAL CONSTANTS FOR OUR GALAXY

Slobodan Ninkovic

A3TR0N0MSKA OPSERVATORIJA, Volgina 7, 11050 Beogracl Yugoslavia

As dynamical constants for oil." Galaxy are defined values of the dynamical quantities such as the galactic potential and its derivatives, taken at the Sun. In the present paper are considered only the two second derivatives of trie potential in R (distance to the rotation axis) and in Z.The local value of the angular velocity of tne galactic rotation is considered, too. The latter three quantities, as well known, determine dynamically the local value of the galactic density via Poisson equation.

As for the stars examined in the present paper, it is assumed that their motion only slightly deviates f.-ox tne circular one. Thus it is admitted to use the Lindblad system of equations describing motions ~it.i respect to the local standard of rest in a rotating reference frame. The solutions combined viith the distribution of the sample stars in the phase space are used to evaluate the three constants. ^

THE GALACTIC RADIAL GRADIENT OF VELOCITY DISPERSION Edouard OBLAK Michel MAYOR Besancon Observatory Geneva Observatory France France

The model for deducing the local value ofiln*V/^TSis based on the local distribution of Che orbital eccentricity e, the mean orbital radius ES and the velocity perpendicular to the galactic plane W (at z=O), N©(e,5J,W). We apply it to a sample of the Gliese catalogue delimited by stars of F, G and K spectral types. We obtain for the galactic radial gradient of velocity dispersion :)ln«U^a

KINEMATICAL CONSTRAINTS ON A MODEL OF THE GALAXY. Edouard OBLAK Annie ROBIN Besancon Observatory Besancon Observatory France France

Blenayme1, Robin and Creze (1987) computed a dynamical model of the Galaxy constrained by general star counts. By introducing the kinematic! in this model, we predict proper notion* and radial velocities for stars In given galactic directions and try to deduce constraints on the velocity dispersions.

- 62 - THE LOCAL KINEMATICS

Jan Paloug

Astronomical Institute of the Czechoslovak Academy of Sciences, Prague

The radial velocities of star forming regions, young 0-B stars and young open star clusters are investigated statisticaly. Their velocity field, which deviates significantly from the circular streaming, is compared with various kinematical models: neither the linear density wave nor an expansion from a point source can reproduce observations. An alternative model is proposed and we show that it is compatible with the local velocity field of young objects. In the second part of this review we discuss the local kinematics of older objects: we introduce the superclusters, which deform the velocity ellipsoid of local field stars yielding a possible explanation of the deviation of vertex. The velocity dispersion versus age relation of the field stars is also reviewed and it is compared with the motion of the open star clusters.

Near—IR and IRAS observations of Herbig-Haro like objects and cometary nebulae. P.Persi jM.Ferrari-Toniolo1,M.Busso,F.Scaltriti2,M.Robberto ,G.Silvestro3 1) Istituto Astrofisica Spaziale,CNR,CP.67,00044,Fra8cati,Italy 2) Osservatorio Astronomico di Torino,Torino,Italy 3) Istituto di Fisioa Generale,Universita di Torino,Torino,Italy

A selected sample of Herbig-Haro like objects and cometary nebulae,were searched for far-IR emis_ sion using the IRAS Point Source Catalog. Approximately 5°$ of the selected sources,were found to be associated with IRAS sources. The TEAS colour—colour diagrams will be shown for the detected sources in order to derive their nature. In addition J,H,K,L photometry,obtained at the Italian Infrared Telescope (TIRGO)will be presented for the most significative sources. The infrared luminosity is derived for several objects including our near—IR flux densities and the IRAS data. Finally a classification of the young ob£ ots ,according to their energy distribution will be proposed. CCD images in the V»R|I filter will be also shown for the most intersing nebulosities.

METHODS OF STUDYING SELF-CONSISTENT MODELS OF FLAT SYSTEMS

Maria Petrou rinpartment of Geography, WhiteknightS, F 2 BOX 227, Reading, RG6 2AB, United Kingdom.

From the study of orbits and models of galaxies in recent years, 2* nas become clear that Jeana' theorem is not adequate for building self-consistent models of real galaxies. The non-classical integrals play an important role in the dynamics of the system and their non-global nature must be taken into consideration. This work is about a new method for constructing self-consistent models of galaxies, where the distribution function is a function of the actions and the stochastic orbits are properly taken into account. It has been applied to the case of constructing a selfconsistent model of a non-rotating bar, and the way by which this method can be used to construct any sort of disc model is discussed. WHAT IS THE IMP OP PAINT STARS ? A.E.Piskunov, O.Yu.Malkov Astronomical Council USSR Acad.Sci. 48 Pjatnitskaya str., Moscow, 103017 USSR

The local luminosity function - LF is the only observational source for the j'3;F of faint stars (M > 5 ). This explains why the proper LP interpretation, or correct IP-IMP transformation are of great importance for the lower mass IMP construction* We investigated a number of effects which can influence the IMP and reached the following conclusions, 1) If unresolved binaries constitute a substantial fraction of the observed stellar population,then the LP of the components will differ from that of the systems. The effect depends on the distribution of the systems over the mass ratio q. When the bulk of the systems has q ^1, the highest IP deviations (up to 100 per cent) occur at its maximum (M =13 )• With d.eorsasing of the fraction of high-q systems the LP of components increases for fsunter magnitudes. The UUP changes as result, but its general appearance does notc 2) The mass-luminosity relation (MLR) is found to be the main factor, defi- ning the IMP. As analysis shows, different MLRs calculated for Pop I composition Kay result in different IMFs (from a power law, to a lognormal one). 3) Ihe effect of BC-Bcale is smaller than that of the MLR, but an accurate extrapolation is required at the faintest magnitudes for the sure HIP construction. 4) Presence at the faintest magnitudes (M :>, 20 ) of a large number of brown dwarfs, slowly evolving along the MS leads to the depletion of the LP for any IMP (both lognor- i5jil and power one). Hence, the local LF fits suitably both power and lognormal IMPS of low mass f.tava. Prom the point of indirect constraints e.g. the local missing mass, the power Salpeter-like IMP is more plausible.

NEBULAR PHOTOMETRY ON POSS AND ESD/SERC MAPS Pavla Polechova i'lhuervatory and Planetarium of Prague, Petfin 205, 118 46 Praha 1 Czechoslovakia

.:pli? cf the catalogue of galactic nebulae is given. The objects are •ri by i.neir isophotes, fitted via stellar images. Stellar magnitudes used ' "orr'ie'J frr.tr, the UBV system to the color systems of POSS and ESO/SERC maps. i.f- ti'oiisf ormatic:is, KMVUC<: s models and spectral response curves of the M i \ v r). ••v.ij"i--. :".'JC f yce a-ir,n i lutje estimates, an attempt has been made to remove at • •,';.'; ''-••' .'.'re;;; rn:iici stars by means of special filtering procedures. - ; '- ''••.;-_ r,iifri VKCIUII-.U on the- F'tRICClLOR 2000E digital image processing

TOM! :hK: 1 NV i ^ I IG A T I C'A OF lit< Al: 3uCl A1 ] (JN5 IN CA5SJGPEIA

Sof .'

• . i-.-niy iv|.'- oar:ar:, , i'i .1 ' i •'' i <'•<• <•'•<•• abiwabiwii •!•! ' --ijijurijijure iJf.c^rs'KiJf.c^rsKS , ueni.orerueni.orerjj at CCXX : 0' ^ :'' c, . i,'/' ]5 i.i'oCO, are :=,'. u ti i c: c i. flu: ,i:.:.,or, i H ti ui):i liassiopcia OBB 4, GO 7 and

i,i( ; ,;, : ,, , .|,e iiuulil.tu! Ass ib iv ;\-.i I \ \'< ;ire J D:..-I lud in td.s regions. Spectral classes ;)i.;!'i,.ii 'M-iiriM'i.-if n: hiagm l'.irie:j hi 'j.olecAun wavel nnijthr. of about 400 stars are determi- n.'ij. Un: '( h-.er i.itjnns we]-..' carried oul with thP 70-c:m meniscus telescope of the Aba-

;,V,in-,.ni v' [.n'phys ii.al Gbburva t or y in ihe U^iSR, by moans of its 8 -objective prism 'ij iL.[t;r:,if,n let R/irni at lly ). HOB-STATIOHARITY OP MASER RADIO SOURCES IK STAB FORMATION REGIONS G.M.Rudnitskij Sternberg Astronomical Institute Moscow State University, Moscow, USSR

Sources of maser radio emission in the water vapour spectral line at 1.35 cm are considered, which are situated in star formation regions, in the vicinity of young stellar objects. The iUO emission of many maser sources is subject to strong variability; maser activity Is thereby of a cyclic character with a period of a few years* I suggest three models explaining the pagers' cyclic non-stationarity. On the basis of observational data, I accept that the region of maser generation is located in a rotating gaseous-dust disc around a young stellar object* (1) The maser's variability is connected with the variable luminosity of the central stellar object, due to non-staticnary accretion onto it* In this model, correlated variations should be seen for several emission features in the line profile, associated with the central object's variability in the infrared. Correlated variability was really observed in some VUO masers (W49B, W75B). (2) In the central cavity of a large (with the external diameter up to 10'7 cm) circumstellar disc containing the ILo Baser, a smaller disc ( ;£ 10*5 cm) is located, with its axis tilted to that ox the larger disc. The smaller disc is preceesing in the non-uniform gravitational field of the large disc* The stellar-wind jet collimated by the small disc and flowing out from its poles impacts consecutively onto different parts of the large disc's internal surface* This results in a time- and space-variable maser pimp* The existence of tilted circumstellar discs is confirmed by direct optical observations of stellar-wind jets from young stars (e*g., E and T CrA). In this •odel, the displacement of the maser bright spot, connected with the precession of to* stellar-wind jet should be observed* (3) If the maser is unsaturated, then strong maser flares may be connected with radio flares of the central object (due to its magnetic activity) and the occurring thereby increase of the maser's input power* Synchronous observations of radio continuum radiation and maser line emission may serve ss a test for this model.

BURSTS OF STAR FORMATION

John Scalo University of Texas Austin, Texas

There exists a large and growing body of evidence that most galaxies have experienced one or more episodes of strongly enhanced star formation, or "starbursts". After a brief review of the observations, the present paper focusses on the various types of physical mechanisms which may give rise to starbursts. The types of theories reviewed include gas transfer between interacting galaxies, hydrodynamic limit cycle models, periodic and chaotic behavior of deterministic cloud interaction models and models controlled by interactions between phases of the Interstellar medium, stochastic self-propagating star formation, and starbursts induced by low-level tidal fluctuations associated with the sea of external galaxies. Applications to bursts in protogalaxies, ring galaxies, tidally interacting disk systems, and blue compact dwarfs will be discussed. HTEKHAL EVOLUTION OF SPIRAL GALAXIES

J. A. Sellwood

Department of Astronomy, The University, Manchester M13 9PL, England

Disc galaxies which are rich in gas and young stars are dynamically very lively objects. Internally driven instabilities substantially modify their structure and are responsible for many of their observed properties. Spiral instabilities persist as long as the disc contains a significant gas component which affects the dynamical behaviour in three distinct ways.

Gas accumulates in massive molecular clouds which provoke large-scale, transient spiral responses that dominate the appearance of the disc. The associated fluctuations in gravitational potential scatter the stars and cause their random motions to rise quite rapidly. Such heating would reduce the ability of the spectacle to continue - were there no dissipation.

The second role of the gas component is to dissipate random motion energy, which is radiated away. Gas clouds remain on nearly circular orbits, constituting one cool sub-component of the disc. The third major dynamical role of the gas is to form new stars with small peculiar velocities, thereby continually augmenting the overall stellar population with dynamically cool new generations. These processes permit the spiral structure to recur until the gas is used up or removed.

A Centrifugally Driven Wind-Type Flow Model for the Chain HH 7-11 G. Silvestro (1), M. Busso (2), P. Persi (3), M. Robberto (1, 2), F. Scaltriti (2) (1) Istltuto di Fisica General*, Unlversita di Torino, Italy (2) Osservatorlo Astronoalco di Torino, Pino Torinese, Italy (3) Ietituto di Astrofisica Spaziale del C.N.R., Frascati, Italy

The chain of Herbig-Hjro objects HH 7-11 in the NGC 1333 region was recently interpreted with a model (1) of wind-type flow in a channel of variable cross sectional area due to Kelvin-Helmoltz instabilities between the flow and the ambient medlvm. The aodel accounts satisfactorily for the almost constant spacing between the knots and the abrupt velocity changes along the flow. New infrared observational data, which we collected at the TIRGO Observatory (Gornergrat, Switzerland), allow to constrain the parameters of the flow tube modulation. We discuss here the possibility to Interpret the colllnated outflow, as described in the model by Silvestro et al. (1), In the fraae of a aodel of centrifugally driven winds proposed by Pudritz and Korean (PN, 2). On the basis of our observational data, we estimate the parameters of the PH model for the source, and coapuce an instability scale-length which agrees with the value assumed In the model by Silvestro et al. (1).

(1) Silvestro, G., Ferrari, A., Rosner, R., Trussonl, E., Tslnganos, K., 1987, Nature, 325, 228 (2) Pudritz, R.E., Nor»an, C.A.. 1986, Astrophys. J., 301, 571

OPTICAL AND NEAR INFRARED OBSERVATIONS OF YOUNG OBJECTS WITH BIPOLAR OUTFLOWS

H.J. Staude Hax-Planck-Institut fur Astronomie 6900 Heidelberg-Konigstuhl (FRG)

Recent observations of four well known young outflow objects are briefly discussed: proper motions and deep H images of Cep A; infrared speckle inter- ferometry of LkH 198; longslit Coude spectroscopy of HH 24; and deep CCD images of HH 34. Some conclusions about the location of the central source, the sub- arcsecond structure of circumstellar matter and the kinematics of the collimated flows are drawn. Finally, two newly discovered objects are presented.

- 66 - A NEW COMETARV NEBULA WITH BIPOLAR HIGH VELOCITY FLOW AND HERBIG-HARO EMISSION

H.J. Staude, Th. Neckel Max-Planck-Institut fur Astronomie 6900 Beidelberg-Kbnifstuhl (FRG)

We present detailed optical and near infrared observations of a newly discovered cometary reflection nebula associated with a very compact dark cloud embedded in the Cygnus X region. From CCD imaging and polarimetry in R, I and Ho we identified the highly obscured illuminating star (M = 3 ... 5 H^, Av = 16 mag) and a bright Herbig-Haro object on its axis of symmetry. Longslit spectroscopy reveals the presence of a bipolar high velocity flow, whose blueshifted component hits the Herbig-Haro object, and whose redshifted component penetrates into the densest parts (density > 10' cm"^) of the associated dark cloud. The nebula is strikingly similar to the key object R Mon/NGC 2261.

MOLECULAR MASEBS AS tBACIBS Of XABLT SMLLAB KTOLUMOI V.S.Strelniteki;} Aatronoaical Council of th* USSR Acad. Sci. 48, PJatnitakaJa atr., Mbacow, 109017 USSfi

The contemporary atat* of tha problem of Molecular (OH, H-O, S10, CH,0H) m* obeerred in region* of active atar formation ia reviewed. Tha Swjor hiatdrical landaarka of thair diecovery, obaerration and intarpratation ara notad. OH aaaera ara believed to be tba product of deaintegration of danaa Molecular envelope* ("cocooae") aurrogndlng eoapaot HII region* of young OB-atara. They have danaitiaa a- ~10 - 10' ca-5, teaperaturea * <*-100 K. It waa obaervatloaally arguad thatrat laaat In eoae caaaa they fall toward tha atar. Circular polarisation of their aaiaalon reveala Magnetic fieIda of eereral aGa. H-0 (and in exclusive caaaa - S10) aaaara ara connected with earlier etagee at ateflax evolution, when a rary atrong aaaa loaa froa tha atar (up to r^ 10"z aollar aaaaea per year) tatakak a place. BLO aaaar aalaalon la produced by gaa-dynaaleal (•ay be - «HD) interactioion between the'atellar wind and the aurroundlng gaa. She denaitlaa of H-0 aaaara T*Ureac h ~ 1011 car3, taaperature, e are <-^102 - 103 K., expan- •ion velocities - op to aereral hundred tai/a. Linear polarization of tha aaiaalon aakaa hinta about Magnetic flelda of 1-10 0a. CB,0H 1.3-cai aaaara la Orion with their obaerred dlaanaiona and probable danaitiaa and taaparaturaa would be gravitationally unatabla and Bay be protoatara. A tharaodynaalcal aproach to tha inraatlgation of poap aachaniaaa for matro- phyalcal aaaara ia daaeribad. Bqual importance of tba high taaparatura eouroe and the low taaparatura alnk of energy for tha pnap aa a ouantua aechanical heat engine la atraaaad. Iha probable puap ecbeaea for different typea of aaaar aourcea ara outlined. In cooclueion, tha new problea of "auparaaaara" (0B, aUO) in other galaxaa with active atar formation la diaoueaed.

The observational coastratots OB th« cbcalcal aad aer»hoio«ical evolution of the Oaiaxr

Andrxej Strobel

Institute of Astronony, N.Copernlcus University, Chopina 12/10, PL-67-100 Torun, Poland

Abstract The tine evolution of tne •etalllclty within tfie Galaxy has been analysed on the base of published data for star clusters. The resulting aie-aetalllcity relation seeas to split into two independent paths pasting the saae a«e range (over 101" years). One of this paths reseables that for the Magellanic Clouds. Such a picture of the cheaical evolution of the galactic siatter is consistent with the observed separation of the two groups of open clusters in aetailicity. These groups differ also in their spatial distribution both in the galactic plane and in the t direction. Both used kinds of dusters - globular and open - overlap over the significant range of both parameters (aetaillcity and *), indicating for continuous transient of aetallicity characteristic froa the halo to the disk population. It is suggested that the shape of our Galaxy has evolved froa spherical, •etal-poor, configuration through thick disk up to thin, aetal-rlch disk.

- 67 - VERTEX DEVIATION IN THE GALACTIC PLANE

Jaume Sanz Subirana Departament de Matematiques. Universitat Politecnica de Catalunya. Spain. M. A. ffatal^ Poch Departament de Fisica de I'Atmosfera, Astronomia i Astrofisica. Universitat de Barcelona. Spain.

Vertex deviation in the galactic plane is incompatible with Oort-Lindblad1s theory of galactic rotation (stationary system with cylindrical symmetry). However as in shown in this paper, it can in fact be obtained in a stellar systems model, which verities Chandrasekhar's postulates, in a non-stationary state, with axial instead of cylindrical symmetry and with an equatorial plane of symmetry. In our model, vertex deviation is presented as an overall phenomenon, which is a result of the axial, non-cylindrical, character of the distribution of the residual velocities of the stars. Therefore, the existence of local irregularities (local perturbations of density...) is not contem- plated. From the results obtained, the following stand out: 1.- In the galactic plane, the ellipsoid of residual velocities is so positioned that two of its axes are situated on this plane and the third remains perpendicular to it. 2.- In general, vertex deviation decreases uniformly whith the distance to the galactic centre. However, two orthogonal directions exist, -characteristic of the stellar system- , in which the orientation of the ellipsoid remains fixed, even though the size of its axes varies. In one of these directions, vertex deviation is nonexistent, and in the other, it remains constant and equal to u/2 until it reaches a point of degeneration where the sizes of the axes of the ellipsoid situated on the galactic plane become equal. From this point on, vertex deviation in this direction is nonexistent. 3.- For each value of the distance to the centre, maximum vertex deviation occurs at points situated on a equilateral hyperbola positioned according to the aforementioned characteristic of the system direct ions. 4.- The curves of isode/>viation are segments of lemniscate which go from the galactic centre to the above-mentioned point of degeneration. On crossing this point, a jump of 77/2 in the vertex deviation value takes place and this value remains the sane until reaching the galactic centre again.

POTENTIALS SEFMNLE IN AMITION F

Jaime San; Subirana Department de ftsteaatiques. Universitat Politecnica de Catalunya. Spain. J. Miguel Juan Zornoza y R.A. Catala Poch Departament de Fisica de I'Atmosfera, Astronomia i Astrofisica. Universitat de Barcelona. Spain.

