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Broadband Photometry of the Potentially Hazardous Asteroid 251346 (2007 SJ)

ATel #5801; M. Hicks (JPL/Caltech), S. Ebelhar (PCC)
on 24 Jan 2014; 03:15 UT
Credential Certification: Michael D. Hicks (Michael.Hicks@jpl.nasa.gov)

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

The Near-Earth Asteroid (NEA) 251346 (2007 SJ) was discovered by the LINEAR Sky Survey on September 17, 2007 (MPEC 2007-S17). With a Minimum Orbit Intersection Distance (MOID) of 0.045 AU and an expected diameter between 1.3~2.8 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 (October 10 and December 11, 2013) and one night (December 13, 2013) at the JPL Table Mountain 0.6-m telescope (TMO), as summarized in Table 1.

The rotationally averaged colors of 251346 (2007 SJ) [B-R=1.297+/-0.027 mag; V-R=0.484+/-0.019 mag; R-I=0.350+/-0.031 mag] were compared with the 1341 asteroid spectra in the SMASS II database (Bus & Binzel, 2002). The best-fit match was found in 1014 Semphryra, an Xe-type asteroid. The NEA was also well matched by several K and S-type asteroids [ Figure 1 and Table 2]. E-family asteroids typically exhibit high albedos and can be distinguished from S-family asteroids by solar phase behavior (Belskaya & Shevchenko, 1999). Correcting for heliocentric and geocentric distances, our R-band photometry was used to construct the solar phase curve shown in Figure 2 and allowed us to solve for an absolute magnitude H_R=16.68+/-0.01 mag (H_V=17.16+/-0.03 mag) and phase parameter g=0.31, corresponding to phase coefficient as measured between 10 deg and 20 deg of 0.029 mag/deg. This suggests an albedo (rho=0.22+/-0.05) consistent with S-family asteroids. 2007 SJ is likely an S-family asteroid.

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 3 plots chi-squared 4th order Fourier model misfit as a function of assumed rotation period. We found a best-fit synodic period P_syn = 2.718+/-0.007 hr [ Figure 4 ], in agreement with the 2.7 hr period reported by Brian Warner (http://echo.jpl.nasa.gov/asteroids/2007SJ/2007SJ_planning.html).


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 10 17.26  1.411   0.451   18.9    16.8     BVRI     Ebelhar 
2013 12 11.18  1.076   0.207   58.8    15.7     BVRI     Hicks 
2013 12 13.18  1.064   0.199   61.3    15.6       R      Hicks 
 
 
 
 
Table 2:  Best-fit SMASS II spectral analogs. 
 
                           TAXONOMIC CLASS 
MISFIT    OBJECT NAME      (THOLEN)  (BUS) 
0.852   1014 Semphyra                 Xe 
0.915    397 Vienna            S      K 
1.026    513 Centesima         S      K 
1.076    905 Universitas              S 
1.545   1640 Nemo                     S