No. 51 - March 1988

Key Programmes on La Silla: a Preliminary Enquiry H. VAN DER LAAN, Director General, ESO

Allocating Telescape Time is of course based on perceived needs stable and efficient than the 3.6-m is as weil as on experience: if you request now, given the inevitable, large number ESO's raison d'etre is the provision of fifteen nights on the 3.6-m telescope of instrument changes and their associ­ telescope time, a shorthand expression you get nothing and lose credibility in ated overhead at present. for a comprehensive package of ser­ the bargain. For many users the present It is clear that the established manner vices of which hundreds of European practice works weil, their workstyle and of distributing ESO telescope time ade­ astronomers avail themselves every programme scope are adapted to these quately serves a good fraction of current year. The core of that package is the facts of life, there is no reason to change research needs. It seems equally evi­ number of nights during which the visit­ a good thing. dent that the fragmentation of the time Ing astronomer has control of one of La On the other hand, the following on intermediate-size and large tele­ Silla's dozen optical telescopes. We all scenario is also a painful reality for many scopes precludes ESO users from initia­ know the procedure for obtaining those an ESO user. You request five nights in ting certain classes of programmes nights, the composition and submission a judiciously balanced trade-off be­ such as are, for example, successfully of the proposal, the evaluation and tween minimal astronomical needs and pursued on Mount Palomar's Haie tele­ grading by the OPC, the allocation by your estimate of the OPC's range. Then scope and some other American univer­ the DG. ESO has, in its eight member you get three nights, of wh ich one is sities' and Foundations' telescopes on states, nearly two thousand potential partly cloudy; your astrophysical goal good sites. Our current procedures for users whose access to La Silla facilities shifts another year and the substance of allocating telescope time discourage depends on the (relative) scientific merit your Ph. D. student's thesis erodes pre­ the start of efforts of the required mag­ and the technical feasibility of their ob­ cariously. The focus of your own scien­ nitude. The goal for an innovation in serving proposals. Obviously the very tific attention is blurred, you have to these procedures is to remove this large ratio between number of compet­ work in several areas at once and a rival/ handicap for astronomy in ESO member Ing observers and number of telescopes friend on another continent takes a deci­ states. The ND must signal a growth in means that telescope time is a very sive lead. quality as weil as quantity. scarce commodity. If many of the inter­ It is my intention to use the addition of esting proposals are granted time, then the ND to our telescope park for an The NTT, an Opportunity in More a likely result is the fragmentation of experiment in the allocation of telescope Ways Than One telescope time to such an extent that time. This experiment will affect all our most proposers receive some time most Readers of the Messenger are weil major telescopes (and our shares in the of the time. familiar with ESO's New Technology MPG's 2.2-m and the Danish 1.5-m). Let In an accompanying note, Jacques Telescope, now nearing completion. me first sketch the factual essence of Breysacher, head of ESO's Visiting As­ Late this year the ND will be com­ this intention, then provide a brief moti­ tronomers Section, illustrates this frag­ missioned on La Silla; in Period 43, vation and also request a structured re­ mentation. He also provides information starting in April 1989, it will be available sponse from you, our readers/users. wh ich shows that a large fraction of for visiting astronomers. With the ND, Regard the net amount of new tele­ those requests for telescope time that ESO's effective "four-metre class time" scope time gained as a result of having are successful, are nevertheless cur­ more than doubles: both the 3.6-m and the commissioned ND on La Silla, dis­ tailed. The time asked for per proposal the ND will be operationally more tributed among the following six tele- ployment.) Alternatively, observers must Management Changes on La Silla be prepared to spend substantial periods on La Silla. For the information of visiting astronomers I announce some changes in the One can foresee thematic proposals La Silla management. Effective March 1, 1988, the management respon­ wh ich set out a programme of work sibilities at La Silla are shared by five department heads/group leaders. These covering up to four or five years. The are: initial proposal is to contain the scientific H. E. Schuster, VLT Site Services and Schmidt Telescope justification as weil as the observing and Torben Höög, Maintenance and Construction the interpretive strategies. It is to include Daniel Hofstadt, Technical Research Support an overview of the observing nights re­ Jorge Melnick, Astronomy Department quired as a function of time in the total Bernard Duguet, Administration programme period as weil as specify the telescope(s) and instrument(s) to be Together they form the Management Team/La Silla. Daniel Hofstadt is the used. The instruments may be existing chairman of the MT/LaS and he reports to me on behalf of the Observatory's ESO common user instruments, instru­ Management Team. ments to be provided by the observing H. VAN DER LAAN, Director General team or instruments proposed to be constructed in collaboration for the pur­ pose. (In the latter circumstances the scopes: NTT, 3.6-m, CAT, ESO 1.5-m goals in astronomy. In the next decade it planning must take place on a ca se by and ESO shares of MPG's 2.2-m and is essential to prepare the next genera­ case basis.) In addition, an overview of the Danish 1.5-m. Some or all of this tion for an all out exploitation of the the team members, their respective new capacity will be allocated in a re­ VL1's unique potential. specializations and relevant experience, vised manner, such that a number of and the resources available for data re­ programmes can receive very substan­ duction and analysis. Time allocation Schedules and Procedures tial portions of telescope time, to be will be for the whole programme in prin­ made available over a one to four year If we are to make a good start with the ci pie, with an initial annual instalment; period. The net new time available in key programmes in period 43 (April subsequent instalments dependent four years, applying weighting factors through September 1989), then the upon the contents of progress reports. for the intermediate-size telescopes vis­ schedule is as folIows: Readers/users are herewith invited a-vis the NTT, amounts to about 2,000 to submit, before 30 April 1988, a - Initial response to this preliminary en­ nights, half of wh ich on the 3.6-m and statement of their intention to make quiry: before 30 April 1988. the NTT. Some or all of these are to be use of this new part of ESO's pro­ allocated to, say, between one and two - Discussion of principles and pro­ gramme. Forms, specifying the for­ dozen key programmes; allocations to cedures and of response to prelimi­ mat of your response along the lines vary from minimally twelve to maximally nary enquiry in ESO's STC and OPC: of the two preceding paragraphs, are fifty nights per year per programme. May 1988. available upon request from the Visit­ Evidently, the introduction of such a ing Astronomers Section at the ESO - Information and call for proposals in scheme would be difficult to nearly im­ Headquarters. the Messenger, No. 52, June 1988. possible under circumstances of con­ stant total telescope time. It is the major - Proposal deadline for programmes Final Remarks positive increment afforded by the com­ starting in period 43, 15 October pietion of the NTT which provides this 1988. Key programmes are not meant to new opportunity for European as­ simply be long-term acquisitions of - Outside refereeing in November tronomy without negative effects for on­ large databases, which are thought to 1988; time allocation upon recom­ going activities. Whether some or, ulti­ be good for several purposes, some of mendation by the OPC in December mately, all of the new capacity is allo­ which are initially specified and others 1988. cated in the new manner must clearly which have not yet been thought of. depend on the proposal pressure. The Given the large investments in tele­ Such programmes are of course going histograms for the 3.6-m and 2.2-m allo­ scope time foreseen, the proposals re­ on, perfectly justifiably, on the Schmidt cations, shown in Dr. Breysacher's arti­ quire deep and careful argumentation. and on several of the smaller tele­ cle, can in future also be broadened by They must have much added value scopes. A successful key programme the use of some of the additional time. compared to normal proposals, opening proposal will address a major astronom­ research domains not hitherto access­ ical theme, provide (a) very specific ible with ESO facilities. Normally the goal(s) and outline a structured research The Growth of ESO Astronomy proposers who constitute the observing strategy. In the previous issue of the team will represent several institutes; Key programmes can involve post­ Messenger Professor Woltjer gave an hopefully the teams will usually be multi­ graduate students from start to finish of overview of developments within ESO national. Since economic scheduling their Ph. D. thesis programme, providing during the past dozen years. From a will require a good fraction of the ob­ them with a coherent research context position of relative instrumental back­ serving to be done in "service mode", it and using their full time efforts as weil as wardness, European astronomical is highly desirable to involve ESO as­ all of their youthful enthusiasm. Analo­ facilities have achieved world-class tronomers employed on La Silla in the gous reasoning makes the participation status. With the decision to proceed observing teams. (This has the addi­ of postdoctoral fellows very attractive. with the construction of the VLT, we tional advantage of involving these Key programmes, as the term sug­ must now also pay close attention to the young astronomers in community pro­ gests, must open new research do­ further enhancement of the quality of grammes, which will make working on mains. They will require careful peer re­ our community's programmes and the La Silla even more interesting, and will view and will be subject to public development of long-term European ease their way back into community em- scrutiny by the ESO user community. 2 Successful applicants are likely to be key programmes it will be prudent to teams. In addition to your formal re­ required to make their results, calibrated start with relatively few of the four year sponse through the Visiting Astronom­ and documented, available for general variety, in order to commit the time ers Section, general comments con­ use after a prescribed period. available gradually, to the most ambi­ cerning this intention, addressed to me, In a shifting pattern of one to four year tious programmes of the best prepared are welcome.

Some Statistics about Observing Time Distribution on ESO Telescopes J. BREYSACHER, ESO

The aim of this note, which is to be the ESO Observing Programmes Com­ the number of requested nights, the regarded as an appendix to the article mittee and/or during the final scheduling mean percentages obtained for the past written by Professor van der Laan, is to phase, had to suffer from a reduction of four years are as foliows. At the 3.6-m, give some statistical information about the observing time scheduled at ESO over the past four years. Only the five 700 largest telescopes installed at La Silla will be considered here, namely the 00 3.6-m, 2.2-m, 1.5-m, 1.5-m Danish and wW 1.4-m CAT. >_0...... wW wW Needless to say, at ESO as in any WW 0::« other major ground-based observatory, 600 given the heavy oversubscription of telescope time, the selection of the ob­ I i VI Z serving proposals is rather strict. Fi­ o ;::: gure 1, wh ich is taken from the 1987 « ESO Annual Report, allows a compari­ W::::; 0.. son between the total numbers of appli­ 0.. 500 « cations received and finally accepted u... o each year, for almost a decade. 0:: w Let us now turn to the successful CD L ::> proposals. The histograms presented in z Figure 2 indicate how the 1,350 pro­ grammes accepted during the past four years for the use of the five telescopes 400 105m Danish mentioned above, were distributed with 0.9m Dutch regard to the number of nights allocated I October 1979 I to them. I If one considers only the 705 pro­ grammes scheduled at the 3.6-m and 16m I Oetober 1977) 2.2-m telescopes, there were 243 (34 %) 300 observing runs of two nights and 269 j (38 %) runs of three nights. The percen­ tage of programmes wh ich were allotted four nights was exactly the same on these two telescopes: 14 %. It must be noted that amongst the remaining pro­ grammes, most of those getting five or 200 more nights were not sensitive to moon­ light and consequently could be scheduled during bright time. On the two 1.5-m telescopes, 42 % of the programmes were allotted four or five nights. At the 1.4-m CAT, a similar 100 percentage (40 %) is obtained for the observing runs lasting six to seven nights. On these three telescopes the very short runs almost always corre­ Spond to programmes for wh ich obser­ vations on two or more telescopes were combined. 1977 78 79 80 81 82 83 84 85 86 1987 With regard to the amount of pro­ Figure 1: The numbers of observing proposals respectively received and accepted by ESO grammes which, after the evaluation by during the past nine years. Arrows indicate when new telescopes became available.

3 200,.------,.------,------,------,------,

3 6m TELESCOPE 22m TELESCOPE 15m TELESCOPE 15m OANISH TELESCOPE 14m COUOE AUXILIARY TELESCOPE 11.33 programmes) 1272 programmesl 1262 programmesi 1165 programmesl 1218 programmes)

100

50

NUMBER OF NIGHTS Figure 2: Histograms showing the distribution of the numbers of observing runs as a function of the number of allocated nights. For each telescope the total number ofprogrammes is given within brackets. It is recalled that the ESO shares ofobserving time at the 2.2-m telescope of the Max Planck Institute and at the 1.5-m Oanish telescope are respectively 75 % and 50 %.

2.2-m, 1.5-m Danish and 1.4-m GAT grammes concerned was somewhat programmes wh ich were regularly re­ telescopes, about 60 % of the program­ smaller with a mean value of 45 % only. submitted by the same applicant(s) and mes receiving time were affected. At the Finally, and again during these past awarded observing time, has been of 1.5-m telescope, the fraction of pro- four years, the fraction of continuing the order of 15 %.

Wide-field Photography at the 3.6-m Telescope?

This note serves to gauge the interest up to eight 24 x 24 cm photographie Astronomers in the ESO community of the astronomical community in wide­ plates. This instrument is rather compli­ who would like to use the 3.6-m triplet, field photography with the triplet facility cated and after aperiod of declining are herewith invited to write to the at the 3.6-m telescope. use, it was decided no longer to offer it undersigned. If you feel that the triplet As photographie users will remember, to visitors. Gonsequently, the 1-m facility should be reactivated, please the 3.6-m prime focus is equipped with Schmidt is now the only deep, wide­ provide abrief and succinct summary of two Gascoigne correctors (blue and field instrument in regular use at La Silla. the type of research you would like to red, field diameter - 16 arcminutes, In the past, good triplet plates had a do, the number and type of plates m 6 x 6 cm plates). Two grisms can be limiting magnitude beyond 24 . With the needed and also tHe total amount of used with these correctors. There are advent of the new T-grain emulsions and observing time. Kindly note that this in­ also two triplet correctors of Wynne type grid processing, and together with mod­ vitation does not imply any commitment with a field diameter of 1 degree; behind ern reduction techniques, even fainter by ESO. these an automatie plate changer loads limits may be reached in the future. R. M. West, ESO

Opportunities at the ESO Schmidt Telescope

About 90 % of the red plates for the -20° to 0°, it shall be possible to per­ noted that the prism can only be ESO/SRG Survey of the Southern Sky form more observations for "visitors", mounted during a modest part of the have now been taken. Although the starting with period 42 (from October available time. Schmidt telescope is presently engaged 1988). Please remember that applications in the continuation of the earlier Quick As before, the red and blue atlas tor period 42 must be received by Blue Survey in the declination zone plates will have priority. It should also be ESO not later than April 15, 1988.

The final project schedule will be es­ decision will be taken when the final VLT NEWS tablished soon after adecision on the proposals from the two firms have been mirror blank procurement is taken. For received. The mirror thickness has been After the approval of the project on the time being two technologies, fixed to 175 mm for both cases. This December 8, the project management Zerodur from Schott and fused silica seems to be an acceptable compromise structure is progressively being set up. from Gorning, are in competition. The between cost and stiffness. As an alter- 4 These CAD drawings were made in February 1988 with the newly installed Euclid-IS software, running on a VAX 8600 at the ESO Headquarters. The upper one shows one possible solution to the integration of the telescope into the protecting dome structure; further work may lead to refinements. The lower picture shows the mechanical structure in more detail. It is based on geometrical and mass distribution analyses. The studies were made by the ESO VL T Mechanical Group and the CAD figures were prepared by E. Brunetto.

native, aluminium technology is being developed and a 1.8-m test mirror is going to be manufactured. An 8-m aluminium blank could be built in less than 2 years in case (unexpected) difficulties would be encountered with the glass mirrors. A contract on the feasibility of direct drives has recently been issued to ETEUCONTRAVES (Switzerland). The preferred solution would be 2 closed motors of about 2.4 m diameter for the elevation axis and 4 quasi-linear motors, 8 m long, for the azimuth axis. Power dissipated would be about 4 kW peak for each axis. The average power under typical wind speed conditions would not exceed 1 kW, but will nevertheless re­ quire cooling. The advantage of the direct drive is that it is a quasi-linear system with an improved frequency response. The extra cost for the mo­ tors is expected to be compensated by the elimination of expensive gear wheels.

5 Some more refined predesign of the building is under way (see CAO draw­ CNRS-Observatoire de Haute-Provence and ing). The present conceptual scheme is European Southern Observatory based on the inflatable shelter (a half scale model is being erected in Chile). Summer School The centre of the dome will be on the telescope base so that the primary in Astrophysical Observations mirror is always protected from the di­ rect wind stream. Openings at the base Observatoire de Haute-Provence, France, of the building will allow a controlled 4-13 July 1988 flushing of the mirror surface. Wind tunnel tests of this concept are being The school is dedicated to the practice of astrophysical observations and it done at the Lausanne Polytechnic. is organized jointly by OHP and ESO. The aim of the school is to balance the More in the years to come. education of young European students in astronomy, offering them an early a. Enard, ESO opportunity to become acquainted with modern astrophysical equipment. Courses and observations will take place at the Observatoire de Haute­ Provence where the instrumentation and the facilities for the reduction of digital data are in many respects similar to those available at the world largest List of ESO Preprints optical observatories. (December 1987-February 1988) Ouring the school, the students will be asked to carry out a short pro­ gramme of observations at the 1.93-m telescope with a CCO detector, under 550. F. Matteucci: Iron Abundance Evolution the guidance of experienced observers, learn to reduce the data on HP and in Spiral and Elliptical Galaxies. Invited VAX computers and propose an interpretation of the results. talk presented at the New Orleans The courses will mainly be dedicated to the different observational tech- Meeting of the American Chemical So­ niques. The preliminary list of speakers and subjects is as foliows: ciety on "The Origin and Distribution of the Elements", Sept. 1987. World M. Tarenghi (ESO): Modern und future telescopes Scientific, in press. December 1987. S. O'Odorico (ESO): Spectroscopic and imaging instrumentation 551. D. Baade et al.: Time-Resolved High­ M. Oennefeld (IAP): Oetectors Resolution Spectroscopy of an Ha Out­ F. Rufener (Geneve): Optical photometry burst of folCen (B2 IV-Ve). Astronomy P. Bouchet (ESO): Infrared photometry and Astrophysics. December 1987. S. Cristiani (Padova): Low resolution spectroscopy 552. A. Robinson: Photoionization of Ex­ tended Emission Line Regions. Pro­ O. Gillet (OHP): High resolution spectroscopy ceedings of the NATO Advanced Re­ H. Schwarz (ESO): Polarimetry search Workshop on "Cooling Flows in J. M. Mariotti (Lyon): Interferometric observations Clusters and Galaxies", held at the In­ Applications: Students from ESO member countries intending to begin a stitute of Astronomy, Cambridge, UK, 22-26 June 1987. December 1987. Ph.O in astronomy or in the first years of their thesis are invited to apply using 553. M. Auriere and S. Ortolani: CCD Stellar the form available on request from the organizers before May 1st. A letter of Photometry in the Central Region of introduction by a senior scientist is also required. Fifteen applicants will be 47 Tuc. Astronomy and Astrophysics. selected. Their travelling and living expenses will be fully paid by ESO or OHP. December 1987. The Organizers: 554. I. J. Danziger et at.: SN 1987 A: Obser­ vational Results Obtained at ESO. Pa­ A. A. Chalabaev S. O'Odorico per presented at the Fourth George Observatoire de Haute-Provence European Southern Observatory Mason Fall Workshop in Astrophysics, F-04870 Saint-Michel-I'Observatoire Karl-Schwarzschild-Str. 2 "Supernova 1987A in the Large France 0-8046 Garehing F. R. G. Magellanic Cloud", October 12-14, Telex: 410690 France Telex: 5282820 eo (F. R. G.) 1987, George Mason University, Fair­ Bitnet address: fax, Virginia, USA. December 1987. SANORO@OGAES051 555. A. Moneti et al.: High Spatial Resolution Infrared Imaging of L 1551 - IRS 5: Di­ rect Observations of its Circumstellar Envelope. The Astrophysical Journal. cal Astronomy: Present and Future", cation to CW Cas. Astronomy and As­ December 1987. ed. L10yd B. Robinson (Proceedings of trophysics. December 1987. 556. R. Arsenault and J.-R. Roy: Correla­ the 1987 Summer Workshop in As­ 564. T.J.-L. Courvoisier: Multi Wavelength tions Between Integrated Parameters tronomy and Astrophysics at Lick Ob­ Observations of Active Galactic Nuclei. and Ha Velocity Width in Giant Ex­ servatory). December 1987. Invited paper given at the Strasbourg tragalactic H 11 Regions: A New Apprai­ 560. L. Noethe et al.: Active Optics 11: Re­ Colloquium "Coordination of Observa­ sa!. Astronomy and Astrophysics. De­ sults of an Experiment with a Thin 1 m tional Projects", November 1987. cember 1987. Test Mirror. Journal of Modern Optics. 565. A. Renzini and Fusi Pecci: Tests of 557. L. B. Lucy: Modelling the Atmosphere of December 1987. Evolutionary Sequences Using Color­ SN 1987 A. Paper presented at the 561. J. May, David C. Murphy and P. Magnitude Diagrams of Globular Clus­ fourth George Mason University Work­ Thaddeus: A Wide Latitude CO Survey ters. Annual Review of Astronomy and shop in Astrophysics "SN 1987 A in the of the Third Galactic Quadrant. As­ Astrophysics. January 1988. LMC". December 1987. tronomy and Astrophysics. December 566. L. Deharveng et al.: H 11 Regions in NGC 558. B. Reipurth and J.A. Graham: New Her­ 1987. 300. Astronomy and Astrophysics. big-Haro Objects in Star Forming Re­ 562. G. Contopoulos and P. Grosb01: Stellar January 1988. gions. Astronomy and Astrophysics. Dynamics of Spiral Galaxies: Self-Con­ 567. R. H. Mendez et al.: Spectra of 3 Plane­ December 1987. sistent Models. Astronomy and As­ tary Nebulae and a Search for Nebular 559. H. Dekker: An Immersion Grating for an trophysics. December 1987. Emission Around 12 sdO Stars. As­ Astronomical Spectrograph. "In­ 563. F. Barone et al.: On the Optimization of tronomy and Astrophysics. January strumentation for Ground-Based Opti- the Wilson-Devinney Method: An Appli- 1988. 6 568. E. Brocato and V. Castellani: Evolutio­ nary Constraints for Young Stellar Clus­ Tentative Time-table ters. 11. The Case of NGC 1866. As­ From the Editors tronomy and Astrophysics. January In accordance with the new man­ of Council Sessions 1988. agement of ESO, it has been de­ and Committee Meetings 569. R. Arsenault et al.: A Circumnuclear cided that the ESO Messenger for First Half of 1988 Ring of Enhanced Star Formation in the shall above all be a vehicle of com­ Spiral Galaxy NGC 4321. Astronomy munication between ESO and the May 2 Users Committee and Astrophysics. February 1988. May 3 Scientific Technical 570. G. Contopoulos and A. Giorgilli: Bifur­ user community. It is therefore the Committee cations and Complex Instability in a intention to bring the fullest possi­ May 4-5 Finance Committee 4-0imensional Symplectic Mapping. ble information about new develop­ Oberkochen February 1988. ments at ESO, technical and scien­ May 31-June 1 Observing Pro­ 571. J. Surdej et al.: Search for Gravitational tific, as weil as those of a more gramme Committee, Lensing from a Survey of Highly Lumi­ administrative nature. In a similar Liege nous Quasars. P. A. S. P. February spirit, we herewith invite contribu­ June 6 Committee of Council 1988. tions from users, in the form of June 7 Council 572. R. Buonanno et al.: CCO Photometry in articles and also as shorter Letters the Metal Poor Globular Cluster NGC All meetings will take piace at ESO in 7099 (M 30). Astronomy and Astrophy­ to the Editor. Garching unless stated otherwise. sics. February 1988.