In this paper, the potential for a stellar system model is determined following Chandrasekhar1s postulates, with axial instead of cylindrical symmetry, with an equatorial plane of symmetry and in a non-stationary state. The specification of all the cases in which the fundamental system of equations of dynamics of Chandrasekhar's stellar systems and in particular the equations relative to the potential, are compatible is very complex, for this reason only particular cases in which this specification presents no difficulty have usually been considered (Chandrasekhar 1942). In many cases, with cylindrical symmetry, potentials wich are separable in addition for the variables & and Z are obtained. Because of this, in view of the difficulty in finding solutions which sake this system of equations compatible, we introduce the condition of separability in addition as a supplementary hypothesis, which is valid in the first approximation in the vicinity of the galactic plane. In these conditions, from the study of the integrability equations for the potential, we obtain a set of relationships which give rise to different cases, all of which have turned out to be totally integrable. The results obtained generalize those of the cylindrical case. As in that case, there appears a term wich corresponds to the potential created in the interior of a homogeneous sphere and that accounts for the contribution of the galactic halo. As in the cylindrical case, a tern proportional to S~2 is also obtained in some cases, although its coefficient of proportionality is now a function of the 8 angle, which shows a singular behavior - it becomes infinite - in two mutually orthogonal directions. Ue understand that a solution inversely proportional to the square of the distance G to the centre is properly cylindrical, and that the above-mentioned singularity in the angular dependence which appears is a result of the slackening of the symmetry imposed on the system. Finally, terms due to the non-inertiality of the galactic plane regarded as the plane of reference of the stellar systea are also obtained.

- 68 - THE LOCAL CHEiCLSTRY A.A.Suchkov

Rostov State University, Rostov/Don, U.S.S.R.

The locf-1 chemistry gives a major contribution to our understanding of the ' vjlu.; zr. • rj prone: roc ii. tr.c Galaxy. In this context, we discuss four topics: .-.•.•t:Jli-:i ty --i::tri't .-".ion, neliu-T, abundance, age - metallicity relation,metallicity - i'.ir.c:/-'.. •.- rol:.tijri3. - 7hfc metallicity distribution of nearby stars gives viiencc :>.:+. ::.•_: ir. Ti.-.-tal enrichment and star formation occured in at least three iurnti; •..•:.!cii procuc:'' three stellar popul&tions (halo, intermediate, disk) with .i:tir:c: 1;. .-rc-pur'.': I•• rvtLllicities. - Different metallicity groups of stars with [fe/iij^C fro:r. e*termed samples of F stare r&veal more or less distinct main - ^e:Jinc-: tarnoff poir.xc. 'iV.e latters enable to determine the age of the galactic : —,: ai.-_ -;.e tec? - ::.ctellicity relation. - loci of the main-sequence lower envelopes 01 tiic- color - n-.a^mtiidc diagrams for the metallicity groups of P stars lead to a oonclu.3j.c/u ijitit the helium abundance of disk population stare varies with the heavy element abundance BE AY#10&Z and has increased after disk formation by AY ^0,2. - The EGtalii city - kinematics relations show that metal poor disk population P dwarfs tn-j G git-jits ere kineaatically "younger" than metal rich G dwarfs and K oi,-.itc. This paradox can be eznlair.ed by involving an age spread within metallicity f.ro'jps, •.-.i.isn ctron^ly constrains enrichment and star formation histories in the /-.fcjaetic: dick.

\V? VYfilflCs OY "-PEN CLUSTEBS

Ple'ia TcrlovicK

f:-*r-r, ,~v Vr.!-«. .".'jr-L'-. Univr-rcitj , l-aloor, EN1 90H, O.K.

" •'• r->'o1y • .: •.'. I.--i -f iyr^i'j.j»i evolution of open clusters ;- .:.:'< -it - 'D-;r,.<' „'.•'. ai^ij, c^c-.'4-ec* cluster features. Most of the

'•'•'' ''^ ' : . • • r \t.'.\t! SD:;3C-;! J'.'io.inj a power-law mass function of 1 --'."'/. • .''" -r'- '•?'*. '..!'^ " viz* 1 - sri fron stellar evoluH"^/ a '.'""' T,;'"^ --"'J ' '/'*"' ^'-,^'r ^ •"•••*•'•!•'•• --hoclcs h>; Encounters with rI1;' '..-.. . ; ^r-j-^pp':triai, density and space '_ ,"','•• ' '" "'•' ' •!•• • '-. ar" treated by a two-body • -' "-' *' : '•" ' -i . c 1 " . _;-.;.,-y .-vciUlion ir. detail. •-..: .-.•-. - r • ' • •-:• - ;>. tw--. i. ••. i .»•;-: • ,-r cf Jlfetlae for galactic r .1 >-." ;;f? -' *..-- - x, ,,. :; ._. / .r,; Lv£l the Goatir.6d action of . -.3r-. cajr; .^ ^; IT". *.;\ = r -.1 (w^•.-r t'u- • lusUr has 3 realistic Hass "c-..-> "T -r.- . -_-e - ^ -:'.:.;..-« ', t;.l ^•••ztlni( sfcape; the halo of > r -•.-.- ='•" :'-;•_•-. -:;'t.:-;;.-.• -•<-..-.-Ity s •; v = ]-':i .y oictrltut ior,. r:;y •"':«r'j-ir ,-'J- f --).".0 ^ <-i.--*'">-'• ;^ -;-rjctio» 3,' cluste". Fffects of

' • ' '*'' ;-~".'v ~ ?; .*:'- ' if, •' ;_ rr • hsc*rvr-f5 cr?:tr?.l rexicn rA

,:• ,. t.t. "iT,Hj.; ''ft -.' <••/-•'•' '-. -,'• ,? cl^.^t.cr, *»:• stars are being The metallicity dependence of the Initial Mass Function

Roberto Terlevich

Royal Greenwich Observatory, Herstmoneeux Castle, E. Sussex, BN1 4SP, O.K.

ABSTRACT. Detailed observations of Violent Star Forming Regions (I.e. Giant MI regions and Extragalactic detached HII regions) have shown that several intrinsic properties change systematically with the chenical composition. The observed systenatic changes In electron temperature, effective temperature and hardness of the Ionizing radiation, equivalent width of the Balmer emission lines and the •ass-to-llght ratio are discussed and compared with theoretical predictions from photoionlzation models. It is shown that all the available evidence points towards a simple change in the slope of the Initial Mass Function with metal content. An estimation of this change is given.

CHEMICAL EVOLUTION OF THE GALAXY AMD COiETS V. Vanyaek Department.of Astronomy and Astrophysics Charles University Sv6dek6 8. 150 00 Praha 5 - Czechoslovakia

The possible influence of coaets on the chemical evolution of our Galaxy •• has been proposed many years ago by Tinsley and Cameron is newly discussed. The luS£ is tSZZi on a suggestion that in a cloud of comets, formed on outskirts of a prestellar nebula, is confi.if* * •••• **c of condensable elements. This mass is comparable to the total mass of heavy elements in S *?l*r type star. Thus, if 2 is the heavy elements abundance and m# the solar mass, Mc* Z Ma, thus substSntlS?- fraction of He does not enter back into nucleosynthesis process in the Galaxy. Since a considerable fraction of cometary dust is dominated by the light elements group - "CHOH" - , the comets may be a significant sink not only for typical "metals" but in particular for carbc-i too.

-70- THE EFFECT OF MASS REMOVAL ON THE DYNAMICAL EVOLUTION OF A SYSTEM OF YOUNG STARS AND GAS

W. Verschueren, M. David

University of Antwerp (RUCA), Theoretical Mechanics and Astrophysics Groenenborgerlaan 171, 2020 Antwerpen, Belgium

The several possible star formation scenario's which have become accepted during the last decade all lead to a final stage in which the young stars are embedded in a large mass of residual interstellar gas and dust, which is subsequently removed due to energy input from the stars (stellar winds, radiation pressure, HII pressure, supernova explosions). The question which arises then is whether the result'ng 'clean' stellar system will be a bound open cluster or an unbound association. Several studies, both analytical and numerical, have given increa- sing evidence for the idea that both the way in which the residual gas is removed after the star formation process has stopped, and the final star formation efficiency at that moment, are of major importance for the outlook of the emerging new cluster. In analytical discussions one usually assumes that the cluster is in an exact state of virial equilibrium during (rapid or slow) mass loss although it is evident that in reality, a stellar cluster at constant mass oscillates around its virial equilibrium in the sense that its radius and velocity dispersion oscillate around their respective average values which are related to each other by the Virial Theorem. In this contribution, we present in the first place a. general treatment of rapid mass loss from a young cluster which is in contracted or expanded state with respect to virial equilibrium. We also consider the case in which the mass removal alters the instanteneous radius and velocity dispersion of the system, i.e. the case in which the spatial distribution and the velocity dispersion of the gas differ significantly from that of the stars. We show that the critical star formation efficiency for forming a bound or an unbound system can be changed significantly from its value of 0.5 in the case of exact virial equilibrium; the required input energy from the stars to make an unbound association is the same in all case*, provided that the expelled gas ia left with zero energy. Finally, we consider the case of general nas< loss as a function of time in a cluster which oscillates around its virial equilibrium with a period which i« a function of the mass and virial radius. We discuss some simplifications and approximations that can be applied to study this problem.

KINEMATICAL MAPPING OF ELLIPTICAL GALAXIES

S. J. Wagner Landessternwarte, D-6900 Heidelberg - Kdnigstuhl, F. R. Germany

Following the discovery of isophote twists and the unexpected distribution of elliptical galaxies in Vjg vs. ellipticity diagrams, it was suges'ed that this type of galaxies are triaxial. Since such a shape is stable only if supported by anisotropic phase space distributions this hypotheses was tested by combining surface photometry with kinematical maps. The latter were combined from multi- long-slit spectroscopy using the 3. 5 m telescope of Calar Alto Observatory. Velocities and dispersions were measured using correlation and Fourier quotient techniques. We discuss the advantages and disadvantages of the two methods in various wavelenght regimes as well as other steps in the reduction procedure. The influence of the different methods on the final results is studied and implications on their compatibility of data from different authors are given. Kinematical ita of NGC 1395, NGC 1399, NGC 1700, NGC 2974 and IC 1459 are presented.

- 71 - MULTICOLOR SURFACE PHOTOMETRY OF THE EDGE-ON GALAXY NGC 47 32

S. .1. Wagner, S. Dobereiner I,andessternwarte Heidelberg - KGnigstuhl, F. R. Germany

NGC 47G2 is a candidate for an edge-on barred galaxy. Burstein (1979) found this galaxy to be composed of four individual components. We studied the galaxy in several colours using CCD photometry. We confirm the existence of four discrete contributions. Contrary to earlier investigations (Watanabe, Hamatsu, 1984) we found the four components to differ in colors, possibly due to differ- en1 stellar populations. Colour-index frames show small amounts of dust. The scale heights of the individual components were examined by fitting the profiles with various functions proposed in the literature. We find the scale heights of the components to be different from each other, indicating a different kinematical history. Furthermore the scale height of the second and third component (probably a lens and a bar) increases radially from the centre. These components are not isothermal. The central three components are orientated coaxial. The outmost part, the disk, is warped. This warp, first noted by Sandaye (1961) was studied quantitatively. We discuss implications on the mass distribution and compare the data to numerical models of galaxy interactions.

STAR FORMATION IS CHA T1

P.R. Wesselius, R. Assendorp

Dept. of Space Research and Astronomical Laboratory Kapteyn.P.O.Box 800, 9700 AV Groningen, The Netherlands.

Abstract

Around the stars HD 97300 and HD 97048 several IRAS high resolution maps have been made, both with the survey instrument and with CPC. He have combined these sets of maps, identified the infrared sources, deternined fluxes, and calculated energy outputs in the infrared.

We want to present our latest results: presumably a complete description of all infrared sources in the Cha Tf molecular cloud.

DYNAMICAL EVOLUTION OF STAR CLUSTERS

Roland Wielen

Astronomisches Rechen-fnstitut, D-6900 Heidelberg, Federal Republic of Germany

We discuss the dynamical evolution of star clusters as derived from numerical simulations and analytical theorie*. We concentrate especially on the effects produced by the environment of the cluster in its parent galaxy. We present a procedure which allows to predict the dissolution limes of open and globular star clusters in a simple way. As examples, we apply our results to open clusters in our Galaxy, to rich clusters in the LMC, and to globular clusters in galaxies.

- 72 - THE SIMULATIOM OF THE BIMODAL IMF

M. Wolf

Department cf Astronomy and Astrophys±r s O-aries 'ini VITSI + \ . Prague

The hierarchical fragmentation of a molecular cloud is rmipliod TS a random ;irn- fCG'j by the M.inte Carlo p.ethocJ. It 15 proposed that the IMr Inr star forir:iti\n is tu- modal. T.uie probability of the fragmentation 11 each niodi-1 is a functi'jr. •-•! -the clnuij initial mass and defined critical mass, which can be deri\f;d from the suifscp density and tfcirserature of cloud. The modelled IMF is compared with tin; empi 1 1 caj y iiRlernimed functi'.n sn-j the best fit was found fjr critical i.i'bes of 0.3 M^ for 1 uw-ma^r. mL>t1 e and 2.C M for high-tr.ass mode of star formation.

A REVHW .il THT IMF

H. Zinnecker

Royal Ubservatory. tdjnburgh

The !ji]i.;n sr'1 1 *• i» fvii "inr OT T'<. ,'M! ,-i st.ii i n r i'i i n 3 regirii.'. wilj be discussed. 4 •,-•', f-.-'or.'. ' i.i- I"F •• :'.f 1 - t •- J .= t u r • ••ili he : e-. 1 i;.vct1. n,e concept of a hj-

[ . MF v. J i ' tf /•,<•• i;-i'ir, ^n1 rh.-ru.-ii rj'.'jif:'i; th,? r.!;'; n r •. a t : 'jris .

- 73 - SW 2 RAPID VARIABILITY OF SINGLE, BINARY AND MULTIPLE STARS

RAPID SPECTRAL VARIABILITY OP MASSIVE X-RAY BINARIES AND RUNAWAYS Olga E. Aab Special Astrophysical Observatory, Niznij Archya 357147,Stavropolakij kraj.USSA

During the years 1976-1986 spectral investigations of X-ray binaries Cygnus X-1 =HDE 226868, AO535+26=HDE 245770 and runaway supergiant HD188209 were carried out with the 6-m telescope. H^ emission line in the spectra of supergiant HDE 226868 d (Porb »5 6) varies at times "hours-days". The probable orbit of Be-star HDE 245770 with P=35 1 is suggested. P.Harmanec has also found a period of 0d187 in radial velocities. At times of ~ 1 HJJ emission profiles are variable. A search for pulsar period (P«1G4 s) in positional and photometric parameters of H^ emission

has given no positive results. HA profiles of the runaway HD 188209 varies from night to night. The orbit with P»18d85 is found together with probable radial pulsations at times of~1 day.

13 COLOR PHOTOMETRY DF HD 184279. Manual Alvarez. Instituto de Astronomia, U.N.A.M., Mexico. O.A.N. , Ensenada, Baja Cal i-fornia, .Mexico.

This interesting Be star, has been followed at different epochs and by several observers. Ballereau and Chauville (19B7), Horn et.al.(1982) and Alvarez et.al.(1987), have recently shown several observational factsi a.-> An activity period of this star seems to be started around 1968 or even earlier (1960) where after several years of beelng detected as a Be star with V-6.8, its magnitude started to decrease. Around 1973, it reached a minimum of 7.22 (7.51 as reported by Tempesti and Patriarcai 1976). b.-> In 1974, it brightened again, reaching a maximum of 6 7B on Aug.1977. At this epoch, the Rv showed a minimum of -S3 km/sec. A clear ant1-carrelation between the light and the Rv. curves follows as pointed out by Horn et al. and clearly seen from figure 1 of Alvarez et.al. This anti-correlation has been suggested by Ballereau and Hubert-Delpi ace (1982) on this star and by Hubert-Delpi ace et.al.(1982) for some other stars. On this paper, we report the following observed characteristics from our 13-Color photometric survey of Be starsI A comparison with Kuruez models yields different results for the short wavelength range and the slope of the energy distribution for longer wavelengths. The Balmer discontinuity as defined by Divan (1979), gives a value of Dmax"0.239 and a comparison with Kurucz models gives a Teff £ 28,000 K, log g - 3.5-4.0 from this short wavelength range. This values characterize the underlying star. The longward part of the spectrum however, resembles a cool object (Teff - 9,400 K) around 1977 and even a cooler one on 19BO near the minimum of the light curve. At this epoch, the Rv. is close to the maximum observed value. This red and near-Zft excess Is a clear signature of the well developed shell. Ballereau and Chauville from a comparison of the theoretical H$ profiles compute Teff - 27,000 K ± 200 K and log g - 3.72 ± 0.06

- 74 - SMOOTHING THE "SMOOTHING CUBIC SPLINE FUNCTIONS":SEARCH FOE THE PERIOD'S VARIATION I.Iu Andronov Sternwarte, Friedrich-Schiller-Universitat Jena, Schillergafichen 2, DDK 6900; Department of Astronomy, Odessa State University, T.G.Shevchenko Park, USSR 270014

The new method for the investigation of the period and its variations is proposed. The phase curve of the variations of the signal (for example, light curve of the star; is approximated by the linear combination of L spline functions^,(?) :

$(?')= it B^Cy) (1), where Gl(g'ni)=S'lm(=1 ,if l=m;else =0) ,fm is the phase of the characteristical point of the spline. In this case the coefficients B^CsSftpi)) might be calculated from the Eq.(1) by using the method of the least squares: S&k)=yi£, k=1...N, where yfe is the value of the signal at the observed point No.k (phase

RAPID VARIATIONS OF ZETA TAURI

H. Bozic and K. Pavlovski Hvar Observatory, Faculty of Geodesy, Zagreb, Yugoslavia

P. Harmanec, J. Horn and P. Koubsky Astronomical Institute of the Czechoslovak Academy of Sciences, Ondrejov, Czechoslovakia Photoelectric V-colour observations of Zeta Tauri obtained at the Hvar Observato- ry between 1981 and 1986 were analysed. Rapid variations with a period of either 1.6 or 0.8 days and with an amplitude up to 0.1 magntiude were discovered. The period and amplitude of the light curve are changing slightaly from season to season. The period of 1.6 days nicely agrees with the expected rotational period of Zeta Tauri.

The Incidence and Nature of Absorption Line Profile Variability Among the O Stars A. W. Pullerton , D. R. Gies , and C. T. Bolton . \David Dunlap Observatory, University of Toronto TtcDonald Observatory, University of Texas

We present preliminary results from a spectroscopic survey for absorption line profile variations among the O stars. Our data consist of more than 1000 high quality spectra of 46 bright O stars which were obtained with sufficient time resolution to sanple variations with timescales of hours to days. Most spectral types and luninosity classes are represented. We find that about 30% of these stars are not line profile variables. The variability exhibited by the remaining stars may be attributed to the presence of a stellar companion (about 14%), irregularities in the stellar wind and circunstellar gas (about 25%)/ or the presence of structure (most likely organized velocity fields) in the photosphere (about 30%). We shall present examples of each type of variability and discuss selection effects, the correlation of variability with stellar parameters, and the interpretation and significance of these results.

