Electronic Telegram No. 2937
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


2005 YU_55
     Dennis Bodewits, University of Maryland (UM), College Park; Sergio
Campana, Istituto Nazionale di Astrofisica, Osservatorio Astronomico di Brera,
Merate; Jamie Kennea, Pennsylvania State University, University Park;
Jian-Yang Li, UM; Samantha Oates, Mullard Space Science Laboratory,
University College London, Holmbury St. Mary; Stefan Immler, UM and Goddard
Space Flight Center (GSFC), NASA; and Neil Gehrels, GSFC, NASA, report
ultraviolet photometry of 2005 YU_55 (cf. IAUC 9241, 9242), taken with the
Ultraviolet/Optical Telescope (UVOT) onboard the Swift Gamma Ray Observatory
during the minor planet's close encounter with the earth.  Tracking was not
attempted.  Instead, fluxes were measured using 'event-mode', allowing
reconstructing an image 2005 YU_55 as it moved over the detector.  The object
was observed three times with the uvm2 filter (center wavelength 260 nm;
FWHM 70 nm) and once with the v filter (center 546.8 nm; FWHM 75 nm).  The
following magnitudes were measured:  Nov. 8.0717 UT, [uvm2] = 16.07 +/- 0.05;
Nov. 8.0717, [uvm2] = 15.53 +/- 0.02; Nov. 12.1569, [uvm2] = 18.68 +/- 0.08;
Nov. 12.0304, v = 14.27 +/- 0.02.  The best fit to the ultraviolet (UV) data
suggests an absolute UV magnitude of H_uv = 25.6 and G = -0.13.  An absolute
magnitude H_v = 21.2 is found using the same phase curve for the v band.
Assuming the spherical equivalent diameter reported by Merline et al. on
IAUC 9242 implies a visual geometrical albedo of 0.064, and 0.044 at 245 nm
(the effective wavelength of the uvm2 filter; see Li et al. 2011, Icarus
216, 640).  The albedo, color, and phase curve are consistent with values
that are characteristic for C-type asteroids (cf. Roettger and Buratti 1994,
Icarus 112, 496).


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      superseded by text appearing later in the printed IAU Circulars.

                         (C) Copyright 2011 CBAT
2011 December 5                  (CBET 2937)              Daniel W. E. Green