I the Messenger I

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I THE MESSENGER I

No. 69 - September 1992

NTT Remote Observing from ltaly A. BALESTRA, P. SA NTIN, G. SEDMAK, Astronomical Observatory of Trieste, ltaly M. COMIN, G. RAFFI, A. WALUNDER, ESO

1. Introduction The main goals of the collaboration chltectun for the RO computer net- Remote obsenring (RO) from ESO- were: wok and communication system. Garching is by now a well-establishd The study. design and irnplementa- me implementation of a "second" seaice provided far the user community tian of a portable kit, including fiard- generation of RO software, based on by Em. So far it has been concerned ware and sohare for mote obser- UnIx and workstations hardware. An with instrummb located either at the vations with the ESO NlT from a important part of thls was the exten- CAT or at the 2.2-m telescope at IA European astronomical institute. sion of the real-time database of the Silla, operated from Garching shce The definition of the hardware ar- to a geognphidly dlstritwtd 1987. The advantages of this obming mode include reduced travel times, the possibility to accommodate shorter and regular long-term monitoring observing programmes, the possibility for students to participate in the observation and the facilities (people, Ilbrary and computers) normafly available in a European astronomical institute 11 ]. In order to create a new remote obsenring environment for the EMMl and SUSl instruments on the N7T telescope, a collaboratron with the Astronomical Obsewatory of TriHe, Italy, was started In 1989. The Tdeste Observatory has a kq experience In ha field of Unix- based workstations and on distributed mvironments. The project was based on the philosophy of a multi-telescope, multi- instrument system addressed by many usem in parallel in e ftexlbla scheduling environment compatible with the auto- mattc execution of complex observing Figure I ;ASWIMIWS and w'sitws in the Trleste remote obsmtngmm - dngduring s Iang pqrammes. NTT exppsum. La SIlIa Observatory ESO IIeadquartars Astmnodd Institutes image system is uslng only one fifth of Chile &mote Control Centw Ilmnote OklngSitos I..# the available bandwidth. Thirdly, a data Germany Eumpn channel connects the local amnet- works of ESO-Garching and La Silta via routers. A dedicated local area network (LAN) has been created at €SO-Gmh- Voice ing for remote ohwing. This network uses a =patate Interface on the rovter, while all other nodes connected to the general IAN use another interface. Any '\ disturbances on the general IAN are ?sf thereby isalated from the remote observing nem. A dedicated room at €SO-Qmhing MTT local has been allocated as the NIT remote control control room. It houses the remote con- systom trol station and care has been taken to create an ergonomic kstallatian. The w mote controt computer is a Unix workstation supported by two additional X terminals. Normally one of these X sta- LEVEL 0 LEVEL 1 LEVEL 2 tions is allocabd to telescope control, one to instrument control and one to Flgum 2: Block &gram of communbtion system, quiok look adimage pmcedng using MIDAS. A large videa monitor displaying video images is installed above the 3( terminals. At both ends of the cantrol telescope/instrument pafameten' pilot project for the VLT. In particular station 1s a PC, which the user normally database @?oat). new computer technologies, maw does not interact wlth very often. One is I The availability of the same software (user interface, on-line databases) and for video control and the other for re- and features for remote obsenring operational procedures should be aeiving meteo data from the GOES both at the first level site (ESO- tested, which are of Impattame for the satellib. Lastly a movable voice unit Garching) and at a second level slte VLT oontml system In general and not cwrtainFng a microphone and a toud- (user's Institute). only for remote observations. speaker implements access to the voice While the compl&e development af ll is foreseen to repeat the second system. the project tok three years, the first level remota amwing run from other The Nlllocal controt system ts bawd milestcne was reached with tb de- institutes in Europe, poTtlng to them the on two main computers runnlng the vdopmmt and test of the remote ob- set-up, which has been produced as a RTE-A operating system. In addian a sewing system of first level in Garching result: of the ESO-AOT collaborafion and UnIx wwkstatIon Is used for scientific This sptern Is now in the final test leasing jointly a link to Garching. data acquisition. The main characteris- phase and tbe *ration team Is being tics of the software architeaurn are a Wnd. R is foreseen to offer routine decoupllng of the conk11tasks from the rerrrote observing from ESO-Garehlng 2. System Archibetwe user inkface by means of a database on the MT with EMMWSI Wing in a The 2.1 #at Level Remote Observing and command handler. database April 1993. and command handler, togather with Meanwhile, the retevant hardware had ESO-Garchlng Is permanently Ilnked the TCPAP protocol suit, provldes the ben procured and several tesis took to La Silla via a 64 kbps leased satelllre software bridge between the 1-1 and placa, whi b arrangements were made link 121. During remote observing #he remote sites. for the installation of the 64 kbps Pnk bandwidth is subdivided, using time dl- The remote control software architec- from Garching to TrlesW. vislon multiplexing, Into three parallel ture b discussed in ddlIn (31 and only The final mllestbne was reached when channels. A voice channel Implements a s brief overvW is given here. The dad- the second level remote obselvlng run point-to-point voice link between the buted database (Xpool), implemented took place, from the 9th to the 1lth of night assistant at the Mland the re- according b the dmsenrer model and June 1992, at the Astronomical Obaer- mote obsenrer at ESO-Gmhing. A vid- using TCP sockets, allows remote read vatory of Trieste, Italy, during three eo image channel atlows the remote ob- and wrlte access. R is responsible for nights dlocated for remote observatlm sewer to select one vldeo source (e.g. prwiding &us Information t~ the re- with the WIT telescope. The present field acqubition, dlt viewer) for transfer mote control computer mand to allow de- article repork on the resub of this run, in slow-scan-television made. Dm to finil5on of set-up parameters from the which proved Mat the chamn concept the fad that video Images obtalnd by remote control computer. The com- and implemmtatIon were not lust work- the acquWtion camwas are normally mand handler, Implemented In a slm tlar ing but already quite reliable at the pres- very slmple, conststing of only a few way, is ~ponslblefor routing com- ent stag& The systwn was in fact USA sou^ on a black background, the mands, repties and asynchronous for about 30 hours for d mronomical compression algorithm works very well. status and alm messages between obmatlons by a team of eight as- Using a bandwidth of 12 kbps the nor- processes residing on different hosts. tronomers. mal frame repetltlon rate Is one frame These two mechanisms allow a fully In- The aim of this project was not slmply every 3 seconds. This makes R pmlble teractive mote control, providing the to build a remote obmnring environment to use the video imwsystem as fed- remote user with the same functionality for the MT, but right from the beginning back for interactive control, 0.g. offset- available locally at La Silla. It was conceived by Em to serve as a ting the telescope, even when the video Scintlfic data handling makes use- of Teritative Timetabla of CouncB SeWans and &mmWe Mdngs

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implemented. In the perspective of multiple second levels. a dlstribution board for serlal lines has to be for-n. The link connecting first and second levet sites should have a bandwidth of at least 84 bps in order to completely manage all three channels. In a multiple- site configuration, while the first to second level lines wilt maintain this bandwidth, the main link between the zero Figure 8: The €SO-Garching remofe mnfrdt m. level and the first one will obviously need a higher bandwidth, i.e. at least Nx64 kbps where N is the number of secondary sites observing at the same standard network facilities, remote shell, are fo-n in the overall configuration time. ftp and the X protocol to transfer andlor in order to allow flexible scheduling. The A 64 kbpa digital ground-based link display scientific data. It takes about possibility of managlng remote observa- was leased jointly by ESO and OAT for one rnlnute to display an image, fnde- Uons from mare secondary levels on this test for the duration of one month. pendent of detector slre, in a standard more telescopes is therefore a natural Such a connection pmwd to be a novel- MIDAS dlsplay window using the X pro- extension of the system. ty for the German and the Italian PTT tocol. Actual transfer of the raw data Sirroe the data channel connects companies. Soma days at the beginning takes between 3 and 7 minutes for a computers already operating, in most of the connection period were lost ow- lkxlk frame, depending on a user cases on networks, two bridges allow ing to tests on both sides. This kind of setectabb cornpmion algorithm. an easy way to connect the LAN of the problem will hopefully disappear with The User Intedace 161 based on the first level with the LAN of the second the inemlng integration of the Em- Pegasus package developed at CFHT, one. A single Remote Control IAN, pean Community. lnterfaoes to these other packages. It comprehensive of all the three levels, is The control room at the secondary runs on top of OSWMotif and uses stan- thus obtained allowing an easier use of level site is a duplicate of the main con- dard widgets for data presentation and computing facilities. Future extension of trol room at €SO-Garchlng in line with user Interactions. It is completely this channel to multiple second levels is the resources of the institute. As a gen- mnfigurabb in the sense that everything mlg Mfwward. eral rule, one workstation, two X-terrni- that appears on the scrmn and associ- Voice and vldm channet, even tf de- nals and two PCs are required: if the ated control adons are described in voted to different uses, can be treated in need arises, a disk sewer for Image simple ASCll files. the same way, dnee the original signals storage could be used even if it is not they have to manage are intrinsically essential. Specific quipment for volce and vldeo channels (i.e. telephone s&, 22 Second Level Remote Obsewing analogous, This fact, on the other hand, added a faw mow problems to the monitor . ..) is also requir6d. The second levd hardware and soft- channel management. The electrical The extension of the software for sec- ware configuration has been developed and communicat~onprotocols of the se- ond Iwel remote obsewing involved the wlth the aim of implementing a system rial lines (these channels are generally implementation of a hierarchical struc- able to manage remote observations on implemented according to X.21 or V.24 ture. Each node must be defined as a multi-telescope, multi-instrument sys- standards) define a point-to-point link primary or secondary according to its tem from European astronomical in- instead of a distributed environment. levet. Ihe secondary node sends its re- stitutes, and allowing the maln control Therefore, In the simplest configuration, quests (direct access or updating list) to centre of ESO-GareRIng the full control voice and vldeo channels directly con- the primary one. It is up to the primary of the remote operations 141. The basic nect zero level with the second level node to route the request to the final three-channel hardware configuration is observing site. However, a direct con- target, 1.e. the Instrument cw the tele- also maintained for second level remote nection between the zero and first levd scope control computer. Thus, no direct obsming. Full compatibility with the is required to allow communications be- access to zero levd database is allowed Rrst level and userfriendliness are, of tween night assistants and the ESO- from the secondary levd. Even If this course, prwided. Since more than one Garching control centre, In order to mechanism may Induce some time de instrument could be active in the general maintaln a simple hardware configura- lay in response, the resulting filter action architecture, multiple secondary levek tion, a software solution (SUN talk) was obtained is very important for the eon- trol and monitoring actions of the ESO- 3. The Final Test HP-425 as control computer and as dis- Garching centre. play for instrument UIF. Another work- During remote observations, at1 the The final test was carried out on the station HP-375 was configured as X- operations carded out by the second nights of 9, 10 and II of June [5].The terminal for telescope UIF display. A level site can be monitored by an Ilnk created no specific problem, once second HP-425 was used to nm a re- operator in the ESO-Garching control Genan Bundespost and Italian SIP had mote MIDAS session on the SUM con- room. Every updating action, from sec- solved theirs. The connection between trol workstation at La Silla. A Sylicon ondary to zero level and vice versa, Is f rst the OAT LAN and the ESO IAN,with the Graphics Indigo workstation was In- performed by the primary levet on its creation of the extended remote &sew- serted In the network to use its dlsk database. A monitoring process on the ing LAN, was straightforward. space, through NFS, for image storage. primary level contml computer is thus A telephone set was used as data One NCD X-terminal was used to run able to check secondary level operations channel terminal equipment. The only two 'Talk" sessions with the €SO- and, If necessary, also to filter out in- problem encountered with it was the Garching control room and with La Silla correct operations of the secondary "Donald Duck effect" on the voice due through remote togins on two SUN in node. The primary node can obviously to the compression ratio of this channel. Garching and at La Silla. These last perform its own operations toward zero Some problems arose with the video communication sessions were used in level site, thus obtaining a complete con- channel due to the late and incorrect order to have a more complete interac- trol of the remote observing session. ddivety of some boards on the part of tion with the ESO-Garching control All the software configuration is driven the manufacturer. This channel started room and the La Sllla night assistant due by few configuration files and environ- to work mnthuously as from the sec- to the test nature of the nights. Two PCs ment variables, allowing the possibility ond night. were also used for the monitoring of the of easily switching between varlous The OAT controI room was configured data channel and for the display of the contexts, i.e. from simulation to realrty. fn the following way. One workstation Meteosat images.

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Figure 4: Example of the Pegasus User Interface for orhe control af the lnsmment (EMMI/SUS/Jand of the mlescope. The software had to be ported from and prwlde the possibility of dedicating J. Ksrr of CFHT supported us in the the remote control camputer in ESO (an part of the LAN to the remote observ- inltial use of the Pegasus user intetfaca. HP-720) to the OAT HP-425. No probing~tasks in addition to the astronomi- G. Andmi and the people from the La lem at dl was encountered during this cal interest in participating in such an Silla operation group gave their support procedure. A porting of Xpool package experiment. The communication equip- during installation and commissioning, on SUN and Sylicon Graphics was also ment could be provided by ESO for the and M. Piuaro acted as the perfect put into effect,for test purposes, In the purpose of a first test. night assistant during the three test months preceding the final test. The joint procurement of the leased nights. On the first night ten hours were de- link to Garching is another condition to The project has been financially voted to preliminary tests and to identify be fulfilled, and further pdiminary day- supported, for the Italian side, by the and fix some software bugs. From 4.00 time tests and remote test nights will be Italian Council for the Astronomical Re- UT astronomical obsmations could be- necessary. search C.R.A. gin and continued until 11.00 UT. The h an independent parallel activity the second night started wM some minutes first level remote obseming system is of delay due to some minor software now getting its final touch. The opera- problemsand lasted till 11.00 UT.The hst tion team Is being trained and user References night was entirely devoted to astronomi- guides are being produced. It ia planned [I]D. Baade, "Three Years' Experience with cal observations. On the whole, more to start offering remote abservlng with Routine Rernote Observlng at the Euro- than thirty hwrs were entirely devoted to EMMVSUSI to the user community In pean Southern Ob~atory",In Pmead- ings of Workshop on Remote Obsmlng, astronomical observations. Eqht OAT April next year. Tucson, USA, April 1m. astronomers used this time to carry out 121 A. Wallander, "New Communication Link various scientific observations. It should 5. Acknowfedgements between Garchlng and h Sllla", in 7he bestressed that whileanobservation was Messenger No. 60, June 1990. going on, the astronomers were able in Many people have participated in the [3J A. WalIander, 'Remote Control of the remote MIDAS sessions to have a quick development of the described system. ESO New Technology Telescope", In Pto- look at the previously acquired images in The ITIT (local) control system was d~+ ceedlngs of Wwkshop on Remote Db- order to evaluate thevalidity of their data. veloped within the Electronics Depart- swing, Tucsan, USA, April 1992. I41 Accordingly, if necessary, the transfer of ment at ESO-Garching. Major contribu- A. BJestra et al., 'Remote OwingAc- tivities at the Waste Astronomical Obser- to the implementation of the re- the images from La SIlla to Trieste could tions vatory: fhe ESOM Second Level Re- then be carried out. mote control system were made by 0. mote Observing and the Galilea Tele Gilli and J, Brynnel. scope Prow, In Proceedings of Work- At Astronomical Obsemtoy of 4. Conclusions the shop on Remote Obaenring, Tucson, Trieste M. Pucillo was one of the de- USA, Apdll992. This project was successful In proving signers of the second level hardware 15l R Bstestra et al., The ESO/OAT Second the feasibility and reliability of second and software architecture and partici- Level Remote Observlng Prom. Final level remote observing already at this pated In the software developornent, Test on ESO/NTT: 9-11 June 1992", No. stage. and C. Vuerli implemented most of the Technical Report OAT PubIicetlon 1443, June 1992. software utilities. help of P. Mar- During the three nights of the final test The 161 M. Comln, J. Kerr, "A Protw for the over 30 hours were devoted to as- cuccl and R. Smareglia is also acknow- VLT user Interface", in Proceedings of tronomical obmations and, as can be ledged. C. Carte gave his precious Conference on Progress in Telescope inferred by the users' comments, the support during the set-up of the second and lnstnrmentation Technology, ESO- system proved to be very easy and flex- level observing room. Garehing, April 1982. ible to operate, considering also that mast of the obsems had no experience fn the use crf EMMI. In view of the success of the experiment it has been decided not to stop A Fourth VLT Instrument Science here but to pmdalong two lines: To study and Implement a special Team hardwardsoftware system for on- line data compression technique, in At its May, 1992 meetlng the €SO Scientific and Technical Committee order to reduce the quick-look time approved the two Ultraviolet-Visible Echells Spectrogmphs (UVESI and (at present of the order of minutes) UVES2) for the Nasrnyth foci of the second and third VLT telescopes. The and obtain an almost completely in- ESO staff responsible for buildlng these Instruments is now proceeding wlth teractive environment. the design studies of this major facillty which wilt do high-resolution spectres- To identify other interested institutes copy (resolution-sllt width product - 40,000) in the 300 to 1100 nm in Europe to repeat a second level wavelength range. At the same time an Instrument Sclence Team has been remote observing run from there, in formed for this facility. Its members are: order to test portability and reliability of the present set-up. This can also B. Gustafsson (Uppsala) be useful to test operationally the H. Hensbe~e(Brussels) feasiblii of remote access during P. Moiaro (Trieste) flexibh scheduling, where mow than P. Nissen (Aarhus) one observing team can be active during the same night from different The team wlll select its chairman at its first meeting on December 9. As is institutes. the case for the other VLT instruments (see The Messenger 68, page 8), the The modalities are currently under de- ISf members end myself welcome your Input on scientific matters relating to finition. The candidate institute should these Instruments. J. M. BECKERS,ESO haw a network of Unix workstations, "Remote" Science with the NTT from ltaly PRELIMINARY SCIENTIFIC RESULTS M. FRANCHINI, P. MOMRO, M. NONINO, F. PASIAN, M. RAMELM, G. VLADILO, Osservatorio Astronomico, Trieste, ltaly M. CENTURION, Institute de Astro fisica de Canarias, Tenerife, Spain P. BONIFACIO, Scuola lnternazionale Superbre di Studi A vanzati, Trieste, ltaly

I.Introduction CCD THX 31 156 (ESO #18) with ticular, Sz 68 belongs to a sample of f We report here on the preliminary 1024x1024 square pixels, 19 pm In Tauri stars for which the velocity fields in analysis of the observations carried out size. The instrument is described In the circurnstellar environment are under with the Nntelescope during the final Dekker et at. (1991). This detector has investigation. Sz 68 has shown clear test of the "Second Level Remote Ob- been used for all the observations de- variability of the Nal D line profiles: mul- serving Project" at the Astronomical 0b- scribed in this paper. With a slit of 1.2 tiple blue-shifted absorption compo- sewatory of Trieste (OAT). The test took arcsec, a resolution R-25,000 is ob- nents are present, with variable intensity place during the nights of 9, 10 and tained; this can be verified from well- and position. This might indicate the 1 1 June 1992. Detalls on the "remote separated lines of a thorium comparison existence of a complex circumstellar observing" project can be found in the spectrum. Wavelength calibratlon was structure, varying with time. article by Balestra et al. on page 1 of this performed for each order by a polyno- So, the spectrum in Figure 1 can be issue of the Messenger. mial, fitted to 12 lines at least; the r.m.s. compared -taking Into account the dif- A preliminary constraint to the plan- of the residuals is about 0.5 kms-'. ferent instrumental resolution - with ning of the observations was imposed Figure 1 shows the spectrum of Sz 68 preceding obsarvations, made in I985 by the people responsible for the test, (V=10.5), in the region of the Nal D (Finkenzeller and Basri 1987), in 1989 who required frequent changes be- doublet. With an exposure of 1 hour, a (Franchini et al. 1992 a), and in 1991 tween different Instrumental configura- S/N ratio of about 200 has been (Franchini st al. 1992 b). White the actual tions, In order to better evaluate the achieved. This object is a target of a configuration appears to be rather simi- response of the distributed system to a more general research, concerning the lar to the ones observed in 1991 and heavy load. Furthermore, tune-up and basic observational parameters of T 1985 (with the blue-shifted component communication problems occurred at Tauri stars: projected rotational veloci- at about the same u,d,the same cannot different times of the test nights requir- ties and inclination angles, spectral be said for 1989 (when the main blue- ing elther a reshuffling of the scheduled types, luminosities, effective tempera- shifted component - relative to the star observations or the loss of some cali- tures, element abundances, etc. In par- - was at more than -90 km s-'). Clearly brations and/or astronomical targets. In particular, several exposures which were planned durlng the dark time at the end of one night were postponed to grey time of the following night. We believe however that, during the test nights, an acceptable compromise was reached between the technical requirements of the test Itself and the wish of a full use of the nights for real astronomical work. All the targets pointed were selected within research projects currently ongoing at the OAT. These projects are: T Tauri stars (MF), Lithium abundance (PM), high velocity clouds (GV, MC), Planetary Nebulae (FP, PB), Seyfert galaxies (MN), distant clusters of galaxies (MN, MR), gravitational lenses (MN, MR). The following is a brief description of the research projects and an assess- ment of the quality of the data obtained.

2. The Observations 2.1 Nal D Variability in the T Tauri Star Sz 68 We have performed echelle spectroscopy of a T Tauri Star (Sz 68) with the lambda (angstroms 1 NlTusing the EMMl spectrograph in the Flgure 1 : NormaIized Nal D doublet of T Tauri star Sz 68, Radial docities (in km s-7 of blue- REMD mode: grating #lo, grism #5, shiited absorptions are relative to the interstellar component which Is clearly recognizable in decker 5 arcsec. The detector was a the St9/1# pr0fiI~s. the time intervals between these observations are too wide to allow a complete reconstruction of the evolution of a given absorption component. However, more detailed analysis of the present data, together with those of 1991, may provide a quantitative Interpretation of this variability, In terms of mass ejection events andlor sudden changes in the physical properties of the circumstellar material.

2.2 Lithium In the Halo Dwarfs G $437 and G 275-4 The abundance of tithiurn in the Popu- lation II stars hotter than 5500 K shows a characteristic plateau around log N(Li)=2.150.1 (where log NH=12), in striking contrast with that observed in the younger population where the abundances are scattered over three orders of magnitude. Although this is not fully understood, the mast straightforward explanation remains the absence of any significant lithium depletion In halo dwarfs, and thus the atmospheric abundance reflects the pristine lithium abundance of the interstellar gas from whlch these old stars formed. It appears very probable that the lithium in the old halo dwarfs Is pn'mordlal in origin. ln fact the good agreement between the lithium abundance observed in the halo dwarfs and the theoretical predictions of the big-bang theory is very impressive. According to the theory, the llthium yields are particularly sensitive to nu- cleon density, and the knowledge of the precise amount of primordial lithium allows a determination of the pl value (q=ndnb), which is related to the critical mass G!. The astronomical relevance of Figure 2: 7he UI Wdregion for Q 6.4-37 (top pand and Q 275-4 (bottom pane/). me lithium has been recently discussed by spedra me not corrected for the earth moth. Lemoine et al. (The Messenger No. 67, p. 401. Uthlurn observations In th Popula- far here are only few objects studied ter than observed. However, the pres- tion II stars are severely limited by the for lithium with metallicity below ence of the lithlwn line In Gr 275-4 by intrinsic faintness of the known halo [Fe/H]c-3.0. In particular, the low- Itself is of Interest since It extends down dwarfs and by the relatively small equl- est metalllcky dwarf in which Ilthium to pA4=-3.7 the metallicity range in valent widths of the lithium line. We has been detected Is G 84-12 with whlch lithium is observed. In the case of used the EMMl spectrograph on the [Fe/H] -4.5, but the spectroscopic bl- G 64-37 the equivalent width of the MT to observe the halo dwarfs G 64-37 nary CS 22887532, with metalllcity Ilthiurn line is of 17 d According to and G 275-4, taken from the sample of [FW=-4.2, surpldslngly dmnot show Ryan et al. G 64-37 has a Tenof 6350 K Ryan et al. (1991). The obsewations any lithium (Molaro 1991). and is one of the hottest dwarfs in the have been performed with the REMD The regions around the Li 1 ~07Are- present sample of Population II stars. An EMMl mode using the 31.6 groovedmm sonance line for both the stars are accurate determlnatlon for the Ilthlum grating 10 and grism 3 as a cross dis- shown in Figure 2. It can be seen from abundance will be presented elsewhere, perser. S/N ratios of = 180 and = 100 the figure that the lithium features but a comparison wRh HD 84937 and G are achieved for exposures of 3600 set are ctearly present In both halo dwarfs. 64-1 2, which have sirnilarTd and dmilar for Q 64-37 (V= I1-1 mag) and of 3800 The redshift of the absorptions corre- line strength, indicates that the lithium sec for G 275-4 (V- 12.2 mag), respec- sponds to VM = 114 km 9' for G 64-37 abundance for G 64-37 should be also tively. The resolving power measured and Vhd = 142 km s-' for G 275-4, In at the plateau level. from the thorium lines is of = 26,000. agreement with the displacement ob- Interest in these two objects stems served by the stellar Nal lines. Unfortu- 2.3 IntEKstellar/lreIIar/IntergaIacticNal Abmrp- specifically from their particularly low nately, the blue wing of the tine In G 275- tions at High Galactic Latitudes metal abundmces. The- abundancm of 4 Is contaminated by an emission rem- G 64-37 and G 275-4 are of [Fd] nant of a previous observation, and the Interstellar observations in the dim- -4.38 and -3.70, respectively. So equivalent wldth could be slightly grea- tion of distant sources at high galactic latitudes are impwtant to cast light on the hlgh-veWi clouds (HVCs) phenomenon. HVCs were discovered at 21 em, but are exfmmely dmcult to detect In absorption In the optical (see 0.g. knanet al. 1W8). In the framework of the investigations on the interstellarhn- Wgalactie medium carded on at the OAT, we observed the halo star PG 1303-114 (V- 14.0) and the extragalactic object 2155-304 (V-13.1) in a search for sJEll absorption lines. For both ob jech we used the EMMl spectrograph in the REMD echdle mode with the grating s10 and the grim #3. The resolution in the region of the Nal doublet was measured from the FWHM of several Ilnes in a spectrum of the Thorium calibration lamp. We found 61==0.23A, cone- sponding to = 12 km s-'. PG 1303-1 14 belongs to a sample of halo sub-dwarfs (sdO and sdB) for whlch a determination of the distanm was performed by Moehler et al. (1090). BL Lac 2155-304 - 3 In the framework of a collaboration with 1.2 the Stemwe of Bonn we are currently analysing this sample of stars In order to study the gas distribution at large t distances. PG 1303-114 is one of the few stars of our sample which were &sew- able from Ia Silla at the time of the present observations. In Figure 3 we show the portion of the EMMl spectrum of PG 1303-114 in the Nal region. The exposure time was one hour and the resdtinp signal-to-noise ratio WN = 50 (1 o level). An interstellar absorption component close to rest velocity Is vlsi- bleat the red side of the Nal atrnospher- Ic missions: this component is probably due to local gas in the galactic disk. No absorption components are detected at higher or lower radial velocities Figure 3: IMW3telIM N81 rabsorptiOflS Ill Ihe dhCfh of th fW0 h&h&dhl& baemd sourns ffi 1303- i14 and 2155304. Emisdon IInes at rest vt?Wty am atmospherfc.Telluric outside the 3 o level. The minimum de- abmptions wsre rmv& by using me specwrn of the bright stav HR 5825 as a template. tectable equivalent width is of about 14 Pwtrbns of the speetra cleaned up of mkevents are marked Mth mssm mA, corresponding to an upper limit N(Nal)<7 x 10" atom cm4. By adopt- ing the interstellar Nal-HI correlation derived by Fwlet et al. (ID=), this in turn implies N(H~)C~O'~atoms cm" in the w sensitivity and spectrat resolution. In 4 km 6'' component may be pro- direction of the star, which is located at Rgure3 we show the Nal spectrum of ddIn high-velocity gas with a low about 1.5 kpc from the Sun at a galactic 2155-304; the exposure tlme was one projected velocity along the llne of jatitude b=+5I8. H the lack of high- hour and the raulting SM=M.A Nal sight. Woc1ty absorption components will be absorption of =28 mA is dearly present An exciting feature of the 2155-304 confirmed also in the other lines of sight at the blue side of the D2 atmospheric spectrum is the presence of a Dl and of our sample, then the idea that high- mission. The radial velwlty of this fea- 02 absorption at V--"SO km s-' , both velocity gas is generally located at ture, VsR=-9 km a", Is in very good marked in the low panet of Figure 3. lz 1 >l kpc will receive a sound obser- agreement with that of Ule Call compo- These absorptions are close to the de- vational support. nent detected by Morton and Blades. tection lmh, but the fact that the line of Thm BL Lac 21 55-304 was obsewed The Dl absorption at the same velocity sight to 2155504 (I-IS", b=-527 by Morton and Blades (1986)with the is vislble as a weak feature close to the falls in a region of the sky Wre HVCs AAT in Call and Nal at a resotution of noise level. A preliminary estimate of with negative velocities are predominant 17 km s" and 24 km s-' respectively. the Nal column density in our spec- (Wakker and van Woerden 1991) en- They found an absorption component trum, combined with Ule Call column courages us to betieve that they are real. at V-4 krn a*' In Call, but only an density estimated by Morton and The presence of the 40km s-' com- upper limit of 83 d In Nal. We decided Blades, glm NallCall-0.15. This low ponent, ff confirmed by future observa- therefore to reobserve this object in value of the NaVCall ratio is charsc- tions, would provide an almost unique the red spectral nnge In order to teristlc of high-velocity Interstellar g&s opportunity to study a HVC by means of search for Nal absorptions with a high- in our Galaxy. This suggests that the absorption line spectroscopy. 2.4 Wond PN Candidates in Two sion thls check led us to take a second ty of this project to be now wall estab- Galaxies of the Wrgo Cluster exposure with a longer exposure tlme. liished. Some preliminarv work has been The use of PNe as standard candles done at a 'ky --stage using image 2.5 DMmt Clusters: EMSSource has been described in a series of papers were l~ which transferred from Silla to 2337.3-2353 (e.g. Ciardullo ef sl. 1991 and the previ- OAT through the network link. Sum- ous papers in the series), and has been quent data reduction work, aimed at the The target of our ubservations belongs applied to the determination of the dis- detection of PNe candidates. was done to a list of 'dlstanP (z>02) clusters tance of the Virgo Cluster (Jacoby et 81. off-line at OAT on an HP/ApoIb 4000/ of the Southern Sky, identified as 1W0) from data taken at the KPNO and 425 workstatton running MIDAS. The X-ray sources withing the finstein CFHT talescopes. The methd used by images were bias subtracted and dl- Medium Sensitivity Sumy (Gioia et al. the above authors relles on images ta- vided by sky-flat-fields, On each of the 1990, Stocke et al. 1991) and lacking ken through a namw band filter centred calibrated images we ran an automated good optical images. The list has been on p11~07,redshiid at the sys- object finder (MIDAS invent context) compiled in collaboration with as- temic veIocity of the cluster being and, for the time being, the ldentiflca- tronomers of several Itallan Instituters. analysed, and images taken through tions are then checked visually. The purpose of obtaining images for the and intennediabband fllter of FWHM As can be wnfrom the two images clusters in the list is to create a good = 300 A Jacoby et al. (1990) performed of NGC4839 reproduced here (Fig. 4), statistical sample wtth well-determined the detection by '%linking" the on-band them are many objacts which are de- optical and X-ray properties.This sampb and the off-band images and selecting tected in [OHI] but not in V; such objects Is necessary ln ordw to analyse the as candidates those objects which were are our PN candidates. The redshifted evolution of the relatlon between the d&Won the on-band Images but not pllu filter proved to be less Mive galaxis of the cluster galaxies end the on the off-band ones. than the V filter, probably because, due CM from local to distant clusters. That Is it possible to any out this kind of to the limited observing time and the he local relation bween galaxies and scienMc Investigation on the NlT? This fact that this filter is narrow, this Image gas should change In the redshiff range question was raidIn the kamework of is not deeper than the on-band [0111] 0.25~s0.6, is suggested by several a collaboralion including OAT scientists image. Before we can claim that our evidences (e-g. Garilli et al. 1992, Fabric- (FP, PB), a group at the Sternwarte candidates are PNe we must wony ant et al. 1B91, Henry et al. 1992, Nesci et Munchen Igd by R.P. Kudritzky, and I.J. about: (1) detection of spurious objects; al. 1991). In particular them seems to be Danziger, F. M-li and LB. Lucy at (2) misslng true PNe. Them are substan- a trend for clusters of given richness to ESO. The "second-level" Rmote Ob- tially three typ~of objects which we be less X-ray bright and richer of blue smations technological experiment can expect to detect in the [OllW007 galaxies as the redshift incrsases. This carried out at OAT gave us a ~hanoeto flher: Hll regions, Novae and PNe. trend is predicted by some current cos- tast the feasibility of such obmations. Novae are likely to conhmlnate the mological models (e.0. Evmrd 1990). Uslng the genersrl philosophy of sample only marginally since we expect Among the objects of the list we have Jacoby et al. (1990), we tested the per- PNe to be much rnore numerous than obsenred the source 21 37.3-3553 fomnce of the filters available on Novae in outburst at any given time, (z-0.313, Fx=21.78 lri3erg m4 EMMI. Due to the lack of an InWmedl- Thewfore, the only objects we really %-I) since it was observable at a small ate-band fllter in an emission-line-free have to wony abut are HI1 region zenithal angle. We have taken VRI im- region, similar to that used by the Ameri- galaxies. HI1 regions should appear to ages with EMMl In the RllD configurn- can investigators, we used filter #591 be extend& and moreover their ratio of tion and the onty CCD available during (I01111 redshifted at MOO kmls band- [Olll] magnitude to V should be lower the test, the Thompson 1024x1024 width 81 A) and #806 M as off-band than that of PNe, since HI1 regions we CCD @SO a18).Tfre scale on the CCD filters and fllter #589 (IOllrj, bandwidth usually of lower excitation than PNe. Is -44 arcsec/plxel and the field is 56.3 56 A) as on-band filter. Ha images The ofher concern is that a true PN arcmin2. The seeing during our dbserva- wldhave been desirable to help the may be detected also in V, since this tlons was = 1 arcsec. PNe-HI1 regions discrimination but filter indudes Ha and IOlltW07, ai- Metotal exposure time in each of the could not be secured, In the Ilmited ob- though the contribution of the con- three coloun V, R and I Is of 45 minutes, serving time avatlable. tinuum from the central stars of PNe 20 minutes and 30 minutes respectively. For our test we selaed two spiral huldbe negligible with respect to the After the bias subtraction and the flat- galaxies In the Wrgo Cluster: NGC4639 galaxy background. Anyhow, in thls filter fleld correction, a preliminary photome- and NGC3627. These targets were the contrast wlth the galaxy background try In Ule V band shows that we have selected since they have been the host is lower, which makes the detection reached V = 23. As soon as all the galaxies of two recent and well-ob- more difflcuk In ordor to avoid detect- frames will be properly co-added, we wed type la supernwm ISON ing PNe In the V images, one should will separate galaxies from stam and use (leibundgut ef al. 1991, Maaali et at. keep the detection thteshold rather a coloursolwr diagram to Identify 1992) and 1989B (Barbon et al. 19Q0), high, yet low enough to detect safely all background/foreground objects. The fi- and thus present the opportunity to the HI1 regions. nal result we expect from our observa- compare two different distance determi- The next step of this work, to be tions Is the measurement of the main nation methods: the PNLF and the max- carried out In collaborzltton with the properties of the distribution of galaxies imum brightness of SNe la. The images Stemwarte Miinchen and ESO group, In the cluster, such as the richness and were taken in EMMI RlLD mode; the will be to discriminate PNe from HI1 re- the content and space distribution of detailed observation log is rewed in gkns In our candidate list and worm 'blue' gaiaxies. Balestta et al. (1992). The Remote astrometry and photometry on the m- MIDAS facilky allowed us to have an on- didate$. It is not whether the im- clear 2s CandIdat8EiMtein Ring line quick look at the Images, after ages we have will allow a satisfactory 1830-21, acquisition. This was extremely useful diserlminati~naaalnst HI1 mions.- - Ha both for purposes and to Imaga myprOk to ke necessary In PKS 1830-211 is a flat-spectrum assess the Image quality; on one occa- this respect; yet we believe the feasibllt source which shows two lobes in the Figure 4: Two images of tVGC4639 taken with EMMI in RILL) mode. On the left-hand side the image taken through the V filter, on the right-hand side the image taken through the [OIl~A5007filter, Circles surround the positions of objects detected in the [OIlJ image, while squares surround the positions of objects detected in the V Image. The objects which are detected in the [OlllJimage, but not in the V image, are PN candidates. The low cut has been kept lower in the V image to stress the absence d detectable objects. radio (VLA and VLBI observations; Rao rather than ldentlfy and/or separate the leased by an AGN could trigger star and Subrahmanyan 1988, Subrahma- possible optical components of the formation in the surrounding galaxy. nyan at al. 1890, Jauncey et al. 1991). radio source. In fact, as far as angular This interrelation may reflect in pecullar The separation of the two radio lobes is resalution is concerned, our obsewa- morphologies and/or colours in regions 1 arcsec. The shape and spectra of the tions cannot compete with those of surrounding the nucleus. With this prob- radio 'lobes' (ME and SW) suggest that Djorgovsky et al. from the NIl with lem in mind we started a programme to PKS 1830-21 1 is a strong Einstein Ring SUSI (0.1 3 arcsec/pixel) and a seeing of observe both in the infrared and optical (Rao and Subrahmanyan 1988, Sub- 0.75 arcsec. However, their nigM was bands galaxies hosting AGN. Pitot ob- rahmanyan et al. 7990, Jauncey et al. not photometric and magnitudes were servations were conducted during this 1991). This kind of gravitational lenses only roughly estimated. test: targets am selected from the CfA are particularly interesting since they We have taken 5 frames In the 1 band llst (Huchra et al.), 5 galaxies were can be very powerful cosmological centred on the position of the radio selected on the basis of observing time tools, allowing, in principle, the determi- source PKS 1830-211. Each frame has constraints and because we already nation of the Hubble constant and the been exposed for 10 minutes, After the have multi-aperture photometry in J, H, mass distribution of the lensing first three exposures we have offset the K infrared bands for these objects. Im- galaxies. telescope 4'' (or 10 pixels) eastward. ages were taken in V and R bands with Optical observations of PKS 1830- A preliminary analysis of the fields exposure times ranging from 120 to 420 211 have failed, so far, to reveal the shows that the PSF has a FWHM sec; the seeing was =. 1 arcsec; prelimi- counterparts of the two radio compo- slightly smaller than 1 arcsec and that nary analysis shows that we reached at nents (Subrahmanyan et at 1990, Djor- we have reached I = 18.5 in each frame. least 26 mag arc* In shorter exposures. govsky et al. 1992). Djorgovsky ei ak Unfortunately, this is not faint enough (1992) have recently presented the for our purposes. The reason is that the Acknowledgements whde set of data they used in search for brightness of the sky was too high at the optical counterparts of the candidate time our observations took place: the The authors are grateful for the oppor- radio ring. The optical data include CCD moon was still up, even if very tow. tunity they were given to perform scien- Images taken with the ESO 3.6-m (BVR tific observations on the MT in the bands) and ESO NIT (BRI bands) tele- framewok of the ESO/OAT technologi- 2.7 Seyfert Galmfes scopes and with the Palomar BOO-inch cal project on "second-level" remote telescope (K and Gunn 'it bands). One of the most interesting questions observing. They would like to thank h We had planned our remote observa- in extragalactic astronomy is what trig- particular A. Balsstra, C. Corh, P. Mar- tlons wlth SUSI, which, however, was gers the activity in the nuclei of some cucci, P. Santin, R. Smareglia and C. not available for the test run. We de- galaxies (AGNs): 0.g. Norman et al., Vuerli of OAT, and M. Cornin and A. cided to use EMMl in the RlLD config- Scoville et al. suggested a relationship Wallander of ESO who, through their uration (sw section 2.5). Our primary between AGNs and starburst activity In hard work, set up at OAT a temporary goal with EMMl was to reach a falr the sense that the starbursts are the but absolutely functional and efficient depth and obtain good magnitudes for evolutionary precursor of AGNs; on the clone of the ESO remote observing sys- the objects in the field of PKS 1830-211, other hand (9.g. Daly) the energy re- tem. Special thanks to S. D'Odorico, who gave some very important sugges- D. Fabricant et al., 1991,Ap.J. 381,39. PA. Maaali el al., 1992, A&A In press. tions on MT Instrumental set-ups and R, Fdet, A. Vidal-Madjar, C. Gry, 1985,Ap.J. S. Moehfer, U. Herber, K.S. de Eloer, 1990, obswing prdures, and to the IA m,838. A&A 299,285. Sllla night assistant M. Plzzaro who U. Rnkenesllw, GG.Basrl, 1987, Ap,J. 318, P. Mofaro, f 991, Mem. S.A.lt 62, 17. played an essential role for the success 023, C.D. Morton, J.C. Blades, 1986, M.N.R.A.S. M. Franchini et al., 1992a, A&A 2S.525. 220,Q27. of the observing run. M. Franchinl et al., 1992b, in preparation. R. Nescl el al., A&A 252,13. 8. Oarill1 et al., 1992, RJ. in press. C. Norman, N. Scovflle, $988, ApJ, 33a, 724. References I. Gloia et al., 1990, ApJ-S. 72.567, A.P. Rao, R. Subrahmanyan, 1988, M.N. 231, A Batestra et al. la,OAT Publ. No. 1443. P. Henry et al., 1992, 4.J. 356, U5. 229. R. Won et al., 1990, AIA237, 79. J. Huehra, R. Burg, &.JJ 1992 393,90. S,G. Ryan, J.E Norris, M.S. w,1991, Ciardullo et d., 1991,Ap.J. 388,487. Jamby et al., 1990,4.J. 368, 332. AJ. lOa, 303. R. Daly, 1940, Ap.J. 356, 416. D. Jauncey et al., 1991, lVatwe 952,132. N. Scovllle, C. Norman, ?98!3, &J. 332,163. H. Dekker et al., 1491, ESO Operating Manu- F.P. Keenm et al., 1988, AIA192,295. J.T. Stocke et al., 1991,ApJ.S. W,813. al No. 14. B. Lelbundgut et d., 1%I, M.J. 971, L23. R. Subahmanyan et al., 1990, M.N. 240,283. S. Djorgovsky et al., 1942, preptint. M. Lemoine et at., 1992, The Messenger 67, B.P. Wakker, H. van Woepden, lWl, AIA A.E. Evrard, 1990,Ap.J. 343% 349. 40. 260,503.