- 75 - ENERGY DISTRIBUTION MONITORING OF THE T-TAURI STAR RU LUPI F. Giovannelli ', A. Vittone, E. Covino 2, C. Rossi 3 1 - Istituto di Astrofisica Spaziale, CNR, Frascati, Italy 2 - Osservatorio Astronomico di Capodimonte, Napoli, Italy 3 - Istituto dell Osservatorio Astronomico, University di Roma, Italy Within the framework of a large campaign of coordinated multifrequency observations of the T Tauri - type star RU Lupi, we present, as a preliminary result, the energy distributions in the UV, optical and IR spectral ranges, obtained during the period 1984 - 1986. Many low dispersion spectra in the UV were obtained from July 1983 to June 1986 with the NASA-ESA-SERC IUE satellite.. The photometric and spectroscopic (low and high dispersion) optical observations were carried out, from December 1983 to June 1986, at the European Southern Observatory (ESO) in LaSilla, Chile, with the ESO 0.5 m (UBVRI), I.52 m (IDS) and 1.4 m (CAT) telescopes. IR photometry (JHKLM) and spectrophotometry (1.4

A SEARCH OP TIDAL IBTERACTIOI US THE BINARY SYSTEM \ ABD R.Giebocki, E.Bielicz, Z.Pestuseke and J.Sikorski Institute of Theoretical PhyBioB and Astrophysics, University of Gdansk,Poland.

31 UV spectra obtained with the LVR camera of the IUE satellite in the period 1978-83 were analysed. Changes of Mg II h, k emissions ere evident bat there is no evideDt correlation between omission intensity of Mg II and orbital or photometric phase. Using three various methods of analysis of possible periodicity is variation of Mg II h, k emission intensities we have found real changes in h + k fluxes with period equal to the half of the orbitel one, 0.5Po_h * 10°.2606. We interpret this effaot as evidence of direct influence of tidal interaction of secondary component on the ohromoapheric structure of the primary. Evident minimum of the Mg II h, k intensity is observed when the tides are on the line of sight and maximum when both tidal bulges are visible. Difference between maximum and minimum of total flux of k line is equal to about 20*. while the shape of the profile is practically unchanged.

VARIABILITY IN CHROMOSPHERICALLY ACTIVE STARS - AT ALL TIME SCALES

Douglas S. Hall

Dyer Observatory Vanderbi.lt University Nashville, Tennessee 37235

Variability in chromospherically active stars (single and in binary systems) is reviewed. All time scales, from very short (minutes) to very long (decades), are included. The emphasis is on what is not understood. First, observational evidence is summarized: this includes photometry, spectroscopy, magnetic fields, and orbital period variations. Second, physical mechanisms responsible for variability are suanarized, making the distinction between the well-established, the suspected, and the possible. Specific topics include flares, rotation, synchronization, starspots, migration periods, supercycles, spot cycles. Maunder minima, pulsation, convective envelope changes, and orbital Deriod variations.

- 76 - QUASI-SIMULTANEOUS SPECTKOSCOPIC AND POLAKIMETRIC OBSERVATIONS OF Be STABS CX DRA AND EW LAC L. Huang1, Z. W. LI2, and Z. H. Guo1 1) Beijing Astronomical Observatory, Chines* Academy of Sciences, Beijing, China 2) Departaent of Astronomy, Beijing Normal University, Beijing, China

During three observing runs in June, July, and August of 1983, two of us (H. and L.) made H-alpha profile observations and V-band polarimetric measurements of the Be stars CX Dra and EW Lac at the University of Texas McDonald Observatory. The instruments used were the Coude Reticon Spectrometer with the 2.1-meter telescope and the Breger polarineter with the 0.91-meter telescope. The two kinds of observation were made not strictly simultaneously, but there were nights in each observing run for which both kinds were carried out. Additional polarinetric measurements wer* obtained in November, 1983» for both stars, and some more H-alpha profiles were observed in January, 1981* and later for EW Lac. While EW Lac showed no variations with time-scale shorter than one day, CX Dra exhibited rapid variations in H-alpha profiles. Besides, for CX Dra, both H-alpha emission Intensity and the polarization sees to be correlated with the binary orbital motion, with the "period" of polarization variations only half of that of the orbital motion.

SHORT-TIME SCALE VARIABILITY IN Be STARS

H. Hubert, B. Dagostinoz, A.M. Hubert, M. Floquet Observatoire de Paris, Section d'Astrophysique de Meudon, France

The short-time scale spectroscopic variability of some Be stars has been investigated in 1986 August and September at the 1.93 meter telescope of the Haute Provence Observatory, equipped with an optical fiber spectrograph and a CCD camera (resolution 0.18 and 0.70 A in the^6500 - 6700 A wavelength range). No significant changes (^ 2 7.)have been detected during several nights or in one night in the equivalent width of the H«l emission line of if Cas and ^pPer from high signal/noise spectra. At the contrary the Hel photospheric line A. 6678 A of the B6 III star o And has presented notable changes in its profile during the 2 observational campaigns. Changes of asymmetry of the Hel line profiled. 6678 A do not seem correlated to the photometric period 1.57 day found by Harmanec (1984). The nature of the short-time scale spectroscopic changes will be discussed.

RADIAL VIBKAIIOHAL INSTABILITY OF VfOLF-RAYET STAR MODELS

Halil Kirbiyik Physics Departaent, Middle East Tech. University Ankara - TURKEY

Taking soae evolutionary Models of an initially 60 M_ star their radial vibrational stabilities have been investigated. These aodels, evolving with Mass loss, are in the advanced stage* of their evolution, and burn He in their cores. Calculations were done for the first and second harmonics as well as for the fundamental aode. Soae of the aodels were found to be vibrationally unstable in the fundamental aode.

EVIDiMCE Oi1 RAPID VARIABILITY; IN EARL? T'ZPE STABS Pavel Koubsky Astronomical Institute, 251 65 Ondfejov, Czechoslovakia

Though the evidence of rapid variability in early type atars is rather old, we have passed through the ignition stages of a more recent information explosion on this subject. This explosion started with introduction of new detectors capable to detect even very subtle variations. But the old evidence based on much important changes remains. Different types of rapid variability in 0, H, <1R and CP2 stara and their relation are discussed.

- 77 - HIGH RESOLUTION OBSERVATIONS OF IOTA HERCULIS

LE COKTEL, J.-M., DUCATEL, D.,

High resolution spectrographic observations of the variable B star iHer show that the mean RV of tHer changes from night to night within a 8 fcm/s range and a time scale probably longer than one day. In addition, rapid variations are observed with a typical range of 3 km/s and a time scale of about 3 hours. The mean profiles of He I 5876 show only slight variations on the total 0.2 day long integrations. Although the S/N ratio of individual spectra is lower, clear profile variations appear along the different nights on che Si III 4552 line, and weak deformations are present in the peak of the He I 5876 line. Our observations corroborate the multiperiodic nature of i Her :

- on one hand short period variations are observed with a 3 hours time scale, as we had already detected in photometry and lower resolution spectra. - on the other hand larger variations are present with a much longer time scale.

STARSPOT PROPER MOTION IN HK LAC K. Olah+, L. Gesztelyi , A. Holl+ *Konkoly Observatory, Budapest, 1525 P.O. Box 67, Hungary Heliophysical Observatory, Debrecen, 4010 P.O. Box 3O, Hungary

In a recent paper (Olah et al., 1985, Ap. Sp. Sci. 108.137) we found that the active areas of HK Lac exhibited sometimes small, sometimes large scale motions. In the case of the Sun it is well-known that new spots exhibit large proper motions while the old ones move almost together with the surrounding photosphere. On HK Lac, between 2444850-970, when a whole active area was newly formed, this new area, together with the old one, showed rapid motions. A possible interpretation of this feature could be if we suppose that new spots appeared in both the new and the old active area simultcmeously. This time coincidence can be accidental, but may have an other reason: if we suppose that the origin of the new spots is connected with the deeper layers,spots having common deep origin may appear in remote places of the surface at the same time. Similar phenomenon is seen in the Sun, when we observe an emergence of new flux in various parts of an extended active region simultaneously (Zirin, 1983, Ap. J. 274.900). The distribution of the active areas in the star's surface during the past eight years, is discussed.

A MULTIFREQUENCY ANALYSIS OF THE SHORT-TERM VARIABLE Be STAR KY AMD K. Pavlovski Hvar Observatory, Faculty of Geodesy, Zagreb, Yugoslavia

Broad-band UBV light and color observations of KY And obtained in September 1982 at the Hvar Observatory have been analysed using the Discrete Fourier transform and the phase-dispersion minimization. It was found that no single frequency satisfied the data well enough, even in the case that double-wave curve was apparent. Hence, a multifrequenoy fit has been attempted. The alternative interpretations are discussed in some length and a special care has been devoted to the study of color changes which might settle the problem of correct interpretation.

- 78 - STELLAR ACTIVITY

HARCELLO RODONO•

Astronomy Institute of Catania University, and Astrophysical Observatory Viale Andrea Doria 6, 1-95125 Catania, Italy

A review of the various aspects of solar-typa magnetic activity, which occur in the atnospheres of late-type stars on tine scales ranging from tens of seconds to years, will be presented- In particular, the principal characteristics of inhomogeneous localized structures, such AS starspots and plages, as derived from modelling the rotation-induced modulation of continuum and line fluxes, will be critically examined by taking into account the present observational limits. It is shown that the energetic and geometrical characteristics of magnetic activity phenomena on stars overcome by orders of magnitude the corresponding solar phenomena- However they appear to be solar-type as far as it concerns their origin and evolution: active stars have deep convection zones and, possibly, differential rotation, so that a solar-type dynamo can efficiently operate- Nevertheless, in order to detect strictly solar activity signatures on stars, the photometric precision and spectral resolution of stellar observations need to be improved by at least one order of Magnitude.

RAPID TIKE VARIABILITY iN THE SHORT-PERIOD RS CVN-TVPE BINARY SV CAMELOPARDALIS F. Scaltriti, H. Busso, and L. Corcione Osservatorio Astrononrico di Torino J-10025 Pino Torinese (Torino) - Italia

The wave-like distortion shown by the RS CVn system SV Cam exhibits large fluctuations even in short-time scales: shifts of about 0.5 in phase occurring through time intervals of a few months have been observed (Cellino et ai. 1985). Recent and old photometry of SV Can covering about 35 years has been analyzed 1n order to separate the contribution of the wave and of the usual effects shown by * eclipsing binaries. This allowed us to reconstruct the shifts in phase during a long time interval and to confirm the presence of a periodic activity cycle already found from a more limited sample of light curves (Busso et al. 1985). The analysis of all the existing light curves by Fourier fits allowed us to reconstruct a light curve cleaned of the perturbing effects of the wave-like distortion; the resulting trend hes been analyzed by means of the Wood computer code, deducing the actual geometrical and astrophysics1 para= meters of SV Cam.

REFERENCES - Cellino, A., Scaltriti, F., and Susso, «.: 1985 Astron. Astrophys. 144,315. - Busso, H., Scaltriti, F., «nd Cellino, *.: 1985 Astron. Astrophys. 148,29.

The long Tar» Surray of Early Typa Shall St«ra «t tba Hohar Liat Obaerratory Jdrg 0. Scbnaaas Obaerratorlua Hober Liat dcr tTnlTeraltttaatarovtrta Bonn, » 5568 Baun, FMS

Siaee 1976 eta.ff mmmhir: ot Honer Liat Obaarratorjr took more than 600 apactrograma of 150 objaeta fro. BUalmaVa ( 1976 ) list of B* / ahell atsrs on IIa-0 platea. Th« linear reciprocal dlapcraloa »•» 2.9 / ?-1 nm/mm. la vraaaat raanlta of our oaaarvatloaa en* point out cbaofta of Una pr? with vabllabad raaulta.

- 79 - On the variability of 53 Arietis

C. Sterken Astrophyoical Institute, Vrije Universiteit Brussel, Plcinlaan 2, B-1050 Brussels, Belgium

Photoelectric photometry of the runaway star 53 Arietis collected during a timespan of seven years is presented. The photometric measurements do not reveal any variations over a short or a long titr interval. From an analysis of a large nuaber of spectrographic plates it is concluded that 53 Ari does not show radial velocity variations, but that there are snail differences between radial velor ties obtained from different groups of lines.

PHOTOMETRY ANO SPECTROSCOPY OF THE 6 SCUTI Variable AZ Canis Minoris Jozef Tremfco*, Gustav A. Bakos" 'Astronomical Institute Slovak, Academy of Sciences, Tatranska Lomnica, Czechoslovakia and ••Gust** A. Bakos, Department of Physics, University of Waterloo, Waterloo, Ontario, CANADA N2L 3G1

The short period eScuti variable AZ CMi (MR 29M. HO 62437) it a relatively bright star (V=6.29) of spectral type FO. From UBV photoelectric observations Percy (1971) has derived a period of 0.09526 days. The star was reobserved by one of us (G.A.8.) in 1983 and observations continued until 1987. In the fast year observations were conducted at both institutions. Our light curves indicate that tiro consecutive maxima and minima are of unequal range and that a phase shift exists between the early and late observations. Therefore a new set of elements has been derrved from the times of maxima of the following form:

J.D. = £ • Pt • Pt2 • A cos 2» ,E*Eo . max o (—g- -#J 1 where P -- 0.190531 and P, - 3000 days.

In addition about a dozen spectrograms have been obtained at David Ounlap Observatory and these are being measured for '?£'.

Percy. J.R.. 1971. Publ. Astron. Soc. Pacific 83, 535.

80 - DISCUSSION OF NONLINEAR INTERACTION MODELS FOR STELLAR PULSATIONS

Frank Verheest

Iiistituut voor theoretische raechanika Ri jksuniversiteit Genl Krijgslaan 281 B-9000 Gent Belgium

Recent studies have shown interest in the evolution to steady nonlinear pulsation in stellar models. The iinflcsl possible c.jse is a nonresonant coupling between the fundamental and its first overtone, in ,1 description where one is only interested in the behaviour of a few longlived modes. Such a coupling c;3n !>t described by two coupled complex differential equations for the slow time variations of the complex amplitudes of both pulsations. In the nonresonant interaction between two modes the lowest order nonlmeorit je& are cubic in the amplitudes. Trie generic form of these equations is not as such dependent upun a particular stellar model, although the precise determination of the coupling constants will ultirately involve quite some work on a given stellar model. Evidence from recent numerical work shows that the nonlinear coupling coefficients are negative. Describing the complex amplitudes via their r<-al moduli and phases allows one to split the differential equations into their real and icaginary parts. The real parts give the evolution of the moduli without reference to the phases. One coulc! determine the phases once the moduli were knowr For a general discussion of how the moduli eventually evolve, a change of variables is appropriate. The new variables are the moduli squared and co-jl£ serve as some measure of the mode energies. The new equations now have quadratic nonlinearities and can be studied cuch more easily for the long time behaviour of their solutions, even if explicit analytical solutions seem not possible. This yields qualitative ideas about the ultimate evolution of Ihe node energies and thus about the stellar pulsations themselves. Applying general techniques from the study of nonlinear differential equations, one gets four different possibilities, depending upon the values of the coupling coefficients and the linear growth rates. In two of the cases, all the energy eventually ends up in either the fundamental or the first overtone, regardless of specific initial conditions. In a third case, it depends frcw the initial conditions whether the node energy ultimately goes to the fundamental or to the first overtone. So in these three cases one of the modes dominates in the end. In the fourth case, both energies or moduli of the fundamental and the first overtone reach a Gtable nonzero value, regardless of initial conditions, so that here a double mode is possible. Which of the four cases is the enc at hand depends, as said already, upon the of the nonlinear coupling constants and trie linear growth rates and only upon these values.

ANALYSIS Or HON-ttASIAL OSCILLATIONS Of RAPIDLY OSCILLATING 6 SCUT I STARS

C.A.H. Walker, S. Vang, C. McDowatl, C.C. Fahlaan, Ceoprtysics and Astronomy Dept., U.S.C., Vancouver, t.C. VtT 1W5, Canada

We have reported elsewhere our discovery earlier this year of high-order, non-radial oscillations for several rapidly rotating 6 Scut) start. In this paper we demonstrate the differencing technique and Fourier filtering by which the modes and characteristics are Isolated from the variations in the absorption lines. Some discussion wl11 be given of the significance of these results for stars with connective envelopes.

UttLBCH FOB JUPID YAMABILITT. OP AIPKl AMMKMZDAI J. Zverko, J. Zittovak?, L. ffric, M. Zborll ', M.S. Polosukhina 2 1 Astronomical Institute, Slovak Academy of Sciences, 099 60 T.Loanica, Czechoslov. 2 Crimea Astrophysleal Observatory, Academy of Sciences USSB, Mauchnyi, USSR

During recent years rapid variability of several of CP-atars has been demonstrated while tor others the evidences are inconsistent. To find the variability spe- ctroscopically, 51 high-dispersion (.25 and .5 na/am, W 375 * 440 na) spectra were obtained at the 6 aetre teleacope of Spetsial Aatrophyslcal Observatory, Zelcnchuk- skaya, USSR. The spectrograms have been aeaaured by a laser-interferoaeter TV-Abbe comparator at Skalnate Pleso Observatory to search for short-time variations of radial velocitiea and intensity registrograas were aade to analyse line-profile variations. This contribution is to report on this work.

81 CP 1 ULTRAVIOLET STELLAR SPECTRA

Atlas of the ulavelength Dependence of Jltraviolet jixtir.ction in the Galaxy

S.Aiello , a.iaraella.iaraellaa ,, G.Chiewickir»G.Chiewickir»44,, J.:..ayJ.:ayo GreenbergGreenberg44, P.Patriarchi5, :... Perinottoo'J

partxceaio di /isica, University of Florence, Ital^, 2 Inatitato di Astronomia, University of flea, Italy, 3 Laboratory astrophysics, Jniv. of Leiden, The Netherlands, 4 Laboratory for Space Research and Kapteya Astronomical Institute, Univ. of Groningen, ï'ise i'etiierlande, 5 Oas»rvatorio Astrofisico di Arcetri, ?lorence, Itily, 6 Institute dl Astronoata, Jniversity of Plorenc«, Italy.

The paper presents a collection of 115 extinction carves derived from low dispersion IJ£ spectra. Tiie spectra have been reduced with the use of techniques designed to reduce the effects of random noise and the influence of residual spectral features due to classification mismatch. The magnitudes of other instrumental and interpretaiional uncertainties are estimated. The extinction curves are presented with normalization to t, ., » 1 and the far ultraviolet portion { 1700A) is aleo shown for *"1>-17 i* The atlas includes examples ot extinction originating in the diffuse medium and several eajor nebulae and dense clouds.

The extinction in Carina iiebuls

".Aiello, i^.rarselXa, S.Chlewicki, J.iu.Qreenberg, Jf.fatriarchl, U.Perinotto y dl fislca dell'Jniverslta, i-'irenze, Italy, Instituto di Aetronomia 'Jnlveroita, i"iea, Italy, laboratory for Space research, CJroningen, Holland, Laboratory AstropbysicB, 'Jnlvereity of Leiden, Holland, Osoervatorio -istrofieico dl Arcetri, Firsnze, Italy.

The Carina uebola Is one of tiie most appropriate object for the study of the properties of dost in the regions where the interstellar medium is disturbed by the effects of resent and on-going star fonaation. Jtilizing the data obtained fros IJs (partly froc observations by the authors, partly from IJ2 data bank), we have obtained the extinction curves in the direction of 16 atara located in the nebula. She stars were chosen so as to cover a wide Interval of reddening values (i(b-V)*0.25—1.O0). Ihe extinction observed tor the etara in Carina appears to be rather unique «srmg the curves so tar reported for regions of recent star formation although It shows certain similarities with the UV extinction in Orion. In the Tar UY ((130—17O)nta), they are lower than the dlffuoe Bedlam average, but their curvature appears to be normal. She buap la, instead, somewhat weaker than average. Ihe peculiar extinction In Carina Complex nay be associated with the disruption of the cloud by young xaasslve stars*

- 82 - Ultraviolet Spectra of Stars:Review of Hals Discoveries A.A.Boyarchuk Aatrononlcal Council of the Academy of Sciancas of tha USSR 48, PJatnitskaje St..Moecow 109017, USSR

Investigations of ultraviolet apactra of atara which have beoone available due to apaca station* In many caaaa drastically changed our notions about tha nature ot calastrial objects. In mntroui works the following should be underlined: a) Structure of aiternal layara of stars. Prasanoa of chroBospharas, transitioBAl lajar sad corona*. b) Stallar wind and aass loss of stars, o) Taaiparatma scala of hot stars. d) Praeanca of hot satellites of "any unatationary stara and their origin. e) luresti^etiona of rheaiJ rmi csoaposltion and taajparatura distribution of lataratallar Bedim,

uv spscTBDSccmr or TMX SWBIOTIC STAB AG PIG D. Chochol \ Z. Itomarek 2, A. Vittone 3 1 Aatronoaical Institute, Slovak Acadevy of Sciences, TatrantM Loanlca, Czechosl. 2 People's Observatory, Michalovce, Czechoslovakia 3 Osaervatorio Astronoaico dl Capodiaonte, Napoli, Italy High resolution UV apeetroacopic observations of the binary symbiotic star AG Teg obtained with the ZUI aatellite in the period 1979 - 1961 are analyzed. The variability of t<•;<•> fluxes and the radial velocities of emission lines according to the orbW riiase are presented. The observstions support a binary Bodel with aass transfer xroa a hot rotationaly unsteble aubdwarf to a cool H giant.