SN 1987A: Spectroscopy of a Once-in-a-Lifetime Event R. w. HANUSCHIK, G. THIMM and J. DACHS, Astronomisches Institut, Ruhr-Universität Bochum, F. R. Germany

When Supernova 1987A in the Large trometers wh ich are especially designed tained enough observing time at large Magellanic Cloud was discovered by lan to achieve the highest possible sensitivi­ telescopes in order to study and monitor Shelton at Las Campanas Observatory ty for extremely faint radiation sources, it in sufficient detail for a long time. And in Chile on February 24, 1987, it immedi­ and which therefore are in great danger again, the distance to a supernova be­ ately became apparent that this would to be destroyed when exposed to a yond our Local Group of galaxies would turn out to be one of the most important naked-eye objecl. This problem has be quite uncertain as compared to the astronomical events in this century. The been discussed in greater detail in two well-defined and well-known distance to timing of the supernova could not have papers by Michael Rosa and O.-G. the LMC. been better - although the light from the Richter (Observatory 104, p. 90 [1984]) So it is not surprising that starting on site of the stellar collapse had to travel a and by Theodor Schmidt-Kaler (same February 25 literally every telescope in distance of as much as 170,000 light­ volume, p. 234). Furthermore, a nearby the southern hemisphere was directed years before reaching our planet Earth, supernova could not tell us very precise­ towards the newly-born supernova (un­ it arrived precisely when state-of-the-art Iy its distance due to the strongly vary­ fortunately enough, no spectrum exists photoelectrical detectors had become ing amount of dust in the galactic plane. from the night before when lan Shelton available at modern telescopes situated If SN 1987 A were a distant supernova made his discovery). This was of course at the best observing sites all over the such as they are detected almost once also the case at the European Southern world, together with highly sophisti­ per month, nobody would have ob- Observatory in Chile at La Silla where cated spaceborn instruments working in the X-ray and ultraviolet regions of the electromagnetic spectrum. Even The Proceedings of the ST-ECF Workshop on elementary particle physicists were well-prepared (except for some prob­ Astronomy trom Large Databases ­ lems with their clocks) to catch two do­ zens of the neutrinos emitted by the Scientitic Objectives and Methodological dying star thereby providing for the first Approaches time the precise date of the collapse. (Only gravitational wave astronomy has which was held in Garching from 12 to 14 October 1987, have now been still to wait to be born: all potential de­ published. The 511-page volume, edited by F. Murtagh and A. Heck, is tectors had been switched off or did not available at a price of DM 50.- (prepayment required). Work properly.) Payments have to be made to the ESO bank account 2102002 with Commerz­ To render the combination of bank München or by cheque, addressed to the attention of privileges for earthbound observers ESO even more impressive, SN 1987 A is just Financial Services at the optimum distance for convenient Karl-Schwarzschild-Str. 2 measurements in the optical window: a 0-8046 Garching bei München galactic supernova would be too bright for professional astronomical instru­ Please do not forget to indicate your full address and the title of the volume. ments such as photometers and spec-

7 This colour-coded plot ot optical spectra depicts the dramatical spectral evolution otSN 1987A within the tirst 110 days (Feb. 25 to June 14). All spectra have been measured with the spectrum scanner attached to the 51-cm telescope ot the University Bochum located at the European Southern Observatory at La Silla, by observers Joachim Dachs, Reinhard W. Hanuschik and Guido Thimm. The wavelength range covered is approximately 3200 to 9000 Ä, the resolution is 10 A. Absolute fluxes have been colour-coded according to the colour bar on top ot the tigure: colours run trom black (zero flux) to blue-white (5.7 10- 10 erg s-, cm-2 A-'). Time series starts on February 25 (= day 2 since explosion); time scale is continued trom bottom to top day by day. Last date is June 14 (= day 110). one of us (J. D.) happened to work with rather sceptical about this event.) A few wavelength range of these spectra ex­ the 51-cm telescope of the Ruhr-Univer­ hours later, the first spectra of the tends from 3200 Ato 9000 A; the stan­ sität of Bochum. supernova were obtained at La Silla, dard resolution is 10 A. For limited He was working on a long-term pro­ about 170,000 years plus 42 hours after spectral ranges, spectra at higher reso­ gramme to monitor spectral and photo­ the stellar collapse in the LMC. lution, 3 to 5 A, are being obtained in metrie variability in Be stars and original Due to an agreement between ESO addition. Proper flux calibration of the plans were to change instrumentation and the University of Bochum, the spectra is always performed by means just in the afternoon of February 24, Bochum Astronomical Institute has of bright southern spectrophotometric from the spectrum scanner equipped access to this telescope during a total of standard stars such as t Puppis or with a red-sensitive gallium-arsenid eight months per year. In addition, ESO a Crucis. photomultiplier to the single-channel Director General Prof. Woltjer generous­ This data set will certainly belong to photometer. This plan, however, was Iy agreed to dispense with the four­ the best available spectra of the super­ rapidly given up, when the Acting Direc­ month ESO period at the Bochum tele­ nova; maybe it is unique. Especially re­ tor, Hans-Emil Schuster, walked into the scope as long the supernova could be markable is the fact that these high­ Hotel Dining Room during tea-time - the observed. precision data were obtained with a La Silla astronomers' breakfast - and So Joachim Dachs, and following small-sized telescope and relatively announced the discovery of a superno­ him, Reinhard Hanuschik, Guido modest equipment compared to large va in the Large Magellanic Cloud. (In Thimm, Klaus Seidensticker, Josef observatory standards. fact, the first lAU telegram did not men­ Gochermann, Stefan Kimeswenger, Ralf Between May and July when Super­ tion that SN 1987 A had been discov­ Poetzel, Gerhard Schnur and Uwe Lem­ nova 1987 A was below the celestial ered at Las Campanas Observatory, mer established a homogeneous series south pole all night, the 51-cm Bochum only some 30 km from La Silla, and of flux-calibrated spectra obtained with telescope turned out to be the only tele­ Hans-Emil Schuster first appeared to be a fixed instrumental configuration. The scope at La Silla able to follow the 8 Supernova and to take spectra even at shift, i. e. the decreasing velocities of on February 25; extrapolation back to airmasses as large as 6 (corresponding spectral lines produced in the expand­ February 23 even yields a velocity in the to zenith distance 80°). For that pur­ ing envelope. The intensity minimum of vicinity of -40,000 km/s as the velocity pose, observers had to work very Glose the Ha absorption trough is at of the fastest ejecta, that is 13 % of the to the limit switches protecting the tele­ -17,400 km/s on February 25, falling off speed of light. These enormously high scope against mechanical damage. The to -6,200 km/s by April 14 and velocities are now commonly believed Bochum telescope certainly had never -5,400 km/s by July 14. This general to be responsible for the rather unusual before been pointed at such extreme trend is al ready weil known from other lightcurve of the supernova, i. e. its ex­ coordinates, at least not intentionally. In supernovae and is due to the fact that tremely long rise until maximum was order to be able to look into the tele­ outflowing material is diluted by expan­ reached at a relatively low absolute scope's eyepiece without burdening the sion and is assorted according to in­ level. telescope axes with its body's weight, creasing velocity and decreasing densi­ Our continuous time series of 'one author (R. W. H.) invented a rather ty: in the expanding supernova shell, at homogeneous spectral measurements unusual method for guiding the super­ any time velocity is proportional to dis­ offers a unique opportunity for safe nova: he installed a rubber rope at the tance from the centre of explosion. identification of the bewildering amount dome wall and, hanging himself on the Therefore, expanding layers may be of absorption and P Cygni-type lines in rope and balancing on top of a ladder opaque at some time and later become the supernova spectrum. Work on line two meters above the ground like a optically thin, revealing lower, less identification and radial velocity deter­ mountaineer, carefully moved his eye rapidly expanding layers. Thus, in front mination is in good progress. towards the eyepiece which was at of the supernova, optical lines charac­ Meanwhile, forbidden lines such as some "impossible" position on· top of teristic for the most abundant elements [Ca 11] A. 7291/7363 A and [0 I] A. 6300/ the telescope tube. in the supernova atmosphere (hydro­ 6363 A have become visible in the By now, more than 300 days of gen, helium) or for particularly strong supernova spectrum marking the begin­ Supernova 1987 A have been covered transitions (e. g., of calcium or sodium) ning of the nebular phase. As a whole, observationally. The first 110 of them are visible at the highest velocities to­ the dramatic evolution of the optical are depicted in a compressed manner in wards the observer (corresponding to spectrum of SN 1987 A has slowed the accompanying figure. This plot the lowest discernible densities in the down, but certainly will provide further shows the temporal evolution of the outermost layers of the ejecta), while surprising features in the visible. Our spectral fluxes of SN 1987 A between lines indicating less abundant con­ time series will be continued as long as 1987 February 25 and June 14. stituents of the atmosphere are pro­ possible and certainly provide invalu­ The most obvious advantage of this duced at lower velocites and higher able information about an event wh ich compact representation is the visualiza­ densities. Then, as time goes on, it is happens at most once in the lifetime of tion of the well-known photometrie possible to look deeper and deeper into an astronomer. lightcurve: the flux distribution changes the ejected atmosphere of the exploding dramatically in the very first days due to star. So far, no indication has been de­ Acknowledgements the steep decrease of the effective tected for interaction of the ejecta with temperature of the outflowing gas. After the surrounding pre-outburst material, We are greatly indebted to our Insti­ about day 10 since explosion, flux dis­ and consequently supernova matter is tute Director, Prof. Th. Schmidt-Kaler, tribution remains approximately con­ still in free expansion. Decreasing velo­ who invested a lot of time in organizing stant; the absolute flux level, however, cities therefore result only from decreas­ financial and personal support for the increases steadily until, around May 20, ing opacity of the expanding shell. continuous observing campaign, and to the visual maximum is reached. After­ Maximum outflow velocities can be the former Director General of ESO, wards, flux decreases more rapidly. inferred from the blue edge of the ab­ Prof. L. Woltjer, who generously gave The next obvious feature in this plot is sorption component of the Ha P Cygni­ several months of ESO time at the 61­ the dramatic evolution of the Doppler type profile: we measured -31,000 km/s cm telescope to our observers.

SN 1987A (continued)

It is now one year aga that SN 1987 A during the decay of Cobalt-56. The in­ of the intensity in the 6-16 keV and in the LMC exploded. Since then, this tensities corresponded to about 0.0002 16-28 keV bands during the first days unique event has continued to fascinate solar masses of exposed Cobalt-56 at a of 1988. The intensity in the first of these astronomers and physicists. The large distance of 55 kpc. No obvious changes bands more than tripled over a two­ number of scientific meetings, TV pro­ were observed during this period. Furth­ week period. grammes, newspaper articles, etc. er y-ray observations were made from Spectral observations in the ul­ about SN 1987 A at the time of its first balloon experiments flown in October traviolet, visual and infrared regions anniversary prove its popularity. and November and also from a balloon continue. Recent spectra from the IUE During the past three months, since which was launched in Antarctica in ear­ show UV emission lines from a variety of the last issue of the Messenger, several Iy January. During the three-day flight at ions, e.g. CIII, NIII and possibly Hell important observations have been made altitude 36 kilometres, it observed the and NIV. The first detection of [0111] lines public. The first unambiguous detection supernova during 12 hours, permitting has been made with the ESO 3.6-m of y-rays was made with the Solar Max­ the registration of a detailed profile of telescope and the Cassegrain Echelle imum Mission satellite. Accumulating the two Cobalt-56 lines. Spectrograph (CASPEC). From the data from August 1 to October 31, 1987, After a long period of rather constant 4363 A line, when compared to the two spectrallines were seen at 847 and emission in the soft X-ray region, the doublet at 4959 and 5007 A, and 1238 keV, respectively; they originate Ginga satellite observed a sudden rise assuming low electron density, a plas-

9 ma temperature of 40,000 K was com­ be radio-quiet and the longest The supernova faded to magnitude puted. These lines are very narrow and wavelength at which it has recently been 6.4 in mid-January and to about 6.8 in their velocities are near 285 km/sec, in­ detected is 95 ~m. mid-February. After aperiod of linear dicating that they may originate in a Speckle interferometric observations decline on the magnitude scale, corre­ circumstellar shell (ejected from the with the 4-m telescope at the Cerro sponding to the radioactive decay rate progenitor during an earlier mass-Ioss Tololo Inter-American Observatory in of Cobalt-56, the decline became more phase?) November have resolved the supernova rapid. Towards the end of January, ob­ A long-term programme is under way shell at about 0.02 arcseconds, corre­ servers at the South African Astronomi­ with the Bochum telescope on La Silla; sponding to a mean velocity of about cal Observatory found that the bolome­ see the article by Hanuschik et al. , in this 4,000 km/sec since the explosion. Simi­ tric (total) luminosity was 7 % below a Messenger issue. In the far-infrared lar observations with the 4-m Anglo­ straight extrapolation from the linear de­ spectral region, several flights with the Australian Telescope, also in November, cline between July and October 1987. Kuiper Airborne Observatory (KAO) have show that if there is a secondary object The light in the U-band wh ich had been showed emission lines from iron-group within about 0.8 arcsec of SN 1987 A, constant over a long period, again elements, synthesized during the super­ then it must be at least 4 magnitudes started to fade in late December 1987. nova explosion. SN 1987 A continues to fainter. The Editor (February 23, 1987)

Same Prospects of Galactic and Extragalactic Studies* v. A. AMBARTSUMIAN, Byurakan Astrophysica/ Observatory, U. S. S. R.

The main purpose of the astronomical and particularly space interferometry in stars. By studying the distribution of work is to obtain information about all different wavelengths) will play an in­ early-type stars in the Galaxy we arrived kinds of bodies and systems existing in creasing role, but they cannot replace, at the concept of OB associations, and the Universe, about their past and fu­ at least during the next several decades the nearer study of OB associations has ture, and regularities of processes going and probably during the next century brought us nearer to the solution of the on in them. Studies and the observa­ the work of optical telescopes. origin of early-type stars. In the same tional work with this purpose are de­ Therefore, let us concentrate our way the study of the distribution of veloping in three main directions: the attention on galactic and extragalactic dwarf variables of T Tauri and RW Au­ study of the Solar system and of its research, though we must not forget rigae stars has immediately demon­ members (planets, comets, meteorites), that the solar-system studies can have a strated us the existence of T associa­ the galactic research which studies our great indirect influence on the studies of tions. From this the concept of the origin stellar system and its members (stars, phenomena on the stellar and galactic of stars in groups has followed. nebulae, clusters of stars), and the ex­ scale. Inversely, the understanding of the tragalactic research. What is the main purpose of as­ fact of desintegration of stellar associa­ Since the discoveries of Galileo, as­ tronomical research in the galactic and tions has opened many questions on the tronomers have applied and continue to extragalactic fields? kinematics of open clusters and indi­ apply optical telescopes in all three di­ I think it is (1) to understand the vidual stars wh ich are the remnants of rections mentioned above. However, constitution of stars and nebulae as stellar associations. during this century new methods have weil as of systems, including the increas­ Thus there are two problems: the ori­ been invented. It is sufficient to mention ing volume of the Metagalaxy and (2) gin of stars and their distribution in the here the ground based radio telescopes, to study the origin, Iife, evolution and Galaxy, and they are closely connected. the X-ray receivers and telescopes, the future destiny of these bodies and On the other side, the observations y-ray receivers which are observing systems. show that the formation of stars in the from the space around the Earth. But, of . This is the general formulation of association is taking place in smaller course, the recent technical progress goals of these fields of science. Howev­ subgroups in the, so to say, recent star has affected in the strongest degree the er, in the practice of scientific work formation regions wh ich have linear planetary astronomy. Some of the these general goals dissolve into count­ sizes smaller than one parsec and com­ space vehicles give us the possibility to less subjects, problems, questions and prise only a very small part of the vol­ observe the planets, comets, satellites topics, each of wh ich can prove its im­ ume of the associations. from the immediate vicinity. There is no portance and can require a special The study of such regions where the doubt that the role of investigations with programme of studies. complicated phenomena of the ejection space vehicles in planetary studies will And you know weil that very often the of gaseous matter, of H20 and other enormously increase in future and this solution of each problem raises a large masers, as weil as the formation and means that the role of ground based number of new problems, wh ich in the ejection of Herbig-Haro objects are telescopic observations in this field will past were under the scientific horizon. characteristic is to be carried out with diminish. The difficulty of formulating the mul­ many different techniques, among Of course, in the fields of galactic and titude of special problems, of program­ which optical and infrared telescopes extragalactic research the modern ming the ways of their solution is com­ are playing an important part. methods (radio astronomy, X-ray as­ plicated by the fact that they very often Last Wednesday Dr. Moorwood tronomy, far infrared, space missions intersect and penetrate each other. showed us some infrared pictures of Let us take one example. Everybody such a region in Orion where the Beck­ understands that we have two important lin-Neugebauer object and other in­ • Talk given at First School for Young Astronomers and seemingly independent problems of frared sources are situated. Organized by ESO and the Astronomical Council of the U. S. S. R. Academy of Sciences (see the stellar astronomy: the distribution of the We are sure that the study of these Messenger 50, p. 43-44). stars in the Galaxy and the origin of phenomena will bring us much nearer to 10 the understanding of the origin of stars association in a molecular cloud must At the same time it is very important to of the disk population. lead to its destruction and dissipation. consider deeper the connections be­ I am convinced that the study of such We do not know the exact percentage of tween the world of Seyfert galaxies and regions of "recent star formation" by GMC wh ich contain OB stars. Apparent­ quasars. For this the detailed study of direct, spectroscopic, infrared, radio Iy, 30 % or 50 % is a good estimate of the nearest quasars is important. methods promises to become one of the order of the magnitude. But this will For us, theoreticians, quasars are the most rewarding fields of observa­ mean that the life-time of a GMC cannot galaxies which have a very bright nu­ tions. be longer than the life-time of an OB cleus. The stellar surroundings of them But if we know the direction in which association by more than one order of are sometimes of the scale of usual we can strongly hope to find the solution magnitude. On the other hand, the life­ giant galaxies. But apparently there are of the problems of the origin of stars of time of OB associations was estimated cases where these surroundings are re­ Population land of galactic nebulae, the (until now) as 107 years. This means that latively faint. To understand the reg­ situation in regard to Population II stars the life-time of GMC must not be longer ularities of relationship between nuclei is not so hopeful. than 108 years. The urgent problem of galaxies and of stellar population Anybody who has some experience in arises on the origin of molecular clouds. around them is one of the major prob­ the treatment of the problems of stellar Of course, this is also a problem for lems of extragalactic astronomy and origin will agree that the problem of the theoreticians. However, it seems to me in this respect the study of the near­ origin of Population 11 stars must be that the solution can be found on the est quasars must be of the greatest closely connected with the problem of basis of detailed observational studies value. the origin of globular clusters. of the whole problem of connection be­ On the opposite flank of extragalactic But apparently our Galaxy at its re­ tween the molecular clouds and young research is the study of dwarf galaxies. cent phase of evolution is deprived of stars. The most important regularity here is the young Population II objects, at least As I have insisted in some of my pa­ their irregular structure. Another proper­ we don't see them in our neighbour­ pers, the problem of the origin of ty wh ich apparently is connected with hood. It seems therefore that the prog­ nebulae and particularly of molecular the question on their evolution is the ress towards the solution of this prob­ clouds is now not less actual than that relatively high mass of the neutral lem will be accelerated by combining of the origin of stars. atomic hydrogen in them. It is a great the information obtained from observa­ Of course, there are countless prob­ priviledge for us and specially for ESO tions of galactic and extragalactic ob­ lems wh ich are to be solved in the frame that our Galaxy has two of them so near. jects. of pure galactic observations. But to recognize the regularities within Let me bring here two more problems As an example, we can consider the the irregularities apparently will require which require the combination of galac­ nature and cause of changes in T Tauri the study of a larger number of objects tic and extragalactic data. stars. A special problem is the variability and therefore the detailed study of a We observe in our Galaxy a limited of very faint red dwarfs (of visual abso­ number of objects on intermediate dis­ number of Wolf-Rayet stars. They are lute magnitude of about +17 or +18). We tances of the order of several millions of young objects. We observe them as a know that we can find the flare stars parsec is necessary. But there the rule in OB associations. But there are among very faint dwarfs. But are there stronger ti es with radio astronomy, many OB associations which don't con­ also T Tauri variables among them? This especially with 21-cm astronomy, are tain any WR stars. The best example is requires the observation of very faint necessary. May I remind you that during the Orion association. It contains no WR stars (of apparent magnitude of 21 or the last years objects have been dis­ star in spite of the fact that different 23) both in open clusters and the gener­ covered which are giant HI c10uds of parts of this association are apparently al field. galactic dimensions and at the same at different stages of evolution. There­ In this connection I would like to re­ time have no discernible stellar popula­ fore, the evolutionary status of WR stars mind you that by building larger tele­ tion. It is of interest to find intermediate is not quite clear, but of course we are scopes we acquire the ability to study objects where gas and stars have sure that they are comparatively young more distant objects as weil as to ob­ masses of equal orders. objects. serve intrinsically fainter objects. Com­ Between these two fields (very faint But the remarkable fact is that in 30 paring in this respect the requirements dwarfs and quasars) we see the vast Doradus, which is a superassociation of galactic research we notice that for field of investigations of normal galaxies (or giant H 11 region), in its central part we extragalactic research both abilities are and processes in them, the work on observe at once a whole group of WR equally important. However, in the more detailed and apparently mul­ stars which form together with a number galactic research the second is relatively tidimensional classification of normal of 0 stars a compact nucleus of the more important. This is why I emphasize galaxies. superassociation. With great probability here specially the problems connected Of special importance are studies of we can suppose that many super­ with extremely faint red dwarfs. But of active galaxies and specially of their nu­ associations in other galaxies also con­ course the study of white dwarfs is of no c1ear regions, of wonderful changes of tain WR stars. We know also, that some less importance. brightness and spectral properties of Markarian galaxies contain not one, but Passing to extragalactic problems the nuclei of active galaxies and several superassociations. and taking into account our last remark quasars. The future large telescopes will allow we begin of course with the most distant The problem of large-scale distribu­ us to establish the abundance of WR objects - the quasars of very high red­ tion of galaxies and their clusters is a stars in them. shifts. It is quite natural that astronom­ bridge between extragalactic astronomy The last problem which requires both ers are awaiting with deep emotions the and cosmology. And I am sure that the the galactic and extragalactic informa­ discovery of new record redshifts. But it large telescopes of the near future will tion is connected with the giant molecu­ is necessary to tell that we need also the open fascinating prospects also here. lar clouds. As is known, the consider­ systematic study (both statistical and One of the important subjects of in­ able percentage of giant molecular physical) of the whole range of quasars vestigation remains the physical nature clouds contains stellar associations. beginning with z = 0.2 to z = 4.5 and of interstellar matter. Now we are sure However, the emergence of the OB larger if they are there. that the bulk of interstellar matter con-