The Giant Arc in EMSS2137-23 M. RA#ELLA and M. NONlNO, Osservatorio Astronomico, Trieste, Italy

During the three nights devoted to the which set very important constraints on the feature is R = 21.5 and its surface test of the 'second level remote observ- the model itself. brightness is 2 5 YO of the sky). The ing' we observed the cbster EMSS We moreover note that at least one spectrosccrpy of the arc would reveal 2137-23 with MTT and EMMI. This clus- substructure of the main arc is probably the nature of the lensed object, sorne- ter is a rather bright EMSS source and bright enough to be observed spectres- thing that has been possible only in four has a redshift z = 0.32. These charac- copicaly (the integrated magnitude of cases so far. teristics make EMSS2137-23 a perfect candidate for the study of the relation between the gas and the galaxian components of a non-local cluster. We wanted to obtain photometry for the galaxies of the clusters in order to build a magnitude limited sample. Details of the observations are found in the article by Franchini et al. in this issue. The choice of the cluster was very fortunate, since our images also re- 'vealed a giant gravitational arc and several arclets su&unding the cD galaxy of the cluster. However, after our observations had taken place we learned that this arc had already been discovered by Fort et al. in 1991, also with the N3T. (See also the artlcle by G. Soucail in this issue of the Messenger.) Our images of the arc are of gaod quality (see the I figure), Because of our original project on this cluster we also have redshifts for about 50 galaxies in the field (the redshifts are available to us thanks to a collaboration with Dan Fabricant at the Center for Astrophysics). The fact that the arc is in a cluster for which we have such a complete set of optical and X-ray information makes the study of this arc particularly interesting for the determination of the mass distribution within the cluster This sh~ws the compact of galaxies EMSS2137-23 and the 15 arcsec long "giant and for the verification of the model of image cluster arc': just rwrlh of the centre of the cluster. as obtained in June 1992 wlh the ESO 3.5-m New the lens. building the model, in Before Technology Telescope (mand the lESO Multi-Mode Instrument (MI) during remote eollabomtion with Emilio Falco (CfA), observations from the Trieste Astronomical Observatory. The frame is a combination of 5 deeper images will be needed in order exposum in V, Rand I, with a tot81 eexposure time of 95 min. The wing was - 1.0ammond. to confirm the several candidate arclets, 1 pixel=0.44 amsecond. The rield measures 7Dx9arcsee; north is up and east is to the left. The Squeeze is on the La Silla Obsewatory H. VAN DER LAAN, Director Get qeral, ESO

Visiting ta Silla in early August, it grammes running now. While I have re- have maintained a high service quality struck me again how our observatory distributed resources for La Silla some- while coping with the greatly augmented and its staff are squeezed between two what over the several departments h quantity of telescopeinstrument mode developments in ESO, developments the Obsenratory, the total manpower re- combinations. It b an impressive in- which by their nature tend to continue sources have actually decreased slightly crease in productivity which is now ap- and which must be adjusted soon If we in the last five years. Yet our teams there proaching its limits. are to maintain a healthy working cli- mate on laSlla. In a talk to all staff on the mountain I raised these and some other issues. The relevant developments are: (1) the increase in both quantity and technical complexity of the hard- and software in the domes, and (2) the slow but steady reduction of resources in favour of the VLT Obsenratory now under construction. Actually thew is a third tendency which is laudable but makes matters mow difficult still, namely the increasing ambition of our users community, manifest in increasing pro- posal pressure and more subtly in in- creased expectations if not demands of services to be provided by ESO/Chi te I staff. CCD ILR'I

The circumstances can be partly in- Cdss Otrert Imagery CCO tcoated GECl 1 ferred from the two accompanying ta- Cass & C Spectr~graph B Bolometer btes, which give the menus offered to Polarrmeter visiting astronomers just five years In Sb Detector 1 Infrared Photometer apart. They are from the Announce- ments for Period 41 and Period 51 re- Rettcon spectively, issued in August five years Cass 8 & C Specfrograph - CCD (coated GECl ago and this year. Close inspection of Ll.!jm 1 Erheler Spectrograph these two menus reveals how much a Coude' Spectrograph CCD IlR-I 1 major observatory changes in just five Camera 11 itamera //I years, over and above the addition of CES Short Camera CfD IHR'I the WIT with all its sophbtication and CES long Camera I corresponding technical fragility. Nearly Scanner all detectors on the major telescopes have been renewed, thanks to industrial developments and a large effort by the Infrared Photometer Bolometer I Instrumentation Groups In Garching to In Sjnq/e Channel in ~b Detector 1 stay on top of this evolution. The readi- ness maintenance for all these detectors on la Silla Is no task. The power small PM RCA 31031 and versatility of EFOSC on the 3.6-m PM EM/ 9789 QB have spawned the second EFOSC now on the 2.2-m telescope as wdl as EMMl PM &HI 96S8 on the NTT and DEFOSC, ready next year for the 1.54-m Danish telescope. 61cm I 1 Sinple Channel Photometer EMMl is a veritable suite of instruments BOCHUM _I all rolled into one compact multi-mode CCD Camera device. Infrared capacities on La Silla Photography 1 I have dramatically improved with the renovated IRSPEC on the MT and LR -Low Resoluhon RCA .I20 jU-3Or the tRAC2 imager on the 2.2-m. Next SOcm ] uvby HO Photometer 1 5 12 prxds year the 10-micron spectrophotornster DANlSH TlMMl adds another infrared state-of- the-art capability to the 3.6-m. '~chrnidtl . with ~rtsrn For Perlods 39 and 40 (1 April 1987 - GPO I 1 ~tthoutPrism 1 31 March 1988) there were 670 proposals while for Periods 49 and 50 (1 April 1992 - 31 March 1993) there were 880. with in addition two dozen Key Pro- Table I. T8Ieswpes and Available Auxiliary Equipment lpW4 1. 1 April- I October 1W). ESO Headquarter resources are now In the Scientific-Technical Committee "caught between a rock and a hard predominantly directed towards the de- a discussion is to take place on the placl and if we do nat make choices sign and construction of the VLT Obser- options for containing the La Slla staff's then the compromises that are the worst vatory. Readers of the Messenger are workload. It is clear that quality and choice of all will arise by default. And so well aware of the new observatory's reliability cannot be compromised. In- the squeeze on La Silla will be diverted, scope and the multiplicity of its tech- stead, the menu of what is offered in any to a squeeze on the STC and subse- nological systems. They are unpre- one period must be simplified. Instru- quently on Council, the next Executive cedented In the hlstoty of ground-based ment changes, with the attendant align- and ultimately on ESO's users. All for astronomy. They are also a daunting ment, stabilization and calibration tasks, the sake of the exciting prospects cre- challenge for the whole of ESO and our are the prime source of technical work- ated on Cem Paranal. I am sure they partnm, Industrial and institutional. I loads. I have asked the heads of the are worth it1 have had no choice but to divert to the Technical Research Support and of the VLT all the resources that could In my Astronomy Support Departments to view be possibly spared In the Science prepare a paper for the November meet- Division and on La Silla We have now ing of the STC. We astronomers are reached the stage where users have to notoriously incapable of deciding what be confronted with resource limits, we do not really need; as a community where the present opportunities on La we usually behave like the character in New ESO Scientific Silla wlll be cwtailed for the sake of the popsong who asserts that "1 want it futum opportunities on Paranal. all and 1 want it now". But ESO is Preprints

(June - August 1992)

844. P. Ruiz-lapuente and L B. Lucy: Nebu- lar Spectra of Type la SNe as Probes for Extragalactic Distances. Reddening and Nucleosynthesk. The Asfr4physi- ca/Journal. 845. M. k Prieto, J. Walsh end Robert FM- bury: IPCS Observations of Extended Gas in Radlo GalaxEes. Gmini. 846. J. Einasto and M. Gramarm: Transition Ss) EMMl Standard Confi~urationRed Scale to s Homogeneous Universe. As- b:~] SB) EMMl Hinh Resolution Echellc Red 1 tronomy and Aslrophysics. SH)EMMl Standard Configuration Blue 847. F. Murtagh, M. Sarazin and H.-M. Direct lma~ing , CCD RCA#8 tl-Res 1 Adorf: Statistical Prediction of As- EFDSC 2 CCD THlK#19 Coated tronomical Seeing and of Telescope Infrared Photometer Bolometer Thermal Environment. ESO Conference lnSb Detector on *Progress h felescape and In- strumentation Techrrotogles". 848. G. A. Tammann: The Cosmic Expansion and Deviatians fmIt CrafOOTd-Syrnp. Cars. B&C Spectrograph *ExtngalaetieAstmrtomy including Ob- 1 1*52m a-1 seruatbns Cmmalaav". L. E. super- CES : Short Camera (Blue] * CCDFAkC27Coated I ~angand J, w-Gmpler: fie - nova St4 1987A: the Nebular Loops and CES : Short Camera [Red) * CCD RCA#9 H-Res "Mapolm's Hat". Astronomy and As- CES : Lonn Camera (Btuc) * CES : Long Camera (Red) frophvsiw. * T. Riehtler, E. K. Grebel, H. Domgwen, Bolometer M. Hllker and M. Klssler: The Glnbular tn Sb Detector 1 Cluster System of HGC 1404. As- trw?#myand AstmphysIcs. 1 Single Channel Photometrr R. F. Peletier: The Steclar Content of P*M.T. EM1 9789 QB Elliptical Galaxies: Optical and Infrared P.M.T. EM1 9658 Colour Profiles of M 32 and NGC 205. 50cm Astmyend Astrophys!~~. ~=,,i~.,I uvby H# Photometer P.M.T. HAM R943.02 R. Siebenmwgen, E. Krtlgel and J. S. Mathis: ~adiitivem ran sf& for Tran- I ~~~~~-1CCD TEKIK# siently Hmted Particles. Astronomy and Astrophysics. 1 Dirt rni -1 [CCD GEC#7 Coated 1 ] 853. M. Della Vale and N. Penagia: Type la 1 1 Supernovae in Late Type Galaxias: Reddening Comction, Scale Height and Akdute Maximum Magnltuck. The Astmnomiml Jwmal, 854. L Pasquint: The Ca II K Line In Solar Type Stars. Astronomy and &trophy- srcs. 1 3.Omm Receiver 1 855. 60 Reipurth and B. Pettersson: Star Nutsar (k)'rha cmLiea~lmd 11- Lelmaper. ik~n~mrlbtfiandalrlqetnpa~an be ~aalmmrltcly I~III Formation In Bok Globules and Low- rha WO Hcodquuran in QarJlilt~. Ha Stars (t) s~/SflOpkion avaiiaLk ~il~lutrancs~laiy. Mass Clouds. V. Emlsslon Near SA 1 01, CG 13 and CG 22. As- Table 2. AvaiIe Telescopes end Auxiliary Equipment fid51, 1 April- 1 October 1993). tronomy and Astrophysiw. 856. P. Dubath, G. Meylan and M. Mayor: Galaxies: The Case of NGC 4472, C 859. S. Heathcote and Bo Reipurth: Kinema- Core Velocity Dispdons and 4296 and NGC 7 144. The Astrophysical tics and Evolution of the HH 34 Com- M&atllcltles of Three Globular Clusters Journal. @ex. The AstmmmIcaI Journal. Belonging to the F~axDwarf Spheroi- 858. P. A. Manali et al.: Models for the Early 860. M.-H. Ulrlch: MuEtiwamlmgth Observa- dal Galaxy. The AsWysicd Journal Time SWEvolution of the 'Scan- lions of the Quasar Q1821+643 During 857. R, P. Saglla el 4.:Stellar Dynamical dard' Type la Supernova 1WON. As- the ROSAT All Sky Survey. Astronomy Mdence for Dark Hdos In Elliptical lvwwmy and AstrophVsrw. and Ast~physlcs.

PROFILE OF A KEY PROGRAMME: CCD and Conventional Photometry of Components of Visual Binaries E. OBlAK7,A.N. ARGUE: P. BROSC* J. cuYPERS4,J. DDOMMANGEP, A. DUQUENN~Y~, M. FROESCHL~?, M. GRENON~,J.L. HALBWACHS', G. JASNIEWICZ~P. LAMPEW: E. MARTINS J. C. MERMILLIOD~,F. MIGNARD~, D. SINACHOPOULOS~,W. SEGGEW/Ss3, E. VAN DESSEL~ 'Observatoirede Besanqon, France; 21nstitute of Astronomy, Cambridge, United Kingdom; 30bservatoriumHoher List, Bonn, Germany; 'Royal Observatory of Belgium, Brussels, Belgium; 50bservatoire de Geneve, Sauvemy, Switzerland; '0bserva toire de la Ci3 te d 'Azur, Grasse, France; '~bservatoirede ~trasbour~,France; 81nstitut Astronomique de Lausanne, Sauvemy, Switzerland; glr?stitutode Astrofisica de Canarias, Tenerife.

1. Introduction tectors in spectroscopic and photomet- procedure (choice of sky, centring) than The study of double stars, apart from ric techniques. in #e case of slngle Jars may be desir- long being recognized as a basic key to The importance of studies of visual able to obtain high-quality data. the understanding of star formation and double stars lies not only in the tradl- - To the extreme other end of the range evolution, actually deserves particular tional determination of stellar masses in In separation, the interest for the very attention for many additional reasons: orbital pairs - however fundamental close binary systems (visually non- (1) the ratio of known double to slngle these may be - but also in the determi- separable) arose during the last decade stars Is continuously upgraded and the nation of the characteristics and the fre- because of the physically interesting rate of detection is steadily increasing, quency of double stars in different stel- underlying mass transfer problem. In bh from ground-based and space ob- lar populations and evolutionary stages. these cases, global photometty Is per- servations; The distributions of the characteristics formed. (2) space obsewations (Hlpparcos, typical of double stars such as periods, - The technbal difficulties of observing HST) significantly improve the quality eccentricities, mass ratios, relative two images in close proximity to one and the Importance of stellar samples. ratios of double and multiple star sys- another are especially pronounced in They permit to better take into account tems are actually not sufliciently well carrying out conventional photoelectric some of the former selection effects as known to provide valuable constraints photometry for the remaining class of they reveal a lot of new double stars, on the different star fmation double stars with separations in the In- especially among the close visual pairs; scenarios. termediate range. This class of objects (3) the high-quality astrometric (and In order to acquire this knowledge, has therefore largely been neglected in partly photometric) data that will be the astrophysical information available past photometric programmes. When made available for a large number of from magnitudes, colourg, specrral available, global photometry in oombi- double stars by the space results should types and velocities is fundamentally nation with visual or photographic es- be matched accordingly wlth accurate needed. The usefulness of photometry timates of the magnitude differences are and homogeneous complementary as- of visual binaries is especially obvious in not mciently precise to match the ac- trophysical Information such as colour applications concerning, for example, tual requirements and the accuracy indlces and spectral types. luminosity calibrations, the mass- achieved in other techniques. (4) Such accurate ground-based In- luminosity relationship, mass-ratio de- With the introduction of CCO detec- formation for each of the components of termination from differential mag- tors on photometric telescopes. it now close visual double stars (angular ssp- nitudes, age and evolution detemlina- also appears feaslble to obtain accurate aratlons less than some hnarcseconds) tlon. But the type and the accuracy of photometric data for each of the com- is almost nonexistent on a large scale - the photometric Information depend ponents of close visual double stars e.g. the astromhc "Catalogue des very strongly on the separation of the with angular separations between 1 and Composantes d'Etoiles Doubles et MJ- binary components: 12". tiples" (CCOM; Dornmanget, 1989) con- - Wide visual double stars (with sep- 65,000 no tains over systems but fewer arations larger than 12") present 2 The Scientific Justification than 10 % have accurate and reliable difficulty to conventional photoelectric photometry -, but is recently made pos- photometry. Individual data are easily A comprehensive catalogue of phys- sible with the breakthrough of CCD de- secured, even though a more careful ical pairs - from the very close to the data on all the components of a double formation, evolution and structure of the Double stars - South or muItlple system. A programme nf Waxy. Indeed, ground-based and systematic and homogeneous acquisf- space obwations reveal that at least - tion of precise cdour indices for several half of the stars bbng to double and thousands of components of double multiple systems but went theories and multiple systems has kndefined still cannot explain the formation of such In both hemispheres, with the foilowing a large number of systems. priormas: (1) to supplement the Hippmos mag- 3. The Obsewatlonal Programme nitudes by aslmphysically significant - colwr indlces providing the additional The sdecfhn of the prNramme stars physical pmeters such as tempera- Qblak and Lampens, 1992) was We - ture and gravity: amongst I1,434 double systems, 1960 (2) to complete the photometric infor- trlpte systems, 538 quadruple systems mation for the components not Included and 237 multiple systems from Annex 1 D in the Input Catalogue. fhts Is important of the Hlpparcos Input Catalogue, con- 135 7 9111315 since accllrafe miormetric data for the taming objects to a distance of $00 pc Angular separation (") wider pairs may indicate whether or not (Turon et al,, 1992). Figure 1: DisMbulb of the angular sqwa- the components are optical. Our princi- In vlw of repeated photometric cam- ths~fhe~soffhedouWepal scientific objective is to provide the paigns distributed over both hemC starsforMeSWthem~C~+l~.misslng photometric data needed to spheres the ohwational programmb supptement the high quality end exten- mistsof a northm (declination of the sive astrometric curd photometric data primary component 3 -1 0) and a swth- on known and newly detected dwble em sample (8 A 5 + 10). fhe omlap- very wkk- ones - with a maximum stars in order to b able to adequately ping Zone in declination -10 c B A I number of sstromtric, spct~osmpic study the medmlgms of formation wd + 4 0 b only omobserved according to and photometric good-qualtty data evolution of double and multiple star Mslbilii. would be a highly valuablsastrPphysical systems. Slm both classfcat photometry and tool bmause R woukl contain several Such a Iess-biasd survey is urgently CCO are cansidered, the selection fur- clues comemlng the mode of star for- needed to improve current theuries on ther included splitting according to mation and oonsequentty also the structure and the evolution of ow galaxy. The wm€mction05 such a basic sample of double stars is now within reach, thanks to the ground-based technological progress as well as to the huge preparational work and flne resuhs from the Hippama space rnissbn. On one side, its systematic all-sky sunrey has permitted the detection of a large numbm of new double stars, with separations small mwgh to partially fill the known "gap" bmthe spectroscopic and the visual double stam, On the other side, the mission will provide accurate parallaxes and proper motions for dl thB dwble stars included In the Hipparcos Inpuf Catalogue (mthan 10 %), allowing to precisely define the distance-limited samples but dso to recognize more surely optical systems. Morea~er,diffemnt groups have almdy addressed the spectroscopb aspect (ESO Key Pmgmmmes far radial velo- citii) of the Hippmos stars, containing at least partially the basic sample we wMto inmtigate. The alm of thls group, wl taborating in the fmof a European network of laboratodes (Oblak et at., 19321, Is to contribute to a systmadalc and unbiased phobmetric survey of the cornpnents of doubIe and multiple stars. The available photometric data, obtained at ground-bawd obsewakories or In space programma, ere mostly con- .. . medwith the global system. To ots- H5 214 tatn the relevant astrophysical informa- Rgure2: CCD~forhstarsHD24445:q=82,2,-18.& V@)= 10.6, htheIIlItsrand tion we need the Individual photometric HD87238:p-613, VtA)-9.4 V#-9.6, In the V#tw(OHP-m?hg-P, OeGemberISW). angular separation and dMerential magnitude. For separations large$ than 12", individual magnitudes and colours are easily obtained from classical photome try on small telescopes. For separations smalbr than 15", CCO photometry is more Micient and adequate as long as the difference in magnitude is smaller than three. Astrmetric information is obtained as a by-product. The overlapping range In separation has been considered for calibration purposes between two very different techniques. A comparison with the "Catalogue Photo- mettique des Systhes Doubles et Mul- tiples" (CPSDM; Oblak, 1988) allowed to identify those systems lacking individual photometric information. Observations have already started In various observatories located in both hemispheres Calw Alto, Jungfraujach, Observatoiw de Haute-Pmvence and La Palma (Argue et a!., 1992) for the north- em part and La SHla for the muthem Plvt. The ESO Key Programme has been introduced to obtain photomatry (occasionally astmmetty) In the Cousins VRI bands for those selecied systems of the southsm hemisphere lacking such pm- 215 220 225 230 235 240 cise information (Fig. 1)- The observa- Position tions are made with the CCD detector ngun 3: CCD image of the double star HD 74 194 obsewed wNh th Wcm Dufch ta- at attached to the 90-cm Dutch telescope ESO: date: l7/la/91; exposure time: 15s; mag R. Q.6; dm - -1, a-29, mdng-1:3. '3.8 for the dose visual pdrs and on the pmliminary WWbngives: dm - 9.058, p. - 2115. 50-cm telescopes for the conventional VRl photometry for that part of the programme consisting of wide double and rnuttiple stars. positions will be obtained wlth hlgh pre- cr-d in the future, with the use of clsion. Emsare also made in writing larger telescopes. ex- For 4. Reduction of the Obsenrations and testing addiional sufhrvare for a bmer evaluation of the multl- traction of indiddual magnitudes and pliclty on our samples, the Information While the conventional photometry colour Indices with an accuracy at the of spectroscopic and speckle interfere will be reduced h a standard way, a 1% level* metric duplicity will be Introduced as preliminary reduction can only be done Standard star measurements allow to well. A double star photometric data with the known packages for the photo- correct for extinction and to transform base, to be integrated in the ''Gentre de metric rduction of CCD frames. the magnitudes to the standard M(1 sys- Donnk Astronorniques de Stras- Cmwdd-field-photometry routines tem. Minction weffidents derived from bourg", will be established at the Obser- cannot be applied wlthout modifications photometric observations at nearby te- Wory of Besanwn. to most of the frames obtained, since no lescopas will be used when available, We gratefully thmk ESO for the dl* reference star images are available Finally, dl obsewatlons will be pro- cation time to the Key Programme and (Fig. 2). Therefore, Individual profile fit- cessed as homogeneously as possible are confident that accurate basic data tings are n-aty. Accurate profiles with a well-defined adopted "standard" for astrophysically wdl-defined samples are needed to sep- the closest pairs procedure. of viW double stars will be within in the programme (fig, 3). reach during the next few years. In one of the techniques in use for the reductions, a row and a column projec- References tion is apptled on each CCD frame and a h order to have a less biased obser- Argue, AN., Bunelark, PS., Irwin, M,J. Ian- Franz's profile is fitted on the data vational programme and to supplement pens. P., Slnachqoufos, D. and Wayman, according to the least-square method In a useful way the photometric data, we PA., 1982, Mon. Not. R. AsW. Sm,In supported by an expert system routine intend to Introduce the double stars not prerss. (Sinachopoulos, 1992). Other tech- yet included in the Input Catalogue but Couteau, P., 1992, CBt8Iagw d# Etolles niques are in use in Geneva and Cam- listed in more recent double star cata- Doubles Couteau, available at Centre de bridge (Irwin, 1985). A further one is stilt logues (Couteau (1!392), Worley and Donnbs Astronomiques de Stm&ourg, 94;or Siwsbwrg. under development at Bann. All these Douglas (1 its new version)). By Star techniques will be compared and the arrangement wlth €$A, we wlll also be Dornqet,J.. 1989, in: CataEogues: A Centennu Trlbut%to AN. mtsky, Eds. most approdate for the stellar images able to include the new double stars Phllip and Upgren, 77-82 on the CCD frames dl1 be accepted for with separations greater than one arc- Irwin, MJ., 1985, Automatic analysis of the final data reduction. second detected in the Hipparcos mis- crowded fields, Mon. Not. R Astr. Soc., Differential magnitudes and relative sion. Thls limit could eventually be de- 214.575. Oblak, E, 1988, Astrophys. Spza Sci, 142, Obfak, E, Lampens, P., 1992, IAU Cdl, 135, Turon, C. el al., 1992, The Hippam lnput 31 -37. PAW Conf. Publ., in press. Catalcrgw, ESA SP 1736, Vol. 6. Oblak, E. et al., 1992, IAU Col1. 135, PASP Sinachopoulos, D., 1992, WJ ColI. 135, Worley, C.E and Douglas, O.G., f 984, The Conf. Pubt., in press. PASP Conf. Publ., In p~ess. Washington Double Star Catalog.