- 83 - CALIBRATED IUZ LWR LOW RESOLUTION SPBCTRA OP G-TYPB STARS

H.L. Malagnini1 , C. Morossi' . L. Rossi*. T. Valente'

1 A»trono»ictl Department and Observatory, via Tiepolo 11, 1-34131 Trieste. Italy 2 Istituto Astrotisica Spaziale. C.H.R., P.O. Box 67, I-00044, Fraecati, Roma. Italy We pr«a«nt bar* a sample of calibrated IUE LWR low resolution spectra of non- supergiant C-type atar». This saapla illustrates tb« sain features of the Atlas whose preparation is no* in progress. The sain objectives of tbis Atlas are: 1) to provide tbe astronomical community with a set of homogeneously reduced data for studying, for example, spectral classification, or for deriving estrophysical quantities such as aetallicities and effective temperatures; 2) to provide researchers working on chromoaphetic structure and activity with reference data useful for establishing possible links between stellar photospheres and outer layers; 3) to create a data-base for comparing atmosphere models with observations. Tbe raw data bave been obtained from the IDE-archive. For each object, we selected tbe best exposed spectrum, according to tbe archive classification, and, when possible, more than one exposure of the eame object were gathered. Data were reduced and calibrated with a standard procedure (Allocchio at al., 15«3), aad. when possible, averaged spectra are obtained. For comparing different C-type stellar spectra with the moXmr energy distribution, we present in each plot both the star aad tbe Sun logarithmic spectra in a suitable format.

<»U£; U TJii Uil.iAVIQWT SPECTRA Of THE ALGOL

L..J. llavec

Jnivcralty of California, Department ot Astronomy, Los Angeles, California,JOQ2l,JSk

Tht ultraviolet spectra of About 20 interacting semidetached binaries of the Alioi typ« have barn studied with lbs IUX satellite , and coaparad with optical spectral tcaoa aad spectrocraJM. Tht axialyals anows the importanct of the ultraviolet spaotra for unaarataadjng tha dimaaaions, atructure, and evolution of ttt«ff« s/ataaw. Two laportaat dlseovariaa will tot reported here. The ultraviolet apactra obtained at full llftht datarmlna tns •pactrml typae of the primary compoaasta aa«h sort reliably than altbar optical soana or optical asactrrngjewas, wfelcs ara affaatad by aacondary coaponaata and circuawtsllar sball llaea. A ai^taawtla traad AMI baas detected for priaaxiea previously olaaalfied aa AU or latari Tna ultraviolet apactra lndlcata aa earlier apactral typa, about U3 iaataad of A2-A3* Tba fl«x Is cartain Halted re»loaa la aa a rule ayataaatioally daprsaaad eoaaaxwt to ataadard single atars, In particular between 2100-2700 X. Tola depreaalom la cauaad by nuatroua blended absorption llnaa of ?a II, Cr IX, tin II, aad Ml II. That thase abaarption linea are formed aalaly la a clrciaaetellar diak or shall aad not la tna star • pbotoapbera, la daaonatratad by apactra taken In total aollpaa of tha primary etar* Tbe daprosed regiona ara than aeen reversed Into aalsaion, co that a troad balsa la obaerved. In ordinary Algola, thla bulca la due mainly to Tt 11, In s ifTm*, * Sarpantla, aad several other Sarpantida, It la diaplacad to aoortar waveleoftha, since It la caiiaed laalnly by 7a III* Sclipee otaarvationa alao show strong aaiaalon linaa oomlnc froa bottar cirouamtallar plaaamt, whicto auat be at electron taaperatura on order of 100,000 K, alnoe we obearve ratonanoa llnaa of I V, C IT, 31 It, as wall M reaonaaoe aad/or subordinate llnaa of 31 II, Si III, Al II, Al III. Va III, aad Ml III. Thla hot and turbulent circuawtellar region la observable la alaost all Algola with •ttffiaiantly deep eellpeee. CP 2 COSMOLOGY AND FORMATION OF GALAXIES

COSMOLOGY: THEORY AND OBSERVATION I.D. Movikov and V.N. Lukash Space Research Institute, Moscow Soriet Union

Invited review lecture

Mo Abstract received until Hay 1967

THI IXACT N0SCL6 OF GBAVXTATIOMAL VAVIS IM THI IKFLATIOIIASX U1IVMSI J. BlCak and J. Podolsk* Oepartaent ef tfatbwaatlcal Physics, Charles University, V Holesoviekach 2, 180 00 Prague, Czechoslovakia

Best ef the work oa exact aedele representing gravitational waves In general relativity has been concerned with spacetlaes which are, at leaat in eone directions, aayaptotleally flat /I/. Soae special heaogeneoas, anlsotropic coaaological aodele ware alee iaterpreted as the waves in the standard Priedaann universe ftf. •ere we give the physical interpretation of the new type-M solutions of lln- •isla's eoaatleae with eeaaelegical eeastaat araaoatoq In a parely aatboaatleal fsra by Oarcfa Bias and newajMfel /J/. % seano ef «ere general argaaents aM by a detailed analysis of the equation ef gaadasic deviation, we show *Jimx (at least sane ef) these exact aolwtlans say be Interpreted, eg gravitational waves af a rather general aatvre propagatlog ia the de Sitter anlverse. (Zt becaae popalar to aodel the "iBflaticsary phase" of owr universe by a de Sitter eolation.) The analysis also reveals that the eolations can serve as the illustration of the cosaolo- gieal no-hair theorwa: they approach the de Sitter epace-tlae asyaptotlcally in ti- arf* /I/ J. Bleak, In: "Galaxies, axisywaetrlc systeas and relativity", Cambridge Uni- versity Press, Caaarlaga 1985, p. 99. f2/ *.l. Lakasb, >aov. Cia. 2SM* 268 (1976). A. Oarcfa Dfas, J.P. Plebanakl, J.Math.Phys. ££, 2655 (1981). The initial phase of coamologleal evolution S. Gottleber, H. J. Haubold, J. P. Racket, V. Mailer Zentralinstltut fUr Astrophysik, Potadam, -DDE - 1591

The evolution of a homogeneous and iaotropic coemologioal model with positive curvature Is examined starting from a finite initial radius a0 of the order of the Planck length with a zero velocity h • 0 (h - Hubble parameter), where this initial stage Is reached by a quantum Jump. The birth of the classical space-time requires an effective source term in the Friedmann equation not fulfilling the strong energy condition. It can originate from a coherent massive scalar field (mass m) with tero kinetic energy ( f0 - 0) and/or the vacuum polarization (considered in the form of a r.odlfied gravitational Lagrangian L_rav * R *«8' with a negative coupling oonstant a of the order of -lpj'i Both these effects drive the universe to expand exponentially for a definite time interval depending on the Initial radius ao and the parameters o and at, during which all other matter being originally present is dilated. The following snail oscillations superimposed on the dust-like power law behaviour of the scale factor cause an Intensive particle production, and the universe heats up to a radiation dominated Friedmann universe. This process must terminate before baryogenesis. The matching of the different phases of the cosmological evolution and the requirement to fit the parameters of the observed universe leads to a definite paraneter range for m and j «r ] well below the Planck values. In consequence the present naso density must" be equal to the critical one (S2. = 1) with high accuracy. FurthercBBe, the combined action of the scalar field and the vacuum polarization eases the fine tuning problems in the inflationary scenarios, and it leads to realistic aodels for the early coeraologlcal evolution. Kef.: GottlSker S. and Keller V.: 1986, PRE-ZIAP 16, Class. Quant. Grav. (in press). GottlBber S., Haubold H. 3., Bucket, J. P. and MUller V.: 1987, Publ. of the Centre for Bath. Sciences, Trivandrum, India (in press).

THE POSSIBLE IirTEHP«ETATIOlf OT THE CENTRAL VOID IM THE JAGXBX0NIAN FIELD

T. GrablAeke and M. Zablerowafcl

Institute of Phyelos, Wroclaw Teohnloal University, Poland

The problaa of interpretation of the •o-oallad Cantral Void /CV/ la tha Ja- oaXmn Flald /JW/ la conaldarad. Tha calaxias In JT rnr* lnollnad to croup a- raiMid CV Into • palllia^llka oonf lcuratloo. Th* popular au«ca«tloQ that CV My r«- flact a raally «xlatinc and canvlnaly «apty rolum* of tha lntar-aultlolustar apaoa la verified. So far any lnt«r«tallar oloud waa narar ragardad a* a poaaibla axpLanatloa«r »oldd» b«cau«* of it. tha oosecant-trpa lava «blch aaka tha caOaotlo axtlnotlan i»- baMa at k>72°k>72, 2. tha Zwioky-Rudalokl*ZwiokyRudalokl• alaial » that JT la fraa ot the axtlnotfcm 3. tba traditioaai view that the Bultlcluatarlallltl c l a not oauaad by anny abaortlvbaortlva 4i4i~ •ty cloud*,i.e. taa aXt«o4ad galactic atrttotvraa mrm not apparent. In tha paper It is proved that a local du»ty claud la projactad juat ento tha re«lon of CV.

THIM SHELLS AXD COfl^CLCCICAL- J. L«nfar Otpcrtsant ot MstbMMtlcal Ptaysica, Cbcrlai University, V HolclovlCkieti 2, 160 00 Pracuc, Cx*cboalovaJcl«

In tbc fr—eirork of tb* I«ra«l tormmllm I«M «pbarlc«lly syiMtrle spatially closed solutions of tba Ilcstcin equations with tbe setter distributed only on the singular tlac-llke hypersurfaces are studied. Tbe extraatcase of tbe expaaelaf end recontractinc shell which separates two Hikowskl space-tlaes Is discussed. The equation of aotlon of the shell Is expressed In tbe basJlltooian fora and tbe naive quantisation is performed. The standard Frledaan Model is constructed as a sequence of non-creselnf shells. However, tbe description of tbe shell crossing- Is also considered In sow* aore fetteral eases.

- So - FORMATION OP HEUTRIUO HALOS Zdenek Stuchlxk Department of Physics, Technical University 708 33 Oetrava-Poruba, Czechoslovakia

A fully general relativistio non-linear model of the formation of massive neutrino halos in an Einstein-Straus universe, i.e. a Schwarzachild geomatry corresponding to a mass condensation matched to a dust-filled Friedman universe, was given by Fabbri, Jantzen and Ruffini. In the PJR model the effect of the Lorentz transformation between static Schwarzschild observers and Friedman cooovlng observers at the matching surface roughly represents the integrated effect of a transition region between the local field and the average cosmological field. Here we consider the role which a non-vanishing, repulsive cosmological constant, admissible by observational limits, can have in the FJR model. We assume the value of the eoamological constant to be the same in the Schwarzschild- de Sitter geomatry and the dust-filled Friedman universe. The main conclusion is that the cosmological constant is not important in the FJR model for massive neutrinos with rest energy ««*15 eV, indicated by recent observations of SN 1987a.

HOT PB0T0GA1AXIES; DXHAMTCS AHD OBSERVATIONAL BACKGROUNDS A.A.Suchkov Rostov State University, Rostov/Don, U.S.S.R.

The large aaount and nearly solar abundance of iron in the hot lntracluater gas, the large discontinuity in age, abundance and geometry between halo and disk of spiral galaxies (as nanifeatated by our Galaxy) could be explained if the formation of metal rich stellar populations in giant galaxies is preceeded by a phase of a hot protogalaxy. We suggest that such a phase arises due to supernorae of the first generations of stars (now observed as sjetal deficient stars). The ffupeznorae enrich a protogalaxy by aetals and simultaneously heat it up to T ^10 K, asking it"hot*. Hot protogalaries expel a significant part of Its Mass, thus producing aetal rich Intracluster gas. The inner part of Massive protogalaxies is retained, contracts finally again, and after several 10° years It produces aetal rich stellar populations. We have Investigated the drnaalcs of hot protogalaxies by nuaarical Integration of gas dynamics equations for a series of Models, the hidden aasa, energy losses due to radiation, theraal conductivity, and soae other effects being taken into account. The results have both qualitatively and quantitatively substantiated the picture given above, and added nany details to It; for exaaple, they clearly show how the hot coronae of galaxies could have been foraed and existed.

THE WMI-StllUBCTTVTTr OF THE AJfTHROPIC PRINCIPLE Miroalav Zablerewskl Institute of Pbvalos, Wroclaw Teohnloal University,Poland

At the Cracow Cop-rnioaa Svatpoeiuei in 1973 Carter pointed out the extended Everett'a Interpretation of the Universe state vector as an explanation tool la oosmologv of mrnnj world*. In the present paper the acoeptifellitr of the anthre- pio principle In emdsrn oomatology ia considered. Tbe Mutual relation of the OsW verse evolution to the ean appearance and tbe aeal-Coperaioan prlnolple la the •any world coamologr are clarified. On the oontrarr to Oavles view It Is are* seated that tbe reduction of tbe strong version of aothroplo principle te ttie weak one la not possible In the aaav world ooamology. It la skews that the pri- ce for thle reduction la very hl«b. It leada to further extension ef aetapbrel- cal ideae In ooaaologjr.

- 87 - CP 3 MODERN ASTROMETRY

THE ASTROPHYSICAL INTEREST OF THE ESA ASTROMETRIC MISSION "HIPPARCOS" F. Crifo, A.Gomez, C.Turon DA5GAL , Observatoire de Paris, section de Meudon, F92195 Meudon, France

The Hipparcos satellite should be launched in 1989. It will measure positions, proper motions, and parallaxes of 115 000 selected stars brighter than 13, with a precision of 2 milliseconds of arc. Accurate positions (up to 1.5 arc second at the date of observation) and magnitudes (up to 0.5 mag) have to be known in advance. The star selection has to be optimized with respect to both scientific priorities defined by the ESA selection comittee, and to technical contraints for satellite operation. The input catalogue under construction contains stars selected among the 700000 ones proposed in 1962 by the world-wide astronomical community. The Input Catalogue Consortium is in charge of Making the identifications, providing the necessary data with the required accuracy, and making the selection. A first provisional version has been established in February 1987 and its contents is described: - " survey " of bright stars, about complete up to a Uniting magnitude function of both galactic latitude and spetral type, about 55000 stars. - Fainter stars fro* proposed programs: Nearby stars, Stars with high proper notion, Variable stars, in particular Cepheids and RR Lyrae for distance scale calibration, Open cluster stars, Stars for Galactic structure studies, Magellanic clouds, Reference franc, link to the extragalactic System, Minor Planets.

THE NON-ROTATING ORIGIN AND ITS APPLICATIONS

Jean Souchay Observatoire de Paris, 61, Avenue de 1'Observatoire, 75014 Paris, France

B. Guir.ot, in 1979, suggested that a new point on the celestial equator be choosen instead of the vernal equinox to neasure the sidereal motion of the Earth. He called this point the "Non-Rotating Origin" because it is determined in such a way that the reference system which should be tied with it should have a component of rotation along the pole of instantaneous rotation equal to zero. The aim of the paper is to show all the theoretical determinations of the Non-Rotating Origin, the Means to realise its practical localisation, and the conceptual advantages it can bring. The problems associated with the Non-Botating Origin have been deeply discussed in a paper which has been accepted for publication in Celestial Mechanics. A GENERALIZED METHOD OF ESTIMATING STAR CORRECTIONS FROM LATITUDE AND TIME OBSERVATIONS

Jan Hefty Observatory of the Slovak Technical University Radlinskgho 11, Bratislava, Czechoslovakia

Long periods of regular astrometrical latitude-longitude measurements at observatories participating in determination of Earth's rotation parameters are frequently used for estimation of corrections to star catalogue mean places and proper motions. The proposed method is an extension and generalization of the usually exploited chain method. It is possible to estimate simultaneously the corrections of declinations and right ascensions for instruments which determine both latitude and longitude. Additional unknowns - amplitudes of short-periodic terms (e.g. corrections to nutation amplitudes, tidal variations, nearly diurnal polar motion, instrumental parameters and refraction anomalies) can be included into total adjustmer.t. It is not necessary to fulfill the condition of closing the chain. The constraint for unknown parameters is the minimum of a chosen quadratic form. The problem is solved using the theory of generalized inverse of matrices. Method is demonstrated on determination of the right ascension corrections from observations with visual transit instrument. Other applications of the proposed method are outlined.

ABOUT POSSIBILITIES OF THE INTERPRETATION OF CIRCUMZENITHAL MEASUREMENTS

Georgij Karsky and Jan Kostelecky Research Institute of Geodesy, Topography and Cartography, Geodetical Observatory Pecny, 251 65 Ondfejov, Czechoslovakia

Time and latitude observations, made by the circumzenithal at the Geodetical Observatory Pecny (Ondfejov) in the years 1970 - 1983, were analyzed and some secular and periodical terns were proved. These results are studied from the standpoint of possibilities of their geodynamical interpretation: detection of the secular, Chandler and annual polar notion fro* optical measurements at a single station, and tidal influence on the variation of the local plumb-line.

ASTROMETRY WITH PHOTOGRAPHIC ZENITH TUBE At ONDftEJOV

Jan Vondrdk Astronomical Institute of the Czechoslovak Academy of Sciences Budecskd 6, 12023 Prague 2, Czechoslovakia

Photographic Zenith Tube Zeiss (PZT) has baen regularly used at Ondfejov Astro- nomical Observatory to determine latitute variations and clock corrections within the frame of Earth rotation service since 1973. About 45 thousand star transits near the zenith of the Observatory were observed and used to improve positions and proper motions of the stars three times during the history of the observations. To derive the first two catalogues, PZT78 and PZT83 (based on the observations in 1973-1978 and 1973-1983 respectively), PZT observations were combined with star positions in AGK2 and AGK3 catalogues in order to obtain proper motions with higher precision. The most recent catalogue, PZT86, is based solely on PZT observations in the period 1973-1986. The algorithms used to derive all these catalogues as well as their precision and accuracy are discussed in the paper, and their comparison with AGK2/AGK3 given.

- 89 - CP 5 HIGH-ENERGY ASTROPHYSICS

IN NOVA EVENTS J.M. Burgos l)pt. Fisica Tierre y Cosmos, Univ. de Barcelona, Dlogonal 645, 08028 Barcelona, Spain

We have used a Le^rangian, implicit, hydrodynamic computer code to follow the evolution of thermonuclear runaways in accreted envelopes on white dwarfs belonging to a close binary system in order to study nova explosions. The hydrodynamic code incorporates an extensive nuclear reaction network - with the rates carefully updated, specially the reactions of electron-capture on proton rich nuclei- composed by 48 isotopes of H, He, C, N, 0, F, Ne, Na, Mg, Al, Si, V, 3 and Cl. This network allows to follow with accuracy the nucleosynthesis of the outburst, either via the hot-CNO cyole or a possible rp-process responsible of the production of the heavy elements in nova envelopes (nova CrA 81 and Aql 82). Preliminary results are presented and compared with prior necleosynthetic calculations carried on density-temperature profiles but no coupled in a hydrodynamic code.

SEARCH FOR OPTICAL FLASHES FROM GAM.1A-RAY BURST SOURCES R. Hudec, J. Borovi£ke, R. Pefesty, B. Velnifek Astronomical Institute of the Czechoslovak Academy of Sciences, 251 65 Ondrejcv, Czechoslovakia

Preliminary results of an extended program of examination of the Ondfejov and Sonneberg plate collections for possible opticul counterparts to gammo-ray bursters are presented. One optical image was found on 3 different plates at the same position suggesting it may be related to gamma-ray burster 1979 larch 25 B. Results of both archival end time-correlated searches are discusstj both for GRBS as well as for the Perseus Flasher.

