ESO SL9 NEWS BULLETIN ===================== Issue : 9 Date : Monday, July 18, 1994, 08:00 UT (10:00 CEST; 04:00 Chilean time) Items : 9-A: Observations continue at La Silla 9-B: Plumes rising over all impact sites 9-C: Reflections from the moons 9-D: Spectroscopy 9-E: The G-impact 9-F: Press Conference in Santiago 9-A. OBSERVATIONS CONTINUE AT LA SILLA Last night, all telescopes were in action at La Silla. Nine were observing Jupiter and the cometary impacts; the SEST will start today. Much of tonight's effort was directed towards the F-impact, predicted at 00:29 UT. At about 1:27 UT, the plume of impact F was observed at the south-east limb of Jupiter. The plume remained at the limb for more than 20 minutes, indicating that the plume was observed prior to the time it actually crossed the limb. It is inferred that the plume extended to a substantial altitude above the cloud tops; determination of the precise altitude will depend on detailed analysis of the impact-spot's longitude. The F-impact was detected in infrared filters from 5 microns to 12 microns. It later became clear that the spot seen at shorter wavelengths was not F, but that of the E impact that took place about 9.5 hours before and which had in the meantime performed one full rotation. The F spot is unusual in that observations at 10 micron were still possible more than 1 hour after the first sighting (Benoit Mosser) in contrast to the behaviour of the earlier impacts. Klaus Jockers (2.2-metre) reported the following intensity ratios, measured at 01:34 UT: Wavelength I(E)/I(D) total I(E)/I(D)max.surf.brightness 2.09 micron 2.4 1.4 2.36 micron 18.6 4.5 Laurent Jorda and Nick Thomas (DK 1.54 metre), at 02:00 UT found that the F-spot was well visible at 8937 A (CH4), but not at 7271 A (CH4), nor 8920 A (continuum). The spot was elongated in latitude (about 2.5 arcsec). The visibility at 8937 A was confirmed by U. Carsenty at the 60 cm Bochum telescope. Two new infrared images of Jupiter are available in the ESO WWW Portal and also as photographic prints at today's Press Conference at the ESO Headquarters. 9-B: PLUMES RISING OVER ALL IMPACT SITES Following the observations of plumes over the A, B and C impact sites, such features were also observed over those of fragments D, E and F. Although the plumes were of very different size and brightness, the fact that all of the impacts have produced this phenomenon does hint at a certain similarity of these events. The possible, double impact associated with fragment C (item 8-C) soon turned out to be the sighting of the C imapct plume, together with the A-plume that had made one full rotation. While the features seemed to persist rather long when observed in near-infrared light, the far-infrared brightness peaked steeply and then disappeared within one hour or less. This wavelength-dependency is not yet fully understood, but points to a high-altitude phenomenon, in the stratosphere. In addition to the observatories mentioned in yesterday's issue of this Bulletin, the fireball from the impact of fragment A was also observed in the K-band (2.2 micron) with the PtSi camera mounted on the SAAO 0.75 m telescope at Sutherland. It appeared at the predicted location on the SE limb of Jupiter. The images were taken at 30 second vintervals. The earliest faint signs of the fireball appeared at about 20:17-20:18 UT, and at peak brightness it was comparable in brightness to Io. After 10 minutes, the fireball image seemed to change shape, becoming elongated along the limb, presumably as the heated plume settled back. The last traces along the limb were visible at least as late as 20:38 UT. The rise in brightness was much faster than the decline. In the first report from Okayama Astrophysical Observatory (Japan), J. Watanabe, T. Yamashita, H. Hasegawa, S. Takeuchi, M. Abe, Y. Hirota, E. Nishihara, A. Mori and S. Okumura report observing the plumes of C and D with Near-IR camera attached to 188cm telescope at Okayama Astrophysical Observatory, National Astronomical Observatory of Japan. The plume of C appeared 07:17 UT on July 17 on 2.36 micron images and it was brightest around 07:21. The decay phase was followed over one hour. The thermal plume of D appeared 12:01 UT on July 17, and was fainter than that of C. The SPIREX (South Pole) fragment D data were significantly compromised due to the sudden onset of low blowing snow. The telescope was heroically cleared of accumulated snow by Joe Spang of the AMANDA project, and John Briggs of the ATP project, in strong winds at temperatures of -60 degrees Celsius. The impact of fragment