Central Bureau for Astronomical Telegrams
IAUC 6026: 1993e
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Circular No. 6026
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)
Further reports, received in part via the SL9 message center,
indicate considerable confusion concerning the detection of the
impact of fragment F = 16. This had been predicted to occur 95 percent
of a jovian rotation after the E impact, but because the F prediction
was early this impact point almost coincided with the E impact point,
which was still very active. Nevertheless, it appears that the plume
from the F impact was observed at the European Southern Observatory,
but only at wavelengths of 5-12 microns. B. Mosser, T. Livengood
and H. U. Haufl made the detection on July 18.060 UT, and the plume
remained at the limb for more than 20 min.
As expected, the impact of fragment G = 15 was the most
spectacular so far, and the first report received was that from H. Nguyen
at the South Pole. The University of Chicago's South Pole Infrared
Explorer (SPIREX), a 0.60-m telescope operating mainly at 2.36 microns,
reported this event on July 18.320 UT. CASPIR 2.34-micron images and
IRIS K-grism cubes (cf. IAUC 6024) showed an initial flash on July 18.315
(attributed to fragment G2 = 15b), half as bright as the C-impact site,
brightening by about a factor of four on July 18.316 and then stable
until 18.319, at which time the G (or G1 = 15a) impact saturated
the detectors and produced brilliant diffraction spikes. After July 18.340
the G impact site had decreased in brightness in K to about four times
that of the C impact site, but it was detectable in IRIS bands from J to M,
as well as in the visible. S. Nakano, Sumoto, Japan, communicates that
many amateur astronomers, some using telescopes of aperture only 0.10 m,
have visually detected the G impact site; according to A. Nakamura and
K. Ito the region--larger than the Great Red Spot--was very dark, with a
wave to the west like that of site A.
Although some observers have suggested that there is substantial
drifting of the impact sites in longitude, M. Brown, P. Nicholson and
others find that the rotational velocity of the impact sites is in fact
very close to that of System III (period 0.413538 day). As further
impacts occur, and as many of the impact sites persist, confusion is
likely to mount. The following tabulation gives the first
central-meridian passage on July 18 UT for each impact site as derived
from Nakano's predictions and adjusted (with a constant shift) to
recent observations of sites A, C, E and G: site G, July 18.017 UT;
D, 18.025; S, 18.028; R, 18.035; Q, 18.056; B, 18.070; N, 18.070;
H, 18.101; F, 18.138; T, 18.145; E, 18.161; V, 18.161; A, 18.199;
C, 18.241; P, 18.269; K, 18.307; U, 18.311; W, 18.314; L, 18.386.
1994 July 18 (6026) Brian G. Marsden
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