A study of the physical properties of an active asteroid (6478 Gault)

In 2019 January, the appearance of asteroid 6478 Gault immediately attracted attention because this object exhibited a long and thin tail that was quite different from the usual asteroids. This unexpected morphology placed asteroid 6478 Gault into the catalogue of active asteroids. We acquired photometric and spectroscopic observations on 37 nights from 2019 January to April using several telescopes, including LOT (1m telescope) and SLT (40cm telescope) at Lulin Observatory, and the 2.4m telescope at Lijiang station of Yunnan Observatory. We did not find any reliable value for the rotational period of Gault during 2.5 hr and 5 hr observations on 2019 January 26 at Lijiang station and March 25 at Lulin Observatory, respectively. We classified 6478 Gault as a Q-type asteroid using visible spectrum and photometric measurements, including colors (B - Vavg = 0.764 ± 0.045, V - Ravg = 0.450 ± 0.023), and relative reflectance. By using Finson-Probstein analysis, the grain size for Gault's tail 2 is larger than 20μm.