D was detected just before 11:55 UT (July 17) with the CASPIR infrared camera on the Australian National University 2.3 -metre telescope and the IRIS instrument on the Anglo-Australin Telescope at Siding Spring. Both the CASPIR 2.34 micron images and the IRIS K-grism cubes revealed a faint flash that faded within seconds; it was four times brighter than the fragment C impact site (Peter McGregor, Mark Allen, David Crisp, Vikki Meadows, Stuart Lumsden and Jonathan Pogson). Calar Alto reported the detection of the fireball from fragment E with the 3.5-metre telescope in the 2.3 micron band. The event was first noted at 15:17:30 and rapidly increased to more than 30 times the brightness of Europa. By 15:23, the fireball has dimmed to less than Europa's brightness. At 18:26 UT, three spots were visible, a bright one just past the central meridian, a fainter one approaching the central meridian, and the faintest one just coming over the East limb. The positions of the spots corresponded to the predicted locations of fireballs E, A, and C, respectively. At 2.3 micron, the brightest spot was 15-20 times fainter than Io, and the fainter spots were down by further factors of about 1.5 and 2.2. SPIREX detected the fragment E impact site shortly after expected impact at 15:18 UT on July 17, at a comparable brightness to fragment A, at a wavelength of 2.36 microns. This data only became available 12 hours later as the South Pole communications satellites are only intermittently visible from this distant site (Mark Hereld, Hien Nguyen, Bernard J. Rauscher, Scott A. Severson Astronomy & Astrophysics Center, University of Chicago, USA). Impact E was seen at 10 microns with the CAMIRAS camera mounted on the Nordic Optical telescope at about 15:17 UT. It was fainter than impact A seen on July 16 (French-Swedish-Spanish team) 9-C. REFLECTIONS FROM THE MOONS Heinz Barwig and Otto Bearnbantner observed the light of the Jovian moons during the F-impact, but due to non-photometric conditions, it will be difficult to decide whether a reflection of the initial flash has been observed. The astronomers will continue these difficult observations and hope for better sky conditions tomorrow. Mike A'Hearn has performed CCD imaging at the Perth observatory (Western Australia) of Io, Europa, and the limb of Jupiter did not reveal any obvious flashes associated with the impact of fragments D and E. D. Rabinowitz and H. Butner at the Las Campanas observatory (just north of the La Silla observatory) may have obtained an interesting result. The believe that Io may have changed colour during the time that fragment B impacted Jupiter. The spectrum became increasingly red starting around 02:50 UT (July 17) compared to its colour 20 minutes later and 3 minutes earlier. The reddening continued to increase until 2:53 UT. Then the color started to drop back to the color we consistently observed from 2:57 until 3:07 UT. These observations were obtained with a coronograph/spectrograph built by Steve Larson of the University of Arizona. If Io's colour change is the effect of reflected light from the impact, then the observations imply a duration of 7 minutes for the impact flash from fragment B. This would be an indication that fragment B was a diffuse cloud of large meteors by the time it hit Jupiter. 9-D. SPECTROSCOPY Spectroscopic observations of the plumes will be extremely interesting in order to determine their composition. Will they for instance contain unknown molecules which come from the inner part of the cometary fragments or from deep down in the Jovian atmosphere. Near IR spectra were recorded with the IRSPEC spectrometer at the 3.5-metre NTT Telescope with a 4.4 arcsec slit aligned along the parallel of the impact sites. On July 17 around 01:00 UT, the 2.12 micron H2 quadrupole line was detected with a resolving power of 2000 at the position of the A impact site as it moved along the jovian disk. On July 17, 22:30 UT, H3+ has been detected in 4 transitions around the strong 3.534 micron line, with a resolving power of 1700. The region of the emission appears significantly extended in longitude with respect to the site of impact C (T. Encrenaz, R. Schulz, J. A. Stuewe, G. Wiedemann), A team of Milagros Ruiz, Chad Engelbracht, George and Marcia Rieke, and Patrick Frawley observed the fragment A impact site with a near infrared spectrometer on the Steward Observatory 90-inch telescope. The spectrum of the plume, with the spectrum of the belt next to the plume subtracted off, is flat and featureless between 2.1 and 2.4 microns. If the plume were