568. E. Brocato and V. Castellani: Evolutio nary Constraints for Young Stellar Clus Tentative Time-table ters. 11. The Case of NGC 1866. As From the Editors tronomy and Astrophysics. January In accordance with the new man of Council Sessions 1988. agement of ESO, it has been de and Committee Meetings 569. R. Arsenault et al.: A Circumnuclear cided that the ESO Messenger for First Half of 1988 Ring of Enhanced Star Formation in the shall above all be a vehicle of com Spiral Galaxy NGC 4321. Astronomy munication between ESO and the May 2 Users Committee and Astrophysics. February 1988. May 3 Scientific Technical 570. G. Contopoulos and A. Giorgilli: Bifur user community. It is therefore the Committee cations and Complex Instability in a intention to bring the fullest possi May 4-5 Finance Committee 4-0imensional Symplectic Mapping. ble information about new develop Oberkochen February 1988. ments at ESO, technical and scien May 31-June 1 Observing Pro 571. J. Surdej et al.: Search for Gravitational tific, as weil as those of a more gramme Committee, Lensing from a Survey of Highly Lumi administrative nature. In a similar Liege nous Quasars. P. A. S. P. February spirit, we herewith invite contribu June 6 Committee of Council 1988. tions from users, in the form of June 7 Council 572. R. Buonanno et al.: CCO Photometry in articles and also as shorter Letters the Metal Poor Globular Cluster NGC All meetings will take piace at ESO in 7099 (M 30). Astronomy and Astrophy to the Editor. Garching unless stated otherwise. sics. February 1988.
SN 1987A: Spectroscopy of a Once-in-a-Lifetime Event R. w. HANUSCHIK, G. THIMM and J. DACHS, Astronomisches Institut, Ruhr-Universität Bochum, F. R. Germany
When Supernova 1987A in the Large trometers wh ich are especially designed tained enough observing time at large Magellanic Cloud was discovered by lan to achieve the highest possible sensitivi telescopes in order to study and monitor Shelton at Las Campanas Observatory ty for extremely faint radiation sources, it in sufficient detail for a long time. And in Chile on February 24, 1987, it immedi and which therefore are in great danger again, the distance to a supernova be ately became apparent that this would to be destroyed when exposed to a yond our Local Group of galaxies would turn out to be one of the most important naked-eye objecl. This problem has be quite uncertain as compared to the astronomical events in this century. The been discussed in greater detail in two well-defined and well-known distance to timing of the supernova could not have papers by Michael Rosa and O.-G. the LMC. been better - although the light from the Richter (Observatory 104, p. 90 [1984]) So it is not surprising that starting on site of the stellar collapse had to travel a and by Theodor Schmidt-Kaler (same February 25 literally every telescope in distance of as much as 170,000 light volume, p. 234). Furthermore, a nearby the southern hemisphere was directed years before reaching our planet Earth, supernova could not tell us very precise towards the newly-born supernova (un it arrived precisely when state-of-the-art Iy its distance due to the strongly vary fortunately enough, no spectrum exists photoelectrical detectors had become ing amount of dust in the galactic plane. from the night before when lan Shelton available at modern telescopes situated If SN 1987 A were a distant supernova made his discovery). This was of course at the best observing sites all over the such as they are detected almost once also the case at the European Southern world, together with highly sophisti per month, nobody would have ob- Observatory in Chile at La Silla where cated spaceborn instruments working in the X-ray and ultraviolet regions of the electromagnetic spectrum. Even The Proceedings of the ST-ECF Workshop on elementary particle physicists were well-prepared (except for some prob Astronomy trom Large Databases lems with their clocks) to catch two do zens of the neutrinos emitted by the Scientitic Objectives and Methodological dying star thereby providing for the first Approaches time the precise date of the collapse. (Only gravitational wave astronomy has which was held in Garching from 12 to 14 October 1987, have now been still to wait to be born: all potential de published. The 511-page volume, edited by F. Murtagh and A. Heck, is tectors had been switched off or did not available at a price of DM 50.- (prepayment required). Work properly.) Payments have to be made to the ESO bank account 2102002 with Commerz To render the combination of bank München or by cheque, addressed to the attention of privileges for earthbound observers ESO even more impressive, SN 1987 A is just Financial Services at the optimum distance for convenient Karl-Schwarzschild-Str. 2 measurements in the optical window: a 0-8046 Garching bei München galactic supernova would be too bright for professional astronomical instru Please do not forget to indicate your full address and the title of the volume. ments such as photometers and spec-
