Central Bureau for Astronomical Telegrams
IAUC 4151: 1982i
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Circular No. 4151
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
TWX 710-320-6842 ASTROGRAM CAM Telephone 617-495-7244/7440/7444
PERIODIC COMET HALLEY (1982i)
T. Y. Brooke, State University of New York, Stony Brook; T. R.
Geballe, U.K. Infrared Telescope; R. Knacke and K. S. Noll, SUNY,
Stony Brook; and A. T. Tokunaga, NASA Infrared Telescope Facility,
communicate: "We report a probable detection of H2O in the coma of
P/Halley: Unresolved emission (at the nu1+nu3 band at 1.4 microns and at
the nu2+nu3 band at 1.9 microns) was observed at the U.K. Infrared
Telescope on Oct. 29 UT. Observations were made of the Doppler-shifted
(-50.3 km/s) lines through the wings of the terrestrial water
absorption bands. The H2O mass-loss rate was 2 x 10**28 mol/s with a
probable uncertainty of a factor of 2. Confirming observations
are needed where the Doppler shift becomes large again."
Z. Sekanina, Jet Propulsion Laboratory, reports that his new
analysis of 27 dust features on 19 images of comet Halley from the
period 1910 May 7-June 5 (corresponding to heliocentric distances
0.70-1.11 AU outbound), which were digitized, computer enhanced,
and measured by S. M. Larson, University of Arizona, yields refined
parameters for the comet's spin vector: a rotation period of 52 hr
and north-pole position R.A. = 357 deg, Decl. = -49 deg (equinox 1950.0),
implying an obliquity of 30P. The features are identified on up to 6
consecutive images, and their evolution is understood as a manifestation
of sunrise-to-sunset emissions of dust from 5 separate linear sources
(perhaps systems of freshly opened fissures in a dust layer with an
underlying base of ice) delineating a trapezium-shaped area that
covers about 7 percent of the nuclear surface. The 5 sources are
restricted to a segment of 235 deg in cometocentric longitude. One of
the sources is found to have been active during three rotations.
The observed copious dust emission appears to be a semi-stochastic
process that is triggered by thermal stresses due to a considerable
temperature gradient in the surface layer of dust. Many sources of
this kind may temporarily be activated at various locations of the
nuclear surface depending on its morphology and thermal properties.
To extend this type of analysis to 1985/86 for the benefit of the
flight projects, observers -- especially the IHW Near Nucleus Studies
Network members -- are requested to transmit recent high-resolution
images of the comet to: S. M. Larson, Lunar and Planetary
Laboratory, University of Arizona, Tucson, AZ 85721, U.S.A.
1985 December 20 (4151) Daniel W. E. Green
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