11 sists mainly of molecular clouds. The The other components are connected interests, the interest of a theoretician. so-called Great Molecular Clouds with the general structure of the Galaxy May I repeat here what I have said in my (GMC) are individual objects of great as a whole as weil as with external in­ welcome to this school: interest and the problems of their origin fluences on the Galaxy. We are only The real essence of our knowledge of are not less intriguing than those of stel­ beginning to understand their role in the the Universe is contained in the obser­ lar clusters. But at the moment our Galaxy. vational data. The role of the theory is to knowledge of them is very superficial. My talk, as I mentioned, reviewed only systematize the data and to connect Great efforts are necessary. some aspects of the problems of galac­ them logically between themselves and But GMC clouds form only one of the tic and intergalactic research and re­ with the data from other sciences. components of interstellar matter. flects mostly my personal views and

Galactic Chronometry with the Coude Echelle Scanner H. BUTCHER, Kapteyn Observatory, Roden, the Nether/ands

Introduction same abundance for thorium as found in The proposed chronometer is the meteorites. The line, therefore, appears ratio of the strengths of these two lines. I have recently proposed that obser­ to be largely unblended and a good This ratio has the property that it can be vations of the radioactive nucleus candidate for use in setting up a measured to high accuracy. Whether it 232 Th in stars may be used to derive a chronometer based on thorium. It will in the end provide a useful and reli­ new kind of galactic chronometer (Na­ should also be remarked that the ele­ able chronometer depends on the de­ ture, vol. 328, pp. 127-131, 1987). The ment thorium has only one long-lived tails of the measurement errors and on extraordinary performance of the Coude isotope, 232 Th, so that measurement the reality of a crucial assumption. Echelle Spectrometer on La Silla has of the elemental abundance is expected played a central role in making possible also to give the isotopic abundance of the difficult observations required. I con­ A Crucial Assumption interest. gratulate the ESO staff on producing To have a useful chronometer, it is such an outstanding instrument. necessary to be able to compare the The idea is simple - if G-dwarf stars The Chronometer abundance of the radioactive species at sampie a weil-mixed interstellar medium synthesis, which is normally a quantity in the Galaxy at the time of their birth, Figure 1 shows the region around predicted theoretically, with the ob­ and if the compositions of their atmo­ Th I1 4019.129 Ain alpha Cen B, one of served abundance. For the U-Th data in spheres have not changed since birth the stars in my final sampie. The thorium meteorites, for example, one can esti­ except for radioactive decay, then the line is seen to appear in the wing of a mate the relative production ratios of abundances of radioactive species in stronger line, wh ich turns out to be a 232 Th, 235 U, and 238 U, rather accu­ these stars will represent an integration blend of a Fe land a Ni I line. Also indi­ rately, because they are very close to of element production and destruction cated is a nearby absorption line of each other in atomic mass and in a (via radioactive decay, astration and neodymium, Nd 11 4018.823 A. This line mass range expected to exhibit a rela­ possibly dilution) in the Galaxy, up to the has a lower level excitation only 0.05 eV tively smooth variation of abundance moment of stellar birth, followed by free above that of Th 11 4019.129, and neody­ with mass in the r-process. Neverthe­ decay still observed today. If one can mium has a first ionization potential less, a major source of uncertainty in develop a sampie of stars with accu­ close to that of thorium. Both lines are, applying U-Th data in the solar system rately known ages, then one has a re­ therefore, from the dominant ion for chronometry are the uncertainties in cord of the history of nucleosynthesis, at throughout late-type stellar atmo­ the production ratios. least for thorium and the r-process ele­ spheres, and will behave with tempera­ The situation in the stellar case is, in ments, which may help resolve the mod­ ture and pressure essentially identically. principle, much, much worse. Thorium el dependencies inherent in using solar Furthermore, both lines are unsaturated system data alone. That is, solar system in G-dwarf spectra, so that their material provides an integration of ele­ strength ratio is proportional to the ment production and destruction activi­ abundance ratio of these two elements, 10 ty up to 4,6 Gyr ago; observations of and is largely unaffected by unknown or 08 radioactive species in the oldest stars poorly estimated stellar atmospheric known will yield an integration over only properties. And finally, it is important a short period at the beginning of the that there exist two rather good Galaxy; and data on the youngest stars continuum points, at 4018.66 and give an integration over the whole galac­ 4019.67 in the near vicinity (see for A, 01 tic history. example the high resolution but com­

Thorium has several faint absorption pacted plots of the solar spectrum dis­ 00 lines in the solar spectrum, and the played in Figure 5 of Rutten and van der

strongest of these, at 4019.129 A, even Zalm, Astron. Astrophys. Suppl. Sero 55, 40188 1.0190 1.0192 40194 has an accurately measured transition 143-161, 1984). Because the lines are Waveleng I h I AI probability (Andersen and Petkov, As­ so close together in wavelength and are Figure 1: CES spectrum of a Cen B in the tron. Astroph. 45, 237 -238, 1975). bracketed by good continuum points, region of Thll 4019.129 A. The thorium and When combined with the measured the ratio of their strengths may be deter­ neodymium lines used to form the line strength, this probability yields the mined with considerable reliability. chronometrie quantity Th/Nd are indicated. 12 r-process element europium, do not measure of the noise in the line strength vary among dwarf stars in the solar estimates, and I have argued that the neighbourhood, at least for stars having resulting scatter in the data points about metallicities greater than about 3 % of their mean is to be understood entirely solar. The best measurements to date as due to this noise. If that is so, then limit any such variation to certainly no individual points may be appropriately ~-.::::::- __ BGyr more than about 25 % (Butcher, Ap. J summed to display the total statistical 12 Gyr 199, 710-717, 1975; Lambert, Astro­ weight of the data set. 075 16Gyr phys. Astr. 8, 103-122, 1987). Hence in Such a display is given in Figure 2. any star having strong enough lines for Each of these data points is the average the thorium line to be measurable, the of 3 to 7 stars. The horizontal error bars

10 15 20 contribution to the neodymium abun­ give the range in age of the stars in each 51ellar Evolullon Age {Gyr} dance from the s- and r-processes has point (but also a rough estimate of the Figure 2: Variation of normalized Th/Nd with been sensibly constant over all time. reliability of the age estimates), and stellar age. Individual data points have been And when it becomes possible to ob­ those in the vertical direction the one combined here to show the statistical weight serve thorium in very metal deficient sigma uncertainty in Th/Nd for the point. of the whole data set. Also shown are two stars, it will be possible to apply a The age estimates for the sampie models for the predicted variation of Th/Nd. correction to account for any r/s evolu­ stars, except for the four youngest stars, The initial event model supposes that essen­ tion, because such stars are all very old are derived from trigonometric parallax­ tially all thorium and neodymium were syn­ and hence represent an integration of es (being all bright stars, the quality of thesized before the sampie stars formed; it only a very brief period. They will not the parallax data is quite reasonable), predicts constant Th/Nd vs. age, and fits the data weil. The second model supposes that therefore produce uniqueness problems available broad band photometry, and net element production has proceeded con­ in the analysis. the isochrones of Van den Berg (Ap. J tinuously and at a constant rate over all time. Suppl. Sero 58, 711, 1985). It is these The stellar ages are on Van den Berg's scale, isochrones wh ich have given globular The Data but the laffer model is shown assuming three cluster ages above 15 Gyr, although different total timescales, as indicated, Aseries of spectra were taken at the there is now some suggestion that for stretched to overlay the data points appropri­ CAT and CES on La Silla, during 2-6 large (factors of five) overabundances of ately. Total durations of synthesis above Sept. 1983 and 3-7 April 1985. Study of oxygen in the most metal poor clusters, about 10 Gyr in this model are seen to be the maximum ages may be reduced to excluded. model and real data showed that spec­ trat resolutions of at least 100,000 and 14 Gyr (McClure et al. , Astron. J, 93, preferably twice that would be required 1144-1165,1987). is produced during fission cycling of the to be able to adequately measure the In Figure 2 are also indicated the pre­ r-process. Neodymium also partakes in inflection that is the thorium line. For dictions of two extreme models for the this cycling, but is probably also pro­ reasons of observing efficiency the CES history of synthesis, namely a single duced in the very short-lived process was set to R = 100,000. The efficiency of event at the beginning (initial spike mod­ responsible for the lighter r-process the spectrometer is not optimal at el), and continuous synthesis at a con­ nuclei. Its abundance, therefore, could 4000 A, and with the 1,872 channel Re­ stant net rate. It is evident that the initial very weil evolve over time if the con­ ticon detector and integration times of spike model fits the data very weil, tributions to r-process synthesis vary. up to 11 hours, the faintest star for whereas there is no support for any Furthermore, neodymium isotopes de­ which a S/N of several hundred could be model with constant net production, rive nearly 50 % of their abundance in obtained was about V = 6,5 mag. The even when it is assumed that the stars the solar system not from the r-process, instrument performed very weil, except may be correctly ordered by age but but from the s-process. The r-process is for some difficulty in obtaining a reliable with an incorrect total age scale. If the generally believed to have occurred in instrumental profile using the blue laser thorium line is contaminated by no more explosions, probably supernovae, (that is, the derived profile seemed to be than 10% (a value of 20 % seemingly whereas the s-process is seen to take a function of how saturated the line core ruled out by various tests reported in the place in red giant stars. There is every became on the detector). Given the ob­ Nature paper), then a two sigma upper reason to suppose, therefore, that the vious importance of knowing with some limit on the total duration of synthesis in ratio of r-process to s-process abun­ accuracy and precision just what the the latter model is less than 10 Gyr. dances will evolve over time and place instrumental profile is for a given mea­ On the other hand, these data provide in the Galaxy. If they do, the Th/Nd surement, I suggest that a careful study no independent age limit in the initial chronometer will be compromised, be­ of known absorption line spectra, such spike model. Any total age always yields cause it will be difficult to disentangle as of an absorption cell, should be a uniform composition at any given that evolution from the production and made. Perhaps then the saturation epoch in this case. But then the solar decay history of thorium. That is, for all problems I encountered can be alievi­ system U-Th data provide a sensitive but the oldest stars the observed Th/Nd ated. limit, namely 11 Gyr maximum, with pre­ ratio results from an integration of pro­ ferred values 2 or 3 Gyr less (see Fowler duction and destruction activity over ex­ and Meisl, in Cosmogonical Processes, Results tended periods, and it therefore will not Arnett et al. eds., 83-100, VNU Utrecht, be easy to separate uniquely the effects It proved possible in the end to 1986; and Meyer and Schramm, in Nu­ of variations in the s-process contribu­ acquire data on 18 G-dwarf and several cleosynthesis and its Implications on tion to neodymium in one model for the giant stars with narrow enough lines. Nuclear and Particle Physics, Audouze history of synthesis, from no variations These data have been analysed by fit­ and Mathieu eds., 355-362, Reidel in a different model. ting a model spectrum of the region to 1986, for discussion of results from Fortunately, the situation is not hope­ the individual spectra, of which there are models with synthesis peaked at early less. It has been known for some time typically two or three per star. The epochs). So combining stellar and solar that the abundances of the s-process differences between the best-fit model system data constrains the total age elements barium and strontium, and the spectra and the data are taken to give a scale, with the stellar thorium observa-

13 Th;. Nd 20Gyr 1.25 1.25

1. 00 H-..----t---l--::~"'F_----.----_l: 100 +-----±-~==:+;~--l-

0.75 075

(a)

o 5 10 15 20 0 5 10 15 20 Stellar Evolution Age (Gyrl Stellar Evolution Age (Gyrl Figure 3: Comparison of Clayton's galaetie evolution model with stellar abundanee results. This model assumes the r-proeess is a primary proeess, whereas the s-proeess is seeondary. The resulting evolution of the neodymium abundanee (52 % s-proeess and 48 % r-proeess in the solar system) eompensates for the deeay of thorium for ages above 15 Gyr, as seen in (a). The model prediets the europium (91 % r-proeess in the solar system) to barium (84 % s-proeess) ratio results displayed in (b), however, whieh is elearly ineonsistent with existing measurements of these elements in the sampie stars. tions limiting the constant rate model data suggest that the initial event model considerable interest, of course, to de­ and the meteoritic data the initial spike is to be preferred, so that if negligible termine observationally just how con­ model. amounts of on-going s-process synthe­ stant the ratios of r- to s-process abun­ For models mid-way between the ex­ sis have occurred, then the data are fully dances really are, and for the halo stars tremes, some sensitivity is lost in either consistent. It is only on the major synthe­ to find the corrections needed to the case, and maximum ages of 11-12 Gyr sis at all epochs model, such as would be neodymium abundance for those stars are acceptable within both stellar and relevant if synthesis were directly tied to ultimately to be usable for this sort of meteoritic constraints. But it remains the star formation, that the uncertainty be­ chronometry. case that the best-fit model has synthe­ comes a matter for concern. sis concentrated in a single period at the Several workers have proposed that Speculation beginning of the Galaxy (or before). the conclusion of a young age for the Galaxy is easily refuted, by simply taking Finally, I would like to communicate account of a plausibly separate evolu­ Potential Problems the following, deliberately provocative, tion of s-process and r-process abun­ speculation. The reliable use of Th/Nd for galactic dances over time. Shown in Figure 3, for The so-calied G-dwarf problem - that chronometry rests on two assumptions example, is a model due to Clayton (Na­ the distribution of metallicities among that are still not fully verified. The first is ture, 329, 397-398, 1987) which pos­ dwarf stars cannot be reproduced with that the thorium line at 4019.129 Ais not tulates a gradually increasing contribu­ simple galactic evolution models having contaminated by more than, say, 10 %; tion from the s-process. The fit to the synthesis closely tied to star formation ­ any much greater contamination would Th/Nd data is quite good, even for a has traditionally been explained by make the chronometer too sensitive to galactic age of 20 Gyr. But I have been supposing that infall of primordial mate­ the exact amount of contamination. I able to assemble Eu/Ba ratios for most rial must have been important (although suggested that none of the tests I made of my sampie stars, and display these other schemes, such as metal-en­ would have distinguished blending due data together with the prediction of hanced star formation, have occasional­ to a line from a low Iying level of an ion Clayton's model. Here even though the Iy also been proposed). The Th/Nd data of an r-process element, and proposed Eu/Ba data are not as good as for Th/ suggest that synthesis peaked at early that Tb 11 4019.14 might be a candidate Nd, it is evident that the model fails. epochs is the right model, in wh ich case contaminator at the 10% level. Unfortu­ Mathews and Schramm (submitted to the G-dwarf problem, as weil as the nately, the spectrum of Tb 11 has never Ap. J. Letters) have also constructed a metallicity gradients seen in the Galaxy, been fully analyzed, and I understand complicated galactic evolution model may be due to some other phenomenon now that the line in question may in fact based on a varying s-process produc­ than ordinary stellar nucleosynthesis. not really exist. But Holweger (Observa­ tion. They claim that their model fits the I wonder, therefore, whether the gen­ tory, 100, 155-160, 1980) has pointed Th/Nd data for ages up to 15 Gyr. This erally accepted picture of continuous out that Co I 4019.126 A probably model is displayed in Figure 4, and their star-formation-linked synthesis, fixed up should be considered a candidate con­ claim for Th/Nd is again seen to be via mechanisms which are plausible but taminator at this level. It is clear that a correct. However, the model also for which there is no real positive evi­ definitive discussion of the contamina­ cannot produce constant Th/Nd and dence to fit the metallicity distribution tion question awaits further investiga­ simultaneously constant Eu/Ba, as is results, has any claim to preference over tion. evident in the second part of the figure. the initial spike model. For the latter, The second area of uncertainty is the Simple schemes for compromizing some mechanism will have to be found constancy of the thorium to neodymium the Th/Nd chronometer, therefore, run to account for the metallicity gradients, ratio during synthesis. Of course, the afoul of even existing data. It will be of but this deficiency must be weighed 14 Th; Nd

1.25

20 Gyr

0.75 075

(a) (b)

o 5 10 15 20 o 5 10 15 20 Stellar Evolution Age IGyrl Stellar Evolution Age (Gyrl

Figure 4: Comparison of a galactic evolution model due to Mathews and Schramm with stellar abundance data. This model supposes that the r- and s-processes occur in stars of different masses, so that a gradual change in the contribution ratio for neodymium is predicted which will compensate thorium decay for ages up to 15 Gyr. The predicted Th/Nd ratio vs. age is shown in (a) for this model and three maximum ages. In (b) is shown the prediction for the stable r- and s-process elements, europium and barium. It is clear that such simple models will always have trouble providing nearly constant Eu/Ba and at the same time constant Th/Nd, unless the total age is so short that thorium has not had time to decay substantially in even the oldest stars.

against the absence of a convincing panying the formation of the Galaxy. Rev., D 35, 1151, 1985; Malaney and mechanism in the traditional scenario The short-lived radioactivities found in Fowler, preprint). In such conditions it for producing significant metallicity vari­ solar system material would then have appears possible to generate not only ations without altering the ratio of r- to their origins in such minor on-going the light nuclei, but also to bridge the S-process abundances. I suggest that synthesis as has taken place, and only a mass gap at atomic number 8, to pro­ all available data fit the initial spike mod­ few species, such as the eNO isotopes, duce heavy elements all the way up to U el as weil as they fit the synthesis in will have had their abundances measur­ and Th. The very first generation of stars normal stars idea. One is then left in the ably altered via stellar evolution. following the Big Bang would then have amusing situation of having stars mak­ What might the initial process be? A been responsible for the s-process ele­ ing helium, but with the vast majority of most exciting possibility has recently ments seen in halo stars. Here is a the helium around us having been pro­ been proposed. Models concerning the plausible mechanism for synthesizing duced in the Big Bang, and of suppos­ quark-hadron phase transition in the Big the r-process radioactivities which are ing that although stars clearly make new Bang suggest that inhomogeneous con­ used for cosmochronology in a single elements via nuclear reactions, the ma­ ditions may have resulted during the initial event. I for one will be following jority of the heavy elements were made epoch relevant to primordial nucleosyn­ further studies of this idea with gleeful by some process preceding or accom- thesis (Applegate and Hogan, Phys. anticipation!

High Resolution CASPEC Observations of the z = 4.11 QSO 0000-26 J. K. WEBB, Sterrewacht Leiden, the Netherlands, and Royal Greenwich Observatory, U. K. H. C. PARNELL, R. F. CARSWELL, R. G. McMAHON, M. J. IRWIN, Institute of Astronomy, Cambridge, U. K. C. HAZARO, Oepartment of Physics and Astronomy, University of Pittsburgh, U. S. A. R. FERLET and A. VIOAL-MAOJAR, Institut d'Astrophysique, Paris, France

Introduction (z 2: 3.5) QSOs using IlIa-F objective the Anglo-Austral/an Telescope in Au­ The QSO QOOOO-26 is a newly discov­ prism plate material taken with the UK gust last year. Fortunate timing of a run ered object with an emission redshift of 1.2-m Schmidt telescope at Siding immediately following on the ESO 3.6-m 4.11 and a continuum magnitude at Spring in New South Wales, Australia telescope meant that we were able to ~ 6000 Aof around 17.5. The QSO was (Hazard and McMahon 1985). QOOOO-26 collect the high resolution data we pre­ discoverd as part of a programme to was observed and confirmed as a high sent here only a few days after the ob­ detect bright (m(R) ~ 18.5), high redshift redshift QSO during an observing run on ject was discovered.