PULSARS AS COSMIC RAY PARTICLE ACCELERATORS K.O. Thielheim Institut fUr Reine und Angewandte Kernphysik Abteiiung Mathematische Physik University of Kiel, FRG If one looks for possible candidates for high energy particle acceleration inside our galaxy one has to concentrate on objects, the magnetic fields of which are strong enough to confine the accelerating machine and are changing rapidly enough to provide for the electric fields necessary to accelerate particles to extremely high energies. The idea that pulsars may be powerful accelerators for protons and other types of electrically charged particles obviously has come to a number of people. Recently we have pursued a research work in which partly by analytical methods and partly by numerical Integration of the Lorentz-Dirac-equation we have studied acceleration mechanisms, expected to be present 1n pulsar magneto- spheres. This has led to a conjecture of how pulsars may operate as cosmic ray particle accelerators (K.O. Tnielheim, Proc. 2nd ESO/CERN Conf.Munich, March 17-21, p. 317-320, 1986). New results obtained on the basis of this work will be presented here. CP 6 ACTIVE EXTRAGALACTIC OBJECTS

VLBI OBSERVATIONS OF ELLIPTICAL GALAXIES G. Comoretto^1), L. Feretti^, G. Giovannini (1) Osservatorio di Arcetri, L.go I. Fermi 5, Firenze, Italy (2) Instituto di Radioastronomia, v. Irnerio 46, Bologna, Italy

We present the first results of a statistical study on the milliarcsec structure in a complete sample of 30 active radio galaxies. As a first step, we took a snapshot of the sources using the Mark III, mode B, with the EVN and the Haystack antenna at 5 GHz. All but 2 sources show a considerable fraction of the core flux in a structure less than few arcseconds; most sources show roost of the VLBI flux in a single compact component; some sources show indications of a resolved structure. As a second step we plan to map with better u-v coverage all the resolved and interesting sources, to acquire the information for a detailed study on the properties of cores in radio galaxies and for a comparison with the quasars.

ACCRETION DISKS IN SOFT POTENTIAL WELLS W.J. Duschl Max-Planck-Institute for Astrophysics, Karl-Schwarzschild-Strasse 1, D-8046 Garching b. Muenchen, F.R.G.

The evolution of a gas disk in a soft potential well is described. Especially different possible mechanisms of angular momentum transport and loss are discussed. While due to the lack of radial coupling usual "alpha-turbulence" proves to be a very inefficient source for viscosity at the beginning of the evolution of accretion disks in soft potentials, after the formation of a "seed central object" the region in the disk where radial mass flow can take place grows outwards, thus making accretion more and more efficient. In the short talk or poster numerical examples of accretion disks of galactic dimensions will be shown. One interesting application is the formation of a compact central object in the center of the gala-y that might be the driving engine for activity.

OUTFLOWS FROM ACTIVE GALACTIC NUCLEI

ATTILIO FEMtAKI UHIVEtSITA' DI TORINO and OSSERVATORIO ASTRONOMICO DI TORINO. ITALY Nuacrlcal simulations of the propagation of supersonic beast from active galactic nuclei are reviewed with special attention for the physical parameters (density, magnetic field, colli- gation conditions, temperature, etc.) which determine the various solutions and their features. The evolution of perturbations Is followed to allow a comparison with observed morphological structures which Indicate the Interaction of outflows with the surrounding medium (broad line region, narrow line region, variability, proper motion of bright regions, etc.)

ACTIVE EXTRAGALACTIC OBJECTS R.A.E. Fosbury Space Telescope-European Coordinating Facility, European southern Observatory Karl-Schwarzschild-Strasse 2, D-80*6, Garching bei Mu'nchen, F.R.G.

This paper reviews some aspects of recent studies of activity in galactic nuclei. Observational techniques for diagnosing the nature of the energy source are discussed and the likely impact of new observing facilities suggested. Particular attention is given to the interaction between the central engine and its environment, both with regard to the ways in which the observed radiation is produced on a range of spatial scales and to the ways in which the activity may be triggered by outside influences.

- 91 - SHOCK ACCELERATION OF SECONDARY PARTICLES IN EXTRAGALACTIC JETS Y. Klemens Max-Planck Institut fur Radioastronomie, Bonn, Auf dem Hugel 69, F. R. G.

Diffusive shock acceleration in extragalactic jets accelerates protons up to high relativistic energies. These protons, interacting with ambient matter and dense ambient clouds, can create secondary electrons and positrons. Monte Carlo method is used to calculate the spectrum of those secondary particles, taking in consideration their diffusive shock acceleration and synchrotron radiation losses. The resulting spectra are compared with the observations and their implications on the existing models of active galactic nuclei are discussed.

A PROBABLE MODEL OK COMPACT VARIABLE RADIO SOURCES WITH A "SUPERLUMINAL" MOTION OF VLBI-COMPONENTS B. V. Komberg Space Research Institute, Moscow, USSR

"Ballistic" models are now put in doubt on the strength of the observed properties of "superluminal" components, and preference is given to "screen" models. It is suggested that active nuclei are supermassivt systems, such as SS-433, with two precessing relativistic plasma jets, which flow from opposite directions into the same precession cone. In this case "superluminal" components can manifest themselves as displacements of the interaction between these jets and inhomogeneities in the cir- cum-nuclear medium (clouds). Thus, due to isotropic production of relativistic particles in the interaction area and/or magnetic field distortions, bursts of emission may be observed not only along flows, as would ba the case for BL Lacertae objects, but also at appreciable angular distances from the jets. Moreover, one may understand the observed one-sidedness of VLBI-jets on parsec scales and the symmetrical VLA- -structures on kiloparsec scales as a result of random cloud hits by the precessing flows. We suggest that the observed repetition of active cycles of different objects may be caused by several cloud hits by the precessing flows of a complex mul.tibeam structure once every 50-100 years.

OIII-LINE EMISSION ASSOCIATED WITH RADIO STRUCTURES IN SEYFERT GALAXIES . E.J.A. Meurs^1'3^, M. Whittle^, S.W. Unger(2), D.3. Axon(2), A. Pedlar(2), M.J. Ward(I> (1) Institute of Astronomy, Cambridge, UK (2)- Nuifield Radio Astronomy Observatories, Oodrell Bank, UK (3) European Southern Observatory, Munich, F.R.G. A programme of high (spectral and spatial) resolution long-slit spectroskopy of Seyfert galaxies is described. The observations were obtained with the Isaac Newton Telescope on La Palma. The objects studied are Seyferts for which VLA-maps show linear double or triple radio structures on scales greater than 0.75 arcsec. In several of the objects a distinct component of very narrow OIII emission is detected which is extended along the radio source axis up to 20 kpc from the nuclei. The observed properties of this Extended Narrow Line Region (low velocity dispersion, orderly (rotational) velocity field, high excitation and elongated emission morphology extending well beyond the VLA radio source) would be consistent with interstellar gas photoionized by colllmated energetic radiation from the nucleus. Detailed correspondence between OIII emission features and individual radio components is suggested within the Narrow Line Region of a number of Seyfert galaxies. There is evidence for increased 0111-line emission near or f.round radio components (examples are NGC5929, 3C120, Mark 7B). Where two OIII components are observed, their velocities usually differ substantially from the normal galactic rotation. Rather than following rotation, these components may undergo systematic outflow. The OIII features tend to lie closer to the nucleus than the associated radio components. This radio-related OIII emission could be produced when gas that has cooled down be- hind a bow shock (caused by a radio component moving outwards) is photoionized by the nuclear continuum source.

- 92 - OBSERVATIONAL CONSEQUENCES OF PRECESSING RELATIVISTIC JETS IN EXTRAGALACTIC RADIO SOURCES

E.J.A. Meurs (European Southern Observatory, Munich, FRG) N. Roos (Sterrevacht, Leiden, NL)

Precession of radio jets is a frequent phenomenon among extragalactic radio sources (radio galaxies, quasars; as is evident from the many sources that display inversion (S-shape) symmetry. Such precession may result from the presence of a second massive compact object in the nucle.ua of these objects. Simple model calculations of slowly precessing jets, relativistic to various levels, can reproduce the essentia: features for a range of radio morphologies. Incorporating further realistic physical eCf-r.ts, like deceleration of the jets, leads to improved correspondence between observation and calculation. Interesting applications include the frequency of occurrance of one-sided jets, an explanation of "preferential avoidance" in radio brightness distributions and consequences for the cores of such radio sources. In connection with the underlying cause for jet precession, some evidence for the presence of a binary massive black hole in the centre of our Galaxy is discussed.

THE RADIO STUDIES OP VIRGO CLUSTER SPIRALS AT 10.7 GHz U. Urbanik1, U. Klein^, R. Grave5 1. Astronomical Observatory, Jagiellonian University, Krakow, Poland 2. Radioastronomisches Institut, Universitftt Bonn, Bonn, W. Germany 3..Max-Planck-Instltut fur Radioastronomie, Bonn, W. Germany The unique observational capabilities of the 100 m MPIfH telescope working at 10,7 GHz namely, its resolution sufficient to map nearby spirals with no loss of the flux from weak extended structures have been used to study the radio properties of bright Virgo Cluster spirals. Four objects: NGC 4254, NGC 4321, NGC 4501 and NGC 4569 all lying within 4° from the cluster centre and showing pronounced signs of the neutral gas stripping have been mapped with a resolution of 1'2. Their accurate radio spectra have been obtained as well. The use of beam-smoothed models revealed the existence of narrow bright radio ridges delineating one side of disks of NGC 4254 and NGC 4501. The coincidence of these features with some optical and HI peculiarities suggests collisions with the ambient gas. Apart from these localized perturbations the radio disks seem to be fairly symmetric. The radial distribution of the nonther- mal brightness does not show anomalously small scale length known to be present in the HI data. Implications of these facts are briefly discussed. Despite of large scatter in the star formation rate (a factor of~10) all spirals studied have roughly the same fraction of emission due to young star formation products (~3O?5 from HII regions, £10$ from supernova remnants). Similar values were found for other non-cluster galaxies. Physical conditions in our and field spirals have been compared too: it seems that the cosmic ray electron supply and confinement in the diffuse "thick disk" depends on environemsntal effects only through the exter- nally controlled star formation. Direct interactions of the ambient gas with galactic magnetic fields and trapped-in energetic particles apparently play a minor rtSle. Some more general implications of our study are discussed briefly too.

THE EXTENDED EMISSION LINE REGION OF MRK 3 AND ITS INTERRELATIONS WITH THE SEYFERT NUCLEUS S.J. Wagner Landessternwarte Heidelberg - Kdnigstuhl, F. R. G.

Mrk 3 is a well studied Geyfert galaxy. Amongst other interesting phenomena, It is known '.o have extended filaments of emission line radiation and large amounts of , dust. The authci- examined both the FELR and the Seyfert Nucleus with longslit spectro- metry of high r. paLip! arid kintiinat i cal (0-6 8 ) resolution and with CCD surface pho- tar"f'.!••• in iii::'.,'.J ••.rnJ HMiTow filters, ft io fuunti that the LLI.R is confined to a disk wl.i.;h .•: •:.': ij i IT. 'i TiiTi'ioth i. r; t o n i, l t y prufJle out to 6 kpc. "i r i ••.: disk is rotating and probably ...ho-js an inflow component in its velocity field. KineciHtical data are independent 'il' jf.- r 11 =,:*•. iin 3i.3C(-. Spatial variations of the line pio.f:.ltis from the ULR are fount..1. ThP.y rnij y 'OP. caused 'c\ excessive absorption within or r:. lose to the NLR. The pmnum of dust within the NLR decreases smoothly and stil! exhibits clear patterns at the outrjr edgrs of the LF.I.R. Both the centre about which the EELP rotates and the S e y : e !"•. nucleus are r e ri s h 1 i' t e d with j: e s p e o I to each other and with respect to the ;;tol iai component.

- 93 - CP 7 BINARY STARS

SOME METHODS FOR SOLVING VISUAL DOUBLE STAR ORBITS WITH INCLINATION! EQUAL TO 90°. * # - A. Abad , J.A. Docobo and A. Elipe " Dpto. de Astronomia. llniversidad de Zaragoza. 50009 Zaragoza. Spain. # Observatorio Astron. "Ramon M? Aller". P.O. Box 197- Universidad de Santiago de Corapostela. Spain.

As it is well known,the problem of determination the orbit of a visual binary star, presents a singularity when the inclination is equal to 90 degrees, and the classical methods for solving the orbit can not be used. In this paper, we give three different methods for solving this kind of orbits: i) The first, is obtained from five angular distances, and by solving a system of equations similar to Thiele-Innes method, the orbital elements are obtained, ii) The second, consists in an extension of Docobo's method, which enables to use this method for inclination equal to 90 degrees. iii) The third is based on the use of the Fourier Transform, in a way similar to the used by two of the authors in a previous paper. A comparison among the three methods is made, and applications to the pairs 19192S2442 and 19336S2339 are perfomed.

U B V light curve solutions of T T Here Barone F., Mancuso S., Milano L. Department of Phisycs of Naples University

We introduce a new method of solution of the light curves of eclipsing binaries, which is based on the Wilson and Devinney (1971) Roche-model based approach but uses a more reliable procedure of getting the system parameters than the differential correction one. We performed an interesting application of the procedure, to the binary system TT Her.

THE ROLE OF ANGULAR MOMENTUM TRANSFER TO DETERMINE THE MASS RATIO OF BINARIES M.Bossi (-), P.Paolicehi.M.Bellesi and F.Ferrini (*) (-)Osservatorio Astronomico di Brera, 22055 MERATE (Co) (Italy); (*)lstituto di Astro- nomia, Un. of Pisa, Piazza Torricelli 2, 56100 PISA (Italy).

A thermodynamical approach to the problem of star formation and fragmentation shows how, at least when the last stages of collapse are assumed as adiahatic, the mass ratio of binaries depends on the initial conditions (thermal and rotational energies) and on the distribution of the angular momentum among the spin of the primary, the spin of the secondary and the orbital motion. As discussed in a previous paper, this distribution can be profitably expressed in terms of two parameters, roughly corresponding to (a) the spin ratio as function of the mass ratio and to Cb) the a.m. transfer from spin to orbit. A systematic exploration of parametric models allows to understand the transition from the extreme case of "perfect coupling" (tidal, magnetic ?) leading to corotating objects with a low mass ratio, to the other extreme caso of "no coupling", leading to the formation of close twins. Some conclusions on the initial mass ratio of bi/iaries can be obtained, In particular when we link this problem to that of the formation of protoplanetary discs. ON THE NLTE ANALYSIS OF HE I LINES IN THE ATMOSPHERE OF B LYR

Dimitar L. Dimitrov 1 and Oiri Kubatz 1 - Prague Observatory, Petrin 205, 118 46 Prague 1, Czechoslovakia 2 - Astronomical Institute, Czechoslovak Academy of Sciences, 251 65 Ondfejov, Czechoslovakia

Some more results after an abundance analysis of the primary component of 6 Lyr are presented. Namely, employing a NLTE approach to selected helium lines, the NLTE populations of various He 1 atomic levels were obtained. Their ratios to the LTE populations define the so-called b-factors, representing the departures from the condition of LTE in the stellar atmosphere. Further- more, from the appearance of certain spectral lines the influence of a circumstellar envelope is clearly evident. Here, the run of b-factors with depth in the stellar atmosphere will be displayed as well as their dependence on the adopted helium abundance. The basic model parameters for g Lyr primary

are T eff = 12000 K and log g = 2.5 for all models. Various models differ by the adopted He abundances: the values He/H = 0.1, 0.25, 0.50, 1.0, 1.5 and 3.0 were considered. The effects of in- creasing He abundance are illustrated by means of b-f actors for He/H = 0.25, 1.5 and 3.0. It turns out that deviations from LTE are larger for higher Y,, . Moreover, a comparison between equivalent widths when a NLTE approach is employed versus the LTE approximation will be shown for some He I lines of general interest. Also further evidence will be given, supporting the possibility that certain resonance and shell lines originate in the extended outermost atmospheric layers or in a circumstellar envelope fairly close to the primary star.

LIGHT CURVE VARIABILITIES OF CLOSE BINARIES Djurasevic Gojko Astronomical Observatory, Volgina Y, 11050 Beograd, Yugoslavia

In the paper ia considered a possibility of the determination of the parameters of close binaries of the type RS CVn by means of a comparison of the light curve derived from photoelectric measurements to a synthetic curve obtained on the basis of a model of a binary system. The inverse problem method based on the nonlinear least square method is used. A few test examples and a shorter analysis of the proposed method are given.

MODEL ATMOSPHERES OF BINARY COMPONENTS

P. Hadrava Astronomical Institute of the Czechoslovak Academy of Sciences

Models of stellar atmospheres are based on assumption of their planeparallel or spherical symmetry. Violation of this assumption by tides and rotation in close binaries leads to incompati- bility of hydrostatic and radiative equilibria. Improvement of model atmospheres In this respect is desirable for simulation of light curves and line profile changes. Moreover, atmospheres of contact components of interactinn binaries determine initial conditions of dynamics of gaseous streams and in this way influence the behavior of the binary system. TW CASSIOPEIAE - AN ALGOL-TYPE BIHAHY T. B. Horak 1, D. Chochol 2 t Institute for Information and Management of Culture, BieCna 1, 815 58 Bratislava, Czechoslovakia 2 Astronomical Institute of the Slovak Academy of Sciences, 059 60 Tatranska Lomni- ca, Czechoslovakia Photometric light curves of TW Cas do not exhibit any apparent compications. Yet, a careful analysis of the light conditions in the system leads to some con- tradictory results. A nontraditional explanation is suggested.

BINARY; CHEMICAL PJSCJLIAR STAR »j Ulla JlIH KLLIPTICAL L. Hric

Astronomical Institute, Slovak Academy of Sciences, 05960 Tatranaka Lomnica, Czech.

Own photometric and spectroecopic data with published radial velocities of chemical peculiar (CP2) binary oUUa are interpreted. It is shown, that colFKa is probable eclipsing binary with an elliptical orbit. On the basis synthetic spectrum for a model of atmosphere with T f.f = 10 500 K and log g = 2 (in SI) is derived type of peculiarity coUiia (Sr - Cr - Eu).

&ti OiiJil.tVATj.Oj;iAL j'JPJOflj) J'O.L .I ^Li.n-iZ ..OO^ii OJ ..it Jiang ohi - yan£

g Obcervatory, Acadeiaia Sinica

HD 94033 was discovered by Przybyski in 1975 as an ultra--!iort period dwarf oap- heid with a pulsation period of only about 86 niia. and an amplitude in V band of about 0.8 mag. It is very important to study the duplicity of this ctar. j'roii l'jol to 1984, we have observed this star many times and got 16 times of aaxima. Combined with 25 Tm given by Przyby&ki, we have done sone analysis of the period and found tiiat the 0 - C values of the Tm exhibiting regular variation v.ith a lon^ period of about 9 years. In a short paper we mentioned that the most plausible interpretation of tiiis periodicity is the light-time effect in a binary system. Subsequently we have continued the obaervation and paid attention to tho new observations published in the literature to ciieck this idea, i'our new tiroes of i published by i^cilamara have stimulated us to make a new analysis of the availablble timi e of i a to s if th dt s till i li ith th In;I , variation of the hypothetical binary. The latest obsei-vationa are uade in 1337. After a least squares solution of all the times of waxiua according to formulas Tm = TO + PO £ + 0.5 h E U + A sin 0 + J cos- D, D-esinD=2F(P0 3-t), a similar solution has been obtained as the previous one. Of course the best way to check this binary hypothesis is to measure the mean radial velocities within the pulsation period, to see if there is a variation with an amplitude of 2.8 km/s. The mean R.V given by Przybyski ig 267 kiu/s, but that given by llcJJamara is 268 km/s, both fit well with the phases of a binary orbit.

