Broadband Photometry of the Potentially Hazardous Asteroid (153958) 2002 AM31: A Binary Near-Earth Asteroid
Authors:Tamara Davtyan, Michael Hicks
Mentor:Paul McCudden, Associate Professor of Physics and Astronomy, Los Angeles City College
The near-Earth asteroid 153958 (2002 AM31) was discovered on January 14, 2002 by the LINEAR NEO survey (MPEC 2002-A102) in New Mexico. The object passed within 0.035 AU of the Earth on July 22 2012 and has been identified as a Potentially Hazardous Asteroid (PHA) by the IAU Minor Planet Center. We were motivated by the PHA's favorable 2012 apparition and obtained 6 nights of time-resolved Bessel BVRI photometry and 5 nights of Bessel R photometry at the JPL Table Mountain Observatory (TMO) 0.6-m telescope. We generated a solar phase curve that was used to fit a standard H-G model ( H_R=18.43, G=0.61). The derived G value was found to indicate a high optical albedo and an E-type classification. However, our observations yielded that the object's averaged broad-band colors indices ( B−R=0.217±0.018 mag; V−R=0.066±0.010 mag, R−I=0.001±0.110 mag) were most compatible with an S-type spectral classification (Bus taxonomy). This association obtained through a comparison with the 1341 asteroid spectra collected by SMASS 2 survey (Bus & Binzel 2002) and was best matched by the S-type asteroid 485 Genua. If we adopt a diameter of 0.34 km obtained by Arecibo radar imaging, then we estimate geometric albedo p=0.61. Following this, we determined an Absolute V Magnitude H =18.50±0.02 mag which was significantly fainter than the H=15.08 listed in the JPL HORIZONS database. The dispersion in the phased lightcurve suggested that 2002 AM31 was a binary system, with variations in observed flux caused by an unresolved, tidally locked secondary companion. The TMO Photometry was fitted a 2-period lightcurve model as described by Pravec et al (2000) and revealed the presence of the primary and secondary rotation periods: P_1=3.206±0.004 and P_2=13.35±0.08, respectively.