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Broadband Photometry Of The Potentially Asteroid 277475 (2005 WK4) and Corrected 52762 (1998 MT24) Colors.

ATel #5311; M. Hicks (JPL/Caltech), B. BurattJPL/Caltech), A. Carcione (Moorpark), R. Borlase (PCC)
on 23 Aug 2013; 00:28 UT
Credential Certification: Michael D. Hicks (Michael.Hicks@jpl.nasa.gov)

Subjects: Optical, Asteroid, Planet (minor), Solar System Object, Near-Earth Object, Potentially Hazardous Asteroid, Asteroid (Binary)

The Near-Earth Object (NEO) 277475 (2005 WK4) was discovered by the Siding Spring Survey (MPEC 2005-W79) on November 27, 2005. With a Minimum Orbit Intersection Distance (MOID) of 0.004 AU and absolute magnitude H_V=20.1 mag, this object has been designated a Potentially Hazardous Asteroid (PHA) by the Minor Planet Center. The asteroid made an Earth close-approach of 0.021 AU on August 09.2, 2013 and was extensively imaged by the JPL Planetary Radar Team ( http://www.jpl.nasa.gov/news/news.php?release=2013-254 ).

We obtained two partial nights of Bessel BVRI photometry at the JPL Table Mountain 0.6-m telescope, with observational circumstances listed in Table 1. Although the weather was photometric, equipment problems forced us to reject a large fraction of our data on both nights. No meaningful lightcurve information could be extracted from our photometry. The averaged colors (B-V=1.234+/-0.017 mag; V-R=0.446+/-0.019 mag; R-I=0.304+/-0.14 mag) were found most compatible with an Sk spectral type (Bus Taxonomy) as shown in Figure 1 and Table 2. When reduced to zero phase, assuming a solar phase parameter g=0.15, our photometry yields an absolute magnitude H_V=20.09+/-0.03 mag, consistent with the absolute magnitude H_V=20.071 listed in the JPL Small-Body Database.

We regret that our reported colors for 1999 MT24 (ATel #5306) were incorrect. The correct colors are B-R=1.123+/-0.038 mag; V-R=0.041+/-0.030 mag; R-I=0.401+/-0.016 mag. We are grateful to Gerhard Hahn and Brian Warner for bringing this to our attention.

Copyright 2013. All rights reserved. The research described in this telegram was carried out at the Jet Propulsion Laboratory, under a contract with the National Aeronautics and Space Administration. The student participation was supported by the National Science Foundation under REU grant AST-1156756 to Los Angeles City College.

Table 1:  Observational circumstances. 
   UT DATE       r     delta   Phase   V        Observers 
                [AU]    [AU]   [deg]  [mag] 
2013 08 08.46  1.015   0.021   85.6   14.7      Borlase, Carcione 
2013 08 12.95  1.031   0.026   45.4   13.9      Hicks, Buratti 
Table 2:  Best-fit SMASS II spectral analogs. 
                           TAXONOMIC CLASS 
1.523  5407 (1992 AX)                  Sk 
1.640  4327 Ries                       Sk 
1.758     3 Juno              S        Sk 
1.801  2427 Kobzar                     Sq 
1.960   699 Hela              S        Sq