THE MESSENGER

( , New Meteorite Finds At Imilac No. 47 - March 1987 H. PEDERSEN, ESO, and F. GARe/A, elo ESO

Introduction hand, depend more on the preserving some 7,500 meteorites were recovered Stones falling from the sky have been conditions of the terrain, and the extent by Japanese and American expeditions. collected since prehistoric times. They to which it allows meteorites to be spot­ They come from a smaller, but yet un­ were, until recently, the only source of ted. Most meteorites are found by known number of independent falls. The extraterrestrial material available for chance. Active searching is, in general, meteorites appear where glaciers are laboratory studies and they remain, too time consuming to be of interest. pressed up towards a mountain range, even in our space age, a valuable However, the blue-ice fields of Antarctis allowing the ice to evaporate. Some source for investigation of the solar sys­ have proven to be a happy hunting have been Iying in the ice for as much as tem's early history. ground. During the last two decades 700,000 years. It is estimated that, on the average, each square kilometre of the Earth's surface is hit once every million years by a meteorite heavier than 500 grammes. Most are lost in the oceans, or fall in sparsely populated regions. As a result, museums around the world receive as few as about 6 meteorites annually from witnessed falls. Others are due to acci­ dental finds. These have most often fallen in prehistoric times. Each of the two groups, 'falls' and 'finds', consists of material from about one thousand catalogued, individual meteorites. The total number of frag­ ments is considerably higher, since many break up when hitting the atmo­ sphere. Mineralogically, they can be di­ vided into three classes: stones, irons and stony-irons. Falls are largely stony, while finds have a high percentage of irons. This is due to the stony meteor­ ites' faster erosion and lesser visibility. The geographical pattern of falls is strongly correlated with population den­ sity: most are reported from Europe and North America. Finds, on the other

Supernova 1987A in LMC: Figure 1: The 19-kg fragment in its BO-em diameter erater. The meteorite protrudes about see pp. 26-35 5 em above the erater floor and reaehes approximately 1B em below. It is remarkable that sueh a small strueture has resisted erosion during 166 years, possibly mueh longer. Imilac Meteorites

Other areas where many meteorites are found are some of the world's desert regions, e. g. Western Australia, the North American prairies, and the Ataca­ ma desert in Chile. At the latter, the annual precipitation is lower than any­ where else on the earth, less than 5 mm, wh ich obviously eases the meteorites' preservation. As a result, one of the Atacamenean meteorites, found at Tamarugal, has a terrestrial age of 2,700,000 years, the oldest known. Dur­ ing the last century, many mineral pros­ pectors travelled thraugh Atacama, in search for precious ores. Occasionally, they came upon iron meteorites which they brought home, often unaware of the material's true character. They gave much less attention to stony meteorites, though these undoubtedly also have been preserved in large numbers. f.·'~~!.~~,b"'J~·~' ~v~• The Atacama desert is noted for its / f deposits of nitrates. These were ex­ Figure 2: The 35-kg fragment before exeavation. The diameter of the erater is 125 em. The meteorite reaehed about 6 em above and 14 em below the erater floor. ploited, on a huge scale, during the first decades of this century. In the process, several meteorites were found. Many Chilean meteorites are of the rare Pallasite type (see box), for wh ich way to many museums and private col­ posed, in circular impact craters (Fi­ reason they most likely stem fram a lections, all over the world. The largest gure 1 and 2) of diameter 80 and single fall. They carry names which specimen known, 198 kg, is in the Brit­ 125 cm. In both cases, the crater floors correspond to geographical locations ish Museum. Another fragment, original­ were about 15 cm below level and co­ scattered over a 100 by 100 km area. In Iy 95 kg, is in Copiapo. The total amount vered with sm aller pebbles than the most cases, however, the find site was of recovered material, plausibly originat­ surraunding desert. The edges were reported without precision and, until ing at Imilac, is calculated at 500 kg white, bringing into view a soft under­ recently, it was believed that the (Buchwald, 1975). ground material, rich in gypsum. The meteorites had been picked up inside a crater of the 35-kg meteorite did not 100 by 500 metre area near the small have an elevated rim, except possibly The New Finds salt-pan Salar de Imilac, about 170 km towards east. This can be concluded from Antofagasta. At this place, there is Following the visit of several expedi­ from the inspection of a stereo-photo a crater-like excavation, 8 metres in tions, it was believed that all large taken prior to the excavation. Its depth diameter. This may have been made by meteorites had been collected. We can, is estimated at 5 to 10 cm. The 5-kg iron Indians in search for the fancied iran however, report the recent discovery of was Iying, nearly fully exposed, on top of vein. Several minor excavations on the three more meteorites, totalling 59 kg. the desert surface, and apparently not neighbouring hills indicate places The find was made by one of the au­ 'in situ'. Therefore, we cannot exclude where, in the past, meteorites have been thors (F. G.) who is a geologist'. During the possibility that it is a transported collected. Still, the top-soil contains water prospection for a mining enter­ mass, originally found somewhere else. many small iron fragments, weighing ty­ prise he learned about the meteorite fall The 5-kg meteorite measures 16 by pically 1 gramme. at Imilac. A local resident told him that 13.5 by 10 cm. It is an elongated lump There is no reliable account of the some meteorites had been found sever­ without any sharp corners. The 19-kg meteorite's fall. The first fragments were al kilometres south-west of the 'crater'. meteorite is roughly cubic, 23.5 by 18.5 found around 1820. Buchwald (1975) During his own search he managed to by 18 cm. One of its edges is quite estimates that the fall occurred several locate a further three. They have masses sharp, clearly indicating the meteorite as hundred years earlier. Fram geological of 5, 19 and 35 kg, respectively. a fragment. The 35-kg meteorite is considerations, Martinez (private com­ The new meteorites were spotted at slightly banana-shaped and measures munication) deduces an age of about 3,250 metres altitude, on some promon­ 50 by 24 by 15 cm. All three meteorites 500 years before present. Nearby, an­ tories wh ich stretch towards east and have specific gravities near 4.6 gram­ cient Indian populations could conceiv­ north-east from a 3,870 m high moun­ mes/cm3, which is typical for Pallasites. ably have forged tools or ornaments tain, Morro de La Mina. The find loca­ The submerged parts of the two large from meteoritic iran. This might put a tions form an appraximately equilateral specimens are covered by a thin crust of minimum age to the fall. However, no triangle, with side lengths of 900 metres. corrosion products, due to the presence such artifacts have yet been identified. The centre of that triangle is 7 km south­ of nitrates in the soil. Another dating method relates to the west of the 'crater'. The two largest Universidad dei Norte in Antofagasta decay of radioactive isotopes, activated meteorites were Iying, only partially ex- has inspected two of the meteorites and by cosmic ray irradiation prior to the fall. classified them as Pallasites. For To our knowledge, no such measure­ reasons of similar surface texture and • Editor's note: F.G. is the husband of ESO's ments have been published. secretary in Santiago. Mariam G., through whom specific gravity, we believe that also the Imilac meteorites have made their scientists at La Silla were informed about lhe find. third meteorite belongs to that group.

2 Since, from the whole Earth, only 33 rich in olivine silicates (Greenberg and Pallasite-finds (and 2 falls) have been Chapman, 1984). Following the as­ Tentative Time-table described, this is a strong indication that teroid's colling, the top layer of silicates the new specimens are part of the well­ may have been stripped off, exposing of Council Sessions known Imilac fall. the now contracted and cracked Pallasi­ and Committee Meetings The site of the old crater-like excava­ tic layer to erosion. for First Half of 1987 tion was also visited. In the 'splinters The asteroidal origin could, in princi­ May 18 area' about 1 kg of minor fragments (0.1 pie be ascertained by orbital calculation Users Committee May 19 Scientific Technical to approximately 250 grammes were of meteorite falls. This has been done on Committee collected. A few particles were found up three occasions (the falls at Pffbram, May 20-21 Finance Committee to 1,000 m north-east of the 'crater'. Lost City, Innisfree) but none of the May 26-27 Observing Pro­ Otherwise, we can confirm Buchwald's meteorites in question were Pallasites. grammes Committee, statements as to the shape and extent Ground-based observations may Venice of the area. We estimate that it still holds nevertheless help solving the question. June 3 Committee 01 Coun­ of the order of 1,000 kg of meteoritic By infrared spectroscopy three candi­ eil, Bruges iron. date parent-asteroids have been found: June 4 Council, Bruges 246 Asporina, 289 Nenetta, 446 Aeter­ All meetings will take place at ESO in nitas (Cruikshank and Hartmann, 1984, Garehing unless stated otherwise. The Imilac Strewn-Field Scott, 1984). Their spectra show an ab­ The existence of the splinters area sorption band at 1.06 l-lm, as does indicates that a large chunk of the olivine in its meteoritic form. Also the References meteorite suffered a violent break-up. general trend of the spectra is consis­ This must have happened at a late point tent with the presence of a metallic Buchwald, V. F., 1975, Handbook of lron of the trajectory through the atmo­ phase. Meteorites, University of California press, sphere. Its mass exceeded, by far, those It is rare that asteroids can be associ­ Berkeley, vol. 1-3. which fell further to the south-west. ated with one particular type of mineral. Cruikshank, D. P., and Hartmann, W. K., Therefore, it seems likely that the parent Detailed studies of asteroids and com­ 1984, Seienee 223,281. body arrived from south-west, rather ets will, in general, require spacecraft to Greenberg, R., and Chapman, C. R., 1984, learus, 57, 267. than opposite. The splinters area is ap­ do "sample-return" missions. Such are, Nininger, H. H., 1952, Out of the Sky, Dover, proximately aligned with the new find in fact, being considered. But perhaps it New York. locations, giving a further argument for is superfluous to include Asporina, Peck, E., 1979, Sky and Teleseope, 58, their association. Measured from north Nenetta or Aeternitas in the itinerary: the p.126. over east, the azimuth of the combined stuff may already be in our hands ... Scott, E. R. D., Nature, 311, 708. strewn-field is 47°+/-3°. The new finds show that the strewn­ field is at least 8 km long and about 1 km wide. It cannot be excluded that Pallasite Meteorites the nearby 3.5-km diameter Steinheim Ba­ some of the meteorites collected a long sin. There is geologieal evidenee that both Meteorites ean be divided into three clas­ time aga were found in the 'new' area. are meteoritie, but the proof (meteoritie ses: Stones, Irons, and Stony Irons. A sub­ We did, in fact, notice a small number of materialj is not yet found. It may long sinee group of the latter is quite peeuliar: an iron/ minor holes from where it is conceivable have weathered away. nickel mixture forms a sponge-like strue­ that specimens (in the 1O-kg class) have ture. Olivine erystals, of eross-seetion 1 to been picked up. Indications are that the 10 mm fill out the holes, so that the volume Strewn-fields strewn-field is even longer than men­ ratio metal/olivine is about 1 : 1. The first tioned. This topic, and other aspects of such meteorite was found in 1771/72 by the The hyper-sonie velocity, 15 to 72 km/ the Imilac fall, are discussed in a forth­ German explorer Peter Simon Pallas, dur­ sec, with whieh meteorites enter the Earth's coming thesis work by E. Martfnez, Uni­ ing his travels through East Russia. Palla­ atmosphere, ereates a shoek, whieh offen versidad dei Norte. The total weight of site meteorites are quite rare: less than 1 forees the meteorite to break up. Masses less than a few tons will reaeh the ground recovered material is now about 560 kg. per cent of all falls and 3.5 per cent of all finds belong to this group. with sub-sonie speed, 100-300 metres per To this adds the estimated 1,000 kg of seeond. Small partieles tend to fall along small meteorite particles stillieft in the Meteorite Craters steeper trajeetories than heavier ones. This top-soil. Although impressive, at least ereates a eharaeteristie elliptie distribution one other Pallasite find is larger. That at Upon hitting the ground, a large meteor­ pattern, with partiele size inereasing along Brenham, USA, had a mass of 4.5 tons ite may form a erater. If the terminal velocity the major axis, in the direetion of flight. This (Nininger, 1957, Peck, 1979). It too is suffieiently high, the eonversion ofkinetie simple pieture holds, if just one event of suffered violent fragmentation. energy will lead to the meteorite's instan­ fragmentation took plaee. Strewn-fields taneous evaporation. An explosion erater is ean reaeh eonsiderable sizes. The Gibeon­ thereby formed. Smaller masses may form fall at South-West Afriea eovered approxi­ Asteroidal Origin for Pallasites impact eraters. 13 genuine meteor eraters mately 100 by 400 km. (or erater fjelds) are known and some 100 Pallasite meteorites form a rather others are eonsidered probable. The largest homogeneous group, clearly distinct is the meteorite erater in Arizona, USA, Meteorite Collections from the other type of stony-irons, the whieh has a diameter of 1,200 metres. Third Colleetions of meteorites exist at many mesosiderites. They may hold clues to on the list is the more than 100,000-year museums. Prominent between these are the origin of solar-system bodies. Their old, 370-m diameter erater at Monturaqui. the museums of natural history in London, creation is therefore a much debated This is only 60 km from the loeation men­ Paris, Vienna, and the Aeademy of Sei­ issue between 'cosmogonists'. One tioned in the artiele, but unrelated. Euro­ enees, Moseow. The heaviest meteorite on pean probable meteorite eraters inelude the theory says that they formed in as­ display in Europe is 'Agpalilik', a 14-ton iron 15-million-year-old, 27-km-diameter Nörd• from Greenland, now at the Geologieal teroids, at the interface between a mol­ linger Ries strueture in West Germany and Museum, Copenhagen. ten core and a partially molten mantle,

3 Giant H 11 Regions and the Quest for the Hubble Constant J. MELNICK, ESO

The search for yardsticks with which The Friedmann solutions have a ground out to distances of about 5 Mpc. to measure cosmic distances is one of singularity where the radius of the Uni­ One of the major tasks of the Hubble the fundamental endeavours of obser­ verse is zero and mass density infinite. Space Telescope will be to extend these vational astronomy but this is a difficult In fact the Hubble relation (V = HoR) observations to larger distances. Our task and it was not until the beginning of implies that some time in the past all Milky Way is a member of a group of this century, when astronomy was al­ galaxies were on top of each other. For galaxies (the Local Group) of roughly ready hundreds of years old, that the obvious onomatopoeic reasons the sin­ 1 Mpc in diameter of which the An­ size of our own Galaxy could be deter­ gularity is called the "Big-Bang"; thus dromeda nebula is also a member. The mined. The yardstick which made this the singularity is interpreted as a magni­ Local Group is itself member of a larger possible was the discovery, by Miss ficent cosmic firework which marked the agglomeration of galaxies known as Henrietta Swan Leavitt, of a relation be­ beginning of time. Friedmann cos­ the Local Supercluster which is domi­ tween the period of pulsation of Delta mologies can be parametrized in terms nated by the Virgo cluster, distant Cephei stars and their luminosities. The of the expansion rate Ho, the mass den­ 15-20 Mpc from the Local Group. Cepheid period-Iuminosity relation was sity Qo, and an elusive parameter called Thus, the expansion of the Universe is subsequently calibrated by Harlow the cosmological constant, 1\., which perturbed at small distances by these Shapley who then used it together with has bedeviled cosmology since it was mass concentrations and it is necessary the absolute magnitudes of RR Lyrae first introduced by Einstein himself. to measure velocites and distances to stars to measure the Milky Way. Einstein's theory allows for the ex ist­ galaxies beyond the Virgo cluster in or­ Soon after the galactic distance scale ence of this additive constant which der to derive a meaningful value for the was determined by Shapley, a great represents either an additional attractive Hubble constant. Hubble's own deter­ controversy arose as to whether the spi­ or repulsive "gravitational" force but mination was too large because of a ral nebulae, wh ich were very weil known there is no compelling reason in the n'umber of errors, including a large error at the time from the work of William and general theory of relativity for this force in Shapley's calibration of the cepheid John Herschel and others, were galactic to exist in nature. It is merely allowed by period-Iuminosity relation. But even to­ or extragalactic objects. The contro­ the mathematical structure of the equa­ day, almost 60 years after the pioneer­ versy was not settled until after the 100­ tions. Einstein found that in order to ing work of Hubble and Humason, as­ inch Hooker telescope was brought into construct a statical model for the Uni­ tronomers have not yet agreed on the operation at Mount Wilson, and Hubble verse, he had to introduce arepulsion exact value of Ho although most agree discovered cepheid variables in the term to balance gravity. Of course, in that it lies between 50 and 100 km/sec/ Great Andromeda Nebula (M 31) in 1924 1917 everybody, including Einstein, Mpc. In fact, the opinions are divided in and later in other spiral nebulae. The thought that the Universe was static! two groups; the Ho = 50 camp cham­ "island universe" hypothesis of Kant With no cosmological constant (I\. = pioned by Sandage and Tammann, and was thus proved and for the first time it 0), Friedmann's models give simple rela­ the Ho = 100 camp whose strongest was observationally established that the tionships between the age of the Uni­ advocates are Aaronson and co-work­ Universe extends far beyond the limits verse (Ta, the time elapsed since the ers and G. de Vaucouleurs. Both camps of the Milky Way. Big-Bang) and the Hubble constant and defend their cause with excellent obser­ Soon after the work of Hubble, sever­ Qo' In general Ta is always smaller than vations but the controversy is still far al astronomers began to measure radial Ho-1 and it is equal to Ho-1 if the mass from being resolved. The discrepancy is velocities of galaxies and discovered density is zero (Qo = 0). also philosophical; at Ho = 50, the Big­ that these velocities increased linearly Thus, the calibration of the Hubble Bang age of the Universe is consistent with distance. Thus, if R is the distance relation provides not only the most pow­ with the age of the oldest stars in our of a galaxy and V its radial velocity, the erful cosmic yardstick but also a means Galaxy while for Ho = 100 that age is too two are related as, of determining the age of the Universe. It short and, in order to maintain consis­ is not yet known how important the de­ tency with the Friedmann models, the V = Ho x R celeration and the gravitational repul­ cosmological constant must be revived. where Ho is a universal constant. In sion terms in Friedmann models are but, In this article I would Iike to present a 1931, Hubble and Humason calibrated at least in principle, they can be deter­ new method (in fact a new version of an this relationship in galaxies where they mined observationally and this is one of old method), developed in collaboration had previously found Cepheid variables the major tasks of modern observational with Roberto Terlevich from the RGO and obtained a value of Ho = 558 km/ cosmology. An important constraint on and Mariano Moles from the IM in sec/Mpc for this constant wh ich is now the Hubble constant is that, for !\. = 0, Granada, wh ich uses the properties of known as the Hubble constant. Almost Ho-1 must be larger than the age of the giant H 11 regions as distance indicators. ten years before the work of Hubble and Galaxy. At the time of Hubble's work, Humason, the Russian mathematician this limit was the age of the earth, about Giant H 11 Regions as Distance In­ Alexander Friedmann had found a solu­ 4,000 million years. Today, from the dicators tion of Einstein's General Relativity theory of stellar evolution and from ob­ equations which predicted that the Uni­ servations of globular clusters the age of In the early 1960s Sersic discovered verse should be either expanding or our galaxy is estimated to be more than that the diameters of the largest H 11 contracting according to a linear relation 16,000 million years. regions in spiral galaxies increase with between velocity and distance. Thus, galaxy luminosity. This correlation was immediately after Hubble's results were further developed by Sandage and it The Determination of Ho published, the idea that our Universe is has since been used by many workers expanding gained universal accept­ Periods and luminosities of Cepheids as a cosmic yardstick. The correlation, ance. can be reliably determined from the however, is not useful much beyond

4 HII Galaxies obtained with the 3.6-m and 2.2-m tele­ scopes at La Silla and the line-widths with the Echelle spectrograph at the 4-m telescope of Cerro Tololo. • The slope of the correlation is ...... 4.5 ± 0.3 and rms scatter is ologL (H rl) = ~ • I 0.32 but the dispersion is correlated (f) 41 • • with the chemical composition of the (f) nebular gas. A Principal Component CJ) •• L • • • Analysis of the data leads to the follow­ (1) •• • ing relation. '-.../ • Log L(H } = 5 logo - 10g(O/H} + constant ...... Q::l.. 40 ß :r: '-.../ ... • Figure 2 presents a plot of L(H rl} ver­ --l • •••• sus the distance independent parameter CJ) • Mz = 05/(O/H} for 29 H 11 galaxies with 0 accurate metallicities. --l 39 The linear fit to the data has a slope of 1.03 ± 0.05 and an rms scatter of olog (L(H fl)) = 0.21, which is comparable to • the scatter of the Tully-Fisher relation. Since H 11 galaxies can be easily ob­ 1.1 1.2 1.3 1.4 1.5 1.6 1.7 served out to very large distances, the correlation between L(H ß} and Mz can Log () (km s-1) _indeed be a very useful cosmic Figure 1: Logarithmic plot of the integrated Hf, luminosities ofH 11 galaxies as a function of their yardstick provided its zero point can be line-profile widths in velocity units. Ho = 100 km/sec/Mpc is assumed. accurately determined. As I discussed above, the extragalac­ tic distance scale is tied to the galactic scale via cepheid variables. Thus, in or­ 20 Mpc where the angular diameters of or more extremely luminous giant H 11 der to calibrate the zero point of the even the largest giant H 11 regions be­ regions, others are essentially star-like (L(H 1l), Mz} relation for H 11 galaxies we come comparable with the seeing disks. objects where only the giant H 11 region must use giant H 11 regions in nearby However, the linear diameters of giant component is visible and are probably spiral galaxies. The properties of many H 11 regions correlate very weil with the truly intergalactic, galaxy-size H 11 re­ such H 11 regions have been extensively widths of the nebular emission lines, gions. Figure 1 presents a log plot of studied mainly by Sandage and which in these bright H 11 regions are L(H fl} versus 0 for a sampie of H 11 galax­ Tammann who used the Sersic-San­ extremely easy to measure. ies for which the luminosities have been dage correlation to calibrate distances. Thus, replacing H 11 region diameters by line-widths in the Sersic-Sandage correlations, a new powerful distance indicator is obtained. However, the emission line profile widths also corre­ Giant HII regions late extremely weil with the luminosities of giant H 11 regions and this correlation has the advantages (over the previous 40 • ones) that it does not require inclination corrections for the magnitudes of the ...... '<" parent galaxies and that the reddening I corrections to the giant H I1 region (f) luminosities can be done in a self-con­ (f) CJ) • sistent way using the Balmer decre­ L (1) ments. Thus, the method I am going to '-.../ discuss here relies on the correlation • between Hfl luminosity (L(H 1l)), the emis­ sion line-profile widths (o) and the Oxy­ • gen abundances (O/H) of giant H 11 re­ • gions. Since, to obtain a meaningful value of Ho, we must observe galaxies beyond • the Virgo cluster we have applied the • method not to giant H 11 regions in dis­ tant spiral galaxies (wh ich would be too faint) but to the so-called "intergalactic H 11 regions" or "H 11 Galaxies" wh ich 1.1 1.2 1.3 may be defined as being dwarf galaxies with the spectrum of giant H 11 regions. Log () (km s-1) In fact, while some H 11 galaxies are Figure 2: Logarithmic plot of the integrated HfI luminosities of giant HI/ regions in nearby clearly dwarf irregular galaxies with one galaxies as a function of fine-profile width.

5 TABLE 1: The local distance scale luminosities predicted by this equation to the observed fluxes corrected for ex­ Galaxy Number ot Distance (Kpc) Notes tinction. Before discussing the results, HII regions adopted ST however, I must say a few words about LMC 1 50.1 52.2 Local Group radial velocities and about Malmquist SMC 1 60.0 71.4 Local Group bias. NGC 6822 2 457 616 Local Group M 33 4 682 817 Local Group NGC 2366 3 3160 3250 M81 group Corrections ... NGC 2403 3 3160 3250 M81 group Holmb 11 1 3160 3250 M81 group (a) The Radial Velocities IC 2574 2 3160 3250 M81 group If one knows velocities and distances, NGC 4236 2 3160 3250 M81 group Ho is simply obtained as Ho = V/R. The M101 3 6920 6920 radial velocity of almost any galaxy can be easily obtained with present-day in­ strumentation from the Doppler shift of We have studied the correlations be­ galaxies, the global luminosities of giant their spectral features. In the case of H 11 tween internal parameters for 22 giant H 11 regions are a function only of their galaxies, for example, even at large dis­ H II regions in galaxies whose distances velocity dispersion, radii and chemical tances the Doppler shifts of the emis­ have been determined trom studies of composition. Moreover, the RC 02 de­ sion lines can be obtained with expo­ Cepheid variables. Table 1 summarizes pendence is strongly reminiscent of the sures of only a few seconds. However, the relevant parameters of these galax­ Vi rial theory and Terlevich and I have the Earth, the Sun and the Galaxy are ies together with the distances we have proposed that giant H II regions are moving and therefore we must subtract adopted. Also listed in the Table are the gravitationally bound objects, in which from the observed velocities the motion distances adopted by Sandage and case the correlations would have a very of our frame of reference. Thus, we must Tammann (ST) in their calibration of the simple physical interpretation. But, as remove the motions of the Sun around Hubble constant. .almost everything in astronomy, this in­ the centre of our Galaxy, of the Galaxy in In a few cases there are differences terpretation is controversial and its dis­ the Local Group, of the Local Group between the scale adopted here, which cussion will take us far from our present towards the Virgo Cluster and of the is essentially the scale adopted by goal of getting to Ho. Virgo Cluster relative to the Cosmic Mi­ Aaronson and co-workers in their cali­ From the (L{HIIL Mz) relation for giant crowave Background. In addition, the bration of the Tully-Fisher relation, and H 11 regions we obtain a zero point of galaxies themselves may be falling into the Sandage-Tammann scale. These 41.32 ± 0.08 and therefore the cosmic Virgo or drifting relative to the Cosmic discrepancies have to do with the way in yardstick for H 11 galaxies is the equa­ Microwave Background and these which the Cepheid luminosities are tion, peculiar velocities must also be re­ corrected for extinction in their parent 5 moved to extract the purely expansional 0 galaxies and, although the local dis­ Log L{H f1) = Log (O/H) + 41.32 velocities. Our radial velocities incorpo­ tance scale is still the subject of consid­ rate all these corrections with the ex­ erable controversy, its discussion is far The distances for H 1I galaxies can ception of streaming motions relative to beyond the scope of this article. then be obtained by comparing the the Microwave Background which at Figure 3 shows a logarithmic plot of L{H rj) versus 0 for giant H I1 regions. The slope of this relation if 4.2 _ 0.5 and the HII Galaxies rms scatter is olog (L{H fj)) = 0.23. A Principal Component Analysis (PCA) for H I1 regions shows again the o presence of 3 parameters of the form, 2 Log L{H ) = Log RC 0 - Log{O/H) + • r1 41 - .. constant • . where Rc is a measure of the radius of giant H II regions introduced by San­ dage and Tammann which they called the core radius. This relation cannot be directly compared with H II galaxies be­ cause we lack core radii for these dis­ ••• tant objects. However, in giant H II re­ • • 0 • gions, the core radii corelate with veloci­ 3 ty dispersion approximately as Rc - 0 . Thus, the parameter Rc 02 is equivalent 39 to the parameter 05 which we found for H II galaxies. Indeed, the PCA analysis 5 of H 11 galaxies in the (L{HrIL 0 , O/H) • domain and of giant H 11 regions in the 2 -3 -2 -1 o (L{H 1l), Rc0 , O/H) domain give essen­ tially identical eigenvalues and eigen­ vectors. Log Mz = 5 Log (J - Log (OjH) This leads us to conclude that, inde­ Figure 3: Logarithmic plot of integrated H,! luminosity as a function of the distance indicator pendently of the mass of the parent Mz. O/H is the oxygen abundance of the nebular component.

