[IAUC] IAUC 9177: 103P [25139-2011/04-R1]

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                                                  Circular No. 9177
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
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COMET 103P/HARTLEY
     M. F. A'Hearn and L. M. Feaga, on behalf of the DIXI/EPOXI
science team, report that routine sampling with the Deep Impact
Medium Resolution Imager (MRI) enabled the discovery of an unusual
cometary phenomenon on comet 103P (sometimes known by its old name,
"Hartley 2") that may recur.  Between Sept. 9 and 17, the
outgassing of CN, as acquired with the CN filter (sensitive to both
the dust continuum and CN gas), increased by a factor of five and
then slowly decreased, returning to its prior trend line by Sept.
24.  There was no apparent change in the reflected continuum,
acquired with a clear filter, other than a small, gradual increase
consistent with the increases before and after this period in both
CN and dust due to the decreasing range from the spacecraft to the
comet and the increasing activity of the nucleus as it approaches
the sun.  This long-duration, gradual increase and decrease of
gaseous emission without any increase in the dust is very unlike
typical cometary outbursts, which have sudden onsets and are
usually accompanied by considerable dust.  It is dissimilar to the
activity observed at comet 9P (old-style name "Tempel 1") and not
apparently associated with the dust-free CN jets observed in this
and other comets.  Thus it is not like anything that the authors
are aware of in any other comet.  Observers should be aware of this
type of activity when planning observations and interpreting their
data.  In addition, H_2O and CO_2 have been unambiguously detected
in the coma using the High Resolution Instrument infrared
spectrometer (HRI-IR) on Oct. 16.

     M. Drahus, D. Jewitt, and A. Guilbert, University of
California at Los Angeles; D. Lis, California Institute of
Technology; and W. Waniak, Jagiellonian University, obtained
velocity-resolved spectral time series of HCN at the James Clerk
Maxwell Telescope (JCMT) and the Caltech Submillimeter Observatory
(CSO) on Mauna Kea.  JCMT observations of the J=4-3 transition were
carried out from Sept. 29 to Oct. 1 UT and from Oct. 16 to Oct. 19
UT.  CSO observations of the J=3-2 line were taken from Oct. 23 to
Oct. 24 UT.  A very strong variability of the line area on a time
scale of hours is observed, reaching up to a factor of four, and
accompanied by changes of the line profile.  The variability
appears inconsistent with the 16.6-hr rotation period reported by
Meech et al. (2009, BAAS 41, 1029) and Knight et al. (2010, IAUC
9163 and CBET 2418), and with the 17.6-hr period reported by
Samarasinha et al. (CBET 2512).  It is anticipated that there will
be a much longer rotation period, significant excitation of the
rotation state (cf. Samarasinha et al., CBET 2512), or a non-
periodic nature of the detected variability.

                      (C) Copyright 2010 CBAT
2010 November 4                (9177)            Daniel W. E. Green