THE 3rd ESO/OHP SUMMER SCHOOL: Provenqal Summer, Hard Work and Warm Hospitality M. V~RON,OHP, France, and D. BAADE, €SO

Introduction teleeope with its Cassegrain spectro- of their data, using either MlDAS or Counting the observatories that on graph Carelec, and the other three used IHAP or both. The prediction by the or- the territories of the ESO member coun- the high-resolution coudd spectrograph ganizers that during the School sleep tries still operate several telescopes with Aureiie of the 1-5-m telescope. These would a? best be optional was amply up-to-date instrumentation, requires the two instruments, too, deploy a CCD as confirmed, especially in the night before fingers not even of one hand. Accord- the detector. the last day in the morning of which ingly scarce are the opportunities for The director of the OHP, Phillppe V&- each group had to present its results to students to get practical observing ex- ron, had in his welcoming address em- the other participants. perience before thls experience is really phasized the observatory's efforts in the The diversity of scientific subjects needed. The scope of the ESO/OHP previous weeks to save some good was quite considerable: rotation curves Summer Schools is to help alleviating weather for the Summer School. These of spiral galaxies and triaxiality of their this deficiency. For obvious practical efforts proved, in fact, quite successful. bulges, a search for inhomogeneities in reasons neither La Silla and certainly not Only one group had to depend on one of the internal extinction of a planetary Garching are suitable sites for this pur- the spare nights for a second attempt to nebula, the optical identification of Po=. obtain a useful set of direct images. The ROSAT X-ray sources, photometry of an One of the few remaining obser- amount of observations kept the stu- open star cluster in search for S Scuti vatories in Europe is the Observatoire dents more than busy with the reduction stars and the detection of the spectros- de Haute-Provence (OHP). It is named after one of the most attractive regions in the south of France. However, between July 15 and 25 the focus of the attention of 18 graduate students from nine different countries was not on tour- ism but on the OHP where the third ESOIOHP Summer School took place. Their aim was to partly flll in the observational void in the standard university curriculum.

Practical Work The layout of the School followed the scheme that had proved useful already In 1988 and 1990 (cf. The Messenger No. 53, p. 11, and No. 61, p. 8). Seven tutors (Claude Chevalier, Denis Glllet, Sergio Ifovaisky, and Philippe Prugniet from the OHP, Alain Jorissen, Werner Zeilinger and D.B. from Garching) had designed six small observing programmes for as many groups of three students each. The preparation started already the flrst afternoon, only in- terrupted by a small reception and the subsequent dinner, because the flrst observations were to be done the Figure 1: In the break ofHans Dekker's talk, students, ttrtws, and organizers assembled in the following night. shadow d a tree for a group photogmph. First row (fmm Iefl to right): Math;hs Kunz, Hans Dekker, Nadlne Rons, Jeslls Gallego, lardanka Horissova, Christian Surace, Simon Porlegies- Each group had one night at the Zwart; sitting: LUtz Wlsotzkl; second row: Jean-Phllippe Beaulieu, Sandro Badelli, Helmut 1-2-m telescope for direct Imaging with Jwjen, Salvatore Scuderi, Susanne Vogel, Mira Vhn: third and fwrth row: Dietrich Baadw, a CCD camera. For the spectroscopic Roland Reiss, Richard DaNler, Eugenio Carretta. Nancy Ageorges, Mikael Sahrling, Vdker part, three groups worked at the 1.93-m Ossenkopf,Wemer Zeillnger, Alain Jorlssen, Marc Ferrarl, Karlne Bocchialini. Rgum 2: Data red~tlmaccounted for rna$t of the wwk ddne by the students. (4 &@o IloWsky shows Mathias Kunr, Wmmain], and SImSM (Yrom M to rm0 how to sweep blemishes from a CCD Image. Tutor PhilIppe Pnrgneel and st- V& mkopfmd AdsGallego (fnnn leff to righo seem to ham slightly ditbwt views of the mze of kWYrtKtg tO use PWNmT.

copic signature of high-order nonradial had the opportunity to discuss subjects Relaxation pulsation in such stars, follow-up pho- which were of particular interest to them tometry of some recent supemovae, the in more depth. Ray Wilson also demon- An important contributor to keeping rejection of an earlier suggestion of strated at the 1,2-m telescope what can the level of the intensity of the work as shocks in the atmosphere of a brlght be deduced about a telescope's aberra- high as it actually was were a few social low-amplitude fi Cephei starI a search tions From an image of its pupil. At the activities which were much enjoyed by for technetium in red giants and candi- same telescope Roland Reiss together everyone. On Sunday, July 19th, a full- date-AGB stars, and a new detmina- with the students measured the readout day ex~ursianwas organized by Philip- tion of the velocity dispersion in an etlip- noise and gain of the CCD camera and pe Prugniel to the town of Gordes which tical galaxy which now is in much better its controller. is rnagnlficsntly set on a steep hill and to agreement wlth the general veloc'm dis- Unfortunately, a sudden health prob- the neatby 12th-century Abbey of persion-absolute magnitude calibration. tern prevented Pierre tena from giving Senanque and the museum village des However, the purpose of the School his lecture on high-resolution imaging. Bories with its curious houses made of was not to give the students deep ln- However, on s short notice thls gap piled-up natural stone plates. The Gor- sights into these subjects. Rather, the could be filled by the kind agreement of dian knot had to be cut only a few days topics had been chosen as an illustra- Jean-Paul Schneider of the Atmospher- later during the Petanque (Boule) tour- tion of how an observing programme is ic Research Group and Michel Grenon nament (also arranged by Philippe h- to be carried out from its definition to the of the Genwa Observatory to demon- gnU) when the book keeping of the fornulation of the results and the esti- strate the LIDAR experiment for the de- results of matches between many teams mate of their signlflcance. The aim was termination of the ozone contents of the of ever &anging compositions de- that after these exercises the students upper atmosphere from the back- manded the utmost of Its organizers. would be in a posltion to conceive and scattered light of a laser beam and the However, there was unanimous agree- conduct observing programmes of their CORAVEL stellar radial velocity measur- ment that a team formed by three ladies own. ing engine, respectively. from the OHP hotel (Maison Jean Perrin) Of course, competence in handling an beat all other teams by their outstanding performance. This certainly is explained Theoretical Reinforcement instrument and reducing the data ob- talned with it can only be an intermedi- by all three team members being locals In order to provide the students with a ate goal for an astronomer. The Inter- and thereby having grown up with thls more systematic introduction to the pretative power of cleverly designed ob- national pastime of the south of France. tools they were using, a number of ex- senratlonal experiments and a thought- However, a more relevant inference is perts had been Invlted to give a one- ful analysis of their results was beautiful- the level of quality which the parti- and-a-half hour lecture (cf. box). Most ly demonstrated by Gustav Tammann in cipants enjoy& in the services providd speakers kindly agreed to stay for an a lively talk given in his typical, unmis- by the kitchen. extra day or two so that the students takable style. Judging by the feedback provided by the students, all of them got something out of their stay at the OHP, although tectunrrs subjects everyone differently according to personal kckgroond and inter& On be- H. Oakker (EN): Concept and Oeslgn d Optical Instnlments half of the students, we cordially thank J.-M. Lecantel (Nice): High-resolution Speckosoopy our numerous colleagues who in addi- S. Ortofani (Padova): Crowded meld Photometry tion to their usual workload and in many R. Relss (ESO): Charge-coupled Devises different ways have made essential con- a.A. Tamrnmn [Basel): The hl Extragalactjc and Cosmic Expanston Rdd tributions to what appears to have been M. VBron (OHP), D. Bmde (ESO): Data Reductlonfechnlques a successful summer school in the prac- R. Wilson (ESO): Modem Telescope Layout L WboWi (Hamburg): Low-resolutbn and Slitless Spectroscow tice of astronomical observing techniques. Visiting Astronomers (October 1,1W2 - April 1,1993)

Observim time has now been allocated for 3.5 rn-WIT mbsr 1992: Barblei et al. (2-007- Period 50 (October 1, 1992 - April 1, 1993). As usual, the demand for telescope time was October 1992: De Grww et al. (9-003- January f sS3: ZljlstmlLoup/Waiem/ again much greatw than the time actually 49K), Capacclol~/Pe~f~rini/Plotto/Amcio/ fiams/Omont/de Jong, Nota/Origlia/Ctam- available. Hanwn, D'Worlco et al. (2-013-49K), plnAeitherer. Andersen M. I./Jsnch-%Pen- The following list gives the namm of the Awpardi/ B~char/~u~~x,De Lappa- san/Jergensen, ~loAstrograph Naurnann/Ungruhe. Mathys/Landstrwt/L;tm/ Manfroid, Danks/ October 1992: Vidal-Madjar et al. November 799.2: Oblak et al. 17-099-49W, PenpraselCaulet. November 1992: Vidal-Madjar et &I. Peletier/Burltert, Baada/Kjeldsen/Frandsen, Katgert/Mazure/Oubath/ Le FBvre/Den Har- FWaty 1993: Danks/Penpraae/Caulet, et Grenon / Barbuy, Plets IWaters / Waelkens, December 1992: Vidal-Madjar aJ. tog / Focardi / Giuricln IRtw / Jones IPerea, Vincent / Hackman / Hubrig / Piskunw /Saw/ January 1093: Vidal-Madjar et d. Baa&/ Kjeldsen/ Frandsen, Katgert/Ma- Tuominen / Ryabchlkova, Nuasbaumer / Mur- wre/Dubath/La FBvre/Den HartoglFocar- set / Schmid/Schmutz, Rdpurth /hgo/Cal- Februaty 1993: Vidal-Madjar ei al. di/Giuticln/Rhee/Jones/Perea, Baade/ vet /Pedrosa, Gredel. March 1993: Vidd-Madjar et al. KjeldmlFrandsen. March 1993: Gredel, KiIrsterlHatzesl December 1992: Baade/Kjeldsen/Frand- Cochran /hnerl/ Diibminer, Benvenutil sen, G&el/Richtler/de Boer/Roberts, Porceddu. Jorissen/Mayw/Morth. North Pakull/Beuermann/Motch/Sehaeidt, t)e Monaihrladilo/Molaro/Cenhrrion, Vladilol Rulter/Lub, Turatto et al. (4-00445K),Au- Centdon/CAssola, Mathys/landst#6t/ 1.5-rn Danish Telescope gusteijn/van Paradljs/van dsr Klis. LanziManfroid. Ocfohr 1992: Mayw et al. (5-001-43K), Jmuary 1993: Augustsijnlvan Pamdi]s/ MordsMm, J. Andersen et at., Jorgensen et van der Klis, Bomans/van Rossum. al., Nissen/Schuster. February 1993: cfe Winbr/ThB, Pettersson, 1-m Photometric Telescope November 7992: Nlssen/Sehuster, Surdel DBttmar/Garcia-Barreto/Combes F./Kori- et aI. (2-003-43Kj, Pagel/Copetti/Schmidt/ October 196M: Rmdi&/Gratton/PalIavi- balski, West M. J./Schombert, Lagerkvist/ Castaneda, Rlchtler/Gieren/GMel, Hunt/ cini/Pasquini, ManfroidlVreuxlStefken, Sil- Dahlgmn/ Wllliarns/Fitzsirnmons. Wicenec/ Malkan /Rwh/Spinogllo, Ri&ter/Capac- vottl / Bartolini / Guamieri / Ficcioni / Stan- Snijders. cioll/ FemrioIThanert, Oanzlger/Bouehet/ ghellint, Barwlg/R&mers/Mantet/HIfner. Gouiffes / Lucy / Frenssan / Manall / Della March 1983: Wlmnec/Snijders, Oblsk el November 199.2: %wig/!?eirners/Mantel/ Valle, Longo/Busareflo/Rlfatto/ Riehter/Ten- al. [3-009-49K), Relmers et al. (2-0!4-45!4, H#ner, Jou~lnde Muizon / d'Hmdeeourt/ jes, Wamn / Loveday / Williger / Meller, AlcalB / Wichmann / Krautter / Covlno / Puget, Goehermann/HBppner, Gmhermann/ Vidat-Madjar et al. Schmitt/Zinnecker, Turatto et al. 14-004- HBppner, Bouvler / Cabrit / Fernand- / Mar- 45K), Fesrari/Bucciarelll/Massone/ Koom- December fM2: Vidd-Madjar d at., Sdej / MaHhwb / / Terranegra, Bahierl neefl laskerlb P~Ie/Pastman/Siciliano/ tin Cbvino et al. (2-003-43W,NordMrn/J. Andersen et el al. (2-007-434, ThB/de Winter/van den Lattand/Pi&i. al., Clausen et al., Jeneh-S~rensen,Clausen Aneker. et at. December 1992: Thuds Winter/van den January 1993: Surdej et al. Q-003-43W. SEST Ancker, kust/tagrange-Henrl/Ferlet/Char/ Danziger / Bouchet / Gouiffes / Lucy / Fmna Octobm 1#2: Knee/Mezger, Tomikoski, Weuil IVidal-Madjar / Foing / Gry, Liller / Al- son/Mazmll/Della Valle, Damlger/Camlb, caino/Alvamdo/ Wendemth. Valtaoia, Olofsson, Fuller. Moffat / Leltherer / Drissen / Hubeny / Langer / Nyrnan, January 1993: Couwoisler/Bwehet/Ble- Nota / Robert / St-Louis / Schmutz, West / November 1992: Combes F., Casoli, Dan- &a, Pallavlcint/Halsch/Schmitt/Pasquinl/ Hainautl Marsden/Smette, Surdej et al. ziger, Boulanger, Cox, Lemke, Chini, Omont. Randich, Guglielrnd Epchteln/ Bertre, (2-003-43K), Duquennoy/Mayor. Member 1992: Orgura, Valtaoja, Nyman, Catalano F. A/Lmne/Kmll, Courvoisier/ February 1993: Duquennoy/Mayor, Mer- Haikala, Olofsson, Booth, Knee, Undqvlst, Bouchet/Blecha. rnilliod/Mayor, Rasrnussen/ M. I. Andersen, Olofsson, Wolstencrofl. Kjeldsenl Frandsen, Jsnch-&armsen/ M, I. Fsibnrary 1993 Couwoisier/Bouchetl Januw 1993: Wlkllnd, Galletta, Becker, Blecha, Relnschl Bauermenn/ MotchlPakull, Andersen, RasmussenIM. I. Andemen. Horellou, Cameron M., Olmi, Roueff, Henkel, GIeren/ Moffett / Barnes, Di MartinoLZappalA/ March Wael kens/Mayor, ,lorissen/ Hrm, Israel. ManardBlanco. 1QH: Mayor/North, Ardeberg/ Llndgrm H. /Lurid- February 1993: Wiktind, Tmikoski, Valtao- March 1993: Di Martino/ZappalB/Manara/ stroam, ArdebergILindgren H./LundsWm, ja, Olberg, Harjunpa, Qlofsson, Harju, Sahai, Blanco, Oblak et al. (7-009-4910, Alc&/ Danziger/Bouchet/GouMa/ Lucy /frans- Bergman, Iwine, Olofsson, Rydbek, Knee. Wichmann / Krautter / Covlno / Schrnjd / son/Maz?ali/DeHa Valle, Caon/D'Onofrio/ Zinnecker, Couwoisierl Bouchet/ Blecha, Al- Capaccioli, Tanuediltindgren M./ Rickman/ March 1993: Wielebinskl, Danzlgw, Hen- cal8 / Wichmann / Krautter / Covlno / Schmid / KarnBI, Fusi M/Cacciari/BragagLla/ nhg, Krtigel, Dahmen, Wau, Water, Leone, f inmker, LagerkvistlMagnussonIErikson. Ferraro/Caretla. Loup, Omnnt, van der Hucht, Kastner,

8-1 Figure 2: The V vs. 8-1 dour-magnitude diagram for NGC459Q (Ahino st ab, IW).

reasonably reliable distances and Inter- Then came chargs.coupled devices a range of over two orders of mag- stellar reddening$ for these objects. (CCOs). Suddenly it became possible to nitude. FortunateIy, VandenBerg and Also, approximate metalticities could be carry out photometry with substantially Bell (1085) and Demarque and his col- determined. This work culminated in the higher precision owing to the stability leagues have carried out the calcula- publication of the book, Atlas of Galac- and the linearity of these marvelous de- tions needed to predict the location of tic Globular Clusre# wjth Colour Mg- tectors. especially at bw light levels. isclchrnnes in the tonger wavelength nitude Diagrams (Alcalno 1973). Also, the sensitivity range extended be- bands whew there is much less metallic The early photometry was carded out yond I micron making it possible to absorption than in the blueviolet. arduously In several steps. First, a do- work with ease In more colours than Other advantages are realid by zen or so stars were measured photo- and V which had been the workhorse working into the wd and infrared: an electrically (UBV usudly) covering as wavelength bands for many years. enlarged colour baseline results which wide a range of mlour and magnitude One of the weaknesses of the BV enhances effects seen less clearly and as possible. Then photographs were ta- system is that metallic line absorption In less accurately with a smaller range in ken and star images measured with an the blue and violet can be signEcant, colour, Additionally, observational un- iris photom~tersuch as had been de- especially for metal-rich clusters. The certainties are reduced by having sever- vetaped by Cuffey and which had been inteqmhtion of observations In the al Independently derived colour-mag- loaned to us by ESO. On some tele- context of stellar evolution theory rests nitude diagrams of the same cluster. scopes a thin-wedge prism could k heavily on model stellar atmospheres With the separate evaluations of the age placed before the objective thereby pro- which must correctly predict the effects of a single cluster, one not only can ducing a second, much fainter image of of this metallic absorption in stars where assess more reliably the accuracy of the each star. Thus, in a boot-strap manner, the metalllcity Is aften not well known. It final result, but also can deriveages with the relatively bright photmlectric se- should be emphasized that the metal- a higher precision than attained previ- quence could be extended to fainter Ilcity of globular clusters. usually ously or with only two colours. magnitudes. expressed by the parameter Ir;e/tl] has Since the mid-1980s we have had The majority of our cluster data has been collected with either the 3.6-m, the 2.2-m (Max-Planck), and the 1.54-m te- OPEN CLUSTERS lescopes at ESO La Silla. Much of the recent observing and reduction work NGC 183 M67 has been dons expertly and efficiently by our colleagues at the Institute, Frank- * + lin Alvarado and Erich Wenderoth. Be- sides being now very well known and highly respected at La Silla, they have 47 Tuc often assisted others in the sopllisti- - cated data reduction techniques available to visiting astronomers. To date we have published multi-col- NGC 6362 our results for the galactic globular clusters NGC 104 (47 Tucanae), 1851,2298, - NGC 2808 GLOBULAR CLUSTERS NGC 1261 2808, 3201, 4372, 4590, 5139 (Omega NGC 3201 Centauri), 5946, 6121, 6362 and 6809. NGC 1851 We also have accumulated data for M4 a NGC 2298 large number of Magellanic Cloud clus- - ters. In all we have published over w Cen 100 articles in Astronomy and Astro- NGC 4372 NGC 6809 physics, the Astronomical Journal, and the Astrophysilcal Journal. One of the most significant results of this on-going research programme is shown In the accompanying figure HALP COLLAPSE where we have plottd the age versus metallicity of the galactlc globular elus- ters that we have analysed plus these same quantities for the two oldest known open clusters, M67 and NGC188. It can be seen that the ages derived for alle these objects are 16*2 Gys; hence it is still an open question if the time scale of the galactic coltapse AGES (Gyr) was brief or as long as 4 Gys. These ages set a lower llmR for the age of the Figure 3: The age versus metaIIIcity of the galactk globular clusters that we have so far anam, plus thme same quantities for the two old& known open clusters, M67 and Universe and an upper limit fw the Hub- NGC ISg, N can be seen that the ages derived for all these objmts are 16Y2 Gys equivalent to ble constant of H, = 61 * 8 km s-' H, = 61 2 8 km s-' ~pc-'(& - 0). Mpc-I , assumlng q, = 0.

underway a programme of BVRl pho- tomtry of globular clusters using CCDs and the excellent reduction software (MIDAS-INVENTORY) provided by ESO. For 8ach cluster, and using most often the ESO 1-metre reflector, we set up photoelectric standards in the same cluster fields that we intend to observe with CCDs. Thus, the effects of lnaccu- rateIy known or varying atmospheric extinction are totally avoided, and errors that might arise from slightIy variable exposure times are eliminated. Pahaps most importantly, valuable large telescope time is not wasted moving back and fwth between widely separated fields.

Figure 4: ESO Director General Harry van der Laan (r.1 with Dr. and Mrs. Uller in front of the dome housing the a2-m Schmjdt camera in Viha del Mar. group, and she in turn persuaded Liller to measure orientations of another curiostty of the island, the "sun stones" af Orongo. These initial and totally unexpected adventures whetted Liller's appetite, and together with his Chilean wife Matilde, he began a detailed study of all of the more than three hundred temples on the island in order to discover if some had been designed to be used as astronomical observatories. Several had been considered earlier, but Liller's more thorough study led to the conclusion that over a dozen - perhaps as many as twenty - temples had been intentionally oriented with rislng or setting solstices or equinoxes. The question henarose as to whether simllar results would be found elsewhere in Polynesia. Between 1987 and May 1992 the Lillers have travelled to a number of islands In the vast expanse of the Pacific Ocean twenty so far trip , ". LI,,wI a,lU ,, ,- , -.&.. , "chrnidl posed in front of a moai haad and altar - - platform on Easter Island. frequently made possible by support from the lnstituto Isaac Newton. Of all the monuments measured to date, the best candidates for structures intention- The Vliia del Mar Nova Search mnomy. Two additional novae were ally oriented astronomically are the found in the Large Mageltanic Cloud, massive tritiihon, Ha'amonga, In Ton- In April 1981 the late and highly wc- one of them, discovered in April 1991, gatapu in the Friendly vonga) Islands, cessful comet and nova discoverer, becoming the brightest nova (visual and several long alignments of standing Minoru Honda, discovered a seventh- magnitude 8.7) ever recorded in the stones on Aitutaki in the Cook Islands, magnitude nova In the southern eonstel- LMC. Liller (1 991) has analysed the re- reminiscent of those found In France's lation of Corona Australls at a declina- cent discoveries of galactic novae and Brittany. The hollest of ancient Polyne- tion of -37 degrees. His latitude in Ja- estimates that on the average, each year sian shrines, Taputapu'atea on Rai'atea pan was 33" North; Vifia del Mar, Chile, in our Galaxy, some 75 & 25 novae in the Society (Tahitian) Islands, and is situated at 33" South. Consequently, occur, considerably more than what Arp Llller decided to take advantage of hls once estimated for our near-twin galaxy, far more advantageous location and de- M31 in Andromeda. vote spare evenings to patrolling the The recently Inaugurated search for rich Southern Milky Way using nothing supemovae in nearby galaxy clusters more thm a store-bought Nikon produced its first find in January 1992, a camera. thirteenth magnitude Type la SN in the This project has since grown into an SO/Sa galaxy NGC 1380, a member of extremely frultful search programme the Fomax Cluster. In late 1991 the and has expanded to include the use of Schmidt camera was equipped with a a 0.2-m fA.5 Schmidt telescope on in- CCD detector, and Uller has now bgun definite loan from NASA. (As mentioned to patrol the hundred or so nearest and above, Liller had set up an observing most massive southern galaxies not lo- station on Easter lsland in 1986 and cated in clusters. Wih the CCD Liller employed this Schmidt to photograph can also do more precise photometry of Halley's Comet). Today, the same Nikon novae and supemovae, thereby adding camera is used to patrol the Milky Way; to the scientific output of this humble the Schmidt is employed to photograph annex of the lnstituto Isaac Newton in on a regular basis the Magellsnic Miia del Mar. Clouds and several clusters of galaxies. All the equipment is mounted perma- Polynesian Archaeoastmnomy nently next to Liller's home in a small dome financed partially by the Instltuto Shortly after Liller arrived on Easter and partially by a grant from NASA. Island in 1986 the dlstingulshed ar- Many of the photographic supplies have chaeologist and Governor of the island, been kindly supplied by the Director Don Sergio Rapu Haoa asked Llller if he Figure 6 The &mimI/y&nted moai at Williams of the Tololo In- would measure the orientation of Ahu R.E. Cem th EerernonAal centre of Ahu Huri A Urenga terametican Observatory. Nau Nau, the rnagnifioent ancient stone on Easter Island. The statue lddks almost As of July 1992, Liller has discovered temple (with several collosal statues, or precisely in the dlrecion of the rising winter or co-discovered 15 galactic novae or rn-4 that Rapu had recently restored. sdstice and a sharply peaked hiN in the dis- nova-llke objects, more than any other By chance, archaeologist Dr. Georgia tance. Chilean metBOrdogisf Ju!b Duarte (at single person In the history of as- Lee arrived a few days later with a tour right) worked wiih libat this sf&. sevd similar temples in neighbouring on Earth, wmto have had a special Islands share a common orientation to- desire to record fundamental directions. wards a rising declination of -9". Perhaps the sun rose at that declination Refwences on the date of a since fomotten holv w G. Alcaino, W. Uller, F. Alvarado and E. Wen- deroth: 1990 Astron. J. 99,1831. But of the several hundred temples G. Mno: 1973, Atlas of Galactic GlobuAsr in Polynesia studied so far. Clustm with Cotour Magnitude DIagmms. few, If any others, appear to have an Unhs Catbllea de Chite. W. Lilk 1990, "Orientations of Religious md :A ... * astronomical connection. (See hller , ,# ,::t;, 4 Ceremonial Structures in Polynasla", paper ,, , 19901. The people of Easter Island, I.,. .' called the most remote inhabited island deli4at the Thlrd lnternatlonal Confer- ence on Archaeoastronomy, St. Andrews. Sootland, U.K. W. Ullsr: 1W1, "The Viiia del Mar Nova Search: 3982-1Q9lm,paper delivered at the Workshop on Cataelysmle Variable Figure 7: Erfch Wendemth (standing) and Sim, Vim del Mar. Fmnktin Alvarado analyslng CCD data at the D.A. VandenBerg, RABell: 1985, Astmphys. J. Suppl., S8, 561.

Sporty ESO 7he victorious €SO Teams are fear& by the competifors! No, this is neither th@translation of a phrase in a Latin reading book, nor does it refer to the technotogical and sciwntific achievements of our organization. It describes how sporty ESO staff members have repeatedly destroyed the common myth that astronomy is the realm d dd men who stumble over long and white beards! Football has always been one of our strengths and ESO teams on two continents have taught their advemries many a lesson. ESO-La Silk tennis players are reputed to have the Wtest serves above 2300 metres, and long-distance ESO- runners have been seen on many a mdin Chile and Germany. Bicycling, that noble art ofecological propagation, is in the coming, and €SO people are among the pimeem. At the ESO Headquarters just outside Garching, more and more of these elegant machines are seen, shining in all mlours and In a great variety of shapes. Concerned car-drivers [a few are still left) have noticed an increasing spill-over onfo the sparse parking space. New speed records are being set during the early morning race fmGarching to the ESO Headquarters. And there are unconfirmed rumours that some &SO staff members spend an important part ofthelr free time, riding along the beautihl mads in the hi/& Bavarian countryside. But nowhere has the impact been so great as in the 4th region of Chik! Read the following stow to Ieam how the ferocious La SiIIa mntainbike team conquered the hearts of the Chitean public, won (almostj all of the honours at Tololo, all while ~presenthgESO in the best possible way. Racing up (and down) the mountains in the dty Atscam deserf, they haw shown the world that at €SO power, transmission and response refer to more than telescw and CCD's. Because of the international nature of our organization, the International Astronomical Union some years ago decided that ESO astmnom~tsparticipating in international IAU meetings may be registered as belonging to '%SO: rather than to a particular country. It Is at this moment not known whether the lntmtidnal Olympic Committee will follow this example, when the first €SO athletes show up. . . and what about the anthem? Another Aficionado

The Other Face of La Silla THE ESO AFlCIONA DOS

There used to be a time when driving ago, this activity on the present scale is It all started with the arrival of the a ear up to La Silla one would hardly new for La Sitla. So what's behind the rnountalnbikes in Chile. As a robust and meet a living soul, and the only occa- display of these hairy legs? A sudden all-terrain version of the traditional bike, sional obstacles of appreciable size increase of Interest in a healthy pastime, a mountainbike is particularly well suited were some donkeys. Not anymore. Sev- or does It go further than that7 to wheel on unpaved roads. Although etal La Silla vlsitwa and most of the La The answer is in fact better known by the unpaved parts of the access road to Sil la staff have lately seen cyclista on the the amateur cyclist of the 4th Region In La Silla are among the best maintained local roads, any time of the day, and Chile than by many of the €SO staff and of Chile, they are still unsuitable for golng quite a bit faster downhill than visitoas. Since about a year and a half race-bikes with narmw tires. Hence uphill. ago, these €SO mountainbikers have some of the ESO personnel with interest Although a solitary cyclist could be won all competitions that have been or- in biking brought such a mechanical obswved here and there already years ganized in this area. piece of art up to La Sllla, and a couple about 30 volunteers made this day a real treat. Now on their own territory, ten ESO pedallers participated. The success of the organization itmtf was fully cornplernent;ed by the results of these racers: again Hans Gemperbin comfortably first, Luis Wendqass second, EIjc Allaert third, Walter Rosenfeld seventh (and first senior), Andrea Moneti eighth, Eduardo Matarnom eleventh, Bruno Altrwl sixteenth, WuEudo Ro- bledo twenty-second, Ricardo Otto tfiir- ty-third and Rainer Donmkl thltty- eighth. Many of the outside participants stlll talk wonders about the organization of thls event, where "nothing nor no- body was left unattended*. Which is not surprising conslddng the effotts of the organizers and the support of the ESO management. But success has its price: if you want ngm i: sfad of 70 cyclists at the gate d Cetro Tobb Intmmerican Obsewtory. Photos I to keep it up, you must do something for and 2 by Claudi~Rsforga; photos 3 and 4 by Nelson Muiior). it, 1.9. keep on training, more, longer, harder. That didn't seem to bother many of We iron-horse enthusiasts. €specially not during Chiteen summer, when the after-work training consisted in riding to of them actually staMd using R a few miJion for the organization of a similar La Frontera, to have a cold beer and a tima week. A similar situation was event on the ESO premises. sandwich, w to the world-famous teb seen in other parts of this country, phone booth in Cachiyuyo. And the good results kept on coming: Luis Wm- abounding with dirt tracks, and espe- The La Silla Continuation cicllly also in Tololo. degas$ won the 1st La Serena mountain It didn't take too long to convina tbe race (August 1W1), Hans Gempedeln decision takers, and off went the sports the 1st race to Andacollo (November The Tolola Experience commission to organize this went. 1991), Eric Allaert the Cendyr circuit in Things became a little more serious in Followed many letters and phone calls La Sma(February 1992) and the 1st the beginning of 1991, when Tololo peo- pleading for spomship, collaboration race Vicufia - El Pangue march 1992). ple tal ked about organizing a blke-race on and/or participation, meetings to set up DIGEDER, the sports department of the the Tololo roads. The original rdea came regulations and the like, 'fV interviews, Chilean government, awarded Hans from Bob Willlams, director of Tololo and text processing of all documents, etc. A Gemperfein as the best rnwntainbiker in lifefirne Jqger.More than a real race, he lot of manhours later, on the 20th of 1991 far the fourth region. saw It as a personal challenge for all the Woba 1991, La Silla opened its doors So what about the second race to participants. Induding htmdf. Knowing for its biggest non-astronomical event Tololo? Postpond for the absence of how tough an exercise this is, he stated: ever: 60 cyclists, 120 companions, and its inventor, Bob Williams, and en- "This la where the realmen are separated from the ordlnwy guys". He couldn't know then that also women would parttcl- pate, even some of his own female em- ptoyees. Mere are you, ESO girls? Not exactly unfamiliar wlth this type of road, six ESO cycllsts quickly Inscrlbsd for this test. At the time of the event, end of April 1891, some of the ESO partl- cipants had been rlding a mountainbike for only a week or so. Which was of course'st~~~a lot better than most of the 55 particlaants. The 34 km me, from the-TOIOIOgate up to the top of the I there is some work to be done on La Silla!

Citius - Attius - Fortius The story does not end here yet. The sports commission already started to organize the second ascension of La Silla, after getting an informal approval from the management. Keep your thumbs up for the end of next October! Most of the more conventional articles in the Messenger end with acknowledgements. This one is no exception. In their constant effort to offerheal- thy and active entertainment on La Silla. the sports commission would like to ex- - press its gratitude towards the ESO Figure 3: The (unquiet)ESO bike team just before the start of the La SiNa race. management for its continuous support. Of course we should not forget the main actors of these events, i.e. the fine sportsmen who defend the ESO colours also when the subject is not astronomy, dangered by El Niiio - a periodic Pacific tougher than ever, and the distances and their colleagues for the encourage- ocean stream spelling rneteoro!ogical between the participants are vanishing. ment. Also thanks to alt the car drivers disaster - this race was finally So do not take it for granted that ESO who take care and slow down on the La scheduled for the 21st of June 1992, racers will keep on winning for ever. Silla roads, because there might be a Expectations were high from many After all, between the training sessions cyctist just behind the next curve! sides, as ESO racers had better-than- ever preparation, but at the same time were looked at as the ones to beat.