6 present are very poorly understood. The TABLE 2: The Hubble eonstant most recent results tend to show that as far as they can be observed, all galaxies Redshift Malmquist Number range km/sec/Mpc correction of galaxies move relative to the CMWB with a ve­ locity of several hundred kilometres per Full sampie 94 ± 5 -11 29 second in the direction of Centaurus. Excluding Virgo 97 ± 5 -12 24 Thus, it is not clear at what distance one Redshift > 2000 99 ± 5 -14 21 should start correcting the velocities for Redshift > 4000 102 _ 6 -16 16 this effect or if one should correct them at all!

obtained the wrang value for Ho. This the following works where complete (b) Malmquist Bias illustrates the philosophical prejudices lists of references can be found: This is an unpleasant effect which has involved in cosmology; this is only caused and continues to cause endless natural because Cosmology reaches the (1) R. Kippenhahn: Light from the Depths of troubles to those who engage in the boundary between science and religion. Time (Springer) for the history of the Hub­ quest for the Hubble constant. Malm­ Personally, I find the story of Adam and ble constant. quist bias occurs because all correla­ Eve more elegant and easier to believe (2) A. Sandage: "The Dynamical parameters of the Universe", in First ESO/CERN Sym­ tions used to determine distances have than the Big-Bang! posium, Large Seale Structure ofthe Uni­ Nevertheless, observers must forsake considerable cosmic scatter. So if one verse, Cosmology and Fundamental Phy­ selects galaxies which are brighter than philosophical and theoretical prejudices sies, p. 127, for a modern account of the a certain limiting value, close to this in the analysis of the weak points of our quest for the Hubble constant and the value one tends to observe galaxies own data. In the case of giant H II re­ defence of Ho = 50. which are systematically brighter than gions, the caveat is that the Hfl lumi­ (3) M. Aaronson and co-workers in As­ the luminosities one would predict from nosities of same H 11 galaxies may come trophysical Journal Vol. 302, p. 536 the distance indicator in the absence of from more than one giant H II region (1986) for a detailed discussion of the bias. This causes the distances to be superimposed along the line of sight. Tully-Fisher method, the various radial velocity corrections and a defence of the biased towards lower values. This would not only bias the luminosities Ho = 100 view. towards larger values but also introduce I am very fortunate to have Edmond (4) J. Melnick and co-workers in ESO pre­ Giraud ("Mr. Malmquist Bias") next the gravitational potential of the parent print number 440 (1986) for a discussion doors who showed me how to correct galaxies as an additional parameter. As of the use of giant H I1 regions as distance magnitude limited sampies for this far as we can tell from deep CCD pic­ indicators. effect. Because at any distance H II tures and spatially resolved spectros­ galaxies span a very large range of copy, the effect of multiplicity in our luminosities, and because there are sampie is small. The fact that the scatter luminous H I1 galaxies at sm all dis­ of the H II galaxy correlations is similar to Visiting tances, the Malmquist effect on the dis­ that exhibited by the giant H II region tance indicator is, as we shall see, very sampie lends strang support to this Astronomers small. conclusion. It is clear, however, that if the emis­ (April 1- October 1, 1987) sion-line component of all H II galaxies The Hubble Constant from Giant Observing time has now been allocated for consisted of four identical giant H 1I re­ HII Regions Period 39 (April 1-0ctober 1, 1987). The gions of exactly the same redshift demand for telescope time was again much The resulting values for Ho are given in superimposed along the line of sight we greater than the time actually available. Table 2 for different redshift cuts of the would not distinguish them from single The following list gives the names of the data. objects but our value of Ho would be visiting astronomers, by telescope and in The errors quoted are 1 a deviations overestimated by a factor of 2! chronological order. The complete list, with from the mean of all galaxies and do dates, equipment and programme titles, is available from ESO-Garching. not include the zero point errar. When Epilogue this is included, our best estimate is Ho = 85 ± 10 km/sec/Mpc. this value A large value of Ho is only one of a 3.6-rn Telescope compares very weil with the value of Ho number of new observations which are = 92 _ 1 found by Aaronson and co­ beginning to erade the old edifice of April: MartineVJarvis/Pfenniger/Bacon, workers using the Tully-Fisher relation Big-Bang cosmology. Inflation, dark Franx/illingworth, 1I0vaisky/Chevalier/v. d. (the error they quote does not include matter, superstrings and other scaffold­ Klis/v. Paradijs/Pedersen, Mathys/Stenflo, Frangois/Spite M/Spite F, Jeffery/Hunger/ zero point uncertainties). Gur value dis­ ings are being used to save the "stan­ Heber/Schönberner, Hunger/HeberlWerner/ agrees with the value of Ho = 50 ± 7 km/ dard" Big-Bang but in the end it will Rauch, Miley/Macchetto/Heckman, Kollat­ sec/Mpc obtained by Sandage and surely fall. This should not worry us, for schny/Fricke, MaccagniNettolani. Tammann. If we use the Sandage­ we know that new buildings are always May: MaccagniNettolani, Keel, Ortolani/ Tammann local distance scale (Table 1) more solid than old structures. Unfortu­ Rosino, Cacciari/Clementini/Pn§voVLind­ we obtain a value of 78 ± 10 which still nately, however, there are very few gren, Barbuy/Ortolani/Bica, Gratton/Ortolani, disagrees at the 3 a level with Ho = 50. modern buildings that are nicer than the Lub/de Geus/ Blaauw/dc Zeeuw/Mathieu, old ones they replace. CacciarilClementini/Pn§voVLindgren, Moor­ wood/Oliva, Danziger/Oliva/Moorwood, Caveats Tapia/Persi/Ferrari-Toniolo/Roth, Lacombe/ References Lena/Rouan/Slezak. Recently, a well-known cosmologist June: Lacombe/Lena/Rouan/Slezak, told me: "Your results are very nice, For the sake of brevity I have not Chelli/Reipurth/Cruz-G., Richichi/Salinari/ so ... what's wrong with them?" What included formal references to the work I Lisi, Zinnecker/Perrier, Perrier/Mariotti, Hab­ he meant, of course, was that I had quoted. I have based the discussion on ing/van der Veen, Sicardy/Brahic/Lecacheux/ 7 Roques/Le Borgne/Barucci, Azzopardi/Rich, Alioin/PelaVPhillips M/Phillips D, Pauls/ 50-ern ESO Photometrie AzzopardilLequeuxlRebeiroVRich, Baessgen Kohoutek. Teleseope M/Baessgen G/Grewing/Bianchi. July: Pauls/Kohoutek, Acker/Stenholm/ July: Baessgen M/Baessgen G/Grewing/ Lundström, Reichen/LanziGolay, Cour­ April: ManfroidNreuxiMagain, Mekkaden/ Bianchi, Seitter, AngebauIVPakuli/Beuer­ voisier/Bouchet, MetzlHäfner/Barwig/ Geyer, Kohoutek. mann/Motch, Barwig/Häfner/Mantel/ Schoembs/Roth, Kameswara Rao/Nandy, AI­ May: Kohoulek, Fischerström/Lindroos/ Schoembs, BertolalGuzzo, SchulziSchmidt­ 10in/PelaVPhillips M/Phillips D. Liseau, Manfroid/Arpigny/Häfner/Sterken. Kaler, MelzlHäfner/Barwig, Schoembs/Rolh, August: Alioin/PelaVPhillips M/Phillips D, June: van GenderenlThe, ThelWesterlund, HouziauxiKameswara Rao. Kameswara Rao/Nandy, Mantegazza, Ma­ Busso/Scaltriti/Corcione/Silvestre. August: HouziauxiKameswara Rao, gain, Alioin/PelaVPhillips M/Phillips D, Tanzi/ July: Busso/Scallriti/Corcione/Silvestre, D'Odorico/Pettini, PizzichinilPedersen, De BoucheVFalomolTreves. Group for Long Term Photometry of Vari­ LapparenVMazure, Sparks/Macchetto. September: Alioin/PelaVPhillips M/Phillips ables. September: Ardeberg/Lindgren/Lund- D, Balkowski/ProusVTalavera, Alioin/PelaV August: MetzlHäfner/Barwig/Schoembs/ ström, WebbNidal-Madjar/Carswell/Ferlel, Phillips M/Phillips D, LorteVTestor. Roth, Group for Long Term Photometry of Wolf/Baschek/ScholziKrautter/Reilermann, Variables. Fosbury/Robinson/Danziger, Guzzo/Focardi, September: Group for Long Term Photo­ Rocca-Volmerange/Azzopardi/Guiderdoni/ 1.4-rn CAT metry of Variables. Roland, Danziger/Gilmozzi/GriffilhslWard, Shaver/Clowes/lovino/Cristiani, Christiani/ April: VreuxiManfroid/Magain, Arpigny/ Barbieri/lovino/Nola, Wampler. Dossin/Manfroid/Häfner, Baade, Lucy/ GPO 40-em Astrograph Baade, Malaney, Gustafsson/Edvardsson/ Magain/Nissen. April: Scardia. May: Gustafsson/Edvardsson/Magain/ May: Scardia, BöhnhardtiDrechsel/Ko• 2.2-m Teleseope Nissen, Arpigny/Dossin/Manfroid/Häfner, de houtek. Jager/Nieuwenhuijzen, Pottasch/Sahu, July: Seitter/Duerbeck/Horstmann, Dom­ April: Le Bertre/Chelli/Perrier, MartineV Pottasch/Srinivasan/Sahu/Desai, FerleWi­ manget. Jarvis/Pfenniger/Bacon, Jarvis/Martinet, Ar­ dal-Madjar/Gry/Lallement, Andreani/FerleV August: Dommanget, Elstilvanovai pigny/Dossin/Manfroid/Häfner, VreuxiMan­ Vidal-Madjar, Lagrange/FerleWidal-Madjar, Shkodrov/Geffert. froid/Magain, Trefzger/Grenon, Reinsch/ Reipurth/Lago. September: ElsVlvanovalShkodrov/Gef­ Pakull/Festou, Gouiffes/Cristiani, Loose/ June: Reipurth/Lago, Baade/Stahl, Man­ fert, Debehogne/Machado/CaldeiraIVieirai Thuan/Kollatschny, Röser/H iltner/Meisen­ dolesi/Palazzi/Crane/Hegyi, Crane/Blades/ Netto/Mourao/ZappalaiDe Sanctis/Lager­ heimer, Magain/Courvoisier/Kühr/Surdej/ Palazzi, Crane/Blades/Mandolesi/Palazzi, kvisVProtitch-Benishek/Javanshir. Swings/Djorgovski, SchmutziHamann/ Crane/Palazzi/Lambert, de Vries/van Dis­ Nussbaumer/SmithNogel. hoeck/Habing. May: SchmutziHamann/Nussbaumer/ July: de Vries/van Dishoeck/Habing, The/ SmithNogel, Le Bertre/Chelli/Perrier, Gallel­ 1.5-m Danish Teleseope Tjin A Djie/Monderen, Waelkens, Foing/ ta, Reipurth/Zinnecker, Seggewiss/Moffal, Beckman/Castelli/CrivellariNladilo. Gouiffes/Cristiani, Reinsch/Pakull/Festou, April: LeibundguVTammann, Rasmussen/ August: Crivellari/Beckman/Arribas/Cas­ Capaccioli, Paresce/BurrowsNidal-Madjar, Meiler, Reipurth.. telliNiadilo/Foing, Foing/Beckman/Castelli/ Christensen/Sommer-Larsen, de Jong/v. d. May: Reipurth, Sinachopolus, ArsenaulV CrivellariNiadilo, Chmielewski/Lambert, Ma­ Broek/Lub. Roy, Ortolani/Gratton, Reimers/Koester/ gain, LenhartiGrewing/Beck. June: de Jong/v. d. Broek/Lub, Cour­ Schröder, Giraud. September: LenhartiGrewing/Beck, da voisier/Melnick/Mathys/Binette/Maeder. June: Giraud, de Jong/v. d. Broek/Lub, SilvaiSpite FNieira Costa, BurkhartiCoupry/ July: de VriesNerter/Habing, Gouiffes/ Christensen, ReizlPiirola. van't Veer. Cristiani, Binette/Fosbury/Courvoisier, Ma­ July: ReizlPiirola, VeilletiDourneau/Oberti/ gain/Courvoisier/Kühr/Surdej/Swings/Djor• Mignard/Martins/Lazzaro, Griffin RF/Griffin REM/Mayor/Clube, Mayor/Duquennoy/An­ govski, Fusi, Pecci/Buonanno/Corsi/Ferraro, 1-m Photometrie Teleseope Ulrich, MetzlHäfner/Barwig/Schoembs/Roth. dersen/Nordström, Collins/Stobie/MacGilliv­ ray/Heydon-Dumbleton/Shanks, Schulzl August: MetzlHäfner/Barwig/Schoembs/ April: Le Bertre/Chelli/Perrier, Schultz, Schmidt-Kaler, Castellani/Caloi, v. Paradijs/ Roth, SchwarziAspin/Magalhaes/Schulle­ Persi/Preite-MartineziFerrari-Toniolo, v.d. Klis. Ladbeck, Chini/Krügel, Gouiffes/Cristiani, Reinsch/Pakull/Festou, Mermilliod/Claria, August: Rasmussen/Möller. Skiliman/MelnickITerlevich, Prugniel/ Jockers/Geyer. September: Ardeberg/Lindgren/Lund- DavousVNieto, PizzichinilPedersen, Ortolani/ May: Jockers/Geyer, Reinsch/Pakull/Fes­ ström, ClementinilCacciari/PrevotiLindgren, Piotto/Rosino, v. Paradijs/Pedersen. tou, Silvestro/Busso/Robberto/Scaltriti, de Trefzger/Mayor/Pel, Grenon/Mayor. September: v. Paradijs/Pedersen, Jager/Nieuwenhuijzen, Cacciari/Clemenlini/ Schwope/Beuermann, Coyne/Magalhaes, PrevoVLindgren, Reinsch/Pakull/Festou, Fi­ Danziger/Dalgarno, StangalRodriguez-E.I scherström/Lindroos/Liseau, Bues/Rup­ Binette, Leitherer/Appenzeller, Westerlund/ prechVPragal. 50-ern Danish Teleseope Azzopardi/Breysacher/Rebeirot, Veron, Cel­ June: TapiaiPersi/Ferrari-Toniolo/Roth, April: Franco. ty-Veron, LorteVTestor. Richichi/Salinari/Lisi, Reipurth/Zinnecker, May: Olsen/Gray, Grenon/Hög/Petersen. Perrier/Mariotti, van GenderenlThe, Habing/ June: Waelkens/Cuypers. van der Veen/Geballe, Courvoisier/Bouchet, July: Waelkens/Cuypers, Verschueren/ BoucheVCetty-VeronNeron, Antonello/Con­ 1.5-m Speetrographie Teleseope Sterken/Hensberge. coni/MantegazzaiPoretti. August: Ardeberg/Lindgren/Lundström. April: RafanellilMarziani, Trefzger/Grenon, July: Antonello/Conconi/Manlegazzo/ September: Ardeberg/Lindgren/Lund- Mathys/Maeder, Courvoisier/Bouchet, Rosal Poretti, Kroll/Catalano F, Courvoisier/ ström. Richter, Kollatschny/Hellwig. Bouchet, Spinoglio/Persi/Ferrari-Toniolo/ May: Kollatschny/Hellwig, Schmutzl Coe, Barwig/Häfner/Ritter/Schoembs/Man• Hamann/HungerlWessolowski, Arpigny/ tel, Magain. gO-em Duteh Teleseope Dossin/Manfroid/Häfner, de Jager/ August: Magain, BrazlEpchtein, Wargau/ Nieuwenhuijzen, Pottasch/Pecker/Karoji/ Chini, Steiner/Jablonski/Cieslinski, Barucci/ April: van Genderen/van der HuchtlRött• Sahu, Bues/RupprechVPragal, Ouintanalde Fulchignoni/Harris/ZappalaiDi Martino/Bin­ gering. Souza. zel/Lagerkvist. May: de Jager/Nieuwenhuijzen, Trefzger/ June: Ouintanalde Souza, Schulte-Lad­ September: Barucci/Fulchignoni/Harris/ Pel/Blaauw, de Zeeuw/Lub/de Geus/Blaauw. beck/Kraulter, van GenderenlThe, Tozzi/ ZappalaiDi Martino/Binzel/Lagerkvisl, Cle­ June: de Zeeuw/Lub/de Geus/Blaauw. Donati-Falchi/Falciani/Smaldone, Alloin/ mentini/Cacciari/PrevoVLindgren, Bergvall/ July: Grenon/Lub, Waelkens/Heynderickx. PelaVPhillips M/Phillips D, HunVTrinchieri, Johansson/Olofsson, Liller/Alcaino. August: Waelkens/Heynderickx.

8 61-ern Boehum Teleseope

June: Pauls/Kohoutek, Barwig/Häfner/ Ritter/Schoembs/Mantel. July: Barwig/Häfner/Ritter/Schoembs/ Mantel. September: Debehogne/Di Martino/ ZappalalDi Sanctis.

Italian Delegation Visits ESO

An Italian delegation, headed by the Italian Ambassador to the Federal Re­ public of Germany, His Excellency Prof. Luigi Vittorio Ferraris, and the Acting Italian Consul General in Munich, Or. Lelio Crivellaro, visited the ESO entific and technical activities at ESO. eral; Prof. Giancarlo Setti, ESO; the Am­ Headquarters in the afternoon of Janu­ This photo was taken in the Optical bassador; Ms. Ursula Geiger, Italian ary 14, 1987. After a show of the ESO Laboratory (trom left to right: Prof. Wolf­ General Consulate in Munich; Prof. film, the delegation had the opportunity gang Alles, Seientifie Attaehe at the Ita­ Romano Toschi, Oireetor of the NET to familiarize itself with a variety of sci- lian Embassy in Bonn; the Consul Gen- Prajeet, MPI, Garching).

List of ESO Preprints Deeember 1986-February 1987

476. T.J.-L. Courvoisier et al.: The Radio to H-Burning Stars. Astronomy and As­ 488. O. Stahl, B. Wolf and F.-J. Zickgraf: X-ray Continuum emission of the trophysics. February 1987. Photometry and Spectroscopy of the Quasar 3C 273 and its Temporal Varia­ 486. M. Azzopardi: Small Magellanic Cloud: Eclipsing P Cygni Star R 81 of the Large tions. Astronomy and Astrophysics. De­ Hy Equivalent Widths and Luminosity Magellanic Cloud. Astronomy and As­ cember 1987. Classes of the Brightest Blue Star trophysics. February 1987. 477. T. Le Bertre: The Opacity of the Dust Members. Astronomy and Astrophysics 489. G.A. Tammann: The Cosmic Distance Around Carbon Star IRC + 10216. As­ Supplement Series. February 1987. Scale. February 1987. tronomy and Astrophysics. December 487. A. Tornambe and F. Matteucci: Sub­ 490. A. Robinson et al.: Emission Une Activi­ 1986. luminous Type I SNe: Their Theoretical ty in Radio Galaxies. Monthly Notices of 478. S. Cristiani and B. Koehler: Redshifts of Rate in Our Galaxy and in Ellipticals. the Royal Astronomical Society. Febru­ Quasar Candidates. Astronomy and Astrophysical Journal. February 1987. ary 1987. Astrophysics. December 1986. 479. 1. Le Bertre and N. Epchtein: Optical and Infrared Observations of Two Oxy­ gen Rich Unidentified IRAS Sources. Astronomy and Astrophysics. De­ cember 1986. First Announeernent 480. D. Baade and L. B. Lucy: A Search for Coronal Une Emission from Early-type A conference organized by NOAO (National Optical Astronomical Obser­ Stars. I. Zeta Puppis. Astronomy and vatories) and ESO on Astrophysics. January 1987. 481. E.J. Wampler: Observational Study of the Hubble Diagram. Astronomy and High-Resolution Imaging Astrophysics. January 1987. 482. C. N. Tadhunter et al.: Detached Nu­ by Interferometry clear-like Activity in the Radio Galaxy will be held from 15 18 March 1988 at ESO in Garehing, FRG. PKS 2152-69. Nature. January 1987. to 483. J.-L. Nieto, A. L1ebaria and S. di Serego The scope of this conference is ground-based interferometry at visible and Alighieri: Photon-counting Detectors in infrared wavelengths. Time-resolved Imaging Mode: Image The programme will include the following topics: Recentring and Selection Aigorithms. Astronomy and Astrophysics. January • Scientific Goals 1987. • Interferometric Imaging with Single-Oish Telescopes 484. R. N. Wilson, F. Franza and L. Noethe: • Graund-Based Long-Baseline Interferometer Projects Active Optics I: A System for Optimizing • Methods for Reconstructing Images and Spectral Information fram Optical the Optical Quality and Reducing the Long-Baseline Interferograms Costs of Large Telescopes. Optica Acta. January 1987. For more information please write to F. Merkle, European Southern Observa­ 485. E. Brocato and V. Castellani: Evolutio­ tory, Karl-Schwarzschild-Str. 2, 0-8046 Garching bei München, Federal Re­ nary Constraints for Young Stellar Clus­ publie of Germany. ters: I. The Luminosity Function of

9 Lang-term Photometrie Campaign at ESO and the New Eelipsing P Cygni Star R 81 in the LMC 2 3 4 B. WOLF 1, C. STERKEN , 0. STAHL and J. MANFROIo

1Landessternwarte Heide/berg, 2Vrije Universiteit Brusse/s, 3ESO, 4 Universite de Liege

1. A Programme for Long-term ticipants who work in a tight team with approach is a very efficient and useful Photometry of Variable Stars the principal investigators. From the be­ one. Besides the direct yield of data, the ginning we aimed at obtaining several project also offers to young scientists At the ESO workshop The Most Mas­ months of observing time each observ­ (e. g. Ph. O. students) the possibility to sive Stars in November 1981 (Eds. ing season, and this for a time span of at get into contact with the fields of re­ O'Odorico, Baade and Kjär), C. Sterken least one decade. search of the other participants, wh ich presented results of his observations of A project of that size, including the substantially contributes to their obser­ HO 160529 during a time span of more interpretation of measurements ob­ vational experience. than 8 years. HO 160529 is an A2 hyper­ tained at different telescopes and by giant wh ich was found to be variable by different observers cannot work without 2. R 81, the Counterpart of P Cyg Wolf et al. (1974) in an irregular way with astriet agreement on observing proce­ in the LMC an amplitude of several hundredths of a dures and reduction techniques. Espe­ magnitude. Sterken continued the cially for what concerns the data reduc­ P Cygni is one of the most outstand­ monitoring of this star at every possible tion, high requirements are needed so ing stars of the Galaxy. It had a remark­ occasion in the period 1973-1981 and that the final data may be of the highest able outburst in 1600 and is particularly found evidence for the presence of obtainable accuracy. It was decided distinguished by its unusual spectrum. periodic light variation of about 100 that all reductions would be done cen­ The so-called P Cygni profiles in the days. From the phase diagram he con­ trally (and not by the individual obser­ visual range (wh ich have been disco­ cluded that in spite of the intensive ob­ vers) at the University of Liege by J. vered already in the 19th century) are servations by one person, there still re­ Manfroid. The reduction algorithm is a named after this prototype and indicate main long gaps in the phase diagram. If generalized method developed by Man­ that this star is losing mass at an ex­ sampling of observations happens in froid and Heck (1983) and is charac­ cessive rate. P Cygni belongs to the such an irregular way (gaps caused by terized by the use of practically every luminous (Mbol = -9 to -11) blue vari­ irregularly allocated short observing measurement of any non-variable star. ables (LBV's) which have been recog­ runs), long-term orbital effects may be In doing so, all measurements are trans­ nized during the past few years as key­ hidden by or ascribed to the super­ formed into a standard system and the objects for the understanding of the giant's irregular intrinsic fluctuations. It observations obtained during different evolution of the very massive (initial was therefore suggested that the obser­ seasons and with different instruments masses ~ 50 MCi)) stars. According to vations of e. g. variable supergiants be can be re-evaluated regularly so that the current evolutionary models (cf. e. g. done by a larger team of observers at a homogeneity of the data is assured. Humphreys 1986, Chiosi and Maeder dedicated small instrument. Such an Because of the availability of the suit­ 1986) these very massive stars do not approach would also be very useful for able photometers on the ESO 50 cm become red supergiants; instead a criti­ all differential photometry on a basis of and the Oanish 50 cm telescopes. and cal luminosity boundary exists (calIed one measurement per night or less: for the usefulness for astrophysical in­ Humphreys Davidson limit) beyond supergiants, Be stars, Ap stars ... terpretation of the data. we decided to which the most luminous stars do not Ouring the discussions following the carry out all measurements in the evolve. The LBV's are located close to talk, several colleagues expressed their Strämgren uvby system. Since we deal this boundary and are supposed to be interest in the idea, and by the end of the with variable stars, preference was gi­ the immediate progenitors of the Wolf­ Workshop, the project Long-term ven to differential measurements with Rayet stars. Photometry of Variables was born. In two comparison stars (although we have The physical properties of P Cygni February 1982 a meeting was held at also carried out absolute measure­ have been scrutinized during the past the University of Brussels, and the pro­ ments). few years at a wide wavelength range ject finally started with an application for In practice the participants may ex­ from the UV with IUE to the IR with observing time submitted in April 1982. pect to receive their data not later than IRAS! A drawback of P Cygni is that The participants (originally about 15) three to six weeks after termination of both its interstellar reddening and its merged the objects for wh ich photome­ the observing run. Since 1982 the distance are difficult to determine (see try on a long-time basis was needed into number of participants has doubled, e. g. Lamers, de Groot and Cassatella one object list of about 70 entries, and and this is also so for the number of 1983). For this reason we searched the then the file was split in seven sections stars. At least 30 stars, for which zoo of the luminous blue supergiants of according to the nature of the variable enough data were obtained, have been the Large Magellanic Cloud (LMC). As stars (see Sterken, 1983). Later on, an omitted from the object list. 26 observ­ outlined e. g. in our recent atlas of high eighth section (Peculiar Late Type Stars) ing runs with a duration of about one dispersion spectra of luminous LMC was added. For each section a principal month length each have already been stars (Stahl et al. 1985) the P Cygni type investigator and a co-investigator were allotted by ESO and a huge amount of stars form in fact a populous group appointed. These scientists decide ab­ data are already available. The results among the peculiar emission line stars. out which objects need monitoring, and have already led to more that 20 pub­ Already in 1981 Wolf et al. presented they carry out and/or supervise the lished scientific papers. a detailed spectroscopic and photome­ analysis of the data of the stars be/ong­ The nature of some discoveries (Iike trie study of R 81 of the LMC. R 81 ing to their sections. We agreed that the e. g. the binary nature of R 81 wh ich is turned out to be a particularly close observers would be volunteering par- described below) clearly proofs that this counterpart of the galactic star P Cygni.

10 bound dust envelope since Stahl et al. R 81 I UE, LWR (1987) identified R 81 as an IRAS point source. The dust formation could be a 1982, Feb. 17 !SI (Y) consequence of their slow and dense N ~ Q) N Q) u:> N le N N u:> winds. le le N ~ le le le ~ ~ .... One of the most paradoxical results

~ ~ ~ ~ ~ ~ ::: ::: ::: ::: ::: ::: ::: derived from the IUE spectrum of P .. Cl Cl Cl Cygni (Cassatella et al. 1979) is that this ..,>-.. u.. u.. u.. u.. I I I I hot star with its unusual P Cygni profiles (l) c in the visual range is right the other way ..,CD distinguished by a lack of P Cygni pro­ C ..... files in the ultraviolet (which are other­ CD > wise so typical for hot stars in this .., range). Just this behaviour is found in 0 the case of R 81 as weil. Still more in­ CD L triguing is the fact that e. g. the Fe II lines of both stars agree even in details. The (Y) lf) complex profiles show a multiple com­ ....Cl ­+ + ponent structure (for R 81 see Fig.1) ascribed to the ejection of discrete shells (cf. Lamers et al. 1985 and Stahl et al. 1987). 0. In addition to the major historical out­ 2612. 2622. A[J.J 2632. bursts of P Cygni in the 17th century, Figure 1: A seetion of the IUE high-dispersion spectrogram around 2600 A. This wavelength irregular photometrie variations of 0.1 to range is dominated by Fell absorption lines. Like in P Cyg, different components are present. 0.2 magnitude have been reported dur­ The velocities of these components are indicated for different lines. ing this century by many authors. No strict periodicity has yet been found (van Gent and Lamers 1986). Likewise in the Both stars are (of course) characterized of the Hertzsprung-Russell Diagram case of R 81, which until 1980 was re­ by strong P Cygni profiles of the Balmer (HRD) close to the Humphreys-David­ peatedly observed during various ran­ lines and by very similar stellar parame­ son limit. The winds of both stars are domly distributed photometrie observ­ 1 ters: Teff = 20,000 K, Mbol = -10, and R slow (vmax = 250 to 300 km 5- ) and very ing runs, variations of about this am­ 5 I = 70 R0 for R 81 and Teff = 19,300 K, massive (M = 3 . 10- M0 yr- for R 81 plitude are quoted. Wolf et al. (1981) 5 1 Mbol = -9.9, and R = 76 R0 for P Cygni and M = 1.5 . 10- M0 yr- for P Cyg). regarded these variations as to be "of (for the data for P Cyg see Lamers et al. Like P Cyg (Waters and Wesselius 1986) irregular nature rather than of a periodic 1983). They are located in the same part R 81 is surrounded by a cool loosely one". Shortly after this the programme

I -I--r~ 1 R8l, y band IOllg-lcrm phololllcl.ry or variables lSl'" N'" I ~ o o 0 '80 0 .-< 0 ~o § l ~@ I 0 .-< 000 8 0() 0 0:: '" ~ (§J0 00 o 0 I o 8 0 o 0 0 o 0 0 '" - o '"M 0 0 0 0 I - o 0 0 0 B 8 0

'" 0 lf1'"

N 0 0 rlJj 0 I .-< @~~ ~ ~~.l w ~ ~ 0 fI .. '" 0 "'" I L -l- _1_ L ----l- ---l-- -L- -.L ---l- -L I). ('OO S. 10 6.200 6. 700 JD244- (1000 days) Figure 2: The differential light curve in the y band for the observations of R 81 obtained within the programme of long-term photometry of variables. The upper part shows the observations in the sense C 1-R 81 and the 10 wer part shows on the same scale (but shifted) the differences of the two comparison stars. The y magnitudes of the comparison stars C 1 (= HO 34144) and C2 (= HO 34651) are 9.32 and 8.37, respectively. The scatter in the differences y (C 1-C2) of the two comparison stars is 0.007 which documents the quality of the photometry.

11 tions are shown in Figure 2. This data set was analysed with aperiod search­ ing algorithm and we finally found that the period of the variations was about es> +'. es> 74.6 days. With the period al ready es> o+.~ tn , .. +.;t:G. known with some precision, the obser­ I ~+ t +0 vations of Appenzeller (1972) could also -8 ~ ++ o. be tied in. They then define the period >- es> 0 es> '" particularly weil since they extend the C\J , time base by more than ten additional o o years (which is about 50 cycles). Taking + x + x .. • + all data together, we obtain aperiod of es> ...es> 74.59 ± 0.01 days. The phase diagram , of the y-band data wh ich was con­ o o structed by using this period is shown in Figure 3. This phase diagram clearly im­ plies that R 81 is an eclipsing binary. The light curve is very distorted which N u suggests that both components are in I close contact. -8 Obviously, the detection of a binary P >- Cyg star is very important since we might hope to derive the parameters of the system, specifically the mass. This is a very important undertaking, since Phase there are no direct mass determinations Figure 3: The phase diagram of the data shown in Figure 2. In addition the V data of of a P Cyg star available. So far, we Appenzeller (1972) have been included. The different symbols denote observations performed obtained two CASPEC spectra and one during different observing seasons (0 for 1982/1983,0 for 1983/1984.6 for 1985/1986, + for CES spectrum of R 81. A portion of the 1985/1986 and x for 1986/1987. Appenzeller's earlier observations (JD2441274 - 1292) are CASPEC spectra is shown in Figure 4. It denoted by.. The period of the eclipses is particularly weil defined due to the earlier is clear from this figure that most of the observations of Appenzeller. The eclipse with a depth of 0.4 mag can clearly be seen. The lines have a P Cyg profile or are blue­ shape of the light curve is particularly distinguished by the absence of a pronounced shifted absorption lines originating in secondary minimum and by a pre-eclipse dip of 0.15 mag at phase 0.80. the stellar wind of R 81. They are thus not very useful to determine the orbital velocity of the star. From the very few of long-term photometry of variables addition, we found that the minima re­ photospheric lines in the spectra we described above was initiated. Un­ peated every 300 days. At that point we could so far not obtain a reliable radial doubtedly, a detailed knowledge of the realized that the variations of R 81 might velocity curve. In addition, no secondary time dependence of brightness varia­ be at least partly periodic and we de­ spectrum has been found so far. tions is important for the derivation of a cided to give this star a high priority in Luckily, some information can be ob­ physical model for P Cyg stars. Since "P the further observations since never be­ tained from the photometry: The ab­ Cyg of the Galaxy" has obviously never fore had strictly periodic variations been sence of a pronounced secondary been monitored during several years by found in a classical P Cyg star. Until now eclipse probably means that most of the high-precision photometry at sites with we have collected observations in 240 visual brightness is supplied by one comparable excellent weather condi­ different nights distributed over aperiod component. The depth of the eclipses tions as at La Silla, we included "P Cyg of more than four years. The observa- suggests that the eclipsing body has a of the LMC" (i. e. R 81) in the long-term photometry programme at ESO.

