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IAUC 9241: 2005 YU_55; C/2010 G2

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                                                  Circular No. 9241
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
New postal address:  Hoffman Lab 209; Harvard University;
 20 Oxford St.; Cambridge, MA  02138; U.S.A.
CBATIAU@EPS.HARVARD.EDU           ISSN 0081-0304
URL http://www.cbat.eps.harvard.edu/index.html
Prepared using the Tamkin Foundation Computer Network


2005 YU_55
     Thomas Mueller, Max-Planck Institut fuer Extraterrestrische
Physik, Garching; and Bruno Altieri and Mark Kidger, Herschel
Science Centre (HSC), European Space Astronomy Centre, Madrid, on
behalf of the HSC, report infrared photometry of 2005 YU_55, taken
with the Herschel Space Observatory during its close approach to
the earth (Delta_min = 0.00217 AU on Nov. 8.98 TT).  Color-
corrected (1-sigma-error) flux densities on Nov. 10.62014 UT were
12.2 +/- 0.6 Jy at 70 microns and 2.7 +/- 0.3 Jy at 160 microns;
on Nov. 10.62361, they were 6.9 +/- 0.4 Jy at 100 microns and 2.6
+/- 0.3 Jy at 160 microns.  A retrograde rotation is favored by a
thermophysical chi-squared fit to the data, with Herschel viewing
the warm terminator.  The implied diameter is 309 (+16, -10) m, and
the V-band geometric albedo (based on H-V = 21.1 +/- 1 and G =
-0.12) is 0.0699 (+0.007, -0.008).  The corresponding values for a
prograde solution (cold terminator) are 336 (+15, -11) m and 0.058
(+0.007, -0.008).  The favored retrograde solution required a
thermal inertia of 650 J m**-2 s**-0.5 K**-1, very similar to the
value obtained for (25143) Itokawa.


COMET C/2010 G2 (HILL)
     C. E. Woodward and E. L. Ryan, Minnesota Institute of
Astrophysics, report optical narrow-band "Hale-Bopp" filter
(Farnham et al. 2000, Icarus 147, 180) observations of comet C/2010
G2 on Nov. 18.31 UT (when r = 2.19 AU, Delta = 1.25 AU, geocentric
velocity = +28 km/s) using the prime-focus imager 90Prime at the
Steward Bok 2-m reflector.  Images obtained during a period of sub-
arcsec seeing reveal a spherically symmetric coma, 1'.5 in diameter
in extent, with little evidence of tail structures.  Preliminary
(nucleus-centered) volatile-gas production rates, log Q(molecules/s),
within an aperture of log rho (km) = 4.8, are as follows:  CN =
24.40, C_2 = 23.22, and C_3 = 22.35.  The observed C_2/CN ratio is
commensurate with the range of mean values of observed in comets of
"typical" taxonomic class.  The derived dust-production rate Af(rho)
in the 562.0-nm continuum filter is 351 cm.
     Visual total-magnitude and coma-diameter estimates:  Oct. 7.76
UT, 10.5, 5'.2 (S. Yoshida, Gunma, Japan, 40-cm reflector); Nov.
8.20, 10.0, 6' (J. J. Gonzalez, Asturias, Spain, 20-cm reflector);
17.89, 10.2, 4' (Gonzalez); 21.87, 10.5, 5' (U. Pilz, Leipzig,
Germany, 32-cm reflector).

                      (C) Copyright 2011 CBAT
2011 November 23               (9241)            Daniel W. E. Green

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