ESO SL9 NEWS BULLETIN ===================== Issue : 6 Date : Friday, July 15, 1994, 12:00 UT (14:00 CEST; 08:00 Chilean time) Items : 6-A: News from La Silla 6-B: New impact parameters to become available 6-C: Further HST observations 6-D: Ultraviolet observations from space 6-A. NEWS FROM LA SILLA Last night (July 14 - 15), the sky was again not perfect: there were many cirrus clouds and a thin high altitude haze made the night "non-photometric" (not useable for highly accurate measurements of light intensities of celestial objects). However, the seeing was quite good at the beginning of the night (0.6 arcsec during the SL9 observations with the NTT, see below), but then deteriorated later on. It seems that we have always been rather lucky with the SL9 observations: this is not the first time that the sky conditions become worse, just after the end of these exposures ! The observers for one of the teams at the 3.6-metre telescope, Ulli Kaeufl (ESO-Garching) and Tim Livengood (NASA, Goddard Space Flight Center, Greenbelt), arrived yesterday. Keith Horne (Astronomical Insitute, Groningen, The Netherlands) arrived later at night, to join his co-observer Remco Schoenmakers at the 90-cm Dutch telescope. The first "SL9/J observers meeting" was held during the afternoon; from now on, there will one daily at 15:30 (Chilean time) to exchange the most recent information. Every day, just after the "tea" at 16:00, the "Infrared" observers will rush to their telescopes to start their observations, already before sunset. Heinz Barwig and Otto Baernbantner at the 1-metre assembled their instrument and succesfully tested it; they are now installing it on the 1-metre telescope. It was realised that the IRSPEC detector has to be warmed up ("baked" in the technical language) to about 300 degrees (this to be compared with its operational temperature of 2 - degrees above absolute zero through cooling with liquid Helium !) in order to to clean it and remove some ions that have been deposited on it during the past weeks. The ESO technical team at La Silla with (bicycle champion) Hans Gemperlein in charge of this operation has promised that everything will be done to get IRSPEC ready before tomorrow noon, so that it is able to observe the effects which may follow in the aftermath of impact A. A total of 35 min exposures on SL9 was obtained with the NTT. The straylight from Jupiter is now so strong that the sky background nearly saturates the detector. It looks as if these may possibly be the last images of SL9 with this telescope ... too bad, it was really a nice comet to observe ! Uri Carsenty and Stefano Mottola continue their observations and have now accumulated a huge number of fine images of Jupiter. Finally, yesterday (July 14) was the Bastille Day, the French national day: the La Silla cooks prepared a lot of really tasty and fine dishes to mark it ! For those who do not know the rules of this "dry" place: there was no red wine to accompany it ! With regard to fireworks, there were also none, but let's wait another day...! 6-B. NEW IMPACT PARAMETERS TO BECOME AVAILABLE Now that fragment A is less than 2 million kilometres from Jupiter (less than 10 arcminutes in the sky) and only 34 hours from impact, further observations are becoming impossible. A concerted, very last attempt will be made tonight with the NTT, but the involved ESO astronomers have serious doubts that they will succeed in detecting this fragment (and probably also B, C and D) in the intensive glare of the nearby planet. However, whatever happens, it is now planned that new impact parameters, based on all available positional data and including the exact times and and locations together with the estimated uncertainties, will be made available from JPL tomorrow, Saturday. This will certainly further narrow down the A and B events and make it possible for the observers around the world to concentrate their efforts at the right time and in the right direction, and will give them the best possible chance to observe (some of) the associated effects. 