15 r '-'1 traction of the two-dimensional data to produce spectra was then done using an optimal, seeing profile weighted pro­ (J cedure to maximize signal to noise in the final spectrum. Pixels containing the flagged cosmic rays were discarded and the extracted counts rescaled ap­ ~I propriately. An error array was gener­ ated based on Poisson statistics. Wavelength calibration was carried out in the usual way and the r. m. s. residual on arc line positions was - 0.05 A corresponding to - ~ of a pixel. The final spectrum was produced by adding to­ gether the calibrated orders which had been flattened by dividing by the smoothed flat field. Calibrating in this way does not produce the correct spectral shape but this does not affect l-j our absorption line analysis. The com­ plete spectrum thus obtained is shown in Figure 1. There was a non-uniform increased background count present in ,I "I I) I I' three of the lower wavelength frames, .. which could mean that the zero level is slightly unreliable below 5700 A. Figure 1: The spectrum of 00000-26 obtained using CASPEC on the ESO 3.6-m telescape. To determine accurately the spectral The dense Lya forest, extending right up to [he Lya emission line at 6230 Ais clearly evident. resolution, we extracted the arc spectra, adding together the individual orders in exactly the same way as the OSO The Observations by clipping pixel values above a suitable spectra. By measuring the FWHM of lines in the arc spectrum, we estimate a threshold, and were then flagged. Sim­ 1 00000-26 was observed using CAS­ ple median filtering, or c1ipping and re­ resolution of - 30 kms- . PEC on the ESO 3.6-m telescope on the setting to the local mean is undesirable nights of the 30th and 31 st August 1987. because of the unpredictable effect on The Lya Forest We used the 31.5 Iines/mm grating narrow absorption lines, The two-di­ to collect data in two overlapping mensional frames were converted from Given the high resolution of our CAS­ wavelength regions: approximately AOUs to photon counts, assuming a PEC data, most of the absorption lines 4700 to 5700 A and 5600 to 6600 A. conversion rate of 10 e-s/AOU. The ex- are resolved and we can use profile Four 120-minute exposures were ob­ tained for the first region and two for the second. For the lower wavelength ex­ , ---, posures we binned the CCO (ESO # 3) by two pixels in the dispersion direction and for the higher wavelength ex­ posures we binned by two pixels in both (J directions. The sllt lengths for the low and high wavelength exposures were 1,200 ~lm and 1,600 ~m corresponding to about 8.6 and 11.5 arcsecs on the sky respec­ tively. The slit width for all exposures was 280 ~m, corresponding to about 2.0 arcsecs. This just about matched the seeing profile on our first night, when 3 out of the 4 lower wavelength exposures were obtained, and was somewhat less than the seeing on the second night, when the remaining lower wavelength and both higher wavelength exposures were obtained. o +

Data Reduction Oata reduction was carried out using ~ ~~-'- 5100 5700 ') 300 5400 the Starlink V/>Y.. 11/780 at the IOA in Cambridge. Cosmic rays were located wovelc>n'lll1 \/1) either by subtracting two exposures (at Figure 2: The spectrum in the region of the damped Ly a system at Z.bs = 3.392. The smooth 21 2 the same wavelength setting) or simply curve is a Voigt profile fitted to this feature with a column density of NHJ = 3 X 10 cm- .

16 fitting methods to model each cloud to obtain the column density of neutral

hydrogen, NHh the Doppler (velocity dis­ persion) parameter, b, and the redshift, z (see Carswell et al., 1987). This analy­ sis is currently underway. Here we de­ scribe the results of a preliminary inves­ tigation of some aspects of the Lya data. First we fitted a single cubic spline continuum to the data using an iterative procedure which clips significant devia­ tions below the estimated level. Clipping is carried out such that deviations in the data (excluding discarded points) about the final fit are consistent with the noise properties. The fit was done between 4700 and about 6100 A. Over the Lya emission line, we estimated the con­ tinuum by interpolating over regions containing absorption lines. The Lyß emission line falls immediately short­ wards of a strong damped Lya absorp­ tion line at 5340 Aand our adopted con­ tinuum will be unreliable in that region. Next we estimated absorption line positions (centroids) and the observed equivalent widths using an automated technique (Young et al., 1979; Carswell et al. , 1982) to generate a line list con­ taining all features which deviate from the adopted continuum level by 4 a or more. Our rest equivalent width limit at this level is - 0.2 A or better. Despite the extremely high number density of absorption lines, this procedure seems to work weil. We checked this by com­ paring an expanded plot of the data with the appropriate entries in our line list.

Properties of the Lya Forest Lines

(a) Number density evolution As shown initially by Peterson (1978), the evolution in number of Lya lines per Figure 3: (a) Image of OSOOOOO-26 on lIIa-J+GG 395 plate for the ESO/SERC Atlas of the unit redshift interval increases with red­ Southern Sky. shift at a rate significantly faster than (b) Objective prism spectrum of OSOOOOO-26 on IIla-F+GG 495 plate and 2° prism. can be accounted for purely by cos­ 80th plates were obtained with the UK 48" Schmidt telescape and the reproductions were mological effects, and consequently the made at UKSTU, Royal Observatory, Edinburgh. clouds are evolving intrinsically. This change in the number density is weil approximated by below the Lya emission line, where the 1986; Tytler, 1987; Webb and Larsen, local OSO ionization probably 1988; Bajtlik et al., 1988). This is gener­ dN dz = No (1 + z)Y. (1 ) dominates) we find 68 absorption lines ally, although not unanimously, thought with Wrest > 0.36 A. Equation (1) pre­ to be due to increased ionization levels We have estimated the parameters No dicts a count of 73 and so we find that for clouds in the vicinity of the aso. In and y from a sam pie of OSOs taken the 00000-26 data are consistent with a this preliminary investigation, we merely from the literature (Webb and Larsen; continued increase in the absorption check as to whether or not such an 1988), not including 00000-26, and find line number density up to z - 4. effect is present in the spectrum of y = 2.50 ± 0.46, and No = 2.53 for lines 00000-26. with rest equivalent width, W > In the region 4.06 < z < 4.11 (i. e. res1 (b) The Inverse Effect 0.36 A. These values agree with the es­ within 3,000 kms-1 of the emission red­ timates of Hunstead et al., 1987 for an When considering a single aso, there shift) we find 4 lines with Wrest > 0.36 A overlapping OSO sampie. appears to be an inconsistency in the compared with 7.4 predicted by equa­ Counting lines in 00000-26 between redshift distribution of lines with equa­ tion (1). Counting lines down to our esti­ z = 3.48 (above the damped Lya ab­ tion (1); the number density is seen to mated 4 a limit of 0.2 A, we find 8 lines sorption and Lyß emission lines) and up increase towards lower wavelengths in the same region and 164 in the range to z = 4.06 (approximately 3,000 kms-1 (Carswell et al., 1982; Murdoch et al., 3.48 < z < 4.06. The ratio of these two 17 counts, normalized to a unit redshift in­ associated with the strong damped Lya formation on the nature of the Lya terval, is 0.55 ± 0.20 and so we appa­ line at 5349 A. Strong C IV absorption clouds at the highest redshift so far rently have a significant inverse effect (at is seen at the same redshift in our available. Later this year, we aim to col­ - 2 a level). low resolution data. Profile matching lect more CASPEC data on the spec­ to this feature, which is probably the trum of 00000-26, covering wave­ highest redshift candidate disk galaxy lengths longward of the Lya emission (c) The velocity dispersion parameter yet discovered, indicates that NH1 = line. These will cover many of the metal 21 2 In order to compare our data with 3 x 10 cm- . The Voigt profile fitted to line transitions associated with the two previous analyses of high resolution this feature is shown in Figure 2. At this systems discovered and will enable us data, we selected 10 apparently un­ early stage, we cannot say anything to study the abundances and ionization blended lines in the region 3.48 < z < about metal abundances; many of the conditions at this early epoch. 4.11. Their mean redshift was z= 4.0. transitions of interest (e. g. C 11 A 1334, These lines were then modelIed by us­ Sill A1260, Si 111 A1206, SilV n 1393, ing non-linear least-squares to fit Voigt 1402) are embedded in the Lya forest References profiles. For these 10 lines we find = 6 and a detailed profile analysis is re­ Atwood, B., Baldwin, J.A., and Carswell, 30.5 ± 2.1. This can be compared with quired to obtain column densities (or R. F., 1986, Astrophys. J, 292, 58. the results of Carswell et al. , 1984, for limits). Bajtlik, S., Ouncan, R C. and Ostriker, J. P., 01101-264, and Atwood et al., 1985, for 1988, preprint. 00420-388. For 01101-264 b = 30.1 ± Carswell, R.F., Whelan, J.A.J., Smith, M.G., (b) zabs = 4.133 2.5 for a sampie of absorption lines with Boksenberg, A., Tytler, 0., 1982, Mon. Not. z= 2.0 (this is derived from the com­ This system has a redshift R. Astr. Soc., 198,91. plete sampie rather than just for un­ 1,350 km S-l greater than the Lya emis­ Carswell, R. F., Morton, O. C., Smith, M. C., Stockton, A. N., Turnshek, O.A., and Wey­ blended lines; the absorption line sion line, and so presumably resides in mann, RJ., 1984, Astrophys. J, 278,486. number density is sufficiently low at the same cluster of galaxies as the OSO Carswell, R. F., Webb, J. K., Baldwin, J.A., z = 2 that this should not bias the result itself. Strong C IV absorption is seen in and Atwood, B., 1987, Astrophys. J, 319, too much) and for 00420-388 5 = 30.5 the low resolution spectrum, although 709. ± 2.0 for a sampie with z = 2.9 (for the hydrogen column density is not par­ Hazard, C. and McMahon, R.G., 1985, Na­ unblended lines with log NH1 > 13.75). ticularly high (probably less than a few ture, 314, 238. 17 2 Our preliminary check on the Doppler times 10 cm- ). This feature is not Hunstead, R. W., Pettini, M., Blades, J. C., parameter at z = 4 therefore provides no seen in the high resolution data as it is and Murdoch, H.S., 1987, in lAU Sym­ evidence for redshift evolution in this outside the wavelength range. The high­ posium 124, Observational Cosmology, ed. A. Hewitt, G. Burbidge and L. Z. Fang quantity. er order Lyman lines are present in the (0. Reidel) p. 799. CASPEC data and they should provide Murdoch, H. S., Hunstead, R. W., Pettini, M., an accurate column density estimate. Metal Une Systems and Blades, J. C., 1986, Astrophys. J, 309, Since this object evidently sits fairly 19. From this high resolution CASPEC close to the aso, we might expect the Peterson, B.A., 1978, in lAU Symposium 79, spectrum and a low resolution (10 A gas to be highly ionized, and so we The Large Scale Structure of the Universe, FWHM) spectrum obtained by RFC, searched for OVI absorption. This is a ed. M. S. Longair and J. Einasto (0. Reidel), HCP and JKW at the MT, we have doublet with rest frame wavelengths p.389. discovered two metal containing sys­ 1031.9 and 1037.6 A. The 1031 line Tytler, 0., 1987, Astrophys. J, 321, 69. Webb, J. K. and Larsen, I. P., 1988, to appear tems. appears to be present but this is unfor­ in proceedings 01 the Third IAP Astrophy­ tunately ambiguous since the 1037 line sics Meeting, High Redshift and Primeval is blended with the damped Lya line. Galaxies. (Edition Frontieres) (a) zabs = 3.392 We expect the full analysis of these Young, P.J., Sargent, W. L. W., Boksenberg, The most prominent system is evident data to take some time and that the A., Carswell, R F., Whelan, J.A. J., 1979, from the CASPEC data alone. This is results will supply new and valuable in- Astrophys. J, 229, 891.

Remote Observing: Nine Days in Garehing c. WAELKENS, Astronomical Institute, University of Leuven, Belgium

As announced by G. Raffi in the tional step toward a practice of observa­ carried out from Garching with essen­ Messenger No. 49 and confirmed by P. tional astronomy where most of the tially the same efficiency as at La Silla, Franc;:ois in the Messenger No. 50, the romantic side of the job has gone away. an achievement for wh ich G. Raffi, G. CES spectrograph equipped with CCD My answer was that an observation run Kraus, and M. Ziebell deserve to be (using the CAT telescope) can now be from Garching allowed me to stay a few congratulated. My warmest thanks also . operated by means of remote control days longer with my newly born son, go to the numerous colleagues both in from Garching. I had the chance to be and that there was some romanticism La Silla and in Garching who helped in the first visiting observer with these in­ there too. I could also have replied how rendering the operations as efficient as struments in Garching, and was asked fascinating an experience it is to be in possible. to write down my impressions for the touch with one of the amazing technical My programme was an easy one for readers of the Messenger. developments at ESO. It surely is a re­ remote control, since I have been using Before leaving my home institute, I markable achievement that, so early in the same spectral range throughout, was warned by several colleagues who the development of the remote control watching variations of the profile of the feared that remote control was an addi- technique, observations could be Si 111 line at 4552 Ain some bright Beta 18 gr------,10013 3 PUP Messenger 49, HR 4049 is not anormal "' massive supergiant, but probably an old low-mass star that is terminating its evolution from the red-giant stage to­ ward the planetary-nebula stage. From previous optical spectra, it was clear that HR 4049 is a very metal-deficient objecL It happens that the spectral re­ gion I observed contains some of the strongest lines of the iron-peak ele­ '" "''" ments iron, titanium and chromium in the A2la supergiant standard Alpha Cygni. In Figures 1 and 2 the spectrum of HR 4049 (AOlp) can be compared with "'.'" '" that of another A-supergiant surrounded by a dust shell, 3 Puppis (A2Iabe). One 4544.201 4549.331 4554.460 4559.590 4564.720 does not have to undertake tedious cal­ Figure 1: Some of the stronger Fell, Ti 11, and Crlliines in the spectrum of the A2-supergiant culations in order to know that the defi­ 3 Puppis. ciency of HR 4049 is particularly severe! This star mayaiso become an object for <:> #00 3 HR 4049 <:> observers who are not interested in the In subject of late stages of stellar evolu­ tion, but are just looking for early-type stars that are suitable for observations <:> <:> of stellar flat fields ... <:>I"'~-~~~-.J>-_~~~_~"'V_J"---'-' ...... -~~~-...... ~~--""- My run was rather long, ni ne nights, and maybe too long for remote control observations. The weather was excel­ lent throughout at La Silla, but not so in <:> <:> Garching. After a few nights, it became In_ a frustrating experience not to wake up having access to the familiar sunshine on the mountain, but instead watching the darkness of the northern winter with gl its fog so typical for November. This was 4-:::5-44-,2-0-1----4-5'49-,-33-1-- 4554.460 4559,590 4564.720 entirely my problem, of course, since remote control is not primarily designed Figure 2: The same spectral region as in Figure 1, but for the peculiar early-A supergiant HR for such long runs. Instead, the tech­ 4049. nique is most promising for the possi­ bility it offers to carry out shorter pro­ grammes, that presently aren't sched­ Cephei stars. I could not withstand the favourite object, the peculiar early uled so often at the CAT, in an efficient temptation to spend some time on my supergiant HR 4049. As explained in the and cost-saving way.

La Silla Snowstorm

Skiing enthousiasts among European astronomers - who have suffered because of lack of snow in the beginning of this winter - may be interested in these pictures by K. Seidensticker, obtained in late July 1987. While tall snow-drifts block the inner yard of the La Silla Hotel, a snow plough works its way along the roads under a splendid blue sky.

19 Way was obtained by Claus Madsen being prepared for transport to the Ma­ ESO Exhibitions and Svend Laustsen; a high-quality drid Planetarium, Spain, where the next printed copy was published as a fold­ ESO Exhibition will take place. The An ESO Exhibition was officially out in the ESO Book Exploring the photographer points to the Andromeda opened at the Vienna Planetarium on Southern Sky. Galaxy, one of the many well-known December 17, 1987, by the Austrian This panorama has now been photo­ objects visible on the panorama; note Federal Minister for Science and Re­ graphically enlarged to fill 1.5 x 8 m. It also the Large Magellanic Cloud at the search, Professor Dr. Hans Tuppy. ESO shows the entire 3600 of the Milky Way lower right. The picture on the opposite was represented by Professor Harry van band to ± 30 0 latitude, i. e. about half page is a reproduction at the panorama der Laan, Director General elect. In the of the entire sky, with aresolution of scale of an area near the dark clouds in picture above, the Minister (centre) is about 1 arcminute and down to 11 th Ophiochus. shown the model of the ESO New Tech­ magnitude. On the photo below, it is nology Telescope by the new Director General. Next Locations for the ESO Exhibition: During the past year, the ESO Exhibi­ tion has grown and one more impres­ Spain Madrid Planetario March 1-April 10 sive item has just been added. Recently, Italy Bologna Palazzo Re Enzo May 7-May 27 a photographic panorama of the Milky Sweden Gothenburg Liseberg June 15-August

