Asteroid (3200) Phaethon: results of polarimetric, photometric, and spectral observations

TL;DR

This study provides comprehensive polarimetric, photometric, and spectral data on asteroid (3200) Phaethon during its close approach, revealing its low albedo, polarization characteristics, and surface composition, enhancing understanding of its physical properties.

Contribution

It offers new detailed observational data and modeling results for Phaethon, including polarization behavior, albedo estimation, and surface composition analysis, during its 2017 and 2020 approaches.

Findings

Maximum linear polarization of 45% at 124° phase angle

Geometric albedo of 0.06 for Phaethon

Effective diameter estimated at 6.8 km

Abstract

We present results of polarimetric, photometric, and spectral observations of the near-Earth asteroid (3200) Phaethon carried out at the 6-m BTA telescope of the Special Astrophysical Observatory and the 2.6-m and 1.25-m telescopes of the Crimean Astrophysical Observatory over a wide range of phase angles during its close approach to the Earth at the end of 2017 (19-135 deg) and in 2020 at \alpha = 52.2 deg. Using our and other available in literature data, we found that the maximum degree of linear polarization of Phaethon in the V band is 45% at the phase angle 124 deg. Using the dependence (polarimetric slope-albedo) we have found the geometric albedo of asteroid Phaethon to be 0.06. This value falls into the lower range of albedo values for asteroids determined by different methods. The mean color indices U-B=0.207 and B-V=0.639 of the asteroid are derived at heliocentric and geocentric distances 1.077 au and 0.102 au, respectively. The effective diameter of Phaethon is estimated from obtained absolute magnitude and geometrical albedo, it is equal to 6.8 km. The best fit to the observed polarimetric data was obtained with the Sh-matrix model of conjugated random Gaussian particles composed of Mg-rich silicate (90%) and amorphous carbon (10%).