Central Bureau for Astronomical Telegrams
IAUC 6021: 1993e
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Circular No. 6021
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
Telephone 617-495-7244/7440/7444 (for emergency use only)
TWX 710-320-6842 ASTROGRAM CAM EASYLINK 62794505
MARSDEN@CFA or GREEN@CFA (.SPAN, .BITNET or .HARVARD.EDU)
PERIODIC COMET SHOEMAKER-LEVY 9 (1993e)
For the Hubble Space Telescope (HST) observing team, H. A.
Weaver, Space Telescope Science Institute, reports the following
results from their analysis of HST WFPC-2 images and FOS spectra taken
up to and including July 14: "From July 14 images of fragments G = 15 and
H = 14 it appears that the inner comae are becoming extremely elongated
along the direction of the train. During the period from late January
through the end of June, the isophotes in the inner 0".7 deviated from
spherical symmetry by only about 15 percent (i.e., the ratio of the major
and minor axes of the best-fitting ellipse was only about 1.15). In
the July 14 images the deviation from spherical symmetry is about 90
percent. This change in morphology appears to be associated with a
'stretching' of the coma rather than a fragmentation of the nucleus,
because the images still show sharp cores much like those observed
previously by HST. These core brightnesses (defined as the sum over
3 x 3 pixel boxes centered on the peak pixel; 1 pixel = 0".046) have been
decreasing monotonically with time, but the decreases since January are
only in the range of about 30-50 percent. This decrease in the core
brightness could be due to a decrease in the dust content of the core,
as opposed to a decrease in the brightness in the unresolved point source.
With regard to the temporal variation in somewhat larger apertures
(e.g., 0".3, 1".1 and 2".1; cf. IAUC 6019), our detailed analysis shows
very little change for most fragments. A variation of about 5-10 percent
is typical, but fragment V = 2 shows a roughly 30-percent drop from
January to late June. There is a small 'hump' in the spatial brightness
profile of fragment P2a = 8b1 at about 0".2 from the peak pixel, but
otherwise the variation in brightness and morphology associated with
this fragment has not been particularly noteworthy. No emission features
are seen in a 60-min FOS spectrum of the region 222-328 nm with the
3".7 x 1".2 aperture placed near fragment G = 15. No further
spectroscopic exposures of the comet will be made with HST."
''Final'' astrometric observations of most of the nuclei
have been reported by R. M. West, European Southern Observatory, from
his measurement of images obtained on July 14.97 and 14.98 UT by
P. Dubath with the New Technology Telescope at La Silla. The final
observation of nucleus C = 19 was obtained at ESO on July 14.00 UT.
The final observation of nucleus B = 20 was reduced by W. Owen from
an image obtained by A. and D. Monet with the U.S. Naval Observatory's
1.5-m astrometric reflector on July 13.17. Nuclei A = 21 and D = 18
were last recorded at ESO on July 12.99 and nuclei T = 4 and U = 3
on July 7.98.
1994 July 16 (6021) Brian G. Marsden
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