frozen gas particles, most candidate materials would have features in this range. The data were obtained between 00:00 and 02:00 on July 17. Sang Kim, Christophe Dumas, Jay Elias and Richard Elston have unambiguously confirmed CH4 nu3 line emissions, which appeared in their IRS/CTIO(1.5-m) spectra taken on the first impact area (A) around UT 0:30 (July 17). They made a sophisticated model containing Jupiter and Earth atmospheres and including Doppler shift between Jupiter and Earth. The agreement between the model and the observed emission structure is almost perfect. The covered spectral range is between 3.47 and 3.6 microns. They did not see any notable increase in H3+ emission around 3.53 microns, where a H3+ complex occurs. Monitoring the H3+ ionospheric lines at 3.5 microns with CGS4 echelle spectrometer on UKIRT, Mauna Kea, Hawaii, Steve Miller, Mary-Frances Jagod, Tom Geballe and Tim Brooke saw a fivefold brightening of the emission around the time of impact of fragment B (around 02:50 UT on July 17) on the east limb of Jupiter. The spectrometer slit was approximately aligned on the nominal impact latitude. This faded over 90 minutes. Matt Griffin, Andre Marten, David Naylor, Gary Davis and Greg Tompkins observed the HCN 4-3 line at 354.505 GHz on the James Clark Maxwell Telescope. They tracked on the position of fragment B for over 1 hour, but did not detect anything to antenna noise. Observations of the location of the fragment C impact point over a 30-minute period as it rotated into view produced a detection of HCN. The line half-width is about 10 km/s. Subsequent observations did not result in a confirmation of the detection, but Jupiter was setting and the system temperature rapidly increasing. It is therefore not possible to say whether or not the effect was short-lived. The CGS4 instrument on UKIRT detected dramatic changes in the spectrum near 3.5 micorn at the location where the C fragment struck Jupiter. In addition to a bright continuum (where there previously was essentially none), the relative strengths of pre-existing emission lines of H3+ changed and many new lines appeared, very few of which are identified by us at present. In particular, at the wavelength of a previously undetectable "hot band" transition of H3+, a bright line appeared whose strength surpassed that of all other pre-existing H3+ lines. A second line, unidentified at present, succeeded in saturating its central pixel in a ten second exposure. Some of the lines seem considerably (Doppler) broadened, but, due to the high density of spectral features, confirmation will have to wait until after the observers get some sleep. The emission faded with a 1/e time of roughly 15 minutes. (Tom Geballe, Mary-Frances Jagod, Steve Miller and Tim Brooke). Observations were also conducted with the Fourier Transform Spectrometer on the 3.5-metre Canada-France Hawaii Telescope. Impact C was observed at the limb at the expected position. A strong, broad emission was observed (near 3.3 micron) which could correspond to methane thermal emission. This emission was observed to decrease strongly within a few minutes. The impact sites A and C were observed farther from the limb within a CO 1-0 filter (between 4.6 - 4.8 micron). Some variability in the spectra is observed compared to a region outside the impacts. Further analysis of the data will be necessary to determine if continuum variations can explain the observed variability, or if some molecular absorption of Jupiter constituents are changed. No obvious variation is observed within the CO lines. (J.-P. Maillard, P. Drossart, J. Caldwell). 9-E. THE G-IMPACT The nominal time is 09:29 CEST this morning. It is expected that the first reports will begin to come in soon after 10:00 CEST. We shall give more information in tomorrow's issue. 9-F. PRESS CONFERENCE IN SANTIAGO On Sunday, July 17, at 12:00, ESO organised a Press Conference at its offices in Vitacura, to inform the Chilean media about the important observations that were made the night before of the first impact. More than 50 journalists were present, together with the various Chilean TV channels and CNN. ESO astronomer Patrice Bouchet presented the latest news and described the dramatic events of the night before. Printed material and photos were distributed, and the many questions bore witness to the great interest and desire for knowledge about this unique event. There were many reports in TV and the newspapers in Santiago will today undoubtedly publish much of this information. ---------- 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