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IAUC 9242: 2005 YU_55; C/2009 P1

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                                                  Circular No. 9242
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
     W. J. Merline, Southwest Research Institute (SwRI); J. D.
Drummond, Starfire Optical Range, Air Force Research Laboratory;
P. M. Tamblyn, Binary Astronomy, Dillon, CO, U.S.A., and SwRI; B.
Carry, European Space Astronomy Centre, Spain; C. Neyman, Keck
Observatory; A. R. Conrad, Max Planck Institute for Astronomy,
Germany; C. R. Chapman, SwRI; J. C. Christou, Gemini Observatory;
C. Dumas, European Southern Observatory, Chile; and B. L. Enke,
SwRI, report resolved imaging of 2005 YU_55 during its close
passage by the earth on Nov. 9 in the near-infrared bands H and K_p
using the Keck II telescope (+ NIRC2/AO adaptive-optics system).
At the start of the observations (about 8 hr after closest approach
at 7h15m UT, when Delta = 0.00332 AU with solar phase angle 44 deg),
2005 YU_55 was at magnitude V = 11.1, with an angular size (of the
approximately 88-percent illuminated disk) of about 0".12.  The
images span 2.8 hr, until 10h03m UT (Delta = 0.00407 AU; phase 36
deg).  These data were used to derive dimensions under assumptions
of a smooth triaxial ellipsoid, having principal-axis rotation with
spin period 18 hr (from the JPL Small-Body Database).  There is the
usual 2-pole degeneracy, although the rapidly changing geometry
afforded a preference for prograde rotation.  The preliminary
solution has triaxial diameters of 337 x 324 x 267 m, with
estimated uncertainties of 15 m in each dimension; pole towards R.A.
= 282 deg, Decl. = +64 deg (equinox 2000.0; uncertainty radius
about 6 deg), or ecliptic lambda = 339 deg, beta = +84 deg.  The
spherical-equivalent diameter is then 308 m +/- 9 m.  The
retrograde pole is toward R.A. = 34 deg, Decl. = -24 deg
(uncertainty radius 15 deg), or ecliptic lambda = 22 deg, beta =
-35 deg, with dimensions 328 x 312 x 245 m (uncertainties of 15, 15,
30 m) and a spherical-equivalent diameter of 293 +/- 14 m.
Deviations from the ellipsoidal shape are evident.  Solutions are
also obtained by allowing a shorter spin period, but a shorter
period is not being asserted here.  No satellites typical of
near-earth objects were evident in this initial analysis (here
covering magnitude differences < 3 and orbit radius > 3 radii) of
2005 YU_55.


COMET C/2009 P1 (GARRADD)
     Visual total-magnitude and coma-diameter estimates:  Aug.
19.46 UT, 7.2, 12' (S. T. Rae, Hamilton, New Zealand, 9x63
binoculars); Sept. 26.85, 7.1, 9' (B. H. Granslo, Lillomarka, Oslo,
Norway, 10x50 binoculars); Oct. 22.77, 7.0, 7'.3 (W. Hasubick,
Buchloe, Germany, 10x50 binoculars); Nov. 13.71, 6.7, 3' (U. Pilz,
Leipzig, Germany, 8x24 binoculars); 17.80, 7.1, 9' (J. J. Gonzalez,
Asturias, Spain, 10x50 binoculars; 1.1-deg tail in p.a. 50 deg).

                      (C) Copyright 2011 CBAT
2011 November 24               (9242)            Daniel W. E. Green

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