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IAUC 6542: C/1995 O1; SNe

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                                                 Circular No. 6542
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)

     Z. Sekanina, Jet Propulsion Laboratory; and H. Bohnhardt,
University of Munich, report:  "The comet's persisting porcupine-
like appearance (cf. IAUC 6463), consisting of 6-8 nearly-straight
jets in various directions, is conceptually understood as a product
of dust emission from 3-4 discrete active sources on the rotating
nucleus.  The jet pairs (one pair per source) are interpreted as
boundaries of fan-shaped formations described by dust ejected from
the sources continually between local sunrise and sunset (or
continuously, if for any of the sources should the sun be above
horizon throughout the day), a model that is consistent with
evidence for more material being located in between the jets than
on their outside, as seen on unprocessed images.  One of several
tentative solutions suggested by our computer simulation
experiments that fit the observed jet-orientation pattern on
several R-filter images taken with the large telescopes at the
European Southern Observatory in Aug.-Nov. 1996, places the sunlit
rotation pole near R.A. = 30 deg, Decl. = +45 deg (equinox 2000.0),
which implies an obliquity of the comet's orbit plane to its
equatorial plane of 140 deg.  The three most active areas have
polar distances of about 20, 55, and 130 deg.  These results are
insensitive to both the comet's rotation sense and its spin rate."
     M. Womack and D. Faith, Pennsylvania State University at Erie;
M. C. Festou, Observatoire Midi-Pyrenees, Toulouse; and D. Slater
and S. A. Stern, Southwest Research Institute, Boulder, report
observations of comet C/1995 O1 with the NRAO 12-m telescope at
Kitt Peak:  "The J_K=3_03-2_02 transition of H_2CO at 218 GHz was
detected on 1996 Dec. 15 and 1997 Jan. 17 UT with an average line
flux area of 0.168 +/- 0.008 K km/s.  A production rate of Q(para-
H_2CO) = 2.6 x 10E26 molecules/s is derived, assuming a rotational
temperature of 30 K and expansion velocity of 0.6 km/s.  Comparison
with observations of the J_K=3_12-2_11 ortho transition of H_2CO at
226 GHz on 1996 Dec. 14, 15, and 1997 Jan. 17 indicate a weighted
average ortho-to-para H_2CO ratio of 1.5 +/- 0.3 for C/1995 O1 over
the range of heliocentric distances 1.6-2.0 AU.  This ratio is
lower than that reported for H_2O in comets 1P/Halley and C/1986 P1
(Wilson), is similar to what is observed for H_2CO in cold, dense
interstellar clouds, and may have implications for the thermal
history of C/1995 O1."

     Corrigendum.  On IAUC 6540, line 6,  for  indicates the
discovery telescope:  read  indicates the telescope used to obtain
the redshifts:

                      (C) Copyright 1997 CBAT
1997 January 21                (6542)            Daniel W. E. Green

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