1. 500 3. The Eclipsing Binary R 81 R 81 was already found by Appenzel­ ler (1972) to exhibit variations with the rather large amplitude of 004 mag within two weeks. We subsequently observed ...·c R 81 in several years in observing runs ·c of about two weeks each, but we were ...·> unable to find a similar event. Only varia­ ~ 500 tions of about 0.15 mag, which seemed ~ 0. 1 to be irregular, were found. So R 81 was regarded as an irregularly variable P Cyg star, although the time coverage was I too incomplete to do a meaningful 0.0001 LI , .l.--l-l , period analysis. 4380.000 4430.000 4480.000 4530.000 4580.000 A. [Äl In the first three observing seasons of Figure 4: Comparison of two CASPEC spectra taken at phase 0.97 and 0.27, respectively. the long-term programme we had ob­ Variations can c/early be seen. During eclipse, numerous Felliines could be identified and the served each year once that R 81 had Hel lines and Mg/l ;. 4481 show a P Cyg profile. The velocities of the different lines are faded far below its normal brightness. In indicated in the Figure. 12 radius which is comparable to the radius wind lines, are not irregular but phase­ Macchetto, F., Penston, M., Selvelli, P. L., of the visible star, which is known from dependent. An important point to clarify Stickland, 0.: 1979, Astron. Astrophys. 79, the brightness, temperature and dis­ is also the nature of the secondary. No 223. tance of R 81. The width of the eclipses obvious secondary minimum is present, Chiosi, C., Maeder, A.: 1986, in Ann. Rev. Astron. Astrophys., 24, 329. so the star must be visually faint. New of the star with respect to the period Humphreys, R. M.: 1986, in Luminous stars then allows us to estimate the distance spectroscopic observations of high and associations in ga!axies, lAU Symp. of both stars from each other and thus quality and good phase coverage are No. 116, eds. de Loore, Willis, Laskarides, from Kepler's third law (with the period) badly needed. p.45. the total mass of the system. We find a The more general question is, of Lamers, H.J.G.L.M., de Groot, M.J.H., Cassatella, A.: 1983, Astron. Astrophys. mass of about 35 M0 for R 81. This course, whether many P Cyg stars are result is in good agreement with the binaries. Our finding certainly does not 128,299. expectations for a luminous P Cyg star, prove this. However, the small scatter Lamers, H. J. G. L. M., Korevaar, P., CassateI­ but note that it is the first direct mass around the mean light curve shows that la, A: 1985, Astron. Astrophys. 149,29. R 81 intrinsically is at most slightly vari­ Manfroid, J. Heck, A: 1983, Astron. Astro­ estimate for such astar. We note that phys. 120,302. this mass estimate is very uncertain so able. If other P Cyg stars (wh ich are Stahl, 0., Wolf, B., de Groot, M.J.H., Leith­ far and clearly more spectroscopy is observed to be variable with relatively . erer, C.: 1985, Astron. Astrophys. Suppt. needed in order to confirm this result. large amplitude) are similar to R 81 in 61,237. Interestingly, the scatter around the this respect, then the variability ob­ Stahl, 0., Wolf, B., Zickgraf, F.-J.: 1987, As­ mean curve of Figure 3 is only of the served in these stars requires an expla­ tron. Astrophys., submitted. order of 0.05 mag. This means that also nation. Sterken, C.: 1983, The Messenger 33,10. most of the smaller variability which we van Gent, R.H., Lamers, H.J.G.L.M.: 1986, Astron. Astrophys. 158, 335. observed between the eclipses is due to References Waters, L.B.F.M., Wesselius, P.P.: 1986, the changing aspects of the observa­ Aslfon.Aslfophys. 155, 104. tions and not intrinsic to the star. This Appenzeller, 1.: 1972, Pub!. Astron. Soc. Ja­ Wolf, B., Campusano, L., Sterken, C.: 1974, result leads to the suspicion that also pan 24, 483. Astron. Astrophys. 36, 87. other variations of R 81, e. g. the spec­ Cassatella, A, Beeckmans, F., Benvenuti, P., Wolf, B., Stahl, 0., de Groot, M. J. H., Ster­ troscopic variations of certain stellar Clavel, J., Heck, A., Lamers, H.J. G. L. M., ken, C.: 1981, Astron. Astrophys. 99, 351.

Blue Horizontal Branch Field Stars in the Outer Galactic Halo J. SOMMER-LARSEN and P. R. CHRISTENSEN, The Niels Bohr Institute, University of Copenhagen

1. Introduction dispersion was found to be - 60 km/so fields located at the SGP (I, b) = (38°, It is a well-known hypothesis that Even if one assumes that the velocity -51°) and (I, b) = (352°, 52°). In total galaxies are surrounded by extended distribution of these objects is isotropic, the catalogues cover 54 square degrees massive envelopes of "dark" matter a mass of only M = (2.6 ± 0.8) * 10" of the sky, and they are complete to V = reaching far beyond the visible edges of M0 is inferred. This does not support 18.5. By observing spectroscopically the galaxies. For our own Galaxy this the hypothesis that the mass of the faint blue stellar objects drawn from hypothesis is supported by kinematical Galaxy increases linearly with Galac­ these catalogues, using the selection and dynamical studies of globular clus­ tocentric distance to distances criterion 0.0 :5 B-V :5 0.2, a sampie of ters in the outer Galactic halo. ~ 100 kpc. 131 bhbf star candidates have been ob­ The usefulness of globular clusters as In order to clarify further on the prop­ tained. test objects for probing the mass dis­ erties of distant halo objects we have The observations were done with the tribution in the outer part of the Galaxy is identified and studied a sampie of blue ESO 2.2-m telescope during a number limited, however, for the following horizontal branch field (bhbf) stars in the of observing runs in the period reason: The sampie is small - the outer Galactic halo (r :5 40 kpc). The 1984-1986. The observational setup number of globular clusters with Galac­ observations are described in section 2, and procedure were the same during all tocentric distances between 15 and and the results are discussed in sec­ observing runs: The detector system 40 kpc, which can be used in a kinemat­ ti on 3. consisted of a Boiler and Chivens spec­ ical analysis, is 14. Furthermore, several trograph together with the dual Reticon recent remeasurements of globular Photon Counting System (RPCS) 2. Observations and Data cluster radial velocities have showl1 (Christensen et al., 1984). The two dec­ Analysis some of these to be substantially in ker holes, each projecting down onto its error. We have carried out a search for bhbf own Reticon-array, corresponded to an 2 Lynden-Bell, Cannon and Godwin stars at large Galactocentric distances. area of 4*4 arcsec . With a slit the (1983) studied a sam pie of dwarf Part of the observations have been de­ aperture was reduced to 2 arcsec in the spheroidals situated at very large Galac­ scribed in Sommer-Larsen and Christ­ direction of dispersion. A 600 lines/mm tocentric distances (-100 kpc). They ensen (1985 and 1986). The basic mate­ grating blazed in the first order at found the objects to have quite low line rial was three stellar object catalogues, 4200 A was used yielding a reciprocal of sight velocities (relative to the Galac­ kindly provided by Drs. G. Gilmore and dispersion of -1 Aper channel. The tic restframe) - the line of sight velocity N. Reid. The catalogues cover three wavelength range covered was 13 175 very slowly relative to a Galactic rest­ frame: VROT = 10 ± 32 km/s assuming H31 v0 = 220 km/so This is consistent with 140 what is found in general for metal paar 0' stellar subsystems in the Galaxy. There z tH t t t t are indications that the velocity distribu­ ::> tion of bhbf stars is peaked in the radial >- lOS 0:: direction (towards and away from the <{ 0:: Galactic centre) everywhere in the inner t::: CD Galactic halo. 0:: ~ 70 The observed spatial and kinematical X ::> properties of the system of bhbf stars in -lu... the outer Galactic halo can be modelied without assuming that the Galaxy is em­ bedded in an extended, massive halo " ,,1- 01 , .',",t'\""'" "" .•/"" ,.''., ." ... ' ",,"1 n, ,"." ',I ,'/.,1, '.' "',"',~', "" .,'_ ","\",",.."', ""."~ '.' '.'':"'1 •••\. ,; ....'.....".,\.0\..,•• t,,,"/""'~·:'u,,:,'·,, ~~ ' characterized by an approximately flat ~ O'--_---'-__-L__~_--l__~____l.___"______l__~_ ___.J rotation curve to r 50 kpc. If the 3500 3800 4100 4400 4700 5000 Galaxy is embedded in such a massive WAVELENGTH (AANGSTROM) halo then the motion of bhbf stars in the Figure 1: Part of the spectrum obtained for the bhbfobject H31. The full drawn curve is the flux outer Galactic halo must be predomi­ spectrum. The dotted curve shows the 1 a level due to statistics. The magnitude of the object nantly tangential (Iow eccentricity or­ is V = 18.4, inferring a heliocentric distance of29. 6 kpc. The exposure time was 2, 700 sec. The bits). This contrasts with what is found arrows show the positions of the Balmer lines H 10 (3750 A) to Hf; (4861 A). The radial velocity for halo stars in the inner Galactic halo of this bhbf star was determined to be 20 ± 20 kms-'. and teils us samething about early Galactic history. It certainly does not support a rapid collapse picture for the 3200-5500 Ä. The intrinsic resolution of nique. The rms error was 20 km/s for the outer Galactic halo. It may suggest that the RPCS detector with this dispersion brighter stars, increasing to 25 km/s for the bhbf stars in the outer Galactic halo was - 2.0 Ä, but with the 2 arcsec wide the faintest stars. were formed out of turbulent gas rather slit, the resolution increased to 3.5 Ä. Balmer line widths were used to get a than out of gas with small macroscopic Each object was observed twice, rough estimate of the surface gravities motions. focusing the object in the two decker of the bhbf star candidates. 116 of the Our study of the inner and outer holes subsequently. He-Ar calibration 131 candidates could unambiguously Galactic halo is by no means complete. spectra were obtained after each pair of be identified as bhbf stars. The remain­ Observations of bhbf stars in consider­ exposures. Every star which had an A­ ing 15 may have tao high surface ably more fields probing other parts of star type spectrum, and therefore was a gravities to be bhbf stars and are tenta­ the Galactic halo would be of great in­ potential bhbf star, was exposed until at tively identified as field blue stragglers. terest in the light of the results obtained least 100 (sky-subtracted) counts per so far. Such observations are planned. channel had accumulated in the con­ 3. Discussion tinuum in the centre of the array. No (double) exposure lasted more than An analysis of the data obtained gives References 3,600 s. We were able to obtain such the following results: The system of bhbf spectra for bhbf stars as faint as stars in the Galactic halo is quite round Christensen, P.R. et al., 1984, The V = 18.7 with this combination of tele­ with an axial ratio q - 0.8. The density Messenger 38, 38. scope and detector. Such stars are distribution out to the limit of the sampIe Lynden-Bell, 0., Cannon, R. 0., and Godwin, P.J., 1983, Mon. Not. R. Astr. Soc., 204, located at Galactocentric distances (r - 40 kpc) is weil described by apower Short. Comm., p. 87. r - 40 kpc. A spectrum of a V = 18.4 law with index v - -3. The system of Sommer-Larsen, J. and Christensen, P. R., bhbf star is shown in Figure 1. bhbf stars does neither expand nor con­ 1985, Mon. Not. R. Astr. Soc., 212,851. Radial (Iine of sight) velocities were tract as would be expected for an old, Sommer-Larsen, J. and Christensen, P. R., obtained using the correlation tech- weil mixed system. It rotates, if at all, 1986, Mon. Not. R. Astr. Soc., 219, 537.

And then there were Three ...

At the end of the article about the down'. Persistent efforts by Mr. Syuichi the published positions were somewhat recovered minor planet MALLY Nakano, who is spending one year at in error (one by more than 30 arc­ (Messenger 46, 11), the five remaining the lAU Minor Planet Centre in Cam­ seconds). Based on the improved mea­ 'lost' minor planets were enumerated. bridge, Mass., lead to the identification surements, Dr. Brian Marsden, who Readers of this journal may be in­ of (1026) INGRID with a minor planet heads the Minor Planet Centre, was able terested to learn, once more, that observed in early 1986. He sent the to find identifications with minor planets, things move fast in astronomy nowa­ resulting orbit to ESO, where no less observed in 1940, 1981 and 1986. Three days, not only in front-line areas of high than six further images of this planet additional images were found in the energy astrophysics, but also in the were found on plates in the plate lib­ ESO plate library, definitely confirming classical backwaters of celestial rary. these identifications. mechanics. The remeasurement at ESO of the So, now there are only three left ... By early February 1987, two more original 1901 Heidelberg plates of (473) (there are rumours that some of the MP­ lost minor planets had been 'shot NOLLI, lost since that year, showed that people are busy). 14 Where Peculiars Turn Normal - IR Observations of CP Stars R. KROLL, Universitäts-Sternwarte Göttingen

Upper Main Sequence Stars niche, but a necessity in understanding tric calibrations, curve-of-growth analy­ stellar evolution in the presence of sis, etc. tend to produce rather uncer­ If you make all possible simplifica­ magnetic fields, which is a commonly tain, scattering results. 00 we have any tions in the theory of stellar atmo­ encountered configuration. The CP spectral window which is unaffected spheres -LTE, no convection, gas stars are not an accident in stellar evolu­ from the chemical peculiarity of the star, pressure two times the electron tion, but at least one possible branch, or where we can find astand? pressure, plane parallel atmosphere maybe even astate that every upper­ main-sequence star passes. with solar composition, etc. - and look, Infrared Observations of CP Stars where such a concept could actually But the variety of phenomena is dis­ work, you arrive at the upper main se­ couraging at the first glance; let us con­ In 1983 the last hope, the infrared part quence stars. And in fact, there has sider the most commonly observed of the spectrum, seemed to slip away. been much progress in understanding phenomena. In most cases we find a Large f1ux excesses at 5 microns were such atmospheres, the model atmo­ flux deficiency in the ultraviolet spec­ reported, measured at the ESO 1-m sphere grid calculated with Kurucz's trum and in turn a 'heating' of the visual photometric telescope by Groote and famous ATLAS programme as an out­ part which is understood as a back­ Kaufmann. These observations pointed standing example. warming effect from the enhanced metal to the existence of considerable circum­ Yet there is a large fraction (- 20 %) of abundances found in CP 2 stars. In other stellar matter around CP stars, with upper main-sequence stars that refuse words, flux is redistributed from the UV blackbody temperatures of 300 to to obey such simple physics. They show to optical wavelengths. This process 600 K, which must be connected to the large metal overabundance, photome­ works according to the individual CP phenomenon in one way, either be­ tric variability, magnetic fields, breath­ abundance pattern of the specific star, ing the cause of it, or an unavoidable taking spectra or curious flux distribu­ so all temperature estimates, photome- result. Both could hardly be understood tion. Following the systematic of Pres­ ton (1974) we call these stars 'chemical­ Iy peculiar' or shortly CP stars. ALL VoLues of Nov. 84 Compocgn ALL VoLues of Ocl. 86 Compocgn Two mainstreams are distinguished, ~ one that exhibits no magnetic fields and x consists of the metallic line (Am) stars ­ nowadays called CP 1 stars - and the Mercury-Manganese (HgMn or CP 3) x stars, and one that displays magnetic J fields up to some 10,000 Gauss on the ~+------,----,.------.-----i ~+---r----r---,----.,------!1 other hand. This article will mainly deal with these magnetic Ap stars, and refer­ E~ ence them, more up-to-date, as CP2 ",,0 stars. Here the physical situation is compli­ x x x cated a little, namely by the strong ~+------,----,.------.-----1 ~+---r----r---,----.,------1 magnetic field. This field in turn tries to be kind to the astronomer and keeps the second simplest form possible in most cases, that of a dipole, but inclined by some angle against the rotationa! axis. ~+----.-----.------,------j ~+------'r----r---,----.,------j This working model- the oblique rotator - can explain most of the observed characteristics of CP 2 stars, e. g. the photometric and spectroscopic variabil­ x ity, or polarity changes in the magnetic x L x field, but the question remains, what ~+----.-.,,-----.----r------j ~+---r-----.-----.-----,------j causes the variety of abundance x x x patterns in CP2 stars, which peak in x x x objects like the famous and infamous x x x x Przybylski's star HO 101 065, where " x from the 15 strongest metallic lines 11 ,(' belong to Rare Earth Elements, 6 of M i' M ~+----'-2.-.-"---.-1.-.---.'.•-----1 ~+------'o'.0--'2.-0-----,.'.0--".-0----1 these to the element Holmium, which is Magnitude Magnitude rarely encountered in any other branch Figure 1a: Catalogue minus observed brightness versus intrinsie magnitude for all standard of astrophysics. star measurements during the November 1984 eampaign. The nonlinearity effeet ehanges its Analysing the atmospheres of these slope eontinuously from J to M filter. stars is not a time consuming, unpro­ Figure 1b: Same as 1a, but for the Getober 1986 period. Note that the abszissa spans a ductive work in some astrophysical double range eompared to Figure 1a. Nonlinearity effeets have been greatly diminished. 15 tion a nonlinearity, whatever caused it. resulted in sufficient data for about eight After carefully correcting for that effect, CP stars. Of course we had to restrict

HD3980 none of our programme stars showed ourselves to objects with short periods. any sign of flux excess in the M-band, First of all we checked whether the HD1Z447 though many had been found to be ex­ awful nonlinearity effect was still present HD2Z470 cessive in the Groote and Kaufmann - and were pleased to see that it had HDZ4712 survey. Figure 2 shows this in a Ray­ been nearly totally removed. Note that in HD25267 leigh-Jeans diagnosis. We fitted a Figure 1b the abszissa spans now eight

HD28843 straight line through the logarithmic flux­ magnitudes instead of four in Figure 1a. es in the J, H, K and L filter and plotted it Differently to the observations one HD37017 against the logarithm of the wavelength. year ago we performed differential HD49333 Now the M value is excessive against a photometry, taking comparison stars in HD54118 blackbody flux distribution in the Ray­ the vicinity of the programme stars. This HDn968 leigh-Jeans approximation, if it lays allows a much higher accuracy, be-

HD74196 above this line. But this is not the case

HD203006 for any of the programme stars.

HD206088 J HKL L' M 12 25 60 100 HD220825 I I 1 11 1 1 1 1 1 The IRAS View HD221006 HD 206 088 HD221760 Though the 5 Il flux excess was dis­ 9400 K HD223640 proven this way, we were sensitized for the possible existence of circumstellar ~ ~-o- - <> <:>- -- -I- - I------, matter and looked far it in the IRAS point ... ..e sources catalogue. We found 40 CP stars of various types, for wh ich good Figure 2: Rayleigh-Jeans diagnosis. M values HD 20 320 above line would indicate flux excesses. All near IR data were present. From the observed stars are normal. CP 2 group none showed fluxes at the 8200 K IRAS wavelengths - which are 12, 25, ~ ~-o- - <> ---- 60 and 100 Il - that would not fit to a -I- - I------blackbody flux distribution. Two objects with the most promising attempts to were found where in fact circumstellar explain the forming up of chemical over­ dust was indicated, but they belong to HD 40 312 abundances, like Michaud's diffusion the He peculiar stars, or CP4 group, 24600 K theory. where we also find stars with Be charac­ But other researchers, like Bonsack teristics. Dust shells are not uncommon ~ ~-<>- - "<><:>- -- -I- - I------and Dyck were unable to verify the for these objects. Positively spoken, our claimed fluxes, so a careful reinvestiga­ result from the IRAS data is that CP tion of the subject was desirable. Franco stars show normal main-sequence HD 29 305 Catalano from CataniaiSicily joined a characteristics in the infrared as far as 11900 K group at Göttingen University Observa­ we can observe them. Figure 3 shows tory in that attempt. Our first observing some examples for various CP types. ~ ~-<>- - ~ - - -- -I- - T ------period dated November 19 (84 at the We may now savely conclude that all ESO 1-m telescope, equipped with its flux redistribution, caused by the curi­ liquid nitrogen cooled IR photometer ous chemistry of the CP stars has come HD 27 376 with InSb diode, which had undergone to an end at infrared wavelengths, and 14000 K of course some minor changes since the hence the infrared fluces are a superb time when Detlef Groote and Jens-Peter indicatar for the thermal properties of ~ ~-<>- - ~ ------1------Kaufmann had made their exciting mea­ the atmospheres and a solid stand for surements. further analysis. In the first moment the observations HD 61641 made by Franco Catalano looked puz­ = IR Light Curves zling to us, when they were reduced in 13600 K Göttingen. The calibration with standard The next logical step is to get precise stars from Koornneef's list was not light curves in the infrared, wh ich tell us :r satisfactory, because it showed a large what thermal changes take place, as the ~~-<>--~------scatter. During our attempts to localize stellar rotation brings different parts of 0.0 0.5 1.0 1.5 2.0 the reason for that scatter, we plotted the atmosphere into the line of sight of the difference between the expected the observer. For this project Franco log (A.) and the measured brightness against Catalano and I got ten nights of observ­ Figure 3: IRAS observations. Fluxes above the star's intrinsic magnitude in the ing time at the 1-m in October 1986. dashed line are excessive against a black­ specific filter. And here's the surprise Unfortunately the delayed spring made body with the indicated temperature, de­ (Fig. 1a)! this time shrink to merely four nights duced from the near IR colours. The CP4 star Instead of showing the expected effectively. HO 61641 shows indications ofa dust shell, which gives it Be type characteristics. All scatter around a horizontalline, a clear Another handicap was that in the be­ other stars show blackbody flux distribution correlation was seen, wh ich - even ginning we did not know which stars worse - reversed its trend with increas­ (HO 206088 and 20320 are cool CP2 stars, would show pronounced variability. Our HO 40312 and 29305 hot Si type CP2 stars, ing wavelength, from the J- to the M­ compromise in having many data points HO 27374 is a CP3 star). Error bars indicate filter. This effect may be called by defini- per star as weil as many st~rs checked, 30. 16 line of sight. So we have a total ex­ <-_ variation in flux corresponds to a 3 % X temperature change, which in the case X xX of a Oor gives 350 K. That means, the < x xxx -x< particular star the atmospheric varia­ stellar atmosphere was inhomogenous than the visual. We knew nitude (Fig. 5). The phase shifts and am­ always assumed to be homogenous in that high precision was needed, since plitudes are very similar in every filter their physical parameters. our previous data showed that the ex­ but, because of the few data, the light We will continue this work in July at La pected amplitudes would be lower than curve must be confirmed by subsequent Silla. about 0.03 magnitude. observations. The first results looked disappointing, HO 29305 is a bright silicon type CP2 References one star after the other showed no clear star, with an effective temperature of Bonsack, W.K., Dyck, H.M., 1983: Astron. sign of variability, like in the case of the about 12,000 K. It has a high projected Astrophys. 125,29. well-known cool CP2 star HO 3980 rotation al velocity (v • sin i = 130 km/s, Groote, 0., Kaufmann, J. P., 1983: Astron. (Fig. 4). So we reached the final star on but this value may be overestimated). Astrophys. Suppl. SeI'. 53, 91. Gur list, a Ooradi or HO 29305. Though Together with its rotation al period of Koornneef, J., 1983: Astron. Astrophys. Suppl. SeI'. 51, 489. we had only seven data points per filter, 2.95 days, this teils us that the rotation al Kroll, R., Schneider, H., Catalano, F.A., Voigt, we observed in all filters a clear variation axis is tilted close to a right angle to the H. H., 1987: Astron. Astrophys. Suppl. SeI'. 67, 195. Kurucz, R. L., 1979: Astron. J. Suppl. SeI'. 40, 1. HO 29305 Michaud, G., 1980: Astron. J. 85, 589.

/ ...... - .... X 0 ~ ~ I*' "'v / ESO Press Releases ~_ )q ~ X Y. x'" XIX E \ I . " I - I \ I <10 I I The following Press Releases have I I "I I " I "I .- " I ~ been published since the last issue of l.O / " '~/ / .... / 0 the Messenger. J I H I 0 , PR 01/87: Possible Planetary System I , Photographed Around Nearby Star l.O (31 Oecember 1986; with BfW photo on 0 request). 0 PR 02/87: Quasar-like Activity in the Outskirts of an Elliptical Galaxy (29 January 1987; with BfW photo and Colour photo on request). PR 03/87: Bubbles From A Oying Star Supernova Since 0, +-r-"'--'-'---'---.---,----.-,---r--.---r-rlI , Four Hundred Years Explodes in Large -0.2 0.5 1.2 -0.2 0.5 1.2 Magellanic Cloud (25 February 1987). Phase Phase PR 05/87: Supernova in Large Figure 5: IR light curve of HO 29305 in foul' filters. The mean amplitude is 0.028 mag. Mean Magellanic Cloud: Overview of First Re­ errors are indicated in the lower rigltt corners. sults (3 March 1987). 17 SO +03°740: a New Extreme Metal-poor Owarf

P. MAGAIN, ESO

The analysis of the halo stars is an formation of the long-lived lower mass ticular to the new models mentioned important tool, not only for tracing the stars that can be observed now. How­ here, but is common to most models of chemical evolution of the Galaxy, but ever, although these models are very galactic evolution). also for the understanding of the pro­ attractive, they do not, for example, ex­ From the observational point of view, cesses of star and galaxy formation. plain the presence of s elements (e. g. it is weil known since the work of Spite Although the models are able to explain Sr, Y or Ba) in the atmospheres of the and Spite (1978) that these s elements a number of observed features, some most metal-poor stars. These elements are overdeficient in the atmospheres of basic problems remain. One of these should be seen only in the atmospheres the most metal-poor stars. However, al­ problems is the absence of Population of the dwarfs of the third and subse­ though low, their abundances are not 111 stars, i. e. stars of the first generation, quent generations: a first stellar genera­ zero, and this is the problem. Where which would have formed out of the Big tion is required to synthesize the "pri­ would be the stars of the second gener­ Bang matter (basically Hand He) and mary" elements (e. g. C, 0, Fe, ...) from ation? would not contain any heavy elements Hand He, while the stars of the second In an attempt to clarify this problem, (that is with atomic nu~ber Z ~ 6) in generation, containing these primary as weil as other problems related to the their atmospheres. Recent models (Cay­ elements, would be able to produce the early galactic evolution, I have observed rel, 1986; Jones, 1985) seem able to "secondary" elements and, in particular, a sam pie of extreme metal-poor dwarfs explain the absence of these stars, basi­ the s elements, wh ich would thus and subgiants during 4 nights (2 in May cally by showing that massive short­ appear in the atmospheres of the dwarfs and 2 in October 1986) with the CAS­ lived stars are likely to form first and of the third generation. (It should be PEC at the 3.6-m telescope. These stars pollute the interstellar gas before the pointed out that this problem is not par- were seleeted mainly on the basis of their Strömgren colours indicating very low metal abundance. Some 25 stars were observed in two spectral regions, SO +03°740 or-....::..::-T--'-'-:-....--__._-~~-_r_--..__-__,_--_r_-___.--__._-___. o centred at 4300 and 5500 Ä. A rapid C\l .... inspection of the spectra immediately showed that one of these stars, namely BO +03°740, had extremely weak lines and should be one of the most metal­ o o (Xl poor stars discovered so far. I would like to present here some results of a pre­ liminary analysis of that star, based on the blue spectrum. This spectrum was obtained on the night 13/14 October, o o with an exposure time of 40 minutes, 'f which gave a good S/N ratio for that 9.8­ mag star. It was reduced using the MIOAS and IHAP facilities at La Silla. A o portion of the spectrum of BO 03°740 o o is shown in Figure 1, while Figure 2 3845 3853 3881 3888 3877 3885 shows for comparison the same region Figure 1: Portion of the CASPEC speclrum of BO +03 740. The dots indicate the two in the spectrum of the classical extreme resonance lines of A", as weil as the H line of Ca 11 and H,. metal-poor star HO 140283. The ex­ treme weakness of the metal lines in the spectrum of BO +03°740 is immediate­ HO 140283 Iy obvious. g,---'--"-;=.::=..--,.--.,---.--..,---.------r--...----.----r---, The analysis was carried out using the ...C\l empirical models of Magain (1985). The effective temperature was deduced fram the V-K colour index, indicating T ff = 6,050 K. The surface gravity was de­ termined by forcing the Fe I and Fe 11 lines to give the same abundance, wh ich led to log 9 = 3.25. The microtur­ bulent velocity was found equal to o 1.5 km/s using the method of Magain o 'f (1984). The abundances were deter­ mined fram a detailed line-by-line analy­ sis, assuming, as usual, local thermody­ namic equilibrium (LTE). The main re­ o o sults are shown in Table 1. As far as I o know, only two stars are known with 3845 3853 3881 lower metal abundance, namely the Figure 2: Same as Figure 1 for HO 140283. giant CD -38°245 (Bessei and Norris, 18 Table 1: Relative abundances [Al/Mg] I I I I

[Fe/H] = -3.13 [Mg/Fe] = +0.59 [AI/Fe] = -0.82 [Si/Fe] = + 0.50 [Ca/Fe] = + 0.50 O. I- Cl - [Ti/Fe) = +0.38 IJ Cl Cl [Cr/Fe] = - 0.18 [Sr/Fe] = -0.22 [Ba/Fe) = -0.62 Cl

Cl

Cl

1981) with [Fe/H] = -4.5 and the turnoff Cl - star G 64-12 (Carney and Peterson, 1981) for wh ich [Fe/H] = -3.5. Inciden­ IJ tally, BO +03°740 is also probably a star near the turnoff. The relative abun­ • dances confirm the general picture out­ I I I I lined in Magain (1985, 1987) and other -3. -2. -1. O. papers, namely: [Mg/H] - overabundance of the "a elements" Figure 3: Plot of [AI/Mg] versus [Mg/H] for the stars of Magain (1987, open squares) and for Mg, Si, Ca and Ti by same 0.5 dex, BO +03"740 (full square). - overdeficiency of the s elements Sr and Ba, - large overdeficiency of AI relative to single resonance line at 3961 A. and References Mg: [AI/Mg] = -1.4. would be in error if the latter was The behaviour of AI relative to Mg is affected by departures from LTE. Arpigny, C., Magain, P.: 1983, Astron. Astro­ subject to some controversy, some' au­ Finally, the analysis of BO +03°740, phys. 127, L7. thors (e. g. Fran<;:ois, 1986) suggesting wh ich is the most metal-poor dwarf in Bessel, M. S., Norris, J.: 1981, lAU Coll. No. 68, p. 137. that [AI/Mg] is constant in the halo, at wh ich s element abundances have been Carney, B. W., Peterson, R. C.: 1981, Astro­ roughly -0.5, while others (e. g. Arpigny determined, confirms the presence of phys. J. 245, 238. and Magain, 1983; Magain, 1987) argue these secondary elements in the atmos­ Cayrel, R.: 1986, Astron. Astrophys. 168,81. in favour of an increasing AI overdefi­ pheres of the extreme halo dwarfs, in Fran90is, P.: 1986, Astron. Astrophys. 160, ciency with decreasing metal abun­ contradiction with the classical models 264. dance. The present analysis ?upports of nucleosynthesis and galactic evolu­ Jones, J. E.: 1985, Publ. Astron. Soc. Pacific this last interpretation, as is shown in tion. 97,593. Figure 3, where the representative point Magain, P.: 1984, Astron. Astrophys. 134, 189. of BO +03°740 is added to the [AI/Mg] Acknowledgements Magain, P.: 1985, Astron. Astrophys. 146,95. versus [Mg/H] plot of Magain (1987). It Magain, P.: 1987, Astron. Astrophys., in should be pointed out, however, that the I wish to thank 1. Le Bertre and H. press. AI abundance in the most extreme met­ Lindgren for providing me same infrared Spite, M., Spite, F.: 1978, Astron. Astrophys. al-paar stars is determined from the and visual photometry of this star. 67,23.

