MESSENGER

No. 54 - December 1988

ESO'S EARLY HISTORY, 1953-1975 I. STRIVING TOWARDS THE CONVENTION

ADRIAAN BLAAUW*, Kapteyn Laboratory, Groningen L'astronomie est bien I'ecale de la patience. From a letter by A. Danjon to J. H. Oort, 21 September 1962. A Historical Statement vention between five of these six coun­ be replaced by joint effort. As my col­ On January 26, 1954 twelve leading tries - Great Britain went its own way ­ league and friend Charles Fehrenbach astranomers fram six European coun­ signed on 5 October 1962. By that time used to say: "11 faut faire I'Eurape." It tries issued the historical statement we almost ten years had passed since the also was a time at which some of the reproduce here [1]. It carries the sig­ notion of a joint Eurapean observatory Eurapean countries . had to deal with natures of Otto Heckmann and Albrecht had been expressed for the first time. serious internal problems. Governments Unsöld of the German Federal Republic, Another year and three months would as weil as astronomers had to face this. Paul Bourgeois fram Belgium, Andre have to elapse until the impatient hands It is perhaps not surprising, then, that Couder and Andre Danjon fram France, of the astranomers would be free to lay the first instigation towards the joint Roderick Redman fram Great Britain, the first solid foundations for the erec­ effort which would become ESO, had to Jan Oort, Pieter Oosterhoff and Pieter tion of the observatory. The date is come from one who, although rooted in van Rhijn from the Netherlands, and January 17, 1964 when, with the com­ European ancestry, had been an on­ Bertil Lindblad, Knut Lundmark and pletion of aseries of parlamentary ratifi­ looker on European astranomy for many Gunnar Malmquist fram Sweden. cations, not only the moral, but also the years fram overseas: Walter Baade of The statement (drafted by Danjon, financial commitments of the respective the Mount Wilson and Palomar Obser­ Oosterhoff and Redman) expresses the governments had been ensured. vatories. wish that the scientific organizations in In this series of articles I shall first Baade, renowned expert on galactic the respective home countries recom­ describe the developments of the first and extragalactic research, had been mend to the authorities concerned, the decade, that is the period preceding the invited by Oort to spend two months at establishment of a joint observatory in signing of the Convention and the Ratifi­ Leiden Observatory in the spring of South Africa, equipped with a telescope cations, and, hopefully, next try to cover 1953, for lecturing and for collaborating of 3 metres aperture and a Schmidt some of the later developments until the in the preparation of a conference on telescope of 1.2 metres aperture. In the year 1975 when I passed on the General galactic research to be held near paragraphs preceding this expressed Directorate of the organization to my (Continued on page 3) wish, they present the considerations successor Lodewijk Woltjer. that led them to this statement. Their The earliest decade was one of ups wish would ultimately lead to the Con- and downs - many downs! - in a strug­ gle which may seem surprising to the TO All READERS

. The aulhor was Secretary 01 lhe ESO Commitlee present young generation of astranom­ Please make sure that the card (which preceded the Council) Irom May 1959 to ers, and can be fully understood only wh ich accompanies this issue of February 1963, Scientific Director 01 ESO (part when seen against the background of a the Messenger is returned, if you time) during the years 1968 and 1969, and Director damaged Eurape, a decade only after Generallrom January 1970 10 January 1975. He want to continue to receive the was a Council member for lhe Netherlands during devastating World War 11. Traditional na­ journal. The editors the years 1979 through 1982. tionalism and mutual misgiving had to lI~s BOuB81gntia. 110 ronomca app l't.tJnun avx pa.va ci-uprcs u~8l.r,n6o: Al1~magno. Bclp'iqu~. ?Tance, Jrand~ Bretap,n~. Pays Baa. Sucdu. r'\U'llS /; Lcydo 10 25" 26 ,janV10r 1'154.

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Ont sll,,,,d:

Prof. O. HecklllQnn o,~, Ihrectc:ur dc l'Uba vo.tolra d, d.'ul'lboUTe; Prof. A. Unsöld Direc'teu.r da 1 'ObR'.1l'Va olre dr 1<1.4:1

Dr. -. Bour~eois Dlrecteur dc l'Obsprvatoirc rov 1 dc B 19lqUt·

Dr ~. Coudr.r AB ronom~ de l'Obs'rvatoire '" Parie Prof. A. lJo.njon Ulract~ur de l'0bserva Olro de PorlS Prof. ft. 0. Hedman Directeur de l'Ob8~rvaLolrd d Cam rld.l,e Prof. J. H. uort Uir.cteur de l'Obo.:vatolrs d' ~yd" Prof. r. 'rh. Oosterhoff Astronome ds l'Ohsarvato~re d Lcyde Prof. P. J. van Rhijn Dir.cteur du labora 0 re Astronomique Groninf?Ua Prof. o. Lind lad Diructour d. l'Obsurvatoira de ~tockho1m Prof. K. Lundmark Diract~ur da l'Obsorvatoire de Lund Prof. K. G. Malmqulst Diracteur du l'Obsarvatoirs d'üppsala

On January 26, 1954 astronomers from six European countries gathered in the stately Senate Room of Leiden University for a discussion of the recently by Baade and Oort suggested joint European Observatory. Under the chairmanship of Bertil Lindblad of Saltsjöbaden they formulated and duly signed the statement reproduced here, meant to strengthen their efforts for government support in the respective countries.

2 Setting Up the ESO Historical Archives

Now that ESO has reached the age and status at which interest in its early ESO HISTORICAL ARCHIVES beginnings is growing, it is desirable to set up an organized system of Inventory per December 1988; Overall Contents documentation that should allow histori­ I. Documents received from outside ESO. cal studies. For that reason, steps have LA. Archives J. H. Oort. been taken by the Director General to 1.A.1. Documents donated by Oort to l. Woltjer, former Director General of ESO. establish the ESO Historical Archives, I.A.2. Documents donated by Oort to A. Blaauw around the year 1976 and transfer­ henceforth to be abbreviated EHA. red by him to ESO Historical Archives. These archives are meant to serve two I.B. Archives J. H. Bannier. Documents donated in 1987 to H. van der Laan by the Dutch organization ZWO purposes: for sponsoring scientific research, pertaining to the directorship of J. H. Bannier of - to form a natural framework for the this organization. incorporation and classification of I.C. Archives A. Blaauw. documentation that may be relevant to I.C.1 Documents pertaining to the Secretariat of the ESO Committee (which pre­ the study of the history of ESO; and ceded the ESO Council) with the exclusion of those concerning the site-testing - to provide students of ESO's his­ expeditions. tory with the necessary basic refer­ I.C.2. Documents pertaining to the Secretariat of the ESO Committee, concerning ences, accessible at the discretion of the site-testing expeditions. the ESO Directorate. I.C.3. Documents concerning lIle ESO Working Group for Buildings, 1963-1965. I.CA. Other documents before 1968. At this moment - fall 1988 - a begin­ I.C.5. Documents pertaining to the ESO Scientific Directorship, 1968-1969. ning has been made with the creation of I.C.6. Documents pertaining to the ESO General Directorship, 1970 through 1974. the EHA by means of some quite valu­ able collections of documentation, per­ 11. Documentation originating from inside ESO. II.A. Documents from the file marked "ESO Allgemein", of the period 1961-1964. taining mostly to the earliest decades, that is from the year 1953. They origi­ nate from persons who have been inti­ mately involved in the creation of the documents originally belonging to J. H. should be mentioned that, of course, Organization. The origins and the nature Oort, category I. B. to those originating apart from the contents of this part of of this documentation can be recog­ from the Dutch organization ZWO, the EHA, there are in the ESO nized in the global descriptions in the category I. C. to documents transferred Headquarters (and perhaps also in box ESO Historical Archives accom­ from my archives at the Kapteyn Chile?) many documents of interest for panying this note. Laboratory at Groningen to the EHA. the study of the ESO history wh ich, For the arrangement and numbering I Clearly this arrangement invites exten­ however, still are part of the body of have chosen a system wh ich clearly sions I. D., I. E., etc. for documents documentation occasionally used for shows the origin of the documents and which, hopefully, may be received from the regular operation of ESO. Of particu­ which, moreover, has a structure allow­ other persons or agencies that were in­ lar significance appear to be the exten­ ing in a natural way the incorporation of volved in the early history of ESO. sive files kept by the ESO Head of Ad­ additional documents without any ma­ Within each of these categories, fur­ ministration, which contain virtually nipulating. Eventually, a more sophisti­ ther subdivision introduces more and complete sets of the minutes of the ESO cated system may have to be introduced, more refined classification. The first Council and its predecessor, the ESO but for the moment the present, simple stages of these are indicated in the Committee, minutes of Finance Com­ one should suffice. The arrangement also accompanying Inventory. Further ones mittee, the series of Council-Meeting allows the description of the documenta­ are used in the more extensive descrip­ Documents, etc. Naturally, access to tion in the inventory to be done in as much tions of the EHA now in the making. As these documents is also at the discre­ detail as appears desirable. an illustration, let me mention the sub­ tion of the ESO Directorate. In my arti­ This arrangement discriminates first division I. C. 2. 8. wh ich pertains to the eies on the early history of ESO I refer to of all between documentation originat­ dealings of the Secretary of the ESO these documents as FHA (Files Head of ing from outside ESO, category I, and Committee (wh ich preceded the ESO Administration). documents from within ESO, category 11. Council) with the Marseilles objective­ Finally, mention should be made of As things stand at the moment, it would prism radial velocity project as part of the collection of old photographs and seem that category I will be the richer the site testing operations, and of which slides belonging to the Photographic one. Within category I, I have discrimi­ the subdivision I. C. 2. 8.a. contains the Department of ESO, wh ich also are of nated according to the source of the correspondence with Ch. Fehrenbach. historical interest, but still to be documents: category I. A. refers to In connection with category 11, it classified. A. BLAAUW

(Continued tram page 1) June 21, 1953, the day before the Council of CERN, the joint European Groningen from June 22 to 27 [2]. It was Groningen conference [4]. They were effort in nuelear research. Over the during this stay that, between Baade Baade, Bourgeois, Danjon, Heckmann, years, the ESO effort would greatly and Oort, the idea arose of a joint effort Lindblad, Oort, Oosterhoff and myself. benefit from Bannier's experience. The by some European countries with lead­ Most of them participated in the participants at the meeting represented ership in astronomy [3]. Groningen conference [5]. Also present five "continental" countries. After the The suggestion was followed up by on June 21 was J. H. Bannier, director of meeting Sir Harold Spencer Jones, As­ Oort immediately. At his invitation a the Dutch national science foundation tronomer Royal of Great Britain, and group of astronomers discussed it on (ZWO) and at that time President of the Richard Stoy of the Cape Observatory, 3 only by means of a large telescope Europe might hope to join in it. In addi­ tion to the two instruments mentioned, the meeting proposed a meridian circle for the astrometrie work that also was much needed in the southern hemi­ sphere. That South Africa was envis­ aged for the location, was almost self­ evident also because it had the best astronomical climate known at that time. The minutes of the meeting con­ tain a provisional cost estimate. Capital investments were estimated at $ 2.5 million, and annual running costs at $ 100,000.-. These included salaries for 3 astronomers, 5 technical personnei, 3 night assistants and 3 administrative posts. Participants of the June 21 meet­ ing were invited to discuss these plans with their colleagues at home. The results of their deliberations were discussed at the meeting of January

Photograph 1: Walter Baade (Ieft) in characteristic pose, talking to C. Schalen of Sweden. 1 1954 mentioned at the beginning of this article [7]. It was chaired by Bertil Lind­ blad and held in the stately Senate room both of whom also participated in the station on the premises of the Union of Leiden University, where portraits of Groningen conference, were informed Observatory, first at Johannesburg and scientists of Leiden's illustrious past, and contributed their views. It appears later at the field station at Hartebees­ looking down on the participants, may from the minutes of the June 21 meeting poortdam; British astronomy had close have inspired their historical statement. that Baade's ideas deeply influenced relations with South Africa through the The statement reflects the positive re­ the discussions and, in fact, his propos­ Radelifte Observatory at Pretoria and sponse they brought from their col­ al then made would become the nucleus the Cape Observatory near Capetown. leaques at home. The meeting decided of the "initial programme" formulated in Rather than enlarging these facilities, to form an ESO Committee to carry the article 11.2 of the 1962 Convention. It is one should pool resources and eftorts project further, consisting of Bourgeois therefore interesting to report in some and strive for equipment comparable in (Belgium), Danjon (France), Heckmann detail from these minutes. research power to that of the large (German Federal Republic), Spencer Baade proposed as principal instru­ Californian observatories that had for Jones (Great Britain), Oort (Netherlands) ments a 120-inch reflector similar to that decades dominated observational as­ and Lindblad (Sweden). The suggestion of Liek Observatory in combination with tronomy. (All reflectors with aperture of was made that some intermediate size a 48-inch Schmidt telescope like the 80 inch or more were located in the telescopes should be added to those one on Mt Palomar. The fact that for northern hemisphere [6].) mentioned earlier. An improved cost es­ both telescopes existing designs could Moreover, some of the most interest­ timate was presented: capital invest­ be used and engineering problems had ing objects of research could be ments should be 1.25 million pounds been solved would speed up the pro­ reached only from the southern hemi­ (then corresponding to about $ 3.5 mil­ ject. The southern hemisphere for the sphere: the central parts of the Galaxy lion), based on preliminary ofters from location of these instruments was an and the nearest extragalactic systems. European manufacturers, and an annual obvious choice for several reasons. At Baade stressed the growing importance budget of 45,000 pounds (correspond­ that time, several European obser­ of extragalactic work and the fact that ing to about $ 126,000). The project was vatories had their own limited facilities in the southern hemisphere, most of them on the premises of South African obser­ vatories, and extensions of these were under consideration. Belgium, the Ger­ man Federal Republic, Ireland and Swe­ den participated in Harvard Observato­ ry's Boyden Station at Bloemfontein; Leiden Observatory had its southern

1 The photographs accompanying this article were taken by the author during a boat trip on one of the days of the Groningen Conference in June, 1953, immediately after the idea of a joint European Observatory had been discussed for the first time by a group of astronomers at Leiden on June 21. Purpose of the trip were lhe reclamation opera­ tions in the area of the former Zuiderzee, now the domain of large, f10urishing farms. All or the participants al the Leiden meeting joined in lhe boat trip, and lhe notion of a joint observatory Photograph 2: From left to right: V. Kourganoff (France), J. H. Oort (Netherlands), H. Spencer must have been one of the holter sUbjects. Jones (Great Britain).

4 envisaged to be realized over the next ten years. The meeting was aware that this financial support might be very hard to obtain from research councils or gov­ ernments, but the suggestion was made that perhaps this might be facilitated if funds from private foundations or societies could be added. It was also realized that the project would need a convention between learned societies or between governments; the former was preferred (but would later have to be abandoned for the latter). Next steps were taken at the Com­ mittee meeting of November 1954 in Paris, chaired by Oort, the principal sub­ jects being the drafting of the conven­ tion and site testing in South Africa [8]. Beginning with this meeting, these two subjects determined the two main lines Pholograph 3: 0. Heckmann (Ieft, German Federal Republic) in discussion with B. J. Bok of the Committee's activity. Later on, a (United States). third would be added: the planning of the instrumentation. Of these three Iines would produce scientific results. They of one member is avoided. The conven­ of activity of the first decade, we shall will be discussed in the section on the tion also stated from the beginning that first follow developments leading to the testing programmes. Over the whole the observatory should be located in the Convention and Ratification, next de­ year 1959 and half of 1960 the total southern hemisphere, no broader geo­ scribe the site testing expeditions, and budget for the site testing and other graphical choice was ever seriously con­ subsequently the first planning of the expenses had been only $ 32,346.-. For sidered. As to the equipment of the ob­ instrumentation. the following one year and a half, how­ servatory, there is the first set-up with In these first years the Committee had ever, a total of $ 363,000 had been esti­ the large optical telescope and the no permanent President or Secretary. It mated. Of this, France and Germany Schmidt telescope referred to before, met in various astronomical centres and were supposed to contribute 1/3 each, but this is called the initial programme usually was chaired by the host, for in­ and the three smaller continental coun­ and the Convention allows in principle stance by Heckmann in Bergedorf and tries about 1/9 each; the chances of extension with any kind of other in­ by Lindblad in Saltsjöbaden, until at the Britain's participation having become strumentation, whatever frequency do­ October 1957 meeting it made Oort its quite small already at this stage. Where­ main of the electromagnetic spectrum it President and Bannier its Secretary and as, so far, the financial resources had may cover. Treasurer. In May 1959 Blaauw come from national science research Wh at slowed down the signing of the succeeded Bannier as Secretary. councils or equivalent bodies on a year­ Convention was not any serious dis­ to-year basis, these new estimates agreement concerning its contents, al­ called for commitments at higher, gov­ though there had been quarreling about Towards the Convention ernment level. details - the fact that CERN successful­ A first proposal for the Convention, The new draft was largely adapted Iy operated on a very similar basis was between organizations, was drafted for from the Cern Convention. Although helpful - but rather the fluctuating and the November 1954 meeting by Bannier ESO is, of course, in essential aspects sometimes very low expectation with and Funke [9]. G. Funke, Director of the different from CERN, especially be­ regard to the governments' willingness Swedish National Research Council, cause it has its principal establishment, to embark upon this project in times of was, like Bannier, a member of the the observatory, outside Europe, its sometimes deep financial problems. Council of CERN. Amendments were constitutional set-up, its financial basis Naturally, in this respect there was a made to this draft, but on the whole the and its personnel regulations have be­ large difference between CERN and matter of the Convention proceeded come very similar to those of CERN ESO: development of nuclear physics slowly during the first years. Little of through this early adaptation of the being a must in the post-war era for what happened within the participating CERN model. At the same time, this virtually every nation, in contrast to the countries filters through in the minutes similarity has often led governments to apparent lack of usefulness of promo­ of the Committee meetings, until in 1960 appoint on the ESO Council the same tion of the study of the sky. An addition­ the matter comes into focus again. In its delegates as on the CERN Council, re­ al, serious drawback was the gradual meeting of July of that year, held in sulting in similar policies. withdrawal of Great Britain. . Heidelberg, the ESO Committee dis­ Some features that have marked the cussed in detail a new draft; it still was drafts from the beginning are worth not­ Withdrawal of Great Britain one between organizations, but its au­ ing here: Every participating country thor, Bannier, stressed the necessity of a would be represented on the ESO At the April 1956 meeting of the ESO convention between governments [10]. Council by two delegates, of which at Committee Great Britain was still rep­ What had caused this change, and at least one should be an astronomer, and resented by R. O. Redman and R. v. d. R. the same time made the matter rather each member has equal vote - although Woolley [11]. The latter succeeded urgent, were the sharply increasing in practice, of course, opinions of the Spencer Jones as Astronomer Royal in costs of the site testing expeditions in largest countries carry strongest weight. 1956. At the April 1957 meeting Redman combination with plans for modest ob­ Financial contributions are proportional was present, but after this, several years servational programmes which, apart to the national income but only up to a would elapse before a British astronom­ from contributing to the site testing, fixed limit, so that excessive domination er appeared again. British interest

5 After an early approach by Oort had not met positive reaction, a renewed application led to the Foundation's deci­ sion in October of the year 1959, to allocate a grant of one million dollars under certain conditions, the most im­ portant of wh ich was, that at least four of the five nations still positively involved at that time, Belgium, France, the Ger­ man Federal Republic, the Netherlands and Sweden, would sign the Convention [17]. This condition was in full harmony with what had become common under­ standing anyhow - that participation of four countries would be a minimal base for further pursuing the effort. In order to fully appreciate the significance of the Ford Foundation's grant, one should realize that at that time the estimate of the capital investment required for the Photograph 4: From fett to right: Mrs Mieke Dort (Netherfands), B. Strämgren (Denmark) and B. establishment of the observatory used Lindbfad (Sweden). to be $ 5 million [18]. The grant thus was equivalent to the average of the five countries' shares, and thereby had the turned towards a Commonwealth Ob­ the meetings of the ESO Committee. It character of pushing the project finan­ servatory in Australia, in preference to also happened through other channels, cially over the threshold in the case of the ESO project. However, the attitude for instance in correspondence between stagnation of one of them. The amount was not univocal. Thus, in a letter of May Bannier and the Office of the Minister for also happened to cover approximately 13, 1959 Redman informed Oort that Science at Whitehall, notably in an ex­ the cost of the mirror blank of the large there had been "a rather unexpected tensive letter by Bannier of February 3, telescope. swing of opinion among a number of 1961 [15]. At the January and June 1961 There can be little doubt that the grant astronomers and physicists in this meetings of the ESO Committee Great has been most beneficial for bringing country -- -" [12], and in July 1960, Sir Britain was represented again, by both the negotiations between and within the William Hodge, Secretary of the Royal Woolley and O. J. Eggen, and at the countries mentioned to a successful Society, wrote to Oort: "You have no November 1961 meeting by A. Hunter. end. A letter of Oort to Dr. C. W. Borg­ doubt heard that the British National Meanwhile, another link had been es­ mann, Director of the Ford Foundation, Committee for Astronomy has been giv­ tablished through which British as­ of April 22, 1960 testifies to this in con­ ing fresh consideration to the possibility tronomy was kept informed: the meet­ nection with the Dutch government's of taking part in an international effort to ings of ESO's Instrumentation Com­ decision to participate [19], and so does construct a 120" telescope in the south­ mittee were attended by a representa­ Heckmann's account on the early ESO ern hemisphere -- -" [13]. tive of the Astronomer Royal, first by history in his introduction to the Annual Later that month, on the 27th, Woolley O. J. Eggen, later by A. Hunter [16]. After Report of ESO for the year 1964 [20], as informed Oort more specifically: "The 1961 no British representative attended weil as in his book Sterne, Kosmos, British National Committee prefers par­ the meetings of the ESO Committee any Weltmodel/e [21]. The grant was trans­ ticipation in a Commonwealth telescope more. ferred to ESO soon after the ratifications to participation in a European telescope, had been completed, on September 21, but would favour participation in a Euro­ 1964 [22]. The Grant 01 the Ford Foundation pean telescope if it is not possible to The history of the grant of the Ford organise a Commonwealth telescope. Whereas the withdrawal of Great Bri­ Foundation has recently been the sub­ -- -" [14]. Moreover, Woolley stated, tain had seriously weakened the basis ject of an investigation by F. K. Edmond­ they "- -- would only favour support in for the ESO project, there appeared at son. A summary, kindly offered by Dr. any scheme if the result of the participa­ least one bright spot above the horizon. Edmondson for the Messenger, accom­ tion was an al/ocation of telescope time, As mentioned before, the possibility of panies this article. proportional to share taken of the ex­ financial help from non-government penses --- and if the affairs of the funds was alluded to in an early stage. I Founding Fathers Observatory - - - were vested in the remember - but this is not documented hands of a Council, on which voting - that on the occasion of a visit to the The archival documents of the last strength was again proportional to the southern Leiden Observatory Station in years of the 1950's and the early 1960's financial share borne by each nation." the 1950's, Oort explored the possibility reflect the extremely difficult political Clearly, on these latter points British of financial help from within South Afri­ circumstances under wh ich especially views diverged from those among the ca, but that it failed because of lack of the French adherence had to be gained. ESO partners. These points might have support from certain astronomical cir­ This was the more serious because from become the subject of further negotia­ cles in the country. On the other hand, the outset it had been agreed that the tions, but that stage was never reached. the case of ESO has much benefitted initiative for convening the represen­ In spite of the divergence between from a grant allocated by the Ford tatives of the member states for the British and continental views and in­ Foundation wh ich has its seat in New signing of the Convention - their am­ tents, British authorities were regularly York. This foundation was weil known bassadors - should be with the French kept informed on developments regard­ for its promotion of international collab­ government [23]. Under the still delicate ing ESO. They continued to be invited to oration on a world-wide scale. political circumstances of those years

6 this seemed natural from a diplomatic point of view. It is also to be understood The Ford Foundation and the European Southern in this context, that the basic text of the Observatory Convention should be the French one, particularly after the withdrawal of Great FRANK K. EOMONOSON, Indiana University, U.S.A Britain [24]. Most of the French governments of The Ford Foundation supported projects around the world and expanded its activities to include science and engineering after Henry Heald became President of the those years were short-lived as a conse­ Foundation in 1956. Garl Borgmann, President of the University of Vermont, was hired quence of internal political division of in 1958 to be the Director of the new Programme in Science and Engineering. Four the country, and on top of this, the Alge­ large grants to support major astronomical programmes in the southern hemisphere rian independence movement made were made during the period from late 1959 to early 1967. The Ford Foundation was great demands on the successive restructured in March 1967 by Heald's successor, McGeorge Bundy, and the Pro­ cabinets from the year 1954 until inde­ gramme in Science and Engineering was discontinued. Borgmann served as Advisor on pendence was agreed in March 1962. Science and Technology until he retired in 1970. The other major partner in the ESO Oort and Lindblad met with Heald and Borgmann on October 9, 1958 to discuss effort, the German Federal Republic, possible Ford Foundation support for the European Southern Observatory. Oort had written to the Ford Foundation in August 1956 but then received a negative reply. Little went through its "economic miracle" in encouragement was given during t1,e 1958 meeting, but a year later the Ford Founda­ these years and seldom posed financial tion Board of Trustees approved an appropriation of $ 1.0 million to be granted if three problems. Naturally, it was aware that a conditions were met. The first condition was that at least four of the five nations positive attitude with respect to matters (Belgium, France, German Federal Republic, the Netherlands and Sweden) must sign of European integration should help the Gonvention to create ESO. The other two conditions were administrative. Borg­ bridge the cleavage caused by the war. mann wrote to Oort on October 2, 1959 to inform him about this action. In the smaller partner countries, how­ Shepard Stone, the Ford Foundation's Director of International Programmes, went to ever, post-war rebuilding programmes Paris three weeks after the $ 1.0 million had been appropriated. He discussed the drew heavily on financial resources and matter with Jean Monnet, the closest advisor to the Finance Minister, Pinay. Stone's personal friend Gaston Berger, who was Director of Higher Education, wrote in October made governments hesitant to commit 1959 a memorandum in French for Stone's signature. Monnet personally delivered it to themselves to a long-term financial obli­ Pinay, who presumably discussed it with Oe Gaulle. The French government decided to gation in astronomy. participate, and this was announced on June 28, 1960. Whereas the project was the subject The $ 1.0 million grant was paid in full on September 16, 1964. This grant was later of frequent consultation between many used to buy the quartz blank for the 3.6-metre telescope. astronomers mutually and with their The great importance of the $ 1.0 million appropriation by the Ford Foundation governments, there are three persons cannot be overestimated. The Ford Foundation's promise of a $ 1.0 million grant was who, due to their key position, emerged the "catalytic agent", a term used in the Ford Foundation staff's recommendation, that as the principal spokesmen in the inter­ persuaded the French government to join in creating ESO. Without it, ESO might never national discourse. They were: Jan H. have been more than the dream of Baade and Oort. The three other grants were: Yale-Golumbia astrograph in Argentina, $ 750,000 in Oort who as initiator and deeply con­ 1960; GSIRO for Australian Radioheliograph, $ 550,000 in 1962, and $ 80,000 in 1966; vinced of the necessity of the project AURA for half the cost of the Gerro Tololo 4-metre telescope, $ 5,000,000 in 1967. constantly strived for its realization; I wish to thank the Ford Foundation for giving me access to the archives for the four Andre Danjon of Paris, leading French grants in Astronomy, and Eldon Jones and Ann Newhall for their assistance in using astronomer and also strong supporter these archives. . who had the difficult task of attaining his government's approval; and Otto Heck­ mann, one of the leading German as­ are type-written, nearly all of Danjon's Under these circumstances, serious tronomers, Director of the Hamburg Ob­ letters in the ESO Archive are hand­ consideration was given to a German servatory and one of the strongest ad­ written. financial guarantee to save the project vocates of the project in his country. He Not all of these Founding Fathers and yet retain broad international would become ESO's first director. have lived to see the dream realized. character [27]. The suggestion received More in the background, but not to be Walter Baade died already on 25 June support from the German astronomical forgotten, were such men as Bertil Lind­ 1960, and Bertil Lindblad on 25 June community [28] and the meeting of the blad (close to Oort by personal friend­ 1965, a little more than a year after the ESO Committee of October 1957 ship and similarity of research interests), ratifications had been completed. Andre accordingly drafted alternative budgets Charles Fehrenbach of Marseilles (close Danjon died on 21 April 1967, only for the cases with and without France to Danjon), J. H. Bannier and G. Funke, shortly after ESO's first constructions on [29]. The guarantee was not really effec­ to mention a few. Deeply interested in La Silla had begun. tuated, and the situation remained the developments was also Pol Swings gloomy. of Liege, but a certain lack of communi­ When the ESO Committee met in Oc­ The Final Struggles cation between Belgian astronomical tober/November 1958 in Uccle, there centres at that time has hampered By the middle of 1957, the chances was no French representation; Danjon Swings full involvement [25]. Without the for approval of the project by the French and Fehrenbach requested to be ex­ growing mutual respect and friendship government were very low. Summariz­ cused because their country seemed to between the people mentioned here, the ing a discussion with Heckmann on Au­ be unable to help support the site test­ ESO project might not have surmounted gust 26 of that year, Danjon wrote that ing [30]. The other countries decided to the many obstacles on its way towards he feared opposition to the project by go on, but the situation underlined once realization. The correspondence be­ the Ministry of Finance [26]; it even more the urgency of arriving at the bind­ tween these men (telephone and cable seemed impossible to obtain funds for ing international contract between par­ messages played only a minor role in the site tests of the years 1957 and ties. lt would take another year for chan­ these days) sometimes was of a strong 1958. Danjon nevertheless thought that ces to become better. personal nature and represents a touch­ the project should be pursued, with In a letter to Oort of 6 November ing "document humain". Not all letters France possibly joining at a later stage. 1959, Danjon could write: "Enfin, le

7 mouvement est declenche. - - -", after "Mon cher ami, tre condamne a rouler le rocher de Si­ having received an invitation for a dis­ Croyez bien que je partage votre in­ syphe pour I'eternite! Mais 1'ai tout de cussion between high officials of the quietude et que je ressens vivement la meme tres bon espoir." [38]. Ministries of Sciences and Finances responsabilite de la France dans les About that time, in correspondence [31]. This move had very likely been ajournements successifs du projet. J'ai between Oort and Heckmann preparing prompted by the Ford Foundation grant ete tente plus d'une fois de vous ecrire for the Committee meeting of July 15, of preceding October. In letters of 10 que je renonr;ais a m'en occuper, mais 16, 1960, the possibility of German ad­ and 12 December, Danjon sounded je suis persuade que votre täche ne vance financing was taken up again, quite optimistic about both the funda­ serait pas facilitee par le retrait de la combined with a Dutch initiative for con­ mental decision for participation and the France, lequel en entrai'nerait d'autres. vening the five governments [39], but financial prospects: "J'ai en effet indi­ Quant a faire des demarches, il m'est this did not appear to open promising que au gouvernement que, compte tenu impossible de m 'y consacrer plus que je perspectives. However, towards the end de la Subvention Ford, la depense des 5 ne le fais. Au mois de decembre, 1'ai vu of the year 1960 French authorities pays de I'Europe Occidentale serait de 4 une dizaine de fois une personne du occupied themselves with the formula­ mitlions $, a repartir sur 8 ans, et que, Cabinet du Ministre, qui avait tout pre­ tion of the text of the Convention, and of tant que d'autres pays n'auraient pas pare pour que I'affaire soit soumise au the Financial Protocol that belongs to it, decide de participer a la realisation du Conseil des Ministres. Mais M. Boul­ so that these texts could be discussed projet, la France devrait en couvrir 1/3. loche, le Ministre de I'E. N. [Education at the meetings of the ESO Committee --- J'attends avec impatience le re­ Nationale] a donne sa demission vers and presented to the Foreign Ministries tour du gouvernement, qui est a Dakar. Noel, pour des raisons de politique inte­ of the partner countries [40]. J'espere que la decision officiel/e de la rieure. D'autres motifs ont determine le Further delay was then caused by participation sera prise et que les invita­ depart du Ministre des Finances et re­ difficulties in arriving at an acceptable tions seront lancees. - - -" [32]. tarde la designation du nouveau minis­ text of the German version of the Con­ On January 12, 1960, Danjon wrote to tre de I'Education. Alas est survenue la vention. Towards the end of 1961 it was Oort that the Prime Minister had issued revolution d'Alger dont vous n'avez the general impression that universal letters to the Ministries of Finances and peut-etre pas evalue les repercussions agreement had been reached, but then Foreign Affairs, and the ESO project sur la vie publique en France. Le nou­ unexpectedly a new dispute arose be­ was to be submitted to the coming veau ministre, M. Joxe, que je connais tween German and French officials on Cabinet Council [33]. And "La demission bien, n'a pas pris ses fonctions imme­ the interpretation of the Convention text du Ministre de I'Education Nationale diatement, car il etait engage dans de concerning the distribution of the con­ nous aura fait perdre 1 mois entier, mais difficiles negociations avec les republi­ tributions of the member states. By the maintenant, les choses en sont au point ques noires d'Afrique. 1/ n'y a guere plus end of March 1962 Heckmann had also ou seule, une crise du gouvernement de 3 semaines qu'il a constitue son ca­ removed this obstacle [41]. At the June pourrait les compromettre. -- -". On binet. Or il a a resoudre les problemes 1962 meeting of the ESO Committee in February 1, Oort, not yet having heard insolubles qui ont cause la demission de Bruges, Belgium, it could be announced from France, enquired discretely son predecesseur! Cependant, au cours that the date for the signing was ap­ whether the Dutch Ministry of Foreign de I'interim, 1'ai pu obtenir que le Pre­ proaching. And on September 21, 1962 Affairs might now expect soon to be mier Ministre ecrive aux Affaires Etran­ Danjon wrote to Oort [42]: approached [34], and he may have geres et aux Finances. J'ai vu le Ministre "Mon cher ami, drawn hope from Danjon's message vendredi 26 fevrier. Des le 8 fevrier, 1'a­ Les Affaires Etrangeres ont fixe au 5 that Dr. Sheppard Stone, Director of In­ vais fait rechercher le dossier de I'ESO, octobre la signature de la Convention. ternational Affairs of the Ford Founda­ et M. Berger en avait entretenu le Minis­ Enfin! --- Je ne saurais vous dire com­ tion, one of these days would take up tre. Je suis retourne au Ministere les 29 bien je suis heureux de voir enfin pren­ the matter of ESO with the new French tevrier et 2 mars, pour prendre contact dre corps votre grand projet. Mais il aura Minister of Education [35]. But then, avec un membre du cabinet qui venait fal/u plus de dix ans! L'astronomie est when by the end of the month Oort has de recevoir le dossier. 1/ fal/ait I'informer bien I'ecole de la patience. - --" not yet heard the good news, the corre­ de I'affaire, toute nouvel/e pour lui. Ce The Convention was indeed signed spondence between the two friends matin, 1'ai eu une autre conversation on that date, at the Ministry of Foreign takes a dramatic turn. On March 1, Oort avec M. Piganiol. A tous, 1'ai affirme la Affairs in Paris, for the foreign countries writes to Danjon [36]: necessite pour la France de prendre une by their ambassadors and for France by "Mon cher ami, decision. the Secretary-General of the Ministry of Je viens de passer une demie nuit Croyez-vous que 1'aufais pu faire da­ Foreign Affairs. That same date, Danjon sans sommeil avec mes soucis concer­ vantage? Toute personne approchant wrote to Heckmann [43]: nant I'ESo. La responsabilite pour ce du gouvernement se rend bien compte "Mon cher Col/egue, projet pese un peu lourd. --- Pourquoi qu'il est obsede par I'Afrique du Nord et Un mot seulement, pour vous confir­ est-ce qu'on nous fait tant attendre? non par I'Afrique du Sud. Soyez assure, mer que les representants des 5 pays Votre ministre ayant pris la decision de mon cher ami, de ma constante et fidele ont signe la Convention aujourd'hui a principe, pourquoi ne peut-on pas pren­ amitie, A. Danjon" Midi! AI/eluia!! dre aussi la decision ferme de participer, From letters of Fehrenbach and Dan­ Bien cordialement votre A. Danjon" de sorte que nous puissions commen­ jon in the months following, it appears After this memorable event, it would cer? --- Vous comprendrez sans that, while adecision in principle by the still take more than one year before the doute que je m'inquiete et que je com­ French authorities had been taken, ex­ Convention would be ratified and thus mence a perdre le courage. --- Je re­ ecutive action was further delayed by governments could assume financial grette, mon cher ami, que je dois ainsi the instabilities within the government. commitments. As it is stated in the Con­ vous faire part de mes soucis. - --" Towards the middle of the year 1960 vention, this situation would be reached In reply, Danjon immediately writes, on Danjon wrote to Oort: "- -- La lourde when at least four of the governments March 3, 1960 an unusually long letter machine administrative -- - depend de had ratified and, moreover, these four which seems so weil to describe the situ­ 4 ministeres dont 3 ont change depuis le would represent at least 70 % of the ation that I like to quote it in full [37]: debut de I'annee! J'ai I'impression d'e- total of the contributions. This implied 8 LIST OF MEETINGS OF THE ESO COMMITTEE (PRECEDING THE ESO COUNCIL)

No. Date PI ace Chairman Minutes made by: Reference in ESO Hist. Archives

1 1953 June 21 Leiden J.H.Oort P. Th. OosterhoH IA1.1. 2 1954 January 25-27 Leiden B. Lindblad P. Th. OosterhoH IA1.1. 3 1954 November 8-9 Paris J. H. Oort P. Th. OosterhoH See FHA' 4 1956 April 20-21 Bergedorf O. Heckmann W. Fricke + O. Heckmann 1.A.1.3. 5 1956 October 15-16 Saltsjöbaden B. Lindblad P.Th.OosterhoH IA1.4. 6 1957 April 1-2 Uccle P. Bourgeois B.G. Hooghoudt See FHA' 7 1957 October 28-29 Leiden J. H. Oort J. H. Bannier IA1.6. 8 1958 July 23-24 Paris J. H. Oort J. H. Bannier I.A.1.7. 9 1958 Oct. 31 - Nov. 1 Uccle J. H. Oort J. H. Bannier 1.A.1.8. 10 1959 May 29-30 Noordwijk alZee (Neth.) J.H.Oort A. Blaauw I.A.1.9. 11 1959 July 4 Paris J.H.Oort A. Blaauw I.A.1.10. 12 1960 July 15-16 Heidelberg J.H.Oort A. Blaauw 1.A.1.11. 13 1961 January 3-4 Paris J.H.Oort A. Blaauw 1.A.1.12., 13. 14 1961 June 12-13 Tübingen J.H.Oort A. Blaauw I.A.1.14. 15 1961 November 6-7 Paris J. H. Oort A. Blaauw IA1.15. 16 1962 March 5-6 Paris J.H.Oort A. Blaauw IA1.16. 17 1962 June 18-19 Bruges J.H.Oort A. Blaauw IA1.17. 18 1962 October 19-20 Stockholm J.H.Oort A. Blaauw 1.A.1.18. 19 1963 February 5-7 CERN, Geneva J. H. Oort O. Heckmann 1.A.1.19. 20 1963 July 23-24 Amsterdam J.H.Oort O. Heckmann I.A.1.20. 21 1963 November 15 Bonn J. H. Oort J. Ramberg I.A.1.21.

