[IAUC] CBET 2515: 20101028 : COMET 103P/HARTLEY

[quai en eps.harvard.edu]

                                                  Electronic Telegram No. 2515
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 en eps.harvard.edu (alternate cbat en iau.org)
URL http://www.cbat.eps.harvard.edu/index.html
Prepared using the Tamkin Foundation Computer Network


COMET 103P/HARTLEY
    J. K. Harmon, M. C. Nolan, and E. S. Howell, Arecibo Observatory;
and J. D. Giorgini, Jet Propulsion Laboratory, obtained 150-m-resolution
radar images and radar doppler spectra for comet 103P/Hartley on Oct. 24-27
using the Arecibo Observatory 12.6-cm planetary radar.  The images show
the nucleus to be a highly elongated, bilobate object with a long-axis
dimension of at least 2.2 km.  The images give a preliminary rotation period
estimate of 18.1 +/- 0.3 hours, although a less-likely period of 13.2 hours
cannot be ruled out.  The radar cross section of the nucleus is 0.04 km^2.
The doppler spectra show a broadband echo component from large (> cm-size)
ejected grains in the inner coma.  The radar cross section of the large-grain
coma is 0.6 km^2.  This echo component is preferentially redshifted,
indicating that the bulk of the grain ejection is in the anti-earthward
direction. The characteristic radial velocity dispersion of the grains is
4 m/s.

     N. H. Samarasinha and B. E. A. Mueller, Planetary Science Institute;
and M. F. A'Hearn and T. L. Farnham, University of Maryland, report that
CN narrowband images taken at the Kitt Peak National Observatory 2.1-m
telescope from Sept. 1-3 UT show coma structure nearly similar to, but with
distinct differences from, that described by Samarasinha et al. (cf. CBET
2512) for the interval 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 by Samarasinha et al. (CBET 2512).
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.

     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.


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      superseded by text appearing later in the printed IAU Circulars.

                         (C) Copyright 2010 CBAT
2010 October 28                  (CBET 2515)              Michael Rudenko