Comoving stars in the Gaia era

Abstract

Comoving stars range from wide binaries to dense open clusters, and provide a unique window into the Milky Way. They are consequences of recent star formation which occurs highly clustered in giant molecular clouds, and the stellar and dynamical evolution that follows. Recent data releases from the Gaia astrometric mission together with the on-going large spectroscopic surveys provide an ideal playground to study the entire spectrum of comoving stars and illuminate the formation and disruption of these objects. This thesis contains a series of projects related to finding and characterizing comoving stars with the Gaia data. After a brief general introduction in Chapter 1, I develop a method to search for comoving pairs of stars using astrometric data based on a probabilistic model selection in Chapter 2. I apply the method to the first data release of the Gaia mission and find 13,085 pairs among 10,606 stars, which make up 4,555 comoving systems. I follow up two of these systems in detail. In Chapter 3, I study the metallicity and abundance differences of a wide binary, HD 240429 and HD 240430. I discuss the possible reasons for the significant and condensation temperature-dependent abundance differences between the two stars and argue that one of the stars has likely accreted a massive, rocky planetary system. In Chapter 4, I confirm and characterize the nearest and largest new comoving group discovered in Chapter 2, using the second data release of Gaia. I extend the candidate members and discuss its morphology in relation to its disruption.