Gaia DR3 asteroid reflectance spectra: L-type families, memberships, and ages

Abstract

The Gaia Data Release 3 (DR3) contains reflectance spectra at visible wavelengths for 60,518 asteroids over the range between 374-1034 nm, representing a large sample that is well suited to studies of asteroid families. We want to assess the potential of Gaia spectra in identifying asteroid family members. Here, we focus on two L-type families, namely Tirela/Klumpkea and Watsonia. These families are known for their connection to Barbarian asteroids, which are potentially abundant in calcium-aluminum rich inclusions (CAIs). Our method is based (1) on a color taxonomy specifically built on Gaia data and (2) the similarity of spectra of candidate members with the template spectrum of a specific family. We identified objects in the halo of Tirela/Klumpkea, along with possible interlopers. We also found an independent group of eight asteroids erroneously linked to the family by the hierarchical clustering method (HCM). Consequently, the knowledge of the size distribution of the family has been significantly improved, with a more consistent shape at the larger end. The Watsonia family is a more intricate case, mainly due to its smaller size and the less marked difference between the spectral types of the background and of the family members. However, the spectral selection helps identify objects that were not seen by HCM, including a cluster separated from the family core by a resonance. For both families, the V-shape is better defined, leading to a revised age estimation based on the memberships established mainly from spectral properties. Our work demonstrates the advantage of combining the classical HCM approach to spectral properties obtained by Gaia for the study of asteroid families. Future data releases are expected to further expand the capabilities in this domain