6-C. FURTHER HST OBSERVATIONS The Hubble Space Telescope is continuing to observe comet SL9 and Jupiter as planned. The Daily Report of the observatory's activities records that observations with the Faint Object Camera (FOC, built by the European Space Agency as part of its contribution to the project) have started and the programme for imaging with the Wide Field Planetary Camera-2 (WFPC-2) is continuing. All observations were completed without problems. The Faint Object Camera made a total of nine images in the f/96 mode. The FOC has a smaller field of view than the WFPC2 but can work at much shorter wavelengths and with higher angular resolution. The observations were made in the far-UV using filters centred around 160nm. The observations began at 21:36 UT on July 13 and the exposures lasted 13 minutes. Different parts of the disc of Jupiter were imaged to study the appearance at this wavelength before the main collisions start. The Wide Field Planetary Camera-2 images were taken between 8:19 and 10:48 UT on July 14 using the camera in Planetary Camera mode. A filter centred at 700nm was used and the Principal Investigator of the programme was Hal Weaver (Space Telescope Science Institute, Baltimore). The aim of this programme is continued refinement of the size estimates of the various components of the comet train. These observations concentrated on the bright fragment G. Spectroscopic observations of Jupiter, the comet and the environment of the planet are also now starting with HST. 6-D. OBSERVATIONS IN THE ULTRAVIOLET Like many other astronomical objects comets emit radiation in the ultraviolet (UV) part of the spectrum. In particular, certain atoms and molecules present in cometary environments are best studied in this wavelength range. Other features of the Jupiter system, in particular aurorae in the planet's atmosphere and the unique interactions between the satellite Io and the torus of material around Jupiter in which it orbits are also ideally studied in the UV. Most UV radiation is absorbed by the earth's atmosphere and hence has to be studied from space. Two satellites devoted to UV astronomy plan to observe the encounter between SL9 and Jupiter during the period of the collisions. These are the veteran International Ultraviolet Explorer (IUE) which has been successfully making UV spectroscopic observations for more the fifteen years and the more recently launched Extreme Ultraviolet Explorer (EUVE). The HST can also perform some UV observations as mentioned above. IUE is jointly operated by NASA, which allocates 2/3 of the observing schedule, and by ESA and the UK Science Research Councils which allocate 1/3. Observing is scheduled in 8-hour shifts and the observatory normally operates 24 hours per day because it is in a high, geosynchronous orbit. Twice a year, there is a period of a couple of weeks when the orbit of IUE takes it through Earth's shadow once per day. The satellite can not be operated while it is in Earth's shadows since there is not enough power from batteries without any charging from the solar panels. Unfortunately, the "summer shadow season" includes the impact week. This means that IUE will lose several hours of operation each day during the the SL9 event. On the US side, three Principal Investigators (PIs) were allocated a total of 30 shifts. Walt Harris (U. Michigan), Tim Livengood (GSFC), and Melissa McGrath (STScI) will be studying the torus, the stratospheric composition, and the aurora. On the ESA-SERC side, two PIs were allocated time. Renee Prange (France) was allocated 21 shifts to study the aurora and stratosphere and Michel Festou (Toulouse, France) was allocated 4 shifts to study the torus. The NASA and ESA-SERC teams will attempt to coordinate their observations, leading to essentially continuous coverage during the impact week. EUVE observes radiation at shorter wavelengths (higher energies) than IUE and hence gets a very different view of objects than any other observatories. It is planned to observe the effects of the comet collision on Jupiter's magnetosphere and Io torus throughout much of the next few weeks. The latest EUVE status report shows that it is functioning very well. Observation of the planet Jupiter in anticipation of its impact with comet Shoemaker/Levy began already on July 13. ---------- This daily news bulletin is prepared for the media by the ESO Information Service on the occasion of the July 1994 collision between comet Shoemaker-Levy 9 and Jupiter. It is available in computer readable form over the ESO WWW Portal (URL: http://http.hq.eso.org/eso-homepage.html) and by fax to the media (on request only). News items contained therein may be copied and published freely, provided ESO is mentioned as the source. ESO Information Service European Southern Observatory Karl-Schwarzschild-Strasse 2 D-85748 Garching bei Muenchen Germany Tel.: +49-89-32006276 Fax.: +49-89-3202362