BD Pavonis, a New Double Lined Eclipsing Cataclysmic Binary H. BARW/G and R. SCHOEMBS, Universitäts-Sternwarte München

Cataclysmic binaries are double stars mary. Magnetic fields can influence the (1939) on star plates taken in 1934. The consisting of a compact primary and a structure of the disk, in same cases no object, never seen before, suddenly had cool secondary component. They are so disk exists at all and matter is forced to brightened to 12.4 mag. After 20 days close that the surface of the secondary flow along the magnetic field lines pro­ the star faded below detection limit fills its so-called Rache limit and trans­ ducing extremely hot X-ray emitting (16.5 mag) again. This led to the classifi­ fers matter towards the primary in a spots above the magnetic poles. cation as a classical nova, wh ich was stream. Oue to the system's orbital mo­ Novae, dwarf novae, several X-ray doubted already by Payne Gapaschkin tion, however, the stream does not im­ sources like AM Her stars, intermediate (1977) because of consequences of the pact on the primary but forms an accre­ polars, OQ Her stars and X-ray bursters decay time scale on the absolute mag­ tion disk around it. Where the overflow­ are examples for the large group of CVs, nitude. ing mass hits the rotating gas, a hot and the variety of classes demonstrates We observed BO Pav with the ESO bright spot is produced. The momentum their complex behaviour. 1.5-m telescape in June 1980 during a of the disk material has to be separated A unique member of this group, BO spectroscopic survey programme before it can be accreted onto the pri- Pav, had been discovered by Boyd searching for cataclysmic systems with 19 1987). The instrument had been used at BO PAVON IS La Silla for the first time in 1983 (Schoembs et al., 1987) and for SO Pav in 1985. Additionally, during the same observ­ ing period, two nights at the 3.6-m tele­ scope had also been allotted to spec­ troscopy. When observations started, SO Pav appeared surprisingly bright on the TV screen, a phenomenon which first was attributed to its red colour, but when the first spectrum was displayed showing broad Salmer absorption lines instead of emissions, it became obvious that the object was caught during an eruption. This outburst is the first one DU IESCENCE known to us since discovery. It immedi­ ately confirmed our suggestion that SO 391313 411313 43013 451313 471313 491313 511313 Pav rather is a dwarf nova than a c1assi­ Figure 1: Averaged spectra of BO Pavonis during eruption and in quiescence. The outburst cal nova. Although it was great luck to spectra (upper part) were taken at the ESO 3.6-m telescope with the B & G and GGO in 1985. Strang broad absorption fines of Hand Hel 4471 are shown together with Hell 4686 in encounter this outburst, we knew that emission. The spectra in quiescence state (Iower part), obtained with the 2.2-m telescope in because of the dominant radiation from 1986 mainly show the Balmer lines in emission. the accretion disk during this active phase, there would hardly be a chance to find spectral features of the secon­ high orbital inclination, i. e. with broad velopments had started, a photometer dary, one important aim of our mission. and double peaked emission lines. Oue with increased efficiency and time reso­ Detection of the secondary spectrum in to its spectrum SO Pav was selected for lution, i. e. with simultaneous USVRI cataclysmic binaries is of fundamental further investigation. capability and much lower sensitivity to importance. In that case much more Photometrie light curves revealed variable extinction was not available to reliable system parameters can be de­ rived than fram radial velocities of the strong flickering and eclipse like fea­ uso Since our photometrie programmes emission or absorption lines originating tures (H. Sarwig, R. Schoembs, 1981). at other sites were also affected by poor in the complex primary accretion disk The data had been seriously affected by weather conditions, the decision to con­ configuration. Typical spectra of SO Pav variable extinction however. Since the struct our own appropriate photometrie during outburst and quiescence are dis­ object is weil observable only during the equipement was taken in 1982. The new played in Figure 1 for comparison. season around June, known for its un­ system allowed to measure three favourable weather conditions, several sources (object, nearby comparison star Immediately after the spectroscopic attempts to complete the observational and sky background) in five colours run, photometrie observations at the 1­ material had to be made. A first analysis (USVRI), all simultaneously and with m telescope started for 8 nights. We of the object was based on data ob­ high time resolution (Sarwig et al., were curious of the first light curve, in tained at La Silla in 1980 and 1981 (H. Sarwig and R. Schoembs, 1983). This PLOOATE: 860823112924 paper reported the orbital period (P = 4.3 hours), the existence of a primary BO PAV 1985.06.17 eclipse and strang effects fram ellipsoi­ UB -0.50 dal distortion of the Roche lobe filling -0.25 U 0.00 component. The secondary turned out B-V ---- V-I -0.50 to be unusually luminous. The complex double peaked emission line profiles were difficult to measure. Radial velocity - - - U-B 0.00 ~~~,,,>,:;,,.;ß;;,.;?-'I-:-;i:,~\,~;...... ;.;..:<~~<·;;.\ ";·~,'i':'i-.·::7,;(:>ti --- ~:O 0.00 variations of 600 km/s were determined .. 1~:?5 ______V-I 0.00 by means of correlation tech­ niques. These results considerably in­ creased the interest on SO Pav. A furth­ er proposal for photometrie observa­ 12.9 tions in 1982, granted with 9 nights at the Walraven Photometer, was totally impeded by terrible weather. It was that period when a blizzard at La Silla stopped all astranomical activities. Oiscussions on the most appropriate observing techniques convinced us that we would need a larger telescope for 0.00 0.10 0.20 spectrascopy and a photometer totally TIME - O. 17B094 [dl different from classical single-channel Figure 2: UBVRIlight curves of BO Pavonis during eruption taken in the first observing night at instruments for observation of SO Pav the ESO l-m telescope with the multichannel photometer. The deep eclipse of a small blue and many other variable objects. Al­ prtmary and disk is shown and a shallow minimum of a larger redder object at orbital though at some other institutes first de- phase 0.5. 20 particular whether the eclipse feature PLOOATE: 860823130555

visible during quiescent state would BQ PAV 1985.06.24 have disappeared or still exist. The latter case would mean that the orbital inclina­ ~:~ -6:88 ti on is so large that even the bright cent­ B-V 0.00 ral accretion disk, the main source of radiation during eruption, is eclipsed. B-V Y\.1tJJr'~.,;.~'j-~.,...-r..);.v::.;;..~.....~~'~vr-..~:JI,;c:..:~;'~~.J~~~~,-4:_,~<:! ..~,~""~ .....~,,,"~.:,.;. V-I -2.00 Somewhat less than one orbital period f------' ---_ after beginning of observation, when we already thought that the eclipse had dis­ appeared, the intensity curve on the ~ ------­ ---- V-I 0.00 graphie screen suddenly began to drop :E while the comparison star stayed con­ stant, indicating that no clouds were V 14.7 coming up. Some 20 minutes later the light curve had returned to its original level. The reduced light curves of this night 15.2 are displayed in Figure 2 while Figure 3 shows BO Pav during the last night of our observing period, when the star had almost reached its normal brightness. 0.00 0.10 0.20 0.30 0.40 TIME - 1.002428 (d) Figure 4 shows the recorded count­ rates of sky and comparison star for all Figure 3: UBVRI light curves of BD Pavonis at the end of eruption, obtained in the last nights. Cloudy skies yield comparison observing night. star counts ranging between their nor­ mal values and the sky counts, while posed by sky brightness variations It is found that atmospheric transpa­ c1ear nights only show the expected de­ (most pronounced in U during moon set rency changes up to 80 % can be com­ pendency on zenith distance super- at beginning of nights 7 and 8). pensated applying the differential

PLOOATE: 860822190255.

PHOTOMETER-CHANNELS: 2 (COMPARISON+SKY+OARK) & 3(SKY+OARK).

U. UIE02

~ ~. .;. " .:" :.' l I ,~, ::, !Li ~.' ~ I Q. '. o '. .". ". U B. B.33E+03 cn \...,/ \----- u.o,o UJ ...J :~~.". ~ • 1." ~ ~ UJ " ',. ',t I- :'\'" . " , • J' ..... ~: •• .;. , :: r'.' o ,'(( :: cn L', , I UJ ',:.{" , .~ "'; .: " % .. .. ~ ~- I­ •"C' • ~. . < ":":: . >.e u : :'.. ~: .. UJ cn :H'::: ""f Z R 5.00E+03 H --~. Y.O.O cn :~~ ". ~: ---.. I­ :", : " Z ...... r " :::l - o : :'..::., ....1 '. .,;y U t" I . '. .:.: '. '\." ~ .~ " R ..( :.: 1 9.O!E+O< ------RO.O " --- - ( " ...... "(( ' . .... \ . '. 1 ..; ", 10.0 O.OOE+

Figure 4: Count rates for comparison star and sky simultaneously measured in UBVRI with BD Pavonis during the whole observing period of 8 nights. In the pairs of curves the lower sky curve is the lower limit for the pure comparison star counts in case ofzero sky transparency. Dark counts are negligable. 21 PLODATE:860821054830.

80 PAV 1985.06.17.

~:a. :~!.., II 3.l2EIOO

a 1.00800 ;~ ~ - -- II 0.0 o u . ~ . "­t­ ~. . • "0-. U ~ UJ ; "') . Y. UliHl lXl Y'!Y'f' o -- --- B. 0.0 t~ : • 1 ~.. lt Z.~l -_.__.- Y.O.O

~~f1 'I~I ,- ,. 1 2.Z7Hl ------lto.O

10.0 . O.OOE+

Figure 5: The UBVRI intensity variations of BO Pavonis during decay from the eruption in 1985. Gondensed representation.

measuring methode. Condensed light lines eould be reeognized to follow a the seeondary eomponent as weil. A eurves in Figure 5 reveal the behaviour sine like eurve eomplementary to the period analysis of the radial veloeity var­ of the intensities relative to the eompari­ emission lines (Fig. 6). - The seeondary iation yielded the photometrie period. son during deeay from eruption. Ouring eomponent had been deteeted! - The In order to derive accurate system bright phases the primary eelipse is a outburst speetra of 1985 had of eourse parameters from the observational data, prominent feature deeper at shorter also been earefully eheeked earlier by several effects have to be taken into wavelengths. Its relative minimum depth plotting all traees in a single figure but aceount as for example the non spheri­ stays fairly eonstant throughout deeay. no definite evidenee for the eompanion cal shape and temperature distribution There is a seeondary minimum around star eould be found. In the last weeks, a of the secondary and the distortion of phase 0.5 shown in Figures 2 and 3, revision of the same speetra using the the emission lines due to the complex whieh is stronger in the red. Ouring the identieal teehnique as in Fig. 6, revealed velocity distribution of the line emitting first two nights this minimum has an eelipse-like shape with sharp edges and Hel 5876 flat bottoms. Later on it rather re­ y sky sky sembles variations eaused by ellipsoidal distortion of the seeondary. Again we 1 1II Ir I 1 found strong evidenee for an unusual bright seeondary whieh eneouraged the attempt to obtain speetra during quies­ eenee in order to deteet the speetrum of the seeondary. Sueh speetra eould be obtained with the ESO 2.2-m teleseope in 1986. While observing, the 74 CCO speetra were sequentially arranged after eaeh expo­ sure into a two-dimensional frame dis­ played on the RAMTEK sereen. Among 5200 5700 6200 the well-known emission line system of Figure 6: Sequential arrangement of 38 GGO spectra of BO Pavonis in quiescence taken with the primary disk eonfiguration suddenly the 2.2-m telescope in 1986. The unlabeled tick marks indicate absorption lines of the after a few integrations faint absorption secondary showing a sine like radial velocity variation. 22 material. Therefore the results obtained so far are still preliminary, however, it is SUMMER SCHOOL ON obvious already that BO Pav has raised from a black dot on a plate in 1934 to an "OBSERVING WITH LARGE TELESCOPES" important star among the CVs. ESO and the Astronomical Council of the Academy of Sciences of the References U.S.S.R. will organize a summer school during the period 21-30 September 1987 at the Byurakan Observatory near Erevan on the subject "Observing Barwig, H., Schoembs, R.: 1981, Inf. Bull. With Large Telescopes". A limited number of advanced predoctoral or recent Var. Stars No. 2031. Barwig, H., Schoembs, R.: 1983, Astron. As­ postdoctoral participants from the ESO member countries will be invited to trophys. 124,287. attend. Persons interested in participating should apply before 15 April 1987 Barwig, H., Schoembs, R., Buckenmayer, C.: to: Office of the Oirector General, ESO, Karl-Schwarzschild-Str. 2, 0-8046 1987, Astron. Astrophys., Main Journal, in Garching b. München. press. Applicants should give their main biographical data, passport number (incl. BOYd, C. D.: 1939, Harv. Ann. 90, 248. date and place of issue), abrief account of their scientific work and a list of Payne-Gaposchkin, C.: 1977, in: Novae and publications. A letter of recommendation from their (thesis) supervisor should related Stars, p. 3. also be included. Schoembs, R., Dreier, H., Barwig, H.: 1987, Astron. Astrophys., in press.

Strengthening Research Links Between Astronomy/Astrophysics and Computing/Statistics 1 F. MURTAGH , Space Telescope - European Coordinating Facility, European Southern Observatory. A. HECK, C. D. 5., Observatoire Astronomique, Strasbourg, and V. DI GESU, Dip. di Matematica ed Applicazioni, Univ. di Palermo, and IFCAI/CNR, Palermo.

In this article, a few current research ern Astronomical Methodology, with a tled Statistical Methods in Astronomy directions are discussed, wh ich relate to current active membership of a little which was held in Strasbourg in 1983 the common interfaces between as­ under 100 worldwide. AbulIetin is pub­ (see Rolfe, 1983), and additionally ad­ tronomy/astrophysics, computer sci­ lished twice yearly, and is currently con­ dresses the topic of centralized data ence and statistics. They relate essen­ tained in the Bulletin d'lnformation du collections wh ich are becoming increas­ tially to organizational matters (working Centre de Oonnees de Strasbourg ingly important. The proceedings of this groups, conferences). Within the next (C. O. S., Observatoire de Strasbourg, conference will be published by ESO. decade contact between researchers France). Further details may be obtained - While it is important to focus efforts over computer networks will become fram Andre Heck or fram Fionn Mur­ among astranomers and astrophysicists increasingly trauble-free, but for the tagh. in order to tackle new problems in in­ present, contact between widely - Faced with ever-greater concentra­ novative ways, it is also important to scattered researchers (and especially tions of astronomical data, new ap­ mobilize computer scientists to bring in­ among those who straddle traditional proaches to data handling and analysis creased efforts to bear on astronomical disciplines) is necessarily in hard-copy need to be discussed and perfected. problems. A trend of relevance in recent form, as for example in this journal! Recent years have seen the well-known years has been the increasing number - Multivariate data analysis could be workshops held at the Ettore Majorana of astronomicai studies published in the viewed as mid-way between statistics Centre in Erice, Sicily (Oi Gesu et al., mainstream pattern recognition litera­ and graphics, and is an important part of 1984; 1986). The next workshop in the ture. One important organ, international­ the armoury of methods and tools avail­ Erice series (1IIrd International Workshop Iy, in computing is the International able to the astronomer. Work to date in an Oata Analysis in Astronomy) will be Association for Pattern Recognitian astronomy and astrophysics, using mul­ held in June 1988. It will address ad­ (IAPR). It is concerned with pattern rec­ tivariate methods, has been surveyed vanced and unconventional data analy­ agnition and image processing in a (see Murtagh and Heck, 1986), and a sis methodologies; knowledge based broad sense. It organizes major biennial text-book motivating methods, detailing systems; and parallel algorithms for conferences (the most recent in Paris in the mathematics, and enumerating data analysis. The use of fuzzy techni­ October 1986 had about 900 atten­ case-studies has recently become avail­ ques and possibility theory is also an dees), sponsors the journal Pattern Rec­ able (Murtagh and Heck, 1987). an-going topic of relevance, for low­ agnition Letters, and publishes a news­ - A working group was set up in 1985 statistics image data. letter. Membership in the IAPR is by way to further contact between researchers -A conference entitled Astronomy of the relevant national pattern recogni­ with an interest in this, and related from Large Oatabases: Scientific Objec­ tion or computing organization. The fields. It is the Working Group for Mod- tives and Methodological Approaches IAPR has a number of Technical Com­ will be hosted by the ST-ECF in Garch­ mittees active in various fields of activi­

I AHiliated to the Astrophysies Division, Spaee Sei­ ing on 12 -14 October 1987. It functions ty, and such a Technical Committee has enee Department, European Spaee Ageney. as a follow-up conference to one enti- recently been set up for astronomy and 23 astrophysics. Further details may be ob­ tained from Vito Oi Gesu or from Fionn A conference, hosted by the Space Telescope - European Coordinating Murtagh. Facility, on The foregoing trends serve to illus­ trate how "computational astronomy" Astronomy from Large Databases: has now become solidly established as a subdiscipline of importance in as­ Scientific Objectives and Methodological tronomy and astrophysics, closely Approaches following in the footsteps of its sister­ subdiscipline, image processing. will be held in Garching from 12 to 14 October 1987. Topics will include statistical analysis of complex databases, object classifica­ References tion problems, astrophysics from large data collections, together with state of 1. V. Di Gesü, L. Scarsi, P. Crane, J. H. Fried­ the art reviews of astronomical database technology and expert system applica­ man and S. Levialdi (eds.) (1984): Data tions. Analysis in Astronomy, Plenum Press, New The Proceedings will be published by ESO. York. Further information may be obtained from F. Murtagh, ST-ECF, ESO, Karl­ 2. V. Di Gesü, L. Scarsi, P. Crane, J. H. Fried­ Schwarzschild-Str. 2, 0-8046 Garching bei München, FRG. man and S. Levialdi (eds.) (1986): Data Analysis in Astronomy 11, Plenum Press, New York. 3. F. Murtagh and A. Heck (1986): An anno­ Astronomy and Astrophysics Supplement ate Data Analysis, D. Reidel, Dordrecht. tated bibliographical catalogue of mul­ Series (in press); ESO Scientific Preprint 5. E.J. Rolfe (ed.) (1983): Statistical Methods tivariate statistical methods and of their No. 465 (Sept. 1986). in Astronomy, European Space Agency astronomical applications (magnetic tape). 4. F. Murtagh and A. Heck (1987): Multivari- Special Publication 201 (270 pp.).

Crowded Field Photometry Using EFOSC and ROMAFOT K. J. MIGHELL, Kapteyn Observatory, Roden, The Nether/ands

EFOSC from the ESO 2.2-m telescope. Using data, etc. By using the ESO Munich both real and artificial data, I found Image Oata Analysis System (MIOAS) The ESO Faint Object Spectrograph OAOPHOT to be potentially useful as my main image processing system, and Camera (EFOSC), instrument of the for the 2.2-m data (0.35 arcsecond per I only needed to use the few program­ ESO 3.6-m telescope, can be used as a pixel) and totally inadequate for the less mes wh ich actually did photometric re­ very efficient CCO camera for wide­ weil sampled EFOSC data (0.675 arc­ duction. I have converted these pro­ band photometry of crowded stellar second per pixel). The results of this trial grammes to run on VAX computers and fields. EFOSC was designed to match experiment do not bode weil for the have renamed the package ROMAFOT. the RCA SIO 501 EX CCO (320 x 512 ability of OAOPHOT to work adequately I have also written a C language pro­ pixels, 30 x 30 microns pixel size). Each with data from the Hubble Space Tele­ gramme "Personal Astronomical Work pixel corresponds to 0.675 arcsec and scope. Station" (PAWS) which effectively trans­ the total field of view is 3.6 x 4.7 arcmi­ forms a standard Commodore Amiga nutes (1). Using the instrument in direct personal computer into a complete ELiA imaging mode, the limiting magnitude of MIOAS work station consisting of emu­ a 15 minute exposure with seeing of ELiA (4) was developed at the Obser­ lations for (1) a VT-1 00 terminal, (2) a HP FWHM = 1.3 arcseconds in the V band vatory of Rome specifically to do photo­ graphics terminal and (3) a OeAnza im­ is about 25.5 for a signal-to-noise ratio metric reduction in crowded stellar age display. By replacing the Tektronix of 3 (2). fields - in particular globular clusters. I terminal that ELiA previously required A typical EFOSC field of the Small visited the Observatory of Rome in Oc­ with an Amiga running PAWS, I have Magellanic Cloud will yield hundreds to tober 1985 and reduced some EFOSC been able to substantially improve the thousands of stars in less than five mi­ images of an extremely crowded field in performance of ROMAFOT. By judi­ nutes! In good seeing conditions the the SMC. Although the image was quite ciously using coloured images (instead central cores of star images will be par­ complex, ELiA made excellent fits to of shades of green), ROMAFOT has tially undersampled due to the 0.675 over 1,400 stars. ELiA employs a non­ been improved to make it easier for the arcsecond per pixel scale. The combi­ linear least squares fitting algorithm user to quickly produce more accurate nation of crowded stellar fields with par­ which was found to be remarkably suc­ results. The combination of ROMAFOT tially undersampled data presents a cessful at ignoring cosmic rays and with MIOAS provides the astronomer challenge to the astronomer who wishes other image defects. with a very powerful tool to do accurate to do accurate stellar photometry with photometric reduction of crowded stel­ EFOSC data. lar fields. ROMAFOT and the Personal Astronomical Work Station DAOPHOT ROMAFOT/MIDAS Features and At the Rome Observatory, ELiA Abilities In March 1986 I visited ESO Garching serves as a complete image processing to see if the photometric reduction system. Thus there are programmes to • Reads FITS tapes package OAOPHOT (3) was suitable for read and write FITS tapes, programmes • Automatic location of most stars on a use with EFOSC data and CCO data to flat-field images, programmes to plot eco image 24 metric reduction in crowded stellar photometry for many faint stars with fields is shown in Figure 1 (all plots were short exposures. The ability to reach a made with PAWS). visual magnitude of 22 in just 30 sec­ Figure 1a shows a gray-scale repre­ onds will be very useful to those as­ sention of a crowded stellar field near tronomers who would like to determine the centre of Carina, a dwarf spheroidal the colour-magnitude diagrams of galaxy in the Local Group. The data globular clusters and stars in the Galaxy were collected with the ESO 3.6-m tele­ and nearby Local Group galaxies. scope using the EFOSC instrument with seeing of FWHM = 1.35 arcseconds in The Future of ROMAFOT the V band. The integration time was 30 seconds. The subfield is 16.9 by 16.9 Roberto Buonanno (Observatory of arcseconds in size. The intensity scale is Rome), Rein Warmeis (ESO) and I will be linear with black representing the max­ working in the next few months to offi­ imum and white representing the cially implement the ROMAFOT pack­ minimum intensity. age as apart of MIOAS. The exact form Figure 1b shows the same subfield in of the MIOAS version of ROMAFOT has the form of a three-dimensional plot. yet to be finalized but it will probably be The brightest star has a flat core be­ very similar to the system I have de­ cause it was clipped for the plot to scribed above. show better the fluctuation of the background. The second highest peak is composed of two closely spaced References stars. (1) O'Odorico, S., Oekker, H., "The Five Ob­ Figure 1c shows the residual field aft­ serving Modes of EFOSC, the ESO Faint er all five stars were fitted. The visual Object Spectrograph and Camera Oe­ magnitudes of the stars are 19.16 signed Around a CCO Oetector". ± 0.01, 20.56 ± 0.05, 21.38 ± 0.11, (2) The Messenger 41, p. 26, 1985. 21.03 ± 0.06, 22.00 ± 0.16, respec­ (3) Stetson, P. B., "OAOPHOT User's Manu­ tively. The peaks of the two closely al", Dominion Astrophysical Observatory, spaced stars (V = 20.31, V = 21.13) are Herzberg Institute of Astrophysics, 5071 separated by only 2.12 pixels. The full West Saanich Road, Victoria, British Col­ umbia V8X 4M6, Canada. width at half maximum (FWHM) for (4) Buonanno, R., Corsi, C. E., Oe Baise, these data is only 2.00 pixels, so these G. A., Ferraro, 1., 1979, in Image Process­ two stars are just barely resolved. ing in Astronomy, eds. G. Sedmak, M. The above example shows how Capaccioli, and R.J. Allen, Trieste, Italy, EFOSC can be used to obtain useful p.554. Figure 1. Storm Petersen and Astronomy • Examination of each stellar image to check for image quality, potential Robert Storm Petersen (1882 -1949) wrote prolifically, he is more famous for blending and missed fainter stars started his career as a butcher, but be­ his drawings wh ich appeared regularly • Fast nonlinear least squares fitting came a symbol of arch-Oanish humour in Oanish newspapers from 1905 to his routines that allow up to five blended during his lifetime. Although Stürm P. death. Many of the early drawings dealt components to be fitted simultane­ (as he is known by his countrymen) with social injustice, but he soon found ously his own, less offensive way of expres­ • Accurate and believable error esti­ sion. A museum dedicated to his works mates are determined for all fitted pa­ has been opened in Copenhagen and rameters also exhibits many of his cartoons. • Examination of the final fits by dis­ Many of them concern the exact sci­ playing the original data and residuals ences which Storm P. approached with •A proficient user can process 500 to asound measure of down-to-the-earth 1,000 stars per day (depending on the scepticism. But his dry humour always crowding complexity of the fjeld) treated members of the astronomical • Transformation of coordinates from profession and other employees of the one CCO frame to the system of state with due reverence ... another frame • Transformation of instrumental mag­ nitudes to a standard photometric EDITOR'S NOTE system The information about the bright • Plots the results on a standard HR supernova 1987 A in the LMC wh ich diagram is brought on the following pages • Artificial stars can be randomly in­ was received on March 2,1987. The serted into the data at known flux publication of this issue of the levels to allow the user to find the Messenger was delayed in order to systematic measurement errors. 'The police now col/aborates with the as­ inciude a first overview of the excit­ A visual example of how ROMAFOT tronomers to determine the exact time when ing results. and MIOAS can be used to do photo- bicycle lights must be lit. ' 25 The Supernova in the LMC

During the night of 23/24 February, I. Shelton at the University of Toronto station at Las Campanas discovered a supernova in the Large Magellanic Cloud - the first naked-eye supernova to be seen since Kepler observed his "nova" in 1604. From the following night on, most ESO telescopes have been used to observe this object. The extraordinary brightness of this supernova for the first time allows very detailed observations to be made of the still mysterious supernova process, which involves the collapse and subsequent explosion of a star at the end of its evolution, and the probable genesis of a neutron star. In addition, this brightness allows studies to be made of the halo of our Galaxy and of the intergalactic medium by observations of absorption lines produced by the intervening matter. The absorption line data obtained with the High Resolution Spectrograph at the 1.4-m CAT have been unexpected and qualitatively superior to anything obtained before in the LMC. In the last decades, supernovae have been observed in other galaxies; these supernovae, however, were always more than a hundred times fainter than the one in the LMC. While studies made with large telescopes at La Silla and elsewhere have yielded interesting data, no very high resolution studies were possible. With the full light gathering power of the VLT, however, fainter supernovae in other galaxies as weil as some stars in the LMC will be observed with the same spectroscopic resolution as has been possible now for the LMC event. This supernova thereby gives us a preview of the discoveries that can be made with the VLT. Following the discovery of the supernova, the telescope schedules have been changed and many planned programmes have not been executed. All observers at La Silla have switched over to the supernova with much enthusiasm. While for their coinvestigators it may be disappointing not to receive the data from their planned programmes, we expect that they will understand that it was not possible to continue business as usual in the light of this event. The initial data will be published very rapidly to ensure that the scientific community be fully informed. L. WOL TJER, Oirector General ofESO

The Initial Impact of the LMC Supernova Between 2 o'clock and 7 o'clock uni­ to a factor of 100) fainter at maximum can probably resolve these questions. versal time (UT) on Monday morning, light than expected. This might be due There is one characteristic of the LMC February 23, 1987, a star in the Large to the fact that the progenitor is a B star supernova that is not modest. The Ha Magellanic Cloud (LMC), at the position rather than an M star. It has been sug­ line shows structure 1 000 Ä wide. This of the B3 I supergiant Sanduleak gested by Truran, Höflich, Weiss and corresponds to velocity outflow of -69202, began to brighten rapidly. By Meyer (private communication) that the 25,000 km/sec. If the envelope con­ 10 o'clock UT it had brightened by a difference between this supernova and tinues to expand at this rate it will sub­ factor of 200. And the next day it had Type 11 supernovae in other galaxies is tend an angle of nearly 1/4 arcsec at the increased in brightness by an additional attributable to the low metalIicity of the end of a year. When the VLT is com­ factor of 10. As L. Woltjer notes above, Large Magellanic Cloud. Brunish and pleted about 10 years fram now, the this star is the first really bright superno­ Truran (1982, Astrophysical Journal, envelope will be big enough for detailed va in the modern era. Because of its Suppl. 49, 447-468) have shown that study by the VLT. southern declination it can only be seen metal poor B stars may never become M Early excitement was generated by by southern observatories and space supergiants prior to the onset of carbon CES spectroscopy of interstellar (and observatories. burning. According to Peter Höflich at intergalactic!) atomic lines. The Ca 11, H The excitement generated by the the Max Planck Institute for Astraphy­ and K lines were broken into over 20 supernova is intense. It is unusual in a sics, the B star envelope has a steeper components with velocities ranging number of respects and it is bright density gradient than the M star en­ from the Galactic value to the velocity enough to be studied in great detail. It is velope. The denser inner envelope may corresponding to the LMC, and numer­ nearly certain that the progenitor of the trap the photons and result in a fainter ous lines with intermediate velocities supernova is Sanduleak -69202. Since maximum than would be the case if an showed the presence of intergalactic B supergiants were not believed to be M star had exploded. Because of this, c1ouds. When CES spectra are com­ evolved enough to undergo the core more energy can be converted into kine­ bined with far ultraviolet spectra taken collapse necessary to produce a super­ tic energy in the outgoing matter. Since with IUE it will be possible to determine nova, it had been thought that only M the LMC is metal poor, this model may the details of the ionization structure giants or supergiants could be the pro­ explain the explosion of Sanduleak and abundances of the interstellar genitors of supernovae. The LMC super­ -69202. These authors also note further clouds in the line of sight to the super­ nova is the first type 11 supernova to be that it helps us to understand why we nova. The LMC supernova is al ready a seen in an irregular galaxy. It has long have not previously observed Type 11 bright radio source and it is very likely been a mystery why type 11 supernovae supernovae in irregular galaxies. In any that it will become sufficiently bright for were not seen in irregular galaxies. Also case, the future development of the radio observations to determine the this supernova is 2 to 5 magnitudes (up supernova and more detailed modelling neutral hydrogen column densities in 26 these clouds. Such studies illustrate the value of exploiting a temporarily bright A workshop will be held at the ESO Headquarters in Garching from July 6-8, source in order to study the physics of 1987 on the intervening material. These reflections are being written "The Supernova in the LMC" one week after the explosion. We still Oata obtained during the first half year of the supernova will be presented and have much to learn. Ooes the LMC other evidence and theories about supernovae confronted with the data. supernova represent a new, previously unknown class of supernova? Will we For further information please contact: see changes in the interstellar lines that Or. J.1. Oanziger, European Southern Observatory, Karl-Schwarzschild-Str. 2, will indicate the size of these gas fila­ 0-8046 Garching. ments? Can model calculations to­ gether with early observations accurate­ Iy pinpoint the moment the envelope the Mont Blanc Neutrino Observatory? fusion? Surely this supernova will be began to expand? If so, what is the time When will we be able to see the inner one of the most actively studied objects delay between the beginning of the ex­ part of the expanding envelope with its in the sky for years to come. pansion and neutrino burst detected by rich soup of the products of nuclear J. Wampler (ESO)

Walraven Photometry

The measurements were converted from log intensity to magnitudes.

