Electronic Telegram No. 3870
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 209P/LINEAR
     Carl Hergenrother, Lunar and Planetary Laboratory, University of Arizona,
reports broad-band photometry of the nucleus of comet 209P/LINEAR, the parent
of the forthcoming expected May 24 Camelopardalid meteor outburst (cf. CBET
3869).  R-band measurements obtained on 2014 Feb. 10, 19, 20, and 21 UT, and
on Mar. 4, 8, and 10, with the Vatican Observatory Lennon 1.8-m telescope
yield two synodic-rotation-period solutions consistent with the data:  10.930
+/- 0.015 and 21.86 +/- 0.04 hr.  The 21.86-hr period produced a better fit to
the data, and its resulting lightcurve contains the typical dual maxima/minima
appearance for elongated bodies.  The amplitudes for the 10.930- and 21.86-hr
period lightcurves are 0.44 and 0.65 magnitude, respectively.  Color indices
were determined from broad-band Harris B, V, and R photometry obtained on Feb.
20 and 21 UT:  B-V = +0.74 +/- 0.06, and V-R = +0.53 +/- 0.03.  These colors
are consistent with those measured for the nuclei of other Jupiter-family
comets (Hainaut et al. 2012, A.Ap. 546, 115).
     Phase-function analysis of the lightcurve photometry found a strong
linear relationship between brightness (normalized to 1 AU from the earth and
sun) and phase angle.  A phase-function slope in the R band of 0.042 +/- 0.002
magnitude per degree of phase angle is consistent with the nucleus being a
dark object with an albedo > 0.08 (Belskaya and Shevchenko 2000, Icarus 147,
94; Hergenrother et al. 2013, Icarus 226, 663).  The H_R of the linear fit is
16.45 +/- 0.06.  Solving within the IAU H-G system found an H_R = 15.86 +/-
0.10 and G_R = -0.12 +/- 0.03.  Converting H_R to H_V using the measured V-R
of about +0.5 yields H_V = 16.7 +/- 0.3.  Using albedo constraints of 0.02-
0.08 and H_V constraints of 16.4-17.0, a diameter between 1.9 and 4.9 km is
inferred.  Such a large nucleus will provide a strong target for radar
observations during the comet's late-May close approach.
     The dust-activity level of the comet was measured by analyzing photometry
reported to the Minor Planet Center for the 2004, 2009, and 2014 apparitions.
The difference in the measured brightness of the comet was compared to the
expected brightness of the nucleus (using the linear phase function described
above).  The start of activity was found to be at a heliocentric distance of
1.4 AU pre-perihelion and the end of activity to be at a similar distance
post-perihelion (though the number of photometric measurements post-perihelion
is too sparse to make an exact determination).  The level of activity looks to
be close to symmetric about perihelion during all three apparitions.


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

                         (C) Copyright 2014 CBAT
2014 May 17                      (CBET 3870)              Daniel W. E. Green