- 96 - oosctral Investigation of riclipsing binary Stars at the Stag6 of Llaas Exchange

V.G.Aaretnikov

Actronomical Department of the Odessa State Jniversity, park Shevchenko, Odessa, 270014, J.3.S.R.

spectrograms witn dispersion 9-37 A/mm the spectral characteristics of si^iat eclipcin^ biniry stars hive been studied showing the effects of ;.iasses exchange. Spectral types o£ stars have been determined as well as temperature of excitation, parameters of dainoin^, turbulent velocities, electronic concentration, caeaiiciil composition of stars atmospheres and displacements of lines in radiation and absorption, variations in characteristics of lines with the phase. It ij shewn that appreciable differences of physical conditions from normal ones havs not neon'observed. Schemea-models of stellar systems studied have been olofcied and diacuased.

MODELS OF ACCRETION DISCS IN INTERACTING BINARIES Svatopluk Kffz Astronomical Institute, 251 65 Ondfejov, Czechoslovakia

Every attempt to model accretion discs necessitated some drastic simplifications. If one neglects the. old calculations of particle trajectories, two distinct approaches can be distinguished: (i) Some simple assumption about the vertical structure of the disc is used and the two-dimensional problem is solved in the orbital plane. The authors either solve the partial differential equations of fluid hydrodynamics directly, or simulate gaseous flow by many-particle calculations. The results of different works are not consistent, the available models do not provide us with the prediction of the emergent spectrum. (ii) Axial symmetry of the disc is assumed. Usually, some modification of the alpha-viscosity is used. Some models of this kind include a sophisticated treatment of the vertical structure of the disc. The calculated distribution of continuum radiation agrees with the observed one only in some cases. There are several sequences of time-dependent models, however, we are still unable to decide, whether the observed changes in the discs are due to the changes of mass transfer rate or due to an instability of the disc itself.

• I ilie ro.isiuil ity of T.-skin.-r into Account tlie rieciroraa<;netic ifadiation i.i the Atmospheres

oi' Close Binary Stars. I gOr KUDZEJ

ukresna IUCIOVL livezduren , 0G6C0 ;iUM!iS,\''.

The calculation procedure of optical characteristics of stellar atmospheres is described for the ::iodel of homo.";eous partially ionized nonrelativistic isotropic plasma with the ,'iccount of individual particles collision,A advance is described for calculation of the refracted electroaaoietic railintion m;<:;iiitude of an eclipsed component in the atmosphere of ;.ri oclipsinc 'me iii the olose Li.-inry system during total eclipse.The frequencies of the incident

- 97 - I Ht SPECTROSCOPIC BINARY Xi CYGNI

B. Onderlicka and 0. Handlirova Department of astronomy, Purkyne University, 61137 Brno, Czechoslovakia and N. Copernicus Observatory and Planetarium, 61600 Brno, Czechoslovakia

Radial velocity variations of the K supergiant Xi Cygni are investigated on the basis of published as well as new values from spectrograms in the visual and infrared region obtained in the period of 1977-1984 at Ondfejov, Shemakha, and Crimea observatories. The preliminary period derived by Paersons (1983) is confirmed, the scatter, however, of the values is considerable. Sources of errors are discussed. The need of homogeneous material and a suitable selection of lines is stressed for this low-amplitude binary.

STATISTICAL PROPERTIES OF ECLIPSING AND VISUAL BINARIES P.Faolicchl.M.Alongi (-),M.Fofi ( + ) and M.Scardia (*) (-) Istituto di Astronomia.Un.of Pisa, Piazza Torricelli 2, 1-56100 PISA (Italy); (+) Osservatorio Astronomico di Monte Mario, ROMA (Italy); (*) Osservatorio Astro- nomico di Brera, MERATE (Co), (Italy).

The catalogues of eclipsing and visual binaries have been analyzed by means of a multivariate statistical method, in order to put into evidence mutual relations among the observed quantities as well as clustering properties in the multi-dimensional space. Preliminary results of the analysis show several interesting features, and a physical interpretation can be attempted. Nevertheless, observational selection effects play an important role. The way back to the understanding of formation and evolutionary properties is extremely difficult, and unbiased conclusions about fundamental parameters as the initial period and mass-ratio distributions cannot be obtained.

Narrow-band, high resolution imaging of the Inner nebula of tbe pynabiotic variable R AquarH*, Franeeaco Paresee*, ChrUtophsr Burrow*', and Keitri Hcme, Space Telescope Science Institute, Homewood Campus, Baltimore, MB., USA 21218.

Some of the moat exciting phenomena occurring in the R Aquarii system occur deep within the inner nebulosity extending out to 10-15 arcseconds at most from the central object. The morphology and physical characteristics of this nebulosity sre cot well known, principally because of the difficulty of imaging accurately and reliably within a few arcsecoods of the bright Mira whose visual magnitude varies periodically from m, = 6 to 11 in 387 days. We have developed a solution to this problem by using a coronograph whereby the bright Mira is occulted by a 2 arcsecond wide wedge. This allows long integration time exposures through narrow-band filters tuned to bright emission lines such as Ha and the forbidden [Nil] 6583A. Short duration broad band R exposures appropriately subtracted from th.> narrow band images allow an even better view of the line emission region around this object. The potential of this technique 5e illustrated graphically as both previously known and unknown bright and faint fe&turers throughout the inner nebulosity can be readily discerned and accurately measured down to approximately one arcsecond of the Mira without difficulty. Esp-cieJlv obvious is the famous jet made up of seven-,! knots extending in a generally northern direction, but faint wispa, knots, and a counter jet extending to the limits of our image in the southwest are also clearly discernible againet the sky background. Direct comparisons of images taken in Lhe light of several emission lines of elements in varying ioniiation stages show remarkable differences revealing a complex temperar.ure and electron density structure within the nebulosity. This data should prove quite useful in establishing and elucidating the mechanism responsible foe the observed activity iu this enigmatic syetem.

t Affiliated to the Astrophysics Division, Space Science Deu irlment of ESA. * Data collected at the European Southern Observatory, (Jhi'ii.

- 98 - SPECTRAL .FLUX DISirtlilJTIOH OF DETA LX.U^, 910 - 8150 £ 1.1.J. Plavec University of California, Department of Astronomy, Loa An^eleo, Calif omia 90024, 'JSA

Combined are optical spectral scans covering the region 3200 - 8150 2 with ultraviolet IUE spectra covering the interval 1220 - 3200 A and with far-ultraviolet spectral scans by the Voyager spectrometer of the region 910 through 1700 A. A total of 29 optical scans, 28 pairs of low-and high-dispersion IUE apectra, and 13 Voyager scans provide a satisfactory phase coverage over the entire orbital period. Great oare has been taken in removing the effects of circumstellar emission, which lifts the apparent continuum at places, in particular in an extensivs bulge at about 1700 - 2100 A. Separation of the fluxes from the two components ia a very difficult problem, since the eclipses are only partial. 1'he model proposed in 1974 by R.B. Wilson has been found ratisfactory for the optical B region, and has been used to separate the two components, .both objects in Lyrae have in fact anomalous flux distributions! The secondary since it is .irobaoly a flattened accretion disk, and the primary because it probaoly fills its critical Roche lobe. As a consequence, the value of surface gravity and hence of ths local "effeotivs" temperature varies greatly over the distorted surface. If time and/or space permits, a comparison will be made of Lyrae with several other strongly interacting binaries.

LUMINOUS ACCRETION DISKS AND HIGH IONIZATION EMISSION LINES IN INTERACTING BINARIES

Ronald S. Polidan

Lunar and Planetary Lab, University of Arizona Tucson, Arizona 85721

Multifrequency (500-7000 A) observations of a variety of interacting binary stars are reviewed, discussed and intercompared. Emphasis is placed on the character of the continuous flux that is thought to arise in the luminous accretion disk in each system and the (possibly) related high ionization emission lines. Data from the Voyager ultraviolet spectrometers (UVS), IUE high and low resolution images, and ground-based spectrophotometry are used in this analysis. Detailed comparisons of the emitted spectrum of the accretion disks in active Algol systems and in cataclysmic variables show important similarities and very few significant differences. Recent high resolution IUE observations of the UV emission lines in the active Algol system V356 Sgr supply new insights into the physical conditions and geometrical properties of the high ionization emission line region. This work has been supported by NASA Grants NAGW-587 and NAG5-4A1.

The UV Spectra of Cataclysmic and Symbiotic Variables

P.L.Selvel1i , Osservatorio Astronomico di Trieste-Italy. R.Viotti, CNR-Istituto di Astrofisica Spaziale-Frascati-Italy.

UV observations of cataclysmic and symbiotic variables with the IUE satellite have given -*rd are giving a fundamental contribution to our k".owledqe of the nature of these object-.,. T'r>? s':udy of the !'V resonance air 'ntercomM' na'.; en lines of the m most abundant e ; o.ê-'.- '--s beer, used a:. - diagnostic of t • physical c nditions in tne disk, •-.: rcurnst--. ' lc- .-<-',-P, and eje.".'..1.. '.:: ••'..5»- f IUL *as allowed tie r s t ,-.' / -. f t. <: ;e ••••':".'.'" d'j - i r g •' i f f -. • i -• . 11 « ". "y ; ales ê vi''us phases of the f ! t 'r/jtst ? se-'ei'i- r.atiir.al nr,V66 -.• of **.;: cT a: :i:. nov ' .• '-•v: iôen monitored •j". ii" the -e'.'i'ar st^:< . In the rucurrît nov? " C- _• d--.~- '. UV i: iatians have r teen oo:e-v-' du'-ir.'; p-:.:>!s of 'jptical qj ie .cen^-;. "'*" pirti-iâr '-Urest ha-; êen •Mr L'V stii.-'y r* the recent outbursts ^f the syr.iictic s'a.-s AG 0-, L An: a-.d PU •1, 3S wfe" 1 tna: of CH Cyg during the ictivit;y nhases acS('C1"'i" to '_tv= formation : ! je:. The results of mi; 1 t i-f req..en LV obs?rvations (from -9' '.c to s-rj. ) --" iome cataclysmic and symbiotic variables and their impl i r.s t -"n- - •• • models .re- si- discussed. REGIONS OF RADIATIONS IN THE SYMBIOTIC BINARY CH CYGNI

A. Skopal

Astronomical Institute of the Slovak Academy of Sciences, 059 60 Tatranska Lomnics, Czechoslovakia

Spectroscopic and photometric behaviour of the symbiotic 3tar CH Cyg in the period 1981 - 1986 is given. Observed variations of the intensities of emission lines, absorption shell lines and resonance line Ca II K are discussed. An analysis of these lines support an idea, that a few different regions of radiation exist in CH Cyg. Drop of brightness, development of jets and changes of the amplitudes of flickerings are interpreted as a consequence of an accretion disk evolution.

A COMPARATIVE STUDY OF CATACYLYSMIC VARIABLES: EVOLUTIONARY TRENDS vs OUTBURST ACTIVITY TRENDS Zdenek Urban Astronomical Institute of the Slovak Academy of Sciences, Observatory Skalnate Pleso, CS - 059 60 Tatransk£ Lomnica, Czechoslovakia

The physic; parameters of known interacting binaries - members of the various classes of cataclysmic variable stars, including the magnetic ones, are compiled, on the basis of the published observations. The physical structure of each system is determined, as specifically as the data allow. The resulting mosaic is compared with the existing studies of the white dwarfs, low-mass main sequence and interacting binary evolution. Possible evolutionary trends changing the physical parameters of the component stars and the binary as a whole, expected on the basis Df these latter studies, are then analysed within the context of the current models for various forms of the cataclysmic outburst activity. The results are compared with the observational database of cataclysmics. Cyclic vs parallel evolutionary pictures of the outburst activity are discussed. The cyclic picture with the secular changes in cycle characteristics is shown to be quite compatible with the current observational/theoretical view of cataclysmics.

ACCRETION DISC BI 01 CARIHAiS DURING RISJS i'O

Krzyeztof Jlodarezyk

Pedagogical University, Department of Physics, Podchorazych 2, 30-084 Cracov., Poland

0'f Car is the only eclipsing dwarf nova which W3s oi.;e.-v4r :-.t ri^s to an normal outburst. Such unique photometric observat.lo.-is Dita^'a-j t- V;-t (1^5^,) are rsanalysed. The disc eurface brightness dig-tribaticr. i •; -ii e. •'.I--~6eter.-._:le and the changes of the resulting distribution aiv dis;:ci'si _.-. c-: i:c..:t .-iz'.."".-^ nova outburst ir.odalo.

- 100 - REGISTER OF AUTHORS' NAMES

The register contains the names of authors and co-authors of the published abstracts which arrived at the organi- zer's address within the specified time limit and which have been included in the thematic blocks of this publication. (The first entry on page 85 is the only exception). We have retained the surname and the initials in the same form in which they are mentioned under the heading of the individual contributions. We have arranged the names in alphabetical order. In the case of indentical surnames, the alphabetical order of the first name is decisive.

The selected author's name is referred to a page number in the publication. In case that the same author appears several times on a given page, then this number is qualified by means of a letter. In this way the sequential cder is also defined. The abstract placed at the top of the page is referred to by means of the letter "a", the next ones with "b", "c", etc. This is to explain why some references are expressed by means of mixed notation.

3. Zavfel

oeckman, J.E. 53 Bellesi, M. 94 Bellout, A. 20 Aab, O.E. 74 Abad, A. 94 Bertin, G. 50 Afanasiev, V.L. 47 BiCak, 3. 85 AielJo, S. 82 a,b Bielicz, E. 76 Akyol, M.O. 47 Blitz, L. 51 Alcaino, G. 48 Bolton, C.T. 75 Alfaro, E.3. 53 Borovifka, 3. 90 Alissandrakis, C.E. 3a,b Bosma, A. 51 Along], M. 98 Bossi, M. 9* S3 Alvarez, M. 74 Boyarchuk, A.A. 75 Ambroi, P. 4 Bo2ic, H. 39 Andronov, I.L. 75 Bretagnon, P. Antalov£,A. 19 Burnba, V. 1,4.5 Antz, Ch. 22,37 Burgos, 3.M. 90 Assendorp, R. 72 Burkert, A. 51 Athanassoula, E. 48,51 Burrows, Ch. 98 Aurass, H. 14 Busso, M. 63,66,79 Avedisova, V.S. 48 Axon, D.3. 92 C Cabrera-Cano, 3. 53 B Campos, L.M.B.C. 5 Babadzhanov, F.B. 22,23a,b Carusi, A. 2*a,b BachiHer, R. 49 Catala' Poch, M.A. 6Sa,b Baev, P. 47 Cellino, A. 24 Bajaja, E. 50 Cepa 3. 53 Bakos, G.A. 80 Ceplecha, 2. 22,25 Bala'zs, L.G. 59 Cernicharo, 3. 49 Bally, 3. 50 Chini, R. 53 Banaszkiewicz, M. 23 Chiuderi-Drago, F 3 Barkin, Yu.V. 39 Chlewicki, G. Barone, F. 94 Chochol, D. 83,96 Barsella, B. 82a,b Chrysovergis, M. 58 Baudry, A. 57 Clausen, 3.V. 52 Bavdaz, M. 22 Collados, M. 4,5,6,9,20

- 101 - Comorelio, C. Corcione, L. Covino, E. 70 Garcia de la Rosa, J.I. Crifo, F. Carzon, F. Cnfo, J.F. 25 Gcszielyi, L. Csepura, G. 6 Gies, D.R. 7i Gicse, R-H. 27 Gjmenez, A. 52 Dagostinoz, B. 77 Giovannelli, F. 76 Danz, M. 31 Giovannini, G. 9J Davjd, M. 71 Giuncin, G. 55 Degiacomi, C. 6 Gtebocki, R. Dermend/iev, V.N. 7 Gojko, D. Despois, D. 57 Gomez, A. Dezsb, L. 7 Gopasyuk, S.I. Dialetis, O. 3,7 Goitlbber, S. Dimitrov, D.L. 95 Grabintka, T. Dobereiner, S. 72 Grave, R. Docobo, J.A. 9U Greenberg, 3.M. Ducatel, D. 78 Griin, £. Dumont, R. 25 Guo, Z.H. Duschl, W.3. 91 DzifCakova", E. 17 H Habing, HJ. Hadjidemetriou, J.D. Elford, W.G. 32 Hadrava, P. Elipe, A. 9tt Hagyard, M.3. Elmegreen, B.G. 52 Hajduk, A. Elter, G. 31 Hajdukova, M. Esin (Yilmaz), F. 37 Hall, D.S. Handlffova', D. Harmanec, P. Fahlman, G.G. 81 Haubold, H.3. Fairhead, L. 39 Hefty, 3. Falciani, R. 26 Heinzel, P. Farinella, P. 26 Hejna, L. FaVnik, F. 13 Henning, Th. Faurobert, M. Sa,b Henoux, 3.C. Fechtig, H. 26 Henrard, 3. Feitzinger, 3.V. 52 Hensberge, H. Feretti, L. 91 Hensler, G. Ferraz-Mello, S. fOa,b Hildebrandt, 3. Ferrari, A. 91 Hofmann, A. Ferrari-Toniolo, M. 63 Holl, A. Ferrini, F. 5*a,b, 9 Hora'k, T.B. Floquet, M. 77 Horn, 3. Fludra, A. 20 Home, K. Foli, M. 98 Hric, I. Fosbury, R.A.E. 91 Hsiung, P. Fridman, A.M. 17 Huang, L. Frisch, H. 8 Hubert, A.M. Froescble, C. 27,*0,tl Hubert, H. Fuilerton, A.TV. 75 Hudec, R.