. FHA = Files Head 01 Administration 01 ESO.

that in any case France and the Federal [1] For the text with authentic signatures, [19] In EHA-I.C.1.1.c. Republic of Germany should be in­ see EHA-I.A.1.1. [20] page 6 of English version. cluded. It was accomplished when [2] See EHA-I.B.1. for correspondence be­ [21] Heckmann Sterne, p. 265, 266. France ratified on 17 January 1964 [44]: tween Oort and the Dutch funding or­ [22] ESO Annual Report 1964, p. 6. the Netherlands had ratified on 21 ganization ZWO in preparation of [23] Minutes ECM No. 12, p. 3 in EHA­ Baade's stay. IA1.11. [24] See ref. 23. March 1963 [45], Sweden on 4 [3] I weil remember Jan Oort one day enter­ [25] See, for instance, correspondence be­ November 1963 [46], and the German ing my oHice - opposite to his at Leiden tween Swings and Blaauw in March­ Federal Republic on 10 November 1963 Observatory - to share with me his ex­ April, 1961, 1961 in EHA-I.C.1.1.a. [47]. citement about the ideal [26] EHA-I.C.1.1.c. So, then, from early 1964 on, ESO [4] The Memorandum on this meeting, later [27] See Oort's report in a discussion by the was on solid grounds and could begin called ECM No. 1, is in the FHA; a copy Netherlands Astron. Council on 24 Sept. realizing its long-term building projecl. It of it in EHA-I.A.1.1. 1957, in EHA-I.C.1.1.c. would within a few years do so on an [5] For areport on the Conference see lAU [28] See ref. 27. even broader base, after Belgium had Symp. No. 1, 1955, ed. A. Blaauw. [29] Minutes ECM No. 7, p. 8 in EHA-I.A.1.6. [6] For the distribution of observatories in [30] Minutes ECM No. 9, p. 1 in EHA-I.A.1.8. ratified on 2 October 1967 [48] and a geographic latitude in 1954, see R. [31] See EHA-I.C.1.1.c. [32] See ref. 31. [33] sixth member, Denmark, had even done Coutrez and L. Bossy in Ann. de I'Obs. See ref. 31. [34] See ref. 31. so a little earlier, on 23 August 1967 [49]. R. de Belgique, 3eSer., Tome VI, 1954, [35] See letter by Oort to Heckmann of 13 But before we enter this new phase, we quoted in J. H. Oort, ICSU Review, February 1960 in EHA-I.C.1.1.d. hope to describe, in the following article, Vol. 3, No. 1,1961. [36] See EHA-I.C.1.1.c. [37] See ref. 36. what meanwhile had been accom­ [7] ECM No. 2, Minutes ("Memorandum") in [38] Undated copy in EHA-I.C.1.1.c. plished in the search for the site of the EHA-IA1.1. [39] See correspondence between Oort and Observatory and in the preparations for [8] Memorandum on this meeting (ECM Heckmann in May, June 1960, in EHA­ its instrumentation. No. 3) is in the FHA; a copy of it in EHA­ I.C.1.1.d. I.A.1.2. [40] Undated letter of Oort to ESO Comm' [9] A copy of this draft Convention is in January 1961? In EHA-I.C.1.1.c. ' EHA-IA1.2. It is marked "1 st draft of [41] See correspondence between Oort and References and Notes Bannier and Funke" (in Dutch) in Oort's Heckmann in January-March, 1962, in Abbreviations used: handwriting. EHA-I.C.1.1.d. EHA = ESO Historical Archives. The numbers [10] A copy of this draft is in EHA-I.A.1.11., [42] In EHA-I.A.2.5. following EHA identify the (folder contain­ with accompanying letter from Bannier [43] Heckmann Sterne, p. 267. ing the) archival document according to to Blaauw. [44] Circular letter by Fehrenbach of 23 the Inventory explained in the separate box [11] Minutes in EHA-I.A.1.3. [12] EHA­ January 1964 in EHA-I.C.1.1.f. accompanying this article. I.C.1.1.g. [13] See ref. 12. [14] See ref. [45] Circular letter by Bannier of March 27, ECM = ESO Committee Meeting. The meet­ 12. [15] See ref. 12. 1963 in EHA-I.C.1.1.f. ings of this Committee, wh ich preceded [16] According to a letter of Blaauw to Hunt­ [46] Communication by the Dutch Ministry of the ESO Council, are listed in aseparate er, EHA-I.C.1.1.g. Foreign AHairs of January 6, 1964 in box accompanying this article. [17] See letter of C. W. Borgmann, Director EHA-IA2.5. Heckmann Sterne = O. Heckmann, Sterne, Ford Foundation, to J. H. Oort of Octo­ [47] See ref. 46. Kosmos, Weltmodelle, Verlag Piper & Co, ber 2, 1959 in EHA-I.C.1.3. [48] Communication Dutch Ministry of For­ München, Zürich, 1976. [18] See, for instance, Minutes of ECM eign AHairs of May 9, 1968 in EHA­ FHA = Files belonging to the OHice of the No. 6, in FHA; a copy of il is in EHA­ I.A.2.5. Head of Administration of ESO. 1.A.1.5. [49] See ref. 48.

9 Paul Ledoux (1914-1988) Non radial oscillations did receive a great deal of his attention. He associ­ Paul Ledoux passed away on Oc­ ated the presence of unstable 9 mod­ tober 6, aged 74. President of ESO's es to the existence of a superadiabatic Observing Programmes Committee gradient and presented those results· from 1972 till 1975, he had with his in his "these d'agn!!gation" in 1949. fellow members the difficult task of Among the most famous papers selecting among observation propos­ published in the past decades on Stel­ ais. He was also member of the ESO lar Stability, everyone will remember Council for wh ich he served as Presi­ two 1958 reviews contained in the dent from 1981 till 1985. Handbuch der Physik, signed by Paul His wisdom as weil as a deep kind­ Ledoux, the first one in cooperation ness, essential qualities for such an with Th. Walraven. important leadership, helped him to Celebrated in Belgium as weil as in gain respect and friendship among his foreign countries, he was honoured by colleagues in the ESO Council. Paul the "Prix Francqui" in 1964, the "Prix Ledoux, a student of P. Swings, decennal des Mathematiques appli­ graduated in Physics in 1937 at the quees" in 1968, the "Eddington Med­ Liege University. He soon went to Oslo al" of the Royal Astronomical Society to work with A. S. Rosseland where he in 1972 and the "Medaille J. Jansen" of became interested in the structure and he also showed that no hydrogen can the Academy of Sciences of Paris in stability of stars. This led him in 1941 be present in the central layers of a 1976, to cite but these few. to establish the existence of a max­ white dwarf while only a very limited He became Professor at the Univer­ imum mass value for stable main se­ amount can be acceptable in the ex­ sity of Liege in 1959 and since then, quence stars in a famous Astrophysi­ ternal layers. performed enormous teaching cal Journal paper entitled "On the Vib­ In 1947, Paul Ledoux published an charges covering Astronomy, As­ rational Stability of Gaseous Stars". analysis of the effect of a discontinuity trophysics, Analytical Mechanics, Ce­ The Second World War had already in mean molecular weight on stellar lestial Mechanics, Meteorology and started and Paul Ledoux actively par­ structure. He showed that this situation Hydrodynamics. He was very devoted ticipated in the defense of the allied leads to a partial mixing called semi­ to his students and all of them discov­ countries, serving as a member of the convection. Convection itself was one ered in him not only a talented scientist meteorological service of the Royal Air of his favourite subjects but he also but also a warm although deeply ear­ Force. Just after the war, he returned devoted himself to the problem of the nest man. His death will be feit as a to stability problems, studying the helium content in the Galaxy, propos­ great loss by all his colleagues, col­ effect of a variation of the adiabatic ing a source of helium enrichment laborators and friends in the whole exponent on the onset of a dynamical through homogeneous evolution of astronomical community. instability. Dealing with white dwarfs, massive stars, as a result of rotation. A. NOELS

List of ESO Preprints 614. Z.1. Tsvetanov, I. M. Yancoulova: Red­ 621. A. Cavaliere, E. Giallongo, F. Vagnetti: dening in the Narrow-Line Region of Uncertainties and Apparent Trends in September-November 1988 Active Galactic Nuclei. M.N.R.A.S. the Evolution of Quasars. The As­ 615. A. F. M. Moorwood, E. Oliva: Infrared tronomical Journal.

608. J. Surdej, P. Magain, J. P. Swings, M. [Fell] and H2 Line Emission in Active 622. S. D'Odorico, S. di Serego Alighieri, M. Remy, U. Borgeest, R. Kayser, S. Refs­ Galactic Nuclei. To appear in Proceed­ Pettini, P. Magain, P. E. Nissen, N. dal, H. Kühr: Preliminary Results from a ings of lAU Symposium 134, Active Panagia: A Study of the Interstellar Search for Gravitational Lensing within GalacUc Nuclei (eds. D. E. Osterbrock Medium in Line to NGC 5128 from High a Sampie of Highly Luminous Quasars. and J. S. Miller, Kluwer Academic Pub­ Resolution Observations of the Super­ Communication given at the first DAEC lishers). nova 1986G. M. Workshop in Paris. 616. E. Brocato, R. Buonanno, V. Castellani, 623. G. Meylan: Studies of Dynamical Prop­ 609. F. Murtagh: Hierarchical Trees in N­ A. R. Walker: CCD Photometry of the erties of Globular Clusters. V. Implica­ Body Simulations: Relations with Clus­ LMC Cluster NGC 1866: Observational tions of the Observed Flat MS Mass ter Analysis Methods. Computer Phy­ Results. Astrophysical Journal. Function in 47 Tucanae. M. sics Communications. 617. G.A. Tammann: The Distance of the 624. R. M. West: Halley's Comet (Part I): 610. H. E. Schwarz, S. van Amerongen, Virgo Cluster - a Review. Ground-Based Observations. V.1. M. H. M. Heemskerk, J. van paradijs: 618. J. Andersen, J. V. Clausen, P. Magain: Moroz: Halley's Comet (Part 11): Space Outbursts in TV Columbae: Walraven Absolute Dimension of Eclipsing Studies. Invited Discourses at the XXth Photometry and CCD Spectroscopy. Binaries. XIV: UX Mensae. M. lAU General Assembly. To be published M Letters. 619. R. Gathier, S. R. Pottasch: Properties of in lAU Highlights, Vol. 8 (1989). 611. A. Terzan, Ch. Ounnas: A Photometric Planetary Nebulae. 11. Central Star Study of the Bright Cloud B in Evolution. M. ERRATUM Sagittarius. VI. 1592 New Variable Stars 620. G. Srinivasan: Millisecond Pulsars: a In the article "Active Optics: The ND and 30 Diffuse Objects. M Suppl. New Population of Gamma Ray Sour­ and the Future" (The Messenger No. 53, 612. R. Arsenault: The Preponderance of Bar ces? Invited talk presented at the Sym­ September 1988, p. 1), there was an error and Ring Features in Star-Burst Galax­ posium on Advances and Perspectives in the text of Fig. 7 (p. 6). The text given ies. M. in X-ray and Gamma-ray Astronomy for Fig. 7 (iij should refer to Fig. 7 (iii); 613. E. Oliva, A. F. M. Moorwood, I. J. Dan­ held in Espoo, Finland, 18-21 July conversely, the text given for Fig.7 (iii) ziger: Infrared Spectroscopy of Super­ 1988, as part of the COSPAR General should refer to Fig. 7 (iij. nova Remnants. M. Assembly.

10 NTT Picture Gallery

Figure 1. Figure 3.

Figure 2. Figure 4.

The arrival of the ND mirrors and ESO Workshop mirror cell on La Silla on 22 September coincided with the first and only day of An ESO Workshop on the subject of "Extranuclear Activity in Galaxies" will be snow on La Silla this year (Fig. 1). The held at ESO, Garching bei Muenchen (F. R. G.) during the second half of May mirror was installed near the aluminiza­ 1988 (provisional dates 16-18 May). tion chamber in the 3.6-m telescope The preliminary programme includes the following topics: building, where aluminization of the ND - Observations of warm gas (optical emission lines) and cool gas (Radio lines mirrors will take place in the coming and optical/UV absorption lines) - Cooling processes, ionization mechanisms weeks (Fig. 2). In October the telescope and chemical composition of the gas. mechanics and electronic hardware as - Radio rotation measure and depolarization measurements - the nature and weil as the building were completed location of the magnetoionic medium. (Figs. 3 and 4). Software integration - Relationship between the warm gas and radio structures - jet/gas interac- then started with the first pointing and tions, radiation field anisotropies and beaming. tracking tests on the sky using the finder - Kinematics of the extended gas - galaxy mass distributions. telescope attached to the tube struc­ - Relationships with the hot (X-ray) haloes - the fate of the cooling gas. ture. Integration of the mirror and optical - Implication for the appearance of galaxies at high redshift. alignment are expected to take place in Keynote speakers include F. Bertola (Padua), L. Browne (Jodrell Bank), R. January 1989 when the telescope will Fosbury (ST-ECF), L. Hansen (Copenhagen), R. Laing (RGO), G. Miley (Leiden), have its "first light". M. TARENGHI P. Quinn (STSci/MSSSO) and A. Robinson (Cambridge). The initial registration deadline is 31 st January 1989. It is the intention to house the workshop within the ESO building and so the total number of participants will be limited to 80. Contact address: TO ALL READERS Bob Fosbury (ST-ECF) and Evert Meurs (ESO) Please make sure that the card European Southern Observatory wh ich accompanies this issue of Karl-Schwarzschild-Str. 2 the Messenger is returned, if you D-8046 Garching bei München, Federal Republic of Germany want to continue to receive the Telephone: +49-89-32006-0, Telex: 52828222 eo d journal. The editors

11 Where is Phobos 1?

The Soviet spacecraft Phobos 1, servations were carried out with the not seen, it must either have been out­ launched in July this year and now en Oanish 1.5-m telescope on October 1/2, side the field (did a rocket fire after the route to Mars and its major moon, was 2/3, and 3/4, resulting in at total of fif­ contact was lost?) or it was positioned lost due to an incorrect ground control teen 1O-minute exposures with the CCO so unluckily in space that the sunlight command. Many attempts were made camera. Moreover, ni ne 3-minute ex­ reflected from its surface in our direction to reestablish radio-contact, but unfor­ posures were made with the EFOSC was too faint to be detected, even with tunately in vain. instrument at the 3.6-m telescope dur­ the present, extremely sensitive equip­ On September 21, ESO received a ing the night October 3/4. The observers ment. request for observation of Phobos 1 were visiting astronomers O. Hatzidimi­ A final attempt was made with EFOSC from the Space Research Centre in triou and C.A. Collins (Edingburgh); the on October 9/10, by visiting astronom­ Moscow. If it were possible to obtain a image processing was made at La Silla ers G. Suchail and Y. Mellier (Toulouse). sequence of images of the spacecraft ­ by H.-U. N0rgaard-Nielsen (Copenha­ Four frames, totalling 36 minutes V<{ere of course only as a faint point of light ­ gen) and H. Pedersen (ESO), who was obtained, but again there was no sign of then its accurate position and perhaps also responsible for the coordination. Phobos 1. even its rotational status could be deter­ We show here the central areas of two It is a pity that this last-ditch effort mined. This would help the efforts to re­ images from EFOSC. The one to the left was unsuccessful and that it was not acquire contact. is a direct exposure of the Phobos 1 possible to help our space colleagues At La Silla, the first possible night, field; the right one is a combined frame this time. But it is a good example of the September 22, was lost due to snow in wh ich the 3.6-m telescope was set to collaborative spirit that reigns in our field (see the "ND Picture Gallery" in this follow the motion of the spacecraft; the of science, and which transgresses all issue) and no observations of such a stars are therefore seen as trails. The borders. The editor faint object could be made during the limiting magnitude in both cases is mag­ ensuing full moon period. However, ob- nitude 25 or fainter. Since Phobos 1 is

Open-Hause at ESO

On October 22, 1988, the science in­ stitutes in Garching again jointly or­ ganized an open-house day. With the help of many of the staff members, a well-defined path was established through the ESO Headquarters with de­ monstrations and exhibitions along the route. This year, around 1,800 persons vis­ ited ESO. They were received at the entrance by the most "photogenic" staff members and guided towards the au­ ditorium, where a new ESO slide show was running at 20-minute intervals.

12 Next, the ND and VLT projects were CCO camera ("seeing" in a completely explained in the Council room; this in­ dark room) convinced quite a few vis­ NOTE cluded a full-scale model of an 8.2­ itors about the witchcraft of modern as­ metre VLT mirror! (See the picture; this tronomical technology. ESO/NOAO Workshops room was the only one at the Headquar­ Finally, there was a possibility to par­ In the Messenger No. 52 and in ters which was big enough.) In the termi­ ticipate in the "ESO Astroquiz". Weil the Proceedings of the NOAO/ESO nal room, the advanced image process­ over 1,200 response sheets were Conference on "High Resolution ing systems caught the eyes of compu­ counted in the box at the end of the day Imaging" it was announced that the ter-minded persons of all ages and also and when the prize-winners were next ESO/NOAO Workshop on ex­ the interesting demonstration by the STI drawn, the first three were found to perimental astrophysics with the ti­ ECF of artificial intelligence. An overview come from places as far apart as Mün• tle "Infrared Array Oetectors" would of the Hubble Space Telescope was chen, Wolfratshausen and Regensburg. be held in Tueson, Arizona, in the followed by a visit to the "Remote Con­ Each of them received a copy of the autumn of 1989. trol Room", from where two telescopes ESO Book "Entdeckungen am We regret to inform you that this at La Silla are used for observations. Südhimmel". Workshop has been cancelled. In­ As usual, the names and orbits of For them and many others, ESO was formation on the next joint Work­ minor planets attracted much interest "worth the journey". shop will be given in due time. and an impressive demonstration of a R.M. WEST F. MERKLE, J. BECKERS

Upcoming ESO Exhibitions

As reported in the last issue of the Naturkunde, opening on April 20; contact the ESO Information Service Messenger, ESO organized a special Klagenfurt, Austria, Planetarium, open­ (address on last page), since the plan­ exhibition booth at the XXth lAU General ing end of June; ning for 1990 is about to start. Assembly in Baltimore (see photo). After Copenhagen, Oenmark, Tycho Brahe The exhibition has now been enlarged the exhibitions in Malmö (Sweden) Planetarium, opening in October; to include more information about the which is still running and another in Stuttgart, F. R. Germany, Planetarium, newest scientific and technological de­ Innsbruck (Austria) during November­ opening before Christmas. velopments. Of particular interest is the 2 Oecember, the following are planned for We hope that our local readers will full-scale model of a VLT mirror (53 m ) next year: take the opportunity to visit these and the fischertechnik VLT model of a The Hague, Netherlands, Museon, events. unit telescope, described elsewhere in opening on January 27; Potentially interested organizers of fu­ this Messenger issue. Münster, F. R. Germany, Museum für ture exhibitions are kindly requested to

13 A "BIinking" Satellite Decl. = _5°). Whereas the brightness of Indeed, if the satellite is at an altitude most other photographically recorded that corresponds to one revolution This unusual satellite trail was re­ satellite trails is rather uniform or slowly around the Earth each 100 minutes, corded on an ESO Schmidt plate for the varying, the rapidly changing light along then it rotates about 9 times per second extension of the Quick Blue Survey to­ this trail indicates a very fast rotation. (but it may of course be in a higher, wards the equator. lt was obtained on Also, the "blinks" are different, and do slower orbit). What kind of instruments August 31, 1988 and covers field 815 of not repeat in a uniform sequence, show­ are on-board? Or is it just another piece m the ESO/SERC grid (R. A. = 21 h20 ; ing that the rotation axis changes. of tumbling space junk?

1 Report on lAU Colloquium 112 , on Light Pollution, Radio Interference and Space Debris (Washington, 13 to 16 August 1988)

Light Pollution a better long term efficiency when Radio Interference school children are concerned. Astronomers are the only minority The main cures for light pollution are Radio astronomers represent a small concerned by this problem and thus the generalized use of low pressure percentage of radio wave users, all of have to lead the fight without expecting sodium lamps because their radiation is them being concerned with maintaining any help, apart from the lighting industry easier to filter out, and a better shielding some good order in the radio communi­ which recently discovered that com­ of street lighting (60 % of the total pollu­ ty. With the expansion of satellite radio puter alded design could help improv­ tion). Outdoor sport facilities remain a communications, there is a growing ing the efficiency of lighting equip­ problem but most are fortunately not need for frequencies. The distribution of ments! lighted during the whole night. Time the radio spectrum is made on a world­ Kitt Peak observatory reported en­ control of residential area lighting can wide basis during a so-called "World couraging news from the results of light help darkkening part of the nighttime. Administrative Radio Conference" pollution control in Tucson. Mount An argument to convince city may­ (WARe). Palomar Observatory, where the sky is ours to take actions is that the young The U. S. radio astronomers have sev­ 0.75 magnitude brighter than it would be urban generation is raised without hav­ eral channels in their administration to without light pollution, is now trying to ing the possibility to enjoy the vision of get a voice at WARCs, the situation is follow the same path. Apart from getting the night sky (of course, in that case, as somewhat more difficult in Europe a legislative support, it is advised to for amateur astronomers, the low where each country has its own regula­ acquire comprehension, understanding pressure sodium does not help much). tions. The newly created European and help from the population. This is Planetariums are also considered as a "Committee on Radio Astronomical Fre­ possible through a long term policy aim­ way to sensitize the population and quencies" (CRAF) tries to be present ing at raising interest about the science should include some striking examples during negotiations. Radio astronomers made in astronomical observatories, for in their shows (polluted versus non­ are advised that it will be practically instance by means of guided tours, with polluted sky). impossible to get new frequencies in the As shown on Figure 1, La Silla lies in a future and that they have to keep on particularly favourable area now, and so justifying the usefulness of the already 1 This colloquium was organized by D. L. Crawford (Kitt Peak National Observatory) and T. Gergely did Mount Palomar observatory when attributed ones. (National Science Foundation, Div. Ast. Sei.) the site was chosen ... Among the most affected users by

14 The Earth at night: this photo-composition of many satellite pictures iIIustrates the different sources of light pollution. In addition to ligl1t emission from urban areas, note the agricultural savannah fires in central Africa, natural gas flares from oil fields (Persian Gulf, North Sea .. .) and also the Aurora BoreaJis in the north. Credits: United States Air Force / DMSP Archives, National Snow and lee Data Center, NOAA, University of Colorado / W. T. Sullivan, 11, University of Washington, Seattle / Kerry Meyer.

radio frequency interference, one could lision with objects other than posal" orbit could create a belt of debris mention the SETI programme, dedi­ meteoroids may be severe and the around the earth. A third solution is the cated to the Search for Extraterrestrial pressure for reducing the threat will be re-entry through the earth atmosphere Intelligence in the 1-10 GHz band. stronger and stronger. ESA created in for disposal. The main pollution is created by 1986 a working group on space debris As for consequences on astronomy, radars but in urban areas, there are vari­ and areport will soon be available. each photographic plate of the new ous other less known sources such as It is estimated that 70 % of debris Palomar sky survey includes an average defective home appliances or high come from military explosions wh ich of five tracks from satellites or debris. success gadgets like garage door re­ have now been banned. More than The space telescope will see 4 debris of mote openers. U. S. regulations allow 7,000 objects larger than 10 cm are 10th magnitude per hour per degree of observatories to proceed to inquiries in tracked by the North American Aero­ field of view and 1,000 debris of 20th case of nuisance from such local sour­ space Defense Command (NORAD). A magnitude per hour per degree of field ces of radio pollution. catalogue is available to civilians and of view. A geostationary satellite is seen A satellite dedicated to the detection astronomers from the Naval Space sur­ from ground with mag 14. The space of radio frequency interference from veillance Center (Dr. S. H. Knowles, shuttle is mag -3. Solar panels send space will be operational in 1992 in fre­ Dahlgren, VA, U.S.A). bright flashes to ground and may inter­ quency bands near 300 MHz. The number of debris increases con­ fere with gamma ray burst observations. stantly because of mutual collision and According to the relative position of the the critical density could be reached in Sun, one square inch of solar cell can be Space Debris 50 years if nothing is done. Cleaning the visible with the naked eye. At least one This is an issue wh ich goes far be­ small debris by retrieval is considered as optimistic information to conclude: yond the astronomical community. Any unrealistic nowadays because of the those problems usually occur only until new spacecraft design has to include an cost. Short term solutions such as pro­ two hours after sunset and start two anticollision shield. Damages due to col- pulsion of obsolete satellites to a "dis- hours before sunrise. M. SARAZIN

50 Years of RGU Photometry A. SPAENHAUER, C. F. TREFZGER, L. LABHAROT, S. GABI, Astronomisches Institut, Universität Basel, Switzerland

1. Introduction which are too faint for spectral c1assifi­ by the properties of existing instru­ Fifty years have elapsed since W. cation. He stressed that the choice of ments. The three passbands were cho­ Becker (1938) proposed to use three­ the passbands had to be guided by the sen such as to reflect the two basic colour photometry for the study of stars properties of stellar radiation rather than characteristics of the visible spectral

15 energy distribution of astar: a long­ TAßLE 1: Characteristics of the photographie RGU system. wave colour index (G-R) as a measure of temperature and a short wave colour Emulsion Filter A(FWHM) index (U-G) defined by two weil sepa­ '''' U Kodak 103aO UG2 (2 mm) 3593A 530A rated passbands measuring the UV-de­ pression caused by line blocking and G Kodak 103aO GG5 (2 mm) 4658A 495A the Balmer depression. Since then a multitude of different R Kodak 103aE RG1 (2 mm) 6407 A 430 A photometric systems have been estab­ lished, each serving a different purpose. confirmed that progress in the following (e. g. H 11 regions) and thus proved the The UBV system (Johnson and Morgan fields could be expected (Becker and power of the method. The basic data of 1953) as the most similar one to the Steinlin 1956): the Basel cluster work is contained in RGU system has become the most 1. Identification of faint main sequence two cluster catalogues (Becker and Fen­ widely known and used because it could stars as weil as statistical absolute mag­ kart 1971, Fenkart and Binggeli 1979). be established both photographically nitude determinations (photometric pa­ In the next phase the more ambitious and photoelectrically. Although a sys­ rallaxes). goal of exploring the distribution of the tematic comparison of the RGU and 2. Determination of interstellar redden­ field stars of our Galaxy was envisaged. UBV system has not been undertaken, ing along the line of sight. In the late 1950's, but especially after we refer to Fenkart and Esin-Yilmaz 3. Distance determination of galactic 1961, when the first RGU plates with the (1985) and the third section for some clusters. Palomar Schmidt telescope were taken aspects of this comparison. Due to the 4. Distinction between late-type main by U. W. Steinlin, the foundations were lack of red sensitive photocathodes, the sequence and giant stars. laid to the Basel Galactic Structure pro­ RGU system was originally defined as a Among the first objects studied with gramme. At that time (and probably still photographic system (see Table 1, the RGU system during that period were nowadays) most of the information Becker 1946, Becker 1965, Buser 1978). the open clusters (Becker and Stock about the structure of the galactic halo In the past 10 years the photoelectric 1958) using the still widely applied tech­ (today often called spheroidal compo­ RGU system has been established nique of main sequence fitting (both nent SC) came from the study of globu­ (Trefzger et al. 1983) and we want to with a long and short wave colour-mag­ lar clusters and RR-Lyrae stars, whose present here some new results based nitude diagram) in order to determine masses may constitute as little as 1 % of on photoelectric measurements along distance as weil as interstellar redden­ the total SC. Therefore the investigation with abrief historical outline of the ing. This technique led to an internally of the field SC was achallenging task photographic RGU programme. consistent distance scale with random and led to a halo survey consisting of errors less than - 15 % together with systematic, three-colour photometric in­ 2. The Photographie RGU System crude relative ages (main sequence vestigations of starfields down to limit­ From -1940 through - 1960, the first turnoff). The distribution of the very ing magnitudes of 18 m to 19 m. These photographic RGU measurements were young open clusters (Becker 1963) fields were chosen more or less in the carried out with the Hamburg, Ann Ar­ clearly revealed part of a spiral arm meridional plane passing through the bor, Asiago and Cleveland Schmidt tele­ pattern in the solar neighbourhood con­ Sun and the galactic centre and, if pos­ scopes. The interpretation of the data sistent with other optical spiral tracers sible, overlapping with Selected Areas.

Figure 1: Distribution of the programme fields of the Basel survey superposed on a Panorama of the Milky Way (Lund Observatory).

16 The so far published 10 photometrie gions of the Galaxy, several important exploited in the context of "Galaxy mod­ eatalogues (ean be distributed on re­ features ean be noted, which reflect the elling" (Buser and Kaeser 1985, Bahcall quest) eontain the RGU data of 16 star­ sampling of photometrically distinct et al. 1985, Fenkart 1989). The main fields of the halo survey (- 30,000 stars) populations. As an example, Figure 2 reason preventing to extract the full in­ as weil as of 33 starfields of the disk shows the two-colour diagrams of formation, especially the one contained survey (I b I < 10°, - 55,000 stars). The SA 57 (pointing to the galactic north­ in the U magnitudes because of their distribution of these fields projeeted on pole) and of a field in the galactic anti­ metallicity dependence, was the lack of the sky is shown in Figure 1. The field centre. Four groups of stars, which are asound physical calibration of the RGU

sizes were chosen in order to give a marked with different symbols and colours in terms of Teff, log 9 and [Fe/H]. statistieally signifieant number of stars which are described in the caption, can Two basic approaches exist to achieve between 1,500 and 2,000. The typieal statistically be identified by the photo­ this goal, both of which have been halo field sizes are between 1 and 3 metry. So far, the RGU data have been undertaken during the past 10 years at square degrees whereas the typieal disk used to select complete sam pies of F Basel observatory. On the one hand, field sizes are between 0.1 and 0.3 and G type dwarfs and subdwarfs at the one has to define the photoelectric RGU square degrees. For every field the stel­ galactic north and southpole regions for system with a set of standard stars as lar spaee densities along the line of sight more detailed studies with intermediate weil as a grid of programme stars with have been determined for those stars band photometry (PeI et al. 1988, known physical parameters. On the which can be photometrically classified Spaenhauer and dei Rio 1989). Special other hand, one can use synthetic pho­ using the stellar statistieal tools as de­ interest deserves the fact that the mean tometry in conjunction with spectral scribed by Becker (1965). Furthermore, loci of the late-type giant stars show a scans or theoretical model atmospheres these data can serve as a powerful pre­ large variation (Fig. 2 b). This led to the provided the system is weil defined. selective tool for sampling specific stel­ distinction between "Ieft" and "right Both approaches should ideally go to­ lar populations in order to study them side" giants (relative to the main se­ gether controlling each other and giving spectroscopieally or with intermediate­ quence) and was qualitatively inter­ additional information. For instance, be­ band photometry as will be exemplified preted as a metallicity effeet (Becker cause model atmospheres can be con­ next. 1979, see also the next section). Up to structed as a function of continuously When comparing the morphology of now only a small part of the RGU data varying physical parameters, synthetic the two-colour diagrams in different re- contained in the catalogues has been photometry will fill the gaps in the dis-

0 0 oIr. 8", 1.0 0 1.0 00 o ... 0 I) o<\l 0

~Y~;o 0 ~oo 0 ' .."-':' ... o ..800 \- :::~~1' ... :~ 0 "::'. •• ~ 0 ••,.,•.(_. 0°;' • ~~'• ~, .. "'~"'". J.',~ ., .'.....~. ' • p~o . '._, .. .,-"...... 0 . .: :":: ....:< . 0° . 2.0 •• "".rt 2.0 . . . ~ . ••0 ··Y .. "

<.:> •• 0 <.:> 1..' I . .. I 0 .. ::> \ o 0 a. .t.. ... ::> ~ ... .tot ",' 0 ... 0 ...... 352 3.0 0 3.0 0 0 273

00

GALACI NORTHPOLE ANTICENTRE 407 479 421 SA 57 field neer NGC 1664 li CJ o 4.0 G: 15.0 - 16.0 4.0 G: 14.0 - 16.0

I 1.0 2.0 1.0 2.0 G-R G-R Figure 2 a: RGU two-colour diagram ofstars in the galactic northpole region SA 57 (Fenkart 1967). Only stars in the apparent magnitude range 15 m < G < 16 mare shown. Two groups of stars can be statistically identified: main sequence stars of population I (e) and main sequence stars of population" with large UV excesses (0). 2b: RGU two-colour diagram of stars in the galactic anticentre region (Becker and Fang 1973). Only stars in the apparent magnitude range 14 m < G < 16m are shown. Three groups of stars can be statistically identified: main sequence stars of population I (e) which are split into two groups because of a steplike increase of interstellar reddening caused by a nearby cloud; giant stars of population I (0, "Ieft-side" giants) and giant stars of population" (.6, "right-side" giants).

