Electronic Telegram No. 2589
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
CBAT Director:  Daniel W. E. Green; Hoffman Lab 209; Harvard University;
 20 Oxford St.; Cambridge, MA  02138; U.S.A.
e-mail:  cbatiau@eps.harvard.edu (alternate cbat@iau.org)
URL http://www.cbat.eps.harvard.edu/index.html
Prepared using the Tamkin Foundation Computer Network


COMET 103P/HARTLEY
     E. Jehin, J. Manfroid, D. Hutsemekers, M. Gillon, and P. Magain, Liege
University, report narrowband imaging of comet 103P using the TRAPPIST 0.60m
telescope at the European Southern Observatory, La Silla.  Three to four hours
of observation were secured on 26 clear nights from Oct. 29 to Dec. 7, using
six different cometary filters (Farnham et al. 2000, Icarus 147, 180).  The
flux of five gaseous species (CN, OH, H_2O+, C_2, C_3) and the dust continuum
(via the C/1995 O1 green continuum filter, GC) was measured in a 26" aperture.
Periodic variations of the gas species are observed, superimposed on the
long-term trend, with CN showing the strongest variations (0.4-mag amplitude).
The dust light curve is nearly flat.  No gas or dust outburst has been
detected during the above period of observation, although CN and OH show a
slow flux increase with respect to other species during several days in early
November.  A period search with the first two weeks of data gave a smooth
phase diagram for a period of 18.4 +/- 0.3 hours.  These observations are in
good agreement with the period reported from Arecibo radar observations of
the nucleus (18.1 +/- 0.3 hours on Oct. 24-27; IAUC 9179).  Including two
more weeks of data, it became clear that the period was increasing.  A change
from about 18.2 to 19 hours was derived during the above observing window that
might be related to a change of the rotation period of comet 103P of about 2
hours in 100 days.  Such a rapid slowing down is in agreement with rotation
values reported before perihelion (16.6 +/- 0.5 hr on Aug. 13-17; IAUC 9163).


NOTE: These 'Central Bureau Electronic Telegrams' are sometimes
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                         (C) Copyright 2010 CBAT
2010 December 14                 (CBET 2589)              Daniel W. E. Green