Electronic Telegram No. 1123
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
M.S. 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
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CBAT@CFA.HARVARD.EDU (science)
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COMET 17P/HOLMES
     Further to CBETs 1111 and 1118, B. Gaillard, J. Lecacheux, and F. Colas,
Paris Observatory, elaborate on observations of comet 17P obtained from Oct.
24 to Nov. 4 with the 1-m telescope at Pic du Midi Observatory.  During this
10-day interval beginning just at the outburst, they have followed the
evolution of dust streams and condensations inside the expanding "coma blob".
The dust streams appear to come from cometary fragments that quickly recede
from the nucleus, though such fragments remain below their detection
threshold.  Nevertheless, they have measured (with a 2000-km precision) the
increasing distance from the nucleus of the well-defined head of these
streams.  Apparent velocities ranging from 50 to 100 m/s (projected on the
sky) have been found for four of these stream heads, showing no trace of
acceleration.  The separation of the parent fragments from the nucleus
is calculated to have occurred at different times between Oct. 23.7 and
24.8 UT, so the most probable scenario is that the comet outburst began a
few hours before Oct. 24.0.  Different discrete releases of dusty material
took place over the two subsequent days, with a dominant event around Oct.
24.40 (cf. CBET 1111) being perhaps responsible for the final brightness
rise of the comet, and undoubtedly for the obvious circular shell that
continues expanding at 570 m/s.  The measured dust streams are no longer
fed by new material and will vanish via increasing dilution in the space.
On the other hand, the pseudo-nucleus, which seemed inactive until Oct.
29, now is active again:  its brightness, which was declining since Oct.
24, has stabilized, and a thin permanent dust trail is observed, perhaps
announcing another outburst.


NOTE: These 'Central Bureau Electronic Telegrams' are sometimes
      superseded by text appearing later in the printed IAU Circulars.

                         (C) Copyright 2007 CBAT
2007 November 7                  (CBET 1123)              Daniel W. E. Green