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IAUC 4176: 1982i

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                                                  Circular No. 4176
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)
     P. Schloerb, W. Kinzel, D. Swade and W. Irvine report detection
of HCN at 88.6 GHz with the Five College Radio Astronomy
Observatory's 14-m antenna on Feb. 8 and 9: "The F=2-1 hyperfine
component of the J=1-0 rotational transition has an antenna temperature
(corrected to outside the atmosphere) of 50 +/- 10 mK, with FWHM
1 km/s and a velocity redshifted by ~ 0.5 km/s relative to the
nucleus. The line was not detected at this level on Feb. 7, and
there is evidence for an increase from Feb. 8 to 9.  The ratio of
the F=1-1 to the F=2-1 hyperfine component appears to decrease
over this same time interval."

     The comet seems to have been first observed optically after
perihelion by R. M. West and H. Debehogne with the 0.4-m GPO
astrograph at the European Southern Observatory on Feb. 15.406 UT.
Their precise positions, given below, are in excellent agreement
with the elements on IAUC 4156.  During the Feb. 15 exposure (
duration 30 seconds) the comet's altitude was 15' and its elongation
from the sun 15.3 deg; the coma diameter was 2', but no tail was
visible. The Feb. 16.405 image was somewhat trailed.

      1986 UT             R.A.  (1950.0)   Decl.        m1

      Feb. 15.40573     20 50 12.32     -12 05 56.8      3
           16.40469     20 48 24.77     -12 22 36.2
           16.40807     20 48 24.88     -12 22 36.7
           17.40116     20 46 38.69     -12 39 20.9
           17.40446     20 46 38.30     -12 39 24.8

     T. le Bertre, European Southern Observatory, provides the
following infrared magnitudes (1-m reflector, 30" diaphragm, 30"
east-west beamswitching, uncertainty 0.10 mag): Feb. 16.44 UT, J =
4.22, H = 3.80, K = 3.15, L = -0.19, M = -1.57; 17.44, J = 4.95, H
= 4.53, K = 4.04, L = 0.74, M = -0.67.

     Many observers photographed a spectacular tail-disconnection
event on Jan. 10.  P. Simon, Observatoire de Meudon, attributes the
event to solar wind of very low velocity, a source for which could
be the heliosheet crossed by the earth during Jan. 11-19, reversal
of the interplanetary magnetic field being likely on Jan. 16.  He
remarks that the earth should again cross the heliosheet from Mar.
1 to 10 and anticipates the comet to be affected by low-velocity
wind during Mar. 7-17, with field reversal around Mar. 12-13.


1986 February 18               (4176)              Brian G. Marsden

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