17 1 I I I I 001- , - 00 (a) (b) ~" o o .. 00 o .. 101- ~ . . o _ 10 \t";c00,"'0"0)o~ .. ~. 201- - 20 o \0·0 o I o. '0, I °i011' ::> o • ::> o~'. o t 0 ~ : . 30 I- .. -.. - 30 o ~ o 0 o

cdJ'Q) 0°0 00 • dwarfs 4.0 I- 40 - o (sub)gl8nls .. lale-lype val'

11 supcr"glanls

5.0 I I I I I 0.0 1.0 2.0 3.0 4.0 50 00 1.0 20 30 4.0 5.0 ;-R ,-R Figure 3: The two-c%ur diagram for the photoe/ectric RGU system: a) compilation of 275 well-observed stars covering a broad range in both c%urs. The samp/e comprises stars covering a /arge metallicity range and they are not corrected for reddening; b) measurements resulting from synthetic-filter photometry of the spectrophotometric data by Gunn and Stryker (1983). Due to the chemica/ homogeneity of the samp/e, the dereddened stars show very /ittle scaHer for a given /uminosity c/ass. Different /uminosity c/asses are marked by different symbols.

crete grid of photoelectrically observed sampies were chosen for this purpose: GS fluxes were dereddened employing stars. Furthermore, the internal consis­ - Main sequence stars of different the interstellar reddening law as given tency of a photometric system or cata­ effective temperatures, both field stars by Seaton (1979) and Howarth (1983). logue essentially depends on the proper and members of open clusters, in order Furthermore, the corrective function re­ transformations between the standard to determine the position of the main cently published by Rufener and Nicolet system and the instrumental systems, a sequence in the two-colour diagram and (1988) was adopted. Synthetic colour problem that can be tackled by synthe­ to establish a calibration in terms of indices were obtained by numerically tic photometry. For a discussion of the absolute magnitude. multiplying the relative response func­ use of synthetic photometry concerning - Stars of different luminosities, espe­ tions of the photoelectric RGU system the photographic RGU system, we refer cially cool stars, for luminosity calibra­ with the intrinsic energy distributions of to Buser (1979) and the references tion of field stars. the stars in the GS library. The resulting therein. - Dwarfs and giants in a large metallici­ two-colour diagram is shown in Fig­ ty range with the aim of calibrating their ure 3 b for different luminosity classes. It UV excesses as a function of metal will be used as a guide for the proper 3. The Photoelectric RGU System: abundance, thus providing the empirical interpretation of an observed two-colour Steps Towards the Physical basis for a statistical study of the chemi­ diagram like the one shown in Fig­ Calibration cal structure of the galactic halo (Trefz­ ure 3a. The detailed comparison of the The photoelectric RGU system is de­ ger 1981). observed and calculated two-colour fined by a combination of a photomulti­ Figure 3a shows the two-colour dia­ diagrams is subject to further investiga­ plier with an S-20 cathode and three gram of a compilation of our stellar sam­ tion and will be published elsewhere. broad-band interference filters for the pies. The S-shaped lower envelope in In the following we want to discuss pass-bands R, G and U (Trefzger et al. the left part of the diagram indicates the some results obtained from photoelec­ 1983) matching c10sely the photo­ main sequence for unreddened stars. tric observations of dwarf and giant graphic system. Observations of north­ Those stars Iying above the main se­ stars belonging to different stellar popu­ ern standard stars were carried out us­ quence are either affected by interstellar lations of our Galaxy. Figure 4 shows ing the 1-m telescope at the Gornergrat extinction and/or metal deficiency (see the two-colour diagrams of Hyades Observatory in Southern Valais, Switzer­ below). In order to determine the shape dwarf stars with spectral types between land, during several observing runs be­ of the two-colour diagram for normal A 1 and K2 for the UBV and RGU sys­ tween 1980 and 1983. The observations (solar abundance) stars, we derived col­ tems. Also indicated are measurements on La Silla were carried out using the ours from observed stellar energy dis­ of 46 mostly metal-poor dwarf stars, 1-m telescope and the ESO 50-cm tele­ tributions by digitally simulating the selected from the comprehensive cata­ scope during 5 observing runs between photoelectric RGU system. The library logue of Cayrel et al. (1985) of stars with 1984 and 1987. of stellar spectrophotometric data pub­ known parameters Tetl, log 9 and (Fe/H]. The goal of these observations is the lished by Gunn and Stryker (1983, Their metallicities vary in the range -3.5 study of the photometric properties of hereafter GS) provides a large sampie of < (Fe/H] < +0.6; their temperatures are stellar sampies with well-known physi­ various normal stellar types and repre­ between 6260 K and 4800 K and their cal parameters, e. g. effective tempera­ sents a valuable tool for the calibration gravities are around log 9 = 4.3. We ture, gravity, absolute magnitude, of photometric systems (cf. Labhardt used the UBV colours published in the metallicity and reddening. The following and Buser 1985, Labhardt 1988). The catalogue mentioned above to compare

18 always remains low due to the small -0,5 cl bl cl amount of stellar flux in the blue part of U-B U-G 6IU-GI the spectrum. However, there is a 1.0 strong interest in learning more about +++ ~ t O,f. the RGU colours of the reddest stars: a + + + + ++ good fraction of the photographically +t.+ .-t ... . 0,0 . recorded field stars are red and in order .,'1":G + .' ../ to understand their contribution to the .J. ~ + ~ •• i/I" local galactic structure we would like to • .:,+. 1.5 •• 0,2 /

+ IC)I· / distinguish between late-type dwarf and . /'45D . '. ,( + ..+ giant stars. By observing a representa­ . / +* '/ tive sampie of both M-type dwarfs and 0,5 ~, - O? • .. giants, all of which are MK standard .. +. + / " +... ­ ...... '" - 0.0 stars, we are in the process of tackling / "'... 2,0 . / . these problems. The reduction of the +.. / . .­ / . relevant measurements necessitates a ++ safe extrapolation of our transformation 1.0 -0.2 + equations, as the colour range of our standard stars does not yet include very 0,1 0.5 0.5 1.0 0.0 0.2 red stars. For this purpose, the GS li­ B-V G-R 6 lU-BI brary was used to establish the relations Figure 4: The two-e%ur diagrams of the Hyades main sequenee (.) and meta/-poor dwarfs between the photoelectric RGU colours (+) are shown for the UBV system (Fig. 4a) and for the RGU system (Fig.4b). Figure 4e and MK spectral classification. For a compares the UVexeesses as measured in the two photometrie systems (UV exeess = verliea/ large part of the diagram given in Fig­ distanee of a parlieu/ar star above the Hyades main sequenee). ure 6 the relations are monotonically in­ creasing and are almost identical for dwarf and giant stars. It is interesting to the UBV system with the results ob­ provide a statistical method to estimate note the large range covered in (U-G) by tained in the RGU system. In both metallicities of large sampies of halo the stars of the MK spectral c1asses K photometrie systems these stars show stars based entirely on three-colour and M, and the ambiguity of the relation substantial UV excesses relative to the photometry thus allowing a physical in­ in the right-most part of Figure 6a. (somewhat metal-rich) Hyades. This is in terpretation of the large data base of the Nevertheless, these relations turn out to qualitative agreement with the proper­ Basel halo and disk survey. be defined weil enough in order to cali­ ties of halo stars as observed in the As mentioned already in the preced­ brate the intrinsic colours of late-type photographie survey. ing section, giant stars sampled from stars. However, the UV excesses /) (U-G) fields in different parts of the galactic measured in the RGU system are con­ disk and bulge show systematic dis­ siderably larger than the b (U-B) values placements in the two-colour diagram. It of the UBV system. Figure 4c displays a was suspected some time aga (Becker star-by-star comparison of the corre­ 1979, Spaenhauer and Thevenin 1985) U-G sponding UV excesses as measured in that this could be related to variations of the two photometrie systems relative to the mean metallicity within the galactic .. .. the Hyades main sequence. The slope disk and inner halo. In order to study the . .. of the linear relationship is 1.52 showing properties of metal-poor giants in the 1.5 clearly the higher sensitivity of the RGU RGU system, we observed a sampie of system to separate metal-poor stars stars from the list of extremely metal­ : , from metal-rich ones. The stars with the poor giants published by Bond (1980). .. highest UV excesses are expected to be Their metallicities were determined from . those with the lowest metallicities, be­ Strämgren photometry and are in the 2.0 .... cause weakening the lines predomi­ range between -2.7 < [Fe/H] < -1.5. In . .... nantly enhances the stellar flux in the U Figure 5 we compare the positions of band. This is confirmed by the spectro­ these metal-deficient giants with the 10­ scopically determined [Fe/H] values. It is cation of the giants of the old disk clus­ . . ,~ . interesting to note that those stars in our ter M 67 (Tammann 1963). The large .. .. 2.5 ... sampie that are still more metal-rich displacement of the metal-poor giants . .. than the Hyades are located below the towards the upper right is obvious and .. Hyades main sequence, showing nega­ is related to the same kind of UV excess '. tive UV excesses. Again, this effect is in these weak-line stars as is observed more pronounced in the RGU system in halo dwarfs as weil. This strongly than in the UBV system. supports the conjecture that metallicity 3,0 .. The variation of ö (U-G) as a function differences between giants in different of [Fe/H] depends on stellar temperature parts of the Galaxy show up in the two­ and therefore on (G-R); the lines of colour diagram; after proper calibration 1.0 1.5 2.0 G-R different metallicities and temperatures this gives us the possibility to map the Figure 5: Two-e%ur diagram of meta/-defi­ in Figure 4 b can be drawn on the basis metallicity gradient within the galactic eient giants se/eeted from the list of Bond of our empirical data in combination disk, see e. g. Neese and Yoss (1988), as (1980) marked by crosses. The dots indieate with theoretical colours calculated from weil as within the inner halo. the /oeation of giants of M 67 in the photo­ model atmospheres (Buser 1979). This Measuring very cool stars is a quite graphie RGU system. The fine shows the work is still in progress. It will eventually difficult task because the U-band signal position of the main sequenee K stars.

19 40 () 40 (b)

0 dwarrs dwarCs O~~ 0 0 (sub)g••nls 0 0 o (sub}glanls superglants superglanls 30 0 30 ~§ '0 -83 0 := '0. '0 e 0 n::: 01 I 8 I ;:J 20 0 2.0 8~. .8 0 '0 0 " • S' 0 ., '. 1. 0 • , I' • ' 0 10 10 ,0'11

0 0' ~

~ 00 : 00 I

o BA F' G K MOB A F' G [( M 56789 0 123456789 0123456789023567001235600123450123456789 5670 0 123456709 0123456789023567001235680123450123456709 MI< sp lral ·1 ss MI< spe lral 1 ss Figure 6: Galibration ofphotoelectric RGU colours in terms of MK spectral classification. These relations are based on synthetic photometry of the GS library and MK spectral cJasses obtained from the Gentre de Donnees Stellaires (Strasbourg).

4. Conclusions to this projeet, and we would like to Fenkart, R. P., 1989: in preparation. The photographie RGU system was thank the ESO staff on La Silla for valu­ Gunn, J. E., Stryker, L. L., 1983: Astrophys. J. proposed 50 years aga by W. Beeker as able help as weil as the Swiss National Suppl. 52, 121. a tool for the study of galaetie strueture Seienee Foundation for finaneial Howarth, I. 0., 1983: Monthly Notices Roy. Aslron. Soc. 203, 301. and has been the foundation of the support of this projeet. Johnson, H. L., Morgan, W. W., 1953: Astro­ Basel RGU survey. The establishment of phys. J. 117,313. the photoeleetrie RGU system was Labhardt, L., Buser, R., 1985: in lAU Sym­ naturally required in order to extraet the References posium No. 111, "Calibration of Funda­ full information eontained in the photo­ Bahcall, J. N., Ratnatunga, K. U., Buser, R., mental Stellar Quantities", D. S. Hayes, graphie RGU database. The photoelee­ Fenkart, R. P., Spaenhauer, A., 1985: As­ L. E. Pasinetti and AG. D. Philip eds. trie measurements deseribed in the pre­ trophys. J. 299, 616. (Reidel Dordrecht). p. 519. eeding seetion along with the use of Becker, W., 1938: Z. f. Astrophys. 15, 225. Labhardt, L., 1988: New Direclions in Spec­ Becker, W., 1946: Veröff. Univ. Sternwarte synthetie photometry will provide the tropholometry, AG. D. Philip, D. S. Hayes, Göttingen, No. 79. S.J. Adelman, eds., L. Davis Press, essential physieal ealibration needed for Becker, W., Stock, J., 1958: Z. f. Astrophys. Schenectady (in press). Galaxy modelling as weil as for the pur­ 45,269. Neese, C., Yoss, K., 1988: Astron. J. 95, 463. pose of preseleeting speeifie stellar Becker, W., Steinlin, U. W., 1956: Z. f. Astro- Pel, J. W., Trefzger, Ch. F., Blaauw, A, 1988: sampies. With respeet to Galaxy model­ phys. 39, 188. Astron. Astrophys. Suppl. 75, 29. ling we expeet that the inelusion of ul­ Becker, W., 1963: Z. f. Aslrophys. 57, 117. Rufener, F., Nicolet, B., 1988: Publ. Obs. de traviolet data will put essential eon­ Becker, W., 1965: Z. f. Aslrophys. 62, 54. Geneve Serie G, Fase. 26. straints on the ehemieal strueture of the Becker, W., Fenkart, R. P., 1971: Astron. As- Seaton, M.J., 1979: Monlhly Nolices Roy. prineipal galaetie eomponents (halo, lrophys. Suppl. 4, 241. Astron. Soc. 187,73. Becker, W., Fang, Ch., 1973: Astron. Aslro­ bulge, thiek disk and disk). The majority Spaenhauer, A, Thevenin, F., 1985: Astron. phys. 22, 187. Astrophys. 144,327. of the stars appearing in the photo­ Becker, W., 1979: Astron. Astrophys. Suppl. Spaenhauer, A, dei Rio, G., 1989: in prepara­ graphie survey belong to the eolour do­ 38,341. tion. main eovered by the photoeleetrie ob­ Bond, H.E., 1980: Aslrophys. J. Suppl. 44, Tammann, G.A, 1963: Z. f. Astrophys. 58, servations: dwarf and giant stars rang­ 517. 100. ing from speetral type 0 through K and Buser, R., 1978: Aslron. Astrophys. 62, 411. Trefzger, C. F., 1981: Aslron. Astrophys. 95, eovering the metallieity range from ex­ Buser, R., 1979: in Dudley Observalory Re­ 184. treme population II to extreme popula­ ports No. 14: "Problems of Calibration of Trefzger, C. F., Cameron, L. M., Spaenhauer, tion I. The extension of the photoeleetrie Multicolor Photometrie Systems", A. G. D. A, Steinlin, U. W., 1983: Aslron. Astrophys. Philip, ed., p. 1. system to the very eool (M-type) stars is 117,347. Buser, R., Kaeser, R., 1985: Aslron. Aslro­ under way. Furthermore, eeo RGU ob­ phys. 145, 1. servations have been earried out on La Cayrel de Strobel, G., Bentolila, C., Hauck, Silla in order to make faint objeets ae­ B., Duquennoy, A, 1985: Astron. Aslro­ eessible for RGU study. phys. Suppl. 59, 145. NOTE: Photographer Gudrun Ewaldt Fenkart, R.P., 1967: Z. f. Aslrophys. 66, 390. also participated in the making of the Acknowledgements Fenkart, R. P., Binggeli, B., 1979: Astron. As­ centrefold image of the ESO Headquar­ trophys. Suppl. 35, 271. ters in Messenger No. 53 (September We gratefully aeknowledge the ESO Fenkart, R.P., Esin-Yilmaz, F., 1985: Astron. 1988). teleseope time that has been alloeated Aslrophys. Suppl. 62, 39. 20 cember. It will thereafter be included in The ESO VLT as fischertechnik-Model the ESO exhibition. It would be interesting if a smaller VLT The first fully steerable VLT has a/­ nology. It is too big and complicated to model could also be made, similar to ready been bui/t! travel with ESO's own exhibitions, but those of airplanes, cars and rockets, Early in 1988, the well-known German ESO will receive a similar model of a which are available as build-it-yourself firm "fischerwerke" approached ESO single telescope to be shown for the first kits. However, this has not yet been with an interesting suggestion. Having time at the Council meeting in Oe- decided. read in the local press about the deci­ sion to build the VLT, one of their en­ gineers thought that a model of the VLT, built with the "fischertechnik" building The Astronomy and Astrophysics Review blocks, might become an eye-catching centre on the next toy-fairs in Germany. This new review journal will be started All reviews will be commissioned by The ESO people involved in the VLT in 1989 to publish critical reviews of the the Editor, who will be assisted by the project feit the same way and after worldwide astronomical literature that Associate Editors M. C. E. Huber some consultations, fischerwerke built a are reasonably complete and balanced. (ESTEC), P. Lena (Meudon), P. G. 6-metre long model, here seen during It will encompass all subjects in as­ Mezger (Bonn), F. Pacini (Florence) and the final checkout in their workshop. It is tronomy and astrophysics and bound­ S. R. Pottasch (Groningen). While the controlled by a small computer (PC) and ary areas with other fields. Oevelop­ new journal will be an independent pub­ the telescopes move individually and in ments in atomic, molecular, or particle lication, a loose cooperation has been unison during a demonstration se­ physics directly relevant to astronomy established with Astronomy and As­ quence. Light guides illustrate the light­ may be included as weil as cosmic-ray trophysics. Subscription information (in­ paths through the system, all the way physics, solar-system studies, and rel­ cluding a special rate for individuals) down to the combined coude focus in evant computational procedures. All im­ and sampie copies may be obtained the auxiliary building. A giant crane lifts portant fjelds will be reviewed periodi­ fram Springer-Verlag, attention: Ludwig one of the enormous mirrors and moves cally with the frequency a function of the Kuhn, P.O. Box 105280, 0-6900 along its rails. level of activity. Within about six years, Heide/berg 1, Federal Republic of Ger­ The model went on display at the the collected volumes should present a many, except for the U. S. (Springer­ autumn toy fair in Cologne and will later view of the important developments in Verlag, attention: Margo Martin, 175 be shown in Frankfurt. It attracted at lot all of astronomy. The relatively rapid Fifth Ave., New York, N. Y. 10010). of attention and made good publicity for publication schedule aims at four issues L. WOL TJER, Editor fischerwerke, ESO and European tech- per year.

21 Infrared Emission from the Sub-Arcsecond Vicinity of SN 1987A A.A. CHALABAEV, CNRS, Observatoire de Haute-Provence, St-Michel-I'Observatoire, France C. PERRIER and J.-M. MARIOTTI, Observatoire de Lyon, St-Genis-Laval, France

Introduction spectral range. It provides a one-dimen­ the telescope focal plane across a The fireball in the LMC called sional spatial spectrum of an image up narrow slit. The width of the slit is cho­ SN 1987 A offered an exceptional to the maximum frequency of 3 to 6 sen according to the spectral band and/ 1 opportunity to study spatial structure of arcsec- , depending on the spectral or the seeing conditions: for example, a supernova phenomenon. Obviously, band and seeing (for more details, see for the L'band in good seeing conditions special high angular resolution tech­ Perrier, 1986). The observing procedure we use a 0.2 arcsec wide slit. The scan­ niques at large telescopes had to be consists in scanning a stellar image at ning must be fast enough to "freeze" the employed. The results of speckle inter­ 1.1 r------,-----.-----..,.-----,------,,------, ferometry in the visible spectral range, carried out at CTIO and AAT were re­ a viewed by Meikle (1988). Here, we 1.0 ••••• t t • t t t t t t t t t tt t tt t would like to present the results of speckle interferometry in the near in­ .90 frared (n 2-5 flm), carried out at the ESO 3.6-m telescope during May-Au­ gust 1987. In contrast with the work in b the visible range, mainly concerned with ',:}" • • • • t t t t t t tttttj j 11111 j the ejecta (= 10 marcsec), the near IR speckle interferometry deals with the structure of the close environment of the J supernova (= 100 marcsec). In particu­ lar, it addresses the interesting question wh ether this environment contained t!11 ! t +tt jtt! t \j 11 j c dust and thus provides a useful test of ',:!. ···· current models of the progenitor evolu­ tion. Indeed, some models suggest that I the exploded blue supergiant (BSg) Sk­ 69°202 has once been a red supergiant t t t t t t t t t tt t! j d (RSg). Part of the dust, condensed ',J ····· jj around the progenitor during its RSg phase, could survive destruction by the I fast and hot wind of the BSg (Chevalier, 1987; Renzini, 1987). The burst of + t t t!t tt j j!t t t tt j j j e supernova radiation at shock breakout ',:l' ····· 43 44 with 4, - 10 _10 erg· S-1 should heat this dust up to 1,000-2,0000K. 1 The corresponding thermal emission should then appear as an infrared echo 1.0 +t tt tI! Ht t t ttIj jjj f (Bode and Evans, 1979). The size of the I'·.. · dusty region was expected to be of the order of 1017-1016 cm. At Earth, the ." j I corresponding angular size of 0.1 -1.0 arcsec is weil within the possibilities of ~ speckle equipment. Shortly after the ',: ••••• t t tIttj Ii j j j 111 jjIj announcement of the supernova, we g began to study the feasibility of obser­ vations. Computer modelling showed .,....(f) that the IR echo, if it existed, could be > .60 resolved already during the first months L' (3.8 j.lm) following the arrival of the explosion .70 light. Independently, Prof. L. Woltjer, ESO Director General at that time, re­ . 50 L-_~_ _L.._~_--L__~_....L-_~_-L_~_---'__~__' served 5 nights in May 1987 at the ESO 3.0 4.0 5.0 5.0 3.6-m telescope for IR speckle observa­ .00 1.0 2.0 tions. After an exchange of telexes, we Frequency (1/arcsec) were in a plane to Santiago. Figure 1: Evolution 01 visibility curves 01 SN 1987A in the L' band in May-June 1987: We used the ESO general user's IR a: May 9, NS direction; b: June 8, EW direction; c: June 16, NS direction; d: June 17, NS specklegraph designed for the 1-5 flm direction; e: June 18, EW direction; I: June 22, EW direction; g: June 22, NS direction. 22 speckles; typically, the image is crossed TABLE 1. Journal of observations. in 50 ms time. Each scan is Fourier 3 transformed; the average power spec­ Date 1987 Day' Band Direction Qualitl er marcsec trum of the object is divided by that of a May9 75 L' NS 3 non resolved reference star thus giving the visibility May9 75 M NS 1 non resolved curve. More details on the observing June 7 104 L' EW 2 non resolved procedure, data and their discussion June 8 105 K EW 3 non resolved can be found in accounts given by June 8 105 L' EW 4 non resolved Perrier et al. (1987) and Chalabaev et al. June 8 105 M EW 1 non resolved (1988 a, b). Note, however, that, as a June 16 113 K NS 2 non resolved rule, the presentation of speckle results June 16 113 L' NS 2 marginally resolved June 17 114 L' NS 4 144 ± 44 makes extensive use of technical terms. June 18 115 L' EW 4 92 ± 18 Let us recall that, as it is always the case June 22 119 L' EW 4 126 _ 19 of interferometric methods, we deal with June 22 119 L' NS 4 73 ± 49 measurements of Fourier transform of August 5 163 K EW 4 330 ± 80 light pattern. Often, a speckle observer August 6 164 K NS 4 330 ± 80 has no possibility to "come back" into August 6 164 L' NS 4 350 ± 50 the image space, i. e. to present a nice, August 6 164 M NS 2 390 ± 100 easily understandable reconstructed Notes: image. Then, he is bound to "live" in 1 Day is counted trom the arrival of the neutrino pulse, 1987 Feb 23.4 Fourier space which is not an every-day 2 "Eye-estimated" quality of a visibility ranging [rom 1 (acceptable) to 5 (exce/lent) experience of everybody. The necessity 3 For days 114 -119, öcp is the FWHM of a Gaussian disk contributing 15 % to the total flux; for days to use terms like Fried parameter, MTF 163-164, 'f' is the separation of a secondary spot from the supemova. of speckles, phase of Fourier transform and so on, makes articles on speckle in­ terferometry difficult to digest. We restore the image is subject to extrapo­ spot(s) and a disk halo emission. Three would like to take advantage of writing lation of the recorded tendency beyond images can equally account for the visi­ for the Messenger to try a more friendly the maximum frequency of the equip­ bility curves in L', measured on June way of reporting on speckle data. Let us ment. Due to extrapolation, the image 17 -22, namely: (1) two "point-like" use where it might help terms of fishing, reconstruction is not unique. Theoretical spots, one in the NS direction (180° at least in parentheses. This may be visibility curves produced by the most ambiguity) and another one in the EW especially important for our June obser­ plausible images are given in Figure 5 direction; (2) one "point-like" spot, re­ vations. together with typical observed visibili­ sulting from the combination of two ties. [There was a fish in mid-June. It spots, and laying in one of the inter­ Bendings of the Rod was not possible to get it out of the mediate directions: NE, NW, SW or SE; water. But we kept record of the rod and (3) an axially symmetric disk halo The Journal of observations is given in reaction. Now we go to a fish shop, take around the supernova. To estimate the Table 1. The evolution of visibility curves different fishes and see the reaction of angular scale, we need to know the rela­ in the L'band is illustrated in Figure 1. [In the rod. It turns out that only fishes of a tive contribution, E, of the source(s) to terms of fishing, we were observing the certain kind and of a certain size can the total flux from SN (cf. Perrier et al., L-rod ...]. Visibility curves, measured reproduce the observed reactions ...] 1987). [Stronger the fish, smaller its on May 8-9 and on June 8, could be They come in two kinds: a "point-like" size ...]. The lowest value of E which is described merely as a horizontalline, corresponding to the unresolved super­ 1.11-~--'---~-"--~--'--~--'---~--r--~---. nova. [The rod was straight, no fish ...). On June 16, the visibility curve showed a first, though marginally perceptible, L' •••• I I t I + + I t I I j IIIII II I sign of emerging spatially distinct struc­ ture: namely, the high frequency part of .90 the visibility curve began clearly to devi­ ate from a straight line. [The rod got bent: a fish began to bite ...]. This was .BO confirmed by further observations on June 17, 18 and 22. [See Fig. 1; it bit 1.0 even stronger ...]. No significant differ­ >- ...... • + + t f + + t + f t t t t t f f f f t t t t ence was found between the visibility .-. Curves measured in the North-South ...... 90 D and East-West directions of scans. The ...... curves in the K and M bands remained (f) those of the unresolved supernova (see > .80 Fig. 2 and 3). The type of visibility curves like those .70 observed in the L'band from June 16 to K (2.2 Jl.m) 22 is usually referred to as "partially resolved": that is only a fraction of the .60 '-:::"-~---:-':--~--::~-~_...I...-_----_...I...-_~_....I-_~_-.J .00 1.0 2.0 3.0 spatial spectrum of a resolved object •. 0 5.0 ·6.0 could be measured. One can also say Frequency (1!arcsec) that the size of the object was less than Figure 2: Visibility curves of SN 1987A in the K band; top: on June 8, EW direction; down: on the Rayleigh resolution. Attempting to June 16, NS direction.

23 still compatible with the observed shape 1.1 of the visibility curves is about 10% or 17 Jy. On the other hand, the relative 1.0 smoothness of the light curve in L' be­ • t • tttttttt • + tween June 8 and 18 seems to discard + + t t t t t any "flare", exceeding 20 % of the total .90 flux. We adopt E = 15 %. Then, in the K case of two spots, their angular separa­ tion from the supernova is (» = 55 marc­ .80 sec and the projected distance p = 17 light-days (I. d.). If the spots are com­ 1.0 >- • t • + t ++ t t bined in one, then = 78 marcsec and +J t tt i rl • + p = 24 I.d. Finally, if the real image was -. t +I tI t j rl .90 an axially symmetric disk halo, which we D rl favour as the most simple case, its (f) L' weighted average FWHM was about rl .80 109 ± 24 marcsec (Gaussian distribu­ > 1 tion of brightness was assumed). The corresponding projected distance from 1.0 1t the supernova to the edge of the halo at Iljtl!+t \ half maximum was p = 17 I. d. On August 5 and 6, the visibility .90 curves (Fig. 4) displayed a different

pattern: an oscillation with the am­ .80 M plitude of about 4 % and the first 1 minimum at about 1.25 arcsec- , superimposed on the visibility of the un­ .70 SN 1987A resolved supernova. [It bit once again, August 6, 1987 but that was a different fish ...]. This is .60 a very faint signal, comparable to the .00 1.0 2.0 3.0 4.0 5.0 6.0 level of systematic errors. However, Frequency (1/arcsec) none of the numerous test observations of unresolved stars showed this pattern, Figure 4: Visibility curves of SN 1987A on August 5-6, NS direction. and we must conclude that the oscilla­ tion was related to the supernova. It appeared in all three bands: K, L' and M, ruled out. Only secondary "point-like" North-South direction (180° ambiguity) scanned in North-South. One visibility spots match the observed oscillations. and separated from the supernova by curve, in the K band, was measured in Yet, as far as the phase of the Fourier 350 ± 40 marcsec. This corresponds to EW; it showed a similar oscillation. transform is not restored (although we the projected distance p = 106 I. d. A Since the August visibility curves display hope to resolve this problem), there is similar secondary spot in the East-West secondary maxima and minima, there is an ambiguity concerning the number of direction explains the visibility curve no necessity in extrapolation, and in­ spots (one or two) and their positional measured in the K band. As in the previ­ terpretation is less ambiguous than for angle. [We got some fish parts out of the ous case, the spots can be combined in the mid-June data. A disk halo is easily water. However, the puzzle is not one, Iying at 495 ± 60 marcsec (p = 150 ruled out. We have suggested a ring assembled ...]. One needs a secondary I. d.) in one of the intermediate direc­ of light of 420 marcsec diameter spot, contributing 2.6 ± 1.0 % tions. (Chalabaev et al., 1988a). However, it (3.0 ± 1.2 Jy) in K, 2.7 ± 1.0% produces too strong a damping of sec­ (2.5 ± 0.9 Jy) in L' and 1.8 ± 1.0% What Was It? ondary oscillations (cf. Fig. 5) and is also (2.8 ± 1.6 Jy) in M, situated in the The first fact we wish to point out is the projected distance from speckle source(s) to the SN: in June 17-22 it 1.1 was about 20 I. d. which implies the ap­ parent velocity of the source(s) to have >- 1.0 been 18 % of the speed of light c. In .+J I I t j\ August, the distance was at least ·rl Ijjj ...... 106 I. d., and the velocity was at least ·rl jj .90 .D 0.65 c. Clearly, the speckle sources ·rl (f) must be located outside the ejecta. We ·rl .80 see two possibilities to explain the ob­ > served velocities. Following Rees (1987), one can consider a relativistic .70 jet. However, the apparent June-August M (4.6 J.1m) acceleration makes this explanation un­ likely. Instead, we suggest a light echo .60 .00 1.0 2.0 3.0 4.0 5.0 6.0 to be the origin of the speckle sources. In this case, the apparent velocities Frequency (1/arcsec) close to the speed of light find a natural Figure 3: The visibility curve of SN 1987A in the M band on June 8, 1987, EW direction. explanation. The second fact we wish to

24 1.1 ing from the inner edge of the shell at R = 10'8 cm or 400 I.d. At this distance, 1.0 a the temperature of dust, heated by the ••••• ++II +III tI tIII I I jjj light burst with the luminosity l..o = 1043 erg's-1, should be about 500-600 °K.

.90 The detection of speckle emission at Tco1 - 2000 °K in the form of spots or halo, and not of a ring, and at a distance to the supernova c10ser than expected 1.0 then looks surprising. However, even at b this distance, dust could partially sur­ •·••• +II I tttttItIIIIII III vive the destruction by the BSg wind if it .90 is concentrated in clumps, formed when the RSg wind material fragmented due .80 to the Rayleigh-Taylor instability (Ren­ zini, 1987). The observed IR speckle sources can weil be the emission from the c1umps of the relict dust. Thus, the following three spherical regions can be distinguished in the environment of SN >- 1.0 c +J 1 1 1 1987 A: .....'rl · .••• ++1++ + + 1II+I! (1) the inner cavity, free of any dust ·rl .90 because the dust supply by the RSg .0 ·rl wind had been turned off; its radius R, = Ul ·rl t,Vd' where t, is the time elapsed since > .110 the RSg wind ceased to blow, and Vd is the velocity at which dust f10wed away from the star; (2) an intermediate region where the fast BSg wind is passing 1. 0 t--.::=---....~_ through the RSg wind material; it is ~_._.-=- -.:.~.::-.:-=.----..:.:::=~._--...... -- d .. delimited by a shell of swept RSg wind -- material at R = t v h, where t is the time .90 - -.- 2 2 s 2 elapsed since the BSg wind began to blowand Vsh is the velocity of expansion .BO of the BSg wind into RSg wind material (Chevalier, 1987) and, possibly, (3) the region of the unperturbed RSg wind at .70 R > R2. This is illustrated in Figure 6.

