A GALAH View of the Chemical Homogeneity and Ages of Stellar Strings
  Identified in Gaia
  The advent of Gaia has led to the discovery of nearly 300 elongated stellar
associations (called `strings') spanning hundreds of parsecs in length and mere
tens of parsecs in width. These newfound populations present an excellent
laboratory for studying the assembly process of the Milky Way thin disk. In
this work, we use data from GALAH DR3 to investigate the chemical distributions
and ages of 18 newfound stellar populations, 10 of which are strings and 8 of
which are compact in morphology. We estimate the intrinsic abundance
dispersions in [X/H] of each population and compare them with those of both
their local fields and the open cluster M 67. We find that all but one of these
groups are more chemically homogeneous than their local fields. Furthermore,
half of the strings, namely Theias 139, 169, 216, 303, and 309, have intrinsic
[X/H] dispersions that range between 0.01 and 0.07 dex in most elements,
equivalent to those of many open clusters. These results provide important new
observational constraints on star formation and the chemical homogeneity of the
local interstellar medium (ISM). We investigate each population's Li and
chemical clock abundances (e.g., [Sc/Ba], [Ca/Ba], [Ti/Ba], and [Mg/Y]) and
find that the ages suggested by chemistry generally support the isochronal ages
in all but six structures. This work highlights the unique advantages that
chemistry holds in the study of kinematically-related stellar groups.