20

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Variability in stars is very common. It very red and cannot be measured at detail: OH/IR 285.05+0.07 and OH/IR makes observations more difficult and short wavelengths with the 1-m. During 286.50+0.06. They have been selected their interpretation more complex, but it nighttime, through a 15" diaphragm, for several reasons. Although their ener­ can be useful as a mean of probing limiting magnitudes (S/N = 1, in 1 minute gy distributions (4) are similar, very ear­ stellar properties. In particular, it can be integration) are typically 14-15 in the Iy, their periods appeared to differ by a used to derive information on stellar in­ near infrared (J, H, K); due to telescope factor greater than 2. Furthermore, they teriors. When a star is surrounded by thermal emission, they degrade at are close to each other on the sky, circumstellar matter, variability can also longer wavelengths, and one reaches a facilitating a comparative study, and be used to probe the latter. limit of - 9.5 in Land, depending on their southern position (6 - - 60") OH/IR stars are among the most weather conditions, 7-8 in M. Thanks to keeps them away from the Sun all the spectacular variable sources. They are the good pointing and tracking of the year round, allowing, in principle, a per­ primarily characterized by the coinci­ telescope, daytime observing is also fectly continuous monitoring. Finally, dence of a hydroxyle (OH) maser emis­ possible. However, performances are both are bright enough so that they can sion with an infrared (IR) source. These reduced in the near infrared due to sky almost always be measured easily in the stars are enshrouded in circumstellar background; in these conditions one five photometric bands. In Figure 1, the envelopes. Dust in the shell absorbs loses typically 3 magnitudes. Also, im­ K lightcurves of both sources are pre­ light from the central source and re­ ages are normally worse during daytime sented. The coverage is almost continu­ radiates it in the IR range; OH radicals (especially in the afternoon), and one ous between Julian Dates (JD) 2446000 are formed by photo-dissociation of wa­ may have to use a larger diaphragm and 2447100; there is an interruption of ter molecules in the outer Part of the which induces, at all wavelengths, a 150 days around JD 2447000 due to the envelope, and, excited probably by 35­ further lowering of performances. explosion of SN 1987A which obliged ~lm photons, produce a maser emission Nevertheless, daytime observations are us to stop the programme for a while in the satellite line at 1612 MHz. The necessary to get a continuous coverage and to observe preferentially that un­ central stars appear to be in the late of the lightcurves. Except for a few foreseen event. stages of stellar evolution, generally as cases, stars have been selected so that OH/IR 286.50+0.06, with aperiod of extreme Miras, at the top of the asymp­ they could be easily measured with the - 550 days, appears to be an extreme totic giant branch (AGB), or as red 1-m anytime, at least in K, Land M. member of the Mira class at the top of supergiants (1); sometimes they may be In this sampie of OH/IR sources, two the AGB. Its broad-band spectrum indi­ still more evolved and on their way to objects have been studied especially in cates that its average total luminosity is the planetary nebula stage (2). In this latter case, pulsations are damped out 70 r------,------,,------r------r------, and strong variability is not observed (3). 1 I 1 1 Most OH/IR stars known in the south­ ern hemisphere have first been discov­ ered as OH emitters during systematic surveys made with the parkes antenna. Many have been recovered in the IR at ~ f~"+f+ the ESO 1-m telescope (4). Time-spread 6.0 t measurements have shown that these ++ sources are variable and a systematic K ++ monitoring of a few of them was started in late 1984 with the same 1-m tele­ OH/IR 285 05 + 0.07 scope. As OH/IR stars have periods in + ++ the range 500-2,000 days, this is a t+ 50 long-term programme from which only - preliminary results can be given now. + The monitoring is made in the J t+ (1.25 ~m), H (1.65 ~lm), K (2.2 ~lm), L :::~ (3.8 ~m) and M (4.6 ~m) photometric bands. Depending on circumstellar dust shell optical depth, some objects are 6.0 - ++ + ... In the eentral part of the Gum Nebula, just + north of the Vela supernova remnant, we find + several relatively unknown nebulae. The K + northernmost part of the filamentary Vela + SNR is seen near the lower right edge of the - pieture, whieh was photographieally en­ 50 OH/IR 286.50 + 0.06 + haneed by C. Madsen from a red plate from + ++ ++ + the ESO/SERC Atlas of the Southern Sky ++ (lIIa-F + RG630; 120 minutes with the ESO Sehmidt teleseope). The large nebula to the upper right eontains several areas where stars are now being born (the densest is NGC 4.0 '-- -1.1 -'--1 '--' -'1 ---' 2626). Many dust lanes are also visible in this 5500 6000 6500 7000 negative pieture and there are several open stellar clusters, notably NGC 2671, just to the J. D. (244000 +) right of the nebula in the lower left part. Figure 1: K lighteurves of OH/IR 285.05+0.07 and OH/IR 286.50+0.06. 24 4 I I I I I I 353.60-0.23 from 5 10 to 25 104 Le (in 300 days). Such intense variations in stellar objects are surpassed only by those of novae or supernovae. 11.0 f- - OH/IR 353.60-0.23 It is generally assumed that OH/IR source lightcurves are quasi-sinusoidal f (1); this assumption has never been K checked. Although the sam pie of ob­ (0 ) ? jects that we monitor is smalI, it seems that strongly non-sinusoidal lightcurves 10.0 f- ? - are, in fact, common. Also, in some cases (e. g. OH/IR 285.05+0.07), the shapes are wavelength dependent. Clear correlations between lightcurve ,d:: shapes and presence of OH (6) or H20 t (7) maser emission have been found in 4.0 f- - Mira stars; it is believed that they indi­ cate a relation, between the pulsational 9 properties of central stars and the physi­ L cal properties of circumstellar matter, (.) originating in the mass-Ioss phenome­ non. Such correlations have not been 30 - - established in the case of OH/IR stars for lack of data. In fact, as some light­ curve shapes are wavelength depen­ M dent, the story might be more com­ (6) plex; however, observations of such wavelength dependency (Iike observa­ ~ tions of time variability) would be useful 2.0 f- + + - in providing supplementary constraints on stellar and circumstellar models. The success of this work would not be conceivable without the efficient and friendly support of all the La Silla in­ frared staff. Also, I am grateful to the I I I I I I numerous visiting astronomers who are 6200 6400 6600 6800 7000 7200 spending, sometimes, a large amount of their precious time in discussions with J. D. (244000 +) their support astronomer, and, thus, are Figure 2: K, Land M lightcurves of OH/IR 353.60-0.23. making of La Silla a place of scientific exchange. 5 around 10 ., and its mass loss rate, period is at least 1,000 days. The 5 1 References ~ 1.5 10- Me .yr- (3). The case of OH/ observed lightcurves consist of two IR 285.05+0.07 is less straightforward. If branches in wh ich magnitudes are vary­ (1) Jones, 1. J.: 1987, in Late Stages of Stel­ periodic, its period (defined as the lapse ing linearly with time. The declining lar Evolution, ed. S. Kwok and S. R. Pot­ of time between successive extrema of branches last at least 500 days and the tasch, D. Reidel Publishing Company, 3. (2) Le Bertre, T.: 1986, The Messenger44, 6. the same type) should be larger than rising ones at least 300 days; at (3) Le Bertre, 1.: 1987, Astron. Astrophys. 1,000 days. In fact, comparison of data minimum, there is no evidence for a 180,160. acquired in this programme with earlier plateau of more than 100 days. This (4) Epchtein, N., Nguyen-Q-Rieu: 1982, As­ data (e. g. around JD 2445200) shows broken line lightcurve shape, without tron. Astrophys. 107,229. that the lightcurve presents irre­ plateau, is similar to that of OH/IR (5) Le Bertre, T., Epchtein, N., Gispert, R., gularities. Also, one notes a strong 26.5+0.6 (see Figure 5 in 1); however, Nguyen-Q-Rieu, Truong-Bach: 1984, As­ asymmetry in the lightcurve. It exhibits a the latter's lightcurve shape is symmet­ tron. Astrophys. 132, 75. linear variation for ~ 500 days followed ric, which is not the case for OH/IR (6) Bowers, P.F., Kerr, F.J.: 1977, Astron. by a plateau lasting at least 250 days. 353.60-0.23. Finally, from the available Astrophys. 57, 115. (7) Vardya, M.S.: 1987, Astron. Astrophys. Then, the object passed from minimum data there is no evidence that the shape 182, 75. to maximum in less than 150 days. Quite of the lightcurve might change with surprisingly, the lapses of time corre­ wavelength. On JD - 2446200, i. e. near Sponding to the linear part and to the maximum, an H magnitude of 14.2 ± .2 plateau are wavelength dependent. was measured at the 1-m; obviously, to OH/IR 353.60-0.23 is another pro­ study the J and H lightcurves would Visiting gramme object. The infrared counterpart require a more powerful system. of the OH maser was also discovered at As dust shells are heated by central Astronomers the ESO 1-m (4). Its energy distribution stars, variations observed in the IR re­ (April 1-0ctober 1, 1988) peaks at 10 flm (5) and is similar to that flect, among other effects, changes in total output luminosity of the central of the prototypical object, OH/IR Observing time has now been allocated tor 26.5+0.6. This kind of source is very red stars. From minimum to maximum (in ~ Period 41 (April 1-0ctober 1, 1988). The (K-L 6); in general, they cannot be 150 days or less), the central source of demand tor telescope time was again much measured at wavelengths shorter than OH/IR 285.05+0.07 is varying from greater than the time actually available. 4 4 2 flm with the 1-m telescope. The K, L 410 to 610 Le, the one of OH/IR The tollowing list gives the names ot the 4 4 and M lightcurves are displayed in Fi­ 286.50+0.06 from 6 10 to 15 10 • (in visiting astronomers, by telescope and in gure 2. As for OH/IR 285.05+0.07, the 250 days) and. finally, that of OH/IR chronoloqical order. The complete list, with 25 dates, equipment and programme titles, is stensen/Sommer-Larsen/Hawkins, Moeller/ Festou/Beuermann, Reipurth/Olberg/Booth, available from ESO-Garching. Rasmussen. Eriksson/Gustafsson/Olofsson, Schultz, Reinsch/Pakull/Festou/Beuermann. 3.6-m Teleseope 1.5-m Speetrographie Teleseope May: Reipurth/Zinnecker, Reipurth/Ladal Bally, Le Bertre/Epchtein/Perrier, Tapia/ April: Moorwood/Oliva, Danziger/Moor­ April: Faraggiana/GerbaldilBoehm, Persi/Ferrari-Toniolo/Roth, Spaenhauer/ wood/Oliva, Dennefeld/Bottinelli/Gouguen­ Doazan/SemaklBourdonneau, Danziger/Fos­ Labhardt, Reinsch/Pakull/Festou/Beuer­ heim/Martin, Reimers/Koester/Schröder, bury/LucylWampler/Schwarz, Courvoisier/ mann, Le Bertre/Epchtein/Perrier, Cour­ Rhee/Katgert, Cristiani/Guzzo/Shaver/lovino, Bouchet, Bues/RupprechVStrecker, DurreV voisier/Bouchet, Spinoglio/Malkan, de Jager/ Danziger/Guzzo, Cristiani, Chalabaev/Per­ Boisson, Danziger/Fosbury/LucylWampler/ Nieuwenhuijzen, Lorenzetti/Berrilli, Sarace­ rier/Mariotti, Mathys/Stenflo, Moneti/D'Odo­ Schwarz, Acker/Jasniewicz/Duquennoy, no/Berrilli/Ceccarelli/Liseau/Lorenzetti, Hes­ rico. Eriksson/Gustafsson/Olofsson, Danziger/ selbjerg Christensen. May: Tapia/Moorwood/Moneti, Tapia/Per­ Fosbury/LucylWampler/Schwarz, Spite F.I June: Hesselbjerg Christensen, Gouiffes/ si/Ferrari-Toniolo/Roth, Miller/Mitchell, Keel, Spite M. Cristiani, Gahm/Bouvier/Liseau, Antonello/ Meylan/Shaver/Djorgovski, Ilovaisky/Cheva­ May: North/Lanz, Danziger/Fosbury/Lucy/ Conconi/Mantegazza/Poretti, Reinsch/ Iier/Pedersen, Swings/Courvoisier/Magain/ Wampler/Schwarz, Waelkens/LamerslWa­ Pakull/Festou/Beuermann, Antonello/Con­ Remy/Surdej, Husfeld/Heber/ButlerlWerner, ters, Spinoglio/Malkan, Danziger/Fosbury/ coni/MantegazzaiPoretti, Le Bertre/Epch­ Wagner. LucylWampler/Schwarz, Heber/Hunger/ tein/Perrier, Richichi/Lisi/Salinari, Reipurth/ June: Maggazu/Strazzulla, Le Bertre/ Werner, Danziger/Fosbury/LucylWampler/ LadaiBally, Courvoisier/Bouchet. Epchtein/Perrier, Krabbe/Zinnecker/Hof­ Schwarz, de Jager/Nieuwenhuijzen, Mekka­ July: Reinsch/Pakull/Festou/Beuermann, mann, Buonanno/Drukier/Fahlmann/Richer/ den/Geyer, Loden LO/Sundman. Duerbeck, Barwig/Ritter/Haefner/Schoembs/ Vanden Berg/Fusi Pecci, FortlMathez/ June: Kameswara Rao/Nandy/Houziaux Mantel, Simon/Haefner/Kiesewetter/Ritter, Mellier/Soucail/Cailloux, Herman/Smith, L., Kameswara Rao/Nandy/Houziaux L., Brahic/Sicardy/Roques/Barucci, de Muizon/ Chalabaev/Perrier/Mariotti, Le Bertre/Epch­ Gahm/Bouvier/Liseau, Pottasch/Pecker/ d'Hendecourt, Brahic/Sicardy/Roques/ tein/Perrier, Richichi/Lisi/Salinari. Sahu, Metz/Haefner/Roth/Kunze, Cour­ Barucci, Courvoisier/Bouchet. July: Seitter, Simon/Haefner/Kiesewetter/ voisier/Bouchet. August: Brahic/Sicardy/Roques/Barucci, Ritter, Veron/Hawkins, FosburyfTadhunter/ July: Major overhaul - TRS. Di Martino/ZappalalCellino/Farinella, Bou­ Quinn, RigautiMerkle/Kern/Lena, Brahic/ August: Tanzi/FalomofTreves/Bouchet, cheVCetty-VeronNeron, Johansson/Berg­ Sicardy/Roques/Barucci, van der Veen/Ha­ Danziger/Fosbury/LucylWampler/Schwarz, val!. bing, van der Veen/Habing/Geballe, Brahic/ Acker/Stenholm/Lundström, Kollatschny/ September: LortetITestor, Gouiffes/Cris­ Sicardy/Roques/Barucci. Dietrich, Danziger/Fosbury/LucylWampler/ tiani, Liller/Alcaino. August: Brahic/Sicardy/Roques/Barucci, Schwarz, JugakufTakada-Hidai/Holweger, Waelkens/LamerslWaters/Le Bertre/Bou­ HaucklBertheVLanz. chet, Chalabaev/Perrier/Mariotti, Guzzo/Col­ September: Danziger/Fosbury/Lucy/ 50-ern ESO Photometrie Teleseope lins/Heydon-Dumbleton, de LapparenVMa­ Wampler/Schwarz, Johansson/Bergvall, Vet- April: Group for Long Term Photometry of zure, Bergeron/BoisselYee, BalkowskilBa­ tolani/Chincarini, Danziger/Fosbury/Lucy/ Variables, Kohoutek, Morell/Gustafsson, tuski/Olowin, Maurogordato/Proust. Wampler/Schwarz, Balkowski/ProusV Kohoutek, Lemmer/Dachs. September: GuzzofTarenghi, Jarvis/Mar­ Maurogordato, Rhee/Katgert, Danziger/Fos­ May: Carrasco/Loyola, Mekkaden/Geyer, tinet, Danziger/Gilmozzi, MacchettofTurn­ bury/LucylWampler/Schwarz, Gerbaldi/ Loden LO/Sundman. Faraggiana, Khan/Duerbeck. sheklSparks, Heydari-Malayeri, Webb/Cars­ June: Sinachopoulos, Metz/Haefner/Roth/ well/Shaver, van Groningen, Wampler. Kunze. July: Carrasco/Loyola, BeißerNanysekl 1.4-m CAT BöhnhardVGrün/Drechsel. 2.2-m Teleseope August: Group for Long Term Photometry April: Molaro/D'OdoricoNiadilo, Vladilo/ of Variables. April: PrustilWesselius, Persi/Ferrari-To­ Molaro, Gratton/Gustafsson/Eriksson, niolo/Busso/Origlia/Scaltriti, Giraud, Rosa/ Butcher, Artru/Didelon/Lanz, Solanki/ September: Carrasco/Loyola, Foing/Jan­ kov/Char/Houdebine/Butler/Rodono/Catala­ Richter, Rosa/Richter, Reinsch/Pakull/Fes­ Mathys. no S., Foing/CrivellariNiadilo/Castelli/Beck­ tou/Beuermann, Reimers/Koester/Schröder, May: Spite E.lSpite M., Lemmer/Dachs, man/Char/Jankov. Reinsch/Pakull/Festou/Beuermann, Nota/ Waelkens, de Jager/Nieuwenhuijzen, Wilson/ Paresce/BurrowsNiotti/Lamers, Bässgen M.I Appenzeller/Stahl/Henkel, Vidal-Madjar/Fer­ Bässgen G.lGrewing/Cerrato/Bianchi, Rosa/ leVGry/Lallement, FerleWidal-Madjar/Gry/ Richter, Cristiani/Gouiffes, Rosa/Richter, Lallement. GPO 40-em Astrograph Reinsch/Pakull/Festou/Beuermann. June: da Silva/de la Reza, Mandolesi/ April: Scardia. May: Reinsch/Pakull/Festou/Beuermann, Crane/Palazzi, Palazzi/Blades/Crane, Crane/ May: Landgraf. Piotto/Ortolani, Miley/Chambers, Rosa/Rich­ Palazzi/Mandolesi, Danks/Crane, Pottasch/ August: Auriere/Koch-Miramond/Cordoni. ter, Swings/Courvoisier/Kellermann/Kühr/ Sahu, Benvenuti/Porceddu, Magain/Lind­ September: Debehogne/Machado/Caldei- Magain/Remy/Surdej/Refsdal, Rosa/Richter, gren. raNieira/Netto/Zappalalde Sanctis/Lager- Reinsch/Pakull/Festou/Beuermann, Cour­ July: de Vries/van DishoecklHabing, kvistiMourao/Protitch-BenisheklJavanshir/ voisier/MelnicklMathys/Binette/Maeder, Schwarz/Bode/DuerbecklMeaburn/Seitter/ Wosczcyk. Reipurth/Olberg/Booth, Reipurth/Zinnecker, Taylor, Crowe/Gillet. Reipurth/Lada/Bally. August: Gustafsson/Edvardsson/Magain/ June: Metz/Haefner/Roth/Kunze, Le Nissen, Waelkens/LamerslWaters/Le Bertre/ 1.5-m Danish Teleseope Bertre/Epchtein/Perrier, Schwarz. Bouchet, Magain/Lindgren, Didelon, Fran­ July: Bertola/Zeilinger, Pizzichini/ 90is, Lanz. April: Ardeberg/Lindgren/Lundström, Le Pedersen/Poulsen/Belardi/Palazzi, Melnickl September: Foing/Jankov/Char/Houde­ Bertre/Epchtein/Perrier. SkillmanfTerlevich, Ulrich, Tadhunter/ bine/Butler/Rodono/Catalano S., Foing/ May: van Paradijs/van der Klis, Leibund­ Pollacco/Hill, GottwaldlWhite/Parmar, Mel­ CrivellariNiadilo, Castelli/Beckman/Char/ gutITammann, West, Brocato/Buonanno/ nicklSkillmanfTerlevich, Joly, Habing/Le Jankov. Castellani/di Giorgio, 1I0vaisky/Chevalier/Pe­ Poole/Schwarz/van der Veen. dersen. August: Tanzi/FalomofTreves/Bouchet, June: Haefner/Ritter/Reimers. Auriere/Koch-Miramond/Cordoni, Ram- July: Reinsch/Pakull/Festou/Beuermann, 1-m Photometrie Teleseope pazzo/Sulentic, Tadhunter/Fosbury/di Cristiani/Gouiffes, Piotto/King, Gottwald/ Serego Alighieri, Brocato/Melnick, April: Courvoisier/Bouchet, Santos Friaca/ White/Parmar, Azzopardi/LequeuxlRebeirot, Capaccioli/Ortolani/Piotto, Cristiani/Gouiffes. Le Bertre, Le Bertre/Epchtein/Perrier, van BeißerNanyseklBöhnhardVGrün/Drechsel. September: LorteVLindgrenfTestor, der HuchtIThelWilliams, Bues/RupprechV August: Ardeberg/Lindgren/Lundström, Burrows/Paresce, DurreVBergeron, Chri- Strecker, Gouiffes/Cristiani, Reinsch/Pakull/ LorteVLindgrenfTestor, Grenon/Mayor.

26 September: Joergensen/Hansen/Noer- July: v. Amerongen/v. Paradijs. Prusti/ClarkIWesselius/Laureijs, Dettmar/ gaard-Nielsen, Johansson/Bergvall, Grego­ August: Schneider/Weiss. Heithausen/Hummel, Henkel/Wiklind/Wilson, nnl/MessinaIVettolani, Fusi Pecci/Buonanno/ Loiseau/Harnett/Combes/Gerin, Henkel/Wil­ Ortolani/Renzini/Ferraro. son, Pottasch/Pecker/Sahu/Srinivasan, Mo­ SEST neti/NattaiEvans, BajajalHummel, Bajajal 50-ern Danish Teleseope May: Reipurth/LadaiBally, Israel/de Harnett/Loiseau, PeraultlFalgarone/Boulan­ Graauw, Crane/Kutner, LequeuxiBoulanger/ ger/Puget, Dennefeld/PeraultlBottinelli/Gou­ May: Franeo. Cohen, Israel/Baas, Israel/Baas/de Graauw/ guenheim/Martin. June: Grenon/Bopp, Ardeberg/Lindgren/ Douglas, Heydari-Malayeri/Encrenaz P./Pa­ September: Chini/KreysalMezger, Gerin/ Lundström, Group for Long Term Photometry gani, Garay/Rodriguez, Reipurth/Olberg/ Combes/Buta, DupraziCasoli/Combes/Ge­ of Variables. Booth, Haikala, Radford/Cernicharo/Greve, rin/Salez, Combes/Casoli/DupraziGerin/Har­ September: Ardeberg/Lindgren/Lund- Crane/Mandolesi/Palazzi/Kutner, Wouter­ nett/Loiseau, Combes/Casoli/DupraziGerin, ström. 100tlBrand, Stutzki/Zinnecker/Drapatzl Gerin/Combes/Casoli/Nakai/Hummel/van Genzel/Harris/Olberg/Rothermel. der Hulst, Melnick, Lellouch/Combes/En­ 90-ern Duteh Teleseope July: Burton/Liszt, Reipurth/Olberg/Booth, crenaz T./Gerin, Casoli/Combes/DuprazlGe­ Wielebinski/Mebold/Whiteoak/Harnett/Dah- rin, Booth/Nyman/Winnberg/Olofsson/Sahai/ June: Grenon/Lub. lem/Loiseau, BosmaiDeharveng/Lequeux, Habing/OmontlRieu.

Pre- and Post-Perihelion Speetrographie and Photometrie Observations of Comet Wilson (1986 t) c. ARPIGNY, F. DOSSIN, J. MANFROID, Institut d'Astrophysique, Universite de Liege, Belgium P. MAGAIN, ESO, and R. HAEFNER, Universitäts-Sternwarte München, F. R. Germany

Hardly had Halley's comet left our im­ et Halley had been one year earlier at Ultraviolet - Blue Region mediate vicinity when a relatively bright, the same heliocentric distance. How­ "new" comet, Wilson (1986 (), was dis­ ever, as far as spectrography was con­ Particular emphasis was laid upon the covered in the summer of 1986. The cerned, this weakness was, in asense, near ultraviolet because this region has announcement of this discovery was the compensated by the use of CCD detec­ been as yet poorly explored. Besides, more exciting as early predictions gave tors, which had not been available dur­ advantage was taken of the availability Some hope that the newcomer might ing our observations of P/Halley. of a CCD with fluorescent coating for become of similar brightness to Halley's This was indeed a great improvement, ultraviolet sensitivity. The importance of In April-May 1987, just about one year for CCD's are particularly suitable for the UV-blue region stems also from the after P/Hailey had made its own show. the observations of extended objects: in fact that it contains emissions of OH, As the comet would be located in the addition to their high quantum efficien­ CO2+, OW, CO+, hence information re­ Southern sky at that time, and encour­ cy, linearity and high dynamic range, lated to the abundance ratios of the aged by our successful Halley runs at they offer the crucial advantage of two­ major constituents of the cometary ESO, we proposed a programme that dimensional detectors, allowing the de­ material, water and the carbon oxydes. would give the opportunity to make a termination of the spatial distribution of As an example, a spectrum obtained Comparison between two comets of the spectral emissions over an appreci­ at moderate resolution is shown in Fi­ quite different dynamical ages observed able region of the objecl. Furthermore, gure 1. The heliocentric distance (r) of at similar distances from the sun and when they are used at the Cassegrain the comet was 1.21 A. U. pre-perihelion, with similar instrumentation. Another focus, as with the 2.2-m and the 1.5-m and its geocentric distance (f1) was 0.95 comparison seemed interesting: to telescopes, one avoids the loss of spa­ A. U. The upper tracing corresponds to a study the behaviour of the comet before tial resolution caused by the field rota­ strip 10 arcsec or 7,000 km wide, ap­ and after its passage through perihelion, tion inherent to the coude focus (where proximately centred on the nucleus, ex­ which occurred on 21 April, 1987. In­ photographic plates were traditionally tracted from the CCD. The flux unit is deed we were able to carry out observa­ used in cometary spectroscopy). Know­ arbitrary on this and the two other plots. tions in April and in May, both spectro­ ledge of the radial profiles of the comet­ No correction has been applied to take graphic (2.2-m ESO-MPI telescope, 1.4­ ary emissions is absolutely necessary to out the atmospheric extinction and the m CAT + CES, and 1.5-m telescope) analyse the physical processes re­ instrument + detector response, in order and photometric (0.5-m ESO telescope). sponsible for the formation and for the to illustrate the tremendous attenuation Some of the most significant results of excitation of the various emitting produced by these effects. For instance, these observations will be described species, to evaluate their production the difference in overall flux reduction briefly here. They refer to spectra in the rates, to construct or to test models of between 387 nm and 308.5 nm Ultraviolet, blue and red regions, as weil the coma and tail. It can also help in the amounts to about 4 magnitudes in this as to photometry through narrow-band identification of new spectrallines, since case: the OH (0-0) band is, in fact, filters. the extent of a given emission on each appreciably stronger than the CN (0-0) Comet Wilson proved to be consider­ side of the comet centre is related band, outside the earth's atmosphere. ably fainter than had been anticipated to the nature of the particular atom The middle and boUom panels com­ On the basis of the optimistic predic­ or molecule involved (neutral or ion­ pare, at a magnified scale, extractions of tlons. In early April it was estimated to ized species; short- or long-lived par­ the same width as above, but offset by be roughly four times weaker than com- ticle). about 40,000 km on each side of the 27 nucleus. While the emissions fram the neutral radicals are nearly symmetrical, 3 the ionic emissions on the contrary are present only on the side opposite to the Centre sun, at this distance from the centre of the comet. To bring out the latter emis­ sions, their contributions have been in­ dicated qualitatively in black on the tail­ ward spectrum. A striking difference with P/Halley's spectrum in this wavelength range con­ cerns the strength of the CO2+ emis­ NH sions as compared to the OW band, OH n wh ich was predominant in P/Hailey near rrn 1 A. U. fram the sun after perihelion (C. Arpigny et al., 1986). This was not caused bya difference in the fluorescent excitation of the emissions and since the relative ionization efficiencies in­ 325 400 425 volved were probably similar as weil, it appears that the proportion of released carbon dioxyde relative to water was higher in comet Wilson than in comet Halley at their respective heliocentric CN distances. As for the CO+IC02+ ratio, it (0 -0) is comparable in the two comets and we reach the conclusion that the relative OH abundance of carbon monoxyde too llIl NH was larger in Wilson. 10-0) 11-1) We note that the emission near 413 nm has been assigned to CO2+ on >" .05 the basis of a higher resolution spec­ :;:l., trum where we measured the same Gi 0:: features at 410.9, 412.3, 414.6, and 416.2 nm that we had discovered in PI u u Halley (ibidem). The identification of CH CH these emissions was possible thanks to B-X Ä-X the kind help of S. Leach, who is cur­ Sunward rently analysing further the CO2+ spec­ trum in this region. Looking back at some older spectragrams, we found 325 350 375 400 425 that this 413 nm feature was present in Wavelength (nm) comets showing CO+ and CO 2+, like Bester, Humason, Bennett, West. At lower resolution it tends to be mistaken for the (4-1) CO+ band, which has but a very small contribution in the ca se of Wilson. In view of the importance of the car­ 1111 11 111 bon compounds, especially those con­ b.v: +2 +1 0 -1 taining the C-H band, as revealed by Halley's comet, the analysis of the CH emission seemed attractive. Thus, we took a spectrum of the Rand 0 bran­ ~ .05 :;:l., ches of the A-X (0-0) band of this radi­ Gi cal (Figure 2). The high resolution used 0:: (50,000, or about 0.01 nm) allows the Ll.-_---LII 11 separation of the satellite lines such as (3-0) (2-0) 0 21 or R12 from their companion princi­ co pal lines. This yields useful additional Tailward information since these lines are issued from different upper energy levels. Another unusual characteristic of this 0l-L...JL....l-l-.L-L---'---L.--I.--L-'-....L-...L--l..-.l....-.L.-L...JL....l--l-L-L---'---L.-L-'-....l...... J spectrum is the weakness of the R (2) 300 325 350 375 400 425 1 Wavelength (nm) line. Comparing with the CH spectrum Figure 1: Spectrum o{ comet Wilson (1986 f) in the near UV-violet region (12 April 1987, r = of P/Halley, for example, we see that the 1.21 A. u., = 0.95 A. u.; 2.2-m telescope + Boiler and Chivens spectrograph with coated GEC excitation rate of this line was indeed CCO, resolution - 0.5 nm; exposure 45 min). Extractions corresponding to three different raughly twice as low in comet Wilson. It locations in the comet are shown on an arbitrary flux scale (see text). should be pointed out that although the

