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IAUC 6344: C/1996 B2

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                                                  Circular No. 6344
Central Bureau for Astronomical Telegrams
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
Phone 617-495-7244/7440/7444 (for emergency use only)

     D. Schleicher, Lowell Observatory, reports:  "Narrow-band
photometry of comet C/1996 B2 was obtained by R. Millis using the
Hall 1.07-m telescope at Lowell Observatory on Mar. 19.4 UT (r =
1.16 AU).  Haser-model production rates were log Q(OH) = 28.83, log
Q(CN) = 26.35, and log Q(C2) = 26.50.  The dust-production rate was
log [Af(rho)] = 3.72.  Combining these results with those
previously obtained at r = 1.90, 1.60, and 1.51 AU (cf. IAUC 6311,
6333) indicates that the OH production rate has finally begun to
increase, with an r-dependent slope of -0.9 from 1.51 to 1.16 AU.
During this same interval, the CN production had a slope of -1.7,
after also being nearly flat.  Both C2 and dust have exhibited
steady increases since 1.90 AU, with a slope for C2 of -1.7 and a
slope for Af(rho) = -2.5."
     L. Jorda, Meudon Observatory and Laboratoire d'Astronomie
Spatiale, Marseille; J. Lecacheux, Meudon Observatory; and F. Colas,
Bureau des Longitudes, Paris, write:  "Subarcsecond imaging since
Mar. 9 of the inner coma of this comet with the Pic-du-Midi 1.05-m
telescope shows at least two curved jets rotating clockwise and
changing orientation on a time scale of a few minutes.  From a
continuous broadband (500-900 nm) image sequence obtained during
Mar. 18.97-19.23 under good seeing (0".9) conditions, the activity
of 2000-km-long jets begins at the morning limb near p.a. 200 deg,
is at maximum at noon near p.a. 95 deg, and disappears at the
evening limb near p.a. 350 deg.  The rotation period seems to have
been in the range 5-9 hr (and is possibly near 6.6 hr), from the
comparison of our early images with the ESO-NTT image obtained on
Mar. 19.342 (IAUC 6343).  This suggests that the nucleus shows its
southern hemisphere to earth-based observers and that the sun lies
near its equatorial plane.  Images are available at URL
     L. M. Woodney, University of Maryland (UM); J. McMullin,
Submillimeter Telescope Observatory; and M. F. A'Hearn, UM, report
the detection of OCS J(12-11) emission from the comet:
"Observations were made of the OCS line on Mar. 19 (when Delta =
0.217 AU, with geocentric velocity -51.6 km/s) at the NRAO 12-m
telescope on Kitt Peak (peak antenna temperature 15 +/- 4 mK; area
0.0194 K km/s); the line had FWHM = 1.2 +/- 0.4 km/s and was
observed at -52.19 +/- 0.16 km/s.  Assuming kinetic temperatures of
10 and 30 K (and an expansion velocity of 0.8 km/s), we estimate
the OCS production rate, log Q(OCS) = 26.4 and 25.7, respectively;
comparing this with log Q(OH) = 28.83, measured by R. Millis on Mar.
19.4 (above), yields Q(OCS)/Q(OH) = 0.004 and 0.001, respectively."

                      (C) Copyright 1996 CBAT
1996 March 20                  (6344)            Daniel W. E. Green

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