- 102 - Hugucnin, D. Kulur, L. \u Kim, M. I L Ibadinov, Kh.l. 28 Ibadov, S. 29 Langer, 3. lsaak, G.R. 17 Laskar, 3. 43 15 Ivchenko, l.N. 47 LasloviCka, 3. Lc Cornel, J.M. 78 Lemaire, P. 15 Lenzen, R. 59 lacq, T. 57 Lciius, V. J4 Jakimiec, 3. 12,20 Levasseur-Regourd, A.C 25 Jessberger, E.K. 22,36,37 Li, Z.W. 77 3iang Shi-Yang 96 Liller, W. 4g 59 Joarsater, S. Limboz, F. 37 29 3ovanovic, B. Lin, C.C. 50 Jupp, A.H. 42 Lindblad, B.A. 30 59 Lindblad, P.O. 19 Locans, V. 56 KadrnoSka, 3. 42 Loore, C. de 31 Kapisinski, 1. 23 Lorenz, H. 85 Karetnikov, V.G. 97 Lukash, V.N. 60 Karlicky, M. 12b,c LyngS, G. Karsky, G. 89 Kirbiyik, H. 77 M Kissel, 3. 36 MacDowall, G. 81 Klein, U. 93 Makov, Yu.N. U7 Klemens, Y. 92 Malagnini, M.L. 84 Kliem, B. 14 Malherbe, 3.M. 16 Kloko&iik, 3. 43 Malkov, O.Yu. 64 Kneissel, B. 27 Mamadov, O.M. 30 Kneubuhl, F.K. 6 Mancuso, S. 94 KneJevic, Z. 29 Mangoldt, T. 31 Knochel, A. 22 Mardirossian, F. 55 Komarek, Z. 83 Markova", E. 15 Komberg, B.V. 92 Martin-Pintado, 3. 49 Konovalova, N.A. 23 Martino, M. di 24 Kontizas, E. 57,58 Martres, M.3. 15,17 Kontizas, M. 57,58 Mayor, M. 62 Kopp, R.A. 13 Mein, N. 18 Kostelecky 3. 89 Mein, P. 3,16,17 Koubsky, P. 75,77 Mcisenheimer, K. 61 Kova'cs, A. 7 Mrlnick, 3. 60 Krasinsky, G. 43 Merit1, B. 16 Kre+owski, 3. 5* Mci^j.i, M. ;>8 Krrsa'k, L. 2h,V) Meurs, E-3.A. 92,93 Kresj\(iva, M. 30 Mczger, F.G. 61 Krivsky', L. 13 Vlez/etti, M. 55 97 Kfli, ^:. fvill3HI, A. 44 K.rLigcr, A. 12,14a,b Mllano, L. 94 38 Kub.icek, D. "*-'i :oi;ra<:ii'V-TuT i.-. 61 Kuba't. .1. 95 Mi'! Imann. i'. 31 Kurirc), 1. 97 Mr.ri-.sv, '. . 38 Morozov, A.G. 47 Pittich, E.M. 84,99 Morras, R. 50 Plavec, M.3. 85 Muciek, M. 62 Podolsky, 3. 64 Miicket, 3.P. 86 Polechova, P. 13 Muller, R. 16a,b,c Poletto, G. 99 Miiller, V. 86 Polidan, R.S. 81 Munoz, 3. 53 Polosukhina, N.S. Polyachenko, V.L. 47 50 N Poppel, W.G.L. Porubian, V. 34,36 Nagy, I. 6 Prieto, M. 53 Napier, W.M. 31 Prokakis, Th. 7 Neckel, Th. 6],67 Pycha, 3. 15 NezJin, M.V. 47 Niedzielski, A. 62 Ninkovic, S. 62 17 Nobili, A.M. 44 Raay, H.B. van der 64 Novikov, I.D. 85 Radoslavova, T. Novocky, D. 16 Rahe, 3. 2 Rahmonov, A.A. 28 Rajchl, 3. 34 RamelJa, M. 55 Oblak, E. 62c,d Richter, G. 31 Obrubov, Yu.V. 23 Rickman, H. 35 OJa'h, K. 78 Robberto, M. 63,66 Olsson-Steel, D. 31,32a,b Robin, A. 62 Onderlicka, B. 98 Roca Corte's, T. 17 Rodono, M. 79 Rodriguez, I. 5,6 Padevet, V. 33 Roos, N. 93 Palle, P.L. 17 Rossi, C. 76 PaJous, 3. 63 Rossi, L. 84 Paolicchi, P. 33,94,98 Roudier, Th. 16 Pap, 3. 10 Rubbert, B. 31 Paresce, F. 98 Rudnitskij, G.M. 65 Pasha, I.I. 47 Ruiz, B. 6 Pastorek, L. 15 Rusin, V. 17 Pasiuszka, Z. 76 Rybansky, M. 17 Patriarchi, P. 82a,b Rylov, A.Yu. 47 Pauwcls, T. 45 Paviovski. K. 75,78 Pfau, W. 35,56 Pocma, P. 34 Sanchez Almeida, 4,20 P'.-diar, A. 92 Sarris, E. 7

Peres, G. 20 Scalo, 3. (•'> P??r>•:>'. K- 90 Scaitriti, F. •3,6,'. 79 i:> Scardia, M. v.2a>h Schrnu'dsi, P.. Scholl, h.

S< burnann, J.D. St'lwond. .1-A. 3? .Sclvclii. P.L. 99 64 Sernt-I, M.

- 10-" Serio, S. 20 V Sicardy, B. 45 Valentc, T. 84 Sidlichovsky, M. 45 2,13,90 Sikorski, 3. 76 Valnicek, B. Valsecchi, G.B. 24a,b Silvestro, C. 63,66 Vany'sek, V. 70 Simek, M. 36 Vazquez, M. 5,6 Simnett, G. 17 Verheest, F. 81 Simon, G. 3,18 Verschueren, W. 56,71 Skopal, A. 100 Vial, 3.C. 20 Skumanich, A. 8 Viotti, R. 99 Smaldone, L.A. 26 Vittone, A. 76,83 Snezhkin, E.N. 47 Vondrak, 3. 89 Sobotka, M. 18 Solanki, S. 4,18 W Sole, M. 36 Somov, B.V. 11 Wagner, S.3. 71,72,93 Souchay, 3. 88 Walker, G.A,H. 81 Spurny, P. 35 Wallenwein, R. 22,37 Staude, H.3. 61,66,67 Ward, M.3. 92 Staude, 3. 11,19 Weidlich, V. 31 Stecklum, B. 35 Wesselius, P.R. 72 Stepanyan, N.N. 19 Westerlund, B.E. 58 Sterken, C. 80 Whittle, M. • 92 Stohl, 3. 34,36 Wiehr, E. 21 Strelnitskij, V.S. 67 Wielen, R. 72 Strobel, A. 67 Wlodarczyk, K. 100 Stuchlik, Z. 87 Wolf, M. 73 Subirana, 3.S. 68 a,b Wu, S.T. 18 Suchkov, A.A. 69,87 X Sudova, 3. 13 Svestka, J. 37 Xiradaki, E. Svoren, 3. 36 Sylwester, B. 20 Y Sylwester, 3. 20 Yang, S. 81

37 Tammann, G.A. Zabierowski, M. 86,87 Tandberg-Hanssen, E. 17,18 Zachariadis, Th.G. 21 Terlevich, E. 69 Zappala, V. 24,38 Terlevich, R. 70 Zasov, A.V. 47 ThieJheim, K.O. 90 ZboriJ, M. 81 Torgashin, Yu.V. 47 Zhugzhda, Y.D. 19 4.20 Toro Iniesta, 3.C. del Zinnecker, H. 73 Tpzzi, G.P. 26 Ziolkowski, K. 38 Traxel, K. 37 Zloch, F. 15 Tremko, 3. 80 Zornoza, 3.M.3. 68 Tsiropoula, G. 7 Zverko, 3. 81 Tupikova, I.V. 46 Zvola'nkova', 3. 38 Turon, C. 88 Unger, S.W. 92 Urban, 2. 100 2iinovsky, 3. 81 Urbanik, M. 93

- 105 - Vydalo stfed-sko vSdecky'ch informacf AsO CSAV 251 65 Ondrejov Na'klad: 600 vy'tiskd Vytiskly Tiskafsk^ zavody, n.p. zavod 5, provoz 52 Praha 1 Vytiskly T\skafsk6 zdvody, n. p., provoz 52, Praha 1, Bilkova 17 THE TENTH EUROPEAN REGIONAL ASTRONOMY MEETING OF THE IAU

Czechoslovakia 24- 29 August 1987

LATE LATE ABSTRACTS

Included are abstracts which were received before 6 August 198?

Sessions and Authors

Page PS 1: V.A. Brumberg 2 TS 2: L.M.D.C Campos G. CevoLani, A. Hajduk i V.S. Getman 3 B. Kneissel, R.H. Glese 3 B. Komitov et al. 4 M.S. Staniucha t, TS 3: N. Borderies SM 1: B.C. Elaegreen S j. Koorneef, Ch. Burrows S Ts. Radoslavova 5 O.K. Sil'chenko t, * E.I. Zelwanowa 6 SW 2: M. Auvergne et al. 6 A. Baglin 7 G.A. Bakos, J. Tremko 7 C. Blanco et al. 7 H.-J. Goupil 8 A. Noels e R.K. Prinja s P. Rovithis/ H. Rovithis-Livanlou 9 J. van Paradijs 9 CP 1: A.W. Harris 9 A. Talavera/ A.I. So*«z de Castro 10 CP 2: 1.0. Novikov, V.N. Lufcash to A. Hesziros/ P. Hesziros 10 CP 7: J.H. Burgos, J. Labay 10 C. de Loore 11 COIJftMPOfiARY f".JLt>l5 Jl: ftELAFIVISTIC CELESTIAL MECHANICS AND ASTRDI-1ETRY V.A. Biuniberg !.-•-- .itute of TioocHtjcal Astrono.iiy, 191187 Leningrad

General Relativity snc.i.,J bu uoniiuaLed as a necessary framework in the discussion of high-precision observations and for the construction of accurate dynamical ephemerides. This involves the investigation of the field equations and equations of motion (relativistic celestial mechanics) and the elaboration of the procedures to compare theoretical and observational data (relativistic astroinetry). At present, the most actual developments are as follows: 1. The programme of Lhe parametrized post-Newtonian formalism has resulted in the experimental verification of general relativity. The present discrepancies between the planetary ephemerides and the observational data do not necessitate any modification of the gravitation theory. 2. Recent advancements in Deriving the equations of motion with account of the gravitational radiation made it possible to study the orojtol motion of the binary pulsar PSR 1913+16 by the rigorous celestial mechanics methods. The indirect evidence of the existence of gravitational waves is based on the orbital analysis. 3. Modern approaches to the pronlem of motion using the matching procedure for the field equations solutions valid for the physically specific sub-domains (internal region, buffer region, external region for each celestial body) enable to treat the whole problem more rigorously mathematically and more meaningfully physically. 4. Relativistic theory of reference frames for astronomy and geodynamics is of particular importance. The consistent theory of reference frames should satisfy two conditions: a) utilization of one and the same type of coordinates (harmonic, for example) and n) dynamical adequacy of the relevant metric tensors to the problems under consideration. The hierarchy of the reference system embraces at least, barycentric (GRS), topocentric (TR5) and satellite (SRS) systems admitting a possible rigid body rotation of the systems. Time scales and astronomical units of measurement should be treated in close relation with the relativistic theory of reference frames. 5. Practical relativity includes relativity terms in the planetary numerical (3PL, ITA) and analytical (DDL) theories, relativity terms in lunur and artificial satellite theories in QRS and CRS, relativity bases of astronomical almanacs, rnlativistic discussion of astrometric observations, pulsar timing and other applications.

ON THE COMBINED EFFECTS OF FLUID VISCOSITY AND ELECTRICAL RESISTANCE ON ATMOSPHERIC ALFVEN WAVES, by L.M.B.C. Campos, Institute Superior Tejnico, 109C Lisbon Codex, PORTUGAL.

We consider Alfven waves propagating obliquely in an atmosphere, subject to an uniform magnetic field of arbitrary direction, in the presence of viscous stresses and electrical resistance. The wave equation is solved exactly,.in the case of an isothermal atmosphere, for which the Alfven speed increases exponentially on twice the scale height, and the dynamic viscosity increases exponentially on the scale height; the rate of ioniaaUon is assumed uniform, leading to a constant electrical diffusivity. The exact solution includes, as particular cases, those obtained before for Alfven waves in an isothermal atmosphere, in the non-dissipative case with vertical (Ferwro S Plumpton 19">8) =nd oblique (Schwartz, Cally and Bel 1984) magnetic field, and in Lhe case of resistive dissipation alone (Campos 1983a). The wave fields are expressed at all al-itudos in terms of hypergeoir.stric functions, which are used to plot the amplitudes and phases, for several combinations of wave frequencies, horizontal wavenumber, inclination of the magnetic field to the vertical and viscous and resistive diffusivities. It is shown that, for certain ranges of the values of the parameters, intense localized dissipation of waves can occur, suggesting a viable mechanism for atmospheric heating. The present theory is compared with the RLC-analogy (Ionson 1982), the resonance model (Hollweg 1984a,b) and the phase mixing approximation (Hcyvaerst and Priest 1982, Nocera & Leroy & Priest 1984). ACTIVITY OF THE METEORITIC COMPLEX OF COMET HALLEY

G. Cevolani and A. Hajduk

* Laboratorio FISBAT-CNR, 40126 BoLogna, ItaLy ** Astronomical Institute, SLov/ak Academy of Sciences 84228 Bratislava, Czechoslovakia

Results of radar observations of the Orionid and Eta Aquarid meteor showers carried out in Italy within the IHW program are compared with other simultaneous data. The activity of these shoviers is studied in the relation to the motion of large particles ejected from the comet. The activity was found to be independent on the approach of the parent comet.

THE SEPARATION OF PARTICLES DURING METEOR FLARES

V.S.Getman Institute of Astrophysics, Dushanbe, 734670, USSR.

Final meteor flares, which are leading to complete diatruction of the meteor bodies, have been investigated. This.is proved by the escaping of the meteors right after the flare. It is evident that during such flaro the fragmentation to very Bmall particlea la taking place, in other case big particles would have pro- longed the visible trajectory of meteor. In present article a phyelcaly clear no- del of fragmentation of meteor body to many equal particles, offered by B.Levin is used. According to this model summary crose-section n particles ie in n1'3 times more then the croBe-Bection of the body itself. Then the relation of the ve- losity of the mass-loos during the fragmentation (dil/dt)' and evaporation (dM/dt) gives (dM/dt)«/(dM/dt); = (A?/^ )n '3 = I/I , where j ,0 ,A - is the luminous intensity, the specific energy of ablation, the coefficient of heat transfer during the fragmentation and i , % , A - is the same during the evaporation. As we are j speaking about the final flare then Q -a q. , A»jV and that means that n. » (. I / i> ) • In thia case n can be determined directly from photographic observations. The value of J is taken for the flare and i can be taken equal to the value of luminous intensity in the point of the meteor appearance. This ia the result of the screening action of evaporated molecules when the veloeity of evaporation changes not much during the flight, what leads to insignificant variation of i along the flight trajectory. For two meteors, which have veloaity accordingly 24 km/a and 64 km/s, the following dates are obtained: n = 6-10'' and 5-10* ; average masses of particlea - 5-1O"5g and 2-10" g j average radiuses of particles - 150 ^tm and 46 jwa.

THE DYNAMICS OF THE ZODIACAL DUST CLOUO DM ACCOUNT OF GPTICAL AND INFRARED OBSERVATIONS B. Kneissel, R.H. Giese Ruhr-Universitat Bochum, flereich Extraterrestrische Physik, 4£30 Bochum, FRG

On account of optical observations there have been proposed a variety of models concerning the three-dir.iencional density distribution of the zodiacal dust cloud. One can show each model claims a different distribution of inclinations thus the most probable inclination can vary from C° (ellipsoid model) to 14° (fan model) according to model. Even some of the models may be rejected by means of evaluating their inclination distribution, so in the case of one pre-lRAS infrared model. All The remaining distributions of inclinations deviate from the meteoroid distributions or other orbital distributions of small bodies in the solar system. Finally the impact of tne IRAS-Data on the orbital characteristics of the zodiacal dust cloud will be discussed. AuD EiOJORbJTtfx Oi1 COi.JiT rJO-UH 1.. THE *tAi:C;.: 0* 364-400 KM

B.Komitov, V.Shkodrov, V.Ivanova Department of Astronomy, Bulgarian Academy of Sciences 72 Ier.in i31vd., 1784 Sofia, Bulgaria

Over the period April-way 1986 on the 50/?0cm Schmidt telescope of the itoEhen national Astronomical Observatory five photographic images of Coiet Halley were obtained by a rarrow filter at A= 392 + I3nm. Using a inicrodersi- tometer and several program procedures, put forward and applied at the Depart- aent of Astronomy of the Bulgarian Academy of Sciences, average phctometrical brightness profiles were obtained. Applying regreasionul analysis on the basis of Hazer's theory, the scale length of the CM parents' nolecules has beer, obtained, as well as their life time. The problem of their chemical nature was discussed.

ON THE LIFETIME OF COMETS IN THE OUTER OORT CLOUD PI. S. Staniucha

Space Research Centre/ Bartycka 18, 00-716 Warszaua, Poland

, Possible sources of apparent discrepancy between the results of numerical simulations and those obtained from the analytical or semi-analytical approach to the problem of survival of the outer Oort cloud of comets being subject to external perturbations are pointed out. The analytical formulae of Bailey /based on the impulse approximation/ are shown to be probably too conservative, to the effect that they underestimate the energy transferred to comets and overestimate the comets lifetimes. It is concluded that the survival probability of primordial comets in the outer Oort cloud for tines comparable with the age of the Solar System as well as the maximum radius of a possible inner core of comet cloud stable to external perturbations are both smaller than the values suggested by Bailey. Implications for the problem of the origin of comets are i ndi catad.

The Role of Resonances In Planetary Rings

N. Borderies Jet Propulsion Laboratory 301-150 4800 Oak Grove Drive Pasadena, CA 91109

The new observations of planetary rings, including those acquired during the encounters of Voyager with Jupiter, Saturn and Uranus and the discovery of incomplete rings around Neptune, reveal Che extraordinary importance of resonances in deteraining the dynamics and the shape of planetary rings. Two types of resonances play a part in planetary rings: the Lindblad resonances, which are such that the particles are excited with a frequency equal, in absolute value, to their epicyclic frequency, Chat is to say their natural frequency of oscillation, and the corocacion resonances, characterized by a frequency of oscillation equal to zero. Many examples of these resonances can be found at other places of the solar system. For instance Hyperion is in a 4:3 outer lindblad resonance with Titan, and the triangular Lagrange points of Jupiter, where the Trojan asteroids are, represent a particular case of corotation resonance. The talk will deal with new dynamical problems related with the role of resonances in planetary rings. One of the problems Is the confinement of Che narrow rings of Uranus. Another one is posed by the arcs of rings around Neptune. This last problem is particularly important as regards the choice of the trajectory for the Voyager spacecraft during Che encounter and the design of tha occultation experiments. • S'1 \R FORMA I ION ,7J ij« i .•• ;•,:;..

Flrucc G. HliriCgrtt.il

IBM Watson Researi CcnUr, i'.O. BOA 218. Yo!k.!\>.»j, !l:.,;:-i!>, NY '.v'.ih • j.»

A US! RACT: Most of the star formation ii DUI Galaxy aiiJ in o'her spiral {uia.-^c; ... :JP-. -I:I ;fh .^,,.- :;;UJLx..dar clout! complexes thai me located in the main spiral anna. 'I"hi.-c complexes, or superc/oudi. axe iiugri il.a,. ,i,:;.-, ,.-;.^ :;.c.,.:.. _ -.i^v-ui, cacn one typically contains several WMB to !0*Mo molecular .:'.ouds as cores inside an extended gravit»iionJ. atairuc hjlo Supnclouds probably turm by the coagulation of pre-existing sina/er clouds during mild gravitational u- -iabiJiin.i .Lit ;. : u ui in; jmu. .Molecular clouds apparently form by local processes that are inu-'pendent of spiral waves, and by largei-sca.'- r-icccjici ajza\g i-.bcri.-le/i with superdoud formation, such aa condensation and cooliny of the atomic gaa, and coagulation of smaller clouds inside the supcrclouds. This clustering of molecular clouds into superclouds apparently has little effect on ths overall star formation rulcj in uic a! jjaUiicj. although il has a well-known effect on the appearance of star formation in spiral arms, namely, it highlights the arms with brifl,:, r:au!aily-.<;aLc

EXTENDED NEAR-INFRARED EMISSION IN THE SERPENS MOIECULAR CLOUD1 Jan Koornneef2 and Chris Burroivrs2 Space Telescope Science Institute Baltimore, MD 21218

Abstract. Churchwell and Koornneef (Ap. X, 800, 729, 1986} mapped u region of X6' x 2.0' at 2.2fim and centered on the reflection nebula Ser-O toward the core of the Serpens molcculsjr cloud. Thirteen stars were detected in this region and multi-color near infrared photometry was obtained for the four brightest of these. The observed colors for the objects IRS 1, 3 and 4 are incompatible with those expected for reddened background stars. We have now obtained chopped near-infrared maps at 1.25, 1.65 and 2.2 micron in the Sttxr.ens dark cloud (S68) centered on IRS3. They show unresolved structure, most likely due to illuminat.on d" bcaUermg grains, out to l' from the center. The combination of high reddening (and 3.07 nm absorption) and t-syuimetrica! optical reflection points to a non-apherical dust distribution typical for bi-polar flow sources. In addition to the the maps at J, H, K, which consist of 10 by 47 pixels spaced by 2", we are using (Gunn r and z) CCD imp^tm tal<.>n at Palomax by Be! Campbell. We are developing softwart i process these and similar infrared mapa iiiinga modified maximum entropy technique. The modifications have been necessary to avoid singularities inherent in the standard maximum entropy algorithm when it is applied to data with zero-volume point-spread functions. Our data has a large dy nsxnic range as required to pick up the realtively faint extended emission. This poses a particular challenge as any deco.nvolution procedure has difficulty in generating both accurate photometry on unresolved sources as well as an accurate, artifact free, estimate of any slowly-varying extended emission. Considerable care was taken to fit the observed F'SF accurately. By fitting rather than using the measured PSF, we are able to simultaneously satisfy the requiri-r<;e..t •; -:f ?"m toUl integral for the PSF, arbitrarily fine sampling, perfect centering with respect to the pixel p\

1 Based on observations collected at the European Soulher-n Observttc-r;1 it LL 5:;:E. [ChiioJ. On assignment from the Astrophysics Division, Space Science Departui!;;;.t, £i.;-o!j«i.j Space Agency (ESA).