28 2~ --,-- R 3 2 1 Visual Region i---I--~- R2 1 Besides the C2 Swan band se­ 1----,1- Q21 quences, whose interpretation still meets with difficulties, we selected another interesting wavelength interval, comprising the 9-0, 8-0, and 7-0 bands due to NH 2, the red forbidden lines of oxygen, as weil as the 8-0 and 7-0 bands of the H20+ ion. These emissions were monitored both before and follow­ ing perihelion, the main difference be­ tween these periods being the fading of 1 the comet after perihelion and the in­ crease in night sky contamination in Mayas compared to April. The 590­ 670 nm region recorded after perihelion is illustrated in Figures 3 and 4, where we see that the contribution of the night sky (n. s.) is indeed quite substantial. Even the weak (9-3) and (6-1) bands of the Meinel system of the hydroxyl radi­ 429.5 l.30.0 430.5 431.0 431.5 cal show up clearly, near 630 and Figure 2: High-resolution spectrum of the A 2/'; -X 2n (0-0) band of CH showing the complete 655 nm, respectively (see Kvifte, 1959, resolution of the Rand Q branches. The slit was approximately aligned (± about 10°) with the for line identifications); the red [0 I] radius vector from the sun during the 70 minutes exposure obtained with the 1A-m CAT + CES doublet is dominated by the telluric and CCo. The tail is in the upward direction on this reproduction. The vertical bar represents emission; at 656.3 nm the situation is 10' km on the comet (7 April 1987, r = 1.22 A. u., = 1.10 A. U.). rather complex, with three contribu­ tors coming in: nightglow Ha, cometary 2 Ha, and a line of the H 0+ 7-0 band electronic transitions are produced by field is quite short, - 10 sec (Singh and 2 (which, incidentally, is quite weak com­ resonance-fluorescence, collisional pro­ Dalgarno, 1987) and their velocity pared with the 8-0 band in this spec­ cesses which influence the populations cannot be much larger than 1 km/sec. trum). of the lower rotational levels in the inner Therefore, in order to explain their pre­ The ionic emissions extend to distan­ coma, have to be taken into account sence out to more than 40,000 km from ces of - 30,000 km on the sunward side when interpreting the spectrum of CH the centre, we have to assume that they on our different spectra, which is com­ (C. Arpigny et al., 1987 b). On the other are released by particles which have a parable to what we saw in P/Halley hand, we also draw attention to the spa­ much longer lifetime. The detailed study post-perihelion. This may at first appear tial extent of the emissions. The lifetime of the radial profile of the CH lines contrary to expectation, in view of the of the CH radicals in the solar radiation should be instructive in this respect. lower gas production rate of comet Wil­ son. However, the solar wind conditions may have been different themselves, the relative "softness" of the cometary ob­ stacle being, so to speak, balanced by a weaker incoming breeze in the latter case. As far as the neutral species are con­ cerned, the predominance of NH 2 in this spectral range is a common characteris­ tic among comets near 1 A. U. from the sun or a little beyond. So is the weak­ ness of the Cl Swan v = - 2 sequence. The ß v = - 3 sequence of the same sys­ tem, which should be about three times weaker still, does not appear on our spectra, although its presence on spec­ tra for the same period has been re­ ported by Jockers and Geyer (1987). This detection seems rather surprising, especially at a distance of 5 arcmin or 140,000 km away from the nucleus! In April 1987 we were able to repeat on Wilson the same high-resolution ob­ servations of the [0 I] + NH 2 blend we 500 520 540 550 had made on P/Halley (Arpigny et al., 1987 a). The relative intensities of the Figure 3: Seetion of the spectrum ofcomet Wilson in the visual region (see Figure 4 for detailed various lines turned out to be similar in Identifications). (14 May 1987, r = 1.25 A. u., =0.78 A. u.; 1.5-m telescope with B & C these two objects, although Wilson was spectrograph and CCO, resolution - 0.2 nm; 40 min exposure). appreciably fainter. 29 Photometry This is to be compared with P/Halley. differed appreciably in these cases; for­ Photometrie measurements were made tunately, however, a whole series of Comet Wilson was observed photo­ at approximately the same comet-sun diaphragms were used at the Chiran metrically in March, April and May 1987. distance (- 1.25 A. U.), both before and and in New Zealand. By interpolating The special filters defined by the lAU after perihelion (Haute-Provence Obser­ between the results from the different were used in the standard one-channel vatory Chiran, New Zealand Mount diaphragms it was possible to derive the photometer of the ESO 50-cm tele­ John, ESO). The geocentric distances flux received fram a given volume equi- scope. These filters have narraw band­ passes and isolate essential information 9-0 concerning several molecular emission Cz b.v=-2 features (OH, CN, C3, C2, CO+, H20+) -+.--:---,----;--:--::r----'-,I and the continuum (ultraviolet, blue, and red). Because of the faintness of the object, only the central part of the coma I could be measured. On the contrary, in the case of P/Halley (C. Arpigny et al., 1986) it had been possible to map a wide area (over about 5 arcmin). The main characteristic of comet 1986 e was its stability. While comet Halley varied by as much as a factor of 3 or 4 within one day, comet Wilson proved remarkably steady. Between March 30 and April 10, for instance, the apparent brightness increased by little more than 0.2 magnitude, although the comet was nearing both the earth and the sun. Actually, a more significant quantity can be derived by removing the effect upon the apparent brightness of the varying geocentric distance. Be­ sides the purely geometrical dilution effect, proportional to 1/ 2, we have to NaI (ns.) take account of the fact that the fraction of the coma seen by the photometer also varies as changes. The latter part Ha of the correction can be estimated ap­ praximately by adopting a model repre­ senting the brightness distribution with­ in the cometary disk (e. g. Haser's mod­ el, corresponding to the outflow of "pa­ rent molecules" decaying into the ob­ I served radicals, which are themselves destroyed by photodissociation). When applying the -correction in this way, we find that the intrinsic brightness in the various filters remained very nearly constant as the comet approached its perihelion. There was even a tendency for the scattered continuum to weaken slightly. When we observed the comet again, in May 1987 (4 nights), it was at about the same geocentric distance as in the beginning of April, so that the corre­ sponding data are directly comparable. Unfortunately, the weather was very bad in May and did not allow many measure­ I f ~::. ::.: I : : ments. It seems that comet Wilson was i530 1: I 5~0 1 I I~ 51~0 570 L. .. !..: ~ ..: j 1 !i i somewhat more variable after perihe­ ,··I.········~·· ,· ..,·· ..···i .. · I :OH(n.sJ OH(n.s.) : lion. Comparing the fluxes in various i .! filters, it also appears that it was intrinsi­ [Ol] (n.s.) Ha N TI (n.s.) cally fainter by a factor of 1.5 to 2.0 postperihelion, except perhaps in the HzO+ 7-0 light of OH, wh ich seemed to stay at Figure 4: Same spectrum as in Figure 3, shown here at a larger scale. Numerous emissions about the same level. It should be noted due to the nightglow are seen in addition to the cometary lines. The slit was set parallel to the that this last result is rather uncertain projected sun-comet line with the comet's nucleus near one edge in order to record the tai! 5 because the atmospheric extinction is emissions. The total height of the spectrum corresponds to - 2.5 X 10 km at the comet's not easily evaluated at 309 nm. distance. 30 valent to that delimited by 30 arcsec at TABlE 1. "HeJiocentric" fJuxes corresponding to a diaphragm of 27,000 km projected on the 1.24 A. U. from the earth (as for Wilson). comet. Then, obtaining the fluxes correspond­ (A.U.) r(A.U.) BC ing to a fixed distance of 1 A. U. from the Comet C2 earth ("heliocentric" fluxes), we con­ Wilson 1.24 1.24 b 7.1 (-13)* 1.7 (-10)* clude that Halley's comet did brighten 1.23 1.35 a 4.3(-13) 8.5 (-11) intrinsically following perihelion. It was also more variable. P/Halley 0.82 1.27 b 3.4(-13) 1.9 (-10) To illustrate these results, Table 1 0.46 1.24 a 1.2 (-12) 3.9 (-10)" presents a comparison between the be­ • The Iluxes are given in ergs cm-2s- 1 and the numbers between parentheses indicate the haviours of comets Wilson and P/Halley power 01 ten by which the entry is to be multiplied. before (b) and after (a) perihelion in two •• This point was obtained during a minimum 01 activity. P/Halley was as much as 3 times filters (Blue continuum, BC, centred at brighter at other phases 01 its lightcurve. 484.5 nm, and the C Swan ö.v = 0 L.. __ , 2

We regret that due to a last minute mistake at the printer, the colour photo showing the Supernova 1987 A and the 30 Doradus nebula has been reproduced upside down. The error was discovered when this issue of the MESSENGER was delivered to ESO.

We trust that the readers will understand that under the circumstances it was not reasonable to repeat the entire printing run.

The editors

-1- _. ~ ..... _. - - -,- -_. .. __ .. __ . . tions of SR-12 and Rox 31, two sub­ vations are required to resolve most of speckle studies of S CrA and V 649 Ori arcsec pre-main-sequence binaries in them into their components Gudging (Baier et al. 1985) and the infrared slit the Rho Ophiuchi dark cloud (distance from the statistics of binary separations scans of Elias 22 (Zinnecker et al. 1987, 160 pe). The binarity of these sources of solar-type main-sequence stars for Chelli et al. 1988). These are young bi­ was discovered in arecent 2.2 ~lm lunar wh ich the most frequent separation is of nary stars with separations in the 1-2 occultation observing programme of the order of 30 AU, corresponding to 0.2 arcsec range. We note that infrared ob­ young stars carried out by Simon et al. arcsec at a distance of 150 pe). There­ servations are the appropriate tool to (1987). fore, sub-arcsec observations such as study young stellar objects because Many pre-main-sequence objects in lunar occultation and speckle observa­ these are fairly cool objects that have star-forming regions are now known to tions of the nearest T Tauri stars are of not contracted to the main sequence be binary systems (see the review by great interest, in the optical as weil as in yet. Furthermore, there are objects still Reipurth 1987). It is important to resolve the near infrared. As for speckle obser­ embedded in the parental molecular these systems, otherwise properties vations, Nisenson et al. (1985) discov­ cloud or in their dusty circumstellar en­ such as the luminosity and the colours ered an optical companion to T Tau at velopes so that they can escape optical of young low-mass stars may be mis- 0.3 arcsec separation, and Dyck et al. detection.

31 valent to that delimited by 30 aresee at TABlE 1. "Heliocentric" fluxes corresponding to a diaphragm of 27,000 km projected on the 1.24 A. U. from the earth (as for Wilson). comet. Then, obtaining the f1uxes eorrespond­ /). (A.U.) r (A. U.) BC ing to a fixed distanee of 1 A. U. from the Comet C2 earth ("helioeentrie" fluxes), we eon­ Wilson 1.24 1.24 b 7.1 (-13)' 1.7 (-10)* clude that Halley's eomet did brighten 1.23 1.35 a 4.3 (-13) 8.5 (-11) intrinsieally following perihelion. It was also more variable. P/Halley 0.82 1.27 b 3.4 (-13) 1.9 (-10) To illustrate these results, Table 1 0.46 1.24 a 1.2 (-12) 3.9 (-10)** presents a eomparison between the be­ • The Iluxes are given in ergs cm-2s-' and the numbers between parentheses indicate the haviours of eomets Wilson and P/Halley power 01 ten by which the entry is to be multiplied. before (b) and after (a) perihelion in two •• This point was obtained during a minimum 01 activity. P/Halley was as much as 3 times filters (Blue eontinuum, BC, eentred at brighter at other phases 01 its lightcurve. 484.5 nm, and the C2 Swan /),V = 0 bands near 514 nm). Were the intrinsie brightness depen­ dence upon r expressed as an inverse tacular manner. A possible explanation Sterken for communieating us the Power law, the derived exponents would of the brightening of this eomet follow­ photometrie data on eomet Halley he be in the range 5-8, when our measure­ ing perihelion has been given in terms of obtained at Mount John Observatory, ments pre- and post-perihelion are such a "seasonal" effect (Weissman, New Zealand. compared. Sueh steep variations with r 1986). Did, then, the fading of comet have been reported for a number of Wilson (1986 t) we reeorded reflect comets in the past. However, this kind some general trend in the comet's References of interpretation may not be very sig­ evolution (progressive shortage of vol­ Arpigny, C., Dossin, F., Manlroid, J., Magain, nificant. Not only is our number of points atile material, building-up of a "crust") or P., Danks, A. C., lambert, D. l., and Ster­ post-perihelion too small, but we also was it rather the result of a geometrical ken, C.: 1986, The Messenger, No. 45, 8. have to eonsider that the activity of a effect assoeiated with the rotation of the Arpigny, C., Manlroid, J., Magain, P., and comet, its matter and light output, may comet's nucleus and the presence of Haelner, R.: 1987 a, Proc. Symp. on the be strongly influenced by the combined discrete aetive areas on its surface? "Diversity and similarity 01 comets", ESA effect of the inhomogeneous morpholo­ Hopefully, more will be learned about SP-278, 571. gy of its nueleus and the change in this when we have a complete view of Arpigny, C., Zeippen, C.J., Klutz, M., Magain, orientation of its spin axis with respeet the various observations that were P., and Hutsemekers, D.: 1987 b, ibid., to the sun, as regions of its surfaee with made of eomet Wilson. 607. Jockers, K. and Geyer, E. H.: 1987, The different structures and eompositions We are grateful to ESO and to all who Messenger, No. 50, 48. are suceessively exposed to the solar helped us during our observations. In Kvifte, G.: 1959, J. Atm. Terr. Phys., 16,252. radiation. The recent passage of particular, the kind collaboration of D. Singh, P.D. and Dalgarno, A.: 1987, Proc. Halley's comet has demonstrated this Hofstadt and his team was greatly ap­ Symp. on the "Diversity and similarity 01 very extensively and, at times, in a spec- preeiated. Our thanks are also due to C. comets", ESA SP-278, 177.

Resolving Young Stellar Twins H. ZINNECKER, Max-Planck-Institut für Physik und Astrophysik, Institut für Extraterrestrische Physik, Garching, F. R. Germany C. PERRIER, Observatoire de Lyon, Saint Genis-Laval, France

Introduction judged. Even for binaries in the most (1982) had previously diseovered an in­ nearby dark c10uds (with distances of frared eompanion to T Tau at 0.6 aresee We report infrared speekle observa­ the order of 150 pe), sub-aresee obser­ separation. We also mention the optieal tions of SR-12 and Rox 31, two sub­ vations are required to resolve most of speekle studies of S CrA and V 649 Ori aresee pre-main-sequenee binaries in them into their eomponents Oudging (Baier et al. 1985) and the infrared slit the Rho Ophiuehi dark eloud (distance from the statisties of binary separations seans of Elias 22 (Zinneeker et al. 1987, 160 pe). The binarity of these sourees of solar-type main-sequenee stars for Chelli et al. 1988). These are young bi­ was diseovered in a reeent 2.2 llm lunar whieh the most frequent separation is of nary stars with separations in the 1-2 oeeultation observing programme of the order of 30 AU, eorresponding to 0.2 aresee range. We note that infrared ob­ young stars earried out by Simon et al. aresee at a distanee of 150 pe). There­ servations are the appropriate tool to (1987). fore, sub-arcsec observations sueh as study young stellar objeets beeause Many pre-main-sequenee objeets in lunar oeeultation and speekle observa­ these are fairly eool objeets that have star-forming regions are now known to tions of the nearest T Tauri stars are of not eontraeted to the main sequenee be binary systems (see the review by great interest, in the optieal as weil as in yet. Furthermore, there are objeets still Reipurth 1987). It is important to resolve the near infrared. As for speekle obser­ embedded in the parental moleeular these systems, otherwise properties vations, Nisenson et al. (1985) diseov­ eloud or in their dusty eireumstellar en­ sueh as the luminosity and the eolours ered an optieal eompanion to T Tau at velopes so that they ean eseape optieal of young low-mass stars may be mis- 0.3 aresee separation, and Dyek et al. detection.

31 SR -12 ROX - 31 ...... ". ; .

) 11"

J 400 MSEC 400 MSEC

Figure 1: Flux VS. time during the reappearance of(a) SR-12 and (b) ROX 31 behind the dark limb of the moon (from Simon et al. 1987). The dots represent the data at K (2 millisec integrations) and the solid line shows the binary model fit.

The Objects Under Study useful observations can be made only at depth of the minimum (for two equally the dark limb of the moon). bright components the value of the visi­ SR-12 is a Struve-Rudkj0bing emis­ bility function reaches zero). sion line star. Its spectrum is classified Simon et al.. in their paper, have al­ as an M 1 T Tauri star and its luminosity ready presented infrared speckle data Infrared Speckle Follow-up is estimated to be about 1 4l. The ob­ (on SR-12 only, secured at UKIRT in Observations ject is also an X-ray source (ROX 21, Hawaii by Howell) wh ich were used in Montmerle et al. 1983) suggesting that it We decided to follow up these obser­ conjunction with their lunar occultation is not too heavily obscured. It is coinci­ vations by infrared speckle observations data to derive further vital information on dent with a far infrared source in the in order to confirm and to extend the the nature of the source. We were trying IRAS maps presented by Young et al. lunar occultation data (particularly to to improve on their speckle data and (1986). ROX 31 is also a visible star and obtain an infrared colour of the individu­ add speckle data for ROX 31. Our data an X-ray source (Montmerle et al. 1983). al components). Our infrared speckle were obtained with the infrared specklo­ There is no IRAS source clearly related observations which were carried out in graph at the ESO 3.6-m on the nights with the star, but the object is known to two orthogonal scan directions and in June 16 and 17, 1987 during wh ich the be a weak 5 GHz radio source wh ich on two infrared bandpasses (H and K) have seeing was rather good (1 ':2). For a de­ one occasion underwent a strong radio added 3 pieces of information to the scription of the performance of the flare (Stine et al. 1988). The luminosity of lunar occultation data: specklograph we refer to Perrier's ROX 31 has been estimated to be (1) the "true" separation projected on (1986) article in the Messenger No. 45. around 2 4l. and its spectral type is K7­ the sky Suffice it to say that the seeing was MO (Bouvier, priv. commun.). Bouvier (2) the position angle of the binaries adequate to reach the faint magnitudes also finds weak Ha emission confirming (3) the H-K colour of the individual of the objects (K = 8.5, K = 8.1) and - in that it is a young object. components (of SR-12 only) the case of SR-12 - the S/N high Let us remind the reader that, in enough to get convincingly over the Lunar Occultation Data speckle interferometry, the object is minimum in the visibility function - a scanned across a slit at the photometer goal that the previous speckle observa­ In Figure 1 we reproduce the results in one or more directions on the sky. The tions of SR-12 did not achieve. As a of the lunar occultation experiment from observational result is the visibility func­ consequence we did not have to rely on Simon et al. (1987). The experiment was tion. It is given as a function of angular the depth of its visibility function inferred done at the IRTF on January 7, 1986. (A frequency (cycles per arcsec) and is the from the 2.2 Ilm flux ratio measured in description of a lunar occultation experi­ square root of the power spectrum of the lunar occultation experiment to de­ ment in the infrared done at ESO is the object's scanned signal divided by termine the projected binary separation found in the Messenger No. 50 (Richichi the power spectrum of the scanned sig­ (see Fig. 5 in Simon et al.), although we 1987)). Table 1 lists the derived parame­ nal of a point source, normalized to unity do prefer the lunar occultation flux ratio ters from Simon et al. 's work including at zero frequency. The visibility of a bi­ R (EIW) = 0.85 at K over the flux ratio the "separation" along the direction of nary star decreases from value 1 at zero that we obtained from our speckle data the occultation. frequency to a minimum and then in­ (R = 0.45 derived from the fit in Fig. 2a). The angular separation in the direc­ creases; the shape of the visibility func­ It is noteworthy that Simon et al. 's com­ tion of the occultation follows from the tion is determined by the separation and puted projected separation of 0':30 time difference of the reappearances of relative fluxes of the two components. (48 AU) between SR-12 E and SR-12 W the two components multiplied by the The separation is obtained from the agrees weil with our value measured occultation rate of the moon at the con­ spatial frequency at which the minimum directly from the speckle visibility func­ tact point (0.43 arcsec/sec and 0.47 arc­ occurs and the flux ratio is related to the tions in the E-W and N-S directions. sec/sec for SR-12 and ROX 31, respec­ tively). The flux ratios between the first (eastern) and the second (western) com­ TAßlE 1: Oata inferred from lunar occultation observations (from Simon et al. 1987). ponent of the two binary stars (0.85 and 1.29, respectively) can be read off from "sep." K (E-comp.) K (W-comp.) the levels of the flat parts of the signal 9.17 after the occurrence of the Fresnel dif­ SR-12 0.19" 9.34 ROX31 0.13" 8.72 9.00 fraction pattern. (Note that at 2.2 Ilm 32 SR-12 87-06-16 ESO 3.57111 PA 90d 930 Seens SR-t2 87-06-16 ESO 3.57m PA 90d BOO Scens

1.2 1.2

1.0 >- 1.0 ..., ...,'" .BO ~ .80

.~ n n III .60 .60 .~ III .~ > > .40 .40

.20 .20

.00 .00 .00 .50 1.0 1.5 2.0 2.5 3.0 3.5 4.0 .00 .50 1.0 1.5 2.0 2.5 3.0 3.5 4.0 Frequency (l/arcsec) Frequency (1 /arcsec) Figure 2a: SR-12 E-W at K Figure 2b: SR-12 E-W at H Bottom eurve: fit to the data eonstrained by the measured lunar Top eurve: fit where the separation was fixed at 0.30 arcsec. oeeultation fiux ratio R (SR-12E1SR-12W) = 0.85. The resulting E-W Bottom eurve: fit where the separation was fixed at 0.26 arcsec. separation is 0.28 arcsec. 2nd curve from top: fit where both the fiux ratio and the separation Top eurve: uneonstrained fit to the data. In this ease the resulting E­ were free parameters. W separation is 0.30 arcsec. 2nd curve from bottom: fit where the separation was fixed at 0.28 arcsec (this is the value found at K under the eonstraint diseussed in Fig. 2 a/bottom eurve).

