[IAUC] IAUC 9178: 103P [25139-2011/04-R1]

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                                                  Circular No. 9178
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
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COMET 103P/HARTLEY
     N. H. Samarasinha and B. E. A. Mueller, Planetary Science
Institute; and M. F. A'Hearn and T. L. Farnham, University of
Maryland, obtained CN narrowband images at the Kitt Peak National
Observatory 2.1-m telescope from Sept. 30 to Oct. 4 UT.  The
enhanced images clearly indicate the rotation of a jet feature
centered around a position angle near 30 deg.  This is presumably
the same feature reported by Knight et al. (IAUC 9163).  This
feature moves from the northwest towards the earth's direction,
almost towards the line-of-sight, and then moves to the east-
northeast and finally to the far side before starting the cycle
again; while on the far side from the earth, its level of activity
decreases significantly before starting to increase again.  The
repeatability of the CN morphology is consistent with a periodicity
around 17.6 hours.  Small differences in the morphology during some
cycles suggest that there may be a slight rotational excitation,
probably a low-excitation short-axis mode.  The CN coma morphology
is compatible with a nucleus having a high obliquity and a
retrograde rotation and suggests a low-to-mid-latitude active
region in the negative hemisphere.  A preliminary estimate for the
rotational angular momentum vector is R.A. = 345 deg, Decl. = -15
deg, and the uncertainty is as large as 20 deg in some directions.
The continuum images from the same observing run show the dust tail,
but no clear jet features are discernible.
     CN narrowband images taken at the Kitt Peak 2.1-m telescope
during Sept. 1-3 UT show coma structure nearly similar to, but with
distinct differences from, that described above during Sept. 30-
Oct. 4.  In the images from early September, the northwest jet
moves to the south of the nucleus and then towards the east making
an archimedean spiral-like feature.  This indicates a low-latitude
active region in the negative hemisphere of the nucleus for the
rotational angular momentum direction described above.  There are
subtle indications as to the presence of a second jet, probably
overlapping with the primary jet, in the east/northeast direction.
The best repeatability of the morphology is seen for a periodicity
near 17.1 hours -- in contrast to the near-17.6 hours derived from
the Sept. 30-Oct. 4 data set.  The apparent differences in the
periodicities of the repeatability during different observing runs
is suggestive of a changing rotational state and/or a non-principal-
axis rotational state.  A preliminary outflow speed based on the
CN features is 0.7 km/s.  No obvious feature other than the dust
tail is observed in the continuum images.  Due to rapid changes in
the observing geometry during the coming days, the CN morphology is
likely to show distinct evolutions and observers are encouraged to
obtain additional CN images.

                      (C) Copyright 2010 CBAT
2010 November 4                (9178)            Daniel W. E. Green