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Broadband Photometry of the Large Potentially Hazardous Asteroid 138095 (2000 DK79)

ATel #5591; M. Hicks (JPL/Caltech), S. Ebelhar (PCC)
on 20 Nov 2013; 03:24 UT
Credential Certification: Michael D. Hicks (Michael.Hicks@jpl.nasa.gov)

Subjects: Optical, Asteroid, Solar System Object, Near-Earth Object, Potentially Hazardous Asteroid

The Near-Earth Asteroid (NEA)138095 (2000 DK79) was discovered by the LINEAR Sky Survey on February 26, 2010 (MPEC 2000-E42). With a Minimum Orbit Intersection Distance (MOID) of 0.049 AU and an expected diameter between 1.8 km and 3 km, this object has been designated as a Potentially Hazardous Asteroid (PHA) by the Minor Planet Center. We obtained two partial nights of broadband Bessel BVRI photometry at the JPL Table Mountain 0.6-m telescope (TMO) on November 16 and 17, 2013, as summarized in Table 1. Additional observations were attempted on November 14 and 15, but were unsuccessful due to bad weather.

The rotationally averaged colors of the asteroid (B-R=1.223+/-0.024 mag; V-R=0.455+/-0.018 mag; R-I=0.296+/-0.013 mag) were found most compatible with an Sq-type spectral classification, an association obtained through a comparison of our colors with the 1341 asteroid spectra in the SMASS II database (Bus & Binzel 2002) [ Figure 1 and Table 2]. Assuming a solar phase parameter g=0.15 we determined an absolute magnitude H_V = 15.94+/-0.02 mag. 2000 DK79 is a large PHA: Assuming absolute magnitude as a proxy for size, 2000 DK79 is within the upper 98% of the 1435 PHAs currently known.

After correcting for observational geometry and using our color offsets for the B, V, and I photometry, we performed a rotational period search using standard Fourier techniques. Figure 2 plots chi-squared 3rd Fourier model misfit as a function of assumed rotation period. Assuming a double-peaked lightcurve, we found a best-fit synodic period P_syn = 4.24+/-0.02 hr, as shown in Figure 3.

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. 
                               Solar Expected 
   UT DATE       r     delta   Phase    V      Filters   Observer 
                [AU]    [AU]   [deg]  [mag] 
2013 11 16.16  1.040   0.169   67.8    14.4     BVRI     Hicks 
2013 11 17.14  1.041   0.182   68.6    14.6     BVRI     Hicks 
Table 2:  Best-fit SMASS II spectral analogs. 
                           TAXONOMIC CLASS 
1.503   2427 Kobzar                   Sq 
2.452    312 Pierretta         S      Sk 
2.827    699 Hela              S      Sq 
2.877   1785 Wurm                     S 
2.878   1977 Shura                    Sq