Abstract

Classification of stars based on common chemistry or dynamics form the bedrock of Galactic Archaeology. While both chemical and dynamic tagging are powerful diagnostics in their own right, the combination, i.e., chemo-dynamic tagging, proves more potent. We present two results from this method. The first covers the conatal nature of comoving and the other explores the origins of the fastest stars in the Galaxy. Conatal systems are a gold standard for exploring subtleties of stellar astrophysics since they are expected to exhibit a common chemical pattern. We find observational evidence for an overlooked reservoir of conatal stars, the unbound co-moving pairs. We find systems with separations of 1-50 pc are ~73 +/- 22% conatal. This shows how chemical tagging, with kinematic constraints, can hold at much wider separations than binaries. Encouraged by this, we use the combination of chemical tagging and orbits to address possible origins of 17 candidate hypervelocity stars (HVSs).  An evolving picture of these objects has emerged where they are produced by several mechanisms and thus show a diversity of chemical patterns. We confirm one star is unbound and two are marginally bound. One bound star has an [alpha/Fe] ~0.2 dex, suggesting it may be accreted. The rest of the sample is chemically consistent with the inner Halo, including all the unbound stars. We are unable to associate the unbound stars with known globular clusters or satellite galaxies. Hence we conclude all but one star are from the halo, with the unbound stars being runaways.