Tololo Again! The night before the big event, again morning towards Vicuna. At the Tololo metre above the 70 mountainbikes. Now with experienced organizers and per- fectiv assisted bv Jorne Santana and ~oberto Rojas k an- ESO carry-all (thanks, bass!), the ESO racers had no one to blame in the case of a defeat. Nobcdy really worried, as Hans had said

he was "feeling pretty good", quite opposite to all the other races. Where he LFigure 4: The (smiling winners at La Si ,,a+ had won anyhow. Halfway it didn't look bad at all with 3 racers a few minutes ahead: Hans, Eric, and - wait a minute - an unknown guy hanging on the rear wheel of Hans. Half an hour later Eric had to let the two other ao: "Either 1 hook off and get up there, ;or I hang on and drop dead 1 krn further." This Alive and Kicking into the 90's scenario continued until about 250 m before the finish. In a spectacular sprint Hans left his opponent 20 seconds be- During the past decade in Germany, ciently and successfully, besides giving hind. He finished exhausted in about 10 ESO has established for itself a reputa- a lot of fun. minutes less than last year. When asked tion of a dynamic and successful organi- Some of the matches against the how he felt, he barely lifted his head to zation, with a relatively young staff of strong team of the Universitats-Stern- see who dared to ask him such a mis- highly motivated people. Apart from the warte Miinchen, led by its powerful di- placed question. Eric came in third, astronomy field, this found confirmation rector R. Kudritzki, have not been re- 4 minutes behind Hans, Walter 4th on several occasions on the Bavarian corded in the Annual Report of the Or- (I 1 min), Luis 6th (12 rnin), Eduardo 8th football fields. The ESO team integrated ganization, but are part of the legacy (19 min), and Bruno 19th (42 min). Al- the best of the different national styles that we are passing to the future ESO though a real fine result, this one was and proved that this can be done effi- generations, together with EFOSC, the NTT and the quality. - of the food in the La Sllla cafeteria. Entering the Ws,we started to fear that the driving core of tl-ta team was softening with increasing age, that motC vations were on the low side, that new arrivals did not integrate in the possibly obsolete working schemes in short that we might not be up to the new challenges that ESO is facing. I On a hot Saturday in July. on the Max Planck field in Garching, an €SO team wlth a shaken self-confidence and an average age dangerously approach- ing 40, entered the ASTRO CUP, a one- day mmpdtion wlth the teams of our neighbours and friends of the Max Planck Institutes fiir Astrophysik and fiir Extraterrestrische Physik and of the Obsewatory of the University of Munich. At the end of the day, after four strenuous games where w scored 5 I I L- 4-11 r WIW JW-~~~~~Lvrllpmm - "--", Ulrl rC1 Iw nmua, ". goals and suffered 2, we stmd as Gouiffea, a visitof to ESO, E. ZoN (a friend from NW,A+ W~ltander,E Koeh, J. -tie; baHered but winners with cup b0tlom: L Noethe, Zigmnn, BB,belabre, & D'm,#. mttn*,#. 6asbiItr (ofher team at our feet and glases of ext3ellentmmbm not includ& in this pictwe: B. Buzzoni. D. Chittim, A, van Dijs~~Idonk,G. fishw, P. Fmnpis, 8. Jevgensen, P. Mellm T. and R. Wannets). Bavarian beer in our hands (both cour- Oostedm tesy of the sponsor CONVW). We might well lose the Cup next year to one of our excellent contenders, but we are satis- have energies to spend when needed. tivities of the Organiratlon, but it does fied to have proved this time that we are We are too realistic to claim that this not hurt to secretly play with this feeling. not at our wit's end and that we still victory is a good omen for other ac- LongliveESO! S. D'ODORICO, ESO

Astrometry with ESO Telescopes A Contribution to the Construction of the New Extragalactic Reference Frame Chr. DE VEGT, Hamburg Observatory, Germany

Astronomical research is strongly de- be presented to the IAU during the 1994 history, but only in the last decade the pendent on the availability of a unique General Assembly in The Hague. practical realization of this concept be- all-sky reference frame though most as- came feasible through the mature tech- trophyslcists do not explicitly take nique of VLBl radio astrometry. notice of this complex astrometric 1. Main Properties of the New Using a global net of suitably distri- problem. Reference Frame buted radio telescopes, positions of However, the necessity of very pre- these primary radio sources can now be cise pointing of new generation large Contrary to the present fundamental determined in a routine way to milli- telescopes from ground or space and system which is based on the positions arcsecond (mas) precision and an abso- the unambiguous identification of very and proper motions of bright stars - the lute global reference frame can be es- faint objects in all spectral regions ac- basic FK5 contains 1535 bright stars -, tablished and maintained for the future. cessible from ground and space, in par- the future extragalactic system will be At the same time the high angular ticular in the radio and infrared region, based primarily on the positions of a resolution of VLBl provides comprehen- has sensltired the astronomical com- carefully selected small number of corn- sive information on source structure and munity to this problem. pact extragalactic radio sources;almost their temporal changes with sub-mas During the IAU General Assembly in alt of these sources will display optical resolution. Buenos Aires a resolution by the Work- counterparts, mainly quasars and BL A second group of objects is of equal ing Group on Reference Systems has kc's but also some compact galaxies. importance for solving this problem; been adopted (IAU 1992) which de- This choice is based on the generally namely selected radio stars, the cm scribes the properties of a new, inertial, agreed assumption of cosmic distances radio emission of which has to be strong extragalactic reference frame and a new of these objects with the consequence and steady enough to be measured with intercommission working group has of negligible proper motions and there- mas precision by VLBI, the VLA and been established to provide a practical fore fixed space directions for a long future VLM-net on a routine basis. solution within the corning three years to period. This idea already has a long Absolute positions, proper motions trornstric history is therefore included in the programme stars: for a recent over- view see (A & A, 1992). Thus the HIPFARCOS mission will provide automatically a homogeneous and fairly dense stellar net of about 2.7 stars/sq. deg., maHy in the magnitude 0 Quasars BL- Lac 373 Intmal 7-1 0 (see Fig. 3). Furthermore, the Tycho Mission will 100 add some 500,000 falnter stars with precise photometry although reduced astrometric accuracy. However, If we re- call for example that already the AGK3 on the northern hemisphere and the CPC2 on the southern hemisphere provide stellar densitlee of r 10 stars/ sq.deg. it Is obvious that the HIPPAR- 50 COS net shoutd swn be made denser and extended to much fainter limiting magnitudes by further catalogue projects to keep up with the needs of large tetescopes with their small-fleld, highly sensitive area detectors.

2. Linking HIPPARCOS to the VLBl System

Figure 1 : Magnit- distributbn of 4M radio mum for the Extragalactic Reference Fmme. The rigidly constructed HIPPARCOS stellar net still may contain a small unknown rotation of some madyear which will be reflected in the HIPPARCOS and parallaxes of those stars are ob- any previous fundamental catalogue, proper motions. After this residual mo- tained than in the primary extragalactic provided R can be linked in a unique way tion has been taken out, the HIPPAR- frame. At the same time these galactic to the VLBl based prZmary reference COS net will be adjusted to a fixed ori- objects can be easily accessed by opti- frame. gin, close to that of the FKUJ2000 sys- cal astrmetry because of their bright- Thus a multi-step approach is tem. Because none of the VLBl primary ness thus providing a natural link to the necessary for the construction of this sources is observed by HlPPARCOS di- optical spectral region. new reference frame, on the other hand, rectly, a number of indirect approach While being optimal candidates in the dealing again with stars which will re- has been worked out to provlde the Itnk radio domain, the primary swrces are flect kinematically their gatactic origin to th inerthl (rotation-ffee) extragatac- not vwy suitable to work with In the and the earth's and solar system's mo- tic system (see Table 1). With a view to optical spectral range directly. The tion, precise proper motions (p.m.) and the ongoing problems with HST, several reasons are obvious: firstly, the faint- parallaxes Rave to be determined. Be- ground-based, large observing pro- ness of their optical canterparts (most- cause of unavoidable systematic and grammes are undwway to provide thls ly beyond 18th magnitude, see Fig. I), random errors in this prom,the stellar link. (Fmchle and Kovalevsky, 1982; which requires large telescopes for ob- net will deteriorate substantiatly as a A & A, 1992; de Vagt et at., 1991). sewation, the astrometrically usable function of changing epoch. To maintain However, whereas the extragalactic field of which is << 1 degree, with an the initial high precision of the HIPPAR- VLBl net does not display a net rotation additional dramatic decrease of usable COS net and to improve the precision (2 because of the inertial nature of Its field size when CCDs are used instead mas/yr) of the HIPPARCOS proper mu- target objeEts, f he zero point ofthe R. A of the photographic plate. Therefore the tions, future astrometry satellite mis- system has to be adjusted, because object of interest and the reference aims are indispensable. Furthermore, a VLBl provides only R.A. differences, al- frame sources have to be very close in continuous improvement of the main as- though absolute declinatlorw. kd- the sky, e situation which will allow only tronomical constants as for example ing to the quoted IAU miutlon, the vsty occasionally to link any other object precession and nutation are of crucial R.A zero point shall be adjusted to the directly to the primary reference frame. importance to maintain a high-precision FK5/J2000 zero point at epoch J2000. Secondly, there is no redistic measur- reference frame. To achleve this goal, precise optical po- ing technique presently avallabb in the Although the selection of the abt sitions of a suitable subset of the radio optical domain to determine object po- 120,000 HIPPARCOS programme stars sources have to be determined in the sitions relative to these very faint prlma- was based primarily on astrophysical FK5 system. Furthermore, the physical ry sources over large arcs, contrary to proposals, the smning principle used nature of the radio and optical emission the radio. Therefore a practical reaIira- by the satellite and the requiremmt to and the morphology of the sources have tion of the new reference frame must be monitor continuously the satellite orien- to be studied in detail to ensure that the based in addition on a dense, global net tation by a large set of so-called star- optical and radio emission centres will of fairly bright stars. At the same time mapper stars forhrnately had the eonse- coincid to the precision of the VLBl this net should be of comparable preci- quence that the selection of the pro- measurements, Le. wlthin mas. At pre- sion with the radio positions. The antici- gramme stars had to be made as unl- sent, knowtedge is lacking in this re- pated HIPPARCOS stellar net wlll be the formly as posslbte on the sphere. A spect, therefore the number of objects natural choice and will be superior to large body of stars with well-known as- and object types (quasars, BL Lac's, Figure 2: ~~of 413 &I soMees for tAe new ~mkt*ricRefemms Fmm.

AGN's .. .) should be as large as posst low catalogue density of about 1 star/ final HIPPARCOS-based plate solution. bte with the result that possible 30 sq.deg. will provide only a vanishing It should be recalIed here that most of differences of the emission centres in probabilrty to find a fundamental star In the IRS stars are already among the the various wavelengths will hopefully the telescope field (<< 1 deg. dim.) HIPPARCOS programme stars. average out. The same situation obvi- together with the target object and in ously will be met with radio stars, al- additlon no detector can handle the though here the source geometry is 3. Astrometry of Source Plates enormous magnitude differences, A Using ESO Telescopes easier to evaluate. multi-step approach therefow has to be Any successful link methad therefore used. In the first step we are using high To obtain high-precision &strom~ric must be a statistical approach, because preclslon wide field astrographa in both plates for the radio sources, we have no ideal objects do exist with point hemispheres to provide a dense system used the 3.6-rn telescope in the prime source properties h all wavelength re- of secondary reference stars in the mag- focus mode very su~cessfullyand cur- gions. nitude m, - 12-14. The primary refer- rently am using the ESO-Schmidt tele In our long-term programme to estab- ence stars to be used for the astrograph scope, because the 3.6-m telescope un- lish a VLB1-based reference frame plates solutions are taken from the fortunately is no more available for di- (Johnston et al., 1991; de Vegt ei al., AGKBRN and SRS catalogurn in the rect photography. Although both tete- 1991) we have bmn using long expo- northern and southern hemispheres re- scopes provide the necessary limiting sure plates to determine positions of spectively. magnitude and plats field size to compact radio sources from this pri- These transit circle based catalogues guarantee a sufficient number of secon- mary VLBl mt in the FK5 optlcaI funda- form the main body of the global IRS dary reference stars for the d&ermEna- mental system. Figure 2 shows the referen- -em and are transformed iion of precise positions of the target source distribution as presently to the IAU FK51J2000 system. source, the much larger scale of the selected for this reference frame. A sub- The reference stars are mostly from 3.6-m and the plane image field are set of these objects has already been the magnitude interval m, = 6-9 with an more favourable for precise astrometry used successfully for the orientation of a average densrty of 1 star/sq.deg. Both than the Schmidt, although #me accu- first high-pmlsion VLBl reference frame astrographs are used with a &mag oh- racy can be regained by averaging a catalogue. (Ma et al., 1W0). Although jective grating, therefore we can mea- larger number of Schmidt plates. How- the optical positions are less precise by sure first-order diffraction images of dl ever, concerning possible object struc- about a factor 10 (some 0.01 arcsec) reference stars together with their cen- ture and problems with crowded fields than the corresponding radio positions. tral images and also diffraction images there is no compensation for the favour- the large number of sources available of the 1-3 FK5 stars which offen will be able scal~of the 3.5-m telescope. (some 100) will allow to determine the in the astrograph field also. The plate R.A. zero point, also with mas precision. constants obtained therefore allow to 3.1 3.6-m Prime Foous dstromethc As Figure 1 clearly demonstrates, determine the positions of the sewn- Model most optical counterpahs are fainter dary referem stars very precisely In the than 18th magnitude. To link these ob- FK5 system. As a very important addi- The 3.6-rn was used with the 3-lens jects directly to the FK5 system is im- tional step we are measuring all red-triplet corrector whih provides a possible becawa almost all FK5 stars HIPPARCOS programme stars in the usable field of about 50 arcmin diameter are brighter than 6th magnitude and the astrograph field (about 80-100) for a and a flat image ptane, 24 x 24 cm, Tabfe 1. Mahr Fw~TB~~to llnk tb HIPP- #8t to b ExWgaLctIe Syst8n~ 3-2 Schmidt Plates Object M M class Technique Orientation Rowon Global astrometric modelling of ~adbstars VLBl <20 0 Ym W Schmidt plate gecrmetry is a malor prob- ViA ?ah mag- - nitude for practical mutposure ~0nditi~ns. Unfortunately a pmlse global reference star catalogue In thls magnitude range is 1-5-rnm thick Kodak 098-04 ptates have (standard coordinates XI, mA; plate sflll lacking, although definlte plans are been used. However, the corrector in- measurements x, y: unknown plate con- avallable but on hold -use of recent troduces a strong thirdsrder regular stants a, b, c, a, b, c, L, U, V; 1% 3rd- financial problems (de Vm, 1989, geometric distortion term which has to order distortion term, U, V compensa- last). b& taken into account in the plate tion for sera point of distortion). In our application we &e on& in- mode!, Asuccasskl application of thls model terested in modelling the central plate Furthermore, there Is no posslbllity to b only poselbk because d the large area of about I x I deg. As in the case- calibrate the intersection of the optical number of reference stem (50-100) of the 3.6-m, our swrn of secondary axis on the plate, therefore two additim- available in the plate fleld. Fdermom reference st- is perfectly suited for al terms for the zero point of hedlstor- we are only Interested in obtaining the this purpose, Because of the small size tion have to be induded. Because of the target pasttlon which Is at the ptate of the 3rdsPder twm and the r&rlcted limited field size and the position of the centre. The complete astPomIdc mod- fiJd size, a statistically signmeant d&w- target object very dose to the plate elllng of the whole plate fleld turned out rnlnstlon of the distoftlon zero point centre, a 6-constant affine plate model to be much more complex, because of terms is not podbta Furthermore, as (de Vagt, 1991) will be sufficisnt for additional 5th order regular distortSon practical experience has shown, even modelling diimtial refraction and and Imgular field distortions Increasing the third-order term can be pre aberration and the usual prawnonto to the fleld edge, In addltbn the distor- corrected rivitbt affdlng the position the tangentiat plane. tion terms depend an the position and of the central target abject significantly, The linearized plate mod4 therefore optlcal qualtty of the filter also. provkded the odgh of the mngulw 39: plate measurements x, y is carefully ad- XI-= +by +c +LX{$+YZ)-U(~X~+~)-V(~X~) justed to the plate centre a priori. ?3A= aix + b'y + c' + Ly($ + y2) - U(2xfl - VP+ 3f) The appropriate choice of th~plate model can he limited themfore to a &constant dine model, with a possible extension to the Srd-order term, if the geometty of the partbular Schmidt telescope is not well known at the bqin- ni~,or the adopted pIateflIter mbi- nation changes (see above-quoted model, wlthaut the U, V terms). In the omntSchmidt obsenring programme high quality plates for 29 sou- have already been obtained Normally 3 plates/ob]& are Wen using a 098-04*QG5513 emulsion-filter com- blnation. Plafes are unhypered, exposure times are 540 minutes each. All plates are measured on our modemlzed WF-MANN comparator whlch uses a CCD camera for dlrect image digitiza- tion (for detalls see Winter et &I., 1992). A measuring aawcy of 0.5 microns is obtained in routine operation. In addb tion, a new type of astmrnehic measuring machine is under development which wiH allow to digitize a complete Schmidt plate In less than 1 hour wlth 0 submimn accuracy. 6 7 8 9 1011 12m, As an example of our current work, results tsar the QSO 748+126 (m,- 173, Figure 3: Magnitude Distribution ofHipperms Programme Stm. z = 0.889) are presented. This primary refemnce frame radio source shows a parison polnts, as will be pmvlded by de Vegt Chr., Zacharias N., Johnston K.J., stellar appearance on the plates. Using our reference frame prwramme Is re- 1891, Adv. Spece. RB. 11,133. the quoted reduction model, a m.e. of quired for a more detailed conclusive Johnston K.J., Russell J.L, de VVegt Chr., unR weight for the plate solution of analysis. Zacharias N., Hindsley R., Hughes J., c0.1 arcsw: could be obtained. The fi- Jauncey D.L, Rwnolds J.E, Nieholm G., Ma C., 1931, Pmc. IAU Cdl. 127,123. nal FWJ2000 position, based on 3 Acknowledgements de vwt Chr., 1991, Astmph*. Space Sci- plates, Is erne ln,3 = P~OC.IAU COII+ 100. RA(32000) 7h 50m 52.051'; The author wants to thank H.E. +12' 6 Vegt Chr., 1989, Conference on Digitired DEC(J2000) 31 ' 04.84" Schuster and 0. Reipurth of ESO for Sky Surveys, Geneva Bull. Inf. CDS 97, Using the corresponding Vtsl posi- their continuous help with the observing 21. tion from (Ma et al., tQ90), the system programme. Flnanclal support by BMFT de Vegt Chr., Winter L, Zacharias N., 1992, diffwence In 'the sense "optical minus under grant 100001 8-3 (HIPPARCOS) is Dlgitked Qptleal Sky Sump = Astrophys. radlo" then is: gratefully acknowledged. Spaca Sc, Ub. 174, 115 (Kluwer hd. DAcWEC) = +0.073 ar~ec; Publ.). OOEC = M.01 arcsac References Wlnter L, da Vegt Chr. SMnbach M., Zacharias which Is in good agreement with earlier NU, 1992, IAU Inf. Bull. 87 (Jan. 1992), 7, N., 1W2,ibd. p. 123. results (Johnston et at., 1985) and the Resolution 4. Johnston K.J., de Vegt Chr., Florkowski D., recently quoted flrst prellmlnary results A & A, 1092, Asiron. Astrrrphys. 25B, No. 1, Wade C.M., 1985, A J. 90,2390. of a HIPPARCOS-FIG comparison tn (May I), speclat HIPPARCOS Vol. Ma C., Shafler D., de Vegt Chr., Johnston, that sky region (Undegren, 1992). HOW- Froeschlb M., Kwalevsky J., 1982, Asrm. K.J., Rusdl J., 1994 A J. 9Q, 1284. ever, a dense grid of some 100 corn- As&@@. 11689. Undegren L., 1992, ESA SP-349, in press.

The ESO Minor Planet Sky L. D. SCHIWADEL, Astronomisches Rechen-lns titut, Heidelberg, Germany

The European Southern Observatory The many thousands of observations It is interesting to note that in the very was established in 1962 to operate the at ESO have inevitably produced quite a near future ESO is likely to rank fifth powerful La Sllla observatory for the few discoveries. However, there is a long (behind Heidelberg, Crimea, Palomar benefit of many fields of astronomy and way from the detection of a new solar and the Anderson Mesa Station of Low- astrophysics. Only a few programmes system object until it can be definitively ell Observatory) on the list of the most were directly concerned with the survey numbered and named. The new planet successful minor-planet discovering ob- of the solar system and the discovery of has to be observed in - at least - three servatorles. In the ranking list of the minor bodies like comets and minor oppositions before it can be numbered. most successful discoverers of minor planets. In many cases, observations of Therefore, the majority of new detections planets of all times, Henri Debehogne these objects were made only as valu- remain in a "dormant" stage in the Minor now occupies the 13th glace - one able by-products of other campaigns. It Planet Center's computer files. In some place ahead of the famous visual planet was especially the wide-field tete- cases it is possible to identify new posi- hunter A. Charlois in Nice, who detected scopes, the 1-rn ESO Schmidt and the tions with planets observed earlier; this some 99 planets between 1887 and 40-cm GPO Astrograph, which yielded shortens the process. Nowadays, it is a 1904. an enormous amount of positional data. rare exception when a newly discovered The right to name a minor planet During the last decades ESO has always planet can be quickly identified with a essentially belongs to the discoverer. As maintained a leading position in the long series of prior observations. can be seen from Table 1, only a small world, as far as the number of minor The statistics show that until July fraction of ESO discoveries honours planet observations is concerned. 1992, some 186 ESO discoveries have ESO astronomers. This has to be done In 1988, Commission 20 of the IAU reached the status of "established", i.e. by other colleagues, and there are in established a special study group to elu- numbered, minor planets. Table 1 re- fact a lot of names which together con- cidate the meanings of minor planet cords these objects in ascending order stitute a kind of "ESO minor planet sky". names.Thls endeavour, which comprises together with the name (or preliminary While it is very easy to extract all ESO a lot of data for the first 5012 minor designation), the year of discovery and successes from the data base, it is near- planets numbered until the end of 1991, the discoverer(s). Whereas the great ly impossible to find among the 4,000 has now reached completion {L.D. majority was found by Belgian as- exlsting minor planet names those Schmadel, Dictionary of Minor Planet tronomer Henri Debehogne during spe- which have been accorded to ESO offi- Names, X+687 p., Springer-Verlag ,1992). cial surveys for minor planets, most cials, staff astronomers, etc. Since all information in this work has others ware found by chance, malnly The list in Table 3 gives all those been archived in a computer-readable with the Schmidt telescope, and during which are rnentloned in the book about data base, it is very easy to extract the various ESO atlas projects. A total of the ESO history, recently written by material which directly or indirectly per- 16 astronomers earned discoverer Adriaan Blaauw. Still, it cannot be contains to ESO. t have here used the data merits; they are shown in Table 2 to- sidered to be a complete compilation. It base and some recently published, addi- gether with the overall numbers of dis- shows, however, that it is not very ex- tional material to illustrate the "ESO coveries and co-discoveries (in paren- aggerated to speak about the ESO minor planet sky". theses). minor planet sky! Table I: DXsroverles of numbered minor planets made at ESO (2052)Tarnma 1976 R. M. West p673) Holmberg 1S82 C.4. ~srkvlat [2053) Nukl 1Q76 R. M. West (3610) 1981 H. Debehgne md (21 os) audV 1076HrESdWStW B. De DeI8 p115) lrakll 1976 R. M. West (36251 Francastom 1984 W. Fw& (21 18) Mtskhettr 1B76 R. M. West W1)Slgyn 1987 E.W.W (21 17) Danmak 1$78 R. M. West (3634) lwan lea0 C.-I. hgerlN1st (2146) 3- 1976 R. M. West (3646)1885 RK4 1W5 H. Debehqne (2146) Stentor I976 R. M. West 4367Q 1984 DT 1984 H. Oebehogne (2147) me 1976 R. M. west W89) ~auinmn 1W7 W. md~& lal4s) Ew 107%R. M. West (3705)1984 ETl 1984 H. I)ebehogne (21 87) ta Sllla- 1976 R.M. West (5740) Menge 1W1 H. D&ahoQnemd paw) schmadel 1977 H.-E. Schu- 0. De Sands (2275) 1 MH 1979 H.-E S&USW @778)RegW 1884 W. RW (23231 Orthos 1976 H.-E SefKlSter (STas) 1986 QM3 1988 H. Debehogne Q3M)Sailliar 1978 H. Oebehcgm (5820) 1984 DV 1884 H. Wogm P46l) Clad 1981 H. t)ebetrogneand (3821) 1985 RC3 7 Q05 H. Deb&ogna G. De Sands (5848) 1982 FH3 702 H. Debehogne (a5261 AlIsaiy 1079 R. M. West @W)IW7 DM IWH. Debehogne (2S43) MmWo IQB0 H. Debehagne (S866) 1988 AY4 1988 H. Debehogne [256t) ma 1979 0, Plzmand G. Pizarro (SW) 1988 BH4 1988 H, DeMwgne (2589) Daniel 1979 C.-I. Lagethist (98'PO) Mayrd 1808 E. W. Elst mso) Mourio 1980 H. oebehogne @871)Wz 1Q82R. M. West (2595) G~dlachvlll 1970 R. M. West (SBW) l9W PA 1W H.-E. SdtW g596) Vdnu Bappu 1970 R. M,West pal 8) 1981 QM 1981 H. Debehogne @see) sen- 7978 H.-E. Schuster pH9)19840s 1W4 H. Oebehogne (28x3)Losslgnot 1980 H. Debshogne 8m)mga] 1#6 R. M. West @W)Rno Torime 1879 C.-I. Lagwhist (9984) 1984 SB8 IQW H. Oebehogne (2707) Uml Is81 H. Mbehogne (4018) Sambm tQ79 H, hhhogne snd E R. Metto (2765)Dinant T98l H. Oebehogne and (403q 1B84 E01 1984 H. Oebehom Q. De Sanctls (4036) t 987 DM '1887 K Oebehogne Q7W Nsnm 1981 H. aebehogne and (4f!#) Kristina 1987 E. W. Etst Q. De Sanctls (40BO) WPYb '1987 E. W. Ust (27%) Lepage 1979 H. Oebekgne and E R. NMo (4061) Martell1 la88 W. Rrreri (2814) Viein t982 H. Oebehogne (4099)t988AB5 1988 H. hbehogne ma mm 1981 H. Dehhagne (4120) 1985RS4 1985 H. Debehagna (2902) Westerlund tQ80C.4. Lagerkvlst (4123) 1988 QPt lR86H.Oebehogn-a (2928) Caldelra 1980 H. Dehtwgne (418Q)Cel Jus 1QM C.-l. Lagerkvlst @=I Naefum 1876 R. M, West (4172) 1982FCS 1982 fl,DeMwp Psss)&etltO tg81 H. Debefwgne and (4191) 1980 H. Debefwgne Q. De Sanetls (4192) meher 1QSt H, D-ne and (3- Dekalle 1982 H. Debem Q. De Sandls (3m)1976 DD i970 R. M, West (4199 1983 RXZ 1989 H. Debehogne flaw ~~ 1979 C.-I. @&lst (4202) 1985 CB2 IQ85H.Da~e (301 6) Meuse f 881 H. Oebhogne and (4206) 1986 QL 1988 H. Dehhgne (31. De Sanetla (4210) 1887 DY5 1987 H. DeWtogne (3121) Tarnines i081 H, Oebehogne and (4211) 1887RT 1087 H. ~~ne Q. De -1s (4216) Neunklrchen 1988 H. Debbgne (3'138)Clnray 1g8O H. Dekhgne (4218) Demomi 1488 H. OeMogne (5175) Netto 1979 H. Debeftowe and E. R. NeHo (4252) i985 RG4 1485 H. Debekgne (32%) Metohior 1981 H. Debehogne and (431U) Wmholm 1978 C.-I. hgerkvlst Q. De Sanctls (4313) Bouchet 1979 H. bbehogne @see) t a78 PA 1978 H.-E. Schuster (4328)1982SQ2 1982 H. Oabehogns (3288)De Sanctb 1981 H. Debehpsne and (4334)1983 ROS 1983 H. Dekhogne (3. D8 SandlS (4942) Fmd I987 E. W. €hi (3271) 1932 RB 3982 H-E. Schuster (4344)BuHehude 1W EW.Elst 0274) Mlllen i#l H. Debehogne (4345)Rachmaninoff 19M E W. Bst (3288)S&~M~B 1982 H.-E Schuster (4349) Tlburclo 1989 W. Landgmf @wFWWi T981 H. Debehogne and (4378) Vdgt 1988 W. Lsndgraf G. Do Sanctis (4398) f B84 HC2 1ga4 W. Rmrl (33s1 ) KV~- I979 C.4, Lagerkidst (4443) I985 RD4 1W6 H. Debehopne RBcogne '1985 H. Debehogne (4444) I986 SA 1B85 H. U. NergrsaK1-Nletsen, (3374) Mamur 1980 H. Deb&- L Hansen and P. R. Christmn (3S8s) Skot 1W H. D&ehogna (4474) 1981 Q22 lg8i H. Debgtwgne (3390) Oemanet 1W H. Debehogns (4478) Bianm $984 W. Farmrl (3398) 1978 PC 1878 H.-E. Schuster (4479) 1985 CP1 tB85 H. Debehogne (UtI) Debemcourt 1980 H. Debehqne (4601) hrywtm 19W E. W. Elst (34W Darnmanget 1 gag H. Debehogne (4535) 1BM QV2 1986 H. Debehogne (3466)1985 RS2 1885 K Debehogns (4645) 1989 $81 I 1080 H. Oe-ne (3457)1985 RA3 1985 H. Debehagne (4546) Fmck 19gO E. W. EM @45f3) 1985 F1T3 1986 H. Debehogne (4571) Grum~x 't985 H. Dabehogne 01884 SP6 1984 H. bbehagne (4503) Wpurth f 980 C.-I. &-st Ma3 -1 1879R.M.W& (4590) iB85RZ2 1985 H. Debekgns W9e)AvfesD f 977 WE. Sehuster (4600) 1885 RE4 1985 H. bbehogns (3519) 1984 00 j984 H. Debehogne (4608) laS8sw3 1988 H. Oebhogne (4609) Phm 1888 E. W. Dst (4- 1886 CQl 198%H. Debehugne (481 1) VulhmM 1989 M.G&felt (4939) 1986 QLt 1988 H. Debehogne (4627) IN5RT2 1985 H. Debehogne (4942) 1987 DU6 1087 H. Debehogne (4633) 1988 AJ5 19643 H. Debehogm (4985) 1979 QKA 1879 C.4. Lsge3.kvisl (4836)Chlb 1988 E.W.EM (4993) 1883 GR 1Q83 H. Debehogne end (4688)1987 OX5 1487 H. Debebgne GI. De Sanctls (4684) 1978 GJ 1978 H. Debhwne (49943 1mRK3 1983 H. DebAogne (4695)1986 RU3 1985 H. Debehogne (4W) MPC 1987 E. W. Elst (4897) 1986 QO 1986 H. Debehugne (5003) t 988 ER2 1988 W. Fed (4744) 1988 RF5 1988 H. Debhogne (5022) 1984 HE1 1984 W. Femd and V. Zappal& (4761) 1981 QC 1981 H.-E. Schuster (505q 1988 RQ5 1- H. aebehogne (47sls) f 984 OF1 tW4 H. Debehmne (5057) 1987 DCg 1987 H. mgne (4793) 1988 RR4 1988 H. Debehogne (50881 1979 QZl 197QC,-I. WkvU (4798) Mercator tB89 E. W. Elst (so=) 1985 CH2 1985 H. DeWogne (4800) 1989 TQj7 t g89 H. Debehogne (60BQ)1085 DV1 1985 H. Debehagne (48041 Pasbur tGW E. W. Elst (5107) 1987 RS6 1987 H. D-hogne (4817) 1984 DM I084 H. Drhhogm (6108) lmeck 1987 E W. Bst (4821) Blanucci 1g86 W. Ferreri I5l09) 1987 RMI 1987 H. Debshogne (4825) Venturn 1OM E. W, Bat (51151 Frlrnout ID88E.W. Elst (4830) 1888 RQ4 1988 H. Wehogne (51 27) Bruhns 1989 E. W,Elst (4843) 1990 DR4 1WO H. Wehogme- I5lW 1W9YO 1079 H. Dabehopne and E. R. Netto (4864)1988 RA5 1988 H. Debahope (51 84) cavallMs;oll 1990 E W. Elst (4931) 1983 CN3 1983 H. Debehogne and (5204) 1988 CMP 1988 E, W. Elst Q. De Smctls (5229) 1087 OEB 1907 H. Debehogne (4933) 1984 EN1 1084 H. [Pebehagne (5248)1 983 GQ 1X3 H. Debehogne and (4937) 1986 CL1 1986 H. Oabehogns G. DBSands

Table 2: Ranking list of €SO discowrefs Table 3: The ESO minor planet sky

1. Debehogne, H. 100 (19) (3488) Arleso (4380) Geyer (1 670) Mlnnaert (1637) Swings 2. EM, E. W. 20 (4501) BaW (3371) Qiaccont (1 eel) mrt (3765) Texereau 3. West, R. M. 18 (2358) Bahner (1894) Herffner (1738) Oosterhaff (2154) Underhlll 4. De Sanctls, G. 15 (15) (2145) Blaauw (1 B50) Heckrnann (3 629) Pecker (2842) UnMd 5. tagerkvlst, C.-I. 12 (1983)8ok (4Q4)Hlltner (4W) Pizarm (2823)van der Laan Schwter, H.-E. 12 (1 543) ku~eals P573) Holrnberg 89W Portugal g203)van Rhiln 7. Ferteri, W. 8 (1) (3368)Bown (3282) Spencer Jonas (21384) Reddlsh (1 040) Walmen 8, Netto, E R. 4 (4) (4192) Bmysacher (I770) Kuiper (4593) Relpurth (2022) West 3, Landgmi, W. 3 (1120) Cannonia (2187) IASIHa (3871)Relr (2902)Westerlund 10. Christensen, P. R. 1 (1) (4636) CHlr (1851) Lacroute (2605) Sahade (2301) Whltford Geffert, M. 1 (I594) Danjan (1 448) Undbladia (1 542) Schaleh (1 7951 Woltjer Hansen, L 1 (1) (3450) Dammanget (1334) Lundmarka (1743) SchmWt Morgaard-Nl&en, H. U. 1 (3) (1 761) Edmondson (4386) LiIst (1235) Schorrla Piio,G. 1 (

