A GALAH View of the Chemical Homogeneity and Ages of Stellar Strings Identified in Gaia

TL;DR

This study uses GALAH DR3 data to analyze the chemical compositions and ages of 18 stellar groups identified in Gaia, revealing their chemical homogeneity and providing insights into star formation and the Milky Way's disk assembly.

Contribution

It offers the first detailed chemical and age analysis of newly discovered stellar strings, demonstrating their chemical homogeneity and comparing them with open clusters and field stars.

Findings

Most groups are more chemically homogeneous than local fields.

Half of the strings have abundance dispersions similar to open clusters.

Chemical ages generally agree with isochronal ages, supporting chemical clocks.

Abstract

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.