[PPS03-P17] Polarimetric and Photometric observations of NEAs with the 1.6m Pirka Telescope
Keywords:NEAs, polarimetric observations, polarization degree, albedo, taxonomy
Polarimetry is a useful method for investigating asteroids’ physical properties such as the albedo, regolith particle size and taxonomy of asteroids. In general, Pr (the linear polarization degree) exhibits a strong dependence on the phase angle (Sun-Target-Observer’s angle, α).
In order to understand Pmax (maximum Polarization degree) , we attempted to obtain polarimetric data at different phase angles (α=22°-120°). A geometric albedo of pv=0.26±0.06% were derived from a limited α range ( 25°-84°) which is in good agreement with that of S-type asteroids. BVRI photometric data (B-V=0.132±0.002mag,V-R=0.114±0.002mag,V-I=0.180±0.002mag) supports S-type classification.
In October 2017, 2012 TC4 approached to the Earth at about 50,000 km of the closest distance. A fast rotation period about 0.2 hours (Ryan and Ryan, 2017) indicates a monolithic suraface layer which is not covered with a rubble pile. The liner polarization Pr=5.62±5.26% (α=34°) in the R-band is in close accord with that of C-type asteroids, although October run was performed under bad weather.
This asteroid is widely recognized as the parent body of the Geminid meteoroid stream. In December 2017, we had an opportunity to obtain polarimetric data at extremely large phase angle(α=110°-130°). However, only data down to α=58° were acquired. The results of analysis show Pr=1.58±0.22% (α=34°) and 15.02±0.13% (α=58°) in the V-band, which is consistent with those of low albedo asteroids such as B, F, and D-type.