Electronic Telegram No. 3718
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)
     Dennis Bodewits, Tony Farnham, and Michael F. A'Hearn, University of
Maryland, College Park, report results from observations of comet C/2012 S1
using the UltraViolet-Optical Telescope (UVOT) onboard the Swift space
telescope.  They obtained photometry using broadband V (lambda_c = 546.8 nm,
FWHM = 75.0 nm) and UVW1 (lambda_c = 260.0 nm, FWHM = 70.0 nm) filters.
Comet C/2012 S1 was observed on Oct. 7 at r = 1.52 AU from the sun, Oct. 20
at r = 1.27 AU, Nov. 1 at r = 0.98 AU, and Nov. 7 at r = 0.83 AU.  They
derived water-production rates using a vectorial model of 2.0 x 10**28, 1.8 x
10**28, 1.6 x 10**28, and 2.1 x 10**28 molecules/s (+/- 25 percent).  The OH
coma filled almost the entire 15' x 15' field-of-view.  Using smaller, fixed
apertures of projected radius 50000 km at the comet, they measured Af(rho)
values of of 750, 796, 848, and 861 cm (+/- 5 percent), respectively,
normalized to a phase of 0 degrees using the phase function by D. Schleicher
(http://asteroid.lowell.edu/comet/dustphase.html).  In addition, they
further processed their Swift observations acquired in early 2013 (cf. CBET
3608) and can further constrain their upper limits for the comet's water-
production rate; using apertures with radii between 10" and 20", they find the
following 3-sigma upper limits for Q(H_2O):  Jan. 30 at r = 4.95 AU, < 8 x
10**27/s; Mar. 11 at r = 4.50 AU, < 2 x 10**27; Apr. 24 at r = 3.97 AU, < 2 x
10**27; and May 9 at r = 3.79 AU, < 1. x 10**27.

     Quanzhi Ye, University of Western Ontario; Man-To Hui, Guangzhou, China;
and Xing Gao, No. 1 Senior High School of Urumqi, China, report a dramatic
change of cometary morphology of C/2012 S1 (ISON) in unfiltered CCD images
taken with the 0.35-m SASP telescope (+ QHY9 camera) at the Xingming
Observatory from Nov. 13.99 to 14.99 UT.  Seven tails are seen from p.a. 275
to 320 deg in the Nov. 14 images, as opposed to only two in the Nov. 13
images.  After applying the azmuthal median model to images from both dates,
two intense jets are seen at p.a. 0 and 220 deg in the Nov. 14 images, both
being slightly skewed to the anti-solar direction and measured to be about
34" in length.  The two jets were absent in the Nov. 13 images.  Images are
at visible at website URL http://tinyurl.com/kefa4y4 for Nov. 13 and at URL
http://tinyurl.com/l29p5x6 for Nov. 14.


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      superseded by text appearing later in the printed IAU Circulars.

                         (C) Copyright 2013 CBAT
2013 November 22                 (CBET 3718)              Daniel W. E. Green