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IAUC 6625: C/1995 O1

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                                                 Circular No. 6625
Central Bureau for Astronomical Telegrams
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
URL http://cfa-www.harvard.edu/cfa/ps/cbat.html
Phone 617-495-7244/7440/7444 (for emergency use only)

     D. Mehringer, M. Gardner, and D. Benford, Caltech
Submillimeter Observatory (CSO); D. Bockelee-Morvan, Observatoire
de Paris (OP); D. C. Lis and T. G. Phillips, CSO; D. Despois,
Observatoire de Bordeaux; and N. Biver, H. Rauer, P. Colom, J.
Crovisier, and D. Gautier, OP, report the first groundbased
spectral identification of H_3O+ in a comet using the CSO: "On Apr.
6 and 10 UT, we detected the 3(2)-2(2) line of H_3O+ at 364.797 GHz
in comet C/1995 O1.  The integrated line area on the antenna
temperature scale is 0.248 +/- 0.046 K km sE-1 (average of the two
days).  The line is approximately centered on the comet's rest
velocity, and its full width at half maximum is about 3 km/s. The
H_3O+ line at 307.192 GHz was not detected with a 3-sigma upper
limit of 0.09 K km sE-1."
     M. J. Mumma and V. A. Krasnopolsky, Goddard Space Flight
Center, NASA; M. Abbott and B. C. Flynn, Center for Extreme
Ultraviolet Astrophysics, Berkeley; D. K. Yeomans, Jet Propulsion
Laboratory; P. D. Feldman, Johns Hopkins University; and C. B.
Cosmovici, Istituto di Fisica dello Spazio Interplanetario, report:
"Soft x-rays, He I (58.4 nm), and O II (53.8 nm) were detected in
comet C/1995 O1 during 1996 Sept. 14-19 UT (r = 3.07 AU) with the
EUVE orbiting observatory.  The intensity in x-rays (70-180 eV) was
8 x 10E24 photons/s in an aperture of radius 400 000 km, and the
central brightness was displaced from the nucleus by 140 000 +/-
60 000 km in the sky plane.  A region of extended x-ray emission is
also seen, and this is anticorrelated with the dust jets imaged
simultaneously in the visible.  He I 58.4-nm and O II 53.8-nm lines
were detected with S/N = 4.  The absence of Ne lines shows a
depletion of Ne in the comet by more than 25 times relative to the
solar abundance."
     Yu. N. Gnedin and T. M. Natsvlishvili, Central Astronomical
Observatory, Pulkovo; and V. D. Bychkov and V. P. Romanenko,
Special Astrophysical Observatory, report preliminary results of
polarimetric observations of this comet with a 1-m telescope (+
MINIPOL polarimeter and 6" diaphragm) during Mar. 28-Apr. 1.  The
amount of polarization is similar in the coma, the dust tail, and
the ion tail, varying generally from 5-10 percent in U, 10-19 in
B, and 7-17 in both R and I.  The V polarization is generally < 1
percent in the coma, increasing to 10-20 percent in both the dust
and ion tails.  The high degree of polarization and associated
strong wavelength dependence (especially at the center of the comet
on Mar. 28 and 29) give strong evidence for molecular-band
polarization.  The existence of CN, CO+, and H_2O+ species are
considered most probable.

                      (C) Copyright 1997 CBAT
1997 April 14                  (6625)            Daniel W. E. Green

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