Electronic Telegram No. 3090
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/2009 P1 (GARRADD)
     Dennis Bodewits, Tony Farnham, and Michael F. A'Hearn, University of
Maryland, College Park, on behalf of the DIXI/EPOXI science team, report
results from observations of comet C/2009 P1 using the Medium Resolution
Instrument (MRI) on board the Deep Impact spacecraft.  Broadband CLEAR and
narrowband CN filter images show a single-peaked variability (1- and 4-percent
amplitudes, respectively) with a period of 10.4 +/- 0.05 hr, assumed to be the
rotation period of the nucleus.  Gas- and dust-production rates gradually
decreased from 2012 Feb. 23 to Apr. 6 UT, as the comet receded from the sun
(r = 1.7 to 2.1 AU).  Additionally, the authors obtained photometry using
CLEAR, OH, and CN filters.  Average production rates, derived from a 50"
aperture for Feb. 23, Mar. 6, and Apr. 6 were 2.3, 1.9, and 1.4 x 10^28
molecules/s for OH; 3.2, 2.7, and 1.5 x 10^26 molecules/s for CN -- both with
relative and systematic uncertainties of 10 and 25 percent, respectively,
with Af(rho) values (cf. IAUC 7342) of 3657, 3270, and 2946 cm (+/- 5 percent).

     Visual total-magnitude and coma-diameter estimates:  2011 Dec. 7.25 UT,
6.7, 10' (J. J. Gonzalez, Leon, Spain, 10x50 binoculars; alt. 8 deg); 2012
Jan. 1.22, 7.2, 9' (S. Baroni, Milan, Italy, 20x80 binoculars); 26.23, 7.0,
10' (A. Kammerer, St. Leon-Rot, Germany, 9x63 binoculars); Feb. 20.93, 6.6,
12' (Gonzalez; 1.4-deg tail in p.a. 280 deg); Mar. 1.05, 6.2, 10' (Gonzalez,
naked eye); 19.82, 6.6, 6' (U. Pilz, Leipzig, Germany, 10x50 binoculars);
28.10, 7.1, 12' (Gonzalez, 10x50 binoculars); Apr. 8.86, 7.4, 12' (Gonzalez);
22.47, 8.0, 8' (K. Yoshimoto, Yamaguchi, Japan, 20x100 binoculars).


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      superseded by text appearing later in the printed IAU Circulars.

                         (C) Copyright 2012 CBAT
2012 April 25                    (CBET 3090)              Daniel W. E. Green