SR-12 87-06-16 ESO 3. 57m PA Od 1200 Scans ROX 31 87-06-17 ESO 3.S7m PA Od 936 Scans

1.2 1.2

1.0 1.0 ...,>- ..., .~ '" .~ ~ .BO ~ .BO .~ 0 D III .60 III .60 > > .40 .40

.20 .20

.00 .00 .00 .50 1.0 1.5 2.0 2.5 3.0 3.5 4,0 .00 .50 1.0 1.5 2.0 2.5 3.0 3.5 ';.0 Frequency (l/arcsec) Frequency (l/arCSec) Figure 2 c: SR-12 N-S at K Figure 2d: Rox 31 N-S at K Bottom eurve: fit to the data eonstrained in the same way as il) The fit to the data gives a N-S separation of (0.09 +/- 0.05) arcsec. Fig. 2a (bottom eurve). The resulting N-S separation is 0.14 arcsec. Top eurve: fit to the data (unconstrained) yielding a N-S separation of 0.09 arcsec (X 2 = 1).

Figure 3: The two Let us recall that the projected binary ROX 31 N direetion of lunar oeeul tation solutions for Rox 31 B separation s is defined in the following The ambiguity is due way: to the 180' phase uneertainty for Rox (----:.~-- 31 Bin the N-S s: + speekle data, indicat­ f 1 (E-W) ed by the two parallel horizontallines O. "09 where f1 denotes the spatial frequency N and S of Rox 31A. of the minimum of the visibility func­ E Rox 31 A at the origin tlon and the index E-W and N-S refers 6 is the brighter to the respective orthogonal scan direc­ eomponent at K of tlons. Figure 2 shows the 4 visibility the Rox 31 binary functions that we obtained (for SR-12: system. K (E-W), H (E-W), K (N-S); for ROX 31: K (N-S) only). Table 2 summarizes the results. TABLE 2: Data inferred from all observations (speekle and lunar oee.)

proj. sep. P.A. K (E-comp.) K (W-comp.) H-K (east) H-K (west) lunar Occultation SR-12 0':29 66 9.34 9.17 0.44 0.09 Versus Speckle Observations ROX 31 0':15' 301' 8.72 9.00 - - Finally we should summarize the rela­ Notes to Table 2: tive merits of speckle observations ver­ (i) The statistical error for the projected separations is 10 %. sus lunar occultation observations: (ii) The position angles (east of north) should be accurate to about 10 degrees. (~0.05 (a) Lunar occultation observations (iii) The K magnitudes are quite accurate mag), while the colours are more uncertain (by 0.15-0.25 mag). The H-data tor Rox 31 were too noisy to derive an H-K can resolve binaries with separations as colour. small as a few milli-arcsec (the limit There is a second (perhaps less Iikely) solution for Rox 31: proj. sep. = 0':55 and PA = comes from the orbital speed of the 261 degrees (see Fig. 3). rnoon and the limitations of fast photo-

33 metry for faint sources). It is practically (c) Lunar occultation observations of­ Thanks also to J. Bouvier and Th. an order of magnitude superior in angu­ ten cannot be repeated (for years) while Montmerle for private communications lar resolution over speckle (speckle speckle observations, if they fail due to on Rox sources, and to A. Richichi for reaches 0.13 arcsec - the diffraction poor weather, can be repeated (at most carefully reading the manuscript. Finally limit of a 4-m size telescope at 2.2 ~lm). a year later). Speckle observations also we wish to thank the staff at La Silla for However, it must be emphasized that can be carried out sequentially in sever­ their efficient help. higher resolution can be reached with al filters while multi-filter observations in speckle given high S/N data and apriori a lunar occultation experiment must be knowledge about the structure of the done in parallel. As far as we are aware, References source (for example, if we knew the such a difficult IR-experiment has not object was a spectroscopic binary, been tried yet for binaries but would be Baier et al. (1985). Astron. Astrophys. 153, 278. speckle interferometry might be capable very useful since it is easier to obtain ehelli et al. (1988). Astron. Astrophys. (sub­ of resolving it down to half the diffrac­ good flux ratios of the components in milted). tion limit). On the other hand, it should lunar occultation observations than from Dyck et al. (1982). Astrophys. J. 255, L 103. be noted that there is an upper limit in speckle data. Montmerle et al. (1983). Astrophys. J. 269, separation (- 0."5) for which lunar 182. occultation yields useful results. Nisenson et al. (1985). Astrophys. J. 297, (b) Lunar occultation observations Acknowledgements L 17. cannot find the projected separation Perrier (1986). The Messenger No. 45, p. 29. since the method is intrinsically 1-di­ We would like to thank M. Simon for Reipurth (1987). ESO preprint No. 548. Richichi (1987). The Messenger No. 50, p. 6. mensional while speckle observations communicating us his results prior to Simon et al. (1987). Astrophys. J. 320,344. get around this by scanning in two or­ publication and E. E. Becklin for drawing Stine et al. (1988). Astron. J. (submitted). thogonal directions so that the position attention to the lunar occultation work of Young et al. (1986). Astrophys. J. 304, L45. angle and the projected separations can M. Si mon and colleagues at an early Zinnecker et al. (1987). IAU-Symp. No. 122, be found. stage. p.117.

When Dark is Light Enough*: Measuring the Extragalactic Background Light K. MA TTILA, Helsinki University Observatory, Finland, and G. F. 0. SCHNUR, Astronomisches Institut der Ruhr-Universität Bochum, F. R. Germany

1. Introduction EBL and the complexity of the compo­ to enable blank fields of - 2' diameter. The extragalactic background light site light of the night-sky. Galaxy models show that the contribu­ (EBL) is an observational quantity of fun­ tion from unresolved stars beyond this damental interest in several fields of limiting magnitude is of minor impor­ 2. How to Separate the EBL cosmology. Questions involved are the tance. If it could be assumed that the decision between different cosmologi­ We have been developing for several scattered light from the interstellar dust cal models, the existence of luminous years a method for the measurement of is zero (i. e. the albedo of the interstellar stellar matter between the galaxies, the the EBL wh ich utilizes the screening grains a = 0), then the difference in sur­ emission by intergalactic gas, and effect of a dark nebula on the face brightness between a transparent evolutionary effects in the luminosity background light (Mattila, 1976; Schnur, comparison area and the dark nebula and the number of galaxies. Early 1980; Mattila and Schnur, 1983). A diffe­ would be due to the EBL only, and an theoretical studies of the problem by rential measurement of the night-sky opaque nebula would be darker by the Loys de Cheseaux (1744) and Olbers brightness in the direction of a high amount of the EBL intensity (dashed line (1823) led to the result which was much galactic latitude dark cloud and its in Fig. 1c). later coined by Bondi (1952) with the surrounding area, which is (almost) free Unfortunately, however, the scattered name of Olbers' Paradox: in a static, of obscuring dust, provides a signal light is not zero. A dark nebula above the homogeneous and infinite universe the wh ich is due to two components only: galactic plane is exposed to the radia­ sky background would be as bright as (1) the extragalactic background tion field of the integrated galactic star­ the Sun's surface. Since al ready the light, and light, which gives rise to a diffuse crude observational fact that the sky is (2) the diffusely scattered starlight scattered light (shaded area in Fig. 1c). dark during the night has led to very from interstellar dust. Because the intensity of this scattered deep consequences for our understand­ The large foreground components, starlight in the dark nebula is expected ing of the universe, it is to be expected i. e. the zodiacal light, the airglow and to be equal or larger than the EBL, its that a measurement of the intensity of the atmospheric scattered light are separation will be the main problem in the EBL will be of fundamental impor­ completely eliminated (see Fig. 1a). The the present method. tance for cosmology. Such a measure­ direct starlight down to - 21 st mag­ The separation method utilizes the ment is, however, hampered by great nitude can be eliminated by selecting difference in the shape of the spectral difficulties due to the weakness of the the measuring areas on a deep Schmidt energy distributions of the EBL and the plate. At high galactic latitudes (I b I > galactic light around the wavelength • See Gingerich (1987) 30°) the star density is sufficiently low A. = 4000 A(see Fig. 1d). 34 (2) It is possible to draw some conclu­ sions about the spectrum of the EBL by using plausible theoretical arguments: Radiation from galaxies and other luminous matter over a vast range of DARK distances, from z = 0 up to z - 3 at NEBULA\ least, contribute to the EBL. Therefore, any sharp spectral features of the THE METHOO source spectrum - lines or discon­ tinuities - are washed out For the pre­ sent study it is important to recognize that the discontinuity at 4000 Ä, al­ though present in all galaxy spectra, does not occur in the integrated t EXTRAGALACTIC BACK- background light a) .. GALACTIC STARLIGHT GROUND LIGHT Figure 2 illustrates how the spectral +DIFFUSE GALACTIC LIGHT energy distribution of the observable t ZODIACAL LIGHT surface brightness difference dark AIRGLOW nebula minus surroundings changes for different assumed values of the EBL in­ tensit~. It can be seen that the drop at t' , 4000 A increases when more EBL is I!" , • . , ? • present (For a more quantitative de­ .. • g scription of the method, see Mattila, ® (\) ~l _'.,~~~~ 1976.) e, • .- The result of the first application of the l't' I ~ above described method to the dark b) : OPAQUE 1* .. " • nebula L134 gave an unexpectedly high , I DARK J,.;. / , ! EBL intensity of 10 4 8 (10m stars •: NEBULA r "STARS+ ,., ± 10 (\) per 0°) at 4000 (Mattila, 1976). Later I : GALAXIES Ä on, the same method was used again by I I I I 8pinrad and 8tone (1978) at the same : I SCATTERED LIGHT FROM DUST nebula; they obtained an upper limit of 1= SURFACE 2.6 8 to the EBL. BRIGHTNESS 10

c) 3. Scattered and Thermal I( EBL) Radiation l(AIRGLOW l The present authors have continued + I(ZOD. LIGHT) the measurements of the EBL with the + I(GAU 0 L _ dark cloud technique using the tele-

SCATTERED GALACTIC I (A) STAR LIGHT(4000A BREAK) EBL(SMOOTH) 39· r'-" d) /' 20. L 134 /(.~:~:~:~~~Q

1-- -1---.---- A (1/ 0 4000A ,,' Figure 1: (a) Princip/e of the EBL measuring method; (b) Opaque dark nebu/a is shown in front of a high-ga/actic-/atitude background of stars and galaxies. Measuring positions within the nebu/a (# 2) and outside (# 1 and 3) are indicated; 10 ,-r' ,;1 --.-+-... ../' ~j (c) Schematic presentation of the surface brightness distribution across the dark nebu/a; J ?-.j (d) the difference in spectra/ distributions of the ga/actic starlight and the EBL 20 / r.J -10 •..••.-_•• ,)

3;9_.... _.~ ....,. (1) The spectrum of the integrated (1980). The most remarkable feature in the spectrum is the abrupt drop of inten­ 3500 4000 4500 5000 starlight can be synthesized by using A(Al sity shortward of A = 4000 Ä. The shape the known spectra of stars representing Figure 2: Ca/cu/ated spectra/ energy distribu­ the different spectral types, as weil as of the integrated starlight spectrum and tions of the surface brightness difference data on the space density and distribu­ especially the size of the 4000 Ä discon­ dark nebula minus surroundings for four dif­ tion in the z-direction of stars and dust tinuity have been found to depend only ferent va/ues of the EBL intensity as indi­ Synthetic spectra of the integrated star­ weakly on the galactic latitude and the cated. The numerica/ va/ues refer to the ob­ light have been calculated by Mattila imagined z-distance of the observer. servations of L 134. 35 Figure 3: Infrared (IRAS) surface brightness distribution at 60 pm in Figure 4: Optical (blue) surface brightness distribution in the area of the area of L 1642. The marked area is shown in the optical image in L 1642. Fig. 4. (This picture was kindly provided by R. J. Laureijs, Space Research Laboratory, Groningen.) scopes of the European Southern Ob­ detected also by means of their 1-m and 50-cm telescopes under excel­ servatory on La Silla since 1979. For scattered light, seen on deep photo­ lent sky conditions. By using the IRAS these observations the southern dark graphic plates down to about the same data we were this time able to consid­ nebula L 1642 at I = 21 O? 9, b = -36? 5 levels as the thermal emission seen by erably improve our measuring pro­ was selected in addition to L134. Based IRAS. The lowest contours of both maps gramme, since we had better means of on our observations in 1980 and data correspond to an extinction of - 0.2 identifying near the dark nebula regions available from IRAS we have recently magnitudes. wh ich are free or almost free of dust. completed a comparative infrared and This investigation is a byproduct of Guided by the IRAS data and our previ­ optical surface brightness investigation the EBL measurements, but it is useful ous photometry we have also been able of L1642 (Laureijs, Mattila and Schnur, also on its own right: to locate probably the darkest and most 1987). Through the IRAS data we have a From the relationship between the op­ opaque spot in the centre of L 1642 very effective method to determine the tical and infrared brightness in L 1642 which provides the best zero point for column density along each line of sight we were able to derive e. g. the optical the EBL measurement. in and near the nebula. The 100 ~m sur­ albedo of the dust and the ratio of visual The photoelectric surface photometry face brightness distribution in the to 100 ~m opacity, wh ich are important of weak extended objects is hampered L 1642 area is shown in Fig. 3. For com­ constraints to grain models. by the time variability of the airglow. One parison we show in Fig. 4 the optical has to repeat normally in single beam surface brightness distribution in the photometry the ON and OFF source 4. New Measurements same area, measured on a blue (11 a-O) measurements after each other. We ESO Schmidt plate. It can be seen that In December 1987 we could spend have been using a method in wh ich the high latitude dust clouds are effectively again seven nights on L 1642 at the ESO airglow fluctuations are eliminated by using simultaneous parallel observa­ tions with a monitor telescope (see Fig. 5). The efficient elimination of the airglow variations is demonstrated by Figs. 6a and b which show the sky brightness for a "standard position" in L 1642 as measured with the 1-m tele­ scope through an 88" diaphragm in u and y during the night 15/16 December 1987. Also shown is the ratio of the 50­ cm signal to the 1-m signal. As can be seen the ratio remains constant to within ± 1 % of the signal, which is the pure photon noise for the 40 sec integrations at the 1-m telescope. The reductions of the observations Figure 5: The principle of elimination of airglow fluctuations by using two parallel telescopes. are still going on at the moment. How- 36 ever, thanks to the extremely good and stable sky conditions during these mea­ ly(1-m) surements and guided by our previous lu(1-m) 400 experience we are already hopeful to get this time a clearcut result on the 300 weakness or the strength of the EBL. 350 References Bondi, H.: 1952, Cosmology, Cambridge Uni­ 250 versity Press, Cambridge. . . Gingerich, 0.: 1987, When dark is light 300 enough (review of the book by E. Harrison: Darkness at Night: ARiddie of the Uni­ 200 verse). Nature 330, 288. Laureijs, R., Mattila, K., Schnur, G. F. 0.: 1987, Astron. Astrophys. 181, 269. 250 Loys de Cheseaux, J.P.: 1744, Traite de la comete qui apparut en decembre 1743, 50 60 ]ul5Gcml/L(1- m) ],(S(}cm) Lausanne, p. 223. Iy(1-m) Mattila, K.: 1976, Astron. Astrophys. 47,77. • ." 0" • . : ." Mattila, K.: 1980, Astron. Astrophys. 82,373. .'O ... Mattila, K., Schnur, G. F. 0.: 1983, Mitteilun- 40 h 50 h gen d. Astron. Gesellschaft, 60, 387. 3 5 6 7 LST 3 4 5 6 7 LST Olbers, H. W. M.: 1823, Astronomisches Jahr­ buch 1826 (hrsg. von J.E. Bode), p. 110. Schnur, G. F. 0.: 1980, Photoelectric Surface Figure 6a: Variation of the night sky brightness in Strömgren u during the night 15/16 Dec. Photometry of Extended Sources, in ESO 1987. The upper part shows the signal measured in a fixed position at the centre of L 1642 9 2 Workshop: Two Dimensional Photometry, through an 88" diaphragm at the 1-m telescape. Units are 10- erg cm- S-I sterad- I k '. The p. 365, P. Crane, K. Kjär (Eds.). steep increase starting at LST 6 h is due to moonrise. Lower part is the ratio of the 50-cm and Spinrad, H., Stone, R. P. S.: 1978, Astrophys. 1-m telescape signals. J. 226, 609. Figure 6b: Same as Figure 6a, except for Strömgren y.

MULTI-OBJECT SPECTROSCOPY WITH EFOSC: Observations of Medium Distant Clusters of Galaxies E. GIRAUO, ESO

1. Introduction the cluster core and the age through sponds to the gravitational amplification dynamical evolution (Hoessel and without multiple imaging by density in­ 1.1 Gontext Schneider 1985). These evolutionary homogeneities (i.e. the mean effect of Advances in the understanding of (a) effects must be understood before any several deflectors in a cluster; Weinberg galaxy and cluster evolution, (b) galaxy conclusion on the value of qo and 1976, Turner et al. 1986, Hammer and and cluster formation, and (c) their large the geometry of the universe can be Nottale 1986). A rich compact cluster scale distribution, have been made in drawn. can be a powerful giant lens acting on the past years, but many questions are Large redshift surveys (Arecibo, Har­ the light of distant sources ideally 10­ still open. vard-Smithsonian CfA) have shown that cated. Colour variations of galaxies as a inhomogeneities in the galaxy distribu­ The observation of distant clusters function of look-back time would arise tion can be characterized by voids, mayaiso give information on the from main-sequence turn-off points and filamentary structures and strong clus­ geometry of the universe (Gunn and would depend on how many stars tering on small scales (e. g. de Lappa­ Gott 1972). For example, at z - 0.9, evolve at what rate off the main se­ rent, Geiler and Huchra 1986). On large whether a cluster had time to form de­ quence, on the star formation history scales, inhomogeneities are still pre­ pends on Ho, qo, and on the richness of and collapse time of galaxies. Demon­ sent at 100 h-1 Mpc. Understanding the the cluster. strating the evolution of galaxies (i. e. the large scale distribution of galaxies is For the understanding of these mat­ more distant galaxies to have a younger certainly one of the fundamental prob­ ters it is essential to have fair samplings population of stars) should be decisive lems of present observational cos­ of the universe. This is a long and for observational cosmology (see e. g. mology. difficult task wh ich would require exten­ Butcher and Oemler 1978, Hamilton Gravitationallenses with multiple im­ sive observational efforts. More precise­ 1985, Spinrad 1986). aging, due to the shear effect of a com­ Iy, it would be necessary to perform a Hubble diagrams for brightest cluster pact mass Iying near the light beam deep photometric and spectroscopic members have shown a remarkably coming from a distant object, have been survey of distant galaxy clusters to de­ small scatter but large uncertainties due observed (Liege Conference 1983). tect evolutionary effects, and a wide to stellar evolution are still present. These spectacular gravitational mirages angle medium deep redshift survey Moreover the properties of these galax­ correspond to exceptional configura­ for the study of large scale in­ les might be related to the density of tions. A more probable case corre- homogeneities. 37 Figure 1: Composite CCO image in the V-band ofthe central region (5.7 x 3.8 arcmin) ofcluster CI 1. Nor/h is up, east is left. The clustercore has been dimmed by - 1 mag in the image processing. The angular separation of the binary central system is 8 arcsec. (ESO 3.6 m + EFOSC; exposure time: 12 min).

