------------------------------------------------------------------- THE ASTRONOMER Electronic Circular No 859 1994 July 18 19.35UT Ed:Guy M Hurst, 16,Westminster Close, Kempshott Rise, Basingstoke, Hants, RG22 4PP,England. Telephone/FAX(0256)471074 Int:+44256471074 INTERNET: GMH at AST.STAR.RL.AC.UK or GMH at GXVG.AST.CAM.AC.UK ------------------------------------------------------------------- PERIODIC COMET SHOEMAKER-LEVY 9 (1993e)/COLLISION WITH JUPITER ESO SL9 Bulletin provides news of the impact of fragment B. The B fragment was much brighter than A in images of the comet train and was hence expected to have a more dramatic impact. The unexpectedly clear detections of the A impact in the infrared and also at shorter wavelengths from HST hence led to expectations of something even more dramatic when the B fragment hit Jupiter about seven hours later. Conditions at Chile were then less good with significant cloud but there were high hopes of detecting the impact in the infrared. This impact was visible from many US observatories but unfortunately not from HST which was on orbits taking it through the "South Atlantic Anomaly" where much higher radiation levels make most observations impossible. Soon after the expected time it became clear that this impact was in fact considerably less prominent than the first one as brief reports of failures to detect anything started to come in. The first arrived at 4:04 UT from Palomar where imaging at 2.35 micron and 7.9 micron with the 5-metre telescope had failed to see anything up to 03:55UT. Soon afterwards the similar lack of success at ESO, with both the 3.6-metre and 2.2-metre telescopes (observing at 9 micron and 2.2 micron respectively) was reported to the "mail exploder" distributing electronic mail to the observers around the world. These were followed by negative reports from the Cerro Tololo Interamerican Observatory (CTIO) using the 4-metre telescope and a detector working at 1.7 micron and 2.3 micron, these observations, from a site close to La Silla were also affected by cloud. Nothing was seen from Stewart Observatory in Arizona, USA either with imaging at 2 micron or spectroscopy covering a wavelength range from 2.0 - 2.4 micron. Similar conclusions were reported by the Apache Point Observatory using the 3.5-metre. This instrument is the second generation of the SPIREX camera at the South Pole which reported a positive detection of A in the same filter. However, not all results were negative. The largest optical telescope in the world, the W. M. Keck Observatory (10-metre) on Mauna Kea, Hawaii, recorded a faint but clear plume at the expected position starting at 02:56 UT and fading around 03:13 UT. This detection was confirmed soon afterward by spectroscopy at 3.5 micron using the UK Infrared Telescope (UKIRT) on the same mountain where a fivefold brightening around the expected time of the collision was detected at the limb of the planet. It faded over 90 minutes. Observations were made in a narrow "L" band around 3.35 micron. These weaker detections suggest that the impact was not totally different in type, but just much weaker than that of A. Was this because the B-fragment was smaller than A, or did it plunge deeper into the atmosphere so that there was less to be seen above the impact site? Guy M Hurst ---------- Forwarded message ---------- Date: Mon, 18 Jul 1994 21:49:18 +0100 (BST)