. 60 L-_~_ __L__~_....L._~__.l..-_~_ __L__~_....L._~_ ____J o 1.0 2.0 3.0 4.0 5.0 6.0 Frequency (1/arcsec) Time Scale of the Progenitor Evolution Figure 5: Comparison of observed and theoretical visibility curves of SN 1987A in the L' (3.8/tm) spectral band: In the favoured case of the Gaussian a: June 8, 1987, East-West direction; b: June 22, 1987, East-West direction; c: August 6, 1987, halo for the mid-June L' visibilities, the North-South direction; d: solid line, the unresolved supernova plus a disk halo with f = 10% heated dust closest to the supernova and the FWHM = 120 marcsec; short-dashed fine, the supernova plus a secondary spot with E grains are at the vertex point of the = 6 % and the separation of 62 marcsec; long-dashed line, the supernova plus a secondary paraboloid, at cT/2. Then, the first de­ spot with E = 2.6 % and the separation of 350 marcsec; dot-dashed line, the supernova plus a tection of the dust echo on day 113 ring of f = 3 % and the radius of 210 marcsec. suggests an upper limit on the radius of the dust free cavity, R, < 56.5 I. d. or 1.46 . 10'7 cm. The corresponding limit point out is the rather low colour tem­ c"t/2 from the supernova, where "t is the on the time interval, elapsed since the perature of the speckle emission. On time interval counted from the arrival of wind of the RSg ceased to blow, is t, < June 16, when we have measured both the explosion light to the Earth. The 4600 . (10 km s-,/Vd) yr. The typical RSg

K and L' visibilities, Tco1 :S 2200 °K. In distance from the supernova to the wind velocity about 10 km . s-, is used August, Tco1 = 2000 ± 900 °K. This is sources is: R = (p2/C"t + c"t)/2, where p is as a first guess for Vd, but the actual close to what one would expect for a hot the projected distance. Therefore, the value of Vd might be greater if dust is dust emission. Thus, as we have sug­ distance to the edge of the disk halo or accelerated by the fast BSg wind. For gested (perrier et al. , 1987), an IR light to the spots, detected in mid-June, is R the halo, R, cannot exceed the distance echo from dust, heated by the light burst = 1.5 . 10'7 cm; for the August spots, R to its edge which is at the distance of at shock breakout, appears as the most = 3 . 1017 cm. Chevalier and Fransson about 1.5 . 10'7 cm from the supernova. plausible explanation. (1987) and Chevalier (1987) also consid­ Consequently, astronger upper limit on Applying the theory of light echoes ered the possibility of the IR echo from t, is 5000 . (10 km s-,/Vd) yr. Finally, (Couderc, 1939), we can deduce the SN 1987A. According to their work, the allowing for the uncertainty of image location of the IR speckle sources. As shock wave of the BSg wind expansion reconstruction, we must consider the seen by a distant observer, the echoing should sweep the relict RSg dust into a most distant unique "point-like" spot dust grains lie on a paraboloid of revolu­ shell. They expected only a weak IR case. Then p = 24 I. d. and R = tion with the vertex point at the distance echo, appearing as a ring of light, com- 1.6·10'7 cm. The corresponding con- 25 Relation to Other Data .. ' Given that the IR speckle data gathered at ESO are unique, we can verify them only indirectly. The first set of data wh ich provides comparison are observations of the fluorescence echo in UV lines of Hell, 0111, CIII, NIII, NIV and NV, detected by the IUE satellite (Fransson et al., 1988) and in the visible lines of 0 III and H, detected at ESO (Wampler and Richichi, 1988). They gave strong evidence in favour of reality of the RSg phase in the past evolution of the progenitor. This is in agreement with the interpretation of the IR speckle emission as due to dust grains, formed in the "antique" RSg wind. Furthermore, Wampler and Richichi (who coined the term "antique" wind) succeeded in measuring the spatial extent of the line emitting region and thus obtained an estimate of the time interval elapsed since the BSg wind began to blow, t2 "" 7,000 . (50 km S-l/Vsh) yr. Taking into account uncertainties in measurements and in scaling factors, we consider the agreement with our estimate of the end

of the RSg wind epoch, t1 ~ 4,600-5,100 yr at Vd = 10 km S-l, as encouraging. Another point of compari­ Figure 6: The elose environment of SN 1987A as suggested by IR speekle interferometry. son may be provided by observations of Parabolae of light eeho are labeled by number of days after the arrival of the explosion light. the far UV scattered echo (the external Double hatehed areas show the loeation of dusty elumps heated by the light burst. For fur/her "invisible" part of the famous rings at 30 explanations, see the text. and 50 arcsec). As proposed by Chevalier and Emmering (1988), such observations could yield an indepen­ dent estimate of L . The third kind of servative upper limit on time scale is: t of the burst of radiation at shock break­ b 1 observations to keep eye on are the X­ < 5100 . (10 km S-l/ ) yr. The upper out, 4,. The upper limit T ~ 2200 °K Vd eol ray data and IR photometry. Indeed, Itoh limits on t are rather small. They imply on June 16 implies the dust temperature 1 et al. (1987) and Itoh (1988) predicted that the evolution from red to blue was Td ~ 1500 °K (we assume that the dust intense X-ray and IR emission at the unexpectedly short, just of the order of absorption depends on wavelength as time when the supernova ejecta will col­ the thermal timescale of the hydrogen f...-1). Solving the equation of the radiative 3 lide with the dense RSg wind material. envelope about 10 yr. Another hint on balance for dust grains, we obtain Lb < 43 Assuming the velocity of the blast shock the time scale of the RSg - > BSg evolu­ 3 . 10 erg· S-l. With similar assump­ wave from the supernova to be tion can be obtained from the absence tions, we obtain for the August 5-6 4 42 2 . 10 km S-l, it should reach the mid­ of the ring-induced pattern on August spots Td = 1,350 ± 500 °K and 7 . 10 June IR speckle source(s) at R = 5-6 visibilities. A ring emission would erg· S-l ~ 4, ~ 5.1044 erg· S-l (the 1.5'10'7 cm in the middle of 1989, giv­ be the signature of the shell sweeped by case of two spots at R = 3.2· 1017 cm) 44 ing rise to a flare of X-ray and IR radia­ the BSg wind. From the August vis­ and 1 . 1043 erg· S-l ~ L ~ 8· 10 b tion. ibilities, the lower limit on the diameter erg· S-l (the case of a unique spot at R of such a ring is 0.5 arcsec. Then the = 3.9 . 1017 cm). Finally, combining the 17 June and August estimates, we obtain shell should be at R2 > 2.6· 10 cm, The Companion Object and the BSg wind should have begun to 7 . 1042 erg' S-l ~ 4, ~ 3 . 1043 erg· S-l. blow at least 1,600 . (50 km . S-l/Vsh) yr The IR speckle emission comes from a A speckle companion (alias the "Mys­ ago. However, the upper limit on the flux mixture of dust grains at different tem­ tery Spot") was announced to have from the ring in the L' band is rather peratures. However, theoretical models been detected in the vicinity of high, 14 Jy. This limit is not that signifi­ give an extremely short burst with the e­ SN 1987 A from the speckle observa­ cant: a faint ring would escape detec­ folding time not exceeding a few tions in the visible range in March-April tion. Astronger constraint on the ring minutes (e. g. Woosley, 1988). There­ 1987 (Nisenson et al., 1987; Meikle et emission will be hopefully set by later IR fore, the echo emission is strongly al., 1987). It was situated approximately speckle observations. dominated by the hottest grains and our South of the supernova. Measured val­ estimate of 4, should be close to the ues of the angular separation vary from value at maximum within a few percent. 52 to 74 marcsec. Our c1osest-in-time The UV Burst It compares weil with the calculations of observations, carried out on May 9, i.e. 43 The colour temperature of the IR Woosley who gives Lb = 3 . 10 erg· S-l 24 days after the last detection in the speckle emission allows to constrain the for the model 10 H (wh ich is also his visible, did not reveal the companion, magnitude of the very first point of the best model to account for the whole yielding an upper limit of 21 Jy on its flux supernova light curve, i.e. the luminosity body of observations of SN 1987 A). in the L' band. Further, as the reader 26 recalls, the partially resolved L' vis­ " ibilities in mid-June can be fitted by .. "point-like" sources, situated about 50 marcsec from the supernova. However, ascribing the NS source to the Compan­ ion would lead to a quite inconsistent picture. One needs a second compan­ ion to explain the EW source. Also, one I would have to explain why none of the companions were seen during the June 7-13 observing period. Therefore, we conclude that the mid-June L' vis­ ibilities, although they show a resolved .. structure, are not related to the com­ .. panion. Further, speckle observations in the visible, carried out between May 30 "., and June 2, did not detect the compan­ ion (Karovska et al., 1987). A number of mechanisms (synchrotron The "Mystery Spot" radiation, bremsstrahlung, line emission from ionized gas) have been proposed to explain the companion. However, ,3.' according to a summary by Phinney lo~ (v/Hz) (1988), the only model without severe Figure 7: The spectral distribution of energy for the companion object, implied by the visible difficulties with observations was a ther­ and infrared data. The solid line corresponds to a black body of 3,000 K. mal emission at T = 3,000 K from a compact object. The corresponding black-body curve together with the visi­ ble and IR data is plotted in Figure 7. to-noise ratio than what we had on plied IR photometry data all along our Our upper limit in L' lies below by a SN 1987 A would allow much more re­ observing runs. A trip of A. C. to Chile factor of 2.8 and provides a useful con­ fined studies. Also, spatially resolved was financed by INSU-CNRS (France). straint. It implies that the temperature of observations of an echo at a high signal­ The analysis of data greatly benefitted the compact object should have re­ to-noise ratio may give the distance to from discussions with W.S.P. Meikle, R. mained constant at 3,000 ° K from the exploded object (Chalabaev, 1987). Chevalier and E.J. Wampler. Last but March 25 to April 14 (dates of observa­ Overwhelming possibilities are prom­ not least, Prof. L. Woltjer, the former tions in the visible) and then dropped ised by the coming new generation of Director General of ESO, allocated tele­ down to below 1,800 °K by May 8, telescopes of 8-10 m diameter. Es­ scope time for this off-schedule pro­ 1988. Phinney also mentioned the timates show that with such a telescope gramme and constantly encouraged our possibility of an echo from melting dust. one could undertake similar studies of work. We are indebted to all these per­ Given the projected distance of about supernovae up to the distance of the sons. 17 I. d. on April 14, the corresponding M31 galaxy. Furthermore, the ESO VLT distance from the dust to the supernova project includes the IR interferometry was about 28 I. d. From the equation of option and will certainly play a highly References thermal equilibrium, we estimate the privileged roje. Bode, M.F., and Evans, A., 1979: Astron. luminosity of radiation, necessary to Astrophys., 73, 113. heat this dust up to 3,000 ° K, as lt, = ESO Workshop on 44 Acknowledgements Chalabaev, AA, 1987: in 2 . 10 erg· S-1. This appears to be in SN 1987A, ed. I. J. Danziger, Garehing, conflict with the non-resolved K visibility Behind the visibilities of SN 1987 A pre­ p.643. on June 16. sented here there is an effort of a Chalabaev, A.A, Perrier, C., and Mariotti, number of persons at La Silla. Jacques J.-M.: 1988a, in George Mason University Roucher spent long sleepless hours in Workshop on SN 1987A, ed. M. Kafatos, improving the electric set-ups of the Fairfax, p. 236. Some Conclusions and Future specklegraph. The electronics were re­ Chalabaev, A.A., Perrier, C., and Mariotli, Horizons J.-M.: 1988b, Astron. Astrophys., in press. fined by Michel Maugis and the control Chevalier, RA, 1987: in ESO Workshop on The reported work iso the first study of software by Flavio Gutierrez. The first 4 SN 1987A, ed. I.J. Danziger, Garehing, a supernova at high spatial resolution in nights out of 5, allocated in May, were p.481. the infrared. Discussion of data from this lost due to a snowfall. Due to the cour­ Chevalier, RA., and Emmering, R.T., 1988: sort of measurements provides valuable tesy of Paul Le Saux, we could get the Ap. J., 331, L 105. information on the past progenitor May 9 visibilities. The detection of the L' Chevalier, R.A, and Fransson, C., 1987: Na­ evolution as weil as on the important source(s) in June became possible due ture, 328, 44. Couderc, P., 1939: Ann. d'Astrophys., 2, 271. parameter Lb , the luminosity of light to the kindness of scheduled observers, burst at shock breakout, which is A. Chelli, I. Cruz-Gonzalez, B. Reipurth Fransson, C., Cassalella, A, Gilmozzi, R, Panagia, N., Wamsteker, W., Kirshner, difficult to measure. More IR speckle and H. Zinnecker, who shared the tele­ RP., and Sonneborn, G., 1988: Ap. J., in scope with uso The August oscillations data on SN 1987 A were obtained in De­ press. cember 1987 and June 1988 and await could be detected thanks to difficult Iloh, H., Hayakawa, S., Masai, K., and their analysis. Further development of technical interventions at the telescope Nomolo, K., 1987: Publ. Astron. Soc. Ja­ this new field can be easily foreseen. We of Daniel Hofstadt, Lo"ic Baudet and pan, 39, 529. think first of all about galactic super­ Jacques Roucher. Patrice Bouchet took Iloh, H., 1988: Publ. Astron. Soc. Japan, 40, novae and bright novae. A higher signal- part in the May observations and sup- 263. 27 Karovska, M., Nisenson, P., Papaliolios, C., and Noyes, R., 1987: As/rophys. J., 320, Phinney, E.S., 1988: Na/ure, 331, 566. and Standley, C., 1987: /AU eirc., L15. Rees, M., 1987: Na/ure, 328, 207. No. 4440. Perrier, C., 1986: The Messenger, No. 45, Renzini, A., 1987: in ESO Workshop on Meikle, W.S.P., 1988: Proc. or As/ron. Soc. p.29. SN 1987A, ed. I.J. Danziger, Garching, or Aus/ra/ia, in press. Perrier, C., Chalabaev, A.A., Mariotti, J.-M., p.295. Meikle, W. S. P., Matcher, S. J., and Morgan, and Bouchet, P., 1987: in ESO Workshop Wampler, E.J., and Richichi, A., 1988: The B. L., 1987: Nature, 329, 608. on SN 1987A, ed. I.J. Danziger, Garching, Messenger, No. 52, p. 14. Nisenson, P., Papaliolios, C., Karovska, M., p.187. Woosley, S.E., 1988: Ap. J., 330, 218.

An Update on the Light Echoes 01 SN 1987A

The ring shaped light echoes found earlier this year around the supernova SN 1987A in the LMC (The Messenger 52, 13) have been under close monitor­ ing ever since. The picture shows an artificially enhanced image of the rings as observed by H. Pedersen and J. Mel­ nick on the nights 29th through 31 st of October 1988, using a CCO camera in the Gascoigne adapter at the prime focus of the 3.6-m telescope. The reso­ lution is 0.58 arcsec per pixel and the seeing was about 1.2 arcsec. In order to enhance the contrast, the photo shows the ratio of averages of five 3-minute exposures in Sand V each. The outer ring has reached a radial distance of about 77 arcsec and the inner ring of about 45 arcsec, very close to the predictions for plane parallel sheets of reflecting material perpen­ dicular to the line of sight. In February the radii measured 52 and 32 arcsec respectively. The most interesting as­ pect is that the echoes retain their near circular shape. 'fhis implies that, at least over the area sw.ept by the echoes since February, the interstellar dust must be highly concentrated into two thin layers located roughly 120 und 320 pc in front of the supernova. The very small devia­ tion from circularity of the rings imposes tight constraints on any inclination and curvature of these sheets of matter, which are likely to belong to the halo of the LMC. M. ROSA

The ESO Schmidt Telescope

The ESO (R) half of the joint ESO/ Most of the missing Atlas plates are in cedes rapidly and more than one quar­ SERC Survey of the Southern Sky will the right ascension interval between 20 ter of the fields have been covered with soon be finished. For more than 90 % of hours and 4 hours and high priority will excellent plates. the 606 fields, Atlas-quality plates have be given to the atlas work during the Other Projects now under considera­ now been obtained. Reasonably good, corresponding season (August to Oe­ tion include retaking the entire QSS, but not quite optimal plates are available cember). For the rest of the year, virtual­ about 15 years after the first survey of of another 5 % of the fields and only for Iy all time is now available for other this type. This would provide a very - 20 fields (3 %) has no acceptable plate purposes. good basis for determination of proper yet been obtained. The Atlas production One of the current programmes is the motions in the southern sky, even of in Garching in also nearing the end; 22 extension of the Quick Slue Survey from rather faint stars. The supernova search shipments out of a total of 24 have been declination -200 to the equator. This programme in brighter galaxies might sent to about 200 customers. It is hoped involves taking about 300 Atlas-quality also be re-activated. Other possibilities that the last two shipments will become 1I a-O + GG 385 plates, each with 60­ include deep infrared plates along the available in the course of 1989. minute exposure time. This project pro- galactic plane or very long exposures 28 (up to 5 hours) of selected objects Performance of the ESO 1-m Schmidt Telescope through the available Ha and S I1 inter­ ference filters wh ich have a useful field Emulsion Sensit. Filter Bandpass Exposure Lim. mag of about 2°. The approximate limiting magnitudes lIa-O no UG 1 UV 60 min -19 for direct plates are quoted in the table. 120 min -20 They depend on the seeing; the num­ no GG 385 B 60 min -21 bers given are for medium seeing and IIla-J yes UG 1 UV 60 min -20 deeper plates are obtained under excel­ 120 min -21 lent conditions. These values may pos­ yes GG 385 B 120 min -22.5 sibly be further improved after the instal­ lation of the new Grid Processing 103a-D no GG495 V 45 min -19 machine in November 1988. At the R 120 min -21.5 same time, tests are being made of the Illa-F yes RG 630 new Kodak T-max emulsion, although IV-N yes RG 715 I 90 min -19 the sensitization appears to be more difficult than first expected. We shall report in one of the next Messenger issues about the initial results. In the future, the 30 x 30 cm plates The ESO Schmidt telescope is will be scanned on the refurbished Monitoring SN 1987A equipped with one of the world's largest two-coordinate measuring machine Since the explosion in late Febru­ objective prisms, giving a dispersion of at the ESO Headquarters (formerly the ary 1987, more than 130 ESO about 450 Nmm at Hy. Under good S-3000 machine). With a new CCO Schmidt plates have now been ob­ seeing conditions, it is possible to ob­ head and much improved software and tained of the LMC area in wh ich tain widened spectra wh ich allow MK large computer storage space, it will classification, down to magnitude become possible to perform "blinking" SN 1987 A is seen. They document 14.5-15.0. Unwidened spectra give of large areas. This will greatly speed its slow decrease in brightness as limiting magnitudes, approximately 2-3 up the extraction of data from the weil as the now famous double light magnitudes fainter. The performance is photographic plates and may give a echo. It is particularly weil visible on critically dependent on the seeing, as is new impetus to the use of the ESO red and infrared plates. The superno­ the case for all objective prism work. Schmidt as a powerful survey instru­ va magnitude was about 10.5 by The UBK 7 glass is ultraviolet trans­ ment. mid-November 1988. parent. H.-E. SCHUSTER and R. M. WEST

Learning About Young Globular Clusters R. CAYREL, I. TA RRAB, Observataire de Paris, France, and T. RICHTLER, Sternwarte der Universität, Bann, F. R. Germany

1. Introduction (see lAU Symp. 126 for more informa­ erations that young globular clusters Even after many decades of intensive tion). provide a unique opportunity to study investigation globular clusters still fasci­ Young globular clusters are ideal stellar mass functions with good statis­ nate astronomers. Galactic globular laboratories for determining Initial Mass tics over a large range of masses. Addi­ clusters are "fossils" of the epoch of Functions (IMF's), which describe the tionally, there is also hope of uncovering galaxy formation and sampies of a very number of stars found per mass interval a possible dependence of the IMF on early, but still reachable stellar genera­ in a star forming region. The IMF is of metallicity. A spectroscopic high-reso­ tion. The situation is different in the fundamental importance for the evolu­ lution study by some of us (Spite et al. Magellanic Clouds where globular-clus­ tion of a galaxy, since it controls the 1986) confirmed earlier suggestions that ter-like objects with a wide variety of energetic feed-back by massive stars to NGC 330, the brightest of the young ages can be found. We see globular the interstellar medium and largely de­ globular clusters in the SMC, has an clusters which, judged by their stellar termines its chemical evolution. Howev­ abnormally low metallicity of -1.3 dex content, cannot be much older than er, the determination of the IMF in stellar (Fig. 1). In contrast to this, the overall 107 yr. Their integrated light is domi­ systems in the Milky Way faces several metallicity of the young SMC population nated by a slightly evolved upper main difficulties. For instance, stars in the so­ is believed to be around - 0.7 dex. sequence. Therefore, they have often lar neighbourhood do not form a coeval Another cluster for which a high-reso­ been referred to as "blue globular clus­ sampie; open clusters show poor statis­ lution spectrum hints of a lower metal ters". the question why such clusters tics; in galactic globular clusters, only abundance than is found in the field are found in the Magellanic Clouds (and the small mass interval 004-0.8 solar population, is NGC 1818 in the LMC perhaps in some other galaxies like M 33 masses is observable and they are so (Richtler et al. 1988, Fig. 2). and NGC 2403) and not in the Milky Way old that the observed mass function It is of great interest to look into the is certainly of significance for the gener­ may be modified by secular dynamical mass function of these objects to find al understanding of galaxy evolution effects. It is evident from these consid- possible differences to a "normal" IMF. 29 Figure 1: A 1O-sec V exposure of the young SMC globular cluster Figure 2: A 10-sec Vexposure of the young LMC globular cluster NGC 330, taken at the 1.54-m Danish telescope. The brightest stars NGC 1818, taken at the 1.54-m Danish telescope. are already saturated.

Theoretical considerations indeed point These investigations do not arrive at a what we know (or not know) and prob­ to differences. The concept of opacity­ common conclusion. Mateo finds that ably most astronomers agree that fur­ limited fragmentation leads to the pre­ the LF's of the clusters he investigated ther investigations are of importance. diction that the IMF for massive, zero­ are (within the given uncertainty) similar metal stars is steeper (Yoshii and Saio, to each other and also cannot be distin­ 2. Observations 1986) than a Salpeter mass-function, guished from a Salpeter function. Eison which characterizes the IMF in the solar et al. find their LF's flatter than a Salpe­ Our data come from two different te­ neighbourhood. ter function and also differences from lescopes. In November 1987, we ob­ These ideas are to some degree cluster to cluster. In a nutshell, this is served with the 2.2-m telescope in re- supported by observational work: strong variations of the IMF in time and space are known to exist in open clus­ ters (Tarrab, 1982). The mass function of galactic globular clusters has been re­ NGC 330 cently investigated (McClure et al. cluster & field 1986), and a significant dependence on 1L..0 metalIicity was found, in the sense that a low metallicity seems to occur with a larger slope. On the other hand, indirect evidence was presented by Melnick (1987) that the IMF of massive stars exciting H 1I regions is metallicity depen­ dent, but this time in the opposite way. These results are not necessarily in con­ > + tradiction because the authors address 19.0 quite different parts of the IMF (15 to 40 MG) for Melnick, 0.2-0.8 MG) for McClure et al.). To confuse this issue further, Eggen (1987) finds a luminosity function of the field metal-poor popula­ tion in our Galaxy nearly identical to that of the solar neighbourhood. During the course of the present work, two papers appeared, dealing with luminosity functions (LF) of young 24.0 Magellanic Cloud clusters. Elson, Fall and Freeman (1988) investigated the LF's of their objects by visual star -2.0 0.0 2.0 counts, while Mateo (1988) employed 1:3- V CCD-techniques to determine LF's of Figure 3: This is a colour-magnitude diagram of all stars measured in the field of NGC 330. Magellanic Cloud clusters of a large Note that most of the faintest stars are probably fjeld stars, since the deep 2.2-m frames have range in age. been taken with the cluster near one edge. 30 mote control to take deep Band V have been taken with the cluster located supergiants bluer than B-V = 0 (the frames in the fields of NGC 330 and at the edge of the frame in order to same is true for supergiants redder than NGC 1818. The CCD camera No. 5 was minimize saturation effects. Very con­ B-V = 1.6), so transforming observed

attached to the Cassegrain focus. Pixel spicuous is the bulk of stars belonging colours and magnitudes into the MSOL ­ size was 30 !Am leading to a scale of to an older population. The comparison Teff plane enlarges error bars more than 0':36 pixel. The exposure times were as of Figure 4a and 4b demonstrates the 10 times. long as 40 minutes in Band 30 minutes dominance of the field population. Fig­ One of the most obvious difficulties in V. The 1.54-m Danish telescope had ure 4a plots stars closer than 50" to the connected with observations of been employed a few nights earlier to cluster (1.54-m data). Figure 4 b shows Magellanic Clouds clusters is the severe take frames of shorter exposure time. all stars more distant from the cluster crowding. The density of the field popu­ Here the CCD-camera operated in centre than 100". NGC 330 is embed­ lation near NGC 330 is 350 stars/square binned mode (30 x 30 ~lm2) with a scale ded in a field population which has a arcmin down to 23 mag and 100 stars of 0':47/pix. Exposure times ranged from component almost as young as the down to 20 mag. Even in a good seeing 10 s to 1200 s. In both cases, the seeing cluster itself. with a FWHM of 1", the stellar profile was of medium quality of about 1':6, so A very remarkable feature in the clus­ extends from the photometrist point optimistic astronomers can say that in ter CMD is the gap visible between 13.2 of view to a diameter of at least 4", spite of binning the stellar images were and 14.4 mag. The stars above the gap which means that the sky is 1.2 times weil sampled. are with high probability cluster mem­ overcrowded with stars as faint as After basic processing (flat-fielding, bers, since such stars are completely 22.5 mag. etc.) the photometric information has missing in the field diagram. Carney et The cluster itself exhibits a further tre­ been extracted with the DAOPHOT al. (1985) already noted this gap and mendous enhancement in star density package (Stetson, 1988). presumed that these stars were He­ over this background field. If we assume The transformation of instrumental to burning supergiants, i. e. stars which are the cluster radius to be 50", we expect standard magnitudes was performed via at the blue end of their supergiant 760 background stars down to photoelectric standard stars in the field evolutionary loop (e. g. Maeder and 22.5 mag within this area. In Figure 4 b, of NGC 330 measured by Alcafno and Meynet, 1988). The number statistics of 270 stars are fainter than 17 m and 140 Alvarado (1988). For the photometry of such stars may be of great importance of them are statistically field stars. When NGC 1818 we used the same colour for testing stellar evolution theories going to fainter magnitudes, this fraction terms, but with the zero-points from the since the respective lifetimes of blue favours even more the field contribution: photometry of Robertson (1974). These and red He-burning supergiants are of all stars fainter than 18 mag, 60 % are last data have to be considered as pre­ sensitive to properties of evolutionary field stars. The reason for this is the liminary until an accurate calibration be­ models as effects of overshooting and/ growing incompleteness of the photom­ comes possible. or metallicity. Presently, a comparison etry in the cluster region. with theory seems impossible since a With NGC 1818, the situation looks much better. Figure 5a shows all stars 3. Colour Magnitude Diagrams suitable grid of massive, metal-poor stellar models is still lacking. Further­ within 50" of the cluster and Figure 5 b is Figure 3 shows the CMD of all stars more, these models should be given in the field population outside 100". As a measured in the field of NGC 330. A observable parameters, i. e. colour­ young cluster, NGC 1818 is projected large fraction of these stars are probably magnitude diagrams. We recall that the on a field population of intermediate field stars since the deepest frames slope I'> BC/I'> (B-V) is larger than 10 for age, which with 35 stars/square arcmin

120 12-0 + NGC 330 ++~ NGC 330 + + + cluster +-t+ field ++ + ++ + +*++... .t+ + + + + +++ + + + + -P.j: + 16·0 16.0 + > > + ++ + +

+ + + 20·0 20·0

-2.0 0.0 20 - 2.0 0·0 2.0 8-V 8-V Figure 4 a: This is a colour-magnitude-diagram for all stars within a Figure 4 b: In this colour-magnitude-diagram all stars more than 100" distance of 50" from the centre of NGC 330. Note the disappearance from NGC 330 are plotted. The youngest stars in the field population of the conspicuous bulk ofred stars at V = 19 mag. in Figure 4 b. It is have ages larger than those in the cluster. also striking that the group of blue supergiants above the gap in the "blue sequence" are only visible for the cluster, thus arguing strongly that these stars are cluster members.

31 100 10·0 I- I I I - NGC 181'2> NGC 1818 cluster fieLd I- -

+ ++ + 14·0 + + + + 14·0 f- +-jl- - -tt ++ + > ++ > $'+ + '-t - ++ + 18.0 + + -

f- I - -20 00 20 - 2.0 0·0 2·0 13-V 8-V

Figure 5a: A c%ur-magnitude diagram for stars nearer than 50" to Figure 5 b: A c%ur-magnitude diagram for stars far/her than 100" the centre of NGC 1818. Comparison with Figure 5b revea/s that the from the centre of NGC 1818. fie/d population is much /ess dominant than in the case of NGC 330.

down to 20 mag is also 3 times less Reducing them means a huge amount For that pracedure the age of the cluster dense than in the case of NGC 330. of computing time which actually is the must be known. We can use the limiting factor. It turned out that in the luminosity of red supergiants to esti­ cluster field the completeness quickly mate the age of the cluster. Using 4. Derivation of LF's becomes uncomfortably low at fainter evolutionary tracks of the apprapriate Once the photometry of the stars is magnitudes. To be on a safe side, one metaliicity kindly provided before publi­ established, it should in principle be has to consider, at least in a first stage, cation by Castellani and Chieffi, we have easy to derive a luminosity function by counts only down to magnitude 18.0 or found that the gap between magnitude simply selecting the main sequence 18.5 to avoid completeness factors too 14.4 and 13.2 is weil explained if the stars and counting the stars in defined different fram 1.0. magnitude 14.4 represents the end of magnitude bins. However, during the re­ Having made counts both in the clus­ the main sequence at an age of 12 Myr, duction procedure, we became aware ter area and outside, each with their own whereas the stars at mag 13.0 are blue that counting stars can be a very difficult completeness corrections, we sub­ supergiants in their He-burning phase task. tracted the fjeld counts from the (cluster with masses near 18 MQl. Assuming The photometry performed with + field) counts. As we have a colour­ that age, we find that Ö Mv bins trans­ DAOPHOT is a complex interaction be­ luminosity diagram, the counts have form into fairly unequal Ö logm bins at V tween the rautines and the charge dis­ been restricted to the main sequence, = 15 and V = 18. Our computations lead tribution on the chip, which especially the evolved phases (blue and red super­ ·to an IMF index x near 1.2 (we remind for the long-exposure frames exhibits a giants) being taken out. complicated structure due to charge The derived luminosity function is overflow of the bright stars. The star shown in Figure 6. The number of stars finding rautines do not find all stars, in roughly doubles per magnitude interval. particular not the fainter ones. N DAOPHOT offers a comfortable possi­ 5. Initial Mass Function bility to determine quantitatively "incom­ 100 pleteness factors". One can create ran­ In case of a zero-age main sequence, - r- domly artificial stars (the point spread it would be relatively easy to convert our function, PSF, is known) in a selected luminosity function into an IMF. We '-- magnitude range. Then these stars can would have first to convert our Ö Mv bins - be searched for by the normal DAO­ into Ö MSOL bins, and then use the zera­ 50 PHOT procedure. A comparison of the age mass iuminosity relationship (L ­ original artificial star list with the list of all m" with a = 3.0 to 3.5) to transform it in ,..--- stars found by DAOPHOT gives directly stars per Ö logm bins. Actually we ob­ the required incompleteness factors serve an evolved main sequence, so ~ (see Mateo 1988 for a deeper discus­ evolution renders the mass-Iuminosity 13 14 15 16 17 18 19 20 sion). Since the data sampie is built up relation unusable and the number of v from frame pairs (8, V) of different expo­ stars initially in a logm bin ends up in an Figure 6: Luminosity function of NGC 330. sure levels, we had to calculate incom­ evolved M SOL' MSOL interval, different The contribution of the fie/d has been esti­ pleteness factors separately for each fram the one on the ZAMS. It is then mated and subtracted. F/uctuations on the frame pair. To achieve statistical reliabil­ necessary to use evolutionary tracks in bright side are due to Poisson statistics. ity we added a large number of artificial order to obtain the relevant (M SOL' MsoJ Crowding is the factor /imiting the accuracy stars, about 1,000 stars for each frame. bin corresponding to the initial logm bin. on the faint side. 32 that x = 1.35 for Salpeter law). Although of young blue populous globular clus­ References this value is in good agreement with the ters in the SMC. result of Mateo, we feel that more elabo­ Alcaino, G., Alvarado, F.: 1988, Astron. J. 95, rate work, particularly under outstand­ 1724. 6. Conclusions ing seeing conditions, has to be carried Carney, B.W., Janes, K.A., and Flower, P.J.: out before we can state that the mass The study of the young globular clus­ 1985, Astron. J. 90, 1196. function slope of a metal-poor popula­ ters in the Magellanic Clouds is rich in Eggen, O.E.: 1987, Astron. J. 92, 393. Eison, R. A W., Fall, S. M. and Freeman, K. C.: tion is different or not from the value hopes, because it is the most direct 1988, STScl preprint No. 292. found for normal metaliicity Pop I ob­ check available for the theory of stellar Lequeux, J., Peimbert, M., Rayo, J. F., jects currently =2.0 (e. g. Tarrab, 1982, evolution of massive stars with non Serrano, A, Torres-Peimbert, S.: 1979, As­ Lequeux 1979) for the upper main se­ standard metallicities. In particular, it tran. Astrophys. 80, 155. quence. gives some evidence on what could Maeder, A and Meynet, G.: 1988, Astron. A large potential lies in the many still have been the early evolution of galactic Astrophys., submitted. unstudied young Magellanic Cloud clus­ globular clusters. However, the distance Mateo, M.: 1988, Astrophys. J. 331, 261. ters in understanding the morphology of of over 60 kpc of these clusters make McClure, R. D., VandenBerg, D.A, Smith, the IMF and the evolution of massive quantitative work difficult, in particular G. H., Fahlmann, G. G., Richer, H. B., Hes­ ser, J. E., Harris, W. E., Stetson, P. B., Bell, metal poor stars. However, very careful because of the confusion of stellar im­ R.A: 1986, Astrophys. J. 307, L49. observations, reductions and the availa­ ages at this distance. In the future, other Melnick, J.: 1987, Astron. Astrophys. Suppl. bility of evolutionary tracks for a wide corrections are to be applied to the pho­ 71, 297. range of parameters are necessary to tometry than a simple "completeness" Richtler, T., Spite, M., Spite, F.: 1988, submit­ use it. If these conditions are fulfilled, factor. Stars wh ich are "lost" are prob­ ted to Astron. Astrophys. then ground-based observations of the ably affecting the luminosity of other Robertson, J.W.: 1974, Astron. Astrophys. upper mass function will not be stars of the field, and most visual Suppl. Sero 15, 261. superseded by the HST whose resolving binaries, when observed in the solar Spite, M., Cayrel, R., Francois, P., Richtler, power is definitely necessary for fainter neighbourhood, are seen as single stars T., and Spite, F.: 1986, Astron. Astrophys. 168,197. magnitudes. in the SMC or LMC. The Hubble Space Stetson, P. B.: 1987: Publ. Astron. Soc. Pac. Also other clusters should be studied, Telescope will drastically change the 99,191. because NGC 330 is not one of the prospects in a few years, but this is not Tarrab, 1.: 1982, Astron. Astrophys. 109, 285. easiest objects to work with, although an excuse for doing nothing in the Yoshii, Y., Saio, H.: 1986, Astrophys. J.301, being often presented as the prototype meantime. 587.

