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IAUC 6355: C/1996 B2; C/1996 B1

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                                                  Circular No. 6355
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)

     M. Festou, Observatoire Midi-Pyrenees, Toulouse; P. Feldman,
Johns Hopkins University, for the IUE ToO Team for Comet
Observations; and R. Gonzalez and P. M. Rodriguez, European Space
Agency IUE Observatory, report:  "Observations of the comet were
made on Mar. 23.12 and 24.15 UT with the International Ultraviolet
Explorer (IUE) using the new One-Gyro mode of operation, which had
to be implemented after a major spacecraft problem on Mar. 6.084.
The operational modifications associated with this limit the
duration of exposures on moving targets.  Low-dispersion spectra
were recorded with both cameras, both with the nucleus in and out
of the aperture.  The LWP spectrum (range 200-330 nm) reveals the
presence of strong OH emission, from which a water-production rate
of 3.5 x 10E29 sE-1 is inferred (r = 1.05 AU).  This indicates a
sevenfold increase from the water-production rate measured by
Schleicher et al. (IAUC 6344), while the heliocentric distance
decreased by only about 0.10 AU.  Emission features usually seen in
LWP range, such as those due to C2 (231.3 nm), the CS bands, and
the CO2+ B-X and NH 336.0-nm bands, also appear on top of a strong
continuum.  The SWP spectrum (115-199 nm) shows the presence of
weak carbon and oxygen emissions.  The fourth positive band system
of CO is identified by its bands longward of the 0-0 band, the
strongest being 0-1 at 159.7 nm.  The intensity distribution of the
bands indicates a significant opacity of the CO atmosphere.  The
optical thickness of the 180.0-nm component of the S I 181.3-nm
triplet is very large.  It is likely that many cometary emissions
seen throughout the spectrum will be optically thick (OH, CN, etc.)."
     Naked-eye m1 and tail-length estimates:  Mar. 24.10 UT, +0.1,
30 deg (K. Cernis, Moletai, Lithuania); 24.33, -0.5, 70 deg (C. S.
Morris, Lockwood Valley, CA); 25.58, +0.9, about 80 deg (S. J.
O'Meara, Volcano, HI); 26.00, -0.4, 90 deg (A. Baransky, Kiev,
Ukraine); 26.34, +0.3, about 100 deg (J. V. Scotti, Corona de
Tucson, AZ); 26.58, +0.9, 100 deg (O'Meara).

     Total visual magnitude and coma-diameter estimates:  Mar.
8.81 UT, 7.2, 18' (K. Hornoch, Lelekovice, Czech Republic, 10x80
binoculars); 13.08, 8.0, 12' (J. E. Bortle, Stormville, NY, 10x50
binoculars); 22.77, 9.3, 8' (A. Baransky, Kiev, Ukraine, 0.11-m
reflector); 25.18, 8.8, 8' (C. E. Spratt, Victoria, BC, 0.10-m

                      (C) Copyright 1996 CBAT
1996 March 26                  (6355)            Daniel W. E. Green

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