Main-belt and Trojan asteroid phase curves from the ATLAS survey

Sparse and serendipitous asteroid photometry obtained by wide field surveys such as the Asteroid Terrestrial-impact Last Alert System (ATLAS) is a valuable resource for studying the properties of large numbers of small Solar System bodies. We have gathered a large data base of ATLAS photometry in wideband optical cyan and orange filters, consisting of 9.6 × 107 observations of 4.5 × 105 main belt asteroids and Jupiter Trojans. We conduct a phase curve analysis of these asteroids considering each apparition separately, allowing us to accurately reject outlying observations and to remove apparitions and asteroids not suitable for phase curve determination. We obtain a data set of absolute magnitudes and phase parameters for over 100 000 selected asteroids observed by ATLAS, $\sim 66\, 000$ of which had sufficient measurements to derive colours in the ATLAS filters. To demonstrate the power of our data set we consider the properties of the Nysa–Polana complex, for which the ATLAS colours and phase parameters trace the S-like and C-like compositions amongst family members. We also compare the properties of the leading and trailing groups of Jupiter Trojans, finding no significant differences in their phase parameters or colours as measured by ATLAS, supporting the consensus that these groups were captured from a common source population during planetary migration. Furthermore, we identify ∼9000 asteroids that exhibit large shifts in derived absolute magnitude between apparitions, indicating that these objects have both elongated shapes and spin axes with obliquity ∼90 degrees.