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IAUC 6363: C/1996 B2

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                                                  Circular No. 6363
Central Bureau for Astronomical Telegrams
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
Phone 617-495-7244/7440/7444 (for emergency use only)

     Contrary to what was implied, the analysis in the second paragraph
of IAUC 6360 by Z. Sekanina of a highly decelerated fragment of the
comet's nucleus does not involve the observations discussed in the
first paragraph.  With reference to those observations, and amplifying the
remark about the Hubble Space Telescope observations, H. A. Weaver,
Applied Research Corporation, reports the following, on behalf of
his HST team: "A detailed analysis of several R-band HST WFC images of
the comet taken near Mar. 26.063 UT shows no evidence for companion
condensations of the type described in the first paragraph of IAUC 6360,
either in the raw images or after division by a symmetrical model coma.
WFC pixels are 0".0996 across, and this projects to a distance of 7.6 km
at the comet.  Multiple nuclei with separations of more than about 0".2
would be easily resolved in the HST images.  The inner coma is
reminiscent of the coma of 1P/Halley during the Giotto encounter, with
multiple jets in the sunward-facing hemisphere, the strongest jet
pointing directly toward the projected solar vector.  In contrast to
1P/Halley there is in C/1996 B2 a bright jet that appears to emanate
from the night side of the nucleus, but we cannot rule out the
possibility that the emission is really on the illuminated portion
and only appears to be on the night side because of projection effects
(the solar phase angle being 72 deg).  The remnants of the "knots"
in the tail detected two days earlier by Lecacheux et al. (IAUC 6354)
are clearly seen in the HST images.  We identify at least three separate
entities: a "streak" having a sharp sunward-pointing spike, a faint
condensed feature and an elongated "puff".  The offsets from the nucleus
are Delta alpha = -8".6, Delta delta = -14".6; -8".4, -16".6; and
-9".4,-18".8, respectively.  We cannot yet say anything definite
regarding the size of the nucleus."

     H. E. Matthews, Herzberg Institute of Astrophysics, Ottawa, and
Joint Astronomy Centre, Hilo (JAC); D. Jewitt, M. Senay and T. Owen,
University of Hawaii; J. K. Davies and W. R. F. Dent (JAC); and N. Biver,
D. Bockelee-Morvan, J. Crovisier, H. Rauer and D. Gautier, Observatoire
de Paris-Meudon, communicate: "We detected submillimeter continuum
emission from C/1996 B2 using the James Clerk Maxwell Telescope on
Mauna Kea.  Preliminary estimates of the flux density at 350 and 800
microns are 6.8 +/- 1.3 Jy and 0.55 +/- 0.04 Jy, respectively, on both
Mar. 23 and 24 UT.  These are by far the strongest continuum detections
ever achieved in a comet.  From these and other measurements we deduce a
a relatively flat spectral index, -2.9 +/- 0.1.  The estimated dust mass
in the 19" (1700 km) diameter beam is of order 10**8 kg.  Assuming a
dust outflow velocity of 10 m/s, the dust production rate is 1200 kg/s."

                      (C) Copyright 1996 CBAT
1996 March 28                  (6363)              Brian G. Marsden

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