The Nebular Stage of Nova Ga Muscae: Physical Parameters from Spectroscopic Observations

J. KRAUTTER, Landessternwarte Heidelberg-Königstuhl, F. R. Germany, and R. E. WILLIAMS, Cerro Tololo Inter-American Observatory, La Serena, Chile

Nova GO Muscae 1983, a classical write an article about this nova for the nounced overabundance of nitrogen re­ nova which had its maximum in January Messenger. lative to carbon and oxygen, and there 1983, might already be familiar to the Before we discuss our new observa­ was an indication of a He/H overabun­ readers of the Messenger, since it was tions, we want to shortly summarize the dance. However, no abundance of any already twice the subject of articles in most important results from the early metal relative to H or He could be deter­ this journal. E. Oliva and A. Moorwood phases. GO Muscae, which had a visual mined. The line profiles were very com­ (1983, The Messenger 33, 30) reported brightness V = 7.0 mag at maximum, is plex; during the early phases the usual P on infrared CVF spectrophotometry a moderately fast classical nova: t3 , the Cygni absorption systems (principal, carried out within the first four weeks time for a decrease by 3 magnitudes diffuse enhanced, and Orion system) after maximum. J. Krautter, K. Beuer­ fram maximum brightness, was about with velocities of the absorption compo­ mann, and H. Ögelman (1985, The 40 days. The outburst amplitude was nents up to -2000 km/sec were found Messenger 39, 25) described the results more than 14 mag, one of the largest as weil as up to 4 emission components. wh ich were obtained from coordinated outburst amplitudes ever observed for The distance was found to be D = 4.8 ± observations from X-rays to the infrared novae. The lightcurve was somewhat 1 kpc. This allowed a lower limit for the regime carried out in 1983 and 1984. unusual for a fast nova, since the visual luminosity around maximum of about Apparently, these authors had some magnitude remained nearly constant at one Eddington luminosity to be derived, foreboding, since they closed their arti­ a level of 3.5 mag below maximum assuming a 1 MG) white dwarf. c1e with the words "... This, at present, brightness for aperiod of about 11 Of special interest were the X-ray ob­ concludes the story of Nova Muscae months (April 83 to March 84). It should servations carried out with EXOSAT, 1983." In fact, that was not the end of be mentioned that no indication for dust since GO Muscae was the first classical the story of Nova GO Muscae: since formation, which quite often happens in nova from wh ich X-ray radiation was then, exciting results of new observa­ novae of this type, was found. observed during the outburst or decline tions of GO Muscae have been obtained The spectrascopic observations dur­ from outburst. Since no spectral energy which provide the justification to again ing the early phases showed a pro- distribution could be determined, two 33 I ~ oJ 1 er ~ 0 ~ March 29, 1984 ~ lune 11. 1986 ~ - l 1 ~ 8 '"~ ~ ...: ~ ~ ?i 0- x x0- I ~~ ~ i ...: ;: ~ ~l 8 i5 ~ > ~ b ~~ ~ .... ffi .... Wl i x ;;; CD ul ~ ~ l l .... ~ ;;;; !8 u~ > bb 8 l I' L- I ul

I ~ N er l x0 ~ - Apri 1 14, 1985 lonuory 24, 1987 -8 8 ~ !ll ;: ...: 8 Q ?i ~, b x0- > ~ I b ...... : 81 ;; '" ~ - ~;: b ~ ~~ ~8 .... ul -- ~ ;; bb \ I ~;; I) ~b i5 !6

I ul 4öOO SlIOO ssoo 6001! 'lim 500ll S5ll0 6001! 5SOO HA! Figure 1: Aseries of spectra of Nova GO Muscae 1983 from March 1984 to January 1987. The fluxes are given in relative units. The strongest lines are not shown in full intensity. From Krautter and Williams (submitted to Astrophys. J.).

possible explanations were given at the were obtained with IUE using, in all High Resolution Observations time: either a shocked shell of circum­ cases, the facilities of the ESA Villafran­ stellar gas emitting 107 K thermal ca satellite tracking station. When we finally obtained in April 1985 bremsstrahlung radiation or a white Figure 1 shows a representative (two days before the second spectrum dwarf remnant emitting blackbody radi­ series of low resolution ( A= 7 A) spec­ in Figure 1) high resolution spectra ( A ation of several hundred thousand K at tra taken in March 1984, April 1985, = 0.2 A) using the Echelle spectrograph about one Eddington luminosity. How­ June 1986, and January 1987. The CASPEC attached to the 3.6-m tele­ ever, there were arguments which spectra are displayed in the range scope, we were rather surprised by the strongly favoured the latter mechanism 4600 A-6700 A, and the fluxes are line profiles we saw. As an example, (Ögelman, Krautter, Beuermann, 1987, given in relative units. Note that the Figure 2 shows a tracing of the [0111] Astron. Astrophys. 177, 110). strongest emission lines are not shown n 4959, 5007 emission lines: as many We shall come back to the X-ray in full strength; they have been cut in as at least 22 different emission compo­ emission mechanism at the end of this order to show weak lines on a reason­ nents can be distinguished! All the small article. able scale. peaks in the emission lines are real The spectrum from March 29, 1984 emission components and not noise, (upper left) is shown in full scale in since they show up in both [0111] lines. Spectroscopic Observations Krautter et al. (1985, The Messenger 39, The line profiles of the other emission During the Nebular Stage p.29). lines in the CASPEC spectra have the We now turn to our spectroscopic The general character of the spectra same general structure, i.e., the same observations, carried out in irregular in­ did not change during this period; they line width and the same radial velocities tervals during the nebular phase from are dominated by strong emission lines of the individual components. There are, 1984 to 1988. Most observations in the superposed on a weak continuum. however, variations in the relative fluxes optical spectral range were performed However, since the emission line fluxes of the emission components: For in­ using the ESO 1.5-m, 2.2-m, and 3.6-m continuously decreased while the con­ stance, in the [0111] the blueshifted com­ telescopes on La Silla. Low and medium tinuum f1ux remained about constant, ponents are on the average stronger resolution spectrograms were obtained the average equivalent widths de­ than the redshifted ones, whereas the with the Cassegrain Boiler & Chivens creased from 1984 to 1988. All lines are Balmer and the [Fe VII] lines have a more spectrographs and recorded with lOS or very broad and have half widths at zero symmetrie structure. These line profiles CCO detectors. Two spectra were ob­ intensity of about 800 km/sec which re­ c1early show that the ejection of the tained with the 1-m and 4-m telescopes fleet the velocity of the expanding en­ expanding envelope of GO Mus was of the Cerro Tololo Inter-American Ob­ velope. Oue to the low resolution, only anything but spherically symmetrie. The servatory and recorded with a 20-frutti two emission components can be dis­ individual emission components appear photon counting detector. UV spectra tinguished. to be emitted by individual blobs of 34 TAßlE 1: Te and ne at different dates. the UV range. These lines are formed by TAßlE 2: Element abundances in the ejecta different pracesses - NV by collisional ofGa Mus (mass fractions). For comparison Date Te [K] log Ne excitatipn, N IV by dielectric recombina­ purposes the solar values are also given. tion - and have, therefore, different tem­ Apr 1984 14500 7.5 Element GO Mus Sun Apr 1985 18000 6.9 perature dependences. In order to cal­ Jan 1986 17500 6.6 culate the electran density, we used the H 0.42 0.77 Jan 1987 s25000 6.0 line ratios of the collisionally excited for­ He 0.38 0.21 bidden [0111] n 4363, 4959, 5007 lines C 0.004 0.0034 which are found in the optical spectral N 0.12 0.0013 material. Such "blobs" can be seen on range. The relative intensities of these 0 0.07 0.0083 direct images of old nova shells which lines depend on Te and neo Using Te as "Z" 0.20 0.018 are close enough to be spatially re­ calculated from the UV spectra, we ob­ solved. Nice examples are presented in tain a unique value for neo In January arecent article by H. Duerbeck (1987, 1987 (and later on) both N IV A 1719 and continues to some critical value, where­ The Messenger 50, 8). Because of its the [0111] lines had become too weak to upon hydrogen burning via the CNO cy­ larger distance (4.8 kpc) the shell of be used for diagnostic work. Hence, we cle starts and the thermonuclear runa­ Nova Muscae should now have an ap­ extrapolated ne from the earlier values way begins. One of the predictions of parent diameter of only 0.3 arcsec and and determined an upper limit for the the TNR model was that the energetics cannot be spatially resolved. The minor temperature from [Fe VII] line ratios. of the outburst should depend on the differences in the emission characteris­ Of special importance is the knowl­ abundance of the intermediate mass tics of different lines may be due to edge of the chemical composition of the elements C, N, and O. Fast novae, different excitation conditions and/or shell. In order to understand why, we which undergo a more violent explosion slightly different chemical abundances have to shortly review the basic ideas of than slow ones, should have strang in the individual blobs. the 'thermonuclear runaway model' CNO overabundances. In fact, no fast We should not forget to mention that (hereafter TNR model) which very suc­ nova could ever be (theoretically) pra­ the high resolution spectra allowed us to cessfully describes the general features duced with solar CNO abundances. determine the wavelengths of the emis­ of the nova outburst. For those readers Therefore, the CNO abundance should sion lines with a much higher accuracy who are interested in more details of this be a very critical observational test of than is possible fram medium or low model we refer to reviews by e. g. Starr­ the TNR model. resolution spectra. On the basis of the field and Sparks (1987, Astr. Spae. Sei. Up to now, reliable abundances for CASPEC spectra we could remove 131, 379) or Truran (1982, in: Nuelear only a handfull of novae (= 9) have been some uncertainties in the line identifica­ Astrophysies, ed. Barnes, Clayton, available. For the determination of the tions; for instance, we are now sure that Schramm, Cambridge) who have done element abundances in the ejecta of GO coranal lines like [FeX] A6374 were not the basic work of the TNR model. Muscae we used emission lines fram present in April 1985 (more about cora­ It is now generally accepted that a both the optical and UV spectral range. nal lines later). nova outburst occurs on the white dwarf The He/H abundance was calculated component of a close binary system in fram recombination lines in the optical Element Abundances which the secondary is transferring spectral range, whereas UV lines were and Physical Parameters mass thraugh the inner Lagrangian point used for the N/He ratio. The mass frac­ in the Expanding Shell into an accretion disk and ultimately tions are given in Table 2, where for onto the white dwarf. The build up of the comparison purposes the solar values Emission line ratios can be used to hydrogen envelope on the white dwarf are also shown. He is overabundant with derive physical parameters of the ex­ panding shell, particularly ne, Te, chemi­ cal abundances, and the mass of the 1.2 shell. One has to keep in mind, however, that the derived numbers are mean val­ Nova Mus 83 ues for the entire expanding shell. As we have seen, there could be slight varia­ [0 IIIJ 1\1\4959,5007 tions fram blob to blob. Unfortunately, 0. 9 only a limited number of lines can be t used for diagnostic work. Because of x the large line widths many lines are ::J heavily blended with other lines and, CL (l) hence, no reliable fluxes can be deter­ :;:;> 0. 6 mined. Striking examples are the [N 11] 0 (lj n 6548, 6584 lines, which are hope­ 0:: lessly merged with the strong Ha line. Since the line profiles are very complex and vary fram one species to the other 0. 3 one, deconvolution procedures can be applied in a limited way only. Table 1 shows Te and ne for those epochs at which the (quasi-)simultaneous UV and optical data allowed us to derive num­ 0. 0 r:::::----::':-=-----~=====::::::=;::::..-----+--~~d bers for these quantities. The kinetic 4930 4950 4970 4990 temperature Te at the gas in the expand­ 5010 5030 ing shell was determined using the line Wavelength [A 1 -­ ratio of NV A1240/NIII A1719, both in Figure 2: High resolution line profiles of the {Dill] lines of Ga Muscae taken with CASPEC. 35 3.50E-15 A 6374. However, [FeXIV] could not be NOV A GO MUSCAE 1983 identified in the spectrum. <1" 9 JUNE 1988 • The increase of the ionization state 3.00E-15 '"<1" requires a shock whose strength in­ ;;:'" creases with time. There is no plausible "'0'" 0 explanation, however, why a shock 2.50E-15 "'''';;;'" - = = should develop that way. o:x:" :x:" • The range of ionization is very 2.00E-15 narrow. In the case of collisional ioniza­ '" o tion one would expect a much broader '" I{) :x: "'<1" <1" I{)'" i[)tl1 cn '" range in the ionization. <1"<1" <1" 1.50E-15 > Ql> o ~ ~ :x: Z I{) I{) Taken together, all these arguments - I{) - -< lead to the conclusion that the ionization 1. OOE -15 must be due to photoionization from a hot source. The increase of the ioniza­ tion indicates an increase of the temper­ 5.00E-16 ature T of the ionization source. To get a more quantitative estimate of T we have used the He li/He I line ratios in 0'-'------!- --l- --l ...L-_..L-J order to calculate Zanstra temperatures. 3000 4000 5000 6000 7000 We obtained T = 3· 105 K, 8.105 K, lambda langstromsl and 2: 1.5 . 106 K for 1984, 1985 and Figure 3: Speclrum of GO Muscae taken with the eno 4-m telescope and recorded with a 20 1986, respectively. These values are ap­ frutti photon counting detector. The red [FeX} A 6374 coronalline is the strangest line in the proximate and represent upper limits speclrum which has - to our knowledge - not been found yet in any other astranomical objecl. because we have assumed a radiation­ From Krautter and Williams (submitted to Astrophys. J.). bounded sphere. This is still approxi­ mately fulfilled in 1985 as the presence of [N 11] shows, but in 1986 the devia­ respect to H by more than a factor of the spectral appearance had changed tions might be larger. two. Of the heavy elements, N and 0 are even more: the [0111] lines had become For the interpretation of these results strongly overabundant, whereas C has rather weak, and the [N 11], Hel, and even we consider the phase of 'constant about solar abundance. "Z" is about [Fe VI] lines had disappeared. On the bolometric luminosity' of the TNR model 0.20. We would like to note that the other hand, the red [FeX] A6374 coronal of the nova outburst. The hydrodynami­ CNO abundances are preliminary num­ line was present as a relatively strong cal calculations show that, during the bers only; the final numbers might be line. The first sign of this line was found early hydrodynamic phase, only part subject to slight changes. However, the in a spectrum taken 10 months earlier, in (anywhere from 10% to 90 %) of the result is obvious: GO Mus has a CNO August 1985 (not shown in Figure 1). In material accreted on the white dwarf overabundance, just as the TNR model January 1987, [FeX] was as strong as has a velocity high enough to be ejected requires for a fast nova. Hß and stronger than [Fe VII] A6087. as an expanding envelope. The velocity This increase of the ionization continued of the remaining material quickly drops for at least 17 more months until June 9, and a hydrostatic equilibrium is estab­ The Increase of the lonization of 1988, the date of our last spectrum (Fig­ lished. We now have a configuration the Optical Spectrum ure 3). [FeX] A 6374 is now the strongest with the white dwarf core, an inert He A very interesting feature of the spec­ line in the spectrum - even stronger shell and the hydrostatic envelope with tral evolution of GO Muscae is the con­ than Ha. This is extraordinary, as we are a radius of 10"-10'2 cm (the size of a tinuous increase of the ionization from not aware of any other astrophysical red giant!). On top of the degenerate March 1984 to June 9, 1988 (the date of object wh ich has an [FeX] or any other core, where the temperature is high our last spectrum). Already in March coronal line of comparable strength! enough, the hydrogen burning con­ 1984, 14 months after maximum, the In order to understand this spectral tinues hydrostatically at a constant level general ionization is rather high (upper behaviour, a crucial question must be of roughly one Eddington luminosity. left part of Figure 1). Apart from the hy­ answered: what is the source of the The effective temperature of the whole drogen Balmer and the He I recombina­ ionization, collisional ionization or system exceeds 105 K. tion lines, all other lines of neutral ele­ photoionization? The movement of the In the further evolution, the mass of ments had disappeared at this time. On ejected envelope through the interstellar the envelope decreases. Hydrogen is the other hand, emission lines of rather medium might produce a shock front used up by the thermonuclear reactions highly ionized species like [Fe VI], [Fe VII] giving rise to temperatures sufficient to and material is ejected by radiation and [Ca VII] are found. One year later, in cause very highly ionized species like pressure-driven mass-Ioss. The radius April 1985, the ionization had increased. [FeX]. There are, however, many argu­ of the envelope decreases. On the other Lines of higher ionization have in­ ments which exclude any significant hand, there is a constant production of creased in strength relative to e. g. Hß, shock contribution to the formation of energy from the shell hydrogen burning whereas lines of lower ionization like the highly ionized species: wh ich continues as long as some mate­ [N 11] A 5755 have decreased. A striking rial is left in the envelope. As a result, the example is the line ratio of [N 11] A 5755 • The kinetic temperature Te in the effective temperature T of the remnant vs. [Fe VII] A 5721. In 1984 [N 11] was ejecta is low at all times (:::: 25,000 K). increases with decreasing radius. much stronger, whereas in 1985 the • The post-shock temperature of But that is exactly what we observe in situation was reversed. Also the Hell/ 1.9 . 107 K for an expansion velocity of the case of GO Muscae! The photoioniz­ He I ratio had considerably increased. 800 km/sec would require [FeXIV] ing source is the white dwarf remnant Another 14 months later, in June 1988, A 5303 to be more intense than [Fe X] whose temperature increases. Of 36 course, the high temperature of the none will be available until the launch of case of GO Muscae, we have demon­ white dwarf also easily explains the X­ ROSAT. Only very little observational strated how long-term observations of rays from GO Muscae. Unfortunately, material on the late phases of the c1assi­ novae in the optical spectral range can after the termination of the EXOSAT cal nova outburst is available yet. Many help to improve this situation. The ob­ mission, for several years no X-ray crucial questions remain: How long servations appear to constitute an im­ satellite sensitive to soft X-ray radiation does the hydrogen shell burning really portant verification of the TNR model of has been available for some time and last? When does a nova turn off? In the the classical nova outburst.

Violent Activity in the Bright Quasar 3e 273 T. J.-L. COURVOISIER, Observatoire de Geneve, Sauverny, Switzerland

Observations of the optical variability characteristic times were then not of the were able to obtain during the flares, the .in the bright quasar 3C 273 date from order of an month as during the previ­ flux variations were so fast that we long before this source has been found ous years, but rather of the order of a could not resolve them satisfactorily. to be a quasar. Almost a century of day. This violent activity in 3C 273 came The period of violent activity lasted (mostly photographie) data are available at a very appropriate time, when our from February to April 1988. During this (Angione and Smith, 1985) and display collaboration was weil established and interval, we observed 5 optical maxima variations on many timescales longer could react rapidly to the observed separated on average by - 15 days, al­ than -10 days. In more recent years, a changes. We were thus able to observe though 2 of the maxima are separated programme of multi-frequency observa­ very frequently, even daily for part of the by 2 days only (Fig. 2). The amplitude of tions of the quasar from the radio do­ time, in the optical and infrared do­ these maxima is of about 30 %. The main to the X-rays has been conducted. mains. The observations were per­ fastest change we observed was a flux The first results of this programme have formed at the ESO 1-m telescope, the decrease of - 15 % in 24 hours. This been described in the Messenger No. 45 ESO/MPI 2.2-m telescope, the 70-cm flux decrease corresponds to a change (September 1986). In summary, we Swiss telescope on La Silla, the UK in­ in luminosity in the source of about 40 found variations by a factor - 2 in most frared telescope (UKIRT) in Hawaii and - 6.10 erg S-2 or to the switching off of observable spectral domains. The typi­ with the mm telescope SEST at ESO - 10 million suns per second for 24 cal variability timescale was of the order and JCMT in Hawaii. The results of hours (assuming a distance to 3C 273 of one month. The different components these observations have been published based on a cosmological model with Ho 1 of the source varied at different epochs, (Courvoisier et al. 1988). Even with the = 50 km S-l Mpc- and a source emitting showing little correlation between them. temporal and spectral sampling that we' isotropically). This complex variability pattern allowed to identify distinct components and showed that most of them must be emitted in regions not larger than about 35 one light-month. This multi-waveband campaign of ob­ servations started in late 1983 and has been pursued during each observing season (December to July) since then. Until now, different types of variability behaviour have been observed each year. Figure 1 illustrates this by showing ...... 30 the V band f1ux as a function of time .....,>- since January 1985, when the Swiss telescope on La Silla joined in the pro­ E gramme with regular and precise photo­ ~ (.... metrie measurements. A slow flux in­ crease can be seen in 1985, followed by a year of very small variations in 1986. Ittl During the observing season wh ich 25 started in December 1986, the UV flux (measured with IUE) decreased by I -40%, the decrease was much less important at Ionger wavelengths but can still be seen in the figure. The most striking feature of the figure, however, is the change of the behaviour of 3C 273 in February 1988. At this time, wh ich is 20 weil within the observing season, the source changed from astate charac­ 1986 1987 1988 1989 terized by relatively slow changes to a DATE state of rapid and recurrent flares. The Figure 1: The V-band light curve obtained with the Swiss telescope on La Silla since early 1985.

37 40 I I I I I I I I I I I 12,2 25,2 10.3 13,3 5.4 a II I V 35 - - ....-.. :>, 1 -:> I 1 S II I I I 30 - ~IIII! I - :> I ~ I (i.. I IIIII I II IIIIIJll

25 - -

I I I I I I I I I I I I 0 10 20 30 40 50 60 70 80 90 100 110 120 130

I I I I I I I-ro-r-,~~,~- T~~I 23.2 9.3 I 60 J ...... >- I 'J 50 lj' E

:> 1 (i.. 40 1I

30

I I ! 0 10 70 80 90 100 110 120 130 DAY 01" 1988 Figure 2: The V (a) and J (b) observed fluxes during the 1988 flares of 3e 273. The dates of the observed maxima are indicated.

In the infrared domain, we also ob­ The observation of a decay time for the normal state has a very low level of served repeated f1ares, but only 2 maxi­ flare (about 2 days) allowed the estima­ polarization. Our observations show ma have been seen (Fig. 2), coincident tion of the magnetic field in the emission therefore that the same processes can with two of the visible maxima. The am­ region. This was found to be - 0.7 be at work occasionally in quasars as plitude of the maxima with respect to Gauss, about the same field as is exist­ are normal in BL Lacs, although both are the "quiescent" emission measured the ing on the Earth. This estimate of the very different types of sources. We also previous year was larger than in the magnetic field is important as it is free of know that the BL Lac like behaviour of visible and amounted to roughly a factor the large uncertainties normally linked quasars is a relatively rare event, be­ 2. The fastest change in the observed with measurements based on the overall cause we observed it only once in sev­ infrared f1ux was by - 40 % in 24 hours, shape of the synchrotron emission. eral years of monitoring. it was a flux increase rather than a de­ The polarization of the incoming flux One of the optical flares, the last on crease. This change in the infrared flux was also observed daily for a week in April 5, seems to have had quite diffe­ corresponds to a change in the luminos­ late February. The polarization was rent properties, its maximum amplitude 40 ity of -+6.10 erg S-2, i.e. to the found to be about ten times more impor­ was not in the V band but at higher switching on of about 10 million suns tant than normally in 3C 273, and to vary frequencies, further in the blue. This in­ every second for 24 hours. It can be significantly from day to day. dicates that it was not an infrared flare, seen on Figure 2 that the fastest mea­ The observed properties of the 3C as is also suggested by the appearance sured flux variations need not be the 273 flare component as described here of the infrared light curve at this epoch. fastest source variations, because the are very similar to the typical behaviour If interpreted in terms of synchrotron sampling of the light curve is not suffi­ of another type of active galactic nuclei: emission, this last event must have been cient to resolve the variability. the BL Lac objects. These latter objects caused by a very peculiar population of Infrared and optical daily observa­ are weil known for their rapid variations electrons, in which the more energetic tions around the March 10th flare and for the night to night changes in electrons are more numerous than the allowed to follow the spectral evolution their (high) polarization. Their emission less energetic ones. This type of dis­ around this date. In general it was seen is also usually ascribed to synchrotron tribution is very unusal. Which other that the spectral energy distribution be­ emission. BL Lacs and quasars differ emission process could explain the came steeper as the flux decreased. however in many respects: BL Lacs energy distribution and the very fast var­ This type of behaviour is characteristic have no prominent "blue bump", which iations is not c1ear yet. of synchrotron emission, the radiation of dominates the optical UV emission of Very fast variability is often a (distance relativistic electrons in a magnetic field. quasars (and of 3C 273 in particular), BL independent) indication of relativistic The steepening of the energy distribu­ Lacs do not show emission lines, which motion in the source. The argument is tion happens because the electrons are also a prominent feature of quasars that the high energy electrons in a syn­ emitting the higher frequency photons (and 3C 273), and BL Lacs usually are chrotron source also scatter the infrared loose their energy faster than the others. highly polarized, whereas 3C 273 in its synchrotron photons and give them 38 some of their energy, shifting them thus event is similar to the February 25 max­ served and led to quite different conclu­ to the X-ray domain. This combined pro­ imum or if rapid variability also occurred sions. Also the very structured nature of cess is calied synchrotron self-Compton around February 25 (both are probable the flares may be somewhat discourag­ emission and is a function of the source but neither can be established with our ing for observers, as it indicates that size: smaller sources have a larger self­ spectral and temporal sampling), then daily observations at least are required Compton component compared to the the brightness temperature is in excess to study this type of events. However, synchrotron component. Sources for of the Compton limit. Further evidence this structure also indicates that there is which the luminosity and size are such along these lines comes from the mm a wealth of information to be obtained that the brightness temperature is in ex­ observations performed this year: Pre­ on the source geometry, on the acceler­ cess of -1 0'2 K should emit much more liminary results (Robson et al., in prepa­ ation of electrons to relativistic energies in the X-rays than in the synchrotron ration) indicate very rapid variations and and on emission processes. This infor­ branch. This is known as the Compton therefore extremely high brightness mation will certainly prove important to catastrophe, and is not observed in ac­ temperatures, weil in excess of the constrain detailed models of the emis­ tive galactic nuclei. In quasars, the Compton limit. It is therefore possible sion region. Future observations will source size is estimated using the varia­ that the source of the flares is moving at have to find the relationships between bility timescale of the source, and if the relativistic speeds towards the observer. the flaring activitiy and the other proper­ brightness temperature calculated with The evidence for a brightness temper­ ties of the quasar and try to find what the infrared or radio flux and variability ature in the flares of 3C 273 weil in triggers the beginning of a flare, and so timescale is in excess of the Compton excess of the Compton limit, and thus of maybe help understand the nature of limit, one can deduce that the true relativistic bulk motion of the flare the superluminal jet. source luminosity is smaller than what source, is important as it suggests that We could obtain a dense spectral and can be calculated from the observed the emission region is associated with temporal sampling of the 3C 273 flares flux using an isotropic emission geome­ the superluminal jet observed with VLBI only with the help and assistance of try. The simplest anisotropy is that the (Cohen et al. 1987). This jet is highly many rapid reactions to our requests at source is moving relativistically towards structured with new knots appearing at ESO and in Hawaii. the observer, thus boosting the syn­ more or less regular intervals and mov­ chrotron flux in the direction of the ob­ ing away from the source at very high server. velocities. The flares could then weil be In 3C 273, the observations described the first signs of a new knot appearing in References here imply a brightness temperature the jet. weil below the Compton limit. However, The very rapid variations observed Angione R. J. and Smith H. J., 1985, Astron. J. 90 (12),2474. we have some observations at longer during the flare of the bright quasar 3C Gohen M. H., Zensus J. A., Biretta J. A., wavelength close to the February in­ 273 cast some doubt on the observa­ Gomoretto G., Kaufmann P. and Abraham frared maximum, and these observa­ tions of previous flares in this source. It Z., 1987, Astrophys. J. 315, L89. tions indicate that the flux continues to is clear that observations with a less Gourvoisier T. J.-L., Robson E. 1., Blecha A., rise towards the longer wavelengths, so dense temporal sampling would have Bouchet P., Hughes D. H., Krisciunas K. that, if the spectrum of the March 10 missed most of the structure we ob- and Schwarz H. E., 1988, Nature 335, 330.

UM 425: a New Gravitational Lens Candidate G. MEYLAN, ESO, and S. OJORGOVSKI, CalTech, Pasadena, USA

I. Introduction 2237 + 030 (Huchra et al. 1985), To improve our knowledge on the Since the first theoretical discussions 0142-100 (Surdej et al. 1987), and phenomenon of gravitational lensing, more than 50 years aga on the 1413+ 117 (Magain et al. 1988). In other we are conducting an optical imaging phenomenon of light rays bent by inter­ possible cases, e.g., 2345+007 ryveed­ survey for lensed quasars, with a spec­ vening mass in the universe (Eddington man et al. 1982), and 1635+267 (Djor­ troscopic follow-up for the promising 1920, Einstein 1936, Zwicky 1937 a, b), govski and Spinrad 1984), there has so cases. The quasar UM 425 = aso gravitational lensing has steadily grown far been no detection of lensing galax­ 1120+019 (MacAlpine and Williams to become one of the most active fields ies, and thus they should possibly be 1981) is one of the objects selected as of research in extragalactic astronomy considered as genuine pairs of interact­ potentiallens candidates on the basis of today. There are numerous theoretical ing quasars, similar to the probable bi­ two criteria: a large apparent optical investigations (Refsdal 1964, 1966, nary quasar PKS 1145-071 (Djorgovski luminosity (Mv :s - 28), and a relatively Turner et al. 1984, Blandford and Naray­ et al. 1987). Recently, so-called giant large redshift (z ~ 1.5). These simple an 1986, Blandford and Kochanek luminous arcs have been observed in a criteria, chosen to reflect possible gravi­ 1987 a, b), but the observations of good few clusters of galaxies. They are inter­ tational magnification (Iuminosity) and to gravitationallens candidates are still preted as segments of Einstein rings, provide a large intercept length (red­ rare. It is only during the last decade that created because of an almost perfect shift), increase the apriori probability a few quasar systems have been found alignment of the lensing cluster potential that a quasar selected from a mag­ in reasonable agreement with the gravi­ weil with the lensed background object nitude-limited sampie is lensed. The tational lensing interpretation, viz., (Soucail et al. 1988, Lynds and Petro­ efficiency of such simple criteria is de­ 0957 + 561 (Walsh et al. 1979), sian 1988). Blandford and Kochanek monstrated by the present case, by a 1115 + 080 (Weymann et al. 1980), (1987) provide the most comprehensive few other candidates from our survey 2016 + 112 (Lawrence et al. 1983), and updated review on these subjects. which are still awaiting confirmation, 39 ~ ~ " r":'''-:-'''I1'''::~~_''~'''''r'- :0, :...rl,.~ " ';.~.~~ '.:~. ::.f~ N •&v~'. L.'," •. ~.. ~ ~'.L.,;.. . "';';'.' ~ ,0::'. ,.. ' "',. ,-....""',-.. .;."',..~ Jr.- ,'",''t", .:, ...... ':,"1 'l:'"," .. -r~' ...... • '. • <. : ~ .•....': " ~::':~""::":<:" :", ;.; :" .:"., • • .;'. .',. ', ' ...... ', . '...... " ... '. "'" ",' ... ..:.".\ ...... ,; '.;' ~.". ' .. , '. ", '. ,.' .".,." ., '-'' .. .;.'.'. '-:.'.-:;..> ".-,.:". 1:\)':; ,!...... :. '.' '. t,.":- . ",e:' • '. .,'~ .. !,~1 '".'''r, '...... •'. I;, :. '.' II~ ~;-o.j':'_"'-'....~~,_' . • " •.'. : ••••• 01,; -." " ""\l'":" ."" '. • •••• ...... ' .•-,... '"• '~'~".?-.,' , •• " •.•. " -',J ' •..' '." ~~,.-. -'..,..'. ~."'(';''1'. ,.,.,~"l'. '.';"'''~'-;;;'.''rI,;.J.,:N., ""'.'-;"~~.o:...". • "' .. ' .... 'I •• '.:•• .';" L.~ J~ • .. '. r < r:"~' . •B . ,... '.' l "'. '.' ',. " . -. .,.•••...,. > . '.- ., :""" .•.' ;~ i··~..~·.,.. 'I~'" ~.. :' • 1 E • w • I. ..,.~,',• r • • ft""::"'. • ,•••• '.• '7" ,. "• ,', "," ....•. ,'. ' .... ' ...,. ,.; ' .... c­ -UM 425 (A) ~ ~.:; I '.':'~:""': ". '. "J<.. ,.:. '"/ :.:;', ,t~," .•;.• . D ..... ·L. ~'''''':I'• , ...... ",~ "~'~', •. '~~.,"_"" •.; • • •.....\ ",.' .•'. :,'.•...... -... :":'". ;';':~'"•.. .".->: ',"., <""":~"l?··"'·'·'~:·'~.'·"·-:·~l'·c 'y. .' _.' <;",",.~ ::t..~.:,.,::;. !,.~""':'l " •• ••••.;: : ••.• •• ; •.••. •.:" .• •• -~ '~. ... . '. ',, I· ~ _ ':. " ~ ••.•.• ; ••'~ c· . ". _ , •• • • ~ :~ ';~;: ~. ,~, >~ -,~. ".~. ::L: .~::.'" '~'..:::;::;.~..':{ r~J):,'. i-....:.", .' ~ "~::".:':.'::..._. -.•'.. _"<.,.... '.' .'.{."._ . '.:'..;. ~~~':.; :-;', .,.~ 30 aresce ..." ... !t'' .. -. ~.~, .,'.'.•...... '•.', -A' ,:", I I -:::":. ,- I ...... ,"'"--.J • s Figures 1a and 1b: Central part (Fig. 1a in false colours and Fig. 1b in grey scale) of an image of the quasar UM 425 (digital stack of V and R frames) obtained with a charge-coupled device (CCO) and the Cerro Tololo Interamerican Gbservatory (CTlG) 1.S-m telescope, on UT 1987 March 2. The high luminosity quasar is resolved into at least four images. Two quasi-stellar images, the main component A and its brightest companion B, separated by6.S arcsec, have V = 16.2 mag and V= 20.8 mag, respectively. The C component (V= 21.8 mag) and the even fainter o component are similar to the numerous nonstellar objects in the fjeld, suggestive of a rich foreground (z = 0.6?) cluster of galaxies.