7 This colour-coded plot ot optical spectra depicts the dramatical spectral evolution otSN 1987A within the tirst 110 days (Feb. 25 to June 14). All spectra have been measured with the spectrum scanner attached to the 51-cm telescope ot the University Bochum located at the European Southern Observatory at La Silla, by observers Joachim Dachs, Reinhard W. Hanuschik and Guido Thimm. The wavelength range covered is approximately 3200 to 9000 Ä, the resolution is 10 A. Absolute fluxes have been colour-coded according to the colour bar on top ot the tigure: colours run trom black (zero flux) to blue-white (5.7 10- 10 erg s-, cm-2 A-'). Time series starts on February 25 (= day 2 since explosion); time scale is continued trom bottom to top day by day. Last date is June 14 (= day 110). one of us (J. D.) happened to work with rather sceptical about this event.) A few wavelength range of these spectra ex the 51-cm telescope of the Ruhr-Univer hours later, the first spectra of the tends from 3200 Ato 9000 A; the stan sität of Bochum. supernova were obtained at La Silla, dard resolution is 10 A. For limited He was working on a long-term pro about 170,000 years plus 42 hours after spectral ranges, spectra at higher reso gramme to monitor spectral and photo the stellar collapse in the LMC. lution, 3 to 5 A, are being obtained in metrie variability in Be stars and original Due to an agreement between ESO addition. Proper flux calibration of the plans were to change instrumentation and the University of Bochum, the spectra is always performed by means just in the afternoon of February 24, Bochum Astronomical Institute has of bright southern spectrophotometric from the spectrum scanner equipped access to this telescope during a total of standard stars such as t Puppis or with a red-sensitive gallium-arsenid eight months per year. In addition, ESO a Crucis. photomultiplier to the single-channel Director General Prof. Woltjer generous This data set will certainly belong to photometer. This plan, however, was Iy agreed to dispense with the four the best available spectra of the super rapidly given up, when the Acting Direc month ESO period at the Bochum tele nova; maybe it is unique. Especially re tor, Hans-Emil Schuster, walked into the scope as long the supernova could be markable is the fact that these high Hotel Dining Room during tea-time - the observed. precision data were obtained with a La Silla astronomers' breakfast - and So Joachim Dachs, and following small-sized telescope and relatively announced the discovery of a superno him, Reinhard Hanuschik, Guido modest equipment compared to large va in the Large Magellanic Cloud. (In Thimm, Klaus Seidensticker, Josef observatory standards. fact, the first lAU telegram did not men Gochermann, Stefan Kimeswenger, Ralf Between May and July when Super tion that SN 1987 A had been discov Poetzel, Gerhard Schnur and Uwe Lem nova 1987 A was below the celestial ered at Las Campanas Observatory, mer established a homogeneous series south pole all night, the 51-cm Bochum only some 30 km from La Silla, and of flux-calibrated spectra obtained with telescope turned out to be the only tele Hans-Emil Schuster first appeared to be a fixed instrumental configuration. The scope at La Silla able to follow the 8 Supernova and to take spectra even at shift, i. e. the decreasing velocities of on February 25; extrapolation back to airmasses as large as 6 (corresponding spectral lines produced in the expand February 23 even yields a velocity in the to zenith distance 80°). For that pur ing envelope. The intensity minimum of vicinity of -40,000 km/s as the velocity pose, observers had to work very Glose the Ha absorption trough is at of the fastest ejecta, that is 13 % of the to the limit switches protecting the tele -17,400 km/s on February 25, falling off speed of light. These enormously high scope against mechanical damage. The to -6,200 km/s by April 14 and velocities are now commonly believed Bochum telescope certainly had never -5,400 km/s by July 14. This general to be responsible for the rather unusual before been pointed at such extreme trend is al ready weil known from other lightcurve of the supernova, i. e. its ex coordinates, at least not intentionally. In supernovae and is due to the fact that tremely long rise until maximum was order to be able to look into the tele outflowing material is diluted by expan reached at a relatively low absolute scope's eyepiece without burdening the sion and is assorted according to in level. telescope axes with its body's weight, creasing velocity and decreasing densi Our continuous time series of 'one author (R. W. H.) invented a rather ty: in the expanding supernova shell, at homogeneous spectral measurements unusual method for guiding the super any time velocity is proportional to dis offers a unique opportunity for safe nova: he installed a rubber rope at the tance from the centre of explosion. identification of the bewildering amount dome wall and, hanging himself on the Therefore, expanding layers may be of absorption and P Cygni-type lines in rope and balancing on top of a ladder opaque