Messenger (June 1987). They presented est galaxies, and (c) the approximative 1.2 Photographie Surveys enlightening results on the probability to number of objects brighter than - m (3) A deep photographie survey of detect a cluster as a function of redshift. + 2 within a counting erea. These clus­ specific areas was carried out by Gunn, A medium deep photographie survey ters should have redshifts almost entire­ Hoessel and Oke (1986) with the 5-m of Abell clusters in the southern hemi­ Iy at z :'S 004. 1 Prominent structures de­ Haie telescope and the 4-m Mayall tele­ sphere, by Abell, Corwin and Olowin is tected near the limit of the catalogue scope. This survey has led to the dis­ nearly complete. In its present form, this provide a basic list for observing covery of clusters up to z = 0.92. Coppi catalogue gives information on (a) the medium distant (i. e. z - 0.2 - DA) et al. reported observations of one of apparent size of clusters, (b) the mag­ southern clusters. these clusters in the 48th issue of the nitudes of the 1st, 3rd and 10th bright- 2. Observations SOUTI-IERN CENTRAL CALAXY 11 Candidates were selected from this catalogue on the basis of the apparent luminosity of the first ranked object, the diameter (i. e. the compactness), and an estimate of the density enhancement over the expected background. Four superb clusters were observed with EFOSC mounted at the Cassegrain focus of the 3.6-m ESO telescope at La Silla. Photometry in S, V and Gunn I was recorded. The sky was clear and the seeing - 1.5 arcsec. The multi-object spectroscopic mode of EFOSC (MOS) " = 0.27 was used to take spectra of the bright­ est objects. The techniques to operate the instrument and the automatie 3999 ~6a3 5367 6051. 6735 punching machine (PUMA 11) are de­ WAVELE:NCTII (X) scribed in the Operating Manuals (Dek- Figure 2: A spectrum of the southern central galaxy of CI 1, extracted from a multislit exposure with the B 300 grism. The measured redshift is z = 0.27. Spectra of 7 othergalaxies were taken 'Appreciable evolution is not expecled in thaI during this exposure. (ESO 3.6 m + EFOSC; aper/ure plate produced by the PUMA 11 machine.) range. 38 CI2

z = 0.316

Figure 3: CCO frame in the V band of the 4200 488-4 5568 6252 6936 central part (2.8 x 2.8 arcmin) of the compact WAVELENGTII (~) cluster CI 2. North is up, east is left. (ESO 3.6 m + EFOSC; exposure time: 18 min.) Figure 5: Spectra of two galaxies of cluster CI2 extracted from the same 90-min multislit exposure as in Fig. 4. Magnitudes are V = 20.8 and V = 21. 1 respectively. One of the spectra was shifted up for clarity.

ker and O'Odorico 1985, 1986; Oupin plished with a helium lamp through the shift distance is z = 0.27. A spectrum of and Oekker 1986). Results of MOS ob­ mask after each programme exposure. the southern central galaxy is shown in servations can be found in the Proceed­ Spectrophotometric stars were ob­ Figure 2. ings of the ESO-OHP Workshop on served for flux calibration. This spectrum was extracted from a CCO detectors (O'Odorico and Oekker The image of cluster CI-1 presented in 75-minute multislit exposure after filter­ 1986) and in the Messenger No. 47 (Ou­ Figure 1 is a mosaic of CCO frames ing for cosmic ray events and sky sub­ pin et al. 1987). taken in the V-band. Exposure time is traction. The detector was ESO CCO No. 11, 12 minutes. This cluster is regular, very Cluster CI 2 (Fig. 3) is regular, rich, which is a high resolution RCA CCO rich, with two giant cD type galaxies in compact, and has a tri pie core. The (15 ~m pixel). Oirect images needed to its centre imbedded in an extended en­ central galaxy (V = 19.3) is surrounded prepare the masks for multi-object velope and surrounded by a number of bya corona of E or SO galaxies (V - 21). spectroscopy were acquired in the 2 x 2 smaller elliptical or lenticular objects. It has a redshift of z = 0.315 (Fig. 4). The binned mode. The masks were punched The central part of the image has been similarity in redshift and the angular sep­ during the afternoon preceding the sec­ dimmed by 1 mag in the image process­ aration of CL 1 and 2 (60-70 h- 1 Mpc) ond observing night. Most spectra were ing. Oisk galaxies are found at larger could infer that they belong to the same taken through 20 arcsec slits. Round angular distance from the centre. large-scale structure. holes centred on field objects were used Brightest edge-on galaxies may be fore­ The central galaxy is very red (B-V = for the alignment of the masks on the ground objects. There is some evidence 1.6 mag). This is partly intrinsic (Iarge fields. Two iterations and a final check of subclustering around a third large 4000 Abreak amplitude) and partly due (about 15 min) were necessary to make galaxy 80 arcsec NNW. The apparent to the shift of the spectral energy dis­ the alignment. The spectra were ob­ magnitudes of the first ranked central tribution (K term). A large amplitude of tained with the B 300 grism, that gives a objects are V = 17.9 and V = 18.4. The the 4000 Abreak is generally suggestive dispersion of 230 Nmm and a total projected separation of their centres is of no ongoing star formation. Low val- wavelength coverage of 3700-7000 A. 8 arcsec. Reliable magnitudes can be Wavelength calibration was accom- measured down to V = 22.5. The red-

CENTRAL GALAXY 12

.D bO '0 c::: ." ::<: .D"'" '.:

z = 0.315 Figure 6: A blue image of the central part of cluster C12, showing an elongated structure

~200 488~ 5568 6252 6936 near two large elliptical galaxies. The pro­ jected angular distance between these two (1~) WAVELENGTII galaxies is 7.5 arcsec. The arc-like structure Figure 4: A spectrum of the central galaxy of cluster CI2 extracted from a 90-min multislit and the centre of the nearest galaxy are expOsure. The measured redshift is z = 0.315. Magnitude of the galaxy is V = 19.3. separated by 2.8 arcsec in projection.

39 ues of the 4000 Abreak amplitudes are Results based on the photometry of Soucail et al., 1988, Astron. Astrophys. Let­ mainly due to present or recent star these cluster and on first spectroscopic ter, in press. formation, or dilution by the continuum measurements will be published in Turner et al., 1986, Nature, 321, 142. of an active nuclear region (Dressler and forthcoming papers. Weinberg, 1976, Ap. J, 208, L 1. Shectman 1987). Spectra of galaxies extracted from the same MOS exposure Acknowledgements are shown in Figure 5. Examination of blue images of cluster I would like to express my thanks to CI 2 shows an elongated feature near ESO for the observing time allocated to two large elliptical galaxies (Fig. 6). In the project, to Dr. H. Corwin for com­ STAFF MOVEMENTS the V band, the images of the northern munication of his list of clusters, and to galaxy and of this possible arc-like Dr. H. Arp for his suggestions. I thank Arrivals structure are blended. The B band, that Dr. P. Magain for the introduction at the Europe: corresponds roughly to ultraviolet various modes of EFOSC. GUIRAO SANCHEZ, Carlos (E), wavelengths in the rest frame of the Associate cluster, is weil suited to register arc LONGINOTII, Antonio (I), Fellow structures located near an old-popu­ RUPPRECHT, Gero (0), Physicist­ lated elliptical galaxy. The present struc­ References Astronomer ture is bluer than most cluster galaxies WEIGLE, Renate (0), Secretary/ Butcher and Oemler, 1978, Ap. J, 219, 18. and, in that sense, is similar to other Administrative Assistant to the de Lapparent, Geiler and Huchra, 1986, Oirector General discovered giant arcs (Soucail et al. Ap. J., 302, L 1. 1988, and further references therein). O'Odorico and Oekker, 1986, in ESO-OHP Chile: The proximity of two large galaxies, Workshop: The Optimization ot the Use ot GREOEL, Roland (0), Fellow probably interacting, suggests an in­ CCO detectors. terpretation in terms of enhancement of Oressler and Shectman, 1987, MWLCO pre­ Departures print. star formation. On the other hand the Europe: Gunn and Gott, 1972, Ap. J, 176, 1. compactness of the cluster would be MATIEUCCI, Maria Francesca (I), favourable to the observation of gravita­ Gunn, Hoessel and Oke, 1986, Ap. J., 306, 30. Fellow tional lensing phenomena. High resolu­ Hamilton, 1985, Ap. J, 297, 371. tion imaging in subarcsec seeing and Hammer and Nottale, 1986, Astron. Astro­ Transfers spectroscopy are needed to pursue phys., 167, 1. MELNICK, Jorge (RCH), Associate (trom these possibilities. Hoessel and Shneider, 1985, A. J, 90, 1648. Europe to Chile)

Wirtschafts-Attache-Club Bayern Visits ESO Headquarters

On November 25, 1987, a visit was paid to ESO by the Wirtschafts-AttacM-Club Bayern, headed by Mr. P. Grillet from the Belgian General Consulate. The commercial attacMs from more than 15 countries were given a general introduction 10 ESO and an overview ofthe scientific and technological research carried out at this organization. After the formal session in the auditorium during which many questions were asked, in particular about the VL T project, a light lunch was served, later to be followed by a tour of the Headquarters. The photo was taken in the foyer, at the moment of arrival of the officials.

40 First Observing Run with DISCO was Successful F. MAASWINKEL, S. O'OOORICO, F. BORTOLETTO, B. BUZZONI, B. GILLI, C. GOUIFFES, G. HUSTER, and W. NEES, ESO

The Direct Image Stabilized Camera Option DISCO was tested for the first time from 29 November to 5 December at the 2.2-m telescope with a CCD cam­ era. The instrument was described in Messenger48, p. 51. It comprises a new adapter for the 2.2-m telescope with a newly designed XYZ oftset guider. It ofters the possibility to observe at the conventional f/8 focus, or alternatively at an f/20 focus. In the latter mode it is Possible to correct the motion of the astronomical image 50 times per sec­ ond. DISCO was mounted at the tele­ scope with the precious support of the TRS group and operated without prob­ lems from the first night. The aim of the run was in particular the test of the image correction system (fast tilting mirror, ICCD camera, VME based micro­ processor). As had been expected, the system gave only minor improvement in mediocre seeing conditions; during very good seeing, however, it provided a rather impressive image improvement. As an illustration, Figure 1 shows a Comparison of two exposures of 47 Tuc made without (Ieft picture) and with (right picture) image stabilization. The exposure time was 45 sec for both and a red gunn filter (I,c = 668 nm) was used. The stellar image diameters without stabilization were 1':2 FWHM, with that it was possible to improve the particularly useful. as the seeing was stabilization 0':9 was achieved. Thanks FWHM of the stellar images in long in­ observed to change on a rather short to the superior light concentration the tegrations from 0':85 (non-stabilized) to timescale (- 1 hour). stabilized image reveals more details 0':66 (stabilized). The possibility to A more detailed report on this test will and reaches fainter magnitudes. During switch remotely in a few minutes from be given at the Very Large Telescope part of a night the seeing was so good the f/8 to the f/20 mode was found Conference at ESO in March.

New Operational Limits for 1.5-m Danish Telescope

.A 14.5 cm thick spacer ring has been pages 4-7. Observers are urged to take sible to reverse the teleseope during the Installed between the mirror cell and the these into aeeount, when planning their night, as the CCD electronics would instrument adapter. Its purpose is to programme. have to be disconnected. eliminate residual spherical aberration. As the telescope can be used either For Coravel. the corner is at h. a. Recently analysed Schack-Hartman west or east of the base, there are two > +00: 10, decl. < -43 (west) and h.a. tests have shown the correction to be sets of limits; they are however symme­ < -00: 10, deel. < -43 (east). These Complete. trie. Telescope operation west of the limits appear more restrictive than those The longer focal length of the tele­ base has the advantage that tracking mentioned above. However, the control seope has changed the foeal plane (but not presetting) can be done into cable for the Coravel permits the ob­ seale from 16.07 to 15.83 +/- 0.02 part of the "danger" zone; the observer server to reverse the teleseope at night. aresee/mm. may override a first warning signal. Objects wh ich are inaccessible from Unfortunately. the extra length below The inaccessible corner for the CCD one side of the base, can therefore be the mirror cell implies restrietions for the camera is h.a. > +01 : 10, decl. < -47 observed from the other. use of eertain pieees of auxiliary equip­ (telescope west) and h. a. < - 01 : 10, A two-channel and a six-channel ment, in addition to those described in decl. < -47 (telescope east). In the west photometer have limits whieh are rather ESO Users Manual No. 3 "Danish 1.5-m position, tracking is allowed to decl. similar to those of the CCD eamera, and teleseope and Auxiliary equipment", -53, for h.a. > +01 : 10. It is not fea- telescope reversal is possible.

41 Mr. P. Nelrregaard, Brorfelde, has re­ gratings efficiencies, etc. will be added convenience of people who also want to programmed the microprocessor-based later. participate in the MIDAS workshop, the safety-system so that physical collisions Image Processing Group has scheduled between telescope base and auxiliary this workshop for 28th April, 1988. The 2. Portable MIDAS equipment remain impossible. programme will include sessions on H. Pedersen, ESO The developments of the portable general developments and new applica­ version of MIDAS are proceeding tions. Since the Portable version of according to schedule. The portable MIDAS will be made available during monitor has been tested successfully on this summer, a significant part of the allVAX ULTRIX system while internal MIDAS Workshop will be devoted to this verifications on a SUN and Bull SPS 7 topic. We anticipate giving a demon­ system are in progress. The full Table stration of a prototype of the Portable MIDAS Memo File System has been ported using the MIDAS during the workshop. A tentative ESO Image Processing Group new set of table interface routines. The agenda will be sent out to all MIDAS Fortran application code has been con­ sites together with other material for the verted from VAXNMS Fortran to stan­ Data Analysis Workshop. People in­ dard Fortran with 5 simple extensions terested in participating in the Work­ 1. Application Developments (i. e. INCLUDE, IMPUCIT NONE, !-com­ shop should contact either the IPG or An extended CCD reduction package ments, ENDDO and long internal the ST-ECF. made by S. Jörsäter, Stockholm Obser­ names). A preprocessor was made for vatory, has been implemented in Fortran compilers which do not support 4. MIDAS Hot-Line Service MIDAS. This package includes tools for these extensions. standard reductions of CCD frames We are also happy to announce that a The following MIDAS Support ser­ such as dark current and sensitivity new UNIX system programmer, Carlos vices can be used in case of problems corrections. A set of sophisticated rou­ Guirao Sanchez, has joined the IPG. to obtain fast help: tines also allows the user to make One of his main responsibilities is to • EARN: MIDAS DGAES051 mosaics of several frames including develop and maintain the system de­ • SPAN: ESOMC1 ::MIDAS photometric adjustments of the indi­ pendent interfaces of MIDAS. He will • Tlx.: 52828222 eso d, attn.: MIDAS vidual exposures. therefore be strongly involved in the im­ HOT-UNE A calibration directory structure is be­ plementation of MIDAS on new sys­ • Tel.: +49-89-32006-456 ing created. This will contain general tems. Also, users are invited to send us any calibration data useful for reduction of suggestions or comments. Although a telephone service is provided, we prefer data from La Silla. The first data to be 3. MIDAS Workshop included are tables of spectral lines, that requests are submitted in written flux of standard stars, and extinction The next Data Analysis Workshop, form through either electronic networks data. Information on filter transmission arranged by the ST-ECF, will be held on or telex. This makes it easier for us to curves, performance of ESO CCD chips, the 26th and 27th April, 1988. For the process the requests properly.

Unusual Building for the ESO NTT Arrives at the La Silla Observatory

Early in February, M/S Cervo arrived in the harbour of Valparaiso, Chile, with the packaged parts for the building which will house the ESO New Technol­ ogy Telescope (NTT). Soon thereafter, the 350 ton load was hauled by road to the ESO La Silla observatory in the Atacama desert, same 600 km north of Santiago de Chile. Here, at one of the best astronomical sites on earth, the giant mechanical puzzle will now be put tagether to form one of the strangest telescope domes ever seen. The ND will be mounted in a rotating building with an unusual octagonal shape. It has been designed to ensure maximum exposure of the telescape to the external environment during obser­ vation, while protecting the structure from strong winds and dust. Further­ more, the floor of the building is actively cooled and the temperature in the tele­ scope room and in the instrument rooms is maintained at the level of the The 3.58-m NTT main mirror being polished at Zeiss, Oberkochen, F.R.G. 42 Aerial view of La Silla. The site for the NTT building is indicated byan arrow. Photograph by C. Madsen, February 1987.

outside temperature at night. These European industries. One of these is Here are some data for the ND pro­ features will improve the ND perform­ RKS France who manufactured an ex­ ject: ance, as compared to other telescopes, tremely precise roller bearing with Estimated price of the ND project: since there will be less turbulence in the diameter of no less than 7 m, a key 25 million DM surrounding air and the images of as­ component of the rotating system. Size of ND building: 18 m (high) x 17 m tronomical objects will therefore be x 17 m sharper. It will take almost six months to com­ Weight of building: 250 tons The exact shape of the building was plete the erection of the rotating building Length of telescope tube: 8 m determined by wind tunnel tests at the at La Silla. Weight of telescope: 125 tons Technical University of Aachen. The ND itself has now been dis­ Main mirror material: Zerodur The building was conceived at ESO mounted and will be shipped to Chile Size of main mirror: Diameter 3.58 m; and designed and manufactured by a with arrival in the course of May 1988. It Thickness 24 cm; f/2.2 consortium of Italian companies (MEC­ will then be erected inside the rotating Weight of main mirror: 6 tons NAFER, Mestre, ZOLLET, Belluno, and building and it is expected that the first Foci: 2 Nasmyth platforms, f/11, with ANSALDO Componenti, Genova) in sky observations begin at the end of fixed infrared and visual multi-func­ close cooperation with a number of 1988. tion instruments.

ALGUNOS RESUMENES

Observaciones infrarrojas de estrellas variables, con el telescopio de un metro.

Muchas estrellas son variables. EI primer gigantescas: su radio mide entre cien y mil de la luz de la estrella central es absorbida; observador de estrellas variables fue el veces el radio dei Sol, 10 que las hace enton­ en este caso detectamos solamente una holandes Fabricius, quien a fines dei siglo XVI ces mas grandes que la orbita de la Tierra. Su fuente infrarroja. descubrio, en la constelacion de la Ballena luminosidad es mil a cien mil veces la dei Sol. Muchos de estos objetos infrarrojos fueron (Cetus), un objeto estrario que aparecia y Las teorias de evolucion estelar predicen descubiertos por el astronomo frances N. desaparecia, con un periodo de un ario. Este que, en algunos billones de arios, el Sol tam­ Epchtein, utilizando el telescopio de un me­ fenomeno estaba en plena contradiccion con bien sera una Mira por un millon de arios tro, en La Silla. Ahora, despues de tres arios, el dogma cl

43 pag.24) tiene un periodo de 550 dias y las 353.60-0.23, en 300 dias la luminosidad estrellas OH/IR 285.05+0.07 (Fig. 1, pag. 24) cambi6 de 50 mir a 250 milla dei Sol. En tales y OH/IR 353.60-0.23 (Fig. 2, pag. 25) de mas condiciones, es muy importante tener per­ de tres alias (todavia no se conoce su manentemente telescopios einstrumentos periodo con precisi6n). Estos objectos san en condiciones perfectas para poder obser­ sitios donde ocurren cambios fenomenales; var estos fen6menos cuando ocurren. la estrella OH/IR 285.05+0.07 estuvo estable EI autor agradece a todas las personas que durante 200 dias, con una luminosidad 40 mil en La Silla se esfuerzan para que el Obser­ veces la dei Sol y, en menos de 150 dias, su vatorio, los telescopios y los instrumentos luminosidad creci6 hasta lIegar a ser 60 mir funcionen 6ptimamente. veces la dei Sol. En el caso de OH/IR T. Le Bertre (trad. R. Huidobro)

Noticias dei Gran Telescopio (VLn

Despues de que fue aprobado el proyecto aluminio de 8 m podria construirse en menos el dia 8 de Diciembre, se esta constituyendo de dos alias, en caso de que se presentaran progresivamente la estructura dei manejo dei (inesperadas) dificultades con los espejos de proyecto. vidrio. Se establecera el plan final dei proyecto Se esta preparando un prediselio mejor tan pronto se tome la decisi6n sobre el mate­ elaborado dei edificio (ver dibujo CAD en rial dei cual sera confeccionado el espeja. pag. 5). EI presente concepto dei esquema Par el momente se encuentran en competen­ esta basado en el cobertizo inflable (se esta cia dos tecnologias: Zerodur de Schott y montando un modele a media escala en silice fundida de Corning. Se decidira cuando Chile). EI centro de la cu pu la estara ubicado se reciban las propuestas finales de las dos en el nivel de la base dei telescopio, y asi el firmas. En ambos casos se ha fijado el es­ espejo primario estara siempre protegido dei pesor dei espejo en 175 mm. Esto parece ser viento directo. Aperturas en la base dei un compromiso aceptable entre el coste y la edificio permitiran una ventilaci6n controlada rigidez. Como alternativa se esta desarrollan­ de la superficie dei espeja. Se estan hacien­ do la tecnologia de aluminio y se fabricara un do pruebas de este concepto en el tunel de espejo de prueba de 1.8 m. Una pieza de viento dei Potitecnico de Lausanne. D. Enard

Contents H. van der Laan: Key Programmes on La Silla: a Preliminary Enquiry ...... 1 Management Changes on La Silla ...... 2 J. Breysacher: Same Statistics about Observing Time Distribution on ESO Telescopes .. 3 R. M. West: Wide-field Photography at the 3.6-m Telescope? ...... 4 Opportunities at the ESO SchmidtTelescope ...... 4 D. Enard: VLT News 4 ~~~P~~ 6 Summer School in Astrophysical Observations 6 R. W. Hanuschik, G. Thimm and J. Dachs: SN 1987A: Spectroscopy of a Once-in-a- Lifetime Event 7 From the Editors 7 Tentative Time-table of Council Sessions and Committee Meetings for First Half of 1988. 7 The Editor: SN 1987A (continued) ...... 9 V. A. Ambartsumian: Some Prospects of Galactic and Extragalactic Studies ...... 10 H. Butcher: Galactic Chronometry with the Coude Echelle Scanner...... 12 J. K. Webb et al.: High Resolution CASPEC Observations of the z = 4.11 aso 0000-26 .. 15 C. Waelkens: Remote Observing: Nine Days in Garehing ...... 18 La Silla Snowstorm ...... •...... 19 ESO Exhibitions ...... 20 Central area of the Gum Nebula 22-23 1. Le Bertre: Monitoring OH/IR Stars at the 1-m Telescope 24 Visiting Astronomers (April 1 - October 1, 1988) ...... 25 C. Arpigny et al.: Pre- and Post-Perihelion Spectrographic and Photometrie Observations of Comet Wilson (1986e) 27 H. Zinnecker and C. Perrier: Resolving Young Stellar Twins ...... 31 K. Mattila and G.F.O Schnur: When Dark is Light Enough: Measuring the Extragalactic Background Light...... 34 E. Giraud: Multi-object Spectroscopy with EFOSC: Observations of Medium Distant Clusters of Galaxies ...... 37 Statt Movements ...... 40 Wirtschafts-Attache-Club Bayern Visits ESO Headquarters ...... 40 F. Maaswinkel et al.: First Observing Run with DISCO was Successful ...... 41 H. Pedersen: New Operational Limits for 1.5-m Danish Telescape ...... 41 ESO Image Processing Group: MIDAS Memo 42 Unusual Building for the ESO ND Arrives at the La Silla Observatory 42 Aigunos Resumenes ...... 43

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