UT V V-B B B-L L B-U U U-W W

WAVEL. (A) 5467 4325 3838 3633 3255 BANDW. (A) 710 420 220 230 160

Feb. 25.02 4.64 -0.19 4.83 -0.12 4.95 -0.13 4.96 -0.14 5.10 25.15 4.57 -0.19 4.76 -0.11 4.87 -0.11 4.87 -0.10 4.97 26.01 4.55 -0.26 4.81 -0.24 5.05 -0.31 5.12 -0.18 5.30 26.20 4.53 -0.26 4.79 -0.28 5.07 -0.33 5.12 -0.14 5.26 27.01 4.48 -0.39 4.87 -0.48 5.35 -0.65 5.52 -0.57 6.09 27.17 4.45 -0.40 4.95 -0.50 5.45 -0.71 5.66 -0.65 6.31 28.01 4.46 -0.56 5.02 -0.72 5.74 -1.26 6.28 -1.09 7.37 28.10 4.45 -0.54 4.99 -0.72 5.71 -1.27 6.26 -1.02 7.28 28.24 4.45 -0.56 5.01 -0.76 5.77 -1.35 6.36 -1.02 7.38 +/- 0.02 0.02 0.04 0.02 0.04 0.02 0.06 0.02 0.09

Observed by F. Steeman on the Dutch 91-cm telescape on La Silla. P. Monderen, H. E. Schwarz (ESO), and F. Steeman (Leiden).

Geneva Seven Colour Photometry

The Supernova 1987A in LMC was va photometry (Golay, M., 1980, Vistas SN 1987A was measured together measured 46 times between February in Astronomy, vol. 24, 141) at the ESO with the comparison star HO 37935, a 25 and March 2 in the seven filter Gene- La Silla observatory. Geneva standard star. It should be , I I I 1 I ... II I I I 1 '- 61 108 - ... - I- - '" I 2 . .. " Vl , U " :< \ , .... .> f- ~'. ) - 6 : " .: - - , - ..) , "\ V ~ I- - ..... ~;l: ,. .... '.. "0:' ~ - 62 ~ - - , 12 . !' :

-J 1 I I I ,- -I I I 1 I 1- FE625.0 26.0 27.0 28.0 MAR 1.0 2.0 FE625.0 26.0 27.0 28.0 MAR 1.0 20 FE625.0 26.0 27.0 28.0 MAR 1.0 2.0 Figure 1: (a) U magnitude relative to the comparison star HO 37935; (b) 81, 8 and 82 magnitudes relative to the comparison star HO 37935; (c) V1, Vand G magnitude relative to the comparison star HO 37935. 27 Table 1 I- I I I I - Date DV/DT DU/DT DB/DT I 004 Feb.25.0 -0.08 0.23 0.03 ~ '. V1 -G - Feb.26.0 -0.10 0.40 0.08 Feb.27.0 0.01 0.83 0.18 Feb.28.0 0.02 0.74 0.22 I- - Feb.29.0 0.01 0.55 0.17

I- - noted that the values presented here are (Table 1), we conclude that the curve only preliminary, the final reductions will became considerably smoother after be performed in Geneva. Figure 1 the inflexion point. - - .," shows the different magnitudes, relative The decrease in B1, Band B2 (Fi­ to the comparison star. A first important gure 1B) is much slower, the B2 curve ~ feature to be noticed is the retardation even remains almost constant during IIIII 1- of the intensity drop in the Ion ger the first two nights. Nevertheless, these FEB 25.0 260 27.0 28.0 MAR 1.0 20 wavelength V 1, V and G filters with re­ curves too show an inflexion point. In Figure 2: V1-G index relative to the compari­ son star HO 37935. spect to the B 1, Band B2 and especial­ contrast, the V1, V and G curves have a Iy to the U filter, which was al ready pronounced maximum during the third decreasing significantly during the first night (February 27.0) and a slow de­ night of observations. In Figure 1A, re­ crease afterwards. The V1-G index, in correlated with the disappearance of the ferring to the U filter, we see that after a Figure 2, shows a completely different P Cygni He I 5876 line observed simul­ strong decrease in brightness between behaviour from the other colour indices. taneously by Danziger, Fosbury and February 27.0 and 27.9, the curve ex­ It has a strong peak towards the blue, Dachs at the 3.6-m telescope. hibits an inflexion point. From the calcu­ coinciding with the time of maximum J. Babel (Lausanne/Geneve), lated gradients of the U light curve light in the V filter. This feature can be 0. Heynderickx (Leiden)

Strömgren Photometry As of March 2, the supernova SN SN 1987 A 1987 A was observed with the Danish 50-cm telescope on every night since its I I 1 I I I 4.2 I-- - discovery. The Strömgren uvby inter­ Y mediate band system was used. This ..... -., ... combination of a sm all telescope and 4.6 I- .'" - - band widths of about 200 A turned out - to be ideal for observing such a bright .", ... f- - star. 5.0 - -.. - b . The bands in the uvby system are 5.4 - ... - centred at 5490 A(y), 4690 A(b), 4110 A (v), and 3500 A(u). From spectra of the supernova obtained by other observers 5.0 - ~ - on La Silla we know that y essentially - measures the continuum while both b 5.4 -V -- - .. - and V fall on edges between emission .. lines and their P Cygni absorption 5.8 - - - throughs. The y magnitude is very simi­ lar to the visual V magnitude. -. 5.4 - "'e( Preliminary light curves in the instru­ - mental system are shown in the figure. It 5.8 U .. - is obvious that u peaked before obser­ - ."" vations began and is now declining 6.2 I- - rapidly, while a maximum in y probably was reached around February 28, 1987. .... 6.6 I- - However, the changes in y are smal!. In . addition to the uvby light curves, some 7.0 I- - H ß observations are made to see whether changes in the Hß structure 7.4 I-- '. can be detected by studying the flux - through the narrow (30 A) beta filter. 7.8 I- '" - B. E. He/t (Copenhagen), L. P. R. Vaz I I I I I (Säo Paulo) and H. E. Jergensen I (Copenhagen) FEB 25.0 26.0 27.0 28.0 MAR 1.0 2.0 28 Detection of the Diffuse 15 Band at A5780 Ain the Large Magellanic Cloud

The band at A5780 Ais one of the 39 UIlIl98 diffuse IS absorptions in the region n 4400-6850 A wh ich are generally correlated with the colour excess E(B-V) (Herbig, Astrophysical Journal, 196, 129, 1975), and whose origin is still unknown. G. Vladilo (Osservatorio As­ tronomico di Trieste, Italy) took an expo­ sure of 1h15 m of SN 1987 A in the spec­ tral range around A5780 A, with the CAT+CES+Reticon and a resolving power of 100,000. In Figure 1 one can see an expanded detail of the resulting

calibrated spectrum. It is clear that two <0 features have been detected: one close Savage, M.N.RAS., 217, 126, components, once normalized to the found by Herbig (1975) in his survey of 1985). This is the first extragalactic de- continuum, are 0.023 and 0.018 respec- galactic lines of sight. G. Vladilo (Trieste)

The Temperature of 1987A analysis does not reveal significant -6.21977 periodic or non-periodic variations on short timescales. The 3 sigma level for the detection of periodic variations was -6.78887 I 0.0004 relative amplitude. 1 The system at the GMS telescope is normally used for monitoring gamma­ -7.35796 ray bursters and has been described by Bouchet and Gutierrez (Messenger, 45, 32). Thanks to the frantic work of J. -7.92706 Alonso and F. Gutierrez, it was possible to adapt it for monitoring the SN 1987 A on every clear night since the discovery, -6.49819 with a time resolution of 10 millisec and 1 millisec in the Johnson V band and in white light. It has not been possible to -6.06529 detect any periodical fluctuation in the frequency interval between 0.0003 and

-0.00206 -0.33276 -0.06351 0.205751 0.475022 0.744293 Visible photometry and infrared CVF seans. Oata were eol/eeted on the night between February 28 and March 1, 1987, with the standard photometer attaehed at the ESO 50-em in the broad Johnson bands UBVRI, and with the INSB deteetor at the 1-m teleseope for the .·B :. '.;., infrared, at La Sil/a. IR data have been eol/eeted by P. Bouehet and R. Stanga. The eontinuous . "'~'" line is the fit of a blaek body with a temperature T = 5900 K. Vertieal axis: Log (flux density 2 (ergs em- S-I Ilm-~). Horizontal axis: Log (J. pm). B·'

Fast Photometry of 1987 A ...... ,'.: ..-..'.:...... [01' ,., Fast photometry of the SN 1987 A has were obtained with time resolution of ...... been carried out with the 1-m and the 0.5 sec and 40 millisec respectively. Fi­ GMS 0.28-m telescopes at La Silla. gure 1 shows a cOl,densed version of , The 1-m telescope was equipped with the data plotted in bins of 8 seconds. ..~,.". ..,...... --. ,. -~.... '.~.""" .. the multi-channel photometer of the The U-B decrease is due to the U fading I!JD·1loll(6.~1l6· Universitäts-Sternwarte München. of the supernova. B-V and VoR are al­ "0 0.0> D.m 0.15 UBVRI data were obtained, observing most constant during the night. The irre­ Figure 1: Condensed UBVRI (Kron-Cousins) sky and comparison star in two gular variability in V-I is due to the I band light eurves of the SN 1987 A, obtained on channels simultaneously with the ob­ and is probably caused by fluctuations February 28. Eaeh dot eorresponds to an ject. Two photometric data sequences of the comparison star. A preliminary integration time of 8 seeonds.

29 These two c%urphotos 0' the Large Magellanic C/oud show the sudden appearance of the bright supernova 1987A. They were obtained with a 6 x 6 Hasse/b/ad carnera rnounted piggy-back on the GPO and Danish 1.5-rn telescopes, respective/y. The fett-hand photo was taken on February 23, between 01: 00 and 01: 20 UTand is the last c%urpicture taken before the supernova exp/oded. probab/y a few hours later. The

1.1

flecting the importance of this superno­ 6MS 3-4 ~ 1007 5N1007A 116 2046fE va, the Central Bureau for Astronomical Telegrams issued no less than 15 lAU •9 Circulars in the course of 9 days only. breaking all records in the history of astronomy. At ESO, these circulars were .B read through a computer link to the Headquarters in Garching as soon as they were issued, and immediately sent .7 on to the observers at La Silla by telefax. In this way, and also by numerous telex .6 messages and phone calls, the scien- 400000 440000 480000 400000 500000 tists were kept informed about what was Figure 2. F!ElLENCy c.t lLLlli:RT11 going on in other places. The time immediately following the 500 Hz. In Figure 2 a portion of the Chronology of a discovery was particularly hectic. Here Fourier transform of the GMS data is is a provisional compilation of the main shown. Calibration of the system is in Once-in-a-Lifetime events during the first hours, drawn from Progress and the monitoring of the SN the information available on March 4: 1987 A will continue until it becomes too Event UT faint for this telescope. Only 48 hours separate the two H. Barwig, R. Schoembs (München) photos above. but during this brief inter­ Feb. S. Cristiani, C. Gouiffes, J. L. Sauvageot val an event happened that excited an 22.4 Photos obtained with the Univer­ (ESO) entire generation of astronomers. Re- sity of Aston satellite tracking 30 right-hand photo was taken exaetly two days later, on February 25, also at UT 01 .' 00. On that date, the supernova had reaehed visual magnitude 4.5. It is weil visible, left of the eentre and above the LMC main bodyas the lower right (round) of the two bright objeets. The other objeet, whieh is extended and more diffuse, is the Tarantula Nebula (30 Doradus). (Agfaehrome 1000 RS emulsion, C. Madsen.)

camera in Australia (R. H. 24.02 Shelton starts 3-hour exposure 24.72 McNaught now thinks that it has McNaught) show the progenitor with the 25-cm astrograph of the brightened to 4.4 Sanduleak -69 202 at normal University of Toronto station at 24.8 Spectral observations com- magnitude 12. Las Campanas. mence with the International UI­ 23.06 C. Madsen at La Silla obtains col­ 24.2 Suspected visual sighting of the traviolet Explorer, a satellite tele­ our photo of LMC (above). supernova by O. Duhalde, also at scope in orbit around the Earth, 23.08 I. Shelton at Las Campanas ob­ Las Campanas. jointly operated by ESA and NASA. tains photo of LMC (not yet 24.23 Shelton discovers the supernova showing the supernova). on his plate after development. 24.8 Night falls in South Africa and 23.12 Five pulses, above 7 MeV, are The lAU Telegram Bureau is in­ multicolour photometry observa­ detected during a 7 sec interval formed soon thereafter. tions start at the SAAO. with the neutrino telescope in the 24.37 Independent discovery by A. 24.9 A spectrum obtained with the 1.9 Mount Blanc tunnel. This experi­ Jones, at Nelson, New Zealand, reflector at SAAO shows few fea­ ment is a collaboration between who estimated it at magnitude tures and appears to indicate Istituto di Cosmogeofisica, To­ 5.1 that the object may be of Type I. rino, Italy, and the Institute of Nuclear Studies in Moscow, 24.4 A telegram announcing the dis­ 25.0 Night falls in Chile and observers USSR. covery of the supernova, now de­ at all telescopes on La Silla turn their attention to 1987 A ... 23.44 The supernova is recorded as a signated "1987 A", is sent to all 6.1 magnitude object on plates major observatories from the lAU 25.05 The second colour picture of taken with the satellite tracking Telegram Bureau. LMC, now with the supernova, is camera in Australia, but it is not 24.46 McNaught estimates it at mag­ obtained by C. Madsen. yet detected by the operators. nitude 4.8. R. M. West (ESO) 31 The Spectrum of Supernova 1987A

In the early phase of a supernova, the 1Il216 ESO 3. 614 LA 5I LU Z7-FEB-87 dense atmosphere of the progenitor star ...: is blasted off with a high velocity. This surface radiates like a "black-body" and, as such emits a continuous spec­ trum wh ich is essentially independent of the chemical composition and whose energy distribution is determined solely by its temperature: the light is radiated by charged particles as they scatter off one another. As the "atmosphere" grows in size, the range of depths from which the photons can escape increases and the chemical composition becomes impor­ 3483.1151 4 .052 51 1152 004 .052 6003.1152 tant in determining the opacity of the WAVELENGTH CA) gas at different wavelengths. This is when spectral lines start to become ap­ parent. But still, and indeed for a long "" ,--:..:*1il09=-4:--=SN::.:.1;.:98;:..:7.:.:.A-=0~11-=2=-5.;..UT:...... ,.._--,-_,....::LA.:...::.:SI-=LL::.A~3::.• .::.6M:....2::.M::;:AR.::..••:.:I.::.987::.:.....:U::.:.T,, -,-__-, time after maximum light, most of the ~ energy is radiated as an approximately black-body continuum with a tempera­ 33 ture - at least in type 11 supernovae, which are supposed to be hydrogen rich - corresponding to the layer where the hydrogen becomes fully ionized. The lines just im pose a modulation on this underlying continuum. The outer part of the atmosphere, weil above the con­ tinuum emitting surface, will radiate emission lines while that part between the surface and us will absorb the same "" lines. Since the atmosphere is expand­ "" ing, the absorbing part will have the 5251. 911 610 911 6961. 911 greatest component of velocity towards us and so will produce "blue-shifted" Figure 1: Spectra of 1987A, obtained by J. Oanziger and R. Fosbury al Ihe ESO 3.6-m lines. Such an emission/absorption telescope with the Boiler and Chivens spectrograph. The upper spectrum (a) was obtained on structure is known as a "P-Cygni" profile February 27.05, four days after the explosion and already shows the strong P Cyg profiles after the prototype Be star with an ex­ mentioned in. the text. The lower spectrum (b), although qualitatively similar, displays importanl panding atmosphere. Measurements of changes in the amplitude and also in the velocities of the main features. the positions (in wavelength), strengths and shapes of such profiles provide as­ are also becoming stronger as the vol­ other, more subtle, changes as broad tronomers with the means to study the ume of the emitting gas increases and spectral features appear and fade as the composition and the velocity evolution the temperature of the absorbing col­ ionization conditions in the atmosphere of the expanding shell. umn decreases (Fig. 1b). There are change. Because they are so broad, The first optical spectra of SN 1987A obtained at ESO on the night of 24-25 February show very weak spectral fea­ *0096 SNI987A R+8 LA SILLA 3. GM ZMAR.. 1987 UT tures and an overall energy distribution wh ich corresponds to that of a hot star. Over the next two days, strong, broad < spectral features began to appear and o by 27 February (Fig. 1 a), strong P-Cygni ~!8 <. lines are seen which correspond primar­ -l I ily to the Balmer series of hydrogen. The -l L.!- shift of the H-alpha absorption trough with respect to the rest wavelength W :::l:j corresponds to a velocity of over I- . < 17,000 km/s when the first measure­ -l W ments were made. The spectrum now IX appears to be evolving in the sense that the overall energy distribution is becom­ ing redder (a cooling of the continuum 3S00 52111 6920 8630 10340 emitting "photosphere") and the velocity WAVELENGTHCA) shifts of the P-Cygni absorption compo­ Figure 2: Spectrum of 1987A, obtained by R. Fosbury (3.6-m + B & C spectrograph + RCA nents are slowly decreasing. The lines CCO) on March 2.1 and covering the 350-950 nm spectral region. 32 these features are notoriously difficult to was higher in the initial phase was good fore, using as background sources attribute to different chemical elements news for the IUE for which the superno­ bright stars in the Magellanic Clouds but it appears likely that the strongest of va now provides a greatly weakened and much more distant Quasars and them can be identified with singly source. Seyfert galaxies. These, however, are ionized calcium and iron. When the opti­ Another aspect of the spectroscopy very faint objects and the opportunity cal and infrared data are combined, the which is causing great excitement is the presented by a naked eye supernova temperature of the "black-body" con­ possibility such a bright object in the has already resulted in a Bonanza of tinuum is readily measured; it was LMC provides for the study of the inter­ results from the very high resolution 5900 K on the night of 1-2 March (see stellar/intergalactic medium between us spectrograph (CAT/CES) at ESO (see the plot of the infrared - optical photo­ and the supernova. Sight lines outside contribution by Andreani, Ferlet and metry). The fact that this temperature our own Galaxy have been studied be- Vidal-Madjar). R. Fosbury (ST-ECF)

High-resolution Spectroscopy of 1987A

Observations at the 1.5-m CAT tele­ tervening main structures in the direc­ same; 121-127 km/s, strong Ca 11; Scope with the Coude Echelle Spectro­ tion of the supernova: 7- 22 km/s 160-169 km/s, same; 206-218 km/s, graph and the Reticon Detector at reso­ (heliocentric), strong Na I, Ca 11, K I; strong Ca 11 and Na I; 248-253 km/s, lution 100,000 (3 km/sec) have led to the 38 km/s, weak Ca 11; 55-63 km/s, weak Ca 11 and Na I; 264-269 km/s, identification of the following eleven in- strong Ca 11, weak Na I; 70-74 km/s, same; 278-283 km/s, strong Ca 11, Na I, K I; 293 km/s, weak Ca 11. Many of these main structures are resolved into two or

.;'~3~92:::0:-.-::63:-r---,---.----..----,---.,...... --:-r----r::l---:t-:-h--r-:3;:9-:5-:-1 -::37 3936.00 epproximate wave eng . Figure 1: The spectrum of 1987A, around the Ca II (K) line at 393.3 nm, as obtained on February 25.05, with the CA T + CES + Reticon detector at resolution 100,000. The exposure time was 1,200 sec. This figure shows the main absorption structures only; up to 22 absorption lines from interstellar and intergalactic clouds were detected.

eh 1670 oh 1 Sn 198;'; HAI 'o.. } ibra ~ed)

This red photo (098-04 + RG 630, 60 min) of Sanduleak -69202, the suspected progenitor of supernova 1987A, was obtained with the ESO 3.6-m telescope on December 6, 1979. The star has at least two companions; one of them is clearly seen here (as a prominent bulge) to the northwest at a distance of only 2.6 arcseconds. It is not the progenitor, since its position does not coincide with that of the supernova. A third star lies about 1 arc­ second southeast of Sanduleak -69202, but 5063.82 ••• ,LO 5069.00 it cannot be seen on this photo. The stellar Figure 2: A spectrum taken by G. Vladilo on February 28 with the CAT + CES + Reticon images are very close to the edge of the plate detector, around the Na I doublet at 589 nm. The strongest lines correspond to absorption in and are somewhat elongated, due to less the Galaxy and in the LMC. than optimal optical adjustment. 33 The star that exploded on February 23 in the Large Mage/lanic Gloud (the progenilor of supernova 1987A) has now been identified. It was catalogued in 1969 as an OB star of 12th magnitude and given the designation Sanduleak -69202. Observations at the European Southern Observatory in the mid-1970's a/lowed to classify it as ofspectral type B3 I, that is a very hot, supergiant star. It is here shOwn on a photograph, obtained with the ESO Schmidt telescape in ultravialet light on December 9, 1977 (/la-O + UG 1, 60 min). Glaser inspec/iOn has now revealed that two other stars are seen very close to this star. On this photo, the image of Sanduleak -69202 is somewhat elongated towards nOl1hwest, since one of the companions lies in this direction at a distance of only 2.6 arcseconds. This companion cannot be the progenitor, since its position does not coincide with that of the supernova. Ho wever, there is a third star within 1 arcsecond, just southeast of the main star. Further investigations are needed to ascertain wh ich of the two became the supernova. Observers: H.-E. Schuster and 0. Pizarro. 34 This blue photo (11 a-O + GG 385, 15 min) of the bright supernova in the LMC was obtained with the ESO 1-m Schmidt telescope on February 26 ~ 01 : 25 Ur. On this date, the supernova had reached visual magnitude 4.4. The photo should be compared with the ultraviolet photo showing e supernova progenitor which was taken with the same telescope in 1977. The enormous increase in brightness, around 2,000 times, is ~vldent. The background nebulosity emits strongly in the ultraviolet and is therefore better visible on the ultraviolet photo. Otherwise more or t~SS the same stars are seen on both photos. Note that the "cross" around the supernova is an optical effect in the telescope which is caused by e support of the plateholder. Observer: G. Pizarro.

35 CASPEC Observations of sdO Stars: Are Some sdOs Lazy Remnants from the AGB? u. HEBER and K. HUNGER, Institut für Theoretische Physik und Sternwarte der Universität Kiel, F.R.G.

The hot subdwarfs are ideal test ob­ = 0.2 M0 , finally, would be progenitors very weak 0/V, (4471) =:; 100 mAl or even jects for the theory of stellar evolution. of the central stars of planetary nebulae. absent. This clearly indicates very high Their core masses are pretty weil This simple distinction, on account of effective temperatures (> 55,000 K) known, as they originate ultimately from the envelope mass is not actually quite which are hotter than in any "classical" the horizontal branch, Me = 0.5 M0 , and correct; there are 8 newly discovered sdO star studied previously (Hunger et their envelope masses lie in the narrow subdwarf 0 stars which seem to be of a al.,1981). range 0 < Menv :s 0.2 M0 . Moreover, particular nature and which seem to in­ The high spectral resolution (0.25 A) their atmospheres are weil understood dicate that the above sketched picture also allows metal lines to be searched through detailed NLTE model atmo­ may be tao simple. But first let us report for and these have indeed been found in sphere analyses which appear especial­ on the spectral analysis of these ob­ 6 objects. They are lines of highly Iy suited to this class of hot high gravity jects. ionized elements (e. g. CIV and NV). LSE objects. It appears from these analyses 153, LSE 259 and KS 292 are remark­ that the subdwarf B stars are extended able in that they show a strang carbon Data Reduction horizontal-branch stars and thus have spectrum. Surprisingly, same lines Menv:S 0.02 M0 . The same is true for the The stars were observed with CAS­ occur in emission (see Fig. 2) rather than subdwarf OB stars, only that the latter PEC in the blue spectral range in absorption. (Note that all emission have even smaller envelope masses (3900-4800 A). In the beginning (1984), Iines are allowed transitions. No for­ 3 (:s 10- M0 ). For both classes, further the 31.6 I/mm grating was employed bidden lines which are typical for nebula evolution proceeds directly towards the while for the later observations the 52 I1 spectra are found.) The most extreme white dwarf domain. The subdwarf 0 mm was preferred because it yields case in this respect is LSS 1362, the stars, on the other hand, belang to the wider separations of the orders. The spectrum of which shows all metal lines subgroup with envelope masses of the spectra were reduced in two steps: first, in emission. In two objects, ROB 162 order of 0.1 M0 . They reached their pre­ the ESO-MIOAS software was used for and LS IV-12°001, no trace of a sent position in the HR diagram along a both wavelength calibration and extrac­ metallic line can be found, in spite of the rather complicated track (Fig. 1, for a tion of the Echelle orders. Then high spectral resolution. The discovery detailed discussion see Groth et al., background correction and flat fielding of faint metal lines, especially those in 1985). After they had left the horizontal were performed in Kiel using a computer emission, is particularly valuable as it branch they moved towards the AGB; programme written by G. Jonas. Oata will supply the clue as to the nature of there was not enough fuel remaining in obtained with the 31.6 I/mm Echelle our programme stars. the envelope for them to throw off grating suffered from contamination of planetary nebulae and thus to become the background by scattered light from NLTE Analyses central stars. They then contracted to­ neighbouring orders, while no scattering wards hotter temperatures, which are was experienced with the 52 I/mm grat­ NLTE analyses of the hydrogen and typically Teft = 40,000-60,000 K. Further ing. The fraction of scattered light could helium line spectrum were carried out evolution would again follow a direct be determined from the observations of with the Kiel programme (Kudritzki and track to white dwarf dimensions. So the standard stars (observed with both grat­ Simon, 1978; Simon, 1980; Husfeld, small differences in the initial mass of ings). The last step of the data reduction 1986). For illustration, we have display­ the envelope decide whether a horizon­ procedure was the correction for the ed the line-profile fits for the helium lines tal branch star evolves to either a sub­ Echelle blaze. The Echelle blaze func­ in ROB 162 (Fig. 3). The resulting at­ dwarf B (ar OB) or to a subdwarf 0 star. tion ("Ripple function") was empirically mospheric parameters, i. e. effective Those with envelope masses exceeding determined for every order using the temperature, surface gravity and helium sdOB star Feige 110 plus the helium star abundance, are summarized in Table I. BO-9°4395 as standard stars, since the Three programme stars have normal spectra of the two stars are com­ helium abundances, whereas the others e o PN jecl ion;/ plementary: Feige 110 displays a line­ are enriched with helium. In LSE 153, paar spectrum, the only strang lines be­ LSE 259 and LSE 263, no hydrogen is logg ing the Balmer lines, whereas BO­ detectable and only upper limits to the 2 9°4395 displays only very weak Balmer hydrogen abundance can be derived. lines. The "Ripple function" was deter­ The position of our stars in the (g, Teft)­ mined empirically from a least-square fit diagram is plotted in Figure 4, together to the normalized continuum of BO­ with the position of previously analysed 9°4395 for those orders containing "classical" sdOs. Stars with normal Balmer lines, while for all other orders it helium abundance are shown as open was determined form the normalized circles, intermediate helium-rich stars as continuum of Feige 110. filled circles and extremely helium-rich stars (no hydrogen detectable) as cros­ 1..5 1..0 3.5 Une Identification ses. The programme stars are indicated log Teff by error bars. Also shown are evolutio­ Figure 1: Post-horizontal-branch evolution Strang lines of ionized helium are pre­ nary tracks descending from the asymp­ (schematic). sent in all eight stars, whereas He I is totic giant branch for masses between 36 out ejecting a nebula. This is not a satis­ factory answer (at least for helium rich stars) since it cannot explain the enrich­ ment of helium and carbon. (ii) After ejection of a nebula, our stars evolved much more slowly than the other CSPNs and, therefore, the NV nebulae had al ready been dispersed be­ fore the stars became hot enough to ionize it. Calculations (Schönberner, 1979; Iben, 1982) show that there may be a discriminating factor: the metalIici­ I'0% ty. The rate of evolution, namely, is slow unid for post-AGB stars when the metaliicity is low and vice versa. The effect, how­ ever, is small. It might explain the cases of ROB 162 and LSIV-12°001, as ROB 162 belongs to the metal-poor cluster NGC 6397 ([Fe/H] = -1.83) and LS IV­ 12°001 has a metal-poor line spectrum (see above). The laUer has an unusually NV large radial velocity (-178 km/s) and, therefore, is probably also a population [,610 [,630 [,650 [,670 11 star. For the other 6 candidates, this hypothesis does not apply. Figure 2: Caspee speetra of LSS 1362 (top), KS 292 (middle) and 80-3°2179 (bottom). Note (iii) The third and most interesting ex­ the metallic emission fines. 10% eontinuum height is indieated by a vertieal bar. planation is the concept of "born again"

0.546 Mev and 0.76 Mev (Schönberner, 1979, 1983; Faulkner and Wood, 1984). As can be seen from Figure 4, our stars (as weil as BD+3r442, Giddings, 1980) do not lie in the region where the classical sdO stars are to be found. In­ stead, they can be identified with post­ AGB tracks of about 0.6 Mev and with a 10"/0 3 8 I mean luminosity of about 10 . ~. These masses and luminosities are typi­ cal for central stars of planetary nebulae (CSPN) and, indeed, the spectra of our programme stars reveal a further simi­ larity to CSPN, i. e. the presence of the metallic emission lines, for similar emis­ sion lines can be observed in some 4471 4542 Hell '0 CSPNs (Mendez et al., 1981). Hence, 1"/0 Hel spectroscopically, the programme stars I 10"10 mayaiso be termed as CSPNs except that they lack the nebulae (or perhaps it wasn't noticed?). A careful inspection of the ESO sky survey plates did in fact reveal the existence of a very extended faint nebulosity around LSS 1362. All other stars, however, do not show 4686 He Ir nebulosities. Why is this the case? I10"/0 According to the theory of evolution 4713 the age of our CSPN candidates, after they had left the AGB, should not have Hel exceeded a few thousand years; if they had ejected nebulae at the tip of the v AGB, they should still be visible. The question arising from these facts is whether there are further parameters b which distinguish our stars from CSPNs. There are three conceivable reasons -20 o 20 -10 o 10 why no nebula can be detected: (i) The stars simply left the AGB with- Figure 3: Comparison of observed and theoretieal helium line profiles for R08 162 (V = 13.23). 37 Table 1: NL TE analyses of sdO stars Acknowledgement We thank D. Ponz (ESO) and G. Jonas Carbon (Kiel) for their kind assistance in various Star To,/K log g nHJ(nH+n Ho) line Reference spectrum aspects of the data reduction.