at some time and later become the supernova spectrum. Work on line two meters above the ground like a optically thin, revealing lower, less identification and radial velocity deter mountaineer, carefully moved his eye rapidly expanding layers. Thus, in front mination is in good progress. towards the eyepiece which was at of the supernova, optical lines charac Meanwhile, forbidden lines such as some "impossible" position on· top of teristic for the most abundant elements [Ca 11] A. 7291/7363 A and [0 I] A. 6300/ the telescope tube. in the supernova atmosphere (hydro 6363 A have become visible in the By now, more than 300 days of gen, helium) or for particularly strong supernova spectrum marking the begin Supernova 1987 A have been covered transitions (e. g., of calcium or sodium) ning of the nebular phase. As a whole, observationally. The first 110 of them are visible at the highest velocities to the dramatic evolution of the optical are depicted in a compressed manner in wards the observer (corresponding to spectrum of SN 1987 A has slowed the accompanying figure. This plot the lowest discernible densities in the down, but certainly will provide further shows the temporal evolution of the outermost layers of the ejecta), while surprising features in the visible. Our spectral fluxes of SN 1987 A between lines indicating less abundant con time series will be continued as long as 1987 February 25 and June 14. stituents of the atmosphere are pro possible and certainly provide invalu The most obvious advantage of this duced at lower velocites and higher able information about an event wh ich compact representation is the visualiza densities. Then, as time goes on, it is happens at most once in the lifetime of tion of the well-known photometrie possible to look deeper and deeper into an astronomer. lightcurve: the flux distribution changes the ejected atmosphere of the exploding dramatically in the very first days due to star. So far, no indication has been de Acknowledgements the steep decrease of the effective tected for interaction of the ejecta with temperature of the outflowing gas. After the surrounding pre-outburst material, We are greatly indebted to our Insti about day 10 since explosion, flux dis and consequently supernova matter is tute Director, Prof. Th. Schmidt-Kaler, tribution remains approximately con still in free expansion. Decreasing velo who invested a lot of time in organizing stant; the absolute flux level, however, cities therefore result only from decreas financial and personal support for the increases steadily until, around May 20, ing opacity of the expanding shell. continuous observing campaign, and to the visual maximum is reached. After Maximum outflow velocities can be the former Director General of ESO, wards, flux decreases more rapidly. inferred from the blue edge of the ab Prof. L. Woltjer, who generously gave The next obvious feature in this plot is sorption component of the Ha P Cygni several months of ESO time at the 61 the dramatic evolution of the Doppler type profile: we measured -31,000 km/s cm telescope to our observers.
SN 1987A (continued)
It is now one year aga that SN 1987 A during the decay of Cobalt-56. The in of the intensity in the 6-16 keV and in the LMC exploded. Since then, this tensities corresponded to about 0.0002 16-28 keV bands during the first days unique event has continued to fascinate solar masses of exposed Cobalt-56 at a of 1988. The intensity in the first of these astronomers and physicists. The large distance of 55 kpc. No obvious changes bands more than tripled over a two number of scientific meetings, TV pro were observed during this period. Furth week period. grammes, newspaper articles, etc. er y-ray observations were made from Spectral observations in the ul about SN 1987 A at the time of its first balloon experiments flown in October traviolet, visual and infrared regions anniversary prove its popularity. and November and also from a balloon continue. Recent spectra from the IUE During the past three months, since which was launched in Antarctica in ear show UV emission lines from a variety of the last issue of the Messenger, several Iy January. During the three-day flight at ions, e.g. CIII, NIII and possibly Hell important observations have been made altitude 36 kilometres, it observed the and NIV. The first detection of [0111] lines public. The first unambiguous detection supernova during 12 hours, permitting has been made with the ESO 3.6-m of y-rays was made with the Solar Max the registration of a detailed profile of telescope and the Cassegrain Echelle imum Mission satellite. Accumulating the two Cobalt-56 lines. Spectrograph (CASPEC). From the data from August 1 to October 31, 1987, After a long period of rather constant 4363 A line, when compared to the two spectrallines were seen at 847 and emission in the soft X-ray region, the doublet at 4959 and 5007 A, and 1238 keV, respectively; they originate Ginga satellite observed a sudden rise assuming low electron density, a plas-
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