Central Bureau for Astronomical Telegrams
IAUC 6020: 1993e
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Circular No. 6020
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)
Z. Sekanina, Jet Propulsion Laboratory, writes: "Preliminary
results of analysis of CCD photometry obtained with the Hubble
Space Telescope's Planetary Camera in late January, late March, and
early July suggest that the deconvolved signal for the largest
fragment in each nuclear condensation does not appear to depend
strongly on the law employed to subtract the contribution from the
dust cloud within about 0".35 (equivalent to about 1350 km in late
January, 1100 km in late March, and 1200 km in early July) around
the brightest pixel. Two different laws employed for the
brightness distribution of the extended source, about exp[-(rhoE2/2
sigmaE2)Enu] and about [1 + (rho/sigma)Enu]E-1 (where rho is the
angular distance from the source's center and sigma and nu are
parametric constants), imply the presence of a major point source
[defined as a body that is characterized by a single point-spread
function (PSF)] in the center of most of the condensations and
offer consistent values for the dimensions of the largest fragments,
which for an assumed geometrical albedo of 4 percent in the R
filter and a phase coefficient of 0.035 mag/deg yield the effective
diameters listed below. In addition, most of the brightness
profiles imply the presence of isolated clumps of slightly elevated
signals, which fit the PSF's profile and may represent companions
that recently split off from the parent fragment. Most of them may
break up further before they can be detected from the ground. Their
positions are found to be independent of the brightness law assumed
for the extended source, but their numbers and configurations vary
with time. Their signals suggest effective diameters generally
between 1 and 2 km (about 1 km is the smallest size that the HST
can individually detect at the comet's distance). Following are
listed the fragment designation, its largest effective diameter (km)
in Jan., Mar., and July, and the number of possible companions
detected during the same times: F = 16, 2.3, -, -, 1, -, -; G = 15,
4.2, 3.6, -, 2-4, 6-8, -; H = 14, 3.2, -, -, 2, -, -; P1 = 8a, 1.3,
<1, -, 2, -, -; P2 = 8b, 2.4, -, -, 3, -, -; Q1 = 7a, 3.9, 3.0,
3.7, 2-5, 2-3, 3-5; Q2 = 7b, 3.2, 1.6, 2.4, 2, 2-4, 1-2; R = 6,
2.7, 2.2, -, 0, 2, -; S = 5, 3.6, -, -, 6, -, -; T = 4, 1.4, -, -,
1, -, -; U = 3, 1.3, -, -, 0, -, -. The peak of the dust cloud is
found to be displaced with respect to the primary fragment in the
general direction away from the sun. Although the evidence points
to an apparently continuing disintegration of the large fragments
in numerous discrete events, objects a few km across still seem to
have been present in early July, and the temporal variations in the
effective diameters are likely to be primarily a rotational effect
of strongly irregular shape."
1994 July 15 (6020) Daniel W. E. Green
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