A Honeycomb in the Large Magellanic Cloud L. WANG, Deparfment of Astronomy, University of Manchester, UK

The beautiful image shown in the cen- It Is purely by chance that this strange roughly the same size; (3)thy are rather trefold was taken by the €SO MT on nebulosity, reproduced in negative In circular. These features have led F. D. January 17, 1992. It was obtained with the picture on the opposite page, was in Kahn to suggest that this is a "honey- the €SO Multiple Mode Instrument the field of our CCD detector. As shown comb" in the LMC. The same bubbles (EMMU, in a narrow Ha filter and the in the picture, it consists of over ten were also observed in a narrow-band integration time was 10 minutes. The loops wlth a size of around 12 arcsec, or [0111] 500.7 nm fitter image. original purpose was to observe the in- about 3 parsec at the distance of the Bubbles in the interstellar medium are ter/circum&llar material around LMC. The most remarkable features are: not a rare phenomenon, especially in the SN1987A; the results of that work can (1) all the bubbles are clustered along a MC.The present "honeycomb" nebula be found in the paper by Wang and filamentary nebula, I .5 arcmin long and is in fact located In a complex environ- Wampler (1992). 30 arcsec wide; (2) the bubbles have ment which is full of bubbles with sizes up to 30-40 pc across. These "super" duced by the stellar winds from massive References bubbles may be due to OB associations stars. Dyson, J. E., de Vries, J.: 1972. A & A, 20, or supernova explosions (Dyson and de If the "honepmb is indeed due to 223. Wes, 1972; Weavar et al., 1977). stellar activity, it wilt set very strong mn- Elmegrm, B. G., hda, C. J.: 1977. Ap.J., Still, the origin of the "honeycomb" stralnt on the nature of the underlying H4r 725. may be quite different, although it stellar objects. In order to produce a Wang, L and Wamptw, J. E: 1992. A d A, seems that them are only two cluster of bubbles of similar size, the 282 L9. possibitities - R is either related to the underlying stars have to be born at the Weaver, R,, McCray, D., Caster, J., Shaplro, activities of the underlying stellar ob- same time, with the same initial mass P., Moon, R.: 1977, &J., 218,377. jects or it is independent of, or weakly and they must evolve at the same rate. dependent on, the stellar activity. The "honeycombwwill then be a unique However, direct Images taken in the object for the study of sequmtlal star continuum band do show an enhance- formation (see, for example, Elmegreen ment In the number densities of stellar and Lad& 1977). objects in the neighbourhood of the The morphology of the "honeycomb Centre fold 'honeycombw. This implies that sorne- makes it an interesting object In Its own fPmin Ha liame, obtained with the NTTand thing pecullar might be happening here, right. Morework will now haveto bedone, mMI. 77-m frame has been rotated 30" and that the "beesnwho made the "hon- both obswvationat and theoretical. clockwise for typgrephllcal reasons; the eycomb" are perhaps the swarm of This work is supported by SERC. I am north direction is thmfwe et 1 o 'clock, SN stars that is resident in the cloud. 8ub- thanMul for several helpful diseusslons 1987A is at the centre and the stmge "hon- bles of similar size can be easily pro- with J, Danziger of ESO, eycomb" is visible in the lower left erea. b

Comet PIGrigg-Skjellerup Obsenrations at ESO La Silla During the GlOlTO Encounter Period H. BOEHNHARDT, Universitats-Stemwarte, Miinchen, Germany K. JOC KERS, N. KISELEV, Max- Planck-lnstitu t fiir Aeronomic, Katlenburg- Lindau, Germany G. SCHWEHM, A!. THOMAS, ESTEC, Noordwijk, the Netherlands

In total 4 half nights (from 7/8 to 1011 1 buted only 10 hours after the observa- Introduction July 1992) at the ESO 3.6-m telescope tions and about 5 hours before the en- On July 10, 1992, the GlOnT) and at the ESO 1.5-m spectroscopic counter to the GlOTO experimenters, spacecraft of the European Space telescope were devoted to observe to the scientists and to the press who Agency (ESA) became the first satellite comet P/Grigg-Skjellerup. Two even- were following the fly-by at the G10ITO to pass within 500 km of the nucleus of ings were lost due to douds over La control centre, the European Space Op- a comet. G10lTO encountered the Silla. In the night July 9/10, 1992 some erations Centre (ESOC), in Darmstadtl periodic comet P/Grigg-Skjelterup and direct images could be obtained Germany (Jockers, 1992). returned a wealth of interesting in situ through cirrus clouds. Only the last night On the day of the GlOrrO encounter measurements of the cometary coma to of July 10/11, 1992 gave reasonably (see Figure 1) an ellipsoidal coma of Earth. After the fly-by of comet Halley on good atmospheric conditions for our about 30 x 20 arcsec apparent exten- March 14, 1986, the spacecraft com- observations. However, the small elon- sion surrounded the central brightness pleted the first ever Earth gravlty assist gation of the cornet from the Sun (about eondensatlon whfch contained the wm- manoeuvre on July 2,1990, placing it on 45 deg.) restricted the observing win- etary nucleus. The major axis of the cwrse for an encounter wRh comet P/ dow to just 1 hour aRer evening twilight coma ellipsoid pointed towards position Grlgg-Skjellerup. At launch, operations with the comet positioned tow above the angle 130 deg. (counted east from after the fly-hy of comet P/Hatley were western horizon (below 25 deg. sleva- north), i. e. about 15 deg. out of the anti- unforeseen but the remarkable perfor- tion). In fact, special precautions were solar direction. Numerical simulations of mance of the spacecraft and its in- needed to operate the 3.6-m telescope the dust tall orientation for the encount- strumentation allowed the extension of at such large zenith distances and even er day support the interpretation of the the mission. GlOlTO has now com- then guiding on the comet with non- elongatd coma as baing formed mainly pleted 7 successful years in space. siderial rate was not at optlmum. by cometery dust particles. No indica- Unlike comet P/Halley, met P/ Comet P/Grigg-Skjellerup reached Its tions of a plasma tail were detected in Grigg-Skjellerup was previously a large- perihelion of 0.99 AU on 22 July 1992. It any of our exposures. This Is partly ly unexplored comet (for a summary of was predicted to show a late onset of its caused by the moon-la sky which does the results published so far see Birkle nuclear activity and to exhibit a steep not allow to reach the low surface and Boehnhardt, 1992; additional infor- brightness increase {Green, 1991 ) be- brightness of the plasma tail (a plasma mation can be found in Osip et al., 1992, fore perihelion. Actually, it looks as if the tail was detected by GIOlTO) and also Schmidt and Wegmann, 1992). ESO has comet only initiated significant coma limits the extent of the visible coma. The supported the G10TO fly-by at comet development by the beginning of June radial renormalization method was ap- P/Grigg-Skjellerup by providing urgently 1992 (that was 1% months later than plied to the superimposed CCD image needed astrometrlc positions before the expected) when it was already at a of P/Grigg-Skjellerup of Figure 1. How- encounter and by granting observation heliocentric distance of about 1.2 AU. ever, apart from the dust tail extension time to four authors of this article for However, the steepness of the light- no further structure was found in the physical obsewations. In this adicle we curve was approximately as predicted (n otherwise symmeMc cometary coma. glve a preliminary account on these ob- of about 30 to 40). Before perihelion the An analysis of the radial profile of the servations and provide some highlights total coma brightness was estimated to integrated coma brightness exhibited a of the spacecraft encounter. be about 1 mag fainter than the light- rather llnear increase with aperture curve prediction published by Green diameter. Both phenomena (the don- (1991). At a wavelength of 620 nm the gated coma towards the dust tail dim Observing Programme The brightness of the comet in a square tion and the radial coma brightness pro- The main scientific goals of our ob- aperture of 20 arcsec was 15.5 mg on file] support ideas that most of the light sewlng programme at ESO-La SIlla July 11, t 992. in the R filter exposures of July 9/10, were: to determine production rates of In the night July 9/10, 1992, just 15 1982 arose from sunlight scattered by the very abundant HaO molecutes and hours before the GIOTTO encounter the dust. An analogous Image process- other gasmus coma species, to provide with P/Grigg-Skjellemp, 4 broad-band R ing of the R filter CCD observation of P/ direct images of the comet for the en- filter CCD Images were obtained with Grigg-Skjellerup obtained on June 29, counter period which could be used for the ESO 3.6-m telescope at La Silla 1942 at the ESO New Technology Teb an analysis of the coma geometty and through cinus clouds low at the western scope MT (Stom and Meylan, 1992) overall dust environment, and to collect horizon (below 20 deg. elevation). The has been performed by one of the au- information on the cornem ion tail. Be- images were processed at La Slla and thors and led to sirnllar results as for our cause of the damage of two important Immediately transmitted via satellhe link images of July 9/10, 1992. onboard experiments (the Halley Mul- to ESO-Garching. The co-addd coma In the night July 1W11,1992 7 images ticolour Camera and the Neutral Mass image of these exposures is shown in (exposure time 30 s each) through a Spectrometer) GIOlTO was unable to Figure 1. Thanks to the night work of wide-band red filter (dust + NH2) and 3 collect detailed data on the questions people from the €SO Information Ser- plasma filter exposures (10 minutes addressed by our observing pra- vice and by staff at ESO-La SIlla a hard- each, but trailed due to guiding prob- gramme. copy version of Flgure 1 could be distri- lems) were obtained at the ESO 3.6-rn telescope. The photometric calibration and the analysis of these data is stilt In progress. While the cometery imaging continued at the 3.6-m telescope, 2 CCD spectra in the 370 to 1000 nm wavelength range were exposed on July 1D/t 1, 1992 at the ESO 1.5-rn spectroscopic telescope. The spectra show the strong emission band of CN at about 388 nm and also the C2 emission around 517 nm. A weak dust continuum was found in the red part of the spectra. For the spectra the calibration and data analysis is presently performed. ESO has also supported the fly-by targeting of the GIOTTO spacecraft by providing high-quality astrometric posl- tions of the comet to ESO before encounter. The data were measured by Richard West from CCD frames obtained with la Silla telescopes. Post-fit residuals of 0.1 to 0.2 arc% were derived for the ESO data from the comet orbit determination at ESOC Darmstadt. Figure 1: Comet P/Grgg-Skjellmp on July 10, 1992, just 15 hours befm the GIOT70 Astrornetric positions of the comet were encwnter. also determined from our CCD frames The Image is a composite of 4 R filter expostrres obtained at the €SO 3.8-rn telescope. The of July 9/10,1992. These data were also field of view is about 70 x 50 affisec(73,000 x 52,000 km at the comet). North is up and east to transmitted to ESOC Darmstadt and can the left. The Sun direction is Indicated by symboi 0,that of the dust tail by symbol D. The be used together with data from other direction of the cometary motion on the sky is given by symbol V. that of the GIO7TO observers for the post-encounter analy- spacecmft by symbol G. The four tralls In the lower image section am background stars. sis of the GIOlTO fly-by trajectory at the comet.

Further detalls on the GlOlTO Extended OPE started to detect emissions from The GIOTTO Fly-by at the Cornet Mission to cornet P/Grigg-Skjdlerup the gas coma about 50,000 krn from the On July 10, 1992 15:30:36 UTC have been given In Schwehm et al. nucleus. The first indi~ationof entering (f 46 sec) GlOlTO passed within (1 991). Spacecraft orbit and attitude as- the dust coma occurred around about 200 km of the nucleus of comet pects of the fly-by have been described 20,000 krn from the nucleus (at about the P/Grigg-Skjelletup. During the P/Grigg- by Morley (1 991). same distance as the dust coma extent Skjellemp encounter GIOTtO was actu- The payload was switched on in the in our ground-based observations). Data ally overtaken by the comet in its orbital evenlng of July 9, 1992. 7 out of the from OPE provided the first estimate of motion around the Sun. At the same origlnal complement of 11 on-board ex- the spacecraft-nucleus distance at clos- time it passed through the orbital plane periments were operated during the en- est approach. A value of approximately of the comet from north to south. The wunter: the Magnetometer (MAG), the 200 km was derived. In combination with relative velocity during the fly-by was Johnstone Plasma Analyser (JPA),the the MAG data, there is good evidence about 14 km/s which was almost 5 Energetic Particle Analyser (EPA), the that GIO7TO passed the nucleus on the times slower than during the Halley en- Optical Probe Experiment (OPE),the anti-sunward side, 1.e. through the tail counter in 1986. he heliocentric dls- Reme Plasma Analyser (RPA), the Oust forming reglon of the coma. The data tan* of the cornet at encounter was Impact Detection System (DID), the Ion from OPE also suggested that closest 1.01 AU, the Earth distance 1.43 AU. Mass Spectrometer (IMS). In addition, approach occumd a few seconds after GtOlTO approached the nucleus from the signals from the spacecraft were the nominal predictions. I1 deg. behind the terminator. For on- analysed for perturbations by members DID reported Rs first impact at board power reasons and because of of the GIOTTO Radio Science Experi- 15: 30: 56 UTC - probably &er closest communications constraints (the high- ment (GRE) team. approach. A totat d three impacts were gain antenna needed to be kept Earth At about 600,000 km from the nu- recorded, the first being the largest. It is pointing) GlOlTO had to fty through the cleus (12 hours before dosest ap- conceivable that the impacts occurred coma of comet P/Grigg-Skjellerup al- proach), JPA detected the first presence when GIO7TO crossed the orbital plane most side-on with the solar cells fully of cometary ions. At a distance of of the cornet. exposed to the cometary dust and gas 18,000-1 5,000 km both JPA and RPA At 15:31:02 UTC, shortly after the environment (at comet P/Halley the reported what looked like a bow shock first impact, the High-Gain Antenna of bumper shields of the spacecraft were or a bow wave of the coma, much more GIOlTO appeared to be osciHating front-on in order to protect the experi- distinct than had been predicted for slightly around Rs nomhal value. An in- ments and the other satellite hardware such a faint comet. MAG measurements crease of the spin rate by 0.003 RPM from damage by cometary partictes). carried out during the inbound trajectory was also observed while the solar as- could not confirm this finding, but re- pect angle readings were fluctuating be- ported Interesting wave phenomena not tween 89.26 and 89.45 deg., indicating All times in this section are stallon-receive times of Lhe GlOTTO signals In WC. The time for signals to seen in a natural plasma before. How- a nutation of about 0.1 deg. This was reach Ear(h hwn OIOlTO at the tlrne d the en- ever, on the outbound trajectory MAG also recorded by the GRE and is awalt- munter was 11 mlnutes 52.6 seconds. saw clear indications of a shock. ing further evaluation. €PA saw clew Indlcatlons of the Refermces acceleration regions and surprising K. Birkte, H. Boehnhardt: 1992, Earth, Moon D. J. Osip, D.G. Schleicher, R. L. Mlllls: t902, dierences in the stntcturee betweem ?/ and Planew6?,191. Icarus, in press. Halley and PIGrigg-Skjellerup. Last but D. W.E. Wen: W91, Intem~~tiona,Comet H.U. Schmidt, R. Wegmann, D.C. Bdce, not least IMS recorded good data: how- Quarterly 13,91. W. F. Hueher: 1992, MPA 670. ever, the data analysis for this instnl- K. Jackers: 1992, ESQ Photo 08/92. G. Schwehm, T. Morley, H. BoshnhaPdt: ment is qulte cumbersome and com- T. Morley: ISl,bmedinp d the 3rd Inter- 1991, The Me$88ngsbrBS, 37. en- national Symposium on Spacecraft Flight J. Storm, G. Meykn: 1902, ESO Press Photo plex, due to the comparatively low Dynamics, ESA SP-326, 487. 05/92. counter velocity. A ffiorough test of the Halley Mu[- tlcolour Camera (HMC) onboard GlOlTO on 7 July 1992 could only eon- firm that the optical path was very effec- tlvely btockad. However, on July 12, 1992 a number of tests were petformed A Minor Planet with a Tail! with the detectors of the MMC, which provided engineering and calibratron R. WEST, H.-H. HEYERandJ. QUEBATE, ESO data on the long-term behavlour of CCD's in space. Minor Planet 1g79 VA was discovered (Center for Astrophysics, Cambridge, by Eleanor Helin at Palomar on Mass,, USA) that the earlier tmqes were November 15, 1979 as a "fast-moving "unusud", he immediately recalled that The Future of GlOfTO object" of magnitude 11 (IAUC 3422). an object on the Nov. 19 Palomar plates Further observations were made, and had already been catalogued in 1949 as About one weak later than previously when a reasonably accurate orbit be- Comet Wilson-Harrington (1949 111). planned, on July 21, 1892, another rna- came available, R was found that 1979 There was also the strange circum- jor manoeuvre put the spacecraft orblt VA belonged to the select "Apallo" class stance, however, that thls comet was into an that will bring it close to orblt, of Earth-crossing minor planets. Its descdbd as havlng a point-likeappear- Earth (distance 200,000 kmj in about perihelion was just Inside the Earth orbit, ance on plates obtained the following July 1999. There are still 4 kg of fuel left at 0.98 AU, and It had passed within nights. onboard for attitude and further orbit 0.1 AU, w tess than 5 million km, of the So here was an object that was a correction manoeuvres. This leaves, Earth In late October 1979. The eccen- seemingly normal minor planet in 1979 though with rather hard constraints, the trlclty was rather large, 0.63, and the and thereafter, but wHch looked like a open for some further activities in door orbit was therefore vmy elongated; the comet on a pair of plates in 1949. How 1999. After a final orbit trim manoeuvre priod was somewhat over 4 years. could thls be explained? Were the tails on July 23, 1992 at 17:07 UTC the After more observations had become perhaps some kind of plate fault, or was GtOrrO spacecraft was put into hiber- available In the 1980'9, 1979 VA was this a real effect? nation for the third time. duly assigned the ddnitive number Brian Marsden asked hutour opin- Meanwhile, spacecraft experimenters 4015, but it has not yet recdved an ion and we decidd to have a very care- and telescope observers have started Meid ful look at the glass copies of the POSS I the scientific evaluation of their data, name. Nothing very exciting about that. But AUas plates, stored in the vault at the which may stilt hold surprises. The next this August, Minor Planet (4015) ESO Headquarters in Garching. space exploration of comets, after can- suddenly baame an object of intense Our first cxlnclusion was that the cellation of the American CRAF (Cornet interest among solar system as- "tails" are unllkdy to be photographic Rendezvous Asteroid Flyby) project will tronomeml faults. Although a great variety of artifi- be ESA's ROSElTA mission which is cial dots, lines, etc. is ofim found on the supposed to bring a cometary sample very sensitive emulsions used in as- back to Earth. It will take place in the The Palomar lW9Obsewations tronomy the first Palomar Atlas con- next century. Meanwhile, cornetat-y ex- - Extrapolating the motion of (4015) tains many so-called "Kcdak stars" ploration will continue from the ground - backwards in time in the hope of finding the emulsion structure around the "tail" and we expect that, together with other earlier recorded Images of this obiect, is uniform on both plates and does not branches of astronomy, it will profit from Ted Bowetl of the Lowell Observatory at indicate any artificial origin. It is of €SO'S progress in Mescope tech- Flag&#, Arizona, USA, found that It cwrse true that we were only able to nology. should be vtslble on a pair of plates. study second-generation copies of the obtained with the 4&lnch Palomar original plates in the plate vault at Cal- Schmidt telescope for the first Palomar tech in Pasadena, but from our expepi- Acknowledgement Sky Survey on November 19, 1849. ence with many thousand Schmidt These plates were some of the first ob- plates over the years, this conclusion The authors like to thank very much tained with this telescope, red-sensitive still seems quite safe. the staff at ESO-La Silla and at ESO- no. 9 (45 min: 10%-E + a red plexlglass The tail la rather weak, especially on Garchlng who supported - partly in filtre) and bluesensitlve no. 10 (12 min; the red plate, and we therefore photo- night work - the fast data transmission unfiltered 103a-0). graphidly enhanced the two Palomar and hardcopy production of our P/ The image of (1101 5) was myto flnd, plates in order to see the structure more Grigg-Skjellerup observations on the but Bowetl and his colleagues were clearly. The amplified images am repro- encounter day. We would dm like to most surprised to discover that it did not duced in Figure 1a and 1b. There is no acknowledge the hdp of Richard West look Itke a normal minor planet trail - it doubt that on both pJates, the "tall" has from ESO-Garching in obtaining the as- had a tail! the normal appearance of a comatary tmmetric positions of the cornet from When a hint was passed to Brian tail. It extends only to one side of the our CCD frames. Marsden at the Minor Pbnst Center ball, is attached to the trail over the full Figure 1 : ?hwephotogmphicaIly enhanced photos show MimPAanet (4015) = Comet Wkn-Hmington on {a) a blue- (12 mln) and @I a & sensitive (45 min) plafe, obtained on Nomk19,1949, w'th the #-inch Schmidt telexape at Palomar. The tail is well visible below and to fhe left of the MI. 7Re Theiml line in the lower right comer of (4is an muIsion faulf. In {c), Me same sky fmld is shown on a recent @ate obtatnsd with fh8 same telescope tor the POSS 11: the# Is no diffuse in the field. In (d), a ig7$ image of minor planet (4015) from a piate obtained with the 48-inch UK Schmldt telewope dmons~testhe sb~ssof the short trail (at the centre) - there is absolutely no tail vkible. On te)and Ib), the distanm Irom the Earth md the Sun was 34 mit/ion krn and 172 million km, respectively; on (dl the com6ponding distam were 58 millfm and 178 rn/llion km. Y7?e object appws brighter in 1949 (a, bJ than in 1979 Id), partly because it wes closer to the Earth, but most prWyalso because H was at that Urnsurrounded by a small dust cloud. AN photos are reproduced at the same scale, approximately 8.5 arcsedmm; north is up end east is to the led, The photo was pwmd at ESO from fhe Pelomar Obwvatory Sky Srrrveys I and N and the ESWSERC Survey of th~Smhm Sky (@CallfamiaInstitute of Tedrndagy (c) and UK Science and EngiMng Research CounciI @ERG) (dl)).

length, does not extend beyond the trail cause of the dierent emulsion sensitivi- tion proves that It must at least once ends and has the same general direction ty. It is for this m80n that comets 8re have had an outburst of some kind, giv- on the two plates. In other words, the tail much easier to discover on bluesensi- ing it the oemporary) appwance of a really "moves" with the object and it is tive plates; that is also why very few perfectly normal comet. So what Is it therefore very unlikely to be a ghost carnets were found on the ESO(R) sur- really, a minor planet or a comet? reflection from a bright star in the field. vey. This does not apply to comet ob- Possibly both. There has recently Moreover, a look at the same sky field servations with CCDs, since these de- been a growing interest in studying the on the J plate (Figure 1c), recently ob- tectors are more sensltlvs in the red relationship Weenthese two types of tained for the POSS II survey (which is spectral region. solar system objects and various evi- now being reproduced at ESO) shows So we are convinced that minor dence for interrelation has become that there are no nebulae or galaxies in planet (4015) really had a dust tall in available during the recent years. For this area which might simulate a cornet 1949. example, minor planet (2060) Chiron, In tail. a SO-year orbit between Saturn and is dso Important to note that the Uranus, developed a large coma in 1988 It Minor Planet/Cornet weakness of the tall on the red pfate Interrelations on Its way towards perihelion in 1986. does not necessarily mean that the tail Earlier this year, another minor planet consists of gas only. Even dust tails Until now, the object (4015) had ful- with an even larger comet-like orbit was which shine by reflected sunlight, and filled all requirements for classification found and was provisionally designated which are generally redder than gas as a minor planet; its trail (Figure Id) as 1992 AD (cf. The Messenger 67, tails, are normally weaker on red than on was perfectly sharp, without any hint of p. 34, March 1992). It has in the mean- blue photographic Suwey plates be- a coma or a tail. But the 1949 observa- time received the number (5145) and 41 the name Pholus (mother Centaur), but comet. first discovered in 1E125. It was orbits in the inner sofar system, are in contrary to Chiron, Pholus has not seen to split Into two piec~In 1846, it fact dead comets. It may well be that we shown any activity (yet). faded in 1852 and was not seen at dl at actually witnessed the dmth throes of Other minor planets are known to its predicted return in 1866. When no comet 1949 111, and that its inactive nu- move In highly eccentric comd-like or- more ice is available on the surface of cleus was "re-discovered" in 1979 as bits much nearer the Sun. One of them, the nucleus of a comet, or if the Sun's minor planet 1979 VA. It isthe first direct (3200) Phaeton (discovered by IRAS in heat can no longer penetrate through observation of this kind and R will surely 1983 and designated 1983 TB), moves the insulating surface to tfie reservoirs stimulate much activity in this Interest- in the same orbit as the Gemlnid meteor of be that may still be presmt inslde the ing research field. stream. It seems that it is the parent nucleus, no coma and tail will develop. body of the materid In this stream. This The comet will have become "inactivem Minor planet (4015) again passed Zs strange, because only a comet, and and its small nucleus will only shine by through its perihelion in late August not a solid minor planet, is thought reflected sunlight. This implies that It will 1992. There is little doubt that il wlll be to be able to disperse dust along its be very hint and its image, if obsewable extensively observed during the comlng orbit. at all, will from then on be indistinguish- months. Unfortunately, R will be located Several comets in well-known orbits able from that of a minor planet. This In the northern sky and will not be eastly have been found to disappear from type of object is appropriatety referred accessible from La Silla. Initial observa- view, probably because their source of to as a "dead" or "dormant" comet, tions (IAUC 5585 and 5586, August 14, volatlles is exhausted. One of the most It is widely believed that at leas? some 1892) have not revealed any signs of well-documented cases is that of BUa's of the minw planets, mrw In curnet-like activity whatsoever.

A Very Low Resolution Spectrophotometric Nova Survey A. BIA NCHINI, Dipadimento di Astronomia, Universita di Padova, Italy M. DELLA VALLE, ESO H. W. DUERB ECK, Astronomisches lnstitut der Westialischen Wilhelms- Universitat, Miinstet-, Germany M. ORIO, Ossewatorio Astronomico di Torino, Italy

The Aims of the Survey Since we are engaged also in the sp- portant to understand the physical A very low resolution spectre tematic study of novae at minimum in mechanisms powering novae and the photometric survey of classical novae at other wavelength ranges. especially UV nature of the different systems. minimum is of greet interest for a more and X (Bianchini et al. 1991, Orio et al. thorough understanding of these ob- 1992), this survey in the optical range Fim jects. As it was stressed in a previous becomes an important tool when the account (BiancHni et al., 1991), up to level of the continua is correlated with The spectral atlas we are building now only Williams (1983) studied a that in UV and IR or certain details of the consists atready of 50 different objects, number of spectra of old novae. There is optical spectra are used to understand all observed in the range 13000-9000 A. therefore a strong need of a systematic the mechanisms of X-ray emission (the In three obsewing runs at the ESO study of the post-outburst spectra of a typical example is the Hell h4686 line, 1.5-m telescope (Februaty 1991, Da- large number of these objects, in order which has been shown by Patterson and cernber 1991, July 1992) we have kn to be able to derive statistical conclu- Raymond (1984) to be the result of re- able to study 31 novae using a CCD sions. processed soft X-ray emission for high detector and the Boller & Chivens spec- With very low resolution spwtroscopy accretion rates). Moreover, many &- trograph. In addition there are spectra of we can cover a wide wavelength range jects were poorly studied at maximum 23 objects taken by Duerbeck in the for many novae at minimum, obtaining a and their classification is uncertain. Us- years 1986-1988 with the same tele- statistically meanhgfd sample, and de- ing the ESO 1.5-m telescope, we are scope and B 8 C spectrograph: the ma- tect the following features: able to distinguish between the spec- lority was observed with the somewhat - the slope of the continuum; trum of an old nova and that of a sym- ageing image dissector scanner (IDS) - the ratios of the intensities of different biotic star or a red variable up to Mv = instead with a CCD, resulting in a poorer emission lines of H, Hel and Hell, all 20; a proposed classification as dwarf S/N and a lower spectral resolution. meaningful to understand the acere- nova (with long cycle length) instead of However, these observations are useful tion mechanbrns; classical nova can be rejected on the In order to establish secular trends h the - the presence of a nebular spectrum if basis of a strong A4886 Hell emission data - e.g. dedining continuum fluxes this still exists; line, which is typical only of classical and decreasing strengths of He I1 emis- - sometimes the spectrum of the see- novae or magnetic CV's and is an indi- sion. Such findings are useful to find ondary; cator of accretion rates m > 10" g s-' indications for a secular decrease in the - the possible discovery of peculiar (Patterson and Raymond 1984). accretion rate, which Is postulatd hy variabtlities (see Biancllini et al., A systematic study of classical novae the hibernation hypothesis (Prialnik and 1991). at minimum is therefore extremely im- Shara 1986, Shara et al. 1986). Accwd-

hwbmk,H.W.,1987,Sp;ateSd. FEev.,46,1. Fu, A, Tam, R., tag, Ap.J., M9, 563. Hamwrj, J.M., King, A.R., Lasota, J.P.. 1988, &J., 353,85871- Haswwall, C.A., 1992, Ph. D. Tbsls at the University of Texas at Austin. Huang, U. Wheeler, J,C., 198& &d, 343, 229. Lloyd, H.M.. O'Blim, T. J., Bods M.F-, Pm- dehl, P.. Scbm, J.H.M.M., Triimper J., Watson, M.G., Pounds, K.A., Ig31, #a- bte, 368,m. McQintock, J.E, Rernlllard, R.A, 1986, Ae ibphp, J., 808, 110, Minesbige, S., Wheeler, J.C., 1989, Ap.$, 343,241. MlmMge, S., Kim, S.W., WMer, J.C., 1w0, dp.J., 958, L6. Orio, M.,bgelman, H., ~etwh,W., Wchtnl, A, Della Valle, M., KW,JJ StaAeId, S., contribubd paper to the hmrMmt- ing, washington, September 1992, 0 Patterson, J., bymond, J.C,, 1W, Ap.J., 4000 5000 6000 7000 292,550, Plialnik, O., Sham, M.M., 1986, &.J., 311, 172 Figure 1: 7wo spmof W16 Won @m2O-WI taken in mberIM1. Flux88 In 10-"erg m-2 --' A-1 Shara;M.M., Uvio, MOfiat, RF,J., OrIo, M.. 1986. A~.J..314,163. Mfliarns, G., 1'983, Ap.J. Suppl. Sm,53,523. resemble a classical or recurrent nws: were never noticed before and they the only feature was the late appearance were not correlated with the orbital of emhion Ihes qulte like those of phase. An explanation for the phenom STAFF MOVEMENTS dwarf novae (Dueheck 1977). Moddlhg non could be a sudden variation In the the physical mechanism powering the mass transfer rate, causing a shrinking Arrivals outburst d A62040 and Its associate of the disk that appears bluer, but less sources has always appearad a luminous. However, the contribution of k*oW challenge because there are problems the disk to the total flux does not seem BEDDING. Tlmolhy (AUWGB), Fellow both with mass overflow InsWillty mod- to exceed 15% in any band (Haswell, CONZELMANN, Ralf (Dl, Wigmr- els implying X-ray Wing of the secon- 1$92). These results appear therdore breughtsman (Mmhanies) et vwy pdhgand thy should be eon- HAINAUT, Ollvier 0,Student dary by the compact object (Hameury (OW, al., 1#6,199O), and with disk insfabllity needed also wlth the secondary star, MELDSEN, Hans Fellow RASMUSSEPI, RQ (OK), Technician models (Mlneshipe and Wheeler, 1989, which must have undergone some kind (softwm) Huang and Wheeler, 1989, Mineshige et of imtabillty. For better understanding it RODRIGUEZ UUOA. JBUS(E), Om- al., 1991) that need a higher mss trans- is undoubtedly n- to study pos- tion Tecfurleian (Rarnota Control fer rate to work than the one inferred by sible new spwfral variatbns, monitoring Equimt) Fu and Taam (I 989). For a detdled dis- the object regularly. This could offer a cussion see Haswell, 1992. key to understanding the complex Transfers Two spmhwere obtained on Febru- phsnomerra th& are happening and the AtLbERT, Eric 0,Engineer (Software) ary 18md 19,1991, threeon December mechanism that powers the outbursts, (fmrn La Snla to Barchlng) 2, 3 and 4, 1991, and two more at an beaause it is crucial for any model to Interval of a few hours on December 5, kmw If and how there is variabitity of the Departures t s91. Although the two spectra of Feb- mtransfer rate and what is the rsa- ruary are dike and their slope and ture of the disk. Europe CharaCt~rjstlCSappear to match those of Such serendipitous discoveries of UU, Xlaowel (RC), Assmiate Haswell of November 1987 (see Has- verriabWty, already known not to be In- MAZAU. Pado (U, Fellow well, 1992), the spectrum of December2 frequent for cdnsyrnblotics and X- PRAT, Serge 0,Mechanical-Project show8 that the flux in the red can de- ray binaries, can be detected dwfor Engineer crease significantly and re-increase wt a clasical novae during a survey of this STEFL, Smislav (W),Associate time scale of one day (see Fig. I, whetre kind and certainly be meaningful to VAN MWRSEL, Qustaaf (NU, Scientific the two spectra were taken at the same understand the nature of the syslems. Programmr/hdpt he WARREN, Stephen [GB), Fellow orbital phase). On Demmber 5, de- ZEUNQER, Werner (4,Fellow crease of the red flux murred again, but a second apectlum reappeared References . 'normar' again after a few hours. The Bianehini, A, Della Valle, M., Orlo, M., bet- msn, H., Blanehi, L, 1991 me Mwsew luminosity fluctuations In the red region Erratum (Wnw 08, p. 2, Jun~ of the spectrum were up to I mag NO. M,32 Boley, F., Wrrlfson, R., Bradt, H., Doxaey, R., 1992) (t- arnptitude at longer wave- Jemigan, G., Hlltner. W.A, 1976, Ap.J., The 6.5-m MMT msntroned In the llst of bngths?) and the slope of the con- 203, L13. IbQe telescope pro]edts Is of couw tlnuum totally changed (see Fig. 1). Duerbeck, H. W., 1977 In Novae and Relafed I- on Mt, Hcrpklns, not on Mt. Such sudden, irregular vadatians in the mm, ed. M. Friedlung, Dordmht Reidel, Graham. flux and In the slope of the continuum p. 150. Obsewation of the Central Part of the P Pictoris Disk with an Anti-Blooming CCD A. VIDAL-MADJAR, A. LECAVELlER DES trANGS-LEKALLOIS, G. PERRIN, R. FERLET, F. sWRE,Institut d'Astrophysique, CNRS, Paris, France F. GOUS, J. -E. A RLOT, Bureau des Longitudes, CNRS, Paris, France C. BUIL, CNES, Toulouse, France H. BEUS T, Sewice d 'Astrophysique, Saclay, France A. -M. LAGRANGE-HENRI, Observatoire de Grenoble, France J. LECACHEUX, Observatoire de Paris, Meudon, France