BD+3]o442" 55000 4.0 1.0 + Giddings (1980) References LSE 153 70000 4.75 2:0.9 + 1 Faulkner, D.J., Wood, P.R.: 1984, Proc. ASA LSE 259 75000 4.4 2:0.95 + f Husfeld, Heber, 5,543. LSE 263 70000 4.9 2:0.9 - J Drilling (1986) Giddings, J. R.: 1980, Ph. D. thesis, UCL, b b b BD-3°2179 62000 4.5 0.25 - London. LS IV-12°1 60000 4.5 0.1 - Groth, H. G., Kudritzki, R. P., Heber, U.: 1985, KS 292 75000 4.7 0.33 + Aslfon.Aslfophys. 152, 107. LSS 1362 100000 5.0 0.1 - Heber, U., Kudritzki, R. P.: 1986, Astron. As­ ROB 162 51000 4.5 0.1 - Heber, Kudritzki (1986) trophys. 169,244. Hunger, K., Gruschinske, J., Kudritzki, R. P., " based on photographie spectra b preliminary values, analysis is not completed Simon, K. P.: 1981, Astron. Astrophys. 95, +: carbon strong lined -: carbon weak lined 244. Husfeld, 0.: 1986, Ph. D. thesis, München. Husfeld, 0., Heber, U., Drilling, J. S.: 1986, Proc. lAU Coll. No. 87, p. 353. post-AGB stars. After ejection of a that were once CSPNs but were born Iben, I.Jr.: 1982, Astrophys. J. 260, 822. nebula, such a star crosses the HR dia­ again just before they reached their final Iben, I.Jr., Kaler, J. B., Truran, J. W., Renzini, gram in the usual way, i. e. as a true destiny, the white dwarf cemetery; a last A.: 1983, Astrophys. J. 264,605. CSPN, and finally reaches the hot end of thermal pulse brought them back to life Kudritzki, R. P., Simon, K. P.: 1978, Astron. the cooling sequence of white stars. as a post-AGB star. While the true Astrophys. 70, 653. According to Schönberner (1979) and CSPN lives on H-burning, the reborn Memdez, R. H., Kudritzki, R. P., Simon, K. P.: 1981, Astron. Astrophys. 101,323. Iben et al. (1983), a last thermal pulse post-AGB star lives on He-burning, Schönberner, 0.: 1979, Astron. Astrophys. may occur in this phase. Such a pulse which prolongs the active lifespan by 79, 108. brings the star back to red giant temper­ some 10,000 years, a good fortune that Schönberner, 0.: 1983, Astrophys. J. 272, atures and dimensions. During the only a sm all fraction of the central stars 708. pulse, most of the hydrogen left to the will experience. Simon, K.P.: 1980, Ph.D. thesis, Kiel. star at the onset of the pulse is mixed into the helium-burning convective shell and thus is completely burned. The star is now almost devoid of hydrogen and proceeds to burn helium in a shell. The ~o evolutionary track in the (g, Teff) diagram y;~',\'0 <-,0;'0 ,<><-' <-,"'0 1\:>' 1\:>. is approximately the same as that for I\:>'? I\:>'~o hydrogen-burning post-AGB stars I. + (CPNs). However, no new nebula is ex­ pelled and the old one has long since disappeared. log g This scenario can also solve the riddle r-b;]/? of the helium and carbon enrichment (the latter is found only in a few cases, see Table I). The theory of evolution 5 ~r!/ (. does not predict any helium enrichment for "normal" CSPN since the hydrogen //% 10-4 • + rich envelope is too massive (:=:: M0 ) • ++ to allow any helium to be seen at the • surface. Indeed most of the CSPNs / studied so far, have a normal helium abundance. However, the situation is 6 • different for post-AGB stars that experi­ • 0 ence a final thermal pulse when they al ready have reached the cooling se­ quence. Theoretical calculations (see + Iben et al., 1983), namely, predict a final hydrogen burning episode during the peak of the final thermal pulse and a 7 mixing episode during the giant phase. Both mechanisms can mix processed material (He and N from the CNO-cycle; C from the 3 a-process) to the surface. 5.1 5.0 1..9 1..8 1..7 4.6 1..5 1..1. log Teff /K Conclusion Figure 4: Position of subluminous stars in the (g, To,,)-diagram. The programme stars are marked by error bars. The dashed lines are theoretical evolutionary tracks for stars of The NLTE analyses have revealed the 0.546 M(i), 0.565 M(i), 0.598 M(i) (Schönberner. 1979, 1983) and 0.76 M(i) (Faulkner and Wood, existence of a new group of sdO stars 1984) descending from the asymptotic giant branch. 38 P/Halley: Characterization of the Coma Dust by Polarimetry A. DOLLFUS and J. -L. SUCHAlL, Observatoire de Paris

The new photopolarimeter of Ob­ to La Silla for an intensive polarization servatoire de Paris, at Meudon, was analysis of the eomet with the 1.52-m first used on Comet P/Hailey with the ESO speetroseopie teleseope. Nine 1OO-em teleseope of Meudon Observat­ nights were alloeated from 7 to 16 April, ory from September to Deeember 1985. 1986. Of these, eight nights showed a After full tests were seeured and eomet perfeet sky with exquisit seeing! In addi­ polarization measurements reeorded, tion, the teleseope, perfeetly weil the instrument was paeked and shipped adapted for the purpose, was aeeurately

operated by Messrs. Miranda and o Borguez, under the supervision of Mr. FIC I d dlCmc tet .. 120 ore scc Le Saux. 0(119', Figure 1 shows the first of our polari­ zation mappings over the inner eorona on April 7-8, 1986. At the top, the eoma is seen at the eyepieee with a magnifiea­ tion of 1,000, in a field of 25 areseeonds diameter. A dust streamer is ejeeted to­

I Ficlddiameter:250rcsec ward south, at 45° from the direetion of VII Phose ongle=22.S· Vettor P.J0 2+ UlII N ~10.10-J the Sun. The sizes and the sueeessive APRll15.1986

... @ 0 positions of photopolarimeter holes over Figure 3: Same as Figure 2 but for April 15, I 60 this field are shown at bottom left in the 1986, at phase angle 22? 5. 52/6 60 52 (60 ~o/sV@ figure, together with the values mea­ 53~53/ sured for the degree of eireular polariza­ 55 3 tion VII, expressed in units of 10- . At 0 bottom right, the measurements of the "9!'1

VII Phose ongle=i,O,7' Oll degree of linear polarization Oll are gi­ 3 APRil 8.1986 ven, also in units of 10- , together with Figure 1: Comet PIHalley. Polarization over the approximate isophotes for the two 3 3 the inner eoma. Photopolarimeter PPHR of values 53 x 10- and 60 x 10- . The , .t)·., I Observatoire de Paris, with the 1.52 mESO azimuth of the polarization was every­ ,,:,::" teleseope at La Silla. April 8, 1986, phase where almost perpendieular to the di­ t-1 10 Oft sec angle 40? 7, field diameter 25 aresee. Top: reetion of the Sun (meaning that the Aspeet ofthe inner eoma and dust streamers. Stokes parameter U/I, whieh is at 45° Field diameter .. 1200rcsec o Bottom lett: Positions of the hole and degree 3 from Oll, is negligible). A wide band of eireular polarization VII in units of 10- . eolour filter was used, eentred at Bottom right: Degree oflinear polarization QII in units of 10-3 and isophotes for 53 x 10-3 500 nm (eirele and dashed line in Fig. 9). and 60 x 10-3 We have eight sueh maps. After April \--/<,.-- \ 10, we extended the eoverage to a .-- wider field of 120 areseeonds in diame­ 01178') ter, and expressed the linear polariza­ 5

I tion by segments giving the azimuth and Vector P.. .{ä1';i}1l ~lO"lO-J the degree P of polarization whieh is P = APRIL 16. 1986 2 2 v0 + U I I. As the phase angle de­ Figure 4: Same as Figures 2 and 3 but for ereased with time, the polarization de­ April 16, 1986, at phase angle 21? 6 for whieh creased also and the effeet of defleetion the linear polarization produeed by isotropie in the azimuth of polarization took more seattering is almost negligible. The linear polarization whieh remains is largely pro­ ~ lOore sec signifieanee. Figures 2, 3 and 4 show at top the full development on the foun­ dueed by orientations and anisotropies in the o dust shapes. Field dlomeler .. 120orc sec tain-line dust ejeetion by the nueleus toward the direetion of the Sun and at bottom right the linear polarization whieh deereases with phase angle and We detailed also the polarization in also progressively wanders in its the inner part of the eoma within azimuth. On April 16 it is almost ran­ 3,000 km from the nueleus, by using domly oriented; at the eorresponding eoneentrie holes eentred at the nueleus. phase angle of 21? 6, the polarization The measurement with a hole is then produeed by isotropie seattering is al­ eorreeted by those with smaller size. VI1 Phase eng le .. 24.2" Vector P• .[(J-';ilil J APRll1!.1986 t-41QII1O- most zero and the polarization effeet The smallest hole had 2.1 areseeonds produeed by anisotropies in the dust diameter, or a radius of 300 km around Figure 2: Same as Figure 1 but over a larger field of 120 aresee. diameter on April 14, configurations remains almost alone. the nueleus. Figure 5 shows the lumi­ 1986, at phase angle 24? 2. The linear polari­ The small and variable eireular polariza­ nenee (in relative units) and the degree 3 zation is expressed by segments giving the tion VII whieh is reeorded probably re­ of polarization (in units of 10- ) so de­ azimuths and the degree of polarization (see sults also from sueh dust shape anisot­ dueed, as a funetion of the distanee of seale). ropies. the nueleus, given in areseeonds and in 39 the polarization increases up to 11~ 'lr-,-,-,--,--,---,---,--r-r----rIV-r~__, 3 38 x 10- . Then the envelope discloses 120 a completely different and smaller Cont Inuum at 500 nm polarization. Towards the Sun, the foun­ correc ted for emISSions 100 ....o •.. Envelope orolmd nucleus tain of fresh dust maintains a high -lC--Fresh dust at IOOOkm polarization. On April 13, at phase angle 80 __Como 0\ 3000 km 36';> 2 (Fig. 6) a gust of fresh dust ejected towards the observer screened 60 completely and temporarily the bright PI1O-ll envelope around the nucleus which dis­ GO J8 appeared. The polarization then unifor­ J. mized all over the field. Next day, on 20

"J2 April 14 (Fig. 7), the dust streamer hav­ JO ing spread out, the envelope was seen Ol-----M\l~------t 28 again with its anomalous polarization, 2. now observed at phase angle 24';> 2. -20 " Phase an le ETA Ufel I 08 Our data include 9 documents such o 10 20 30 LO 50 60 O. as those of Figures 5, 6, and 7, and 8 Figure 8: Oegree of linear polarization as a 0' maps like those of Figures 1 to 4, plus funetion of phase angle: eurves of polariza­ 02 measurements directly recorded around tion for the eoma dust at 3,000 km from the the nucleus. With these data, we derived nueleus (dots), for the freshly ejeeted dust the Figure 8 showing the curve of varia­ observed at 1,000 km (erosses) and for the Figure 5: Oetailed analysis of the polarization tions of the degree of polarization as a bright envelope around the nueleus (eireles). over the inner part of the eoma, close to the function of phase angle, for the dust at The measurements have been eorreeted for nueleus. April 10, 1986, at phase angle the polarization produeed by the gas emis­ 36? 3. Top: Positions and sizes of the holes. 3,000 km (dots), for the fresher dust at 1,000 km (crosses) and for bright en­ sions ineluded in the speetral band transmit­ Middle: Oegree of linear polarization with dis­ ted by the filter. tanee to the nueleus, sunward and anti-sun­ velopes around the nucleus (circles). ward. Bot/om: Same, for the luminenee. These measurements have been sub­ jected to a slight correction due to the

smaller polarization produced by the POLARIZATION PIHALLEY SPECTRAL VAR. emission lines partly included in the Ap,,\ 8.1986 OGhOOm UT kilometres, for the observation of April spectral band isolated by our filter. The 10, 1986, at phase angle 36';> 3. A very Ph ase::: (,07· effect is to increase the polarization for 70 bright point source, almost star-like, the largest phase angles. The un­ was seen around the nucleus (within corrected data are given in the Figure 5 60 hole N6). It corresponds to a sort of of the paper by Dollfus et al. (1987) cited permanent envelope surrounding the in reference. Our measurements with 50 nucleus. At the apparent distance of narrow colour or interference filters, 4,000 km from the nucleus in the direc­ such as those of Figure 9, indicate also GO tion opposite to the Sun, the polarization that there is only a small variation of the 500 550 600 ~nm 3 is 28 x 10- . Approaching the nucleus, continuum polarization with wavelength. I Curves of polarization are related to Decembe, 29. 1985 l'Ihl.5m UT. the nature of the dust particle respon­ 100 I- sible for the scattering; they help to ~~ ~6 o APRIL 13, 1 characterize their physical properties. Afound OLh U 1 ! Phase 262- Without entering here into the details of 50 I- - the interpretation, wh ich is still under , w_ -( 350 LOO LSO 500 550 600 ~nm APRIL IL, 1986 Figure 9: Speetral variation of the polarization hfound OLhUT Pho~.2L 2- in the range from 360 to 600 nm. Top: for phase angle 40? 1. Bottom: for phase angle 54? 2. Measurements eorreeted for gas emission polarization when relevant. -+-...... ~,,-~ t""--, ,,' _8_ 15 10 10 15 Ofe sec w-

08 lIrell progress, we note that curves such as O. those for crosses and dots in Figure 8, 0' " are compatible with, and even sugges­ 12 SUNWARO 02 10 tive for, a model of grains made of fluffy 8 aggregates of small particles. The grains 00 h,k-',=::;r,;-L-+.L-l+LJ+-q,\;=o==i,~, ~",;-;,:-:,,-l 1.000 ]000 2000 1000 0 1000 2000 )000 4000 km have to be very dark and neutral in col­ our. These structures, fragile and un­ Figure 6: Same as Figure 5 but for April 13, I~ 10 5 10 compacted, may be somewhat elon­ 1986, at phase angle 26?3.A dust streamer 3000 2000 1000 0 1000 2000 JooO 1.000 SOOO 6000 7000 km ejeeted in the direetion of the Earth has tem­ Figure 7: Same as Figure 6, but next night. gated or filamentary, as suggested by porarily masked the bright envelope around The dust streamer has spread out, the bright the deflected and the circular polariza­ the nueleus and uniformized the polarization envelope reappears and its polarization is tions. over the field. now observed at phase angle 24? 2. The polarization by the bright halo 40 which is enveloping the nucleus (circles in Figure 8) does not fit as easily with such a model. Other types of grains may MESSENGERINDEX be required, perhaps of higher albedo. An index of all eontributions published in the Messenger from No. 1 to No. 46 Water ice may be considered. (1974-1986) has been eompiled and will be distributed with this issue of the Messenger. The index eonsists of three parts. The first part - the Subjeet Index - lists the eontributions grouped by 20 subjeet titles. In the seeond part - the Author Index - the Reference artieles are Iisted by authors, in alphabetieal order. The third part eontains the Spanish summaries, grouped by subjeet titels and in ehronologieal order. Dollfus, A., Suehail, J. -L., Crussaire, D., Although the division of the eontributions into 20 subjeets and their assignment to these Killinger, R. (1987): Comet Halley: Dust subjeets may not be perfeet, it is hoped that the index will help the reader to obtain a better eharaeterization by photopolarimetry. To overview of the artieles whieh have appeared in the Messenger and permit him to find them be published in Proe. ESA Symposium Ex­ more easily. ploration of Halley's Comet, Heidelberg, In the future, annual indexes will be eompiled. FRG, 27-31 Oel. 1986.

Multiple Object Redshift Determinations in Clusters of Galaxies Using OPTOPUS A. MAZURE and 0. PROUST, DAEC, Observatoire de Meudon, France L. SOORE, lAG, Sao Paulo, Brasil H. CAPELA TO, Sao Jose dos Campos, Brasil G. LUND, Departement d'Astrophysique de l'Universite de Nice, France

Introduction From recent developments of obser­ vational astronomy, the overall view of the structure of the universe appears to be very different from the homogeneous and isotropie one claimed by traditional cosmology. The hypothesis of long, in­ terconnected linear filaments or even large "bubbles" characterizing the con­ centration of galaxies now seems to be weil established, these regions being separated by large voids empty of bright galaxies. One of the fundamental factors in the understanding of such formations is the determination of their structure in the third dimension as opposed to their flat "projected" appearance. If the redshift determinations repre­ sent virtually the only tool giving access to the third dimension, they are also essential to the understanding of struc­ tural dynamics because they provide us with a wealth of information concerning the velocity dispersion in particle sys­ tems. Radial velocity measurements are essential to the understanding of struc­ tures such as galaxy clusters, as dy­ namic analysis of their velocity distribu­ tion can lead to mass determinations and to an estimate of the missing mass in the universe. Analyses of some Abell clusters have recently been published; as an example it has been shown that the A496 cluster o has a complex structure formed essen­ tially by a main cluster (or main sub­ Figure 1: Isoeontours of SC2008-565. The ten brightest galaxies are ploNed. The radial cluster), and another small sub-cluster, velocities ofA and Bare 16,490 and 16,890 km/so 41 order to mlnlmlze refraction effects ..: wh ich can lead to small fibre/image off­ sets during the course of observations. The second half of the last night was almost completely lost because of cloudy conditions.

Data Reduction and Results

Oata reduction was carried out using the IHAP image-processing software at ESO Garching. The programme auto­ matically identifies the positions of the spectra on the CCO frame and extracts 3806 4148 4490 4832 5174 them by adding the contribution of the Figure 2: Spectrum of an elliptical mb 17.26 galaxy in the SC 0004. 8-345 cluster. brightest columns. Wavelength calibra­ tion was performed using the He-Ar lamp reference exposures obtained im­ mediately after each cluster exposure with the cD in its centre, at the same summarized in the Messenger No. 41 , through the same OPTOPUS configura­ distance (Mazure et al., 1986). page 25 and No. 43 p. 1, and in the tion, at the same sky position. The red­ The well-known Coma cluster has corresponding ESO Operating Manual. shifts were determined by measuring also been reinvestigated by Mellier et al. For each exposure, 32 separate optical the most prominent absorption lines and (1987). The isopleth map of 'sequence' fibres were available due to the use of systematically cross-correlating them galaxies determined from a colour-mag­ an f/2.5 dioptric camera, slower than the with a template spectrum of known ra­ nitude strip (Visvanathan and Sandage, usual Schmidt camera, in a field of 33 dial velocity. 1977) to magnitude 20 shows the pre­ arcminutes diameter. The aluminium For a cluster like SC0004.8-345 (Car­ sence of several secondary density starplates were prepared at ESO ter, 1980), we derived 28 reliable red­ peaks in the vicinity of bright galaxies Garching using X-V Schmidt plate coor­ shifts from 32 raw galaxy spectra rang­ and a double structure in the core of the dinates measured with the Optronics­ ing in blue magnitude between 17.0 and cluster. The distribution of velocities re­ 3000 facility, converted into (1950) 18.8, obtained with an exposure time of lative to the brightest galaxies indicates alpha, delta coordinates using the POS 150 minutes Figures 2 and 3 show two also a composite population, one with a software and standard stars from the spectra of resp. mb 17.26 and 18.79 velocity dispersion as small as a = Perth 70 catalogue. At least 3 stars were galaxies of this cluster. The signal-to­ 350 km/so selected on each plate, in order to noise ratio in the latter case is around Using the ESO multi-object facility. check its position and orientation, and five. It represents the extreme ca se of OPTOPUS, we have observed a sam pie the rms residual position error corre­ redshift determination using the cross­ of galaxy clusters such as SC 2008-565 sponded to 0.25 arcsec. correlation procedure. The same (Fig. 1) in order to collect a large set of A dispersion of 114 Älmm was used, number of redshifts was achieved for individual radial velocities, and to pur­ providing spectral coverage from 3800 the galaxy cluster OC 1842. However, in sue similar analyses. to 5180 A. With the fibre spaghetti the case of SC2008-565, the poorly correctly entangled with the appropriate known photometry of this cluster led to Instrumentation plates, cooking times ranging from an underestimation of the required ex­ 90 minutes to 150 minutes were posure time, and thus to a considerable The observations were carried out needed, according to the average blue degradation in the proportion of accu­ during two nights at the end of July 1986 magnitude of each cluster. rately determined redshifts. We were at the 3.6-m telescope, using the multi­ nevertheless extremely pleased to ob­ object spectrograph OPTOPUS. The In all cases, observations were made tain a total of 100 well-determined red­ characteristics of the instrument are in the vicinity of the meridian plane in shifts from 112 nights of observation. In conclusion, OPTOPUS appears to ll8,..------, be a particularly well-adapted instru­ ....: ment for the rapid and simultaneous de­ termination of redshifts in catalogued galaxy clusters.

References ~ I I Carter, D.: 1980, Mon. Not. Roy. Astron. .c .c ~ ] Soc., 190, 307. l' " Mazure, A., Gerbal, D., Proust, D., Capelato, H.V.: 1986, Astron. Astrophys. 157,159. Mellier, Y., Mazure, A., Mathez, G., Chau­ vineau, B., Proust, D.: 1987, preprint. 3810 4152 4494 4836 5178 Visvanathan, N., Sandage, A.R.: 1977,Astro- Figure 3: Same as Figure 2 for an mb 18.79 galaxy. phys. J., 216, 214. 42 Coronography at La Silla: High Resolution Imaging of Faint Features Near Bright Objects F. PARESCE and c. BURROWS, Space Telescope Science Institute, Baltimore, USA, and Astrophysics Division, Space Science Dept. of ESA

Introduction of this article and available from the sponds to 5.10-3 square arcseconds in authors. the sky with a total rectangular field of Some of the more interesting as­ view of 22.5 by 35.9 arcseconds. tronomical sources happen to lie very The optical and detector system just close to bright objects. If the source is Experimental Setup described was calibrated absolutely us­ very faint, it becomes extremely difficult ing bright, stable stars as calibration to discern it against the glare of the The optical configuration of our ob­ sources. Using standard Johnson S, V, bright object. This situation arises, for servational setup at La Silla is shown and Rand Cousins I filters available at example, when attempting to image the schematically in Figure 1. Light from the La Silla (ESO filter numbers 445, 446, ionized tori around satellites such as 10, object under investigation is gathered 447 and 465), we obtained overall peak protoplanetary or circumstellar systems and focused by the f/8 MPI 2.2-metre counting efficiencies between 4,000 and of nearby stars, accretion disks within Cassegrain telescope onto a blackened 8,000 Aof 0.2 to 0.4 CCO counts per close binaries, faint emission photoetched mask located in the focal photon depending on bandpass. The nebulosities in the vicinity of old novae plane. This occulting mask is shaped in transmission of the achromatic doublet and possible fuzz around bright the form of a long thin wedge which can decreases rapidly below 4000 Aand is quasars. In all these cases, it is impera­ be moved longitudinally by a microme­ essentially opaque below 3500 A. Thus tive to reduce dramatically the scattered ter in order to vary its projected width in for U band measurements the lens light in the wings of the bright object the sky from 2 to 10 arcseconds de­ should be replaced by a singlet of fused seeing disk and/or to prevent the bright pending on seeing conditions, source quartz or silica and the detector object from saturating the detector and brightness, etc. It can also be moved changed to the UV sensitive GEC CCO thereby disabling it in the adjacent transversely to occult any desired por­ available at the 2.2 metre. areas. The latter effect can be important tion of the field of view. Following the even for relatively faint objects such as mask, an achromatic doublet reimages 15th magnitude quasars if long integra­ the telescope focal plane with a magnifi­ tion times are required. cation of 5 onto the detector so that the Observing Methodology Accomplishing this objective would effective focal ratio of the system be­ First, the coronograph is focused by open up a very fertile field of inquiry; one comes f/40. adjusting the position of the lens mount that is ideally suited to the performance An apodizing mask especially de­ until the image of the occulting wedge characteristics of modern high resolu­ signed to reduce diffracted stellar light under flat field illumination comes into tion, large aperture telescopes and de­ from the 2.2-metre telescope pupil is sharp focus. The coronograph comes tectors. Success requires a well-de­ located in the exit pupil and is rigidly equipped with internat LEOs to provide signed coronograph coupled to a high attached to the lens mount to ensure such illumination so that the focusing quality photon collecting device located that it remains there as the coronograph can be carried out even when the tele­ on a site with excellent seeing condi­ is focused. The mask obscures 30 per scope is not in operation. Second, a tions. This note briefly describes the cent of the exit pupil close to the images suitable star is made to fall somewhere techniques we have devised in our first of the entrance pupil edges. After this on the unocculted area of the detector attempts with a simple coronograph mask, the light passes through optical through a broad band filter and the re­ mated to the 2.2-metre MPI Cassegrain filters in a rotating commandable two­ sultant image is used to focus the tele­ telescope at La Silla and some of the wheel assembly mounted just in front of scope secondary. The coronograph results obtained in the first year of oper­ the detector. In our two runs of Sep­ need not be refocused if a filter is ation. A more complete description of tember and November 1986 at La Silla, changed since the filters are in an f/40 the experimental and data analysis we employed the 512 x 320 30 micron beam. Third, a suitably opaque neutral techniques and the scientific results can square pixels RCA CCO. In this particu­ density filter (N03 or 4) is moved into be found in the references at the end lar configuration, each pixel corre- the beam and the bright primary source acquired. Using the telescope TV autoguiding system described by Ouchateau and Tele~cope Coronagraph ~---- 1\ Ziebell in the Messenger No. 45, 1986, \ ( the source is placed behind the occult­ ing wedge in aseries of short acquisi­ tion exposures. With aseries of increas­ ingly smaller offsets, the source is pre­ ---- cisely centred behind the occulting wedge. This is accomplished by making the spillover light distribution above and below the wedge obtained with progres­ -- - sively less ND attenuation as symmetri­ cal as possible. Finally, any ND filter remaining is removed and the long ex­ 1: Optical------configuration. Figure posure in the specified bandpass be-

43 set mainly by the time necessary to read ing. Gosmic ray events and local GGO out, process, and display the relevant defects are also located by comparison GGO acquisition images. A detector with neighbouring pixels using standard with real time display capabilities or a statistical tests and iterating to avoid faster data handling system for the GGO including bad pixels in the averaging would obviously shorten considerably process. Finally, the edges of the this set up period and allow a faster turn occulting mask are defined interactively around. This is a critical factor for a and stored in a file associated with the lengthy survey programme. image. No further user interaction is re­ quired in the subsequent processing which can proceed automatically. Data Analysis and Results The results of this process are shown All the raw images are processed in a in Figures 2 and 3 that represent images standard way to prepare them for scien­ of Beta and Alpha Pictoris, respectively, tific analysis. The GGO bias level and the taken with the system we have just de­ variations in response across the detec­ scribed with the R band filter on the tor area are removed by subtracting a night of November 27, 1986. Beta Pic­ constant bias level and dividing by an toris is a star suspected of having a appropriate flat field. Overclocked, satu­ giant protoplanetary system seen edge­ Figure 2: Image of Alpha Pictoris. The image rated pixels, and bad columns are easily on in emission surrounding the central has been flat fielded, and minor blemishes located and masked out so that they will star while Alpha Pictoris is used as the have been removed. The horizontal bar is the not contribute to the rest of the process- reference star. Both images are mainly occulting mask and has been masked black. The masked circular area in the centre with triangular appendages is due to saturated and bleeding pixels. The deviations from cir­ cular symmetry are due to instrumental scat­ tering and diffraction effects. The image is truncated at 5,000 counts, and has been displayed with the image greyscale changed to give equal numbers of pixels at any given intensity. (Histogram equalization.) gun. If a faint feature is expected to be lost in the light from the wings of the bright object seeing profile, the tele­ scope is moved to a control star nearby and the procedure just described re­ peated. After some practice, the over­ head time used to acquire and precisely register the source can be kept within approximately 20 minutes. This time is

Figure 3: An image of Beta Pictoris with trun­ Figure 4: R band image of Beta Pictoris circumstellar disk .obtained as a difference image of cation at 3,000 counts. It is otherwise treated Figures 2 and 1. North is up and East is to the left. The image displayed is about 23 arcsec in identically to that of Figure 1. All instrumental width. The disk extr:mds diagonally from NE to Sw. The dWk portions of the image are due to effects are similar but there is an additional saturated pixels or the focal plane mask. The bright line rUlining vertically through the frame bulge in the image at bottom left (NE) through centre, and light close to the mask particularly to the right of centre are due to residual top right, due to the circumstellar disko diffractive scattering. 44 composed of the stellar seeing disk with small contributions due to scattering within the instrument and, of course, for Beta Pictoris, the circumstellar disko This feature, however, is almost lost in the image shown in Figure 2 without benefit of a direct comparison with the reference image shown in Figure 3. Although a feature running in a rough­ Iy NE to SW direction through the Beta Pic image, without a corresponding one to be discerned in the control image, stands out rather clearly in the image shown in Figure 2, considerably more analysis effort has to be expended in order to generate a photometrically true or correct image of the immediate surroundings of Beta Pictoris. Details of the complex data processing tech­ niques used to subtract the reference image of Alpha Pic shown in Figure 3 from that of Beta Pic in Figure 2 are given in Reference 1. The basic problem to be solved is to make the result of the analysis as free as possible from assumptions, biases and subjective judgements as possible. In other words, it was taken as axiomatic that no user interaction would be permissible and no assumptions about the characteristics or even the existence of circumstellar features would be allowed. This is a crucial but often neglected attribute of any method applicable to the interpreta­ tion of astronomical data of this type. The best algorithm chosen essentially Figure 5: A narrow band Nil image of R Aquarii, a variable binary witl1 known emission of consisted of a truncated least squares ionized knots along a collimated axis. Tl1e knots are resolved clearly in tl1e raw data but are fit between the two images allowing the overexposed in tl1is image to reveal tl1e presence of faint loops of material to tl1e Nortl1 of tl1e relative intensity, overall background star. Tl1e directions are tl1e same as in tl1e previous figures. and spatial registration to vary. The best values for these parameters obtained this way were then used by the pro­ fact that the variations in brightness of hotter blue companion accreting a por­ gramme to subtract the reference from the disk in the broad B, V, Rand le tion of that mass via an accretion disk the Beta Pictoris image. bands quite closely mimic the stellar (see Solf and Ulrich, 1985, and refer­ The result of this procedure for the spectrum, almost certainly implies that ences therein). Although this system is Beta Pictoris case is shown in Figure 3. the emission we detect is due to scatter­ known to be one of the most complex This figure dramatically illustrates the ing of the stellar radiation from particles observed so far, probably, mainly be­ power of the technique briefly described of average size much larger than one cause it is so close (200-300 parsecs here. The image is photometrically micron diameter. This, in turn, indicates by most estimates), some of the most accurate in that counts at any point in that some sort of accretion process has exciting phenomena occur deep within this image are linearly related to the true been active in the protoplanetary nebula the inner nebulosity extending out to emitted intensities of the protoplanetary to form large grains from the approxi­ 10-15 arcseconds at most from the disk through the absolute calibration of mately 0.1 micron sized particles com­ central object. The morphology and the optical and detector system used. A monly found in interstellar space. It physical characteristics of this nebulosi­ standard ratio image, for example, should be noted that the IRAS infrared ty are not weil known, principally be­ would not satisfy these basic require­ excess emission reported for this star by cause of the difficulty of imaging accu­ ments and, thus, cannot represent a Gillett, 1986 (Reference 3) that initially rately and reliably within a few arc­ true image of the stellar surroundings triggered interest in this particular sys­ seconds of the bright Mira whose visual dependent as it still is on spurious and tem does not necessarily have to origi­ magnitude varies periodically from mv = contaminating effects of the specific de­ nate from the same material responsible 6 to 11 in 387 days. tecting system employed in the investi­ for the scattering observed in the op­ An obvious solution to this problem is gation. This and other images of the Beta tical. offered by the coronographic technique Pictoris disk taken at La Silla in the B, V, A slightly different application of the whereby the bright Mira is occulted by Rand le bands represent the first visible coronographic technique just described the 2 arcsecond wide wedge as shown images of this fascinating feature. is shown in Figure 4 wherein an area in Figure 4. This allows long integration The physical implications of these around the symbiotic Mira variable R time exposures through narrow band measurements on Beta Pictoris and Aqr is investigated in some detail. This filters tuned to bright emission lines other candidates are described in detail fascinating system is quite likely to con­ such as Ha and the forbidden [N 11] in Reference 2. For Beta Pictoris, the sist of a mass losing Mira variable and a 6583 A. Short duration broad band R 45 exposures appropriately subtracted establishing and elucidating the construction and calibration of the from the narrow band images allow an mechanism responsible for the ob­ coronograph, to B. G. Taylor, F. Mac­ even better view of the line emission served activity in this enigmatic system. chetto and H. S. Stockman at ESA and region around this object. The image More observations of a number of in­ the ST Scl for constant encouragement shown in Figure 4 also illustrates graphi­ teresting objects with this technique at and financial support, to P. Bely, R. cally the potential of this technique as La Silla are being planned for the near Prange, R. de Grijp and A. Vidal-Madjar both previously known and unknown future. The authors welcome sugges­ for assistance in many aspect of this bright and faint features throughout the tions from readers of this publication for programme. We also wish to thank S. di inner nebulosity can be readily dis­ improvements, additions to and ideas Serego Alighieri for the flat field he kind­ cerned and accurately measured down for new applications of the basic tech­ Iy supplied and F. Noriel, for expert to approximately one arcsecond of the nique described here. If you have a editorial assistance. Mira without much trouble. Especially favourite object that might benefit from obvious is the famous jet made up of an investigation with our coronograph, References several knots extending in a generally please contact us so that we may ex­ 1. Burrows, C., F. Paresce, and A. Evzerov. northern direction towards the bottom plore the feasibility of a joint effort. Instrumentation and Data Reduction of the figure but faint wisps, knots, and a Techniques for the Detection of Circum­ counter jet extending to the limits of our stellar Material, BAA.S., 18, 1027, 1986. image in the southwest are also clearly 2. Paresce, F. and C. Burrows, Wide Band Acknowledgements discernible against the sky background. Imaging of the Beta Pictoris Circumstellar Disk, BAA.S., 18, 1027, 1986. Direct comparisons of images taken in None of this work would have been 3. Gillett, F.C., "IRAS Observations of Cool the light of several emission lines of even remotely possible without the en­ Excess around Main Sequence Stars", in elements in varying ionization stages thusiastic support of Daniel Hofstadt Light on Dark Matter, ed. F. T. Israel, D. show remarkable differences revealing a and his operations group at La Silla, in Reidel, 61,1986. complex temperature and electron den­ particular Paul Le Saux, Gerardo Ihle, 4. Solf. J., and H. Ulrich. "The structure of sity structure within the nebulosity. Michel Maugis, and A. Urquieta. We are the R Aquarii Nebula", Astron. Astrophys., These data should prove quite useful in especially grateful to Anatoli Evzerov for 148,274,1985.