and by, the two cases published by the taken by Or. R. Perley with the Very which corresponds to aseparation of Liege group (Surdej et al. 1987, Magain Large Array (VLA) radio telescope in 6.8 arcsec in the direction PA = + 105°. et al. 1988). More comprehensive re­ September 1987. The system was not The spectrophotometric magnitudes sults concerning UM 425 are to be pub­ detected at 20 cm and 6 cm. of the aso (A), 16.5 B mag, 16.2 V mag,. lished in Ap. J. Letters. The follow-up spectroscopy, in margi­ and 15.7 R mag, are uncertain by a cou­ nal weather conditions, with the Mt. pie of tenths of a magnitude, because of Palomar 200-inch telescope, on the the poorly determined zero point, which 11. Observations and Results night UT 1988 March 8, and with the Las also plagues our direct imaging. The Because of weather conditions, six Campanas 100-inch telescope, on the spectrophotometric colours are much observing runs, spread over more than night UT 1988 April 7, indicated incon­ better determined, since the zero-point 15 months, were necessary in order to clusively possible similar emission lines uncertainties cancel: we obtain (B-V)A = unveil completely the interesting in spectra of components A and B, and 0.33, and (V-R)A = 0.49, with the uncer­ character of the aso UM 425. Our first possibly also C. tainty of a couple of per cent. However, charge-coupled device (CCO) imaging The convincing observations were differences between magnitudes in a observations of this object were ob­ obtained with the ESO Faint Object and given bandpass can be accurately de­ tained with the Cerro Tololo Interameri­ Spectrograph Camera (EFOSC) at the termined from our direct imaging. We can Observatory (CTIO) 1.5-m tele­ ESO 3.6-m telescope, on the 3 nights obtained a relative photometry of the scope, on the night UT 1987 March 2. UT 1988 May 15, 16, and 17. The weath­ components A, B, and C by using the The conditions were photometric with a er conditions were nonphotometric with point-spread function fitting programme seeing FWHM = 1.7 arcsec. Exposures a mean value of the seeing FWHM for stellar photometry in OAOPHOT. For of 600 sec in V and 500 sec in R were =1.4 arcsec. Several direct imaging ex­ the components A and B, we obtain: obtained, with an additional 1000 sec B posures were obtained, with 60 sec in­ B - = -4.68 ± 0.15 exposure on UT 1987 March 5. The im­ tegration with the B filter (ESO # 552), A S V - = -4.61 ± 0.08 ages were processed using standard 45 sec with the V (ESO # 553), and A S R - = -4.42 ± 0.12, techniques. Figure 1a shows, in false 30 sec in the R (ESO # 554). The data A S (computerized) colours, the digital stack were processed and added using stan­ glvlng 21.2 B mag, 20.8 V mag, and of the V and R frames. Three close faint dard techniques. These reasonably 20.1 R mag for the component B. Using companions, labelIed B, C, and 0 (in good-seeing images suggest that the the spectrophotometric colours of the decreasing luminosity) on the grey scale component C is somewhat diffuse (non­ image A as the zero-point, we derive image displayed in Figure 1b, encircle stellar) in appearance. (B-V)s = 0.40, and (V-R)s = 0.68. The the bright image of the quasar (A). Our The separation between the quasar colours of the component B derived preliminary photometry indicated that image A and its brightest companion B from our spectrophotometry are (B-V)s the companions Band C have similar or is: = 0.36, and (V-R)s = 0.67, uncertain by identical colours to the brightest image, UA-S = +3.1 ± 0.1 arcsec a few per cent, and thus in excellent A. There is a large number of V ÖA-s = -5.7 ± 0.1 arcsec, agreement. For the components A and - 22 mag galaxies in the field, suggest­ C, the differences in magnitudes are: which corresponds to aseparation of ing a rich foreground (z - 0.6 ?) cluster. 6.5 arcsec in the direction PA = -29°. toB _ = -6.05 ± 0.25 Thus, the initial optical imaging data A S The separation between the images A V - = -5.56 ± 0.15 were consistent with gravitational A C and Cis: R - = -5.77 ± 0.15, lensing. A C Because of the promising character of !cWA-C = - 6.6 ± 0.1 arcsec giving 22.6 B mag, 21.8 V mag, and these images, snapshots were kindly ÖA- c = + 1.8 ± 0.1 arcsec, 21.5 R mag, with (B-V)c = 0.8, and 40 the emission lines are quite comparable: 63.2 and 69.1 Ain the case of C 111] 1909 UM 425 Q 1120+019 lines, and 74.1 and 70.8 Ain the case of the Mg 1I 2799 line, for A and B compo­ 40 nents, respectively. The comparison between the two spectra is hampered by the strang difference in magnitude between the components, giving very different sig­ 30 nal-to-noise ratios: e. g., (S/N)s - 6 E when (S/N)A - 350. The Mg I1 line 3 appears to be asymmetrie, with a possi­ ble absorption in its blue side. However, ~ 20 the comparison of the spectra is made difficult by the presence of the B band, which we can remove only partly. Some absorption feature could also be pres­ 10 ent in the blue side of the C IV line. Data with a higher S/N ratio are needed be­ fore the situation is clarified. Conse­ quently, the redshift of the quasar A was obtained by using only the C 111] line, the only "clean" emission line in our spectra, 4000 5000 6000 7000 and equals ZA.1909 = 1.465 ± 0.005. A (1) From the C IV line, we obtain ZA,1549 = Figure 2: Spectra of the quasar UM 425 (A and B), obtained with /he Faint Object and 1.469, and fram Mg 11 line, ZA.2799 = Spectrograph Camera (EFOSC) al/he European Southern Observatory (ESO) 3.6-m telescope, 1.476. on the 3 nights UT 1988 May 15, 16, and 17. Because of the large difference in luminosi/y We looked for a possible difference in between the /wo components, /he spectrum of A is divided by a fac/or of 50 for display redshift between the two spectra (A and purposes. The spec/ra are similar in shape and show the same emission lines (C IV 1549, C IIIJ B), using the crass-correlation tech­ 1909, and Mg 11 2799) at the same redshift. nique. The different measurements were done by varying the limits of the wavelength range used (from - 4000 to (V-R)c = 0.3. These colours have uncer­ C IV 1549, C 111] 1909, and Mg 11 2799. - 7200 A) and giving mean value of the tainties of about 0.3 mag. The compo­ The spectra are very similar in the over­ redshift difference 6.zA_S = (-1.5 ± 2.0) nent D, clearly a nonstellar object, is too all shape, and the equivalent widths of x 10-3 , corresponding to the rest-frame faint and too close to the bright image A to obtain any reliable measurements. It is about 4-5 arcsec away in the direc­ tion PA "" + 150°. C'. Given the measurement errors, these 10 (B) (A)/lOO results are consistent with constant col­ (Lens galaxy,:n ours of the three components, but with two hints: (i) B may be slightly redder than A, perhaps by the presence of an o o underlying (Iensing?) galaxy; (ii) C may o be red der than A in (B-V), but bluer in ~ (V-R), and in view of its apparently non­ 5 I stellar appearance, it could be (as weil I V as the component D) a member of a faint foreground cluster of galaxies. During the same 3 nights of May 1988, the spectra of the components A and B were obtained with the B 300 and R 300 grisms of EFOSC. The final us­ o able range in wavelength runs from 3600 to 8000 A, with aresolution of - 7 Npixel. The data confirmed im­ mediately that both objects A and B have quasar spectra, with the same emission lines at apparently the same redshift. The resulting spectra for com­ 5000 6000 7000 ponents A and Bare displayed in Fig­ ure 2. These two spectra are the result A (Ä) of 7 exposures of 1,800 sec in each of Figure 3: Residual spec/rum obtained after dividing the spectrum of the component A by 100 the B 300 and R 300 grisms, giving a and subtracting it from the spectrum of the componenl B. Each original speclrum corresponds total of 14 exposures, or 7 hours of to 3.5 hours of integration time in each grism. The residual spectrum difference is reminiscent integration. The usual strang emission of an early-type galaxy spectrum at a redshift z - 0.6, if /he continuum rise at - 6400 A is lines are present in both spectra, viz., attributed to the 4000 A break.

41 velocity difference t.v1-s = -180 ± 111. Conclusion in Dark Matter in the Universe, Jerusalem 240 km S-1, and a median value ZA-S = Winter School for Theoretical Physics, eds. (+1.3±2.0)x10-3 ,or v1_s=+160± It is worth mentioning that it is a Bahcall, J., Piran, T., and Weinberg, S. generic feature of gravitational lensing 240 km S-1. These very preliminary (Singapore: World Scientific). p. 133. measurements are then consistent with that the closer the component separa­ Blandford, R.D., and Kochanek, C.S. 1987, Astrophys. J, 321, 658 and 676. a zero velocity difference between the tion, the greater the similarity of their Djorgovski, S., and Spinrad, H. 1984, Astro­ components A and B, to within relative intensities, and vice versa. In the present case, because of the relatively phys. J., 282,L1. - 300 km S-1. Additional data are large image separation (6.5 arcsec), a Djorgovski, S., Perley, R., Meylan, G., and needed in order to improve on this mea­ McCarthy, P. 1987, Astrophys. J, 321, large difference in brightness is ex­ surement. L17. The result of the division of the two pected and observed (almost a factor of Eddington, A.S. 1920 Space, time, and spectra (B/A) is fairly constant in the 100). Furthermore, in simple geometry Gravitation, Cambridge: Cambridge Uni­ blue part (3600-6400 A), and a slight model, the lensing galaxy is expected to versity Press. but significant increase in the red part be closer to the faint image B than to the Einstein, A. 1936, Science, 84, 506. Guiderdoni, B., and Rocca-Volmerange, B. (6400-8000 A), which is equivalent to bright image A. However, in the case of UM 425, the lensing potential is prob­ 1987, Astr. Astrophys., 186, 1. the slight difference in colour, noted Huchra, J., Gorenstein, M., Kent, S., Shapiro, above. It is possible to consider the ably fairly complicated, and we post­ pone any modelling of the system to a 1., and Smith, G. 1985, Astron. J, 90, 691. apparent reddening of the component B Lawrence, C., Schneider, D., Schmidt, M., future, more comprehensive paper. as a contribution from a foreground Bennett, C., Hewitt, J., Burke, B., Turner, galaxy which could be apart of the The very similar spectra and colours, E., and Gunn, J. 1983, Science, 223, 46. gravitationallens itself. We divided the the presence of a possible lensing Lynds, R., and Petrosian, V. 1988, Astrophys. spectrum of the component A by 100 galaxy and/or a cluster, and the J, in press. (very close to the flux ratio from the luminosity and redshift bias used to MacAlpine, G.M., and Williams, G.A. 1981, Astrophys. J Supp/., 45, 113. division), and subtracted it from the select the object in the first place, argue in favour of the gravitationallens hy­ Magain, P., Surdej, J, Swings, J.-P., spectrum of the component B. The re­ Borgeest, U., Kayser, R., Kühr, H., Refsdal, sulting spectrum, shown in Figure 3, is pothesis. It is regrettable that the sys­ tem is not detected in the radio, as the S., and Remy, M. 1988, Nature, 334, 325. reminiscent of an early-type galaxy Refsdal, S. 1964, Mon. Not. R. Astr. Soc., comparison of the optical and radio im­ spectrum at a redshift Z - 0.6, if the 128,307. continuum rise is attributed to the ages can be used as a powerful test for Refsdal, S. 1966, Mon. Not. R. Astr. Soc., 4000 Abreak (see Surdej et al. 1987 for lens candidates (Djorgovski et al. 1987). 132, 101. a similar investigation). The rough R Further data are needed in order to Soucail, G., Mellier, Y., Fort, B., Mathez, G., magnitude of this component is - 23 ± tighten the measurements presented and Cailloux, M. 1988, Astr. Astrophys., 191, L 19. 0.5 (about 7m fainter than A and 2m here, and establish the nature of the components C and D. Surdej, J., Magain, P., Swings, J.-P., fainter than B), comparable to what is Borgeest, U., Courvoisier, T.J.-L., Kayser, expected of a luminous elliptical galaxy It is a pleasure to thank the staff of all observatories involved, and especially R., Kellerman, K.I., Kühr, H., and Refsdal, at Z = 0.6 (Guiderdoni and Rocca-Vol­ S. 1987, Nature, 329, 695. H. Pedersen and J. Miranda at ESO, J. merange 1987). The large number of Turner, E. L., Ostriker, J. P., and Gott, J. R. 111 Bravo and M. Navarete at CTIO, W. other faint galaxies in the field is also 1984, Astrophys. J, 284, 1. Kunkel and P. Schecter at Las Cam­ consistent with the presence of a rich Walsh, D., Carswell, R. F., and Weymann, panas, and J. Carrasco at Palomar. foreground cluster at that redshift. Final­ R.J. 1979, Nature, 279, 381. Many thanks also to R. Perley for ob­ Weedman, D.W., Weymann, R.J., Green, Iy, it is possible that the companion 0 taining and reducing the VLA snapshots. R. F., and Heckman, T. M. 1982, Astrophys. (and perhaps even Cl are other mem­ J, 255, L5. bers of this hypothetical lensing cluster Weymann, R.J., Latham, D., Angel, J. R. P., along the line of sight to UM 425. The References Green, R. F., Liebert, J. W., Turnshek, DA, brighter 0! = 17.8) galaxy just NW from Blandford, R. D., and Narayan, R. 1986, As­ Turnshek, D. E., and Tyson, J. A. 1980, Na­ UM 425 is at Z = 0.1265, and probably trophys. J, 310, 568. ture, 285, 641. unrelated to the system. Blandford, R.D., and Kochanek, C.S. 1987, Zwicky, F. 1937a, b, Phys. Rev., 51, 290 and 679.

Binary Nuclei of Planetary Nebulae A. ACKER, G. JASNIEWICZ, Equipe "Populations Stellaires", Observatoire de Strasbourg, France

Introduction Observations ently very similar variations: same be­ About ten planetary nebulae have havior for the radial velocity curve and/ At La Silla we used various tools: late-type central stars, which are too or for the light curve. In addition, in both - Radial velocity scanner CORAVEL cool to ionize the nebula. This implies cases, spectral peculiarities can be ob­ mounted on the Danish 1.5-m telescope either the presence of a warmer com­ served, such as stellar emission lines, (observations taken by Prevot from panion (the true central star), or an un­ wh ich can be explained by chromo­ Marseille): stable central star wh ich was hotter in spheric activity of the star or by mass - Differential photometer P7 of the the past. exchange in a close binary system. Geneva Observatory mounted on the These two phenomena - binarity and The true interpretation is possible only Swiss 70-cm telescope: intrinsic variability -, which are physical­ if coordinated observations are con­ - Spectrograph B & C (CCD detector) Iy very different, may give rise to appar- ducted. mounted on the ESO 1.52-m telescope. 42 together, were especially informative. The comparison (see Fig. 1) of our photometric observations Sept.-Oct. 1988 APRIL 1984, Sept. 1985) with the previous one have shown a phase difference, and new properties of the clumpy shell have been suggested (Acker and Jasniewicz, 1985: Jasniewicz and Acker, 1986). In particular the end of the eclipses has been suspected and confirmed in 1986.

Abell35 11. O~~ }o.t Simultaneous spectroscopic and photometric observations of BO 22°3467, the GB I1I central star of Abell 35, have been performed at La Silla, in Figure 1: Evolution of the light eurve of order to elucidate the origin of the light NGG 2346 (eentral star). 1 to 8 are taken from variations and of the Ha emission stellar Mendez et al. (1984). 1 = Kohoutek, 1982 line shown by Jasniewicz and Acker -----~---'----r----~....__J Jan. - Feb.; 2 = Gathier, 1982 Mar. -Apr.; 3 = 6)71 BQ rm A (1988). Binarity is probably responsible Glaria, 1982 Nov.; 4,5 = Van Oriel, 19820ee.; Figure 2: Speetroseopie variations on the 6 = Mendez, 1983 Jan.; 7, 8 = Kohoutek, for these variations: this assumption is Ha line for the eentral star of Abell 35 (ESO 1983 Jan.; 9 = Kohoutek and Gelnik, 1984 confirmed by recent IUE observations 1.52-m teleseope, B & G + GGO). Feb.; 10 = Sehaeffer, 1985 Feb. The two reported by Grewing and Bianchi (1987). thieker lines eorrespond to our observations: We have conducted the following ob­ 1984 Sept. - Oet.; 1985 Sept. (taken from servations: tested and discussed after full process­ Astron. Astrophys. 160, L 1-L3 (1986). - 43 measurements have been done ing of the data (to appear in Astron. from February to April 1988 using the Astrophys.). P7 differential photometer mounted on For other cold nuclei, data were col­ Results the Swiss telescope (mean probable lected using the CORAVEL system; but Since 1978 we have observed in par­ error on the V magnitude 0.008): the central stars of planetary nebulae ticular four cold nuclei of planetary - 48 spectra, taken with an exposure are very faint objects, and the radial nebulae: FG Sagittae (spectral type K), time of 25 minutes each, have been col­ velocity variatons we detected in three LoTr5 (G5 star), NGC 2346 (A5 star) and lected from 20 to 24 April 1988, using cases must be confirmed by new series Abell 35 (GB star). Here we report briefly the spectrograph B & C + CCO, of observations. on the two southern objects, NGC 2346 mounted on the ESO 1.52-m telescope. and Abell 35. The dispersion was 58 Älmm; all the References spectra were centred around the Ha Acker, A., Jasniewicz, G.: 1985. Astron. As­ line; the final resolution was 1 pixel = NGC 2346 trophys. 143, L1. 1.7 A. Feibelman, W.A., Aller, L. H.: 1983, Astro­ According to Mendez et al. (1982), the The spectra were reduced using the phys. J. 270, 150. central star is an SB 1 and its photomet­ IHAP procedure. Preliminary results Grewing, M., Bianchi, L.: 1987, lAU Symp. ric variations (detected in 1981) are due should be given (see Fig. 2). No. 131, Mexico. to the passage of a dust c10ud in front of The faint Ha emission line is double Jasniewicz, G., Acker, A.: 1986, Astron. As­ trophys. 160, L 1. the binary system. Infrared observations peaked and variable. The spectroscopic Jasniewicz, G., Acker, A.: 1988, Astron. As­ variations seem to occur within a range of Roth et al. (1984) and IUE observa­ trophys. 189, L7. tions of Feibelman and Aller (1983) have of 20 hours, and thus are in agreement Mendez, R. H., Gathier, R., Niemela, V. S.: allowed to confirm the dust cloud in­ with the photometric period P = 0.765 d. 1982, Astron. Astrophys. 116, L5. terpretation. found by us in 1986 and 1987. Rolh, M., Echevarria, J., Tapia, M., Garrasco, The optical observations of The hypothesis related to an accre­ L., Rodriguez, L.F.: 1984, Astron. Astro­ NGC 2346 during the eclipses, taken all tion disk in a binary system will be phys. 137, L9.

Brey 73: a Multiple Wolf-Rayet Star G. TESTOR, Observatoire de Paris, Seetion de Meudon, France, and A. LLEBARIA, B. OEBRA Y, Laboratoire d'Astronomie Spatiale, Marseille, France

1. Introduction really are tight clusters where different ponents respectively in a field of about 2 Oetailed observations of several of types of stars are mixed. Moreover, very 4 x 4 arcsec . The existence of super­ the most luminous stars in the LMC accurate observations of R 136 by massive stars in the LMC is now ruled show that these stars often are multiple speckle interferometry (Weigelt and out, and we must interpret extragalactic systems (Walborn, 1977; Feitzinger et Baier, 1985) and of Sk - 6641 under very young stellar associations very cau­ al., 1980; Prevot-Burnichon et al., 1981; good seeing (Heydari-Malayeri et al., tiously. Lortet et al., 1986). Most of these stars 1988) have revealed eight and six com- Therefore, being interested in the

43 ~ ,'...-: I'! ", I population of massive stars in the LMC , , I we are currently carrying out a new spa­ tial high resolution observing pro­ 11: gramme of all bright Wolf-Rayet stars whose image seems slighty larger than a stellar profile in hitherto published photographs. Apparently composite objects discov­ ered by spectroscopy as the Wolf-Rayet Brey 18 = HO 269227 = R 84 (Allen and Glass, 1976; Cowley and Hutchings, 1979) will be studied later, when spatial resolution has been improved (Iess than 1 aresec) or by speckle interferometry. .Bre)' 70a A good example of such a large and ,';_:1 .-----,- bright Wolf-Rayet is Brey 73. This star, of integrated magnitude V = 12.2 (Brey­ sacher, 1981) and of type WN 4.5 + OB, E is located in the OB association LH 99 (Lucke, 1972) of N 157 B (Henize, 1956) a supernova remnant 7 arcminutes South-West of 30 Ooradus. In 1979 Azzopardi and Breysacher reported that this star had a diffuse image and in 1980 Walborn's observations at the RC focus of the CTIO 4-m telescope showed that Brey 73 consisted of two components separated by only 1.5 arcsec. He noticed that the eastern component was 'ri slightly brighter, but he did not identify the Wolf-Rayet star. The visual examina­ tion of our CCO frames also reveals that Brey 73 is indeed a multiple star. Even though the seeing was only 1.6 arcsec, thanks to the highly sampled

CCO images and using the CAPELLA '. 'j'I_, package for photometry in crowded re­ gions (Oebray et al., 1988), developed at the LAS in Marseille, we have been able 10" to resolve and measure no less than I eleven components.

2. Observations s The observations were obtained using Figure 1: eeo frame towards Brey 73 through the A4686 A filter. the UV coated GEC CCO camera attached to the 2.2-m telescope at La - OAOPHOT, a very weil adapted pro­ and so on) having been applied for both Silla in October 1987. The chip has gramme for crowded fields but non-in­ frames, the image taken in the He 11 line 385 x 576 pixels, each pixel 22 I-i x 22 I-i, teractive (Stetson, 1987). has then been corrected for local de­ corresponding to 0.26 x 0.26 arcsec2 on - BIOIM wh ich includes the following fects (hot pixels, cosmic rays, etc.) with the sky. The field of Brey 73 (Fig. 1), steps: Measurement of the slippage be­ a special "erosion-healing" procedure containing two other Wolf-Rayet (W-R) tween the two frames to a tenth of a made by L1ebaria (bidimensional pack­ age in MIOAS) which restores defective stars, Brey 71 and Brey 70a = MGWR 4 pixel, alignment of one image on the (Morgan and Good, 1987), was imaged other one, determination of standard pixel intensities by means of local inter­ with a 60 A continuum filter centred at coefficients, difference after normaliza­ polation from the surrounding area in an A. 4794 A and a narrower one of 50 A tion. extension proportional to the dimen­ centred on the 4686 A He 11 emission In both cases, the W-R was detected sions of the defects. line, in order to enhance the He II bright­ in the association (Fig. 2) but could not Stars are then measured using a pro­ ness excess of the W-R. The exposure be accurately located and its photome­ file fitting photometry software called times were 3 minutes and 2 minutes for try could not be carried out either. CAPELLA (Oebray et al., 1988). An ex­ the Hell and continuum frames respec­ perimental point spread function (PSF) is determined from isolated stars which tively. The CCO images were reduced The CAPELLA package (flat fielding, cleaning, etc...) using the are interactively chosen in the same MIOASNAX image processing system. The He 11 and continuum frames have field. Stars are recentred to a common been treated individually and indepen­ grid and are averaged together. Pixels dently following the same operating se­ intensities which are too far away from 3. Reduction quence. the mean value of relevant pixels inten­ Before applying the CAPELLA pro­ The standard reduction procedure for sities in the other stellar images are re­ gramme, we used two reduction pro­ CCOs (correction of the dark current, of jected from the computation of the grammes in the context of MIOAS: the cold columns, response uniformity, mean. No modeling being used, it is 44 detected objects are added to the previ­ ous list. For each detection, a contamination coefficient quantifies local blending due to nearby stars. This quantity is propor­ tional to cross-correlation of the star with surrounding stars and inversely proportional to the auto-correlation val­ ue. As the fitting procedure runs, it is adapted with respect to the coefficient value. Fairly contaminated stars (typically field stars which are out of the Brey 73 association) are measured using un­ blended parts of the stellar images for the linear regression fit with the PSF. Two possibilities may occur for very crowded stellar images. If the star is fainter than its immediate neighbours, star measurement is postponed to a next iteration until brighter neighbouring stars have been measured and sub­ tracted. If the star is brighter than its immediate neighbours, they are first evaluated after rough subtraction of the star to be measured, in order to remove them from the wings of the star to be Figure 2 (Upper left): Hell frame of Brey 73 association. (Upper right): Continuum Hell frame. measured using an "up-and-down" pro­ (Lower left): Oifference after scaling and rebinning using the BIOIM package. The Wolf-Rayet cedure. In the case of very blended stars star appears in the middle. (Lower right): Enhancement ofresiduals due to differences between of the Brey 73 association, This "up­ the two PSF. and-down" procedure must be iterated at its turn for the correct evaluation of possible to work as in our case with of the frame with a Laplacian adapted to the neighbouring stars. slightly oval, or irregular PSF. Finally, the PSF FWHM. Detected stars are re­ In the present case, it has been relative fluxes of all stars are measured moved by subtraction of the recentred necessary to perform nine successive using linear regression fit with the PSF. and scaled PSF. A new detection is iterations because of the large overlap Stars are detected using convolution performed over the field of residuals and of the stellar images in Brey 73 (Fig. 3 and 4). The photometric reduction step required one day of interactively assisted work for each image on a VAX 780, with a Deanza IP 8400 station and CAPELLA in MIDAS.

4. Results and Discussion Our work reveals that Brey 73 is in fact an aggregate of 11 components (Fig. 5) including the Wolf-Rayet star at aresolution of at least 1.3 arcsec with an effective seeing of 1.6 arcsec.

Apparent magnitude Figure 6 shows all the stars of the field. Triangles refer to the stars of the Brey 73 association. It immediately appears that the W-R star Brey 73 is of similar magnitude (at A4794 A) as Brey 71, though the mag­ nitudes quoted for these two stars in the literature are very different. The calibration of the W-R component in the Brey 73 association was made on the one hand thanks to the single stars Brey 71 (WN 7) and Brey 70a (WN 3-4) Figure 3: Successive steps in the processing of the Hell frame of the Brey 73 association of magnitude v = 13.76 (Breysacher, (Upper left): Original frame. (Upper right): Residuals after first iteration. (Lower left): Id. for 1986) and 17.64 (Morgan and Good, second iteration. (Lower right): Id. for third iteration. 1987) respectively, in the u'ubvv' photo- 45 11

12 7

8 9

6 10

Figure 5: 0.25 arcsec reconstitution of Brey 73 showing stars detected in the association.

right of the WN 4.5 absolute magnitude histogram (Breysaeher, 1986 - Fig.1) strengthening Breysacher's hypothesis that the mean magnitude of this sub­ class is not very different from that of WN 3 and WN 4, about -4.2. As a conclusion, CAPELLA is an ex­ cellent help, weil adapted for the study of stellar aggregates, even if a great number of intermediate frames must be Figure 4: Successive steps in the processing of the Hell frame of the Brey 73 association used in its present status. In the case of (continuation). (Upper left): Residuals after fourth iteration. (Upper right): Residuals after fifth WOlf-Rayet stars, the detection and iteration. (Lower lett): Id. for eighth (the last one) iteration. (Lower right): 0.25 arcsec reconstitu­ treatment of multiple systems is of spe­ tion of Brey 73. cial interest as it is a necessary step for an accurate determination of the abso­ lute magnitude of each star, which has metrie system avoiding the W-R emis­ the W-R has a mean magnitude v of far reaching consequences for our sion lines deseribed by Smith (1968), about 13.76. understanding of the evolution of mas­ and on the other hand thanks to the sive stars. The comparison with results integrated magnitudes V = 12.11 of the Absolute magnitude obtained in our Galaxy, of different chemical composition (Van der Hucht et Brey 73 assoeiation and V = 13.96 of Adopting a LMC distanee modulus of al., 1988) will also be of great interest. Brey 71 in the UBV eurrent photometrie 18.5 (Westerlund, 1974) the visual abso­ system, obtained by Feitzinger and lute magnitude of a star is given by the Isserstedt (1983) through an 18 aresee References relation Mv = v-Av -18.5 where v is the diaphragm. The differenee in magnitude Allen, D.Ä., Glass, I. S.: 1976, Astrophys. J. apparent magnitude, Av = R, Eb- v the 210,666. v between the UBV and narrow band total absorption in the v band (Lu nd­ Azzopardi, M., Breysacher, J.: 1970, Astron. u'ubvv' system is determined by the re­ ström and Stenholm, 1984). Adopting lation v-V = 0.20 for WN 4.5 and v-V = Astrophys. 75, 243. Eb-v = 0.12 and R, = 4.2 (Breysaeher, Breysacher, J.: 1981, Astron. Astrophys. 0.08 for WN 7 stars (Breysaeher, 1986). 1986), we found a magnitude Mv = Suppl. Sero 43, 203. We have eheeked elsewhere that v -4.99 instead of -6.7. Breysacher, J.: 1986, Astron. Astrophys. 160, (A 4794 A) and V are weil eorrelated with This value draws Brey 73 towards the 185. the slope 0.97, for stars not redder than 0.4. The eorrelation v (A 4794 A), v (Smith) is expeeted to be even better TABLE 1. Magnitudes of the Brey 73 aggregate stars computed from the known measure­ with a slope eloser to 1. ments of Brey 70a, Brey 71, Brey 73. Table 1 gives different magnitudes v of the W-R in the Brey 73 assoeiation. Stars Magnitude (v) Magnitude (v) Magnitude (v) Magnitude (v) Its ealibration fram the magnitude v and otthe trom trom tram tram V of Brey 71 gives two different mag­ Brey 73 Brey 70a Brey 71 Brey 71 Brey 73 nitudes v = 13.74 (eolumn 3) and v = aggregate (v = 17.64) (v = 13.76) 01 = 13.96) 01 = 12.11) 14.04 (eolumn 4) respeetively. The latter W-R 13.43 13.74 14.04 13.99 value is in good agreement with the 2 13.12 13.43 13.73 13.69 magnitude v = 13.99 (eolumn 5) ex­ 3 13.59 13.90 14.20 14.16 traeted fram the integrated magnitude V 4 14.24 14.46 14.76 14.81 of the Brey 73 assoeiation. From the 5 14.45 14.76 15.06 15.02 faint Brey 70a we derived a magnitude v 6 14.57 14.88 15.18 15.14 = 13.43 (eolumn 2), the exeess in bright­ 7 14.31 14.62 14.92 14.88 ness eould be due to the nebula. Finally 8 15.59 15.90 16.20 16.16 we adopted v = 14.01 as the mean 9 15.70 16.01 16.31 16.27 magnitude dedueed from the V mag­ 10 16.46 16.78 17.08 17.03 11 16.07 16.39 16.69 16.63 nitudes of Brey 71 and Brey 73. The 12 15.05 15.36 15.66 15.62 brightest star in the aggregate besides 46 Cowley, A.J., Hutchings, I.B.: 1979, P.A.SP. 90,636. Debray, B., Dubout, R., L1ebaria, A., Petit, M.: 1988, Astron. Astrophys. (submitted). Feitzinger, J. V., Schlosser, W., Schmidt-Ka­ ler, Th., Winkler, C.: 1980, Astron. Astro­ + + phys. 84, 50. + . + Feitzinger, J. V., Isserstedt, J.: 1983, Astron. 4 + ~ + +. Astrophys. Supp. Ser., 51, 505. Henize, K. G.: 1956, Astrophys. J. Suppl. 2, 315. Heydari-Malayeri, M., Magain, P., Remy, M.: 1988, Astron. Astrophys. 201, L 41. Lortet, M. C., Heydari-Malayeri, M., Testor, 0 G.: 1986, in Luminous stars and associa­

2 A Brey 70a tions in galaxies, Proceed. lAU Symp. 116, (l) I A 401.

(l) + Lucke, P.B.: 1972, Ph.D. Thesis, University \J A of Washington. ::J ...... Lundström, 1., Stenholm, B.: 1984, Astron. C 0'1 Astrophys. Suppl. 58, 163. 0 + Morgan, D.H., Good, A.R.: 1987, ::::;E MNRAS. o Brey 73 224,435. 0 + Prevot-Burnichon, M. L., Prevot, L., Rebeirot, E., Rousseau, J., Martin, N.: 1981, Astron. + o Brey 71 Astrophys. 103, 83. Smith, L.F.: 1968, MNRAS. 140, 409. Stetson, P.B.: 1987, P.A.S.P. 99,191. Van der Hucht, K.A., Hidayat, B., Gunowan Admiranto, A., Supelli, K. R., Doom, C.: - 2 l.-----L_--"--_-'-----'_-'-_-'------''------'-_--'-_'------'-_--'-_''------L_--''-----' 1988 Preprint. -2 o 2 4 6 Walborn, N.R.: 1977, Astrophys. J. 215, 53. Magnitude Continuum Walborn, N. R.: 1980 (Private communica­ tion). Figure 6: Plot of the Hell relative magnitudes versus the continuum magnitudes of all stars of Weigelt, G., Baier, G.: 1985, Astron. Astro­ the frame (90 arcsec x 140 arcsec). The known W-R stars Brey 70a, Brey 71 and the Brey 73 phys. 150, L 18. association show a conspicuous Hell brightness excess. The stars belonging to the aggregate Westerlund, B. E.: 1974, Proceedings of the are represented by triangles. Most of the stars follow a close relationship v (A 4686 A) = 0.96 v first European Astronomical meeting in ()... 4794 A) + 0.34 and with a 0 rms of 0.22 magnitude after elimination of Brey 70a, Brey 71 and Athen, September 4-9, 1972, Volume 3. Brey 73. Star 12 is a faint star of the cluster, probably a red one which would need deep, good Springer, Berlin, Heldeberg, New York, seeing Band V photometry. p.39.

Spectroscopic Identification of White Dwarfs in Galactic Clusters O. REIMERS, Hamburger Sternwarte, Universität Hamburg, F. R. Germany 0. KOESTER*, Oepartment ofPhysics andAstronomy, Louisiana State University, USA

The End Products of Stellar fully as a white dwarf or undergoes a local SN 11 rate (e. g. Tammann, 1974) Evolution core collapse with a quasi instantane­ teils us that all stars more massive than ous energy release of - 1053 erg, visible 5 to 10 MG must become supernovae, The end products of the evolution of as a supernova explosion. and Kennicutt (1984) found that SN II's single stars are weil known: low mass Estimates of the maximum initial in Sc galaxies come from stars with stars leave white dwarf remnants, mas­ mass limit M for formation of white masses greater than 8 ± 1 MG' sive stars undergo a supernova explo­ WD dwarfs have been made by various Since the fate of intermediate mass sion with either a neutron star or a black techniques. stars is mainly determined by mass loss hole as a remnant. One possibility is to compare the in the red giant stage, the combination In a first approximation, it appears to supernova type I1 rate with the birth rate of stellar evolution tracks through the be only the initial mass which deter­ of massive stars in our galaxy. Since the red giant stages with empirical red giant mines whether a star ends its Iife peace- former rate is extremely uncertain and mass-Ioss rates also provides an esti­ can be observed only in external galax­ mate of MwD . The difficulty of this ap­ ies whereas the initial mass function can proach is that while mass-Ioss rates in be measured only in the solar neigh­ • Formerly at Institut für Theoretische Phy­ the normal red giant region are fairly weil sik und Sternwarte der Universität Kiel, F. R. bourhood, the constraints on SN 11 par­ known and can be parametrized by Germany ents are not stringent. An estimate of the semi-empirical interpolation formulae 47 .~ . .'0:' ...• .. •• • .. • .. .. •• " • • • ., .... • • • ' • .',: . . .' '. ',f. ; '. • 0•• '. #.. • '. .. " , , • ... •• . , ..: ,: • . ' . ~' • " .' .. ' .. , ' : .. ' .. .~ ... ' " ,.. •• • .~~ " ..... t. • • ... • " . "~\.. ',: .... :...• '7'7.:' . .'. . '.' .' . . ,10. .. .,.. .. '.

. ,- '.• . . " .. ,.'

