Electronic Telegram No. 3680
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
CBAT Director:  Daniel W. E. Green; Hoffman Lab 209; Harvard University;
 20 Oxford St.; Cambridge, MA  02138; U.S.A.
e-mail:  cbatiau@eps.harvard.edu (alternate cbat@iau.org)
URL http://www.cbat.eps.harvard.edu/index.html
Prepared using the Tamkin Foundation Computer Network


COMET C/2012 S1 (ISON)
     H. Weaver, Applied Physics Laboratory (APL), Johns Hopkins University
(JHU); P. Feldman and S. McCandliss, JHU; M. A'Hearn and Dennis Bodewits,
University of Maryland; M. Combi, University of Michigan; and N. Dello Russo,
APL, JHU, report a clear detection of CO in comet C/2012 S1 during Hubble
Space Telescope (HST) observations on Oct. 21.9 UT, when the comet's
heliocentric and geocentric distances were r = 1.23 AU and Delta = 1.53 AU,
respectively.  Ultraviolet spectra taken with the Cosmic Origins Spectrograph
(COS) in two consecutive orbits reveal several emission bands in the CO fourth
Positive Group (4PG) in the wavelength range 140-157 nm.  The CO production
rate was about 3.0 x 10**26 molecules/s.  Contemporaneous HST observations
using the Space Telescope Imaging Spectrograph (STIS) revealed OH(0,0) band
emission near 309 nm, from which the authors derive a water-production rate,
Q[H_2O], of about 2.0 x 10**28 molecules/s.  Both production rates should be
accurate to about 30 percent.  They therefore find CO/H_2O about 1.5 percent,
indicating that C/2012 S1 is not currently CO-rich.  Atomic emission lines
from S were also detected in the COS spectra.  The authors note that Q[H_2O]
is essentially identical to the value that they derived from STIS observations
on Oct. 8.9 (about 2.0 x 10**28 molecules/s), when the comet was at r = 1.50
AU and Delta = 1.92 AU.


NOTE: These 'Central Bureau Electronic Telegrams' are sometimes
      superseded by text appearing later in the printed IAU Circulars.

                         (C) Copyright 2013 CBAT
2013 October 30                  (CBET 3680)              Daniel W. E. Green