Search for Supernovae in Distant Clusters of Galaxies L. HA NSEN, Copenhagen University Observatory H. U. N0RGAARO-NIELSEN, Oanish Space Research Institute H. E. J0RGENSEN, Copenhagen University Observatory

Supernovae and Cosmology SNe I near maximum rival with galaxies It has recently been realized, how­ One of the main problems of cosmol­ in brightness (Mv = -19.7 for Ho = ever, that a subgroup named SNe Ib ogy today is to determine whether the 50 km 5-1 Mpc-'). At a redshift of z = 0.5 exists in spiral galaxies. This subgroup universe is open or closed, i. e. if it will the expected peak magnitude in V is is characterized by the absence of the continue to expand for ever or if it will about 22.7 depending on K-correction A 6150 absorption feature in the spec­ recollapse in a far future. The classical and the cosmological model assumed. tra. SNe 1b will hardly cause any major attempt to settle the question is to ob­ For Friedmann models with qo = 0.0 problem for cosmological applications serve some kind of standard candle out (open) and qo = 0.5 (transition to closed) as they are about 1~ 5 fainter than the to large redshifts, z, and measure the the difference is 0.28 magnitude. A majority of SNe I. If they are not dis­ positions of the objects in the Hubble modest number of SN I events could criminated by other means they may be diagram (log (z) versus apparent mag­ therefore provide the evidence for an discarded because of gross deviations nitude). The brightest galaxies in rich open or c10sed universe. Notice, that from the predicted apparent magnitude. clusters have for example been used for neither Ho nor the absolute peak mag­ this purpose, but significant evolution nitude need to be known. The Search Programme corrections are expected wh ich are hard SNe I as standard candles are not to determine with the required precision, supposed to be plagued by uncertain With the launch of the Hubble Space and no firm conclusion has been corrections, as are other candidates. Telescope (HS1) it will become possible reached as yet. The K-corrections can be accurately de­ to do photometry on distant SNe to A more promising candidate for a termined from nearby SNe I, and no magnitudes fainter than 25, and the cos­ standard candle is the type I supernova change of the supernova characteristics mological goal is then within reach. The (SN I). SN I events show spectra and with look-back time is expected. first and difficult problem is to find the light curves which are very alike, and the A well-developed theoretical model SNe I. G.A. Tammann (1) estimates that intrinsic scatter in peak brightness is for SNe I assumes the deflagration of a a Coma-like cluster at z = 0.5 will show a less than 0.3 magnitude. SNe I occur in white dwarf wh ich is pushed to the rate of 0.5 SN I per year within the field spirals as weil as in elliptical galaxies. Chandrasekhar limit by mass accreted of the Wide Field Camera of the HST. Events in elliptical galaxies are not ex­ from an evolving companion. In this pic­ However, observing time on the HST is pected to suffer from any significant in­ ture virtually the same event happens very expensive, and fortunately the job terstellar extinction in the parent galaxy, every time with no variation of mass and can be performed from the ground. The which would otherwise be difficult to chemical composition. This explains the Danish 1.5-m telescope at La Silla is correct for with the necessary accuracy. reproducibility of the phenomenon. ideal for the task. The observing time is 46 The Procedure Ouring the last part of 1986 we ob­ served using the old ESO CCO camera with a pixel size corresponding to 0':47. The old CCO has many defects and a rather large read-out noise. From 1987 we will use a new one with twice as much spatial resolution, few defects and reduced noise. Of great importance is also the availability of the ESO image processing system, IHAP. Our exposure time is 45 minutes to 1 hour, and generally we use the V­ band, although some exposures have been obtained in Gunn R. However, in­ terference fringes from night sky emis­ sion lines are very prominent in the R­ band and hard to correct for in a satis­ factory way. As soon as a new exposure has been started, the previous exposure is re­ duced. This is only a matter of a few minutes. We then start a large BATCH procedure that compares the new im­ ages with a standard exposure of the field. A number of common objects are identified, and the new image is rotated to coincide with the standard within 0.05 pixel. The seeing is determined, and the image of best seeing is Gauss­ smoothed in order to match the seeing of the other. After scaling the intensity of the objects to the same level in the two images the standard is subtracted from the new, and a difference image is ob­ tained. The next step is the exciting evalua­ tion of the difference image. The stan­ dard frame is displayed in the first quad­ rant of the colour screen, while the three other quadrants show 1/15 of the field in the new, the standard, and the differ­ ence image. With the special colour scale we use, the noisy difference image will look greenish. Pixel-values deviating more than about 2.5 0 will appear either black or red. A stellar image of 24 m and Figure 1: A 1-hour GGO exposure in the V-band of the cluster AG 114 (z = 0.31) obtained with average seeing 1':5 covers some 10 the Oanish 1.S-rn telescape. The seeing was 0:'9 (FWHM). The field is 2:S x 4 '. Most of the objects seen are galaxies. pixels (old chip). If such a star appears between two exposures it will stand out very prominently in the difference as black or red. relatively cheap, the field of view some­ possible each month from September When we examine the field in 15 steps what larger than for the Wide Field Cam­ through April with the Oanish 1.5-m tele­ we notice a number of black or red era, it has a large number of nights with scope. A SN I remains within 1 mag­ features from well-known bad pixels good seeing, and it is known for its high nitude of its maximum brightness for and columns of the CCO. Often we find image quality. Photometry on stars of about 25 days, but because of relativis­ that a few stars are too bright to cancel 24 m can be made with a CCO camera tic effects (time dilation) time intervals when the difference between two large from 30-minute exposures (2). As ex­ are stretched by a factor 1 + z when count-numbers are taken. These stars plained in the text of Figure 2 we have observed at the redshift z. This means are then checked for variability by one or performed realistic simulations of a that for z = 0.5 and less a SN I remains more procedures for magnitude deter­ supernova event and demonstrated the above our detection limit of approxi­ mination. We will also find a number of feasibility of our methods. We have, mately 24 m for more than a month, and it cosmic (radioactive) events in the CCO therefore, initiated a major campaign in cannot avoid discovery if it occurs with­ chip. This is a problem which worries September 1986 with the aim to find in the half year period of our watch. If, our sceptic colleagues more than it distant SNe I in elliptical galaxies. say, 20 clusters are searched every worries uso Cosmics have a very narrow Our plan is to observe rich clusters of month we expect 5 SNe I per year to be energy distribution, and the large ma­ galaxies with redshifts from 0.2 to 0.6 if found. joritiy of events are easily distinguished 47 Figure 2: The colour screen during one of the 15 comparison steps. Part ofa new (upper right) and a standard (10 wer left) exposure of the cluster AC 370 (z = 0.37) is shown. The lower right shows the difference. In the upper left a compressed image of the whole fjeld is displayed. The standard image is ofrather poorseeing (1 :'9), and the new exposure has been rotated, smoothed and scaled to match the standard. A SN I event has been simulated in the following way: A B-exposure ofSN 1985 I in a galaxy ofz = 0.03 obtained by J. Teuber was "zoomed" out to z = 0.37, smoothed to match the seeing and added to the new image. The magnitude of the supernova at z = 0.37 is 22.0. Similarly, an image 01 the parent galaxy cleaned for the supernova was added to the standard image ofAC370. The "event" appears to the left ofand below the centre in the difference. The fake is quite realistic as the noise is always dominated by the background.

by the experienced eye or by comparing too slow because it lacks a floating­ redshifts. We cooperate on the project the profile with that of astar. point processor. At present we must with R. S. Ellis, University of Durham, In rare cases cosmics may simulate a accept a delay of one day, which may and W. Couch, Anglo-Australian Obser­ SN event, e. g. by falling on top of an have sad consequences if a candidate vatory. They have supplied us with a object in the image. Therefore, a prom­ appears on the last night of observing. number of distant clusters, and they ising SN candidate must be confirmed. have obtained over-head time on the We planned that the whole comparison anglo-Australian 3.9-m telescope and Preliminary Results procedure should take less than 30 mi­ the Isaac Newton 2.5-m telescope with nutes. A candidate can then be con­ Until now we have had 5 runs on the the possibility to do spectroscopy with firmed by a second observation the very Danish 1.5-m. We have paid most atten­ short notice of events down to about m same night. This is important for the tion to the clusters in the range V = 22 . follow-up. In practice it is no problem to 0.2 < z < 0.4 because (a) HST is not yet Our survey supplies us with a steadily do the comparison within 30 minutes ­ in orbit, (b) we want to be sure of our increasing list of faint blue variable ob­ at the computer centre! The computer methods, and (c) ground-based spec­ jects. One of the objects for example is on the Danish 1.5-m turned out to be troscopy can be made for SNe I at these apparently an active galaxy possibly at 48 the cluster redshift (z = 0.3). Most likely Coma. One should also notice that the cover SNe. The first season has con­ the majority of the variables are faint local supernova-rate is uncertain with a vinced us that our technique works. If a QSO's roughly in agreement with statis­ factor of 2 according to Tammann (pri­ supernova appears we will find it! tics of QSO's around 22 m (3) predicting vate communication). Further, there is at approximately 1/3 object per CCO­ present no evidence of the rate at earlier References frame. epochs of the universe. After the first 5 runs we have been This campaign will at the very least (1) Tammann, G. A.: 1979, in Astronomical able to do 48 comparisons of fields. The put important limits on the supernova Uses of the Space Telescope, proceed­ expected number of SN I events in 2 rate at cosmological distances. A valu­ ings from the ESNESO workshop, ed. Macchetto et al. according to the supernova-rate given able spin-off will also be the nice selec­ (2) Stobie, R. S., Sagar, R., and Gilmore, G.: above, but we have found non until now. tion of high quality cluster images, be­ 1985, Astron. Astrophys. Suppl. 60, 503. Why? Part of the answer may be that cause sub-arcsecond seeing is not an (3) Koo, D.C., Kron, R.G., and Cudworth, although many of the clusters are really unusual event at the Oanish 1.5-m. K. M.: 1986, Publ. Astron. Soc. Pacific 98, impressive some are less rich than However, the primary purpose is to dis- 285.

On the Rates of Radiation Events in ESO CCDs

Radiation events (cosmic rays and rameters Iike sky transparency, seeing been reported occasionally in the local radiation) stand out in exposures and sky emission line intensities do not Operating Manuals of the instruments taken with thinned CCO devices as vary too much during the sequence of (CASPEC, EFOSC). The data collected spikes covering 1-4 pixels. Their inten­ exposures. here are more systematic and give the sities vary from about one hundredth Billions of radiation events have been possibility to draw a few simple conclu­ electrons (the lower detection limit) duly recorded by CCOs used for as­ sions. A batch programme based on a above the background to a few thou­ tronomy in the last 10 years, but being filtering technique was used to identify sand for the most energetic events. In considered essentially a nuisance, little the events with intensities larger then front-illuminated, thick CCOs energetic has been published on their rate or ener­ about 5 a of the background noise. The particles can produce a short track of gy distribution. As a step towards a bet­ rates are not very sensitive to the value electrons as they cut diagonally through ter understanding of this phenomenon, of this lower cut, most of the events the silicon layer. we have counted radiation events in a being of sufficient energy to be de­ The number of radiation events per number of long (typically one hour) dark tected. No systematic difference is unit time is such that they contribute in a exposures obtained in the last four found between measurements at significant way to the noise in the as­ years with ESO CCOs both in the Gareh­ Garehing and La Silla, with variations tronomical data extracted from the CCO ing lab and at different instruments at La being observed in both directions at the frames. In direct imaging they can be Silla. We list in Table 1 the event rates 10-20 % level. The rates do not seem distinguished from stars on the basis of derived from these exposures. Typical to correlate with the telescope or the the point spread function. The problem values for some of the ESO CCOs have instrument type. It is worth noting that is more serious for spectroscopic ob­ servations. In long-slit spectra where the dispersion direction is aligned with Table 1: Radiation event frequency in eeos the rows or the columns of the CCO, the area where the sky is sampled can be ESO Type Telescope Instrument Number No. efficiently cleaned with a median filter CCD cm-2 min-1 Exposures running in a window which moves per­ Number pendicular to the dispersion (RBLEMISH command in the ESO IHAP data reduc­ 3 RCA SID 501 EX (thinned) 3.6 m CASPEC 5.8 3 tion system). For spectra in the echelle 3 RCA SID 501 EX (thinned) 3.6 m EFOSC 5.2 5 format, the only effective way to identify 3 RCA SID 501 EX (thinned) 2.2 m B&C 5.7 3 the radiation events is by comparison of 5 RCA SID 501 EX (thinned) 3.6m CASPEC 6.6 4 two, or possibly more, spectra taken 5 RCA SID 501 EX (thinned) 2.2 m Imaging 6.1 3 with an identical configuration. Pixels affected by a cosmic ray in a single 6 GEC 8603+ 2.2 m B&C 1.2 2 exposure can be sorted out and re­ 7 GEC 8603+ 2.2 m B&C 2.1 0 3 jected when their signal value is com­ 7 GEC 8603+ 3.6m CASPEC 2.3 0 2 pared with that measured on the aver­ 8 RCA' SID 006 ES 3.6 m EFOSC 5.2 2 age frame. Routines operating on this 12 TEK 512 M -11+ 3.6 m CASPEC 1.4 3 basis exist in both the MIOAS and IHAP data analysis systems. To achieve good • 15 ~lm pixels + Coated to improve UV-blue sensitivity cleaning without degradation of the as­ o Possibly contaminated by electronic noise tronomical data, it is necessary that pa- 49 the same CCO '* 3 was used with dewar . tween GEC and TEK is significant. gin, and further tests are planned in the windows made of two different types of The count rates in GEC CCOs may have near future. fused silica when on CASPEC er EFOSC been slightly affected by electronic Astronomers who have measured or (see Table 1). Event rates in RCA CCOs noise wh ich can imitate radiation suspect that the event rates in their CCO are relatively constant and a factor of events. exposures are significantly different 3-4 higher than in GEC and TEK CCOs. The values are very close to the low from the values given in Table 1 are As the dewars are the same for all CCO limits quoted by C.O. Mac Kay in his strongly encouraged to send their data types, the high rates are probably re­ review article in the 1986 Annual Review to ESO for further analysis. It would be lated to some radioactive component in of Astronomy and Astrophysics. The of particular interest to measure using the RCA CCO package, the support question remains open as to whether a the same algorithm rates from CCOs of glass being the most likely candidate. It fraction of these counts observed in different types and/or located at other is not clear whether the difference be- GEC and TEK CCOs is still of local ori- Observatories. S. O'Odorico and S. Deiries

New Technology Telescope Taking Shape M. TARENGHI, ESO

As an intermediate step towards a 80 % of the geometrical optical energy The function of the azimuth axial hy­ very large telescope (VL1), ESO decided within 0.15 arcsec. drostatic bearing system is to provide a to design and build a New Technology The telescope mechanics is made of stiff support and to allow the accurate Telescope (NTT) with a mirror measuring box-shaped parts in order to achieve and low-friction rotation of the tele­ 3.5 m in diameter. This telescope will high stiffness with low mass. The ND is scope fork on the supporting ring. This help reduce demand on the 3.6 m tele­ expected to have an eigenfrequency of is accomplished by using an oil low­ scope and will offer an opportunity for about 8 Hz. The result is a structure with pressure, multipad (24), hydrostatic practical testing of new ideas for tele­ the turning part weighing approximately bearing with a large carrying surface. In scope design. 110 tons. The manufacturing of the main addition to the low-pressure design of The ND project includes a number of steel structure and the assembly in the hydrostatic supports, which allows innovations: Europe of the complete telescope is be­ for a low consumption of oil and a lim­ (i) thin primary mirror with active op- ing carried out by Innocenti-Santeustac­ ited temperature increase of the oil in tical control of the mirror chio, INNSE, Brescia, Italy. the pads, an active, high-acccuracy oil geometry, The azimuth axis is mounted on an temperature control system avoids ma­ (ii) active control of the collimation axial multipad hydrostatic bearing of 3.5 jor exchanges of heat between oil, tele­ and of the focusing of the secon­ metre diameter. The radial location is scope structure and environment. dary mirror, defined by an axially pre-Ioaded angular The two axes of the telescope are (iii) maximum exposure of the tele­ contact ball bearing. The altitude axis is both controlled by a group of four ser­ scope to the external environment mounted on large self-aligning internally vodrives. The altitude drive system is during observations (better see­ pre-Ioaded ball bearings. composed of two toothed wheels, one ing), (iv) fast switching of the light beam between two different instru­ ments, (v) alt-azimuth mount with high point- ing and tracking accuracy, (vi) flexible and easy control system, (vii) remote control, (viii) rotating compact building. The optical system is a Ritchey-Chre­ tien type. The primary M 1 as weil as the M2 and M3 mirrors consist of Zerodur glass ceramic manufactured by Schott Glaswerke, Mainz, FRG. The meniscus shape and the diameter-to-thickness ratio of only 15 of the primary mirror is thinner than that of any other large opti­ cal telescope built in recent years. The optical figuring is now being carried out by Carl Zeiss, Oberkochen, FRG. The optical quality specification to the manufacturer for the combined opti­ cal train (Nasmyth image) is 80 % of the geometrical optical energy within 0.4 arcsec. However, after correction with the ESO active optics support, the op­ Figure 1: The supporting ring witl7 24 hydrostatic pads in the workshop INNSE, Brescia, in ties should maintain an image quality of February 1987. This is a first element of the European pre-assembly of the NTT. 50 at each end of the altitude axis, each cooled, as are all heat sources located driven by two servodrives via two pin­ on the telescope. ions. The azimuth drive system consists The mobile part of the building is oc­ of a stationary toothed wheel on which tagonal, has three storeys and rotates four pinions, one for each servodrive, on a cylindrical concrete base. are engaged. The instrument rooms are on both The absolute position of the telescope is measured by two directly coupled sides of the telescope behind the side absolute encoders. The tracking is con­ walls of the telescope room. The control equipment occupies aseparate lower trolled by two friction-driven incremental floor. At this level is also a room for the encoders. Each axis is provided with technical services of the building. one absolute and one incremental en­ coder. In order to keep high pointing and An important aspect in the design is tracking accuracies with good ventila­ the maximum exposure of the telescope tion at the same time, the telescope is to the external environment during ob­ protected at the front and back by servation. This approach has been permeable wind-screens which control selected in order to provide maximum the wind speed in the chamber where ventilation to the structure, thus allowing the Telescope tube sits. for thermal stabilization of the telescope The temperature in the telescope to night conditions and avoiding the room and in the instrument rooms is Figure 2: The fork arms on the reference trapping of layers of air at different maintained at the level of the outside plane. The seats (holes) for the drive units temperatures in the path of the optical temperature at night, achieved by and for the big ball-bearing of the elevation beam, which would cause blurring of the means of an appropriate thermal insula­ axis are clearly visible. image. The building floor is actively tion and air conditioning system.

NTT ControllAcquisition Software G. RAFF!, ESO

In these months, while the main Computers has to be comprehensive and clear for mechanical and optical components are the user. The need for a data acquisition Figure 1 shows the ND control com­ being prepared for the ND, the control system has been recognized and im­ puter configuration. As the control elec­ software has also to meet its first dead­ plemented at La Silla al ready some tronics of the ND was designed to be lines. In a few months, members of the years ago. The ND, however, is the first distributed, in order to reduce cabling Electronics Group will be testing the case where a comprehensive system and therefore increase reliability, a main telescope movements at INNSE in design has been done right from the Brescia. number of crates (based on the VME beginning. standard) are used for the telescope This will be the first result of a pre­ The main requirements of the ND paratory work, wh ich started a couple of control functions. The VME crates incor­ system were to accommodate distri­ porate microprocessors of the Motorola years ago. The present description buted control electronics and two in­ should highlight new aspects of the ND 68000 family and are all linked via a struments which will be permanently Local Area Network (LAN) of the Ether­ software with respect to the control/ connected. This in turn led to specify net type. acquisition systems presently in use at that the software should allow multi­ The control computer of the ND is a La Silla. instrument operation and multi-user op­ Hewlett Packard A900, which has the The ND control system design in eration (or multi-station) as a conse­ function of coordinating the distributed general (electronics and software) was quence of the simultaneous use of more control system, perform data acquisi­ designed by the TP Electronics Group. than one instrument and of remote con­ tion, accommodate user interface and People who are specifically working at trol. image processing and support remote the ND software (some part-time or for Additional needs, which had a large control. The A900 minicomputer is the a limited period of time due to other on­ impact on the design, were remote con­ newest member of the HP 1000 family going projects) are P. Biereichei, B. Gilli, trol and user interface. Finally, during based on newer and more compact B. Gustafsson, J. Marchand, G. Raffi, K. the whole design phase of the ND sys­ technology and with computational per­ Wirenstrand from the Electronics Group tem, much attention was payed to see formances a factor of two better than and L. Noethe from the ND Group. that the present design work could also HP 1000 F computers. In this issue of the Messenger the be used for the VLT and thus represent general structure of the ND control/ a first test bench for this instrument. Software acquisition system is summarized. In fu­ Altogether the ND control/acquisi­ ture issues some areas will be expanded Software control and data acquisition tion system can be characterized in the more in detail, like: user interface; pool: systems serve the purpose of managing following way: parameter data base; microprocessor telescope, instrument, detector, image - Distributed system: Programmes software, and acctive optics software. processing operation in a way wh ich can be either on the A900 or on any

51 Outside Inside NTT building NTT building

user station 2

Remote control lines

HP A900 Ethernet

To other computers

Hydraulic system VME 570MB

570MB

OISCS

Figure 1: NTT contral computer configuration. microprocessor connected to Ethernet. tivities. Stations are identical in hard­ (e. g. between instrument and telescope) Rules and protocols had to be designed ware and software. In practice different and a large number of parameters so that commands/replies and data users will choose different tables and needs changing/updating as soon as could be exchanged transparently, i. e. menus in accordance with the work they new modules are added. It has in fact to without differences due to where the are doing, namely: active use, monitor­ be remembered that a control/aquisition programme is running. So one can vis­ ing, off-line work. system has to be open to allow addi­ ualize the ND software as distributed - User interface: This had to be up­ tions. For this purpose a data base, on many CPU's, while up to now mi­ dated not only because of the inadequa­ named Pool, has been implemented, croprocessors were always used as cy of the present terminals, but mainly where the time critical files are kept in "black boxes" , with a special protocol for the need to have a more flexible and memory. Tools will be available to read with every one of them. A very relevant easy to modify user end. To improve the and display what it contains, easily activity in this area was to define and physical user end, the display informa­ monitoring an operation going on in the implement a suitable real-time system tion was brought to a large colour system (e. g. monitoring from a remote for the microprocessors and adequate monitor (with softkey, tables, graphics, si te control operations). cross-support tools. Then interfacing etc....) of the Ramtek type (with the - Remote contro!: For adescription both with Ethernet and with the control advantage that this is interchangeable of the last tests on R. C. see the article in electronics hat to be coped with, namely also for image processing use). To im­ the Messenger No. 44, June 1986. R. C. the writing of corresponding drivers, prove the operational aspects, the user concepts have been embodied in the which is still an on-going activity. sees now a unique set of commands for design of the ND control/acquisition - Multi user/instruments system: different purposes (telescope control, system and it will benefit from the fea­ Many operational environments can run instruments, detectors, image process­ tures described before. One relevant ex­ at the same time (not only one as at ing), rather than a set of terminals. The ample of the impact of R. C. on the present). though clearly certain parts layout of the user end can be easily design is the Pool, where local files are like the control of the light beam will modified, as this layer of software does residing on one computer while global belong to one instrument only at one not belong to any specific control pack­ files are kept updated on two computers given time. Booking of devices enforces age and basically sends commands to (Iocal and remote). Meanwhile R. C. will protections and interlocks and sepa­ any control programme, receives and be operational on the 2.2-m and on the rates users. Image processing can be displays replies. CAT telescopes starting with July 1987, done with IHAP on many independent - Pool: To enforce complete inde­ so that more experience might be data bases. Multidetector operation, like pendence of control modules for multi­ acquired before installing it on the ND. in the case of EMMI, is also implicitly instrument operation and to detach the So far all the basic elements of the included into in this concept. user end from the rest, it was not system have been implemented, while - The system can accommodate enough to define interface rules and work is still proceeding on the specific several user stations, where users will protocols. A lot of information has to be control programmes for the different be doing simultaneously different ac- exchanged between various modules telescope components. 52 lems. This extension will be connected machine took place as planned during MIDAS Memo to the MIDAS support person on duty. May 1986. The machine has since been used for manual measurements of stel­ ESO Image Processing Group 3. MIDAS Workshop lar positions with the old HP 1000 sys­ tem. Due to problems in the electronics The next Data Analysis Workshop, for reading the diode array and delay in 1. Application Developments arranged by the ST-ECF, will take place the software developments, it has unfor­ in Garching in the week of May 4-8, The plotting facilities have been up­ tunately not been possible to offer the 1987. The very positive response to the graded with many new features such as scanning mode yet. Most of the prob­ introduction of aMIDAS Workshop has negative increments on axes and over­ lems have now been solved and it is meant that it will be continued. It will plot of error bars. The INTAPEIFITS hoped that the implementation of the again be arranged just after the Data command was updated so that it now diode array can continue without further Analysis Workshop on May 7, 1987. The reads blocked FITS tapes according to delays. With the present time table, it programme will include sessions on the agreement of the FITS committees should be possible to scan limited areas general developments, new applications i. e. a physical blocking factor of up to 10 of plates on the OPTRONICS this fall. and the status of the portable MIDAS is allowed. The Dicomed commands The usage of the Grant measuring version in addition to aMIDAS Users have been upgraded to allow for spool­ machine has been less than 50 hours meeting. A tentative agenda will be sent ing of the output files. That means the BI over the past year. We regard this to be out together with other material for the Wand colour mode can be used simul­ a result of the very few coude plates Data Analysis Workshop. People in­ taneously at ESO/Garching. taken during the last years and thus a terested in participating in the Work­ The FILTERISMOOTH command now continuing trend. It is therefore under shop should contact either the Image employs an algorithm wh ich is nearly consideration to discontinue the opera­ Processing Group or ST-ECF. independent of the window size. A box­ tion of the GRANT machine if the usage car filtering of 1024 • 1024 image with a does not increase significantly. People 4. Measuring Machines 15 • 15 window takes now 13 sec CPU­ who would like to use it for measure­ time versus 211 sec CPU-time before The mechanical and optical modifica­ ments of coude and image tube spectra (these are VAX 8600 times, approxi­ tion of the OPTRONICS measuring are kindly asked to do so. mately 2.3 times faster than a VAX 11/785). The FFT routines were modified to get rid of the excessive paging ob­ served with large images. For a 1024 • 1024 image the FFT needs now 54,000 page faults (with a working set New CCD Control Camera and First Test size of 1024 pages) and 6 : 30 min CPU­ time (VAX 8600). of a TEK 512 CCD at La Silla It is now possible to run several paral­ lel MIDAS sessions from the same disk At the beginning of February 1987 a B&C spectrograph. The camera is a directory by using the MIDAS login new CCD control camera has been suc­ so-called generation V system from command INMIDAS PARALLEL. The cessfully installed at the 3.6-m tele­ Princeton Scientific Instrument. It has DEFINE/Parameter was added for defi­ scope by R. Reiß and P. Sinclaire. It will been interfaced to the standard ESO nition of parameters in MIDAS proce­ be used with all of the CCD-based in­ computer in Garching in such a way that dure files. This command replaces the struments like CASPEC, EFOSC and the the observers will not detect any differ- commands DEFAULTS, TYPES and LIMIT wh ich have been removed. NOTE: 50 .----.---r---,-----,---.----r---r-----y---.-----,---,-,--r--, if you have used any of these com­ mands lhey must be substituted by the DEFINE/PARAMETER. 40 2. Support of MIDAS at External Sites The MIDAS system has now been ex­ ~ 30 ported to a large number of external o sites (i. e. more than 40 sites on 3 conti­ nents). In order to give these sites a first w class support, a new MIDAS Hot-line d service will be started from April 1, 1987. 20 This service will provide an answer to MIDAS related questions received through either Telex no. 528 282 22 eo d (attn.: MIDAS HOT-L1NE) or electronic 10 mail (SPAN: 'ESOMC 1::MIDAS' or EARN/BITNET: 'MIDAS@DGAES051'). Requests and questions received before noon will be answered not later than the OI---1_---I.._--.l..._--'-_...l...-_1-----'_--'-_---'-_-'-_-'-_'----1._---' next normal working day. 300 500 700 900 In addition, a special telephone no. WAVELENGTH +49-89-320-60-456 will be created for Figure 1: The quantum efficieney eurve of the thiek TEK 512M-11 deviee measured in the ESO general MIDAS questions and prob- deteetor lab after eoating. 53 camera that most likely will be installed at the ESO 1.52-m spectrograph by the middle of this year. In the same test period, we have also used a front-illuminated TEK 512 M-11 CCO on CASPEC. It has 512 x 512 square pixels 27 Ilm in size or the largest collecting areas ever as it goes for CCOs at La Silla. The chip had been coated in the detector laboratory at ESO Garching to enhance the UV-blue sensitivity. The quantum efficiency measured after the coating is shown in Figure 1. In this CCO r the low noise on-chip amplifier was damaged and we had to switch to the C-amplifier and the C-output shift regis­ ter. This is prabably the cause of a read­ out noise of 30 e-/pix, a value definitely higher than one would expect. Given this value and the relatively low quantum efficiency, this particular device it not ...,. better than the CCOs now in operation at La Silla and for the time being is not offered to visitors. Cosmetic and charge transfer efficiency however are quite good (see Fig. 2) and would make this device quite useful on some ESO instru­ ments if operating with a r.o.n. of the order of 10 e-. The radiation event fre­ .-.- 2 1- - - quency is 1.4 events/minute, cm or a CCOs. - factor of four lower than in RCA S. D'Odorico

