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IAUC 6374: C/1996 B2

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                                                  Circular No. 6374
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)

     H. A. Weaver, Applied Research Corporation; P. D. Feldman,
Johns Hopkins University; M. F. A'Hearn, University of Maryland; C.
Arpigny, University of Liege; and J. C. Brandt and C. E. Randall,
University of Colorado, report on their Hubble Space Telescope
spectroscopic observations: "Ultraviolet spectra (range 129.5-327.7
nm) were obtained on Apr. 1.  The region below 220.0 nm is
dominated by emission from CO.  At least 25 bands of the CO Fourth
Positive Group were detected, including bands in the progression v'
= 14 pumped via the solar H Lyman alpha line.  Seven or more bands
of the forbidden CO Cameron band system were detected.  These
latter bands are produced primarily by prompt emission following
the photodissociation of CO2 and provide a tracer of CO2 in the
nucleus.  Preliminary calculations indicate that the molecular
production rates for both CO and CO2 were about 1-2 x 10E28 mol/s,
which corresponds to an abundance relative to water of about 5
percent.  The S2 molecule was clearly detected via fluorescence in
multiple bands between 285.0 and 312.0 nm, at a relative abundance
of roughly 0.01 percent.  This is the first definite detection of
S2 in a comet since its initial discovery during IUE observations
of C/1983 H1 (IRAS-Araki-Alcock) in 1983 (cf. IAUC 3809).  The
C/1996 B2 spectra have several as yet unidentified emissions,
which we are currently investigating."
     M. A. DiSanti, M. J. Mumma, N. Dello Russo, and D. X. Xie,
Goddard Space Flight Center, NASA; M. Fomenkova, University of
California, San Diego; and K. Magee-Sauer, Rowan College of New
Jersey, report observations of various parent molecules in C/1996
B2 on Mar. 24 UT, using the CSHELL cryogenic infrared spectrometer
at the NASA Infrared Telescope Facility, Mauna Kea:  "From the
line flux contained within a 1" x 1".4 aperture centered on the
nucleus, the production rates (in molecules/s) are:  Q(H2O) = 1.7
x 10E29, revised slightly from IAUC 6366; Q(CO) = 9.8 x 10E27,
from analysis of the P2, P3 lines of the 1-0 band; Q(CH4) = 1.2 x
10E27, from the R0 line of the nu3 band; and Q(C2H6) = 6.4 x
10E26, based on the rQ0 and rQ1 branches of the nu7 band.  The
relative production rates for these parent volatiles are thus
100:5.8:0.7:0.4.  The CH4-production rate assumes a rotational
temperature of 50 K; for T = 100 K, Q(CH4) would be about 2.5
times larger.  The Q(C2H6) value represents only the population in
those K-ladders with K = 0-3; thus the production rate could be up
to about 3 times larger, if C2H6 is characterized by a temperature
as high as 130 K.  Our production rates are sensitive to the
direct nuclear source, primarily."

                      (C) Copyright 1996 CBAT
1996 April 9                   (6374)            Daniel W. E. Green

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