The GALAH survey: Co-orbiting stars and chemical tagging
  We present a study using the second data release of the GALAH survey of
stellar parameters and elemental abundances of 15 pairs of stars identified by
Oh et al 2017. They identified these pairs as potentially co-moving pairs using
proper motions and parallaxes from Gaia DR1. We find that 11 very wide (>1.7
pc) pairs of stars do in fact have similar Galactic orbits, while a further
four claimed co-moving pairs are not truly co-orbiting. Eight of the 11
co-orbiting pairs have reliable stellar parameters and abundances, and we find
that three of those are quite similar in their abundance patterns, while five
have significant [Fe/H] differences. For the latter, this indicates that they
could be co-orbiting because of the general dynamical coldness of the thin
disc, or perhaps resonances induced by the Galaxy, rather than a shared
formation site. Stars such as these, wide binaries, debris of past star
formation episodes, and coincidental co-orbiters, are crucial for exploring the
limits of chemical tagging in the Milky Way.
