Polarimetric and photometric observations of NEAs; (422699) 2000 PD3 and (3200) Phaethon with the 1.6m Pirka telescope

摘要

We report on optical polarimetric observations of two Apollo type near-Earth asteroids, (422699) 2000 PD3 and (3200) Phaethon, and BVRI photometric observations of 2000 PD3 using the 1.6 m Pirka telescope in 2017. We derived the geometric albedo of p(v)` = 0.22 +/- 0.06 and the color indices (B-V = 0.282 +/- 0.072, V-R = 0.198 +/- 0.035 and V-I = 0.203 +/- 0.022) for 2000 PD3 which are consistent with those of S-type asteroids (including Q-types). The effective diameter of 2000 PD3 was derived as 0.69 +/- 0.15 km using our derived geometric albedo. We found that our polarimetric data of Phaethon in 2017 is deviated from the polarimetric profile taken at different epoch of 2016 using the identical instrument setting (Ito et al., 2018). This result suggests that Phaethon would have a regional heterogeneity in grain size and/or albedo on its surface.