[ Previous | Next | ADS ]

Broadband Photometry 330825 (2008 XE3): A Potential Binary Near-Earth Asteroid.

ATel #4591; M. Hicks (JPL/Caltech), D. Dombroski (LACC), M. Brewer (VVC)
on 20 Nov 2012; 19:02 UT
Credential Certification: Michael D. Hicks (Michael.Hicks@jpl.nasa.gov)

Subjects: Optical, Asteroid, Solar System Object, Near-Earth Object, Asteroid (Binary)

The near-Earth asteroid 330825 (2008 XE3) was discovered on 2008 December 12 by the LINEAR NEO survey (MPEC 2008-X63). We obtained two nights of Bessel BVRI (2012 November 04 and November 07) and one night of Bessel R observations (November 05) of the object at the JPL Table Mountain Observatory (TMO) 0.6-m telescope. The observational circumstances are summarized in Table 1.

The object's rotationally averaged colors (B-R=1.250+/-0.041 mag; V-R=0.441+/ 0.020 mag; R-I=0.354+/-0.018 mag) were found most compatible with an S-type spectral classification (Bus Taxonomy)/S-type (Tholen Taxonomy). This association was 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, typical for S-family asteroids, we performed a period search using standard Fourier techniques and fit a rotational period P_syn=4.414+/-0.002 hr [Figure 2]. The dispersion in the phased lightcurve was incompatible with changing viewing/illumination geometry (the solar phase angle remains relatively constant through our observations) and suggests that 2008 XE3 is likely a binary system, with the variations in observed flux caused by an unresolved, tidally locked secondary companion. Fitting a 2-period model as described by Pravec et al. (2000), we found that our photometry agrees well with a binary model (P_1=4.412+/-0.02 hr, P_2=29.71+/-0.05 hr) [Figure 3]. Our measured absolute magnitude H_V=16.37+/-0.03 mag implies an effective diameter of the combined system D~1.8 km, assuming a geometric albedo rho=0.15.

Copyright 2012. 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 Time           r    delta  phase   V   Filters  Observers 
                [AU]    [AU]  [deg] [mag] 
2012 11 04.27  1.315   0.361  22.9  15.8   BVRI    Dombroski 
2012 11 05.30  1.320   0.365  22.3  15.8     R     Hicks 
2012 11 07.23  1.330   0.374  21.3  15.8   BVRI    Brewer 
Table 2:  Best-fit SMASS II spectral analogs. 
                          Taxonomic Class 
Misfit  Object Name        (Tholen) (Bus) 
0.491   485 Genua                     S 
0.627  4702 Berounka                  S 
0.658   389 Industria         S       S 
0.668  4327 Ries                      Sk 
0.741    11 Parthenope        S       Sk