Electronic Telegram No. 4004
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/2013 A1 (SIDING SPRING)
     D. Schleicher, Lowell Observatory, obtained two narrowband photometry
sets of comet C/2013 A1 on Oct. 20 (with the comet at r = 1.40 AU) using the
Hall 1.1-m telescope at Lowell Observatory.  These observations were acquired
only about 8 hr after the comet's closest approach to Mars and yield the
following mean production rates:  Q(OH; Haser) = 1.2 x 10**28 molecules/s,
with an uncertainty of about 30 percent, corresponding to Q(H_2O; vectorial) =
1.3 x 10**28 molecules/s at this distance; Q(CN) = 1.4 x 10**25 molecules/s;
Q(C_2) = 1.8 x 10**25 molecules/s; Af(rho) at 524 nm = 260 cm (102"-diameter
aperture).  He also obtained photometry on Oct. 12 (at r = 1.41 AU), with the
following production rates determined:  Q(OH; Haser) = 8 x 10**27 molecules/s,
with an uncertainty of about 30 percent, corresponding to Q(H2O; vectorial) =
9 x 10**27 molecules/s at this distance; Q(CN) = 1.4 x 10**25 molecules/s;
Q(C_2) = 1.7 x 10**25 molecules/s; Af(rho) at 524 nm = 300 cm (78"-diameter
aperture).  These values indicate that the comet has "typical" composition and
a moderate to slightly high dust-to-gas ratio.

     M. Knight and B. Skiff, Lowell Observatory, report narrowband imaging of
comet C/2013 A1 on Oct. 20 (at r = 1.40 AU, also just 8 hr after the comet's
closest approach to Mars) using the Discovery Channel Telescope.  Following
removal of median radial profiles, the dust exhibited no features other than
the tail, while a CN feature was seen towards the north and east.  It was
brightest near position angle 0 deg and extended counterclockwise from p.a.
330 to 90 deg.  Additional CN signal was seen throughout the anti-sunward
hemisphere.


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      superseded by text appearing later in the printed IAU Circulars.

                         (C) Copyright 2014 CBAT
2014 October 21                  (CBET 4004)              Daniel W. E. Green