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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
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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







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Date: Mon, 18 Jul 1994 21:49:18 +0100 (BST)