4959 A 01 I1 UNE IN t:GC3783 ---, "'r------.... STAFF MOVEMENTS Arrivals gj Europe: >­ f-...... FRANvOIS, Patrick (F), Fellow Cf) MEURS, Evert (NL), Fellow Z W RICHICHI, Andrea (I), Student f- ...... Z'" Chile: BOOTH, Roy (GB), Associate Departures '" Europe: I~------..------r------_r------~393.500 479.000 Laboratory 137.000 22 .500 .000 SCHARRER, Rebekka (0), PIXEL NUMBER Cl PI X=0. 14 A) Technician (Photography) 3783 centred at A5500 A, Figure 2: (a) An echelle spectrum of the Seyfert galaxy NGG The orders in the 10 wer part of obtained with GASPEG and the front illuminated TEK 512 GGo. Galactic absorption lines ofNa I the frame show the broad Hß and the [OIIIJ emission fines. The sky in the fourth order from the are seen close to the corresponding emission from the night events. top. Average of two 1-hour exposures cleaned of the radiation of the eche//e spectrum of (b) The profile of the A 4959 Aemission line of[0111] from one order New Statt Association The resolution is X coordinates are the GGO pixels, corresponding to 0.14 A. 0.25A.the galaxy. Committee in Garehing Elections for the renewal of the Staff Association Committee were held in Garch­ ence in the contral programme of the The new system operated without in January. As a result Fons Maaswinkel, Notable advantages with ing instruments. problems from the first night of installa­ Lothar Noethe and Gianni Raffi were elected. system come respect to the previous tion. When used with the ESO CCO #3 Many thanks to Anton van Oijsseldonk and components from the use of electranic on CASPEC, it resulted in an improve­ Claus Madsen, who terminated their duty, as the on-chip newly of improved quality, such ment of the read-out noise of about while L. Noethe is the chairman of the 16-bit con­ Commiltee. amplifiers and high speed 20 % (present value: 35 el, a not neg­ appointed and a sim­ Statt Association Committee verters, shorter read-out time ligible advantage in the observations of The present set-up of diffe­ in La Silla is composed of Gaetano Andreoni, plified pracedure in the faint objects. The implementation of this rent CCO types. John van den Brenk (chairman) and Michel new system has freed a CCO contraI Maugis. 54 MULTIOBJECT SPECTROSCOPY WITH EFOSC: Observation of the Cluster A 370 J. P. DUP/N, B. FORT, Y. MELLlER, J. P. P/CA T, G. SOUCA/L, Observatoire de Tou/ouse, France H. DEKKER, S. o'ODOR/CO, ESO

1. Introduction sponding to 2.1 and 3.6 arcseconds) 2.3.1 Taking direct pictures of the field Since the first experiment with Multi­ allow the choice between two hole ple Object Spectroscopy (MOS - see sizes. It is also possible to punch slits Images of the field are usually taken in The Messenger 41, September 1985) with these widths by punching aseries white light. 1-minute exposures are suf­ made on EFOSC, the announced new of adjacent, partly overlapping holes. ficient to detect all objects suitable for spectroscopy. facility called PUMA 2 has been im­ The relative positioning accuracy of the It is important to note that, depending plemented. This is a smalI, computer­ holes is 10 ~lm, given by stepper motors controlled punching machine with wh ich of the Microcontrole XY tables. The on the grism used and on the desired spectral range, the field image may have the observer (on the site and during his PUMA 2 is linked to the HP 1000 instru­ to be decentred in order to put the own run) can make the aperture masks ment control computer and the file with he or she needs. positions to be punched may be sent spectra of interesting objects in a suit­ The PUMA 2 system was developed directly to the PUMA 2 microprocessor able place of the CCO. As an example, with the B 300 grism, and if the spectral by the Toulouse Observatory from a or temporarily stored on disk or range 4500-6500 is desired, the ob­ prototype PUMA first used at CFHT in cassette. Ä Hawaii (Fort et al. 1986). PUMA 2 was jects must be chosen between the lines 100 and 300 on the CCO frame (decen­ implemented for the first time on the 2.3 Preparing the masks tring of the field about 30" south). 3.6-m ESO telescope in February 1986 during a technical run in order to check To prepare a mask one needs an the machine operation on-site and to EFOSC image of the field of interest. An 2.3.2 Selecting the objects develop and test the software facilities. inexperienced user should obtain it on a Since then several astronomers have previous night, so he/she can go at ease The selection of the objects is done used the system. Two of us (B. F. and through the interactive object selection interactively on an image of the field at G. S.) took part in a run in November process and the preparation of the mask the 2-0 display in the 3.6-m control 1986 to measure velocities in clusters of the day before the observing night. This room. The batch programme used for galaxies. We believe it would be inter­ implies the use of MOS on the second this purpose runs within the IHAP data esting for future users to comment on night of an observing run, except when reduction system and requires pointing the way MOS has been used, and to the preceding observer agrees to take with the cursors at the targets and at the present the performance wh ich can be the short exposures which are required. positions of free sky to be used for achieved with EFOSC. This paper In our case Or. A. Pickles kindly agreed comparison. Mistakes in the entering of should be considered as a run report to take an image of A 370 during his run, the cursor positions can be corrected and will give first results from the data thus allowing us to make the spectro­ and the programme gives a warning if reduction made in Toulouse on the ob­ graphic observations during our first the spectra overlap. The procedure servations of galaxies in the cluster night. It was a real chance as it turned takes less than half an hour if the Abell 370, using partially automated out to be the best night of the whole run. number of objects is less than about 10. software. Results of MOS observations are also presented by O'Odorico and Oekker (1986).

2. Equipment and Procedures 2.1 EFOSC For a detailed description of EFOSC we refer to the ESO Operating Manual. The detector in use during the November run was the ESO CCO #8, f which is a high resolution (15 ~lm pixel) RCA CCO that we used in 2 x 2 binned mode. The quantum efficiency is about 80 % and the read-out noise 35 elec­ trons rms.

2.2 PUMA 2 The PUMA 2 system is a micropro­ cessor-controlled machine with which holes and slits can be punched in thin (0.15 mm thick) copper sheets called Figure 1: GGO frame obtained with MOS using the B 300 grism. The mask has 5 slits and 11 masks or starplates. Two different holes and contains 12 object spectra. Note the number ofradiation events in this 1h 3D-minute punch heads (0.3 and 0.5 mm corre- exposure. 55 For survey-type observing pro­ 2.3.5 Taking the spectra forgotten. Also, when using this method, grammes which require an optimization data and related calibrations are stored The procedure is described in the of the distribution of objects and sky consecutively on the same tape, reduc­ EFOSC Operating Manual and fram the apertures to optimally fill the CCO, a ing the chance of errors during data experience we obtained during our run semi-automatic programme like the one reduction. we would like only to mention some used by the Toulouse group at the CFHT As the exposure times are long, we precautions to be taken to secure accu­ (Fort et al. 1986) is more effective. The always chose to work at hour angles rate results after reduction. objects are automatically detected in smaller than 1.5 hour and zenith dis­ The so-called blue halogen lamp cov­ the field image, using for example tance less than 30° in order to minimize ers very weil the range criteria like magnitude, colour or size. 3500-7500 A the effects of atmospheric refraction. and is normally used for flat-fielding. The batch procedure then optimizes the Figure 1 is an example of a CCO It is necessary to take calibration lamp selection, given boundary conditions frame obtained in MOS with a mask like length of the spectrum, minimum spectra thraugh each mask as the dis­ punched with both slits and holes. separation between the objects, need of persion is not exactly linear and sky reference. ESO is investigating the changes with the position in the field, 3. An Example of MOS Observa­ possibility to implement such a proce­ along the columns. tions: Galaxies in the Cluster dure as weil but intertacing an existing It is useful to keep a short direct im­ A370 Fortran programme into IHAP is not age of the mask (with the halogen lamp straightforward. or the dome lighting) for future auto­ 3.1 The astrophysical programme mated reduction. It gives also informa­ tion about the transmission of the diffe­ Very little is known about the dynamic 2.3.3 Punching the masks rent apertures. evolution of clusters of galaxies and the evolution of the galaxies in clusters. This is a very efficient pracedure as 6 All of these calibration exposures can Multi-object spectroscopy is an ideal masks with a given hole size can be be taken during daytime. However, we preferred to take them directly before or tool to investigate these problems. For prepared at a time. The size of the holes example, the normal evolution models or slits can be chosen at this step. Holes after the science exposure since almost for galaxies (Bruzual 1981, Guiderdoni and slits can be easily mixed on the no telescope time is lost and one makes 1986) do not explain the excess of blue same mask by punching the same mask sure that no important calibrations are twice before dismounting it fram the PUMA 2 table. The hole shapes and sizes are very accurate, better than 10 Ilm. Repeating the punching on the same starplate may remove the burrs that sometimes remain and then give holes a slightly irregular shape. The machine usually runs quite smoothly except for an occasional punch break. Replacing the punch takes a few minutes and is taken care of by the ESO maintenance staff.

2.3.4 Mounting and aligning the masks The masks are put in place on EFOSC by the night assistant or by the as­ tronomer after a short instruction. This operation is easy and the masks are maintained in a very accurate and re­ petitive position. The observer is assisted in the align­ ment of the mask on the field by using an IHAP batch pracedure that compares an image of the mounted mask (illumi­ nated with a calibration lamp) with an image of the field. Provided the guide probe and telescope coordinates have been carefully noted when taking the direct picture, it takes at most two itera­ tions and about 10 minutes to align the mask on the field with an accuracy as good as 0.25 arcsec rms. The operation of the instrument rotator has been improved a few months ago. It now sets to an accuracy of O'? 1. This is sufficient for accurate alignment and makes the rotation of the EFOSC wheel (which is more complex since it also involves a translation of the mask) Figure 2: Image of A 370 cluster of galaxies taken with a B filter on EFOSC (20-minute unnecessary. exposure). The elongation of the images is due to the reproduction process from the TV screen. 56 Table 1: Spectra obtained during the observing run at the 3.6-m with EFOSC in MOS mode objects found in clusters with 2 ~ 0.2 (1-4 November 1986) (Butcher-Oemler effect, hereafter re­ ferred to as B. 0.). This effect raises a lot Cluster Number of apertures Number of objects exposure time of questions on the physical processes involved, the time scales, the initial con­ A 2444 28 holes 140bjects 1h ditions and their role in evolution. It is clear that it is necessary to accumulate A 551 40 mn 26 holes 130bjects spectrographic observations on clusters + 45 mn of varying richness, shape and redshift. For the ESO run, we chose A 370, a A 370 25 holes 130bjects 1h 30 mn + 1h 30 mn very rich cluster at z = 0.374 (Fig. 2), as the first priority target. Some preliminary 11 holes + 5 slits 120bjects 1h 30 mn low dispersion observations at CFHT 16 holes + 4 slits 130bjects 1h 30 mn (Mellier et al., 1987) have shown a very 21 holes + 3 slits 14 objects 1h 30 mn unexpected high content of spirals which had to be confirmed at higher resolution. F,LD 3.2 Observational results Of the 3 nights given for our run only 2 nights were useable for the MOS mode because of bad weather conditions. 79 spectra were obtained with a mean of 13 per mask. Two other clusters were 2 studied besides A 370 and the observa­ tions are summarized in Table 1. No problems arose during the obser­ vations but we feel that if it is to be efficiently exploited, this type of obser­

G vation demands two observers, espe­ cially if most of the programme is de­ voted to MOS spectroscopy and they are not familiar with MOS or EFOSC.

3.3 Data reduction 2=0.379 All the spectra were reduced in 6 full weeks, using the software developed in 500 600 NM Toulouse for the PUMA 1 system on the Figure 3: Spectrum of the brightest galaxy of the cluster A 370 (No. 20, cO type) with a redshift CFHT (see Soucail et al., 1987 for a full of z = 0.379. description). Changes needed for the ESO images were minimal and no par­ ticular problem arose in the reduction F.LD ~ 0111 process. The only remark concerns a rather large number of radiation events '"

4. The Results 4. 1 Performance Oespite the poor weather conditions, the limiting magnitudes are quite good: NM 500 600 in one hour's exposure, with the B 300 Figure 4: Spectrum of a blue galaxy of the cluster identified as an irregular type (No. 41, Z = grism, we obtained spectra of B = 22, 0.379). Note the emission lines typical of H 11 regions and the strang Balmer absorption lines. V = 21.2, R = 20.7 galaxies at a signal- 57 galaxies (50 % as compared with 5 % in F.LD Goma) at a time 2/3 Ho-I. Both more observations and theoreti­ cal investigations have to be made to explain why at about the same redshift, clusters showing about the same overall properties seem to have so different galaxy contents. Gould the pressure 2 effect of the dense intergalactic gas in the centre of rich clusters be a possible answer?

5. Conclusion and Future De­ velopments As a conclusion we shall say that now the MOS mode on EFOSG in its present status is certainly one of the most effi­ cient systems used on 4-metre class telescopes. It is clear from our experi­ ence that the performance in terms of z: 0.548 limiting magnitude is quite good. 600 NM Further improvements could be made soon in the object selection procedure Figure 5: Spectrum ofa background galaxy found in the field of the cluster (No. 14, Z = 0.548). by allowing a mixed (manual and auto­ matic) procedure for selecting the targets. With a more flexible and user­ friendly procedure, the possibility of to-noise ratio on the continuum of 10. active nuclei are present. By comparing mask preparation and observation in the These performances are about 0.7 mag­ these observational results with star same night could be implemented. nitude fainter than the ones obtained at population synthesis models with the An important question is the choice GFHT with a focal reducer that has not same resolution (Guiderdoni and Roc­ between holes and slits. The trade-off is been specially designed for this kind of ca-Volmerange, 1987) one obtains a the number of objects per mask com­ experiment. It is possible to go even good galaxy type distribution. The result pared to the sky subtraction accuracy fainter by co-adding several exposures is an unexpectedly high rate of spiral wh ich depends on the crowdedness of wh ich has the additional advantage of better removal of radiation events. Ex­ ampies of spectra of galaxies in the field of A 370 are given in Figures 3 to 5. • 2-~ • 4 ....-3 \• 4.2 Astrophysical results .. o From a run at GFHT in 1985 and the last run at ESO, we have 90 spectra in the field of A 370, wh ich represents an o unusually large number for such a red­ 67 75b shift (z = 0.374, see Fig.6). About 55 0 T «> spectra are from cluster members and .--~ they give a velocity dispersion of 1300 ~~ ~ (+ 230, - 150) km/sec and a M/L ratio of ~ 130 (with the virial approximation), very o. 0 53 similar to those measured on closer 24 25-" / clusters. A complete study of A 370 will ..

be given in a forthcoming paper (Mellier o 0 .. 36 et al. , 1987) but we summarize here the 57- most significant results. ll-O A 370 is a very rich cluster (richness • ....-38 similar to Goma), X-ray emitting, and 60 \lo-~ • 0...- shows a large population of blue B.O. o 81 ...... • 59-~ objects. The proportion of 21 % given .4.0--.. by the photometry (Butcher and Oemler, .

1983) has been reduced to about 11 % 90 ...... from our spectrographic measurements, because of a better evaluation of the 46 '0 contamination by foreground objects but the B.O. effect is now weil confirmed by the spectroscopic measurements. Figure 6: Field of the A 370 cluster with the identification of all the objects from which a The B.O. objects are more precisely spectrum has been obtained at ESO or at CFHT with the PUMA system. The underlined spirals or Magellanic galaxies but no numbers correspond to objects of which the spectra were obtained at ESO in November 1986. 58 the punching of precise rectangular zation of the Use of CCO Oetectors in As an example, slits do not seem very slits. Astronomy, J. P. Baluteau and S. weil fitted for programmes where a lot of On the data reduction side, further O'Odorico eds., published by ESO, 315. spectra in a rather crowded field are work is necessary to develop optimized Fort, B., Mellier, Y., Picat, J. P., Rio, Y. and needed. The advantage of slits is cer­ software in order to cope with the large Lelievre, G., 1986, Proc. SPIE Instrumenta­ tion in Astronomy VI, Vol. 627, 321. tainly a better sky subtraction in the amount of data generated by this pow­ Guiderdoni, B., 1986, PhO Thesis. case of very faint objects. In the case of erful observing technique. Guiderdoni, B., and Rocca-Volmerange, B., bad seeing, slits are also more efficienl. 1987, in preparation. More accurate extraction algoriths such Hornes, K., 1986, Publ. Astr. Soc. Pac., 98, as e.g. the one proposed by Hornes Referenees 609. (1986) could also be used on slit spec­ Bruzual, A. G., 1981, PhO Thesis. Mellier, Y., Fort, B., Mathez, G., and Soucail, tra. These might yield a considerable Butcher, H., Oemler, A. and Wells, O. C., G., 1987, in preparation. improvement in the S/N ratios and in the 1983, Ap. J. Suppl. 52, 183. Soucail, G., Mellier, Y., Fort, B., Picat, J. P. O'Odorico, S., Oekker, H., 1986, Proceedings and Cailloux, M., 1987, submitted to As­ limiting magnitudes. An efficient future of the ESO-OHP Workshop on the Optimi- tron. Astrophys. EFOSC/MOS facility should allow both round holed and rectangular slits to be used in a flexible way, depending on the NOTE ADDED IN PROOF al ready identified in a poster paper which astrophysical projecl. It should be pos­ was presented at lAU Symposium No. 124 sible to interactively adapt the aperture In arecent note in NATURE (Vol. 325, in Peking in August 1986. A further discus­ 572), B. Paczynski discusses tl1e "disco­ sion may be found in arecent paper by sizes to the prevailing seeing. very" of a giant luminous arc in the core of Soucail et al. (Astronomy & Astrophysics, Work is now being carried out at ESO the cluster A370, as announced in January 172, L14; January 1987). More observations and Toulouse Observatory to investi­ 1987 at the 169111 Meeting of the AAS. It of this interesting structure were obtained in gate other mechanisms for the making should be pointed out that this object was October 1986 with EFOSC. of the mask, such as laser cutting and

Nuevos meteoritos encontrados en Imilac H. PEOERSEN, ESD, and F. GARe/A, elo ESD (Traducido dei ingles por C. EULER, ESO)

Oesde tiempos prehistoricos han sido co­ ticas dei mundo, como el lade occidental de el pasado se han coleccionado meteoritos. leccionadas piedras que caen dei cielo. Has­ Australia, las estepas de Norteamerica, y el Aun la parte superior dei suelo contiene mu­ ta hace poco eran la unica fuente para hacer Oesierto de Atacama en Chile. En este ultimo chos pequeiios fragmentos de hierro que estudios de laboratorio de la materia extraga­ las precipitaciones anuales son menores que pesan tipicamente I gramo. I,ktica, e incluso en nuestra era espacial, en cualquier otra parte dei mundo, menos de Los meteoritos de Imilac han lIegado a siguen siendo una valiosa fuente de investi­ 5 mm, 10 que obviamente ayuda a la preser­ muchos museos y colecciones particulares gacion de la temprana historia dei sistema vacion de los meteoritos. Como resultado, en tode el mundo. EI ejemplar mas grande solar. uno de los meteoritos atacameiios, encon­ conocido, de 198 kg, se encuentra en el Mu­ Se estima que como termine medio cada trado en el Tamarugal, tiene una edad terres­ sec Britanico. Otro fragmento, originalmente kilometro cuadrado de la superficie terrestre tre de 2.700.000 aiios, conocida como la de 95 kg, esta en Copiapo. EI monto total dei es golpeada cada millon de aiios por un mas antigua. material encontrado, plausiblemente de ori­ meteorito con un pese superior a 500 gra­ Mucl10S meteoritos chilenos pertenecen al gen de Imilac, se calcula en 500 kg. mos. La mayoria se pierden en los oceanos 0 tipo "Pallasito'" y provienen muy probable­ caen en regiones con escasa poblacion. Co­ mente de una sola ca/da. L1evan el nombre Los principales hallazgos mo resultado, los museos en el munda reci­ de las localidades esparcidas geogratica­ ben anualmente tan solo alrededor de 6 me­ mente en un area de 100 por 100 km. En muy Oespues de varias expediciones se penso t€oritos cuya caida fuera atestiguada. Otros pocos casos, sin embargo, se pudo indicar que todos los grandes meteoritos hab/an si­ Ilegan por hallazgos casuales que en la con precision el lugar dei hallazgo y hasta do coleccionados. Sin embargo, podemos mayoria de los casos son meteoritos que han muy reciente se creyo que los meteoritos informar sobre el reciente descubrimiento de cardo en tiempos prehistoricos. hab/an sido encontrados dentro de un area tres meteoritos mas, totalizando 59 kg. EI Oesde el punto de vista mineralogico pue­ de 100 por 500 m cerca dei pequeiio Salar de hallazgo fue hecho por uno de los autores den ser divididos en tres clases: piedras, Imilac, que se encuentra aproximadamente a (F.G.), geologo. (Nota dei editor: F.G. es el hierros y hierros petreos. Los meteoritos que 170 km de Antofagasta. En este lugar existe esposo de una de las secretarias de la ESO caen son en su gran parte petreos, mientras una excavacion similar a un crater con un en Santiago, Mariam G., a traves de quien los que aquellos que se encuentran tienen un diametro de 8 metros. Este puede haber sido cientificos de La Silla fueron informados dei alto porcentaje de hierro. Esto se debe a que cavado por indios en busca de la imaginada descubrimiento). Mientras buscaba agua pa­ los meteoritos petreos tienen una erosion veta de hierro. Varias excavaciones en coli­ ra una empresa minera supo de la ca/da en mas rapida y son menos visibles. Geografica­ nas adyacentes muestran lugares donde en Imilac. Un poblador de la zona le informo de mente las ca/das de meteoritos estan muy que algunos meteoritos hab/an sido encon­ relacionadas con la densidad de la pobla­ trados algunos kilometros al sur-oeste dei . Los meleoritos se pueden dividir en lres c1ases: cion, la mayor parte descubiertos en Europa "crater". Oedicandose a la busqueda pudo piedras. hierros y hierros petreos. Un sub-grupo de y Norteamerica. esle ultimo es bastante espeeial: una mezcla de encontrar otros tres con un peso de 5, 19 Y La mayoria de los meteoritos se encuen­ hierro y niquel forma una eslructura de tipo espon­ 35 kg, respectivamente. tran por casualidad. La busqueda activa en joso. Crislales olivinos, con un diametro de 1 a La Universidad dei Norte en Antofagasta general requiere demasiado tiempo para ser 10 mm rellenan los orilieios. 10 que da una relaei6n examino los fragmentos de 5 y 35 kg Y los de interes. Sin embargo, los glaciar s de la de volum n melal/olivina de aproximadamente clasifico como "Pallasitos". Por razones de Antartica han demostrado ser un "buen terre­ 1 : 1. EI primer meteorilo de esta Indole fue eneon­ pese especifico creemos que tambien el hie­ no de caza". trado en 1771/72 por el explorador aleman Peter rro de 19 kg pertenece a ese grupo. Ya que Simon Pallas en sus viajes a traves de Rusia orien­ en tode el mundo se han descrito tan solo 33 Meteoritos de Imilac tal. M loritos dei tipo "Pallasito" son muy eseasos: tan solo menos que un poreiento de todas las hallazgos "Pallasitos" (y dos caidos), es un Otras areas donde se han hecho muchos eaidas y 3.5 poreienlos de todes los hallazgos fuerte indicio que los nuevos ejemplares son hallazgos son algunas de las regiones deser- perteneeen a esle grupo. parte de la conocida caida de Imilac. 59 Tambien se visito el lugar de la vieja exca­ investigarse POl' el calculo orbital de la caida vacion tipo "crater". En el "area de las asti­ de meteoritos. Esto se ha efectuado en tres lias" se coleccionaron aproximadamente oportunidades, pero ninguno de los meteori­ 1 kg de fragmentos menores (0.1 hasta apro­ tos en cuestion eran "Pallasitos". Sin embar­ ximadamente 250 gramos). Aigunas particu­ go, observaciones terrestres podrian ayudar las fueron encontradas hasta 1000 m al nore­ aresolver la pregunta. Con ayuda de la ste dei "crater". Estimamos que en este area espectrografia infrarroja se descubrieron tres aun se encuentran aproximadamente candidatos de origen asteroide: 246 Aspori­ 1000 kg de hierro meteorico. na, 289 Nenetta, 446 Aeternitas. Su espectro La existencia dei "area de las astillas" indi­ muestra una banda de absorbcion en 1.06 ca que un gran trozo dei meteorito sufrio una ~lm, como es el caso con olivina en su forma quebradura violenta. Esto tiene que haber meteorica. Tambien la tendencia general dei sucedido en un punto tardio durante la espectro concuerda con la presencia de una trayectoria a traves de la atmosfera. fase metalica. Meteoritos "Pallasitos" forman un grupo Es extrano que un asteroide pueda seI' bastante homogeneo, claramente distinto de asociado con un ti po particular de mineral. otros tipos de hierros petreos, los "mesosi­ En general, estudios detaIIados de asteroides derites". Podrian dar indicios sobre el origen y cometas necesitaran de naves espaciales de la consistencia dei sistema solar. POl' eso para que colecten muestras. En efecto, se su creacion es muy discutida entre los versa­ estan considerando. Pero quizas seria super­ dos en cosmogonia. Una teoria dice que se fluo incluir Asaporina, Nenetta 0 Aeternitas formaron en asteroides. en el itinerario: el material podria ya encon­ EI origen asteroide podria, en principio, trarse en nuestras manos ...

Contents H. Pedersen and F. Garcia: New Meteorite Finds atlmilac . Tentative Time-table of Council Sessions and Committee Meetings for First Half of 1987...... 3 J. Melnick: Giant HII Regions and the Quest for the Hubble Constant 4 Visiting Astronomers (ApriI1-0ctober 1,1987) ...... 7 Italian Delegation Visits ESO ...... 9 List of ESO Preprints (December 1986-February 1987) ...... 9 First Announcement of an ESO/NOAO Conference on "High-Resolution Imaging by Interferometry" ...... 9 B. Wolf, C. Sterken, O. Stahl and J. Manfroid: Long-term Photometric Campaign at ESO and the New Eclipsing P Cygni Star R 81 in the LMC ...... 10 J. Sommer-Larsen and P. R. Christensen: Blue Horizontal Branch Field Stars in the Outer Galactic Halo ...... 13 And then there were Three ...... 14 R. Kroll: Where Peculiars Turn Normal-Infrared Observations of CP Stars...... 15 ESO Press Releases ...... 17 P. Magain: BD +03°740: a New Extreme Metal-poor Dwarf ...... 18 H. Barwig. and R. Schoembs: BD Pavonis, a New Double Lined Eclipsing Cataclys- mlc Blnary 19 Announcement of a Summer School on "Observing with Large Telescopes" 23 F. Murtagh, A. Heck and V. Di Gesu: Strengthening Research Links Between AstronomylAstrophysics and Computing/Statistics 23 Announcement of a ST-ECF Conference on "Astronomy from Large Databases: Scientific Objectives and Methodological Approaches" 24 K. J. Mighell: Crowded Field Photometry Using EFOSC and ROMAFOT ...... 24 Storm Petersen and Astronomy ...... 25 The Supernova in the LMC ...... 26 U. Heber and K. Hunger: CASPEC Observations of sdO Stars: Are Some sdOs Lazy Remnants from the AGB? 36 A. Dollfus and J.-L. Suchail: P/Halley: Characterization of the Coma Dust by Polarimetry 39 Messenger Index 41 A. Mazure, D. Proust, L. Sodre. H. Capelato and G. Lund: Multiple Object Redshift Determinations in Clusters of Galaxies Using OPTOPUS 41 F. Paresce and C. Burrows: Coronography at La Silla: High Resolution Imaging of Faint Features Near Bright Objects 43 L. Hansen, H. U. Nergaard-Nielsen and H. E. Jergensen: Search for Supernovae in Distant Clusters of Galaxies ...... 46 NEWS ON ESO INSTRUMENTATION: S. D'Odorico and S. Deiries: On the Rates of Radiation Events in ESO CCDs 49 M. Tarenghi: New Technology Telescope Taking Shape 50 G. Raffi: ND Control/Acquisition Software 51 ESO Image Processing Group: MIDAS Memo 53 S. D'Odorico: New CCD Control Camera and First Test of a TEK 512 CCD at La Silla 53 Staff Movements 54 New Staff Association Committee in Garching ...... 54 J. P. Dupin, B. Fort. Y. Mellier, J. P. Picat, G. Soucail, H. Dekker and S. D'Odorico: Multiple Spectroscopy with EFOSC: Observation of the Cluster A370 55 Spanish Summary (Nuevos meteoritos encontrados en Imilac ...... 59 60