1. The f3 Pictoris Disk grangeHenri, Vidal-Madjar and Ferlet, direct starlight (passing through the 1988; Beust et al., 198g). Numerical edgeon disk) would result. Therefore, Since the discovery with the IRAS simulations of infalling bodies which they clalmed that a cleared-up reglon Satellite of a number of main-sequence evaporate when grazing the star are was probably present within 30 AU from stars which show an infrared excess, able to reproduce the observational the star, possibly due to planetary for- direct imaging has proved, in the only data and provide constraints on the mation. kter on, Diner and Appleby case of the southern AS-type star 6 Pic- bodies' nearly parabolic orbits: for in- (1986), using the same cornnographic toris, that this excess is caused by a stance, a specific direction of the orbit's data but coupled wlth the IRAS obser- disk of dust surrounding the star (Smith axis with respect to the line of sight is vations, produced a dl& model cohe- and Terrile, 1984). The favourabb orien- required, along wRh close perihelia 2 10 rent with both dust scattering and tation of the disk, viewed nearly edge- stellar radii. We then came to the con- emissivity, and found that within 1MI AU on from Earth, has permitted the further clusion that the numerous events seen no strong constraint was present in the detection of its gaseous counterpart, could be due to the presence of a giant data: dust distributions presenting very with a typical density n(H) - 10~crn"' planet (or proto-planet) in the P Pictoris small cleared-out inner regions were (Hobbs et al., 1985; Kondo and disk which perturbs a lot of small pass- certainly acceptable. This is due to the Bruhweiler, 1985; Vidal-Madjar et al., ing-by objects and throws some of them fact that, slmHarly to the cormographic 1986). Subsequent observations have towards the star (see 9.g. Beust, Vidal- observations, the low resolution IRAS emphasized the complex time variations Madjar and Ferlet, 1991, and references data are sensitive to relativdy cool (out- of the circumstellar (GS) lines, both in therein), thus posslbty clearing up the er and extended) dust. Then, Arty- the vislble and the UV (Ferlet, Hobbs inner part of the disk. mowicz, Burrows and Parme (1 989). and Vidal-Madjar, 1987; Lagrange, Fer- From their coronographic study, ushg new coronographic data (Paresce Id and Vtdal-Madjar, 1987). Smith and Terrile (1984) have shown and Burrows, 1987) still limlted to more In order to interpret tha extensive data that an r4.3 power law was well repre- than 6 arcsec from the star, along wlth set gathered on the @ Pictoris proto- senting the dust distribution within the the IRAS data, confirmed the radial planetary system, we have proposed a disk. However, at less than 6 arcsec power law (although sllghtly less steep, model in which the sporadlc redshifted from the star (100 AU), i.9. behind the in r-9*6)and the Diner and Appleby (1986) events are the result of the evaporation coronographic mask, they showed that conclusions, i.8. a 5 to 15 AU cleared In the vicinity of the star of solid comet- if this taw was extrapolated to less than inner region is compatible with the ob- like bodies falllng into the star (La- 30 AU, a too strong extinction of the smations.

Figure la: 20-ssc exposure (V filter) of p Picto& corrected for the Figure 1 b: Same correction made on another star (with similar light diffuse light Ievel by the use of a template star (see text). The bright levels) obviously shows no circumstdlar disk. A 6-arcsec-mdius spikes due to the secondary spider cannot be completely corrected, circle is drawn around the star to visualize the limit of previous but do not perturb disk brightness evaluatmns due to their angular coronographic observations. separation. at ta Silla. To probe the disk at different distances, series of images were taken with exposure times ranging from 0.5 s (to see as close as possible to the star) to 300 s (to detect the disk as far as possible and have an overlap with the previous coronographic images). This has been done with the four standard filters: 8 (440 nm), V (550 nm), R (700 nm) and Ic (800 nm). More than 450 CCD images were taken, and an average of 10 was gathered for each filter and exposure time. Additional exposures were recorded with different angular position of the bonette in order to test the effect of the CCD orientation relatlve to the disk. No changes were observed.

Data Analysis Figure 2: The P Pictoris disk image wlthwt the spikes, radially flattened to strengihen the weakest parts of the disk, Nadh is up. A 6-mcsec-radius circle b drawn. This disk is clearly After the classical bias and flat fielding seen down to 2.5 arcsec from the star. Shwter exposures reveal the disk down to 2 arm% (30 corrections of the CCD frames (see e.g. AU. Bull, 1989),one of the difficulties was to properly correct for the diffuse light level by using the template star, observed almost sirntlltaneously with the same in- Simultaneously, Telaca et al. (19881, On the contrary, the use of an anti- strument setting. This correction was completing 10 and 20p ground-based blooming CCD which avoids the con- done by scaling properly the diffuse light observations with 5 arcsec resolution, tamination of pixels adjacent to satu- level of one star relative to the other in were able to constrain more strongly the rated ones, allows the direct obsewa- the two quadrants where the disk is not different models: the P Pictoris inner tion of the disk next to the star without observed. This is not a simple linear disk is relatively clear of dust, possibly the use of any coronograph. Stellar light wrrectlon. The radlal variation of the up to 50 AU (3 arcsec from the star). simply saturates some pixels while the correction factor was evaluated assurn- However, more recent observations nearby ones collect charges related to ing, in a first approximation, that the from 8 to 12p by Telesco and Knacke the light coming from the vicinity of the diiuse llgM (away from the obvious (1991) led to a possible detection of a star. This technique was well developed spikes due to the telescope spider) pre- spectral signature related to silicates, In planetary studies by Colas (l991),and sents a circular symmetry. but only sen within 3 arcsec from the led to the detection of very faint The result is shown in Figure la. in star. satellites (V - 16) near the giant planets. which the Image was rotated in order to From all these observations, it Is The size of the stellar image Is thus have the disk horizontal. The disk detec- plausible to assume that a dust-free simply defined by the seeing and the tion is obvious, particularly when com- zone exists in the inner reglons of the fl exposure time. Typical values are be- paring with Figure I b in which the same Pictoris disk. tween one and two arcseconds, repre- correction was applied to another tem- senting roughly the limit of that observa- plate star with no disk at all, and in tional approach. Use of adaptive optics Obsenrations with an which all light levels are at most equal to Anti-Blooming CCD could furher reduce the effect of the 10% of the ones in Figure 1a, at similar seeing, and observations of the disk at angular distances from the central stars. To obsewe the disk closer to the star, less than one arcsecond from the star It is also very clear in Figure 1 that the we decided to use an anti-blooming should become possible. The limitation correction process is unable to perfectly CCD (THX 7852), instead of a classical is then only due to the diffuse light eliminate the very bright spikes in the one associated to a coronographic ap- characteristics in the telescope, pro- case of f3 Pictoris because they are part- proach. In effect, all the observations duced by both the cleanliness of the ly due to scattered light from the disk published with wronwraphs give very mirrors and the induced diffraction itself. good results far from the star {Smith and pattern. The final image of the p Pictoris disk is Terrile, 1984; Paresce and Burrows, The recorded images with such a shown in Figure 2, where the brighter 1987, but fail close to it, the limit being CCD must be simply centred on the spikes were simply taken out, and the around 6 arcseconds. The difficulty to stellar images in order to give the possi- disk luminosity Is flattened by an rd9 get closer Is due to the diffuse light bility to either add them and improve power law in order to better lllustfate its around the mask whlch is extremely S/N by selecting sharp images (always radial extent. The superimposed circle sensitive to the star posltion behind the corresponding to shorter exposures), or represents a region of 100 AU (6 arcsec) mask, a pasition difficult to control with- correct for the djffuse light effect within around the star, corresponding to the out any adaptive optical device. Auctlra- the telescope by subtracting the groper- inner limit of the coronographic studies. tions producing unrepeatable changes ly centred images of a template star The disk is seen down to 2.5 arcsec of diffuse light levels around the mask which was in our case the nearby star from the star. Shorter exposures allow a make difficult to achieve quantifiable a Pictoris. precise evaluation of the disk brightness obsetvations with such techniques very The observations were performed in down to 1.8 wcwc, i.e. down to less dose to the star. October 1991, at the 2.2-m Telescope than 30 AU. I3 filter V filter

1 f 0 100 1 to 100 distance to the star (arcseconds) distance to the star (arcseconds)

1 filter

.. rn :+ :' ::om -- .bn*.,*'.," rn *?,

I I 10 roo 1 '0 100 distance to the star (arcseconds) distance to the star Iarcseconds) Figure 3: DL& bdghtnass in arbitmty units for the four fill# as a function dihe stellar distance in msec. In 1! R, and le filters, m anr-g.8powerlaw is found, while In the 8 fllter, deparfure from this power kw Is cleady detected at hss than 5 aresec from the star (60 AUJ.

Preliminary Results color of the B Pictoris disk Fmm these different images, it Is possible to reconstruct the dbk brightness between 2 and 12 arcsee by evaluating the total signal above background perpendicular to the disk plane. The results for the different filters are shown in Fig- ure 3. Nearly an r4."wer law is found in V, R and Ic. in excellent agreement with the previous observations of Arty- mowicz, Burrows and Parasce (1989). The striking differenceis seen in the filter. The power law found at more than 6 arcsec from the star matches very well the one found in the other filters and confirms also the previous coronographic results: the dlsk colour does not vary with the distance to the star. Fur- thermore, these disk colours are shown in Figure 4 after normalization with the stellar colours themselves. Our result thus confirms the flat albedo of the dust wavelength (pm) particles, demonstrating again the prob- Figure 4: The disk colour Is given at two different locations in the disk and in the four filters able large size of the grains present in (after nonnalitation with the stellar light). Neutml colwr is seen at large distances, whlle a drop the outer disk (> 1 p). in the B filter is clearly observed in the inner regions. However, at shorter distances from Conclusions more inclined, as the p Pietoris one is the star, we observe a vwy clear drop in still a unique phenomenon. the B filter, showing that the dust albedo We have shown that a new observa- seems to decrease by at least a factor of tional approach does exist to look for 4 when movlng fmm 73 arcsec to 2.5 very Mnt feature8 near bright objects. am%. This slow drop oftbe B albedo Is Compared to dassical stellar coronog- Attymowirx, P., C. Bunows, and F. Paresce, also clearly seen in Figure 3. raphy, it allows obsmations closer Rsrrophys. J., 337, 4Q4. 1989. This is an extremely Interesting and to the star, particularly if quantitative Bern, H., A.M. bgrange-Henri, R Mdal- Madjar, and R. Ferlet, Astm. Rstrophys, seems to results must be reached very totally new result, which indi- close m,304, 1989. cate that the nature of tha grains is to R. Beust, H., A Vrdal-Madjar, and R. Ferlet, changlng when movlng inward. More In the case of the 0 Plctoris disk, we Astm. Astrophys., 247,505, 1991. precisely, a change in the grain size confirmed previous results obtained at Bull, C., ln Astronomle CCD,ed. S. A.P., 1989. could not explain such a variation be- more than 6 arcsec from the star. Colas, F., University of Pads, Ph. D. Thesis, cause larger grains shoutd Induce no Moreover, we were able to directly ob- 1991. colour changes while smaller onea sewe the disk dawn to 2 arcsec. The Colas, F., and J.E. Arlot. Astm. Astrophys., should, on the conmy, favour the blue. mdn results are: 252,402,lWl. However, a change in surfam albedo of Diner, D.J., and J.F. Appleby, Nature, 822, the disk extension continues down to 436, W86. ' the grains could easily explain such a - 30 AU from the star, following an r-"" Rrlet, R., LM. Habb, and A. Vidal-Madjar, behaviour; from materia! albedoes by power law; Mtw. Astmphys., 185,267, 1987. Gaffey and McCord (1979), a sirnllar the disk colarr is neutral in V. R and Ic Gatfey, M. J., and T.B. McCord, in Rsferdds, behaviwr could be found in Icy ma- - at all obsmed distances; 88B, ed. T. Oehrels, 1879. terial more and more covered with Hobbs, L.M., A. Vtdal-Madjar, R. Ferlet, C.E. the disk colour drops down in the dust. - Albert, and C. Gry, Ap. J. Lett., 283, L29, blue (9) when going inward, starting If this explanation is correct, It seams 1986. at about 75 AU from the star, to reach to Indicate that the grains In the Pic- Kondo, Y., and F.C. BruhweiQr, k.J. Lett., 8 a factor of 4 reduction at 30 AU; toris disk are ices more and more dusty 291, Lt, 9985. a slight disk asymmetry (80%) is Lagrange, Ferlet, and when gohg inward. This might be a first - A.M., R. A. Vidal-Mad- present, but is inverted within 100 AU jar, Asiron. Astrophys., 173,289,1997. direct indication that a different situation from hestar. Lagrange-Henri, A.M.. A. VTdal-Madjar, and prevails in the inner regtons of the R. Rrlet, Astmn. Asfivpttys.. 190, 275, disk, namely at less than about 75 AU Obviously, this technique is very 1988. (5 arcsec). where planets are possibly promising and a lot more is still to be Pmce, F., and C. Bums,Ap J. Lett*,319, forming. done to further confirm Wse results 123, 1987. We also have confirmed a slight and observe the disk even closer. From Smlth, B,A., and R.J. Terrile, Sci#ce, a, asymmetry in the disk from one side to our first approach we are convinced that 1421,1984. down Telesco, C.M., E.E. Becklin, R.D. Wolsten- the other, but noticed an inversion of observing the p Picfwis dlsk to FI. less than one arcsec from the Is croft, and Decher, Nature, 335,51,1988. that asymmetry in the inner regions, star Telesco, C.M., and R.F. Knacke, Ap. J. Letl., leading to an average symmetric disk. within the possiblllties. Furthermore, this 372, u9, 1991. This may agaln be the signature of is potentially a very powerful technique Vldal-Madjar, A, LM. Hobbs, R. Farlet, C. planetary formation processes within to search for other protoplanehry disks Gty and C.E. Albert, Astron. Asbophys., the Pictoris disk. around nearby stars, even if they am 107,325,1988.

Spectroscopy of Arcs and Arclets in Rich Clusters of Galaxies G. SOUGAIL, Observatoire Midi- Pyrenges, Toulouse, France

1. Introduction the obsenrations of giant luminous arcs. that we were observing a gravitationally Since 1987, the redshift determination The flrst main resufi, about one year distorted Image of a background source of the giant arcs observed in rich clus- after the discovery of giant arcs in two through the cluster of galaxies. One year ters of galaxies has been a great clusters of galaxies (Soucail et al. 1987, Later we continued our study by showing challenge for observers, as it was mitial- Lynds and Petrosian 1986), was the red- that many clusters were acting as giant ly the only way to confirm the nature of shift measurement of the giant arc in tenses an the numerous population of the gravitational phenomenon. But the Abell 370, a rich cluster at a redshi of faint blue galaxies detected at the same faint surface brightness of most of the 0.37. A strong mission line was de perlod by Tyson (1 988). For example in arcs, only slightly compensated by the tected all along the structure, with a A370, many weakly distorted blue ob- extension of the image, is partly re- curved slit punched with the PUMA sys- jects were detected, with an orthoradial sponsible for the slow progress of such tem installed at the 3.6-m at La Silla. The orientation with respect to the duster obsenrations although their scientific line was immediately identMed with the centre (Fort et al, 1088). These so-called impact is quite large. well-known IOIB line at 3727 A, red- "arclets" were also supposed to be im- Let us begin this paper with some shifted at 0.725. This important result ages of distant background galaxies. chronotogicai steps in the discovery and was the confirmation of the hypothesis But in this case, the confirmation of this idea is less obvious, because their magnitude Is larger than 25, out of the capabilities of the present-day spectro- graphs. Many other clusters have now been observed by many people and a lot of them present similar structures. In particular, Tyson et al. (1990) have detected a strong excess of tangentially elongated objects in the very rich cluster A1689, mainly among the blue selected objects, by using very deep imaging in 0 and R. The scientific interest in these examples of gravitational lensing is quite important, because it is a new tool for Observational Cosmology, and an approach of the mass distribution rather independent of other dynamical methods. The development of the new methods applied on lensed-clusters will be presented in a final report of the Key Programme I-0t5-45K, "Arcs survey in Figure 1 : Ultra-Deep B image of the cluster of galaies Cl2244-02, from CFHT. One can see distant clusters of galaxies", performed some substructures along the glant arc. by the Toulouse group (Fort et al., 1990). The use of the "gravitational telescopen for probing the deep and distant Uni- verse is also very promising and exciting results from the spectroscopic follow- now (Mellier et al., 1991). The stellar and will be discussed here. A major goal up of the main arcs detected in our content seems "normal" with a star for- of the spectroscopic observations is to survey of rich clusters of galaxies (ESO mation rate of a few tens of solar derive the redshift of the largest and Key Programme and CFHT Long-term masses per year, a value far from the brightest arcs, and this for many Programme). The data have been col- high numbers derived from the spectra reasons: lected on different telescopes with vari- of distant radio-galaxies! - it is the ultimate confirmation of the ous instruments (3.6-m and NIT on La gravitational lensing hypothesis, espe- Silla, 3.6-rn CFHT in Hawaii, 4.2-m WHT 2.2. The "Stmighf" Arc in Abell2390 cially in the cases for which other in- in La Palma), but they all correspond to terpretations are possible (cluster faint objects and consequently low res- The spectroscopic data on this pecu- galaxy seen edge-on, manifestations of olution spectroscopy with very long ex- liar arc were collected at the 4.2-m galaxy-galaxy interactions, etc). In a few posure times is required for each Wllllarn Herschel Telescope in La Palma. cases, such as the triple arc in specific object. The surprising straight shape of the arc C10024+ 1654, the identification of a made the slit positioning easy! A total change of parity in the dierent images integration time of about 10 hours led to (from high spatial resolution data) is also 2. Some Peculiar Cases the detection of an emission line at 71 30 a clear evidence of the phenomenon of RedshiDetermination 8( and an underlying continuum, both (Kassiola et al., 1992). compatible with a redshift of 0.913 2.1 The Giant Arc - The redshifi of one an: in a cluster (Pel16 et al. 1991). We were also able to in the Cluster C12244-02 fixes the geometrical scales of the lens- detect a velocity gradient along the arc ing configuration and gives immediately The blue giant arc detected in the with a line shifi of 10 A which we the total mass within the critical radius. centre of C12244-02 (z - 0.329) is one of confirmed further wlth observations on Consequently, the constraints obtained the most spectacular cases of gravita- EFOSC at a better resolution. This gra- on the dark matter distribution are better tional tensing (see Fig. 1). Its very circu- dient is presently interpreted as an in- (see for example the case of MS2137-23 lar shape extends over more than 100" trinsic velocity gradient inside the in Mellier et al., 1992). and its B-R colour Index of 0.8 makes R source, stretched by the gravitational - The redshiff s of two dierent arcs in one of the bluest arcs ever observed. distonion of the cluster field. If so, It is one cluster could be very promising for More than 10 hours of integration were the confirmation of the existence of a constmining the value of qo, provided necessary at the 3.6-m with EFOSC in rotating disk with a maximum velocity of one is able to reconstruct the gravita- order to obtain a good signal on the about 200 km/s (uncorrectedfor inclina- tional potential of the cluster, and the continuum. An emission line was finally tion). It has also Wnused tentatively to two redshifts we distant enough from detected at a wavelength of 3940 A and derive the Hubble constant Ho through each other. identiffed with Lya redshifted at 2.238. the Tully-Fisher relation (Soucail and - Last but not least, the arc sources This identification was also confirmed Fort 199 1). form a sample of very distant field galax- by the detection of several absorption Our first interpretation of the straight ies at redshift larger than 0.6. It is very lines (CIV 1549, Sill and SiIV) and the shape of the arc was the existence of a important to study their properties in the continuum observed in the rest-frame bi-modal deflecting potential with a framework of galaxy evolution and for- wavelength range of 1200-2000 A is source positioned in the saddle region mation, and their stellar content must be compatible with what is expected from between the two clumps of matter. Un- compared with evolutionary models starburst galaxies. fortunately we did not detect any over- (Guidwdoni and Rocca-Volmemnge This rather secure identification dense region of galaxies on the external 1987, Bruzual and Charlot 1992). makes the source of this arc one of the side of the arc, which was somehow Here I will present some preliminary most distant field galaxies known up to problematic. Another possibility was corresponds to a cluster member at z = 0.374. Its very low flux in the near infrared (1 and k bands) makes It rather "intriguing" and it should possibly correspond to a very distant and/or young galaxy, which needs to be re-obsenred. -The glant arc in the cluster C10024+ 1654 @=0.39) is the most interesting one to study in view of its large spatial extension and Its splitting Into 3 pieces. A curved slit was punched with PUMA (October 1989) in order to follow the three main parts of the arc, and despite a total Integration time of 6 hours, a featureless spectrum was obtained, with no evident emission lines. A recent analysis of the image formation in this cluster by Kassiola et al. (1992) led Figure 2: High-resolut/on image of the mtm of AM12390, from CMend with a I-band 1SIfer. them to predict the redshift of the arc The separation betwmn the images of !he two galaxies fming the arc is visible and also a source to be between 1.4 and 1.9 from slight change in the orkntatiwr of each Image. theoretical arguments. Deeper data are expected In order to test their predlc- tions. Let us also present one counter-example of what was initially suspected to be an arclet. From deep imaging in the 2.4 from Mher suggested recently by Kassiola et al. Some Results Clusters cluster of galaxies A483 (z = 0.29) we (1992) that we see two interacting gatax- Many other arcs or arclets were ob- noticed several extended blue images ies at z = 0.913. This hypothesis Is rein- served spectroscopically over the last around the cluster centre. In particular, forced by the infrared data (see below) three years, sometimes with less two structures were detected, one going because the arc presents a strong col- success. In most cases, we did not through the envelope of the cD,and the our gradient in K (Small et al. 1992) and succeed to get a redshift for the arc other one extended over 9" located a bit also from high-resolution CCD frames spectra without emission lines, as it is more than It north of the cO. In De collected at CFHT last year (Fig. 2). The extremely difficult to detect absorption cember 1991, we got 4 hours exposure separation between two smaller images lines on a low S/N continuum. This in spectroscopy on the second of these is clearly evident In the I-band. means that it will be very difficult to objects. After data reduction we found a measure redshifts between 1.I and 2.3: redshift of 0.2741 This object is most 2.3., TAe Multiple Arc System In A2218 0111 h 3727 is too far in the red (A > 7800 probably an edge-on spiral galaxy be- This cluster (z = 0.175) is one of the h and Lya is not redshifted enough (A < longing to the cluster and not an arclet. richest clusters of the Abell catalogue, 4000 A)). Between these two typical One must conclude that people have to with a giant cD in its centre. It shows emission lines, no other emission lines be very careful when they announce the many arclets in the central region, lo- are prominent in normal galaxies and we discovery of arcs or arclet candidates. cated around the cD and also around only expect to see absorption lines. Only detailed multi-cotour photometry the second giant gataxy. A spectros- Presently two arcs fall in this andtor spectroscopic data can give copic survey of the cluster has been category: some confidence in the gravitational performed at the 4.2-m WHT (La Palma) - The arclet A5 In the cluster A370 is arcs hypothesis, if one cannot detect a by Pelt6 et al. (1992). They collected the largest one of the weakly distorted clear multiple arc system with a counter- spectra of several arclets, and got two images detected by Fort et al. (1989). tts image or possibly a parity change be- source redshift measurements with a B-magnitude reaches 22.7, but the sur- tween the images. secure determination. The first one is face brightness is only 25.5 mag. arc- located near the central cD and pre- ~ec-~.A spectrum was obtained with 3. Gravitational Lensing and sents the spectrum of an WSa galaxy EFOSC, with the tentative detection of Orstant Galaxies redshifted at z - 0.702. Its colours are absorption lines giving a preliminary redder than those of the duster redshift of 1.305 (Mellier &t al. 1991). The The sources of the gravitational ares member, contrary to the other known [Oll] line was then predicted at a and arclets are potentially a very useful arcs. The fact that the cluster redshift is wavelength of 8590 A. Our last data sample of very distant galaxies, from only 0.1 7 also favours efficient magnifi- collected in December 1991 on EFOSC which we kgin to gather extensive cation on rather tow redshift sources. using a rism wltll a higher dispersion spectrophotometric data. At least ten of The second arctet is very blue and it lies (R150,31 per pixel) are rather inconclu- them are presently spectroscopicalty around the second brightest galaxy. A sive: no emission line is visible at the confirmed and the spectra generally in- strong emission line has been detected expected wavelength, and the conclude information an the continuum or at 7580 A with an underlying blue continuum level is only at 1 o above zero. the large-scale spectral energy distribu- tinuum, giving an identification of the Anyway, even if the recishi of A5 is not tion (Table 1). [0I[ 1 3727 line at z - 1.034. More data confirmed, the photometric information We must also consider the possibte are being analysed on this cluster, main- available makes this object very peculiar selection biases Introduced in the sam- ly by multl-colour photometry used on and exciting. The colour indices (0-R) ple before any analysis and compari- the numerous populations of very faint and (R-K) are very blue, the continuum sons with other surveys. The arcs and arclets, in order to evaluate their "photo- in the optical range is flat and feature- arclets are generally detected by their metric redshift" distribution. less. It is now quite unprobable that this blue colour (0-R < 1) with respect to the Table 1. Summty of the me^ swvey ofarcs and afcM tent &her with a non-evolutlonary mob el of galaxy or a model with a single Gtusmr b 4 0 R B-R R-K pB y &I, & initial burst of star formation. Thls prob- A370 640)' 0.3740.725 21.1 19.4 1.7 4.1 24.6 12 23.8 22.1 &ly mans that the history of star for- A370 @5Ia 0.374 1.3057 22.7 22.3 0.4 -3.0 25.4 B 24.7 242 matlon in these galaxies 16 rather ccn- C12244& 0.338 2B7 21.2 20.4 0.8 3,O 2S.3 20 24.8 23.7 tlnuous, up t~ a redshlft of about I. M9d 0.231 0.913 21.9 20.0 1.9 42 25.3 12 24.8 22.7 AM18 (# 3w a178 0,702 24.3 21.4' 2.9 - 25.0 4 253 22.9 Ant8 {# 289)' 0.176 1.034 22.5 21.7" 0.8 - 242 5 24.2 B.4 AQE! N' 0206 0.771 23.6 23.1 0.5 3.5 25.5 4 25.1 24-8 ~1~4+1654~0.391 1 23.0 22.3 0.7 3.3 25 4 24.5 23.8 1 have presented In this article the ~506(amoa-24)' 0.321 0.917 21.0 19.8 1.2 4.0- a 232 22.0 status of the survey in 1992, and I A2t63 (All7 0.203 0.742 2442 21 -8 2.4 - - 3 25.4 29.0 should emphasize the fact that the ln- Mi63 MY 0.203 0,728 23,1 21.2 f .9 - - 3 24.;) 22.4 crease of the mple d arcs with a very 'Gunnt filter: 'MI etal., 198RSMMbretal+.t99l: apeitbet al,. 1991:'iWldetaL. 19R flldd., -re mdshift measurement ie 1991; Qlwd 1992. pWnt; 'Sad1 8.,Arnaud M.. bchlbhyM., M&ez Q, in prepmation. Jaw, due to the dlffieulties of the observations and the long exposure times involved for these faint objects. But the detection of new arcs and arclet candidates still goes on, especially in the redder duster members but thL is not 4 Infrared Photometry of Large framework of the ESO Key Progmme afways the case (w for example the Arcs "Arcs and arclets surveymmi the simllar "red arc" in A2218, Pel16 et al. 1992). in order to Increase We observed one at GFHT. We expect some new, More important is the fact that tha sam- spectfal range of the galaxies, a my exciting data over the next year. In ple is limited In surface brightness more photo- rnetrlc survey of the arcs has been pr- particular, we are very excited by the than in magnitude; this Es due to the fact fortned by out colleagues from Durham new arc system dis~overedIn the dus- that to detect the conttnuurn of the @JQ in the K band (Smdt et al., 1992). ter MS2137-26 (Fort et at. 1W2, Fig- spectra of thew objects in a reasonable The main advantage of the band at ure 3): a long tangential arc has been exposure time implies that the surface 2.2 pn is that it scans a portion of the detected as welt as the first case of a brightness does not acead p~ = 25.5. spectrum damlnatd by the old stellar radial arc candidate. This peculiar lens- Rernembw that in gravbgonal lensing. population, and is more hdicathof the Ing cofl~urationhas been expected for surface bri~htness is and conwed history of star formation than blue pho- a tong tim, but as radlai Images are that magnMc&~oo means extension of tometry, vwy sensiave to went star supposed to form near the cluster the image of the source, Finally the sam- firmation. Anyway, the combinertion of centre, in mast cases thq fall in the ple is only based on galaxies with red- both magnitudes a$ well as the redshift envelope of tho giant cmtral galaxies. In shift larger than 0.7 huseIt roughly indieation give a god tool to study the the case of MS2137-23, the radial arc mrrespndrr to the minimum reMR distant galaxies and their entire spectral candidate was detected by Its blue czoC above which lensing is efficient, far a content. Then it is shown that dthough our, and a modelling of the gravitational typical at a redshift of 0.2 to deflector most of the the have blue dour Indb potential of the cluster was proposed by 0.4 @so, 2r~lBt811. ces, none of them remain undetected in Mellier et al. (1992) which takes tnt6 But the of the belong to sources arcs K. But forth- atz > I, the old popula- account a large number of observational family af galaxles the FIELD (which are don do& nQt contribute significantly to parameters. The spechsoopic confir- not their for detected by radio mission the K flux, so the sample is not consis- mation of the radial image would fix one example), and their intrinsic magnitudes, comted from the gravitational rnagnlfibation, arb in the range 124; 25) in B. This ranae is at laast one mmnitude fainter than-the magnitude rmg&d the deepest spectrascopic suweys of field galaxies perfoned by Cowie et at. (1991) for exam pie. So It is interesting ta explow the redshlft distribution which is centred around 1 In our sample. One should not& for example that with the exception of the pecufiar we of C12244-02, about 70% of the galaxies have a redshifl smaller than 1, and the medim mdsh'ift Is 0.9. Moreover, in view of thdr spectra, these ob- are not obserwed in a phase of violent star formation altlsough mission lines typical of HI1 regions are present in most of ham. Moreaver, when we have high- resolution Images of the giant arcs, we often see sub-structures inside the arcs. This still preliminary rewlt could suggest Jfhe4 that we see mrging Figure 3 Imge dfhe arc system in MSafST-23 (z=0,3f &cawed dwiq a run at the lVrr at large z or that inside the dismgalax- in ~ugustfsi IW m uey-mme "wswvw in dustersn. m& resofutfon /- Is disks or spiral arms am already show evfdeoce fora bfue "Widarc" near@ central galaxy, the nmt ease ever dekWof this formed. paculiat le#lsi~gm~umtm of the still unknown parameters, in- The use of the gravitational telescope Guiderdoni, B., Rocca-Volrnerange B., 1987, creasing the number of constraints of for the study of distant galaxies appears A& A188,I. the model. to k a powerful and original tool, which Ellis R.S., Allin~ton-Smlth,J.R., Smail I., For arclets or Uw weakly magnified is probably not yet fully used. for exam 1491, M.N. R.A.S. 249, 184. the Fort B., Prieur J.L. Mathez G., Melller Y., galaxies which are too faint to be ob- pls, we can also expect to find some Swcall G., f 988, A & A 200, L17. served spectroscopically, we also ex- "exotic" magnified objects, such as very Fwt B., Le Borgne J. F., Mather O., Mellier Y., ptsome progress by using multid- distant quasars (kBorgne et d., 1890) Pkat J. P. Soucail G., Pellb R., Sanahuja our photometric data spread over a law or we hope to "see" some spatlal struc- B., IBSO, The -62, 11. spectral range, such as B, R and I col- tures in galaxies at r = 1 through the Fort 8.. Le Fhre O., Hammer F., Cailloux M., ours. In W case we can compare the distortion of the clusters. The arc survey 1892, &J., submitted. colwrr indices d the objects with the opened for us a new window in the z - 1 Kassida A., Kwner I., Blandford R.D., 1992, predictions of spectrophtmetric mod- Universe! M.J.,In press. els of galaxy evolution, in order to evalu- WidaA,, Kovner I., Fort B., 1992, Ap.J. In press. ate a "photornetdc redshift". This Lynds R,, Petmian V., 1986, BAAS, 18, method Is being calibrat6d with the 1014. known arcs, and we are conscious that it I wish to thank all my colleagu~from Le Borgne J.F., Pelld R., Sanahuja B., is only useful in a statldcal way, when a the Twlouse-Barcelona group, namely Swcall G., Mellier Y., Breare M., 1990, large number of arclets is being ob B. Fort, H. Bonnet, J.P. Kneib, J.F. A & A 229,113. served. The preliminary results of the LeBorgne, G. Mathez, Y. Mellier, R. Mellier Y., Fort E., Soucell G., Mathez G., method, applied inthe fietd of A370 show Pe116, J.P. Picat and B. Sanahuja with Cailloux M., 1991, Ap.J. 380,334. that most of the galaxies have colours whom I have worked on arcs and lenses Melller Y., Fort B., Kneib J.P., 1992,M.J.. in compatible with galaxies at redshift for many years in such a friendly envi- press. Peltb R., la Borgne J.F., Soucail G., Mellier around 1, reinforcing the results pre- ronment] Also many thanks to our col- Y., Sanahuja B., 1991, Ap. J. 388,405. sented above (Fort et al., in preparation), labrators T. Tyson (Bell Labs), G. Pelt6 R., Le Borgne J.F., Sanahuja B., last but not lead, in a few optimal Bemstein (Tucson), R. Ellis, M. Fitchstt Mathez G., Foe B., 1992, A & A, sub- cases, we expect to get a complete set of and I. Smail from Durham for all the data mitted. data In some clusters: high-resolution X- provided and the exciting dlscussions Small I,, Etlis R.S., Aragbn-Gslamanca A, ray map with ROSAT, muttiple arcs and a we had about observations of gravita- Soudl G., Mellier Y., Gird E., 1W2, lot of arclets and weakly distorted im- tional lenses. M,N. R. A S, in gm. ages of background galaxies for a recon- SoucaEt GI., Fort B., Mdlier Y., Pieat J.P., 1987, A &A 172, L14. struction of the 20 gravitational potential Soucail G., Mellier Y., fort B., Mathsz G., of the Dark Matter from the centre to the References Cailloux M., 1988, A & A iQ1,L19. external radius of the cluster. The red- Brurual G., CMot S, 1992, submltled to Swcafl G., Fort B., 1991, A& Am, 23. 'shi of the giant arcs is in this case 4.J. Tyson J.A., I=, Ad %, I. fundamental in order to fix the scaling of Cowle L L,Songalla A,, Hu E. M., 1981, N8- Tyson J.A., Vatdes F., Wenk R.A., 1990, the potential in the lens modellings. tun3 354,460. Ap. J. 549, Li.