Figure 1: Central part of NGC 3532 (ESO Schmidt, 11I a-J+ UG 1; 75 min) with marked positions of candidate objects.

(e. g. M- Ug . R, Reimers, 1975, 1987), ades. He found MWD = 4 MG' However, fields - in a number of intermediate age an extrapolation to advanced red giant with a turn-off mass of - 2 MG the Hy­ northern clusters. Based on their find­ phases (e. g. OH-IR stars) where most ades are not favourable for this method ings, they concluded MWD = 7 MG' mass is lost is certainly not allowed. On since according to the cluster luminosity However, the question remained the other hand, high mass-Ioss rates of function, their known six white dwarf whether the excess of blue objects in advanced red giants as observed in members must have had pragenitor the cluster fields were really white thermal GO lines or in OH maser lines masses only slightly higher than the dwarfs. Anticipating the results of our cannot easily be linked to stellar evolu­ turn-off mass. spectrascopic observations over the tion calculations, since for these stars years 1980-88 from both La Silla and masses and evolutionary stages are Galar Alto of all Romanishin and Angel's Faint Blue Objects in Open poorly known. candidates, it finally turned out that only Cluster Fields The only reliable method to determine 6 out of 17 WO candidates in the four Mwo seems to be the identification of A new attempt to determine MWD fram clusters NGG 2168, 2242, 2287 and white dwarf members of galactic clus­ cluster white dwarfs was made by 6633 are cluster members. This means ters with turn-off masses Mt :s MWD' Romanishin and Angel (1980) who that without time consuming spec­ The first attempt with this method was looked for a statistical excess of faint trophotometry of the faint 01 = 19 to 21) made by v. d. Heuvel (1975) far the Hy- blue objects - relative to comparison blue objects in the cluster fields, no safe 48 Confirmed white dwarf members of intermediate age clusters tions of WOs in cluster fields at such m faint magnitudes (-20 ) in the near fu­ 3 Cluster Age Turn-off White Te [10 K] V Mass Progenito ture. (Paper No.) logT Mass Dwarf [MG) Mass [MG) The Present Status

NGC 2516 8.0 4.75 -1 30 19.6 0.95 7.2 How many white dwarf members of (11) -2 36 19.55 1.14 7.6 intermediate age clusters (turn-off -5 34 20.1 1.17 9.8 masses ;;:: 4 MG) are known at present after the spectroscopic observations 4 NGC 2451 ) 7.8 5.3 -6 31 16.75 0.6: 5.9 with the 3.6-m + lOS in the years (111) 1980-84, the new start with EFOSC on NGC 3532 8.3 3.6 -1 28 19.55 0.9 4.1 fainter objects in 1988, and a few nights M -5 28 19.2 0.6 3.9 on the northern clusters NGC 2168 and -6 29 19.9 0.9 4.1 NGC 6633 with the Calar Alto 3.5-m telescope? Altogether we have iden­ NGC 2168 8.0 4.75 -3 38 .20.25 0.7 5.9 tified 12 (possibly 14) WO members of (IV) -4 44 20.05 0.7 5.9 intermediate age clusters (Papers I-VI).

1 Four were from Romanishin and Angel's NGC 2287 8.25 3.9 ) -2 25 20.1 0.6 (I) -5 25 20.1 0.6 (1980) candidate list (two in both NGC 2287 and NGC 2168). Eight (ten) hot OA NGC 6405 7.9: 5.3: -1 3) 82 18.1 1.18 6.5: white dwarfs (the hottest has 82,000 K!) (VI) have been discovered by ourselves on 2 Pie/ades 7.9 5.3 LB 1497 0.85 6.2 ) the ESO Schmidt plates taken for that particular purpose. Only one WO, the ') According to Romanishin and Angel (1980). 2) Weidemann (1987). Pleiades member LB 1497 (e. g. Green­ 3) Cluster membership uncertain, WO is _1 0 from cluster centre. stein, 1974). was known to be member .) NGC 2451 contains two more probable WO members (Paper 111), if conrirmed they have high masses of an intermediate age open cluster be­ and high progenitor masses; : denotes uncertain .or preliminary values fore we started this project in 1980. ESO's superb equipment and dark sky has thus made possible an important conclusions are possible. The results of 30,000 K) are extremely rare in the gen­ contribution to an understanding of the the first two observing years have been eral field and projection onto a cluster is final stages of stellar evolution. described briefly by Koester (1982). therefore highly improbable, two criteria Our first observing run with EFOSC Parallel to this activity we asked for are applied: (i) the theoretically calcu­ and the 3.6-m telescope in April 1988 deep ESO red and UV Schmidt plates of lated cooling time, which depends on conducted by O. K. was highly success­ suitable southern intermediate age clus­ mass M and temperature Te must be ful. We identified 3 WO members of ters with turn-off masses around 5 MG' smaller than the cluster age and (ii) the NGC 3532. Furthermore, we completed White dwarf members of clusters distance modulus V-Mv determined observations on several candidates in younger than about 2 . 108 years cannot from the observed apparent magnitude the clusters NGC 2422, 2516 and 2287 have cooled down below about V and from effective temperature Te and which had been too faint for an unam­ 25,000 K. Therefore one has to search radius R has to be consistent with the biguous identification with the lOS on the for very blue faint objects in the cluster observed cluster modulus. As Chan­ 3.6-m in earlier observing runs. The can­ fields. With typical distance moduli of drasekhar's work, which won him the didate in NGC 2422 could be proven to rich clusters between 8 and ~ 11, hot Nobel prize, has shown, degenerate be a subdwarf, as suspected earlier (Pa­ white dwarfs are expected in the range stars obey a mass-radius relation which per I). The same applies to NGC 2516-4. 1I3 V = 19 to 22. is approximately R - M- . The white A highlight of the April 88 observa­ The plates were blinked at Hamburger dwarf radius R which is needed for clus­ tions was the discovery of the extremely Sternwarte and we could identify further ter membership test is determined in the hot OA NGC 6405-1 (82,000 K, the suitable candidates in the clusters NGC ideal case from gravity which can be hottest known OA?). While the star is 2516,2451,3532,6405,6475,6087and measured from high-quality spectra by - 10 outside the cluster centre, it has IC 2391. Progress in follow up spectros­ comparison with model atmosphere cal­ the same distance according to the copy was slow, since due to the faint­ culations. This was possible, e. g., in model atmosphere analysis. One may ness of the objects only the 3.6 m + lOS cases of NGC 2516 and NGC 3532. If suspect that the near coincidence of was suitable in the years 1980-84, and gravity cannot be determined spectros­ such an extremely rare type of star with the faintest objects as weil as objects copically with sufficient accuracy, a typ­ a cluster is not just by chance. with relatively weak lines had to wait for ical WO mass is assumed in a first ap­ A further surprise was that one of our EFOSC with its improved sensitivity. proximation. In most cases adecision faint blue candidates in NGC 6087 Our first observing run with EFOSC was about cluster membership is then possi­ turned out to be a planetary nebula. It conducted in April 88. ble since for a given effective tempera­ has a hot featureless continuum and ture Te the absolute magnitude varies as nebular lines that extend - 14 arcsec in 2 2/3 Mv - R - M- with mass, and the direction of the spectrograph slit. A Cluster Membership assumptions about WO masses which rough estimate shows that at the dis­ Even if a faint blue object within the have a narrow range anyway are not too tance of the cluster (850 pe) this corres­ cluster field turns out to be a white crucial. As long as consistency with the ponds to a linear diameter of - 0.03 pe. dwarf, it is not necessarily a cluster cluster modulus is found for an This would imply a rather young PN with member. How can foreground and assumed WO mass in the range 0.5 MG a central star of Mv "" - 3 to -4, incon­ background white dwarfs be separated to 1.2 MG' cluster membership is highly sistent with the observed V magnitude from cluster members? Besides the fact probable for a hot WO. Unfortunately, it of 19.3. Conclusion: Unfortunately, the that extremely hot white dwarfs (Te > will be difficult to measure proper mo- PN is a background object. 49 M WD and the Initial-Final Mass I I I Relation NGC 3532 - 1 Oata on the individual cluster white 1.13 dwarfs identified by our spectroscopic observations and on the open clusters are compiled in the Table. A major uncertainty for the determina­ tion of cluster turn-off masses, cluster ~ ~~ 0.96 ~ ~fi~ ~ ages and white dwarf progenitor masses has been recognized in recent years: the amount of convective over­ shooting for intermediate mass main se­ ~ NGC 3532 - 5 quence stars is not known. We have 0.79 always assumed here an overshooting parameter Uc = 0.5. For a full discus­ 1.13 sion of this point, in particular the influ­ " ence of overshooting on the initial-final ~ mass relation, we refer to Weidemann (1987). 0.62 ~ ~~ The best case for determining MWD is - 0.96 the rich southern cluster NGC 2516

(Reimers and Koester, 1982). Using the Vl C observed cluster luminosity function, QJ the mass-interval above the cluster turn­ C off was estimated out of which the ob­ (11 0.79 NGC 3532-6 served number of evolved stars has .....> come. The result was MWD = 8~~ MG' o 4i This statistical method, however, de­ ll: mands that no mass segregation has 1.13 occurred within the cluster due to dy­ 0.62 namical evolution. In cases where it is observed that the massive stars are more concentrated to the cluster centre than the low mass stars as in the case of the Hyades or NGC 3532, the statistical 0.96 method can give only a lower limit to MWD (Paper V), since for a sufficiently short relaxation time the white dwarfs can have aspace distribution different from that of their progenitor stars or the 0.79 upper main sequence stars respectively. An alternative approach is to try to esti­ mate the WO progenitor masses by vir­ tually placing the white dwarfs back onto the main sequence taking into 0.62 account main sequence and red giant lifetimes and the WO cooling ages. For details we refer to Weidemann (1987). Thus obtained progenitor masses (Table) yield both an initial-final mass 0."5 5100 relation (Fig. 3) and an estimate of MWD' 3900 I. 1"0 1.380 1 1.620 1.860 Notice in Figure 3 that the initial-final A[Al mass relation may weil be a strip with a Figure 2: EFOSC spectra of DA white dwarf members of NGC 3532. finite width, which could be explained by differential mass-Ioss in the preced­ ing red giant stage. Clearly more stars and more accurate data are needed, so, called the "jeweIl box" because of its flows. Oue to the higher resolution of the e.g., the accuracy of WO masses (via concentration of blue main sequence CCO, EFOSC images look better. radii) depends on the accuracy of dis­ stars and red giants. It contains - 10 red Follow-up spectroscopy of 23m can­ tance moduli and reddening corrections giants and Cepheids. Oue to its extreme didates at a sufficient S/N for gravity of open clusters! richness and a turn-off mass of - 6 MG determination using the model atmo­ we expect about 15 hot white dwarfs in sphere technique will be a promising m the cluster, however, at V -23 . Our task for the VLT. The Future attempt to find candidates with deep We clearly need more WO members CCO exposures with the Oanish 1.5-m Acknowledgements of rich open clusters with turn-off telescope has so far been unsuccessful masses above 5 MG' One of the best mainly due to the concentration of bright This work would have been impos­ known examples is NGC 6067, also stars wh ich caused severe CCO over- sible without the efficient support of

50 staff astronomers and skillful night 2 4 6 8 10 assistants on La Silla. 1.4 I I II

I- References 1.2 I- Greenstein, J. L., 1974, Astron. J. 79, 964. C> I • Kennicutt, R.C., 1984, Astrophys. J. 277, I- 361. Koester, D., 1982, The Messenger28, 25. 1.0 I- / Koester, D., Reimers, 0.,1981, Astron. Astro­ / . phys. 99, L8 (I). Koester, 0., Reimers, 0., 1985, Astron. Astro­ /P phys. 153, 260 (111). 0.8 I- Koester, 0., Reimers, 0., 1989, Astron. Astro­ / phys. LeIters, in prep. (VI). I- 8 Reimers, 0.,1975, Mem. Soc. Roy. Sci. Liege + x+ o 8,369. 0.6 I- Reimers, 0., 1987, in Circumstellar Matter, I- lAU Symp. 122,307. Reimers, D., Koester, 0., 1982, Astron. Astro­ 0.4 I- - phys. 116, 341 (11). Reimers, 0., Koester, D., 1988, Astron. Astro­ - phys. 202, 77 (IV). Reimers, 0., Koester, 0., 1989, Astron. Astro­ 0.2 I- - phys. M. - Romanishin, W., Angel, J. R. P., 1980, Astro­ 0.1 I- phys. J. 235, 992. I I I I III II I II Tammann, G.A., 1974, in Supernovae and 2 4 6 8 Supernova Remnants (C. B. Cosmovici, M ed.) D. Reidel, p. 155. I v.d. Heuvel, E.P.J., 1975, Astrophys. J. 196, Figure 3: Initial-final mass relation for intermediate-mass stars according to cluster white L 121. dwarfs identified in the course of this programme. Symbols: 0 NGC 2516, + NGC 2287,

Weidemann, V., 1987, Astron. Astrophys. x NGC 3532, 0 NGC 2168, 0 NGC 2451, L'I NGC 6405, P Pleiades. The broken line is the 188,74. relation adopted by Weidemann (1987).

New Results About SBO Galaxies o. BEITONI, Osservatorio Astronomico di Padova, Italy, and G. GALLEITA, Oipartimento di Astronomia, Universita di Padova, Italy

We discuss here the preliminary re­ tics, stellar motions were in the past with good hope of progressing toward sults of a long term project on kinema­ very little studied. A systematic attempt its complete understanding. In recent tics and photometry of SBO galaxies to analyse the kinematics of SBOs (Kor­ years, therefore, new data on stellar begun at ESO in 1983 and not yet fully mendy 1982, 1983) was never com­ kinematics have become available for completed. Beginning this study, we pleted and practically only one galaxy, eight more SBOs (Galletta 1987, Bettoni were particularly interested in analysing NGC 936 (Kormendy 1983, 1984), was and Galletta 1988, Bettoni et al. 1988, the mark of triaxiality that the bar in­ studied in detail (photometry, stellar ve­ Jarvis et al. 1988, Bettoni 1988). The duces in otherwise symmetrical galax­ locity field and velocity dispersion field) observational techniques used in our ies, by perturbing and stretching out the before 1987. Similar projects at other observations reflect the improvement of stellar orbits. But we did not imagine observatories followed the same ESO instrumentation in these years: that, progressing in this almost unex­ course, with observations never com­ starting with the 3.6-m telescope with plored land, so many new and not yet pleted or results never published. Prob­ the Boiler & Chivens spectrograph and fully explained features would be dis­ able reasons for this were the difficulty the 3-stage EMI image tube, the obser­ covered. Now, we feel it would be inter­ of supporting for many years a project vations continued at the ESO-MPI esting to resume here before the com­ requiring many observing nights against 2.2-m telescope with RCA CCDs when pletion of the search the main results so the idea that in the melting pot of billions these detectors became available. Par­ far obtained. of stars moving within the bar it should allel to this study, the inner photometry be impossible to distinguish between of the selected galaxies has been per­ "families" of orbits and, last but not formed using the ESO-Danish 1.52-m 1. A Bit of History least, against the occasional misunder­ telescope. SBO galaxies are good candidates for standing of some (too human) time this study because of the low, but not commissions. But with some vi­ 2. Observations and negligible, quantity of gas and dust pre­ cissitudes and a little bit of luck, obser­ Data Reduction sent in them. But despite the large vations of SB Os continued at ESO tele­ number of theoretical models of bars, scopes, demonstrating that we can look Our sampie includes 15 SB 0 galaxies and the several works on gas kinema- inside the stellar and gas kinematics brighter than the 12 th magnitude and

51 .' produce the stellar velocity and velocity plane. The second case is represented dispersion curves. The emission lines by NGC 2217, a galaxy with almost eventually present have been interpo­ ,[ 0 111 ] Mg round disk isophotes where gas and lated by fitting gaussian profiles, obtain­ stars again exhibit opposite motions, { t 11 ing the gas velocity curve and the equi­ circulating around the bar major axis valent velocity dispersion agas = FWHMI with velocities lower than in the case of 2.53. NGC 4546, but not negligible (Fig. 1). Li The photometric analysis has been In these galaxies the presence of re­ performed on frames recorded in band trograde motions should be interpreted V, land at wavelengths around Ha on as arecent acquisition from outside, bar minor axis. the 1.5-m Danish telescope, with expo­ lacking reasonable mechanisms which sure times ranging from 10 to 30 allow such a clear decoupling between ... .. minutes. They have been reduced with angular momenta of gas and stars hav­ the standard ESO-IHAP procedures. ing the same origin. They fit in the wider The photometric zero point of V band frame of SOs with recent interaction, like ~.'" has been obtained using the mag­ the polar ring galaxies (Schweizer et al. \: nitudes reported by Longo and de Vau­ 1983) and confirm the idea that the gas couleurs (1983), while the isophote in­ in SO galaxies has an external origin, as bar~. terpolation has been performed using suggested for the HI by Wardie and the INMP programmes (Barbon et al. Knapp (1986). .\: 1975). Oifferences between gas and star .. kinematics could enhance particular " NGC?~17 3, Results types of orbits. For instance, in the case of NGC 2217 the peculiarities observed Figura 1: The almost face-on SBO NGC 2217 The main properties of the SB 0 galax­ could be explained if the gas moved on (bottom), and its spectrum along the bar's ies observed until now are resumed in orbits belonging to the families of minor axis (top) showing the opposite tift of Table I, where in addition to the galaxies anomalous orbits (X-tube, see Van Alba­ emission and absorption lines. This is the present in our sampie we added NGC da et al. 1982), which appear retrograde second case of counterrotation between gas and stars found in SB0, after NGC 4546 936 (Kormendy 1983, 1984) and the four when seen from the galaxy pole. This is (Gal/etta 1986). galaxies studied by Jarvis et al. (1988). actually the orientation at wh ich, in an We could resume the more interesting almost face-on galaxy such as NGC findings: 2217, we observe the triaxial ellipsoid represented by its bar. These orbits visible for a whole night in the allotted were originally invoked (Van Albada et 3.1 Velocity fjelds observing period. We selected these al. 1982) to explain the motions ob­ galaxies in an effort to have systems Two galaxies were found where gas served in the class of elliptical galaxies with all possible orientations of the bar, and stars rotate with similar but oppo­ with minor axis dust lanes (Bertola and from side-on to end-on, and with all site streams. This is one of the more Galletta 1978) and represent a typical possible inclinations of the galaxy remarkable features found, and fully un­ case where a single family of orbits disk, from edge-on (i = 90°) to face-on expected, which induces some interest­ should be discriminated from the heap (i = 0°). Among these, 10 systems have ing reflections on the nature of the gas in of galactic orbits, as discussed in the al ready been observed in the previous SO galaxies. Observing NGC 4546, an introduction. runs at La Silla and 7 of these have been apparently normal edge-on SBO, we de­ Another family of orbits that should be fully reduced. tected the presence in the same spec­ disentangled from the mass of the A number (from 4 to 7) of long slit trum of emission and absorption lines others, in the very special case of NGC spectra at different P. A. were taken for tilted because of the rotation but in 4546, is that of the retrograde Z-tube each galaxy, with exposure times rang­ opposite way (Galletta 1986, 1987). The (Contopoulos and Papayannopoulos ing from 60 to 120 minutes, in order to amplitude of the observed motions be­ 1980, Heisler et al. 1982, Teuben and map as much as possible the velocity tween gas and stars is of the order of Sanders 1985). These orbits within the field. The spectral region observed at 400 km S-1 along the apparent major bar are elongated parallel to the bar the 3.6-m telescope ranged from 3500 axis. This gas lies in a - 5 kpc wide disk intermediate axis, a direction perpen­ to 4500 A, including Ca 11 Hand K, not yet relaxed on the main galaxy dicular to the most part of the innermost G-band and the eventually present )..)., 3727-29 [Oll] doublet. The spectral region selected at the 2.2-m ranged from 4800 to 5800 A, due to the different 200 spectral response of the RCA CCDs 150 adopted, and includes Mg I, Fe and 0 ~ bar major axis many other bands. When present, H ß Q) ! j Vl 100 j I ...... and )..)., 4959-5007 [0111] doublet were E ,H~~~~H jI~ also measured. In addition, the spec­ 2:. 50 tl trum of some giant stars of low rotation­ > al velocity were recorded each night, for 0 • use in the reductions as template stars of zero velocity dispersion. All the spec­ -50 o 10 20 30 40 50 tra have been reduced by means of the r (arcsec) ESO-IHAP procedures and analysed us­ Figura 2: The velocity curve along the bar of NGC 7079, folded about the nucleus. The typical ing the FQ method (Sargent et al., 1977) wavy pattern of the velocity curve, found in six more galaxies (Bettoni 1988), is clearly visible. modified as in Bertola et al. (1984) to Different symbols refer to the two opposite sides of the rotation curve. 52 Table I: Properties of the sao galaxies studied. The main geometrie eharaeteristies of eaeh galaxy, as the estimated inelination i with repeet to the sky or the presenee of ionized gas, are listed. In the following eolumns are also indieated: the presenee of Z-motions (perpendieular to the galaetie plane) for almost face-on galaxies; the symmetry of the bar velocity eurve with respeet to the galaxy nueleus; the presenee in it of symmetrie oseillations; the trend of the bar velocity dispersion. A question mark indieates data not yet fully redueed.

GEOMETRY BAR KINEMATICS

Name Bar-Disk i lonized Presence 01 Presence 01 'Double wave' °bar Re!. Notes P.A. gas Z-motions asymmetry effect

NGC 936 59° 49° no - yes yes IIat 1 NGC 1543 - 0° no on both axes no no - IIat 5 Double bar NGC 1574 70° 28° no most on min. axis yes yes peaked 5 NGC 2217 - 24° laint spiral arms most on min. axis ? ? ? 7 Gas retrograde IC 456 79° 48° yes - yes yes flat 6 NGC 2983 51° 4r no - no yes peaked 4 NGC 4371 70° 66° no - ? ? ? 7 NGC 4442 10° 71° no - ? ? ? 7 NGC 4477 58° 24° no on both axes no yes flat 5 NGC 4546 45° 71° irregular disk - no no peaked 2 Gas retrograde NGC 4643 - 0° no most on min. axis yes no peaked 7 NGC 4684 0° 75° spiral arms, - no no Ilat 7 filaments NGC 4754 60° 59° no - yes no flat 5 NGC 6684 61° 48° no - yes yes flat 3 NGC 7079 43° 43° yes - no yes peaked 7

Rererences: 1: Kormendy (1983), 2: Galletta (1987) 3: Bettoni and Galletta (1988), 4: Bettoni et al. (1988), 5: Jarvis et al. (1988), 6: Bettoni (1988), 7: Bettoni and Galletta, in preparation.

stellar orbits, whose major axes lie on Galletta 1988, Fig. 5) and NGC 2983 the values of the general veloeity fjeld the bar's major axis. Sinee gas motions (Bettoni et al. 1988, Fig. 4). Similar (Fig. 2). This veloeity profile might os­ in NGC 4546 are retrograde with respeet shapes were deteeted also in NGC 1574 eillate around zero (systemie veloeity) to the stars, the elongation of the and NGC 4477 (Jarvis et al. 1988), as for galaxies with bar close to the ap­ isoveloeity lines in the two veloeity fields weil as in NGC 7079. In all these galax­ parent disk minor axis (e. g. NGC 6684) (gas and stars) appears at P. A. at al­ ies the veloeities rise from the nueleus or might be superimposed to the main most 90° between them, eonfirming in outward, then reverse their direetion rotation, if the bar is eloser to the major this fortunate (and maybe unique) ease reaehing minimum (or negative) values axis (e. g. NGC 936). This trend must not the existenee of this theoretieally ex­ and turn baek to inerease their am­ be eonfused with loeal minima of the peeted orbits. plitude, reaehing near the end of the bar rotation eurve whieh appear outside the Bar kinematies are sometimes asymmetrie with respeet to the whole galaxy. As generally performed in the reduetion of rotation eurves, the veloeity eurve derived from eaeh speetrum was NGC 4643 folded about the nueleus and the sys­ ° bar major axis temie veloeity. In many eases the rota­ • bar minor axis tion eurves elose to the bar differ from 1400 the generally symmetrie veloeity field. In these galaxies, bar motions are aetually symmetrie, but with respeet to a point not eoineident with the galaxy nueleus, () and independent of the apparent '"Vl symmetry of the light distribution. This E1300 -'<: effeet should refleet areal misalignment of the bar within the galaxy or the pres­ > enee of dark and asymmetrie matter. It is not yet clear whieh of these effeets eould be relevant. 1200 A typieal "wave pattern" of the bar rotation eurve has been revealed in all the galaxies with intermediate inelina­ tion with respeet to the sky so far ob­ served. This effeet, produeing a "double 1100 L::L:i:=i::::::I:::i::::L:::::L=-t-L----L-L.-.L-l...--L---L-..L...l---L-.l...-LL--L....J-.J -60 -40 -20 0 20 40 60 wave" appearanee of the unfolded ve­ r (arcsec) loeity eurves, was brought into evidenee Figure 3: Velocity eurves for the face-on galaxy NGC 4643 (shown in the inset), after a gaussian during the observations of IC 456 smoothing of 2". Along the bar, only an asymmetrie pattern is visible (open squares) with (Bettoni 1988) by eomparing its bar ve­ oseillations of - 40 km S-7. On the eontrary, the velocity inereases as the speetrograph slit is loeity eurve with that already published twisted away from the bar going toward the minor axis (full diamonds). At this P. A., symmetrie of the galaxies NGC 936 (Kormendy motions with an amplitude of 160 km S-7 are deteeted. Due to the orientation of the galaxy, 1983, Fig. 4 b, NGC 6684 (Bettoni and these motions should be perpendieular to the galaetie plane. 53 bar where the bulge fades in the lens or in another component, as is the case of NGC 3945 (Kormendy 1982, Fig. 3) and NGC 4684 NGC 2983 itself, where the two phenomena are present (Bettoni et al. Vband 1988, Fig. 4). On the contrary, no wavy trend around the systemic velocity was de­ tected in NGC 4546 (Galletta 1987), in NGC 1543 and NGC 4754 (Jarvis et al. 1988) or in the two remaining galaxies of the sampie so far reduced (see Table I). As an intrinsic feature, the observed wavy trend around the systemic velocity should be due to the presence of retro­ grade stellar streamings confined to some radii along the bar. A similar fea­ ture is expected in many models of barred galaxies which need some amount of retrograde motions. Among these the Freeman (1966 a, b) homogeneous bar model, the N-body simulation by Zang and Hohl (1979) and the self-consistent model by Pfenniger (1984a, b). The last study suggests that three-dimensional stellar motions within a barred galaxy should periodically re­ verse the sense of rotation because of vertical instabilities. In addition, there is the possibility that these motions are produced by a combination of bar and disk streamings in some sectors of the galaxy plane, as suggested by L. Sparke (private communication) on the basis of the analysis of an N-body model of a barred galaxy (Sparke and Sellwood Ha 1987). A more detailed analysis of this property is in progress, but a clear pic­ ture will be available only when (and if) Figure 4: The inner regions of NGG 4684, in a GGD frame (V band) taken at the 1.S-m Danish the observations of a larger galaxy sam­ telescope. The bar is seen side-on, along the galaxy major axis. In the inset, the nucleus of the galaxy, at the same scale, observed in Ha light. The continuum near Ha has been subtracted. pie are performed. At this moment we Dust lanes, spiral arms and filaments are visible. can only say that this effect is observed only in galaxies with inclination between 28° and 53°, lacking in almost face-on or edge-on systems. Stellar and gas streaming perpen­ the case of NGC 1574, NGC 4477 and tribution of the angular momentum in a dicular to the galaxy plane was de­ may be NGC 2217, whose isophotal stellar system since its protogalaxy tected. This is another unexpected axial ratio is close to 0.9 (- 27" of phase. point, since it is generally believed that inclination for disks as f1at as 0.25). But Many bars have flat velocity disper­ the main part of ordered motions takes this hypothesis cannot explain the not sion profiles. In 7 systems over 12 the place parallel to the main galactic plane. negligible velocities found in NGC 1543 bar velocity dispersion is characterized On the contrary, it has been observed in and NGC 4643, as weil as the amplitude by a constant trend, with the peak of the all the 6 almost face-on galaxies con­ of that observed in the remaining bulge velocity dispersion eventually sidered (see Table I). In the case of NGC galaxies. superimposed. An example of this effect 4643, for instance, the velocities along As discussed previously, the gas in is offered by NGC 6684 (Bettoni emd the bar are quite low (- 40 km S-1), while NGC 2217 should stream in one of the Galletta 1988) or by NGC 4477 (Jarvis et a wide rotation along the bar minor axis two possible families of anomalous or­ al. 1988). This could indicate that the is present, with velocity differences of bits (see Schwarzschild, 1982), while bars are uniformly hot. A more detailed 160 km S-1) (Fig. 3). A similar condition this hypothesis is less plausible for the analysis is necessary to answer this is present in NGC 1574 (Jarvis et al. stellar motions, distributed in a wider point. 1988) and NGC 2217, while comparable range of energies and not streaming amounts of rotation in both axes were according to a specific orbit. It would be 3.2 Photometry and Ha imaging detected in NGC 1543, and NGC 4477 interesting to know if unbarred galaxies (Jarvis et al. 1988). In some of these also share this property, but until nowall Many systems have elongated or tri­ cases, this effect should be due to a not requests for observing time on this axial components. This agrees with the fully face-on orientation of the galaxy problem have been rejected. In any results of statistical works on rings and and/or to the fact that the bar's minor case, this feature must be clarified also bulges (Kormendy 1979, Athanassoula axis is close to the major axis of the from the theoretical point of view, hav­ et al. 1982, Buta 1986). A typical collec­ disko Looking at Table I, this could be ing interesting implications on the dis- tion of these properties is represented 54 by NGC 6684 (Bettoni and Galletta Barbon, R., Benacchio, L., Gapaccioli, M., Kormendy, J., 1983, Astrophys. J, 275, 529. 1988). In this galaxy, the ring is elon­ 1975., Astron. Astrophys. 51, 25. Kormendy, J., 1984, Astrophys. J, 286,132. gated parallel to the bar, in a direction Bertola, F., Bettoni, 0., Rusconi, L., Sedmak, Longo, G., de Vaucouleurs, A., 1983, Univer- sity of Texas Monographs, N. 3. close to that of the line-of-sight. This G., 1984, Astron. J, 89, 356. Bertola, F., Galletta, G., 1978, Astrophys. J, Pence, W.D., Taylor, K., Freeman, K. G., de gives the system the unusual aspect of a 226, L 115. Vaucouleurs, G., and Atherton, P., 1988, galaxy with a ring rounder than the disko Bettoni, D. and Galletta, G., 1988, Astron. Astrophys. J, 134. But the bulge also is triaxial. Its Astrophys., 190, 52. Pfenninger, 0., 1984a, Astron. Astrophys., isophotes are not aligned at the same Bettoni, 0., Galletta, G. and Vallenari, A., 141,171. P. A. of the disk and the observed stellar 1988, Astron. Astrophys., 197, 69. Pfenninger, 0., 1984b, Astron. Astrophys., motions appear to have a "kinematical Bettoni, 0., 1988, Astron. J, submitted. 134,373. line of the nodes" not coincident with .Buta, R., 1986, Astrophys. J Suppl. Ser., 61, Sargent, W. L. W., Young, P. Y., Boksenberg, the disk major axis, both typical signs of 609. A., Shortridge, K., 1977, Astrophys. J, 212, 326. triaxiality. In addition, the bar appears Gontopoulos, G. and Papayannopoulos, Th., 1980, Astron. Astrophys., 92, 33. Schwartzschild, M., 1982, Astrophys. J, 263, displaced by - 2" from the nucleus of Ghristiansen, J. H. and Jefferys, W. H., 1976, 599. the galaxy along its major axis. Off-cen­ Astrophys. J, 205, 52. Schweizer, F., Whitmore, B.G., and Rubin, tring of the bar (but along the bar's Freeman, K.G., 1966a, Mon. Not. R. Astr. V.G., 1983, Astron. J, 88, 909. minor axis) is actually observed in some SOG., 133, 47. Sparke, L.S. and Sellwood, J.A., 1987, barred galaxies, but generally appears Freeman, K.G., 1966b, Mon. Not. R. Astr. Mon. Not. R. Astr. Soc., 225, 653. in late spirals, as NGC 4027 (Christian­ SOG., 134, 1. Teuben, P.J., and Sanders, R. H., 1985, Mon. sen and Jefferys 1976, Pence et al. Galletta, G., 1986, The Messenger, 45,18. Not. R. Astr. SOG., 212, 257. 1988). But with respect to the remaining Galletta, G., 1987, Astrophys. J, 318, 531. van Albada, T.S., Kotanyi, G.G. and Schwarzschild, M., 1982, Mon. Not. R. galaxies of the sampie, the offset of the Heisler, J., Merri!, 0., Schwarzschild, M., 1982, Astrophys. J, 258, 490. Astr. SOG., 198, 303. NGC 6684 bar is quite a peculiar fea­ Jarvis, B. J., Dubath, L., Martinet, R. and Ba­ Wardie, M. and Knapp, G. R., 1986, Astron. ture. con, R., 1988, Astron. Astrophys., in press. J, 91, 23. Short and smooth spiral arms, some­ Kormendy, J., 1979, Astrophys. J, 227, 714. Zang, T.A. and Hohl, F., 1979, Astrophys. J, times forming an incomplete ring, Kormendy, J., 1982, Astrophys. J, 257, 75. 226,521. appear in same of the studied systems, such as NGC 2983, NGC 4546 and NGC 6684. This feature is brought into evi­ dence by means of a decomposition of the images in the main galaxy compo­ Comet Tempel 2 Turns On nents, performed by means of IHAP (see Earlier this year, observers all over the 1873 and has since been seen at no less Bettoni et al. 1988). This procedure also world began to observe Comet Tempel than 18 apparitions. indicates that in our sampie the bars 2, a prime object for the NASA Comet This time it was recovered already in contain less than 20 % of the total light. Rendezvous Asteroid Flyby mission December 1986, by Tom Gehreis and The gas in the SB Os observed is con­ (CRAF) in 1993. This short period comet his collaborators with the Spacewatch centrated in disks or in complex struc­ (P = 5.29 years) was first observed in camera. At that time the heliocentric tures with spiral arms. The Ha imaging of some of the galaxies considered, which possess ionized gas (6 out of 11), indicates a spiral or a not relaxed struc­ ture. NGC 2217, for instance, has faint spiral arms in a structure that should be perpendicular to the bar's major axis. This structure recalls the gas in the warped plane wh ich crosses the minor­ axis dust-Iane galaxies (Bertola and Galletta 1978) and seems to confirm the assumption made previously concern­ ing matter in anomalous orbits. The more extended and complex structures observed in NGC 4546 and NGC 4684 (Fig. 4) represent two more cases of gas whose irregularity strongly suggests a recent acquisition from the outside. Again, as indicated by Wardie and Knapp (1986) for the neutral gas, there are indications of an external origin of most of the gas in SO galaxies.

This work is dedicated to our daugh­ ter Anna, who decided to be born during the drafting of this paper.

References Athanassoula, E., Bosma, A., Greze, M., Schwartz, M. P., 1982, Astron. Astrophys. 107,101.