SPECTR0PH0T0METRIC INVESTIGATION OP CB A5D0C1-XT'-...) . IN CASSIOPEIA Ta. Radoslavova Dep.of Aatr.,Bulg.Aoad.of Sci,, 7?, bivd ,'L-JT/.T. , ."•< ; . - . ,. a

The early type ntars in a fiold of about 60 squire .-;;. •••;?r>. cantered at d= 00h27m, S= +63°13' (1950), are otudied. The aosocio;;. . ;B Caostopeia 0B 4, 0B 7 and 0B 14 and the doubtful Aan 35 (Cas III) ar=- located in this region. Spectral classes and monochromatic magrd tudts it :• •' •:•.;f •= 1 -avis of about 400 atars am determined. The obaervutior.s were u-a^ii'.: i-i- ivith the 70-cm meniscua telescope of the Abastuir.ani Aserorhypltul. •'•M-' '"vaiory in the USSR by means of ita 8°-objectivj priaa (•.': :!>;--;^oi. *,iC k/,*.- c: ;',-). STAR FORMATION RATE IN THE CENTRAL PARTS OF SPIRAL GALAXIES Sil'chenko O.K. Sternberg Astronomical Institute, Moscow, University av.,13

In this work we present the study of star formation rate in the nuclear regions of spiral galaxies using the evolutionary synthesis of galaxies' integrated spectra. It is known that one can explain the blue colour of a stellar system by intense star formation as well as by poor metal content of old stars. Aleo eqiuva- lent widths of metal lines are equally decreased by these factors. Using the evolutionary modelling of UBV-colours and of the absorption line Mgl X 5175 in galaxies integrated spectra we became able to separate the two effects. For some galaxies whose spectral energy distributions were taken from the literature or from our observations star formation rates and average metallicities of stars in central regions having diameters of several hundred parsecs have been determined. The relation between nuclear star formation rate and morphological type of a galaxy has been found: So-galaxies have more intense nuclear star formation than Sb or Sa. The cause of the correlation may be obvious: Sc-galaxies have more neutral hydrogen HI in their central parts and moreover they often have H2 density peak in the nucleus while the H2 distributions in Sb-galaxiea usually are ring-like with the peak at the distance of 4-10 kpo from the centre. To study the influence of galactic dynamical parameters on the giant molecular cloud radial distribution we have modelled the dynamical friction and viscosity effects. The important role of the galactic rotational velocity is pointed out: for example, if the galaxy rotates slowly (as the majority of So'a does) its molecular H2 will always accumulate at its centre.

A PHOTOMETRIC MEMBERSHIP TEST FOR STARS OF THE CORONA OF M 39 SELECTED BY PROPER MOTIONS E. I. ZeLwanowa

Zentralinstitut fUr Astrophysik, Rosa-Luxemburg Str. 17a, Potsdam-Babelsberg, 1591 DDR

Photoelectric UBV photometry has been carried out for 30 brighter /BO/ stars in the region of the open cluster M 39, selected by Artinkhina, Kalinir.;^ from proper motions to be members of the cluster corona. From their position on i»£ color-magnitude diagrams about 2/3 of the investigated stars belong to the cluster. Thus the existence of an extended corona around this cluster is confirmed.

SOfci'E CitAKACTKRISTICS OP A NOHUfJiiAK DiUMMCS IU VARJ.A£SUI V.'iiLli'Ji JX&iJFS

Auvergne, LI. f iia^Im, A. and Goupil, l.;.-J.

iiice Observatory, France

Different techniques or pnase space reconstruction tnrough a single observable are presented.

They are applied to variable white dwarfs for which continuous sequences of data containing several tenth of characteristic timea are possible to obtain.

The sensitivity of these methods to the noise level and to holes in the observing sequences 13 discussed. Til..-. .'JdJi^Li A.:J I'KiJJiUAi. i.-'.JWZUuiiJ iilVk/ii.'Jii)

^ co Ob;;Lrv:.to y, I'l-v-nco i'lio •Uk-.:"..!.i'J.-.1. -ion Ci' U;o n:: tliro a1 i.]^' ttw.-ilur vari^.'-iiity lc "i.j.4. wily \.:..;- to .. -•.'. ....•

Vh'j u j.i':'..i'i,-:: L vi. • .-c: z!!. v.:: r.; .c;ji-.t..ci xo !:JIO\. ;j:y.;iu:-l JMCC.':::.'; occijrin™ i— i. '.:'i—j - .... :.'c\.icv^ :.:•.; .JCL.IOJ IC its £lob:-l :;-..ru:..otcrc (n.as2, lur.ir.csity, ri.'-'iu:.-, :.n£t;li:r vds.-iiy, ... anO to the ^:ysical procos.1.;;;.'; rolatud to its intem:!l structure. 2he censor,-; oJT "IT..J.U variability" i.'j liiscuciod in tJiis dir.-.c-nzionlc•:: tcale. In ;..i.ny c::.;cc, tiz.'.u sctlon ai-o unsuffioicnt to characterise the nEturc oi' tLo "/u:.-ii.V.ij.ily. the distinct.Lor. bctv.OL-n -.•ot&ticn of ^ nan unii'orr. boJy -nd pul.-i'atior. is one cf -i:;;j ci-1 ZLX c]!ollo/:^c- j?or :::jtrono:.;orc. livon in obviouc caoc-.'; oi' ful:;cticr., tJjc intcrprctciio;1. oi' the i'ourJ-o-' :.. octi'io- c;;i tc :-.ijiix. :ii):£ '..ijo^i non liiioc-2- cifocto arc ors.-jc-nt. .'.:U-.ii;ic:v;.l ;.: :-::xt'.:*: ct.ii hoi;; tlio c-ir^noetic r :; for o::;ir plo the ch:r)c of the li-pit curve, tiro m--ivv: oi' i'::< -hi.T.v npeco v.licn it can be rcconstruotod, the- vririr.tion ol' tho energy .lictriiuticn, «::-• ::. .i.u:it oi' energy libor:.tcS curir.^ i. chur^ctcriMtiu ti;i:c ... The rutio oi' tho onci'sy ii:;-.v.t o." ijic instability to tho internr.l enci-cy of the ;r.atori:il invclvofl in this ".roccoc ir.i'lv..j:;:^c ixr; tiue behaviour, t.a o::cr:.ijlod v.hon co:.:_Mz,rir.£ the fjcl^r oscill&tion;; to the joli.r lui-:;-::: -.::» fl.

Variability c:;n bo in so::e oases a powerful tool for the undcrstsnein^ ci' stcll:.r -ti-uQturw but nany uncortF.intliou r&r.ain to be cleared up.

The rapid variable VJl 2969

G.A.Bakcc? end J.Tremko 2

(1)Departaent of Physics,University of Waterloo, Waterloo, Ontario, 172L 3G1 (2) Astronoi.iical institute of the Slovul: Aeadea;y of Sciences, 05960 Tatranskfe Loxaiicct, Caoohoalovakia

Aba tract, fflio variobxlity of the star HR 2989 (HD 62 437) v;es announced by I-crcy ir. 1S-7"'. In tlie lu.-.it ye'-_-r. the ots-r was obsierved in the UBV phota.iotric syste::; ct the University Astronoi.-iical Observatory, Waterloo, Cunr.au and at The Astronomical Oboervj^Gi-y o::alfi:tc Pleso, Cscclior;lova3:ia. In BOi.-iG nights the coinnlctc curve of light changes v.;ic obtsincu. The samplltude of tho ll<;ht changes is fevj hundreds of riagnitude and tile period oli^htly over tivo hours. Eio light curve is acyisactric. The sanalysio of the period, tho lir;'it chances and their explanation is given.

Searching relativistic stars among 0 B runaway. I: V568 Cyg - HD 197419 C. Blanco1, A. Manmano2, R. Margoni3, R. Stagni3, G.B. Baratta*. R. Coluni*. V. Croce11 'Astronomy Institute of Catania University and Catania Astrophyiical Observatory, *Matheaatics Department of Messina University, 3Asiago Astrophysical Observatory, Fadua University, ''Rone Astronomical Observatory ' s <• r '

Preliminary results on the Be runaway star V568 Cyg are given. Fro» photojraphical observations taken in 113 nights from 1983 to 1986 the eventual variability is confined between tm^ - 0.5 ± 0.3. Photoelectric observations, carried out in 42 nights during 1985 and 1986 at Catania Astrophysical Observatory seem to show a rather small variability (Amy < 0.05 ± 0.03) of unspecified nature. From about 30 spectra obtained since 1982, a new transition from Be to normal B (lasting at least one year) and subsequent recovery of Be phase appears. A subset of 21 prisnatic spectra at 42 A/aa at Hy, obtained at Asiago, coupled with 19 slit spectra at 12 A/«» by Gies and BoIton, show an excursion in radial velocity fiRV - 18 ± 3 Km s~]. We are investigating whether periodic phenomena in photometry or in R.V. of V 568 Cyg occur. iv.cv. i^icr/iCAL TO irip.iicuLjUi YAT.IAB. JTY in popui./.vio]; ii cmuci

Lku-io-Jo JAJPIL

Hico Obcerv:i 1; *y, JVuncc

1'hc radial pulaation.3 of Population II êphciu nodule arc numerically ziudicC, When the to iperature is decreased i.e. s one r.ovec to the ri^ht in the l~u Oi-^'iU.i, one observes a sequence of wodels y.-hoee behaviours chance fro::: ôrioiicr.l to irr-tîilr.: ones.

The periodical oscillations arc intcrru.ted by irrusulur bur.its which becoi.ic i:crc and uoro fruquont ao the effective teup.ra.ture iu lov.oreu until the notion ic uiv.'.otic. Such a route to chaos is known as u "t::.icont bifurcation".

THEORETICAL ASPECT' Of NOW RADIAL PULSATIONS \ UotU Init-ittit d'Aitnophi)—(.C[u.e., Univtiiite. rfe L-tege Auenu' de. Cointe, '. 8-4200 Oug/iec Belgium

An Intitoduc-t-lun to the. thzoiy ci, nun ia.di.al modzt o& oici.tla.ti.otxt> i.i pn.eie.nted. Evi.denc.ti o& men pu.tia.ti.oni can be \oand i.n nu.men.oai vaniable ita.n.i. We di-icua heie iome. new ne.&utt& obtained in 4;it* vamjinQ with ptniodi o£ the. oidzi 01 .tonge-t than the hvui, namety the 6 Cep itau, the Line Pio£iie Vaniable Stam and the WR itan.i.

Observations >f Variability in O Star Winds

Raman K. Prinja

Dept. of Physics & Astronomy, Universi.y College London Gower Street, London WC1E 6BT, England

Results will be presented on stellar win.l variability based on recent campaigns of intensive UV observations of selected O stars. The morphology of progressive changes in the resonance line profiles will be described.

The spectra reveal extensive variability on short timescales (~ hours) which may be characterised by broad low velocity absorption enhancements and high velocity discrete absorption components. The data suggest evidence for the broad absorption features evolving into the high velocity discrete components, with recurrence timescales down to < 1 day.

Some phenomenological interpretations of the stellar winds variability will be discussed, including the plausibility of models viewed in terms of radially propagating density enhancements in the wind. FLARE ACTIVITY OH HD 2211

P.ROVITHIS AND H .ROVITHIS- i .'ANIOU

Astononiical Institute, National Observatory of Ather. . P.O.Box 20048, Athens 118 10, Greece

HD 12211 (X Tria) is known as a semi-detached -clipsing binary with variable period (Frieboes-Conde and Herczeg, 1973; Mallana, H'5). In a previous report (Rovithis and Rovithis - ,ivaniou,1983; hereafter refered to as report I) a flare like phenomenon had been uported. Since then, X Tria has been reobserved to find out if a similar phenoraenor would be repeated. Thus, photoelectric observations of X Tria were made during November 1984 as well as during August and September 1986 using the same telescc , instruments and technique. The stars HD 11781 and HD 11680 were used for compariso.and checking, respectively. On August the 27th 1986 a similar, flare li' , phenomenon was again detected (as that on 16/17 September 1983, presented in re ; rt I). Figure 1 gives Am (in V) against U.T. As one can notice from it, the raagnitjie difference at maximum is 0.62 and the whole phenomenon lasted for 20 minutes. Usi/i the ephemeiis formula of Kuka- rkin et. al. (1969): Min I (Hel.JD) = 2437572.199,'0.971 5382-E the observed phenomenon corresponds to phases:0.76f.r-0.7819. Thus, the observed flare activity of HD 12211 was detected just after ma.-ma. The first (that of report I), after Max I and the last after Max II. Moreover, in Figure 2 (a and b) the portios of the light curve of X Tria around the two observed flares are presented.

References Frieboes - Conde, H. and Herczeg, T.: 1973, Ast-jn. Astrophys. Suppl. J2, 1- Kukarki.., B.V. et al.: 1969, General Catalogue :f Variable Stars, Moscow. Mallama, A.: 1975, Acta Astron. Z±, 205. Rovithis, P. and Rovithis - Livaniou, H.: 1983, I.B.V.S. No 2W8.

Suivmnry review on "Punt Var: :bility in Lov;-n)f>SF. X-rcy Eirur.*ier-"

J. van Jradijs

Sterrenioindic Inatituut, Universiteit vun Amsterdam, Roeterstraet 15, Ancterua:.-! - 1010

Quasi-pei-iodic oscillations (QPO) , with frequencies in the- :."•.;•.•>• Lo-j-..c;:.i ~ 't':'.:: .:.C ~ 10 Hz have U.-ii Cicixio:. in tho M-ray : i.u:: of 10 lov.--nacs X-ray binarxec. A Tjvrlef overviov. will be Given of the main charactrristics of those QPO, and the ncaociatct1. rod noise, v;i«i enpliasis on the follov.ine topi:c. - The relation between QFO and the spectral, properties of tho USIE; - The tino ahift between QPO as observed in different X-ray photon energy btindc, and the possible role of Coinptonizatiori in the formation of X-ray spectra of low-nass rC-rr.y binaries.

INTERSTELLAR UV LINES A. U. Harris

Rutherford Appleton Laboratory, United Kingdon

The use of different types of stars as background sources for UV absorption line studies of the interstellar nedium'uiII be discussed, with reference to recent investigations of the local interstellar medium /LISM/, interstellar gas in the galactic disk in general and halo gas. Problems associated uith the analysis and interpretation of interstellar absorption lines in stellar spectra will be highlighted. * STELLAR WINDS IN A-TYPE SUPERGIANTS.

A. Talavera A.I. Gomez de Castro

IUE Observatory, E.f.A. O.A.N. P.O.Box 54065 Alfonso XII, 3 28080-Madrzd, Spai 28014-Madrid, Spain

In a previous study of the A-type supergiants observed with IUE we divided these stars in two groups, the most luminous ones, which showed clear evidence of stellar wind and mass loss in their lint profiles and the less luminous ones which did not show these characteristics.

New observations of some A supergiants confirm the difference between those two groups. Moreover the less .luminous (Ib) A-type supergi .nts do show weak signs of wind and mass loss compared with the most luminous A supergiants and their variation is more spectacular.

COSMOLOGY: THEORY AND OBSERVATIONS V. N. Lukash and I. D. Novikov

Institut kosmi cheskich i ssleciovani y, Moscow, SSSR

The problem of determination of the fundamental cosmological constants is considered. The relation between the large-scale fluctuations of the microwave background radiation and the theory of the origin of the structure of the universe is discussed. We discuss also the new theories of the very early universe.

ISOTROPY OF THE X-RAV BACKGROUND AND THE DISTRIBUTION OF GALAXIES A. Mesziros and P. Meszaros

* Charles University, Prague, Czechoslovakia ** Pennsylvania State University

Three essentially different models of the galaxy distribution are currently in use: the supercluster model, the void model, and the sponge model. If the hard X-ray background radiation is the sum of the radiation of unresolved discrete sources at Large cosmological distances, then it is quite possible that these sources also exhibit the large scale structure of galaxies. The HEAO-A limits on the intensity fluctuations of the X-ray background are used to discriminate between three distribution models. These observations indicate a preference for ths sponge-like model.

NUCLlttSYNIS IN WUvA EVENTS Juan Manuel Uurgos and Javior Lnbay Dupartamento do Fisicn do la Atnidsfora, Astronornia y As trofiiicn. Universidad do Barcelona. We havo used n Loi;rnn(jian, implicit, hydrodynamic computer code to follow the evolution of thermonuclear runaways in accreted onvolopos on white dwarfs belonging to a close binnry syskom in order to study nova explosions. Tlio hydrodyncmic code incorporntos nn axtonsivo nuclear reaction network —with the rntos cnrofully updo tod, specially • the reactions of oloc tron-cojituro on proton rich nuclei - composed by 48 isotopes of H, C, H, 0, I', No, Nn, Me, Al, Si, V, S nnd Cl. This notwork allows to follow with accuracy the nucloosyntoais of tlio outburst, either via tho Iiot-CNO cycle or a possible rp-procoss responsible of tho production of the heavy elements in nova onvolopos (nova CrA 81 nnd Aql 82) Preliminary results nro presented n/id compared with prior nucloosyntho tic calculations carriod on donsity-temporoturo profiles but no couplod in a hyilro- dynnmic code.

10 -It,. I ,' - ... '.•••. 'lit'. - ! I ,-!•.• !J.., -.(., . , L.. Ci: WUi!.Hl5 " VUB ; . . •.„ , ,.. • ,.!..' J.'i-' teltr.iihv'ii;. s- ii-.., •,.(•< -jj ty of Antwerp RUCfi

!... i :!'...-i- i. '.'>• !?«]ntion siqm i :.: jm ]y from single stars, in that • .... . • - ••• •• •••'• •(••n'-it?!-, tu t •» .1,3.: it..Hi b/ tliu presence ot a companion. . i:. .< -•-. Lr dr-'f-r a,":. fn^?.s J 05s pr OLr-ri-.tv^, .iiay occur. .: ...... •. !•-.'. L,< i ! b'Ji. ft..ss exchange processes allcjus the explanation of given '.• ».-. ) .r q- OL.r--- at binaries with well determined char acteri sctics, such as Wolf —

(U.i.i. o;,iariui,, filgaJ syster.s, cataclysmic variables, symbiotic stars, massive X- •-.,y binaries, lew mass X-ray binaries. Ohsc-rvatiDiis show that the evolution o+ close binaries does not always occur according tu the conservative assumptions (total mass and angular momentum ro:••.-,!. .ant ' , fan; that mass ran leave the system (presence of rings, disk's, clouds, r---r,fr,c..-, c°n./.r tripes) . This influence or the mass ratios and periods on the evolution * .... i;.j|..;«irfhfd to eventual contact phases 15 analysed and methods to handle (•'•-••-.^ niiiif.--. ; o ralcaldte evolutionary sequences are discussed. It is argued that o(,%trv£:iori ociicy and observation planning bias the period distribution in the ^t'.£i<= that certain periods are much easier detected than others. The frequency of *.-.= occurrence ot different cases of mass exchange (starting during hydrogen shell bi..r,:-'rJ:-) or alr&^dy during core hydrogen burning) is discussed, and the effect of .//i-rtnoutiM on t.ne crimputat i on of binary evolution is analysed. Although the <•".•=.,- c: i scenario {i.r the formation of groups o-f binaries is reasonably well known, • • ."-u.^a svolLtionary picture for observed particular systems is mostly poorly • ..." -^'-OULJ. Mostly we .la nor know accurately enough the parameters of the ...: :~i : vt?d systems and i f we have detailed information on the two components we do 1 -.i i:,tiw t.r,w e,jcc values of tile parameters governing the mass and angular T.i ...•-. n turn '.rana^r. However Ljre evolutionary sequences for both components, 1 . 1 ./m 1 .ji,: L -. ts , masses, radii, rlreuual composition) to select the progenitors.