Quasar Absorption Spectra: The Physical State of the Intergalactic Medium at High Redshifts E. GIALLONGO, Osservatorio Astronomico di Roma, Monteporzio, Italy S. CRISTiANI, Dipattimento di Astronomia, Universita di Padova, ltaly A. FONTANA, Dipatthento di Fisica, I/ Universiti di Roma, Italy D. TR~ESE, Istituto Astronomico, Universita di Roma "La Sapienza ", ltaly

1. Introduction lines provide typi&i vilues of NN =I 014 mate of the cloud sizes has been ob- An important source of information on atoms ~rn-~and b = flu = 20-30 km tained by Smette et al. (1991) from the the distribution and the physical state of s-' (Carswelt et al. 1987, 1991) corre- spectra of a gravitationally lensed high- the intergalactic medium (EM) up to spondent to T, - 2-5 x 1O4 K, assum- redshifl quasar UM673 (&, = 2.7). They redshift z= 5 is provided by the study of ing thermal broadening. However, derive lower and upper limits of 12 I?;!, the absorption spectra of high redshift Pettini et al. (1390) claim typical b values kpc and 160 hzkpc respectively, for the quasars. The crowd of narrow absorp- as low as b = 17 krn s-I and a tight diameter of spherical clotlds, or 24 kpc tion lines seen shortward of the QSO correlation between b and NHI parame- and 320 kpc, for oblate spheroids with Lyman-u emission is thought to be due ters which suggests lower temperatures an axis ratio < 0.1. mainly to Lyman-a absorptions caused and would imply a further important Under these conditions, gravitational by intervening clouds along the line-of- constraint on the physics of the clouds. energy is overwhelmed by thermal ener- sight (Lynds 1974: Sargent et al. 1980). More data are necessary to resolve this gy and the clouds coutd be confined by Direci measures of column densities controversy. a hotter, highly ionized and diffuse IGM and doppler widths of the absorption The most recent and accurate esti- if non-baryonic dark matter does not quasar atmrptlon spectra pkiiularly suitable to inve8tfgate the ptryslcal propert186 of the diffuse and clumpy components of the IGM. As an example, we present a high resolution spectnrm (R = 22,000) of the quasar (22126-158 at r = 3,27, extend- ing from 4500 to 7000 A, and show how we om extract crucbl Information like the density of the diffuse neutral hydrogen and the dwrlbution of densltl, and temperature of the Lyman-a clouds.

2. Data AcquisitTon and Reduction The quasar Q2126-158 was observed at ESO (La Silk) in August 1991, wlth the NTT telescope and the EMMI instrument in the echdle mode (see D'Odori~o 1090). Two specdm of 7200 s each were oWnerd on August 6, and ma of 9130 s an August 7. The slit was 1.5 arcseconds wide and the seeing always less or equal to 1 arcsee. Partiwtw attention was paid In order to minimize the effects of the atrnoepbric dispersion. The absolute flux calibration was V carrled out by observing the standard 5000 6000 7UQO star EG274. The data reduction has (ll) been carried out wing the standard echelle package de&ibed in the FQW 1: -Ys spdmaf 02126-13. High-msdut,on deta are smoothed to 10 A 97 NOV edition of the MIDAS software resolution. Thkk amrepresents the low-resolufbndata The fitted conthuum fsa/soshown. (Bans9 et al. 1983). 7he weighted mean

contribute appreciably to the gravitational potential of the clouds (see however Rees 1986). The ionization of the IGM can be constrained by the absence of the long looked-for absorption trough shorlward of the QSO Lyman-a emission, wlth the average optical depth TOP S 0.5, (GP test, see Gunn and Peterson 1985). Considering that the background ionizing UV Rwc produced by the uasar population at z = 2-3, J = 10- 3 J-, ergs cW2 s-I HZ-' srl (Madau 1992), keeps both the clouds and IGM ionized, the physical state and evolution of the diffuse IGM can be further constrained under the assumption that' clouds are pressure confined (Sargent et al. 1980, Ostriker and lkeuchi 1983, Steldel and Sargent 1987). Taken together, the above conditions define a region in the density-temperature plane which provides an upper Ilmit to the IGM baryon density PIGMwhich can give information about the efficiency of the galaxy formation processes. Hfg h resolution spectroscopy available with good efficiency over a large range, using the EMMI instru- spectral . , ment at the NlT telekope, will allow to , collect a homcgeneous sample of Figure 2: A selected region in the Ly-a forest, with the fined profiles. example, adoptlng ionization equilib- rium with J-= = 1 and an IGM ternpea- ture0fT,~,~2xl0~Katz=3wefjnd QIOM = 0.006-0.013 for our best fit and 1 o GP estimate respectively (Giallongo, Cristiani and Trhese 1992). This is the first direct measure of the GP opacity carried out using high-resolution quasar spectra with good relative flux calibration as can be obtained from the NTT+EMM1 echelle-mode configuration.

A Properties of the Lyman Alpha Absorption Unes Quasar absorption spectra at a resolution R > 20,000 allow a direct determination of the column density and of the doppler parameter b through ltne profile fitting. The llne detection Is performed In the following way. In regions of the Lya forest with unAm signal-to-noise we construct the histogram of the pixel intensities. In general, because of absorp- tlon line contamination in the normalized sp&mrn, the distribution is not symmetrical in the Lya forest but is skewed towards Iowa intensity values. We fit a Gaussian profile to the high Figure 3: Vdmidisperslonpemterb versus the &@rhm of the mtmlhydrogen column intensity side of the histogram starting dens/& log Nw of Lyu tW. The continuous curve represents our mieetlon cdterion. The dashed curve cornsponds to a central flux of 0.1 where the noise level becomes coinpacable from the maximum of the intensity dis- to the signal and lines start to saturate. tribution: the variance Wined is taken as a conservative estimate of the noise levet In the region considered. AIl the of the spectra has been obtained st the contribution and the GP opacity due to tines whose central relath intsnsi is resolution R - 22,000 and is shown in diffuse hydrogen absorption: r = z~pur~,less than (1 -20) are selected to form a mguw 1 smoothed to - 10 & for illustra- and can be measured once the quasar complete sample. It is clear that a tive purpose. The S/N ratio ran@$ from continuum has been eshbllshed. threshold of this type corresponds to a 6 to 12 In the Ly-a forest region. From composite quasar spectra and well-defined locus in the h - 1% NH1 a21 26-1 58 had previously been ob- from Fiure 1 it can be shown that them plane (b is in km 9-l and NHI in ~rn-~. sewed by us at low resolution (-- 2!5 4, are few regions which can be assumed The usual x2 fitting procedure is udng the B & C spectrograph at the as repmentathe of the true continuum adopted to deblend the line profilea 2.2-rn ESO/MPI Megoope at La Silla on level. The region between Lya and CIV (Carswell et at. 1987,1991). The number September 3, 1989. Two exposures of emissions is affectgd by the presence of of components is assumed as the 30 min each were taken with a 5 arcsec weak emission lines whose broad wings minimum which gives a probability of wide dk in the spectral range 3300- tend to overlap (01 1302, Cll 1335, SiiV random deviation P > 0.05. An example 8650 A. A standard reduction was 1400) and the region betwsen CIV and of the resulting profiles is show in Fig- carried out with the long-slit package of CIII] emissions is affected by Hell 1640 ure 2. In general this objective proce- MIDAS. The absolute flux calibration and Olll] 1663 and by the bIue end of the dure is satisfactory though, in some wan obtained obsedng the standard blended Fell 2000 complex. With this cases,lines with a malt number af pix- star U)S 7498. caution the Wed power-law is shown in ds and poot S/N ratio are classified as The two spectra have then been com- Figure I(a, - -0.62). JngIa although they clearly appear as pared, finding that, apart from the dilk- At this point, regions free of strong double from visual inspection. mce of a factor 100 in resolution and a absorption Ilnes, where the r.rn.s.fluctu- After removing metal line systems, renormalbation factor close to unity, ation about the mean flux becomes mn- which are wily Identified through the there was a Wect mrmpmdence sistent with noise statlstlcs, are selected observation of CIV doublet seen within the noise. The red part h > 7000 to estimate the GP depression. The longward of the QSO Lya emission, a) of the low-resolution spectrum has power-W continuum estirn- long- we obtaln, in the region from 4750 to then been appended (after renormaliza- ward of Lya emlssion is extrapolated in 5200 A, a complete sample of Lya lines tion) to the ecfielle spwtrum as shown the Lyman-a forest and compared with whose distribution in the b - log NHI in Figure 1. Ute local continuum level of the selected plans Is shown in Figure 3. Two curves regions. We obtain an average opacity of constant central line flux containing at z 3 of tm = 0.013k0.026. This new of the sample are also wp- 3. The Quasar Continuum and the - most value of the hydrogen opacity can be resented. The upper envelope repre- Gunn-Petemon Test used to constrain density and tempera- sents wr selection criterion: fines with The total opacity in the Lyman-a ture of the tGM supposed to be kniW central flux less than the threshold are forest is given by the sum of the line by the UV flux of quasars at z = 3. For included in the complete sample. The of the lines which appear as saturated could be unresolved blends of unsaturated lines which should occupy the top (b z 30 and log NH~5 14) of the 8Pw- ently carrelated distrlbuflon, as can be seen in Figure4 where a simulated blend of two lim with the above pan- meters and S/N = 8 has benWed as a single line of b = 35 and log NHl = 15.1, comparable with the line of highest column density in our sample. Thus blendlng plays a mcilrole In the interpretation of the observations, as has been shown recently by T&vese, Giallongo and Carnurani (1992). How- ever, increasing the signal-to-noise ratk would raise the upper auwe In Figure 3 and move downwards the lower one and allow a better deblending. Thus, recognizing a possible intrinsic cmla- tion between b and NHI In the Lyman-a clouds is withln the reach of the present ESO instrumentation.

Re~CBS Elanse, K. et sl. 1983, "MIDASnln Pmc. of DEWS, Zdch, 87. Carswell, R.F. et at. 1987, M.J. 31% 708. FQure 4: Simulated blend of two lines with b - 50, log = 14. I, by I A, with W = Carswell, R.Faet at. tBQ1, Ap.J. 371,36. 6. DaW curve: profile of the lndlvidml components, Continuous curve: single line fi D'Worico, 8. lW0, The Messmgsr61.51. profile, wi'h b = 35 and log NM 5 15.7. Giallongo, E, Cristlani, S. and Them D. 1992, Ap.J.L Qn press). Gunn, J.E. and Peterson, B.A. 1965, Ap.J. $42, 1633, lower curve corresponds to a central not uniformly distributed in the same Lynds, CR.i971,Ap.J. 1g4 U9. flux of 0.1 where the noise level be- range of b occupied by unsaturated Madau,P.1982,Ap.J.I., Ll. comes comparable to the signal and lines. In particular, the absence of clear- Osttlker, J.P. and Ikeruchl, S. 1B83,Ap.J. 2@, lines start to saturate, In the range of b ly single llnes with b < 20 and log N,, m. oonsldd lines on the right of this > 13.5 is not due to any bias. Moreover, Pettinl,M.etal.IWO, M.N.R.A.WW,545. 1W cum be unresolved blends. It is almost all the saturated features appear Wes M.N.RaRS.218,25P. cauld mnt,W.LW. et d. 1880,Ap.J.S.42,41. clear that unsaturated lines show a tight as unresolved blends and the reality of Wrte, A. et al. 1992, M.J. 38% 39. correlation which reflects the selection lines with lw NHI> 14 In our spectrum Is Steidel, C.C. and Sargent, W.tW. 1M7, effects (Iinwdection + non-saturation). cast In serious doubt. The same cauld &.J. W8,L11. However, the saturated lines, which are be me for lines with b > 35. Tr- D., Gidlongo E,, and Camufeni L clearly identified In our spectrum, are According to this Interpretation, most 1992, Ap. J. (In pm).

The Galaxy Population in Distant Clusters A. BUZONI', M. L ONGHETTI'. ', E. MOLINARI1and G. CHINCARIIVI'~ * '~sservatorio~stronomico di Brera, Mitano, Italy; 2~niversitadegli Studi, Milano, Italy

evolutionary status of the galaxy popu- that ellipticals always reside In high- Clusters of galaxh are recognized to lation. density regions like the core of the cbs- be the basic building blocks tracing the Moreover, it is relevant to clarify ters while spirals better trace the low- large-scale structure in the Universe. whether or not clusters are dynambdly density peripheral regions (Oressler Thanks to the large number of coeval relaxed structures and how environ- 1980). objects all at the same distance we get mental conditions constrained galaxy Both the dynamical and photomaric more favourable statistics allowlng to formation among the different mor- questions have much in common as en- explore in much better detail the phological types. We know for instance vironment conditions might have influ- false correlation (see for example Koo have been observed down to the limiting I988 for an exhaustive dlscussion). In magnitude r - 24. Data reduction and the last years however a number of ob- systematic photometry in the flelds have servations converged detecting such a been performed using MIDAS utilities, component in the population of many and the implemented package INVEN- clusters at high redshift confirming that TORY (West and Krusrewski 1981). A despite any possible complication the parallel investigation including multi-ob- effect is real (Butcher and Oemler ject spectroscopy of selected relevant 1984b, Luppino et al. 1991, Molinad et candidates in each field had also been al. 1990, Newberry et al. 1988). carried out allowing to explore In more Three main spectral features seem to detalt the absolute spectral energy dls- characterize blue galaxies: Ii) Most of tribution of the galaxies. them display emission lines (typically Although of the greatest importance, [Oil], [OJ11] and Hf)) as found for instance the spectrosmpic approach cannot be in the star forming spiral galaxies widely pursued as it is largely time-con- (Butcher and Oemler 1984a); (ii)strong surning. Even fully exploiting the Balrner lines in absorption are often de- EFOSC MOS mode we need about 4-7 tected superposed to a normal E-type hours integration time to obtaln spectra continuum (E+A galaxies of Dressier of acceptable signal-to-noise for ob- and Gunn 1982, 19831, (iii) when high- jects fainter than 20th magnitude. For resolution imaging is available Vhomp- comparison, good photometty down to son 1988) most blue galaxies seem to magnitude 24 can be achieved in about display a late-type morphology with 1 hour total exposure time. Our analysis signs of possible interaction. rests therefore basically on the mul- On the basis of our present knowb ticolour photometry using spectral infor- edge It is certainly hard to disentangle mation as a check of our inferences. the various mechanisms leading to such Through comparison with evolutio- profound differences in the population nary population synthesis models of late-type galaxies at early epmhs. (Buuoni 1988,1989) we intend to study This is certainly a problem since it has to how consistently photometric proper- be established how such late-type ties (i.8. magnitudes and colours) of galaxies can "vanish" or transform so galaxies in clusters do evolve in a "regu- drastically by the present time. 0 1 2 Alternatively, one should conclude g-i that looking at high redshlft in some way we are selecting clusters which are in- Figure 1 : (g-r) @-I) diagrams for the clustm trinsically different from the locd &am- A3284, 2158M351 and 1141-283. AN of th@ ple. One reason could be that sinm they objeefs w/th complete photometry are In- are mainly optically selected, the more cluded in the plots. The encircled clump of compact ones are strongly preferred objects, moving to redder colours with in- (Cappi et al. 1989). Moreover, clusters creasing redshift, /$ due to the cluster elliptical galaxy population. The redshifts of the with active galaxies could be more dusters are mpectively 0.15, 0.45 and 0.50. prominent. Finally, due to k-correction effects those with a larger fraction of spirals might become more visible with increasing z (Coleman et al. 1980). That high-redshift clusters might be enced at the beginning the morphologi- somewhat different aggregates also cal and photometric properties of the stems from an extended analysis by galaxies. Therefore, studying cluster Newberry et al. (1988). In particular, it galaxles we get both direct dues about appears that they display a larger vetmi- their evolutionary status and about that ty dispersion (typically more than of their parent clusters. 1000 kmlsec) and, statistically, a more compact stnlcture. 2 The Blue Galaxies' Dilemma 3. The Project One of the most intriguing and em- barnassing problems when dealing with In 1986 we started a systematic sur- the cluster galaxy population is that an vey of clusters of galaxies at intermedl- tllllllllllllllllll increasing fraction of blue galaxies 0.e. ate and large redshift (0.15 < z < 0.6). 0 1 2 bluer than expected for a population of Previous contributions to this long-term g-i quiescent early-type galaxies alone) project can be found in Buuoni et al. populate clusters at high redshift. This is (1988), Molinari et al. (1990), Molinari et Figure 2: Twodour diagram fw the main- sequence stars (upper parno. In the lower the so-called "Butcher-Oemler effect". at. (1992). paw the mlwr excumim for the d/fferent To date a homogeneous set of CCD Since spiral galaxies in the field are galaxy morphobgical type3 8 function of known to display similar colours, It has observations In the Gunn g, r, i system redshift (from z = O to I in the sense of been first questioned that geometrical has been collected mainly uslng the inmasing g-i) are shown w'th the mred- and projection effects as well as bad 3.6-m ESO telescope at La Silla equip- shlft dnk marked by filled dots (from Moli- field subtraction could Induce such a ped with EFOSC. About ten clusters narl et al. 1M). galaxies spread along a diagonal strip in the diagram: (ii) the density along the strip is not constant and one clearly detects In each panel a clump of objects (encircted in the figure) moving to redder colours with increasing redshiff; (Ili) a tail of a few faint objects L always present redward the clump. Their apparent magnitude is correlated with cotours, the reddest ones being also the faintest. A full comprehension of the diagrams can be eased by comparing them with the two panels of Figure 2. In the flrst one we reported the locus expected for Galactic field stars of different spectral type while In the second panel we display the apparent colour excursion of galaxies of different morphological types with increasing redshlft. It is now clear that the clump of objects observed in the colour-colour diagrams is origi- nated by early-type galaxies at a redshift pertinent to that of the parent cluster. Mwaover, as a general rule we can note that foreground galaxies always lie blueward of the colour of the main clump due to the fact that E-galaxies are systematically the reddest objects with- synt in a given redshift. Accordingly, the faint tail of red objects with g-i>2 is mainly contributsd by field galaxies in the background (at z > 0.5) belonging to early types (spirals can never reach such colours as displayed in Rgure 2). Also a 0 few distant QSQs might be expected to lie tn this zone (Irwin at a!. 1991), 3000 4000 5000 6000 A complete support of the fact that Wavelength (A) galaxies in the main clump of the (g-r)/ (g-i) diagram can be the true prcgen- Figure 3: Observed and theoretfcal spsctral distribuiion of elliptical galaxies. In the upper panel itors of present-day ellipticals comes low spectra d red galaxi= In the clustwA52B4 have beerr madded and raduc8d to restfrzme from the analysis of the spectra as (six hours total exposure with the €SO 3.6-m telwcope EFOSC. Grism BS8900 with a time + shown in Figure 3. Here, an averaged 230hmm dispmim). me lower panel shows fix cornpatison an appropMe synthetic model fw a 15 Gyr slng1e bursf stellar population @om Bmi1989, hls model No. 10 in Table 8). spectrum obtained by summing up four red galaxies in A3284 Is compared wlth a synthetic model of a 15 Gyr burst stellar population taken from Buaoni lar" way following the prescription of seeing conditions. That is why we must (1988, his model No. 10 In Table 8). stellar evolution. All those which devlaie rely on colours to identify galaxy types. from the wlll tell us some- A two-colour diagram could be used expectations 5. What Contributes to the Blue thing new, that is about events which effectively to discriminate between late- Excess? have perturbed and/or accelerated the type and early-type galaxies in distant normal course of the evolution. Thls clusters. Furthermore, combining it with A more simple approach to the study mlght be expected especially at high a colour-magnitude diagram we can of the cluster galaxy population rests redshift. also discriminate between fore- and also on the analysis of the single colour background objects (respectively too distribution like in Figure 4. In the figure bright and too faint to be members of we reported the g-i distribution ob- 4. Galaxy Type and Colour Segre- gation similar apparent colour). On the basis of served for the clusters A32M. Gonsid- accurate photometry we showed that ering all the objects available (thick line A 25 kpc linear size galaxy at redshift redshift of distant clusters (up to z - in the figure] one clearly recagnizes the z in a q, = 0 Universe Is about 0.45) can be inferred from apparent major bump due to the early-type com- 1.8h(l+~)~/Iz(l +z/'2)] arcsec across galactic colours within a 10 % accuracy ponent in the cluster population as pre- (where W, - lOOh krn/sec/Mpc). Its sur- (Molinari et al. 1990). viously discussed. A second peak face brightness dims as (1 +z)-~so that In Figure 1 we show some relevant appears to bluer colwrs (g-i- 0.5) that this makm very difficult or even irnpos- (g-r)/{g-i) diagms for three clusters we interpret as late-type galaxies. This slble to estimate the morphology at high of our sample with z spanning between group contains the excess blue galaxies redshift. Beyond z - 0.2 any direct mor- 0.15 and 0.50. In each panel the pho- claimed by Butcher and Qemler. phological clmslication becomes unre- tometry of all objects in the flelds is Following the canonical prescriptions liable even In deep CCD frames when reported. Some striking features are (Butcher and Oemler 1984b) we were taken under typical instrumental and worth of attention. (0 Both field stars and able to derive the fraction fb of blue Butcher, ti. and Oernler. A. 1984b, Ap.J., 28& 426. Bunoni, A. 1988, Erica Works-, Towards Understanding Galaxk at meRedshift, eds. R.G. Kron and A. Renzini (Dordrecht: Ktuwer) p. 61. Buuonl, A. 1988, Ap.J.Supp/., 71,817. Buuonl, k Mdharl, E.C., Manousoyannaki, I. and Chincarlnl, G. 1888, The Messenger, M,50. Cappi, A., Chjncarini, G., Comni, P. and Vettolanl, G. 1989, Astr.Ap., 223, 1. Cdeman, G.D., Wu, C. and Wwdman. D.W. ?980,&. J.WpI., 43,393. Cowie, L L, Songaila, A. and Mu, E. M. 1991, Nature, 354,460. Drwler, k 1980, Ap.J., 236,351. 0 Dmsb, A. andGunn, J.E. 1982, &.J., 283, 533. 0 1 2 Dmrler,A.anllGunnlJ.E.1883,&.d,~0, g-i 7. Irwin, M.J., MeMahon, R.G. and Hazard, C. Figure 4: Histogmm otthe g-1 cdwr distribution in the dusterA3284. The thick line represents 1991, The Space Distributbn of Quasars, the distribution of the whole sample of measured ~~, while the thin line accounts for the ed. D. Cramptan, Astr. Soe. of the Pac. subsample fainter than r = 21.5. The histogmm is -tad by a moving avemge with beam Conf. Ser., vol. 21, p. 1 17. 0.3 mag and step 0.01 mag. Koo, D.C. 1988, Erice Workshop, Towards Understanding Galaxies at Large Redshifi, 4s. R.G. Kron and A Renzinl (Dordrecht: Kluwer): p. 275. galaxies for this cluster and for some whether or not in the clusters at high Lupplno, G.A., Cwke, B.A., McHardy, I.M. others in our sample. The raults are redshii the population of dwarfs was and Ricker, G.R. 1991, Astr.3, 10% 1. summarized in Figure 5 where we corn- more evident, and therefore favours or Mollmrl, E, Btrponi, A. and chincarink G. pare consistently with the work by New- disfavours the hypothesis of a luminosi- f990w N- R-A.sm 246, 576. beny et al. (1988). Our data confirm the ty-dependent evolution, as the recent ~~~~;c~"~b. Butcher-Oemler effect, with the blue results dealing with the dwarf-galaxy Mtzni7iof me Symp. No,7:; ,49 galaxies becoming an increasing frac- nature of the blue excess in the field Pow,ations GalaxIBSw, ds, tion of the high-z cluster population. counts seem to suggest (&wig at al., Barbuy and A. Renzlnl (Dwdrecht: It is remarkable to note however that 1991). KIuwer) p. 460. both on the basis of our photometric Mewkrry, M.V., Klrshner, R.P. and Born, and spectroscopic obsewations cab RefemnCs T.A. 1988,Ap.J.,335,629. Iected to date we do not find any evident Thompson, LA. 1988, M.J.,324, 112. sign that the blue exms is due to an Binggeli, B., Sandage, R and Tarnman. G.A. West, R.M. and Kruszewskl, R 1481, Irish 1988, Ann. Rev.Astr.Ap., 2@,509. ~str.~.,15, 25. pmence Of activeOr peculiarButcher, H, and Oemler, A. 1984a, Nature, Whirnore, B. C. and Giltnore, D. lvl. 1991, galaxies. The radial distribution of the 310, 31. &.J., 987, 64. galaxies in the blue bump in fact seems to closely match the trend observed by Witmore and Gllmore (1991) for normal spirals In a large sample of low-redshift clusters. The question that arises is .4 I I I I I 1 I I 1 therefore whether we are observing - 1 I - somehow "active" blue elliptical galax- - - ies or, more likely, a population of spiral- e - like galaxies. .3 - -- A striking feature which seems to - appear from the observations and could - - be worth further investigation is that - O. - blue galaxies in our sample tend to be- ,& -2 , 0 - come relevant at the faint tail of the - - galaxy luminosity function. This is evi- -L 0 - dent for example in Figure 4 where the - a* - thin line shows for A3284 the colour .1 - 0 - distribution of the objects fainter than r = - 0 - 21.5 (MB>-1 7.5 assuming H, - 50 km/ - - ~PC). d rn - As this magnitude roughly coincides 0 I I I I I I I I t with the limit where dwarf and non- dwarf galaxies contribute at the same 0 .2 -4 .6 level to the luminosity function (Binggeli Z we are not to univocdly Figure 5: Diagmm showing ffre fraction d blue galaxies &. @m dots am taken from Newberry identify the real nature of the blue ax" et a. (1988, fhdr Fig. 2). filled square boftom left is the mean estimate for 8 low-redshin cess. A more complete and dgep data- clusters (up to r - 0.08) from Butcher and Oemler (lQB4b).#lM dots am our data and refer to base will dlow us to discriminate the dustm ,43288,A3305, A1942 and 2158+0351 in order of increasing &shift. Probing Beyond COBE in the Interstellar Medium E. PAlAZZI, M. R. ATOLINI, N. MANDOLESI, lstituto T. E. S. R. E.,Bologna, Italy P. CRANE, ESO

Introduction a The COSE satetlite, wlth Its instruments, has provided new Insights info the origin and evolution of the Universe. The FIRAS (Far Infrared Absolute Spec- 6 trophotometer) has supplied the best demomtaation that the Cosmic Background Radiation is a blackbody (Mather et al., 1990). The DMR pllfer- P ential Microwave Radiometer) has provided what appears to be the first ma- 2 sumnsent of the structure in the angular u distribution of the background radiation (Smoot et al., 1992). What more Is there to do and how can it be done? 2 hidewhat may be done by subsequent satellttes, two important measurements can be made using interstellar thermometers. The first is to provide a prectse check absa- Independent on the o o 10 a0 s3 40 lute calibration of the FIW spec- trophotometer. The sgcoml and most figure 1: MeasW 1-(CN} wlth the associated I a emw imwshg HD nwnber of the interesting from a cosmologfcal point of obsarved sters Pam et al.1. 7313 SOIMIlna nwemta tha CDBEmtt fw Tw,T = 2.735 f vim is to dmonmte the hmogenetty 0.06 K, the deshedlkr@kthe wtedtlm of the T,(CNJk'ah, T-2.318 f K, the dashed of the CBR radjatlon. A third pos~bjlity IIM IS tb ~&hted d the T&C#) dm, T = 2818 f 0.018 K. would be to verify the expansion of the Universe via the (1 + z) dependence of the temperature of the CBR. One of the fundmentd assumptions means that an obaewer anywhere In the Soon after the discovery of the CBR, It In current cosmotogical models is the Unlverse should measure the same glo- was recognized that the rotational excl- homogeneity of the Unlv~rseand hence bal properties. In parflcluar, the tempera- tatlon of interstellar CN could provide of the CBR radlatlon. Homogeneity ture of the CBR should k the same. one of the best thennometem for deter- mining the TcsR.Subsequently, Modern techniques have pwhed the method ,,, , close to the preciston of the best radlometers. Although the radlometers are quite pmbe, they are only able to call K - measure #le CBR temperature tdly - (= 1 AU of the Sun) and they depend on saphtstlcaled and complicated methods far calibration. - On the other hand, Interstellar CN, - whbh has been seen In semi clouds - withln 1 Kpc, Is able to report to us the - intensity of the CBR radlatlon field in Its - vicinity. In addition, the actual tempera- - ture determination dies on a rather dl- - rect technique, - - - - CN Measurememofthe CBR - W - HomogendtywlthlnI Kpc .rt - - - mt rani.= ciw - A recant aornpIlation palazni et al., mpaenm 1992) of the measurements of CN excita- - SK 106 - - - tlon temperatures for bright stmha8 not .Z III~~II~III~III~I+Ishown any large dlffemncm In the TCm in zmm rn 334 ~~36 3938 any dimtion prwlding the largest body F~SILI~I~WI - of data to wppott the hmogenelty of ngure 2: tntersteikr~aN K bwerds ~&SK~~~(slwq, Q- ~a2pehnk the CBR even 1only within about I Kpc. CIwd mponents am well dinstingui~, However, most of the CN excitation temperatures appear atightly above (= 80 f 30 mK)the COBE measurement of TCsR = 2.735 K (Fig. 1). A possible explanation of this excm would be the presence of local excltation mechanisms (such as oolllsional excltation). None of the data necessary to quantify th~emechanisms are of sufficient qualliy to provlde a clear explanation of the observed difference. Improved observations would be needed to obtain better data on local conditions In molecuhr clouds and on CN absorption llne measurements to show if the excess In the CN excitation tempemture is really a result of collisional excitation.