55 2 distance was over 4 Astronomical Units. 9-15, 1988 by O. Jewitt and J. Luu, still - 2.0 x 2.0 arcmin . North is up and East From earlier apparitions, it is known showed an stellar-like image of the is to the right. On this date, Tempel 2 that the onset of activity is rather abrupt, comet nucleus. However, as can be was 135 million km from the Earth and normally about 60-80 days before seen on the picture, GGO images ob­ the heliocentric distance was 278 million perihelion, but at least once (in 1951) up tained on May 16 and 17 with the Oanish km. The magnitude of the central, bright to 100 days before. Since the perihelion 1.5-m telescope clearly show that the part was about 17. would be passed on September 16.7, activity has started: the comet is In the meantime, as reported by sev­ 1988 this time, it was expected that this surraunded by a diffuse coma, which eral journals (e.g. Sky and Telescope, turn-on would happen in June, or extends over 1 arcmin or more. The September 1988, page 236), unfortu­ perhaps already in late May. This means active phase must therefore have nately no funding was received for that the cometary nucleus has been started rather early this time, at least GRAF in fiscal year 1989. This means heated sufficiently to enable gas and 104 days before perihelion. that the launch will have to be delayed dust to escape, so that a coma and a tail The picture, which is a composite of to the fall of 1994 and that therefore are created. eleven 10-minute exposures through a another comet will have to be targeted, Observations fram Kitt Peak on April Johnson V filter on May 17, has a field of probably Gomet Wild 2. R. M. WEST

First Infrared Images with IRAC A. MOORWOOO, G. J=INGER andA. MONETI, ESO

Following its installation and first test a selection of images illustrating the Messenger (52, 50) IRAG provides for in July, a second test of the new infrared kinds of results being achieved in the infrared imaging in the standard J, H, K, array camera has just been completed various camera modes and also to draw and L filters and offers two novel at the 2.2-m telescope. Having returned the attention of potential users to a features compared with existing com­ after the official deadline we have not problem with the detector wh ich has mon user cameras elsewhere - on line had time to prepare a very detailed arti­ developed since the Announcement for selection of four magnifications be­ c1e for this Messenger. We nevertheless period 43 was issued. tween 0.3 and 1.6 arcsec. per pixel and wanted to take this opportunity to show As described in the June issue of the the provision of circular variable filters

Figure 1: tRAG mounted on the F/35 infrared adapter at the 2.2-m tetescope.

56 good read noise (-400e) and average Unfortunately, by October this array dark current (-1000 eis at 47 K) was found to have mysteriously de­ characteristics and a large weil capacity veloped a new fault in the form of sever­ (7·106 e). Unfortunately, about 10% of al lines of saturated pixels on alternate the pixels scattered over the array ex­ columns starting at one side and ex­ hibit excess dark current and saturate tending over about a quarter of the after relatively short integration times array. The rest was still useable but, as spoiling the appearance of the raw im­ planned already in advance, this array ages. They are rather easy to remove was exchanged after a few nights for during image processing, however, another with a 2.3 flm cutoff which it either by median filtering or by combin­ was of interest to test for future applica­ ing two images shifted by a few pixels. tions. This array exhibits a factor of 10 This latter is quite straightforward using lower dark current and relatively few the lens wheel in IRAC which provides a saturated pixels but is only 32 x 32 and more accurate (0.1 pixel) means of dis­ cannot, of course, be used longward of the K band. The cause of the degrada­ Figure 2: The H/I region G 333.6-0.2. placing the image than moving the tele­ K (2.2 11m) band; 0.8 areseclpixel; average of scope. With on-chip integrations of tion of our 64 x 64 array is still not 10 40-s exposures; sky subtraeled; median 10 minutes and equal numbers of alter­ known although some type of surface filtered. nate source and sky exposures the ac­ contamination is a possibility, in wh ich tual 3 0 detection limits achieved in case its performance can probably be 1 hour of observing time were J - 20.5, restored by a special c1eaning tech­ (CVF) for narrow band imaging at H - 20, K - 19.5 mag per pixel and the nique. R - 50. No real problems with the cam­ faintest sources actually measured were As only very few of the October data era itself or its associated electronics the components of the double quasar have been reduced, the images shown and software have been experienced so Q1548+114A, Bat K-17 and here were all obtained with the 64 x 64 far. The detector used in July was a 17.5 mag (-1 % of the sky). As ex­ array in July except for Jupiter, ob­ 64 x 64 pixel Hg: Cd : Te/CCD array pected, the weil capacity also proved served with this array in October, and (Philips Components) with a long sufficient for broad band imaging at NGC 1097 (32 x 32). The only "clean­ wavelength cutoff around 4.7 flm, very L (3.8 Ilm) and even M (4.7 flm). ing" applied has been the application of

Figure 3: The H/I region NGG 3603. Upper panel- K band; 0.8 areseclpixel; average of8 40-s exposures; sky subtraeted; median fil­ Figure 4: The Galaetie Gentre. Upper panels - K band; 0.8 areseclpixel (Ieft) and 0.3 areseel tered. NB. Ihe blaek spot is due 10 a star in pixel (righl) to show effeet ofzooming; eombination of two 300-s exposures shifted by 3 pixels the sky referenee field. Lower panel ­ (see text); divided by sky. Lower panels - L band; same seales as upper panels bul slightly L (3.8 ,11m) band; 0.8 areseclpixel; average of displaeed due 10 lack of eo-eentring belween the differently eoated lenses used at K and L. 60 1-s exposures made wilh sky ehopping at This ean be avoided by using the same lens with a slight loss of efficieney in one of the bands; the FI35 seeondary mirror. average of 125 1-s exposures wilhout sky ehopping; divided by sky.

57 Figure 5: The galaxy A 1409-65. J (1.25 11m) (upper left), H (1.65 "m) (upper right), K (2.2 pm) lower left); 0.8 aresee/pixel; average of 4 40-s exposures; eombination of images shifted by 3 pixels; sky subtraeted. L band (Iower right); 0.5 aresee/pixel; average of 140 1-s exposures with sky ehopping at the teleseope seeondary mirror. Note the point-like nuc/eus at L whose size has been estimated at 0.3 aresee using 1 0 speekle teehniques at the 3.6-m teleseope (Moorwood, Veron-Cetty and Perrier, in preparation). a median filter or the replacement of bad pixels using two images displaced by 3 pixels as described above. Some of the images have been flat fielded by ratioing with the sky while in others the sky has only been subtracted. The actual ob­ serving parameters and reduction pro­ Figure 6: Jupiter (Det. 88). 0.8 aresee/pixel; cedure used in each case are specified sky subtraeted; median filtered with high in the figure captions. threshold. Upper panel - K band. Middle Having offered IRAC in period 43 on panel - CVF at 2.07 pm. Lower panel - CVF the basis of the July test results we are at 2.1211m showing effeet of pressure in­ now in the unfortunate position of not dueed absorption by moleeular hydrogen in the planetary atmosphere. Note the appear­ knowing exactly which array will be anee of a moon on the right side in the CVF available at that time. The 64 x 64 array images whieh were taken later than that in K. has to be returned to the manufacturers who have promised to do their best Figure 7: Nuelear region of the galaxy NGC 1097. 32 x 32 array; K band; 0.8 aresee/pixel; either to restore its performance by sur­ average of 5 60-s exposures; median filtered (but almost identieal to raw image); divided by face cleaning or to replace it with a sky. Note that the "spiral arms" are eomposed ofstar forming regions within about 10 aresee of detector of comparable performance. the aetive nueleus. An improved array is also not excluded, depending on the results of a new Hg : Cd : Te production technique de­ veloped specifically to improve the uni­ MIDASMemo formity and reduce the fraction of bad pixels. 1. Application Developments format. The plotting package has been At the moment therefore we remain extended with commands to draw coor­ confident of being able to offer our first The astrometrie package is currently dinate grids in different geometrie pro­ Visiting Astronomers at least the per­ being developed. Coordinate transfor­ jections. Also, some basic commands formance as advertized and illustrated mations as weil as usual coordinate pro­ have been added to increase the flexibil­ here. jections can be performed on tabular ity of the package. For the same pur- 58 pose the SET/PLOT command is en­ Tektronix, and Masscomp. This first re­ stations. Institutes with other image dis­ hanced: the user now has full control lease contains almost all basic MIDAS play devices should upgrade their over the size of the plot symbols and commands although some of the appli­ IDI implementation to the standard. can produce publication quality plots. In cation contexts are not yet available. Another component which varies signifi­ the ASSIGN/PLOT, SEND/PLOT and This refers to a few very complex pack­ cantly from system to system is the in­ SET/PLOT an option has been built in to ages such as INVENTORY, ROMAFOT, terface to magnetic tapes. This may produce plots on a PostScript laser CCD and Long Slit. They are expected have to be rewritten at the individual printer (see below). to be ready for a minor MIDAS release sites. The upgrade of ROMAFOT to the 89 FEB which will be sent out to sites portable version of MIDAS is nearing that have the 88 NOV version. This minor 3. MIDAS Hot-Line Service completion. This includes several signif­ release will also resolve bugs and prob­ icant improvements of the package lems reported by users. The 88 NOV re­ The following MIDAS support services such as proper handling of undersam­ lease includes several improvements can be used to obtain help quickly when pled images which is essential for e.g. upgraded plotting routines, stan­ problems arise: EFOSC data and eventually also for HST dard IDI routines, a terminal indepen­ • EARN: MIDAS @ DGAES051 images. dent interface and a package for • SPAN: ESOMC1 ::MIDAS INVENTORY is now in the process of IRSPEC reductions. • Tlx.: 52828222 eso d, attn.: MIDAS . being migrated to the portable MIDAS The graphics commands use the HOT-UNE and at the same time is being improved portable version 3.2 of the Astronet • Tel.: +49-89-32006-456 in a number of aspects. Graphic Library (AGL) wh ich supports a Users are also invited to send us any large variety of devices such as suggestions or comments. Although we do provide a telephone service we ask 2. Portable MIDAS TEK 4010/14, VT 640, PostScript and X Window systems V 10.4 or V 11. Since users to use it only in urgent cases. To The 88 NOV release of MIDAS is the we have only recently had access to make it easier for us to process the first to support multiple operating sys­ version 11 of X Window, the 88 NOV requests properly we ask you, when tems namely, VAXNMS and a long list release only provides IDI routines for possible, to submit requests in written of UNIX like systems. It has been im­ Gould IP8500 and X Window V 10.4. form through either electronic networks plemented on machines from DEC, IBM, MIDAS will, however, support version 11 or telex. SUN, Apollo, Nixdorf, PCS, Stellar, Bull, of X Window as a standard for work- ESO Image Processing Group

MIDAS Benchmarks of Work-Stations

P. GROSB0L, K. BANSE, C. GUiRAO, 0. PONZ, R. WARMELS, ESO Image Processing Group

1. Introduction 2. Work-Stations installation and tests were performed, the actual benchmarks could not be The number of computer systems on A typical configuration of a work-sta­ made due to lack of time. which MIDAS can be used has in­ tion for interactive image processing The tests were carried out at the ven­ creased substantially with the introduc­ with MIDAS consists of a 32-bit CPU dor sites on demonstration models tion of the portable version. MIDAS is with a floating point processor, 8 Mbyte wh ich meant that some variation in the now available for both VAXNMS and main memory, 300 Mbyte disk, colour actual configuration was unavoidable. UNIX systems. This opens the possibili­ display with approx. 1000'8008-bit pix­ The whole installation and tests were ty of using a large number of work­ els and an Ethernet interface. The soft­ typically done in less than two days. For stations which offer many interesting ware requirements are a UNIX or VMS that reason it was impossible to spend features for astronomical image pro­ operating system, X Window system for time on optimizing the individual sys­ cessing such as high performance per the display and standard compilers for tems. It is estimated that differences in cost unit, integrated display options and Fortran-77 and C. A number of systems configuration and optimization may in­ good interactive response. with roughly these specifications were troduce up to 25 % variation in the To improve the situation for interac­ tested. The systems are listed in Table 1 benchmark results. tive MIDAS users within ESO, it was including their CPU type and operating decided to shift parts of the image pro­ system. cessing from the VAXNMS systems to In addition to standard work-stations, 3. Scope of Benchmarks work-stations. For this purpose, an early a few larger systems were included for version of the portable MIDAS was im­ comparison e.g. VAX8600, Trace 14, The benchmarks were made to mea­ plemented and tested on a wide variety Targon 35 and Alliant. MIDAS was im­ sure the typical real time performance of of work-stations. A set of typical MIDAS plemented and tested on all the sys­ interactive usage of MIDAS on single applications were used to benchmark tems; the installations on the Trace 14 user work-stations. For this reason the the performance of the different sys­ and the Alliant were done remotely over tests included a number of actual, fre­ tems used in single user mode. These a modem line. The conditions for the quently used MIDAS applications. The performance tests were done in the benchmarks of these two machines important quantity for the user is how spring of 1988 and used to make a final were not weil controlled and for this fast the different systems respond. This decision for the purchase of image pro­ reason the results were omitted. For the depends on the performance of the sys­ cessing work-stations for ESO. IBM PC-RT 6150 system, only the basic tem in three main areas, namely:

59 1. scheduling of new application pro­ elapsed time indicates the system over­ total through-put. Further, tables are grammes, head in executing applications and used in the final analysis of data where 2. speed of disk 1/0 operations, and opening files. the speed of interaction is crucial. Due 3. CPU power. 2. Scaling. The scaling operation of an to the size of the table used in the These quantities were measured with image involves access to the data, a benchmark and the operation done, the different MIDAS applications. Since multiplication and additions with con­ time is set largely by the floating point MIDAS makes most calculations in sin­ stants, and finally the creation of a new CPU performance and only to a lesser gle precision floating point, the CPU file. A frame with 512*512 real pixels extent by the 1/0 bandwidth. performance measured refers mainly to was used in this benchmark. This opera­ The scaling and median tests were the operations with real values. The ex­ tion is used whenever an image is dis­ done also with larger images. For sys­ ecution time of the benchmark pro­ played. The speed of a simple arithmetic tems with main memory large enough to cedures was measured in elapsed time operation is in most systems so high avoid swapping or paging, the elapsed since this indicated the interactive re­ that the performance is Iimited by the times showed a linear increase. When sponse of the system in single user 1/0 rate of the disko This test indicates this was not the case, a dramatic de­ mode. the 1/0 bandwidth of a system which in crease in performance could be ob­ It was not within the scope of these turn shows how many data can be pas­ served. tests to derive absolute values for per­ sed through in a given time. The benchmarks were, in most cases, formance. The lack of optimization of 3. Median. The median benchmark executed several times and showed the individual applications and general applies a median filter on a real image little variation. The results are given in time constraints meant that the bench­ with 512*512 pixels. In contrast to scal­ Table 2 where the mean elapsed time in marks could be used only as a relative ing this task requires a significant seconds is listed. Some values could measure of performance for the tested number of operations per pixel and is not be obtained due to minor errors, pre-release version of MIDAS. Better re­ thus Iimited by the CPU performance of time limitation and lack of disk space. sults can be achieved by tuning both the the floating point unit. Although tasks of Especially the 1/0 limited tasks (e.g. application programmes and systems this type are executed less frequently in scaling) are sensitive to the fragmenta­ parameters. The changes in the hard­ interactive sessions, it shows the basic tion of the file system on which the data ware configuration mayaiso change the speed with which any CPU demanding are located. This may introduce a sys­ results in a non-linear manner. At the process can be executed. tematic bias. Due to wrong compiler time of the tests, graphics and image 4. Table. The benchmark performs a options in two tests (i.e. HP 350 and display applications were not yet im­ number of mathematical operations on SUN 3/60) software floating point com­ plemented. They were therefore not in­ a table with 13 columns and 10,000 putations were used although hardware cluded in the benchmarks. The bench­ rows. The calculations include arithme­ units existed. The Masscomp MC 5450 mark procedures will be further de­ tic operations and trigonometric func­ system can allocate contiguous files on veloped and improved to provide a tions. Tables are often used during re­ disk which improves the 1/0 perfor­ standard performance test of MIDAS on duction of data in MIDAS. The efficiency mance significantly. This option was not computer systems. This implies that of these functions is essential for the used since it is a real-time extension some tests may be modified in the fu­ ture. Reference to the values presented here should therefore include the ver­ TABlE 1: Systems on which MIDAS has been implemented. sion number, i.e. MIDAS Benchmarks Vendor-Model GPU-type Operating System Version 0.9. The results cannot be used HP 9000-835 RISG HP-PA HP-UX to estimate the performance of the sys­ tems with other packages than MIDAS HP 9000-350 MG 68020 HP-UX 6.0 due to differences in the usage of re­ Apollo ON 4000 MG 68020 Aegis sources. Apollo ON 590 MG 68020 Aegis SUN 4/110 SPARG SunOS 4/4.0 4. Benchmarks SUN 4/260 SPARG SunOS 4/3.2 Four of the 18 different benchmark SUN 3/60 MG 68020 SunOS 3.5 procedures used are discussed here. Bull SPS 9/830 RISG-4 SPIX931.5 They represent the general results of the benchmarks and indicate the perfor­ Tektronix TEK 4301 MG 68020 UTeK 2.4 mance of the systems with respect to Matra MS 1326 MG 68020 SunOS 3.4 CPU, 1/0 and scheduling. The four tests Matra MS 1306 MG 68020 SunOS 3.4 were: 1. Schedule. This procedure Masscomp MG-5450 MG 68020 RTU scheduled a simple MIDAS application IBM PG-RT 6150-125 ROMP AIX 2.1 which opened an image file and read a Prime PXGl 5500 MIPS R2000 UNIX SysV 3.1 descriptor. This was repeated a total of OEG ~lVAX 11 VAX Ultrix 2.0 100 times. The execution of this test depends on the time it takes to schedule OEG VAX 8600 VAX VMS 4.7 a new programme and access simple OEG VAX 3500 VAX KA650 Ultrix 2.2 information in a file. This type of opera­ PGS Gadmus 9900 MG 68020 MUNIX 5.2 tion is done very frequently in MIDAS procedures and is therefore important to PGS Gadmus 9933/RG MIPS R2000 MUNIX 5.2 estimate how fast a system can perform Nixdorf Targon 35 RISG UNIX SysV long sequences of MIDAS applications. Alliant FX/1 Alliant Goncentrix Since the actual task only accesses a single piece of information in the file, the Multiflow TRAGE 14 WLlW UNIX 4.3 BSO

60 to UNIX. The values for the VAX 8600 TABLE 2: Benchmark results in seconds elapsed time. are given for comparison and were Vendor-Model Schedule Scaling Median Table Remarks also obtained with a single user on the HP 9000-835 33 13 33 34 system. HP 9000-350 - 39 118 - Software FP 5. Discussion Apollo ON 4000 167 14 - 47 Apollo ON 590 142 13 - 50 The results in Table 2 reflect the be­ haviour of the systems in three different SUN 4/110 25 7 61 30 aspects: Process scheduling in the first SUN 4/260 30 8 41 22 column, 1/0 bandwidth as scaling oper­ SUN 3/60 46 27 124 90 Software FP ation in the second column and floating point performance in the third column. Bull SPS 9/830 24 7 - 17 The table operations included in the Tektronix TEK 4301 97 15 - 46 fourth column give an indication of both Matra MS 1326 40 11 - 32 SUN 3/260 1/0 bandwidth and floating point perfor­ - 63 SUN 3/60 mances. Matra MS 1306 39 16 The times for process scheduling Masscomp MC-5450 73 20 - 79 Standard file system show a surprising spread with almost a Prime PXCL 5500 31 17 58 - factor of 10 between the fastest and OEC!-t VAX 11 115 30 157 89 slowest system. There is little correla­ tion between the speed of starting a OEC VAX 8600 167 10 30 37 new task and general CPU perform­ OEC VAX 3500 38 11 51 44 ance. The Aegis and VMS operating PCS Cadmus 9900 130 34 109 - systems have a significant lower per­ formance than typical UNIX systems. PCS Cadmus 9933/RC 17 13 27 37 This is especially odd in the case of Nixdorf Targon 35 39 10 45 15 VMS, since MIDAS executes application tasks differently for VMS and UNIX machines: In UNIX machines a child process is started and the task ex­ ecuted in the context of that sub­ exceptions is the Bull SPS 9 system machines usually have a much higher process. In VMS a subprocess is cre­ based on SYS V but using a very effi­ rate of executing instructions than CISC ated only once, then, the applications cient disk controller. The SUN 3-4/260, processors. This is not reflected in the are executed in the context of that sub­ VAX 8600, PCS and SPS9 used SMD benchmarks because they mainly mea­ process. Therefore, the measured time type controllers with 8 inch disks which sure the performance of the floating for VMS is just the time for running an give higher performance than the SCSI point co-processor. executable task in an existing sub­ or ESDI interfaces available on most For the evaluation of the total per­ process, not for creating a child process other systems. formance of the systems for interactive as weil. The single precision floating point image processing the four quantities The 1/0 bandwidth indicated by the performance is given by the median fil­ shown in Table 2 were used. The nor­ scaling task depends on three major ter. It is interesting to see how the per­ malized performance for each test was factors namely: physical speed of disk formance of relatively cheap work-sta­ defined as the median divided by the drive and interface, block size of the file tions slowly approaches that of machi­ elapsed time given. The final rating was system and implementation of hashing nes like the VAX 8600. One may even based on the mean of the normalized techniques. Due to the two latter fac­ argue that some work-stations have too performances. This added more weight tors, most BSD UNIX systems have at high CPU performance compared to to the 1/0 performance than to CPU present a higher disk 1/0 performance their 1/0 bandwidth when used for in­ speed wh ich is reasonable for interac­ than those based on SYS V. One of the teractive image processing. The RISC tive systems.

MIDAS Models Interstellar/lntergalactic Absorption Lines M. PIERRE, 0. PONZ, ESO

1. Introduction available at La Silla. Very little effort has features superimposed on a continuum been dedicated to the complementary wh ich mayaiso contain emission lines. Most of the current tools available in problem, the development of analysis The resulting output spectrum is com­ MIDAS, as weil as in other image pro­ tools to bring physical interpretation puted at a given instrumental resolution cessing systems for Astronomy, are de­ closer to the observed data. This article and can therefore be used for a direct dicated to the first step of data reduc- . describes a new MIDAS context ­ comparison with observations (provided tion wh ich is to eliminate the instrumen­ CLOUD - that allows such an analysis, the lines are resolved). This is particulary tal signatures from the observations. namely, to model the absorption of in­ suitable for high resolution spectra, as This is clearly the main priority for such a terstellar or intergalactic clouds as ob­ observed by ESO instruments such as system and continuous development is served in spectroscopic data. Caspec. going on to support all the instruments The programme models absorption The main characteristic of the pack-

61 age is that, on the basis of astrophysical USER : SMAL 11 jUdgement and interpretation of results, 12 (mast?: the user can interactively determine the SYNAGS IC model parameters: the user elaborates {den 1.1 f tea t lon: on the model that will then be compared MAXWELL + DAMP IN( to the observations. No chi-square Area: evaluation is performed by the pro­ X: 800 lO 10G0 gramme wh ich is then not to be consid­ y: 1 1.0 1 ered as an extension of the fitting pack­ Scales: age. ~ X: 0.109 , 8 The software will be available on an y: 0. 999E-02 experimental basis in the next release of Mlnlmum: e.228 MIDAS and is also available in the port­ Mal( tmum: 1.00 able version running under UNIX and Da'e: 13-SEP-88 VMS. T ,me: 09: 52: 05

2. Description of the Method The processes of formation of inter­ stellar or intergalactic absorption lines can be simply described by atoms Ca IIH aggregated in discrete clouds along the line of sight, between the observer and an emitting source. Each cloud is assumed to produce a 3.9G5 3.9Gl 3.9G9 3.911 3.913 3.915 3.911 single line whose position is determined POSition< lE'lIll*3) by the mean velocity of the cloud and whose depth is related to the number of absorbers. Atoms within the same cloud U5ER : 5MALlI have a certain velocity dispersion and [mast?: therefore tend to broaden the line pro­ SYNAG51C file. In our case, we adopt a Maxwellian (den"l ftCatlon: velocity distribution, purely thermal, so MAXWELL + DAMP ING that Gv a 1. Moreover, because of the Area: finite Iifetime of the excited state of the X: 100 lo 340 corresponding atomic transitions, lines y: I to I have also a natural intrinsic width. This Scales: X: 0.101 phenomenon, while negligible with re­ , 8 spect to thermal broadening for rather . y: 0. 999E-02 low column densities, tends to dominate '"y Minimum: 0.228 when lines become saturated. The re­ .0' MdXtmum: 1. 00 ~ c sulting absorption profiles are the so­ ~ Dale: 13-SEP-88 called "Voigt profiles" and are those de­ .= TLme: 09:41:43 rived by the programme. In addition to the commands which perform the calculations, the package contains: •A catalogue of atomic constants, stored in a table wh ich can be updated by the user. •A table containing the user's guess for the cloud model; i.e., for each ab­ 3.930 3.932 19~ 19~ 19~ 3.940 3.942 sorbing cloud: wavelength, column den­ POSllLon \ 113··3> sity, thermal width, atomic transition. Figure 1 a, b: Model (smooth line) tor the Hand K eomponents eompared with the observations •A table containing parameters for (step tunetion). The two eomponents have been modelled simuftaneousfy and eorresponding possible gaussian emission lines to be fine identitieations are given in Tabel1. added to the continuum. • Coefficients for the continuum, assumed to be polynomial, and the de­ 3. Creation of absorption features on age is given in the forthcoming version finition of the sampling domain of the this image according to the cloud model of the MIDAS Users' Guide. An on-line resulting images. table and convolution of this spectrum tutorial, based on high resolution data, The modelling proceeds as folIows: with the PSF. is also available. 1. Creation of the instrumental response 4. Comparison of the resulting spectrum (PSF), as a gaussian of given FWHM. It with observations. The user can then 3. An Example may be also any other experimental modify some of the input parameters function supplied by the user. and repeat the operations until the As an example, we present here the 2. Creation of a 1 D image containing the agreement is found to be satisfactory. modelling of the series of Call absorp­ continuum and possible emission lines. A complete description of the pack- tion doublets in the spectrum of SN 62 1986G in NGC 5128 observed with Cas­ TABLE 1. Cloud model fable. Acknowledgements pec (D'Odorico et al. 1988). The programme ALAS developed by The two images (components K and H Seq.no. VELOCITY BVAL N M. Pettini was a source of inspiration of the doublet) have been pre-reduced 1 -38.37775 13.00 0.5400 E+12 during the design of our package. so that the continuum is normalized to 2 -4.395716 13.00 0.6600 E+13 We are indebted to S. D'Odorico for 1. Sampling is 0.05 A per pixel and the 0.1700 E+12 providing the data used in our example, instrumental resolution, 0.22 A. 3 +102.8715 5.000 and thank D. Baade for useful sugges­ The final model consists of 12 absorp­ 4 +241.7751 8.000 0.3000 E+12 tions. tion clouds (Table 1). 5 +256.8906 15.00 0.5500 E+12 Figure 1 shows the resulting image 6 +313.5179 8.000 0.4000 E+12 References convolved with a gaussian PSF of 7 +339.8785 7.000 0.2500 E+12 D'Odorico, S., di Serego Alighieri, S., Pettini, 0.22 A FWHM, compared with the ob­ 8 +379.1504 13.00 0.6300 E+13 M., Magain, P., Nissen, P. E., Panagia, N.: 1988, submitted to Astronomy and As­ servations. 9 +418.3698 11.00 0.4300 E+13 Comparison of these results with trophysics. "A study of the interstellar 10 +443.2433 8.000 0.1300 E+13 medium in line to NGC 5128 from high those derived by a similar package 11 +459.1050 4.500 0.8000 E+12 resolution observations of the supernova (STAR-LINK) shows complete agree­ 12 +486.2531 16.00 0.6300 E+13 1986G." ment. The example discussed here is also Column 1: velocily of lhe clouds in km/so demonstrated in the MIDAS on-line Column 2: broadening parameter (V 2kT/m) in km/so TO ALL READERS 2 tutorial. Column 3: column densily in number of atoms/cm . Please make sure that the card which accompanies this issue of ESO Book Now Available in Five Languages the Messenger is returned, if you want to continue to receive the With the publication of French and able in five languages. journal. The editors Spanish versions now planned before The publishers are: Danish (Rhodos; the end of the current year, and a sec­ Copenhagen), English (Springer Verlag; ond edition in Danish - the first one was Berlin, Heidelberg, New York), French STAFF MOVEMENTS sold out in less than two months last (Les Editions de Physique; Paris), Ger­ Arrivals year -, the ESO Book "Exploring the man (Birkhäuser Verlag; Basel, Boston), Europe: Southern Sky" will soon become avail- and Spanish (Equipo Sirius; Madrid). PERON, Micheie (F), Astronomical Applications Programmer SCHNEIDER, Karin (D). Secretary SLATER, Roswitha (D), Accounts Clerk VAN DE SPRENG, Jacob (NL), Project Contral Officer

Chile: GEMPERLEIN, Hans (D), Infrared Instrumentation Engineer GUNNARSSON, Lars (S), Associate (Microwave Engineer SEST) NYMAN, Lars (S), Associate (Telescope Scientist SEST) Departures Europe: ARSENAULT, Robin (Canadian), Associate A Celestial Riddle .? bright, round object is the planetary IOVINO, Angela (I), Fellow nebula PK 274 +3'? 1. The object to BUONANNO, Roberto (I), Associate Look at this picture, reproduced the right of it is ... just some galactic from one the ESO Schmidt plates ob­ stars. Chile: tained for the red half of the joint ESO/ Is somebody trying to tell us some­ MAUGIS, Michel (F), Electronics SERC Atlas of the Southern Sky. The thing? Technician

Christian Perrier Receives Award On October 19, 1988 Christi an Perrier in ESO. He spent three years at La Silla as a received the "Prix DIGITAL - Societe Fran­ French Cooperant and ESO Fellow and one <;aise des Specialistes d'Astronomie" for year thereafter at Garching putting into op­ his outstanding research in infrared inter­ eration the ESO Infrared Specklegraph and ferametric imaging. The price is awarded to its data reduction software. Several ESO young scientists, less than 37 years of age, Messenger articles have reported on his who have arecord of scientific research of work. ESO is proud of Christian Perrier's high quality and of international stature. success and congratulates him on this weil Much of Perrier's work has been done with- deserved award. J. BECKERS

63 Mi visita a La Silla dei edificio para el ND. Eche de menos el telescopio suizo y 10 vine a descubrir mas tarde cerca de mi dormitorio. Creo que los EI Director General de la ESO, Harry van astronomos suizos deben de gozar la cerca­ der Laan, me invito a La Silla como consultor nia al holel. duranIe el periode de la realuminizacion y el Fue lindisimo trabajar nuevamenle junto a ajustamienlo oplico dei telescopio Schmidl Hans Schuster, Guido y Oscar Pizarro en el de la ESO. Esta invilacion me alegro mucho telescopio Schmidl. La mantencion realizada porque no solo me dio la oportunidad de por el personal lecnico camino sin proble­ estar un tiempo en el telescopio Schmidl, mas. EI unico obstaculo fue el tiempo; dura sino lambien de encontrarme con muchos baslanle tomar las placas necesarias para amigos en Chile. Ya en el aeropuerto de los distintos tests. Sin embargo, logramos Tobalaba en Santiago, a la salida hacia la con exilo un bastante buen ajustamiento dei monlaiia, me enconlre con algunos de mis telescopio. antiguos colegas, Daniel Hofstadl y su espo­ Durante mi estadia en La Silla fui por pri­ sa Sonia, Wolfgang y Suse Eckert, Erich mera vez a Coquimbo y La Serena con Erich Schumann, Nelson Labrin, Bernardo Leon y Schumann para presenciar la compra de los al astronomo frances Fran<;:ois Spite. Mien­ comestibles. Vi con sorpresa las impresio­ tras viajaba desde el aeropuerto de Pelicano nantes cantidades de comida que se lrans­ hacia La Silla en un confortable coche, mis portan semanalmente a la montaiia. Uno casi pensamientos remontaron al aiio 1964 cuan­ no se da cuenta dei trabajo involucrado hasla do demoraba 5 horas y media a caballo des­ que se encuenlra la comida servida. de Pellcano hasta La Silla. Deseo agradecer a lodos aquellos que me La Silueta de La Silla ha cambiado consi­ proporcionaron una estadia lan agradable en derablemente con la inslalacion dei SEST y La Silla. ANDR~ MULLER Contents A. Blaauw: ESO's Early History, 1953-1975. I. Striving Towards the Conven- tion ...... 1 A. Blaauw: Setting Up the ESO Historical Archives 3 F. K. Edmondson: The Ford Foundation and the European Southern Observa- tory ...... 7 A. Noels: Paul Ledoux (1914-1988) ...... 10 List of ESO Preprints (September-November 1988) ...... 10 M. Tarenghi: ND Picture Gallery 11 Announcement of an ESO Workshop ...... 11 Where is Phobos 1? 12 Open-House at ESO '...... 12 Upcoming ESO Exhibitions ...... 13 A "Blinking" Satellite...... 14 M. Sarazin: Report on lAU Colloquium 112, on Light Pollution, Radio Interfer- ence and Space Debris (Washington, 13 to 16 August 1988) ...... 14 A. Spaenhauer, C. F. Trefzger, L. Labhardt, S. Gabi: 50 Years of RGU Photo- metry 15 The ESO VLT as fischertechnik-Model ...... 21 L. Woltjer: The Astronomy and Astrophysics Review...... 21 A.A. Chalabaev, C. Perrier, J.-M. Mariotti: Infrared Emission from the Sub- Arcsecond Vicinity of SN 1987A 22 M. Rosa: An Update on the Light Echoes of SN 1987 A...... 28 H.-E. Schuster, R. M. West: The ESO Schmidt Telescope ...... 28 R. Cayrel, I. Tarrab, T. Richtler: Learning About Young Globular Clusters ...... 29 J. Krautter, R. E. Williams: The Nebular Stage of Nova GQ Muscae: Physical Parameters from Spectroscopic Observations 33 T. J.-L. Courvoisier: Violent Activity in the Bright Quasar 3C 273 ...... 37 G. Meylan, S. Djorgovski: UM 425: a New Gravitational Lens Candidate...... 39 A. Acker, G. Jasniewicz: Binary Nuclei of Planetary Nebulae ...... 42 G. Testor, A. L1ebaria, B. Debray: Brey 73: a Multiple Wolf-Rayet Star...... 43 D. Reimers, D. Koester: Spectroscopic ldentification of White Dwarfs in Galac- tic Clusters...... 47 D. Bettoni, G. Galletta: New Results About SBO Galaxies 51 R. M. West: Comet Tempel 2 Turns On ...... 55 A. Moorwood, G. Finger, A. Moneti: First Infrared Images with IRAC ...... 56 ESO Image Processing Group: MIDAS Memo 58 P. Grosb01, K. Banse, C. Guirao, D. Ponz, R. Warmeis: MIDAS Benchmarks of Work-Stations 59 M. Pierre, D. Ponz: MIDAS Models Interstellar/lntergalactic Absorption Lines .. 61 ESO Book Now Available in Five Languages 63 A Celestial Riddle ? 63 J. Beckers: Christian Perrier Receives Award ...... 63 Staff Movements ...... 63 A. Muller: Mi visita a La Silla 64 64