Homogeneity wlthln 50 Kpc A very real posstbility exists to determine TeeRIn the Magellanic Clouds If an appropriate sight line wlth sufficient CM column density can be found. Such a measurement is juBf within the posslbillty of the largest telescopes In the southern ngum 3: Inmtdbr CN toweds the star SK 106 (SMCI, Tha pdtlon d the line m'mides with hemisphere. on@ of the strwrgw ccrmponents of the IntersteIlar Ca /I K In the Small M~IImicCloud. The CN i8 We have initiated a prqramme for upper llmlt fof the column density 1 x 10'' obwwlng a sample of lines of sight towards bright and reddened 0 and B stars In the Magellank Clouds. The observa- cltatlon mechanisms such as colllslonal References tions were performed In October 1991 at processes or local UV field are difficult to the 3.6-m ESO telescope (La Sllla, Chile) evaluate. NeverthJess, a determination uslng the CASPEC spectrograph with of Tcsdr) c (1 + ~~TCBR(Z011 at any Bahcall, J.N., and Wolf, RA., 1988, &.J., the 31.6 linelmm grating plus the long redshift would be very difficult to explain 152,701. camera in the wavelength range in the context of the standard cosmologl- Magain, P., and Glllet, D., 1987, Ask.&. Lett., 380d-450d cal scenarios. Though thy are affected 184, L5. Preliminary results show that the Call by large uncertainties, the exlstent upper Mather, J.C.,at al., 1990, ApJ. Lett.,=, L37, Meyer, D.M., Black, J.H., Chaffee, F.H. Jr., H and K interstellar lines (bath galsctte to do the limlts T=BR(Z) not contradict Foltz, C,B., and York, D.G., 1988, Ap-J., and Cloud components) are present In all present theories. 30Br L37. the observed stellar spectra (Flg. 2). In summary, excfting and important Palaut, E, Mandolesi, N., and Crano, P., Molecular absorption lines of CH and CN cosmological rmults are possible from a 1992, WJ., Oet. 10,1992. are marginally visible (Fig, 31, represent- careful study of the Interstellar ther- Smoot,G.F.,etal., 1902, Ap.J. Lett,,598, L?. ing the first detection of the CN species mometers avallable to us, Wamplar, E.J., 1990, Ap.J., 363,40. In the Magellanlc Clouds interstellar medium. Detection of interstellar CH and CH+ has been reported only towards supernova 1987 by Magdn and GiHet (1987). Additional obwwing tlme Is needed New ESO Conference and Workshop Proceedings for improving the molecular detection, In The PrOcedings of the ESO Workshop on HIGH-RESOLUTION SPECTROSCOW particular CN for the measurement of the WITH THE VLT have iust become wallable. The SlO-page volume, edited by M.-H. TeBRat 50 Kpc from us. Uldch, [8 offered at a price of DM 45.-. The following publications we In press and will become available end of September/ beginning of October 1992: Homogeneity on Large Scales ESO CONFERENCE ON HIGH-RESOLUTION IMAGING BY INTERFEROMETRY It may be pmslble to observe the II. These Pmceedings, edlted by J.M. Be&ets and F. Merkte. am divided Into hhro excltatlon of other molecular rotation volumes [Part I and Part 11) and contain more than 140 papers on a total of more than or 1320 pagw. The prlce Is DM 110.-. atomic fine structure lines at quite large 4th ES0/8f-ECF DATA ANALYSIS WORKSHOP. Thls 188-page volume, edlted by distances (Bahdl and Wolf, 1968). In- P. J. Gdtand R.C. E. de Ruijsscher, will be avallable at a price of DM 25.- (all prices deed a few reports (Meyer et A,, 1986; include packing and surface mall). Wampler, 1W0) of upper llmlts to TCsRat Prepayment is required for all publications. Payments have to be made to the ESO redshlft around z = 1.6 and z = 2.5 have bank amount 2102002 wlth Cornmenbank MIlnchen or by cheque, addr~sedto fhe bgen reported for the excitation of CI and attention of CII flne structure Hnes. ESO, Financial Ssrvices In cant& to the measurements in the Karl-Schwamchild-Str. 2 Magellanic Clouds the measurements at 08046 Oarchlng b, Munchen, Germany high mdshif! introduce a rather large Please do not forget to Indicate your complete addmand the tltle of the Prooeed- uncertainty In the local condition of the Ings. specim absmed, for example local ex- IRAC2 at the 2.2-m Telescope A. MOOR WOOD, G. FINGER, P. BIEREICHEL, B. DELA BRE, A. VAN DIJSSELDONK, G. HUSTER, J.-L. LIZUN, M. MEYER, ESO, Garching, H. GEMPERL€IN, A. MONETI, ESO, La Silla

ESO's new infrared camera, IRAC2, is inner cryogen tank respectively. Figure 3 plexer which is structured in four quad- equipped with a Rockwelt 256x256 pix- is a photograph of the cooled optical rants having separate output amplifiers. el NICMOS3 array for imaging through assembly showing the filter wheel on the It is controlled and read by a programm- broad and narrow band filters between left and, on the right, the objective wheel able, VME-based, detector controller 1 and 2.5 ym and a K (2.2 pm) band which is largely hidden by the detector whi~hhas been developed in Garching scanning Fabry Perot. A preview of mount. and contains four AID converters allow- some of its capabilities was already giv- The NICMOS3 array is a hybrid device ing simultaneous reading of the four en in the June 1992 Issue of the consisting of a HgCdTe diode array quadrants. This system also contains a Messenger (68,42) where we showed a bonded via indium bumps to a multi- Motorola 68030 processor which runs 2.1 pm broad band image of a r = 0.2 galaxy cluster and a narrow band Fe11](1.64 pm) mosaic image of the SNR RCW103 obtained during the first test on the 2.2-m telescope in May. In this article we give a description of the instrument and its observing modes together with performance figures derived from the test data and some additional images selected to illustrate some of its posslble scientific applications.

1. Description of IRAC2 Figure 1 is a photograph of IRAC2 mounted on heF/35 Infrared adapter at the Cassegrain facw of the 2.2-rn telescope. The camera itself Is housed in a modified Oxford Instruments 4-1 liquid helium cryatat which is partially hidden by the attached motor control and detector acquisition electronics. (Although the MICMOS3 array has a long wavelength cut-off at - 2.5 pm and requires cooling to only -6OK using pumped liquid nitrogen, a He cryostat was selected in order to keep open the possibility of Installing arrays operating out to 5 pm In the same carnera in the futufk) The black una sandwiched between the camera and the adapter houses the scanning Fabty Perot eta- lon(s) and remotely controlled exchange mechanism used to rotate A in front of the entrance window. Figure 2 shows the layout of the camera optics. The input doublet field lens, which also acts as the cryostat entrance window, provides for a 70-mm diameter (-3 arcmin.) field and reimages the telescope pupil at the cold 4.5-mm diameter cold stop just behind a 24-position filter wheel. The field is re-Imaged on the detector by one of the five remotely selectable objectives mounted on a wheel. In order to minimize flexure, the camera Itself is rigidly attached to the outer vacuum housing vla glass thermal Isolators and the optics and detector mount are cooled via thermal connec- tions to the inner tadlation shield and Figure 1: IRAC2 mounted an the F/55 adsptw at the 2.2-rn telscope. FI~2: CrpticaI layout of the camera. Tms inpul doublet covers a 70-mm (3-mm.) diameter Hlferd and acts both as fhe hld lehs and the c-t wlndow. A 24 pdsrtion flm wheal (not show??)is htedin bnt of the caldpupl stop and the fiwe remotely interchangeable mounted on a whew/ behind ths pup// stop pmvh for magniffcatima kom -0.14- i. 1 "/pixeI,

detector pre-pmslng software under pis. The arrangement used durhg the HP370 which runs control software the OSg operating system. This pro- test Is shown In Flgur84 but Is pmvl- written in Basic which was developed cewr rwives command files specify- siond pending completi~nof a new originally only for laboratory testiw in ing the required detector set-up from standard urninterface and VME based Garehing. TMs wrksta8on is connected the instrument workstation; transmits motor control system on La Sllla. Instnr- to the instrument via CAMAC for the real time Images to a monitor in the msnt set-up and control is via typed motor controls, a GPlB bus for the Fabry cowroom and sends images, with or mmmands and menu bars on the Perot control and ethernet fibre optics wlthout m-averaging, to the Instrument workstatton. The real time display is par- tlcularty useful during set-up on an object field as pixd values and eoordlnates can be measured and cut-levels set using only the we.The observer can set& from a variety of mad-out modes including double and triple correlated and multiple nondestructive sampling. A novel variant of the latter mode, teeted In May but not yet implemented in a very user friendly way, also achieves partial seeing correction by tracking a reference object In the field and applying a shift and add alg~dthmto each non- destructively read sub-image before solution of the error equations for the integration ramps. At present, the minimum time mired to read out a full 256 x 256 image 1s - 700 ms. A faster read-out muld improve the performance of #e real time shift and add mode and wuM be implementad In the future by install- Ing a faster pre-prooessw whlch is now available. In view of the plan to phase out the HP 1000 series computers on La Silla the user interface runs on a wolhsWon and MIDAS is used on-line for data stor- Figure 3: 7he c-nk optcal#wrnbfy showing tfrs Mter whml on the kft end the abjat/ve age, image display and quick-look and- wheel on the right Weft is WLIbhJdden by the detector mnt, links to the detector pre-prmor. Tabla I:lR4C2 chamcwwk There is also an FIS232 link to the HPIODO telescope computer which Is wed to step the secondary mirror dur- Ing fms exposures and to read coordinates which are wdth In the file headers. The HW30 workstation is used to run two parallel MIDAS -ions. One of them is set in the background mode and is used to display images (with or wlthout background subtraction as re- quested) and store them in the correct format while the other is available for Interactive image analysls using MIDAS. The HP370 shou Id become superfluous once the new user Intetface is available when both the control saftvvare and MIDAS will run on the HW30 with a separate XI 1 window terminal aval table for on-line analysis.

2 Obsewing Modes IRAC2 provides for imaging at a varIe- ty of image scales through broad and narrow band filters between 1 and 2.5 pm and a K(2.2 pm) band ming Fabry mot Won yiddlng R - 1 000. The available filters, image We6 and corresponding field sizes are summarized in Table 1. The scales A-D are measured values derived From images of astrometric double stars. Al- though objectives D and E should provide a drwlar 3' field limited by the entrance window this is slightly vignet- ted on two sides at present by the di- chroic mim In the F/35 adapter. For broadhd imaging. when badrground noise dominates, It is recommended in any case to use objective C (0.4#"/pixm) in general. This objective ~RSthe highest efficiency, yields the maximum square field and provides reasonable sampling under average seeing mdi- tions. Objective B(0.27Vplx.) can be used when bettar samplinglspatial reso- lutton Is more lrnpwtant than Reid. The desired observing made, filter, ferentlal focus changes during the nigM waveIengths which are automatically magnification and detector -em due to te1escop hpmture changes writfen in the file headers. are set via the workstation user inter- can be made uslng a ~allbrELtjoncuwe The detector set-up Includes sdec- face. A present, hestandard modes are without needlq to repeat the star mation of the mdmode; the on-chip inte- {i)focus QI) DC observing (staring) and surements. A focus shift is required gration time PIT); the number of Integ- (ill) Faby Perot scan. Chopping and when using the Fabry Perot. rations (NOIT) to be averaged in the pre automatic beamswitching could be im- The DC Meused for obsming re- process~More transmission to the plemented but are not considered par- quires little explanation. Each image is workstation and the number of such ticularly useful with this array. Real time WTWinto a separate 819 with its own measurements to be made (cycles) and shift and add is more complbted to identifier and a header which codm stbred In sew9files. If In doubt, the set-up and Is not yet available as a all the instrument and detwtor pamw read-mode sh~#Idbe set to double- standard mode. ters plus the time and telescope coor- correlatd. MuMple, non-destructive, For focussing on a star the focus dinates. sampllng Is needed for the shift and add mode Is used to automatically step the In the Fabty Perot mde the required Weand yields somewhat lower wad- Mescope secondary mirror through a narrow band order isotatlng filter can be noise for long measurements but invd- specifled range of pitions and record set manually or automatidy and both ves larger time overheads and increases images which are displayed In a line at the filter transmission curve and the the amplifier glow in the comers of the the end d the rneasument. The tieat wavelengths corrmpondng to the dlf- array. The main considerdons in focus can then be determined by fsrent orders displayed on the screen. selecting DIT are that It should be shM measuring the FWHM using MIDAS and R sequence of images can be made enough to avoid saturation (K 4 for DIT the secondary sei to that position. Dlf- by entering a Ilst of the desired - 1s with objective C) but long enough 63 polation/replacement using a bad pixel mask.

Characteristics of the presently installed NlCMOS3 array are surnmarimd in Table 2 and the overall broad band system performance as measured on the telescope is given h fable 3. The magnitude limits obtained in the broad band filters correspond to the background limits expected from the measured counts and fm longer ma- surement times the sin should Improve as 1'". In K', for example, the limit in 20 min should be 1 9.6 mag/(ams&) whlk the value derived from the galaxy cluster Image shown in the June Messenger Is 19.8, 1.9. actually somewhat better than expected but probably consistent within the uncertainties (e.g. the detector electrons/ADU conversion factor). God photometry should be possible wkh this cmZero points deter- Figure 4: Provisional cont~alset-up for the IRAM test in May. mined from standard stars observed over the 7 nlghts (when the sky was clear) agree to within 1-2% &ftw flat to achieve background limited perfor- analysis) but means that only half the adding. The flat fields used were ob mance when observing falnt sources total time is spent on the object and bad taitwd by taking difference images of (typically a few seoonds for the broad- pixels can only be corrected within the the diffusingmeen In the dome with the band filters). Most of the test obsewa- image by median filtering or pixd inter- halogen lamp on and off. This technfque tions were made using DIT = 1s for standard stars and 10-30s for the st- ence frames. The value of NDlT is a trade-off between the s/n ratio m each stored Image and the time between object and sky frames which should not be too long because of sky fluctuations. During the test MDlT was sdected typically such that DlTxNDrr was 2-5 rnln and CYCtES - 1. In order to remove stars and achieve optimal sky subtrac- don It is, in any case, necessary to have several sky frames on different psi- tions. For the optimal removal of bad pixels it is also desirable to have several object frames on different positions. Pmcularly for faint source9 therfore the best obming procedure b to combine all requirements by making a serles of exposures at telsscope positions separated by 10-20 arcsac. on the sky. AIL frames can then be used to derive the mean sky with the stars ramwd and, after reregisteting, be combined into a And object image in which bad pixels haw been replaced with good ones from other framm in the stack. This technique was used to produce the galaxy duster image reproduced in the June 1992 Mr?ssenger. An alternative, used for several of the test images reproduced here, is to use the same ob ject position but different sky positions or, in th% limit, just single object and sky frames. This simpliis the data reduc- Figure 5: K band Image of the m of the gMuk?f cIustw M15. Integmtim time was 60s tion @mtlcularly the on-line quick loak (30x2s) on a~wandsky adthe s& 15 ua7"lpiXal. Figure 0: NGC5247. K4e left panel is a smoothed K' wlcImage; centre panel is the K' image after subtfactian of a fit to the Inner galaxy disk component and the right panel is an R-band image obtained by scanning the POSS Eplate. N L down and E is to the left. The infrared imp have been constructed fmm four 1208 (I Ox 125) exposum with the O.49'Yplxd objective on each of two overlapping fie/& on th galaxy and six sky exposures of the same duraflon offset several arcmin. from the galaxy. Only the tram@ showing systematic differences less than 1 % were used and stars in the sky frames were fitfed with gaussians and moved individmUy before subfractfw,from the object frames. Smoothing using the MIDAS adaptive lglter technique was applied to enhence the vrtsibllity of low surface brightness features. Not8 that a spur off the northern spiral arm is only ~isiblein the POSS U imeand not K' suggasting that It is not part of the grand design density wave 1n the galaxy.

Tabla 2: NIWW mydewtar chrvact&ti. has the advantage of cancelling any "dark pattern to Fomrat (plxek) 256 x256 current" due radiation seen through the filtws and not present Pker she 40 ~m with the dark filter. The images reduced so far do appear to be flat within the Cut-off waverlength 25prn noise and,at least in the K and K' prime filters, are better than can be obtained Bad pixels el %' using sky flats. This seems to be due to Quantum ddeney -0.0 (22rmk 0.4 (1.25pm) the fact that sky-dark frames contain a faint ring-llke structure which dis- Well capaclty - 10% appears in the object-sky Images. Its outer diameter lust matches the size of Dsrk uurrent -30& the array and b independent of magntfl- Read noise -30e cation implying that it origin- In or close to the detectw. As yet, however, 1. Inctudlma a dead column In one qusdrant. no convincing expbnation for this effect 2. WlyUmIHBted by camera fhrrmd backgmund has bmfound. The 0.27"lpixel objective also shows an additional ring which appears in both the sky and dome flats and whose origin is equalty unclear. These effads are typically a few per cent of the mean background and are not apparent h the reduced Images ex- Table 3: Ov%raII system pwfarmsrnce (dbjectlw CJ, cept In one or two cases where the backgmd v#id by large amounts during the measurement due to clouds, Although appanently not significantly affecting the overall performance, themfore, this problem still requlres further investigation. Another aspect requiring further study is the stability of the army response. The reproducibility between images and of the zero points derived from standard star observations over seven nights suggests that thls is not a problem over most of tile array area. Mosaics made Figure 7: K'image of the merging galaxy system NGC3256. The scale Figure 8: K' image 01 the Seyferf galaxy NGW783. Scale is 0.49'1 is 0.27'/pixel and the image is the difference of single 120s (72% 10s) pixel and sky subtraction and bad pixel correclion has been made exposures on the galaxy and sky. using two sels of four 120s (l2x 10s) exposures of the galaxy at different positions on the array and eight interleaved sky frames with the same integration lime. from overlapping images (se~9.g. some instabilities at the edges cauld be rather sharply defined strip along one the RCW103 Image in the June present. These appear to be variations edge. Curiously, however, this effect MessengM, however, suggest that at th6 few % level and are confined to a appears on different, orthogonal, edges in the J and K bands! Pendinn further investigation we assume thw- are in- trinslc to the array 0.0. as opposed to variattons in the background Illumination which would be hard to explain).

4. Sample Images A K' (2.1 pn) image of the z - 0.2 galaxy cluster A1689 and a narrow- band [FelI](1.644 pm) image of the supernova remnant RCW103 were already includd in the June Messenger 1 (68, 42) as examples of (i) "deep" irnag- ing by combining exposures made at slightly different telescope positions and I (i) mosaicking of images displaced by almost the full field respectively. Figures 5-71 are some additional images selected to illustrate other possible modes and applications of the camera. As only single-object positions were used for most of these observations the bad pixels have generally been masked and replaced by interpolation in the surrounding area. Unless otherwise stated In the figure caption these lm- ages are oriented with N at the top and E to the left.

' Conclusions J The overall measured performance of Figure 8: J image of the v~swflyobscured nucleus In the nmdy edge on galaxy NGC4945 lRAC2 is close to that ~redictdin ad- made from three 120s (6x20s) exposures on the galaxy and two on the sky. Scale is o.W/ vance of the test and, although some plxel. aspects still require further investiga- Figure 10: Narrow-bend ;maps of the pkwtaty nebula tVGC6SW at Figure 11: Example of partial wing correction using the software O.Z7"/p,x@ in the ISIW- fl.96#nt) mmal (top), FdIf P.WClmJ shift and add feature ofthe multiple non-destnrctive read mode. The (middle) and (2.1 8 pm) bmlines. The upper and lowimages upper and lower panels show the same smaN region (-3.5~3.57of a were obWNwith the scanning Fabry Parot and a@ diffmt?~of 36x36" K' image of the globular cluster MZ observed at d 14Wxel images measured wtth the eWncentred on the line wawlrnth and with and without real time application ofimage shifts. The integration in the ad-t coIlfInUum. 77~centre image was obtaM Wh the time in both cases was 30s during which time the integration ramp namw bend Fe Ig fiIk and has been sky subtracted. The expo- was non-destructively sampled every 700 msec. In the tracked case, sum tim for each frame was #mi. (8x30s). blots the pro- each difference pair of non-destructively read images was shifted by nounced, extended, Feld IIkmmis WMate twf preserrl In the an amount corresponding to the movement of the brightest pixel in Other lines. the reference star image before computing the slopes of the integm- tion ramps.

tion, thls camera already offers powerful -- new Infrared obsmlng opportunities on "Strasbourg-ESO Catalogue of Galactic Planetary La Sill& NebulaenAvailable The Catalogue whM uampomprlses 1820 objects, Is divided Into Part I and Part II. Part I Acknowledgements (1 95 pages) eontalns the follbwlng subjd: A Explanation of the Catalague - B. Tables - C. References of papers containing 20 objects or more - D. Findlrtg Charts. We are grateful to Klaus Banse for and Part I1 (747 pages) contains The Catalogue, assistance In setting up the MIDAS ses- Editors are A. Acker, F. Oehnkln, 6. Stenholm, R. Tylendrr, J. Marnut and C. sions at tke telescope and to Pmben Schohn. The price of the Catalogue Is DM 135.- Iprepaymant required). Prrymenes have Grosbel and Reynier Peletier for expert to be made to the ESO bank munt 2102002 with Comrnerzbank Miknchen or by assistame with the reduction and evalu- chqm, addressed to the attention of ESO, flnandat Services, DCarl-SchwanBchlld- ation of the test data. Str. 2, D-8046 Garching &I MOmtchen, Germany 8 A New 2048 x 2048 CCD for the CES Long Camera L. PASQUINll, H. W. DUERBECK~~~,S. DE/R/ES I, S. D'ODORICO1and R. REISS7 'European Southern Observatory; a~stronomischeslnstitut der Universifii t Munster, Germany

Introduction Tabie 1. FA 2048, UV-Coated ESO CCD # 2f' The ESO CES spectrograph operates Pixel size 15 micron square with the 1.4-m CAT telescope or it is fed Actlve pixel number 2048 x 2048 by a fiber link from the Cassegrain focus QE I6 % (350nm), 34 % (550 nm), 38 % (750 nm), 7 8 (850 nm) of the 3.6-rn. The spectrograph has two Standard oper. temp. -165" K main configurations: a Short Camera Standard conv. factor 2.9 e- /ADU used with the RCA CCD ESO # 9 and the Long Camera used with the same Read-out noise 6 e- RMS CCD or with a Reticon detector. In July Dark current 3 8- /pixelhour 1992, a large-format CCD, a Ford Aero- Capacity 87000 8- /pixel (3 % devlatlon from linearity) space (now Loral) 2048 x 2048 CCD, CTE 2 ,99997 ESO # 27, wlth a new €SO VME con- Bias value -276 troller has been mounted and tested at Defects A number of warm and dark columns, but most of them the spectrograph and it is likely to re- outslde the central 500 columns oi the CCD place the Reticon and CCD # 9 from Cosmic ray event rate 1 event/min/cm2 now on. The characteristics of this device are summarized in Table 1. The Used at the CES with Ihe Long Camera. main scientific, technical and operational drivers for this change are the following: (1) The Reticon has so far been kept in The first check was carried out on the dure used and prove that deviation from operation for two main reasons: the spectral resolution. Measurements were Ratness in the CCD surface and the absence of interference fringes which performed on spectra from the Th-Ar coating do not Introduce significant de- plague the RCA CCD at wavelengths calibration lamp taken at different gradation of the expected resolution. longer than -6000 A, thus hampering wavelengths at a Resolving Power R - Weather condiions were very poor very high SIN ratios in the observations 100,000. The results were quite satis- during the test run, except for one and Its length which, being almost the factory: with the exception of the bluest photometric night which was used for double of the RCA detector, allows a -150 pixels (see below) the FWHM of absolute efficiency measurements. much broader wavelength coverage per the measured lines was uniform within 11ese were based on the observations frame. The new FORD CCD, a front- 0.1 pixel over the whole chip length and of several standard stars (Hamuy et &I. illuminated device, is much more uni- within 0.04 pixel in the central part. 1992). To have a direct comparison, the form than the RCA CCD and is twice as These values are typical for the Long same central wavelengths as given in long, giving the same spectral coverage Camera, compatible with the accuracy the CAT + CES Manual (Lindgren and per frame as the Reticon. achievable with the focussing proce- Gilliotte 1989) were chosen. The result- (2) The RCA CCD # 9 presents a rather high Read Out Noise (RON) level (33 e-/pixel). When coupled with the Long Camera, the RON becomes the Resporis I we Quantum Ef f \ c:ency dominant source of noise for many of IOCI , , , , , , , , , , , , , , , , , , , , , , , , , , . , , , , , , . - the applicatbns. The Ford CCD has a RON of less than 10 e/pixel. - KCDn: 27 (3) By introducing a dedicated CCD - , .. , ,, - detector for the Long Camera and retir- BrJ ing the Reticon, €SO expects to simplify the camera + detector changes at the ! spectrograph and to improve the relia- ,, ., - - ELL) - . ::,-*.,i.--., bility and performance of the systems. -.>' The CCD belongs to a batch that ESO i has procured from Ford Aerospace in LJ 1991. This particular chip has subse- "-10 . - quently been lurnigen coated at El3 in / -- order to enhance its blue response. The quantum efficiency curve is shown in 1 i -\ *\>. . .- Figure 1. The 15-prn pixel sine is well 25 i *. matched to the spectral and spatial res- 'Icl--tL-L----/A \ olution given by the spectrograph. -\.

0 Results of the Tests 300 400 500 600 700 800 71:C I COO The test were performed during 5 Waue [ nm I nights in July 1992. Figure 1 : Responsive quantum efficiencyof the CCD # 27. Table 2. Effidmcyof the CdT + CES + Long -+ mg27 Wavelength IA) ,3.B % 6450 4.6 % rn 22%

We expect that the advantages of us- - ing Ule Ford CCD will be emmore conspicuous when the CES Is coupled - - with the 3.6-m telescope fibre Itnk (D'Odorico et al. 1989): in this case R - - fact the spectrum is spread over a much - larger number of phtels (typically 220 with the 11 slice image dicer), therefore - the lower RON of the Ford CCD becomes even mom important. - The second advantage of this new mnfigumtian Is the absence of fringes, - evm at vety red wavelengths; in Figure - 4, d flve-minute normalized Wrnof the standard star HR 718 Is shown fn the No binning - region around 8092 A. This spactrum - has not bmflat field corrected and the - variations in the continuum are of h Binning - 2 -- order of 0.9 % or less. tast but not least, in evaluating the I I I I I I I I Instrumental peflormances, we have to consider that almost the doubie of the 12 10 8 6 spectral covwag~is obbaind in ww Magnitude frame; this feature is very ~mportantnot only when the simultaneous absmation Figure 2: Expmted W dmws a function of sfeltar magnfiude and infegmtiPn th.An d weral llncts is required, but dsa in eiti5emy of dB% at 6450 A is assum&. No slit bsw were applied Id the *om~ufaf~. th~gecases where broad lins are ob- wedand a large coverage is essential to determine the continuum level. As a scientific applica€ion,in Figure 3, lryr Mciendes given In Table 2 are in where N, Is the number of detected e-/ a 1-hour Ha spectrum of the recurrent vmy good qreement with what b ex- slhbin for a star of magnttude m,,, T is nova V745 Sco Is &own. Thii object pectd from the ratio of the Ford and the integration time in hwrs, W is the has a vlsual magnitude of 15.9 and an R RCA CCD quantum fl~lencies, width of the spectrum In H, ts the pixels, magnitude of 13.8, as measured from The new conflguratlan has a lower RON, b the binning factor perpendicular absolute cailbrated EFOSC spectra. The overall ePficlency but in order to evaluate to the dipmion, D the dark current and CES spectrum in Flgure 3 shows that a the iwtwrnent mrformmce, all the In e-ipkhwr. The points En Figure 2 WN of 5 is reached in the ctmnthuurn chmcten*~tic~Of the detector mud be ww computed assuming the Ford - close to the Ha line. Wen in amount; in particular its RON charadetistici; as given In Table 1 and Considetbg dl the pwous points It and Dark Current level. This is partiw- an overall efficiency of 446%. Atthough may therefore be advisable to use the lady important in the CES Long Camera, these numbew must be taken only as tong Camera and the Ford detector where the spectrum is spread In the indicattw (slit losses were not consid- l$ofor absewatlons at red wavehgths spatlal dlredlon over a conslderable a, direct comparison with the ered), per- and at lower resolution, for which the number of plxels (typic811y a), Wrth only fmances of the CAT + CES and RCA Short Camera is now used 0.9. R 8 e-/pix RON (compared wjth the 33 e-/ can perfomad. The two almost - CCD be 59000). On-chip binning and the ab- pix of the RCA) the advantage of using constant lines in Figure 2 limit the loci of sence d fringes will compensate in the Ford with respect t0 the RWCCD equal pedonances between the old many types of observations the lower becomes prominent, at [east for all and new configuration, both for un- effickcies of the Ford CCD and of the fhose observations requiring intermedi- binned (continuws lin4 binned and long Camera. ate to high S/N ratios, Figure 2 show (dashed line) CCD's. For observations the expected WM ratios as a function of requiting S/N ratlos lower than -260 in integration time and stellar magnNudes. unMnnad mode and -130 with a bin- Advice to the Users To compute thwn the same formula ning of 2, fhe use of the Ford is more Considering the results obtained from used In the CIS manual was adopted: convenient, this test, fSO will normally offer from 3900 x hT10-"b' now on the Ford CCD on the Long Cam- m= era as a standard wmblnatition. fhls im- (3800 x N,TIUMh-* + (VVb-' NJZ pies that the use of both the Reticon and the RCA # 9 at the same camera will be discontinued and that the RCA CCD will be permanently mounted on the CES Short Camera. We regard this as an optimum compromise between scientific perfor- mances and the severe operational and maintenance constraints of the observa- twy. Users must however be cautioned that this new configuration has not yet kenextensively debugged In the next months, their feedback on the astronomical performance and any gener- d wrnrnents wltl be much appreciated. Some problems have already been identifled and are baing Investigated. Namely: (1) Some vignetting Is present at the Rgure 3: A Smmute, nomalked smof fhe standard star HFI 718 centred at 8090 4, Mo blue edge of the specha and this makes tlat-Tdd mmction has been applied. Note the absence d inttwf#nce fringes.

-13 farmance of the new set-up,it is essen- mm 1 I tial to operate the CCD in an optimal 10.- - r- * ;! way, In particular with ward to the RON - i and the dark current. Durlng the tests. the level of the dark current was some - B.PO - what higher than expected and the on- chip binning introduced variable patterns in the background at a level higher than the measured RON. Both of 6.m - d these problems have already be8n obsewed in the past with other CCDs, but they are transient in nature and hence -Y not easlly debuggd. A careful monitw- -g 4.m- Ing of these CCD parameters by the fl scientific users is recommended and It c wlll be useful to optimize the CCD performance. 2.00 - 31 1 '1' 4 & :9< 3 Acknowledgements bOO - The mechanics and detector groups at I 1 I 4 :I La Silk worked hard and successfully to -w Bj60. m m.m -3 ttm adapt the new CCD to the Long Cam- era. H.V. Winckel kindly provided me Rgure 4: A f-hour Ha spectrum of the mmtnova V745 Soo. fhe S/hr Is - 5 in the of the observations. continuum, References D'OdoPie~,S., Avlla, Q., Mob, P. 1989: The IW6ssanger =,Mi. Hamuy, M., et al. 1992: A. J., in press. the first -- 150 rows of little use. Vignet- Ford shows this problem much more Undgren, tl., Gllllotte, R 1989: The COW ting was present at a lower level in the clearly. Echelle Spectrometer - ESQ Operating Reticon spsctra: the larger format of the (2) In order to reach tbpredicted per- Manual No, 8.

New CCD Cryostat for EFOSC2 At the time of the transfer of EFOSC2 fit from the existing calibration and guid- declination drive freedom to 63" in the from the to the 2.2-rn telescope the ing facilities. south. The Intention was to replace the instrument set-up had to be revised. The mounting extention with the large IR Lab cryostat with a shorter LN2 con- The plan was to interface it to the 2.2-m format CCD cryostat at the bottom of tainer. But the hold time of such a small rotator-adapter (DISCO) in order to pro- the instrument, however, restricted the dewar presented a severe limitation. 1. I1 LV~WU(~)9.V.SrdlAMW %Dlkoaor- L.Ca#p#cger ID. rn aoaoprrw 7.wmshlr~ n, col.- PRlpmh

Therefore we engaged In the deslgn ffOSC2 users at the 2.2-m telescope. cooling is stressed through a 3rd night of a short CCD head connected to an Problems? Occasional slippage in the of autonomy1 Mastorage dewar via a cotd flnger feed, LN2 refilling schedule brings the system L. GO~LU,D. HOFSTADT, In the figures the dewar arrangement Is to an unhappy user's scream when the R. TIGHE, ESO-La Silta sketched, A 70-cm-long copper bar, radiation shletded under vacuum, transfers the LN2 temperature (77K) from the storage dewar to the detector head. The thermal Impedance of the cold finger DEWAR, MODEL HD-2181 plus copper braids and thenal connec- OUTLINE SKETCH tors was carefully designed In order to reach the detector cold plate with a temperature of 140K. This brings the coollng near the operational temperature range of the CCO and allows to minimize the onergy input for the temperature tqutation in the detector head. The results h terms of temperature stability and autonomy are excellent (1.e.: c 0.2" stabilliy and 48 hours hold time at the telescope). The unit was designed and Integrated by Mr. Leonardo Gonzalez, the La Sllla cryogenic technician, while the detector head was machined In the mechanical workshop. The cryostat was mounted early Feb- ruary this year and free access to the MagelIanic Clouds was grantd to the

- Vacwm 10*/1 O4 - Codlng time Istaning from ambient T): 6 hwrsapm. - uJ2 consumptiom 3 Wday - Temperature regulation power Input: (3.4 Watts