Chemical Doppelgangers in GALAH DR3: the Distinguishing Power of Neutron-Capture Elements Among Milky Way Disk Stars

TL;DR

This study demonstrates that including neutron-capture element abundances significantly enhances the chemical differentiation of Milky Way disk stars, reducing the likelihood of false chemical matches and revealing additional information about stellar populations.

Contribution

It introduces the use of neutron-capture elements in chemical tagging, showing their importance in distinguishing stars beyond lighter element analysis.

Findings

Including neutron-capture elements reduces the doppelganger rate from 2.2% to 0.4%.

Neutron-capture elements add a new dimension to chemical space, improving star differentiation.

Chemical similarity with neutron-capture elements does not necessarily imply similarity in age or dynamics.

Abstract

The observed chemical diversity of Milky Way stars places important constraints on Galactic chemical evolution and the mixing processes that operate within the interstellar medium. Recent works have found that the chemical diversity of disk stars is low. For example, the APOGEE "chemical doppelganger rate," or the rate at which random pairs of field stars appear as chemically similar as stars born together, is high, and the chemical distributions of APOGEE stars in some Galactic populations are well-described by two-dimensional models. However, limited attention has been paid to the heavy elements (Z > 30) in this context. In this work, we probe the potential for neutron-capture elements to enhance the chemical diversity of stars by determining their effect on the chemical doppelganger rate. We measure the doppelganger rate in GALAH DR3, with abundances rederived using The Cannon, and find that considering the neutron-capture elements decreases the doppelganger rate from 2.2% to 0.4%, nearly a factor of 6, for stars with -0.1 < [Fe/H] < 0.1. While chemical similarity correlates with similarity in age and dynamics, including neutron-capture elements does not appear to select stars that are more similar in these characteristics. Our results highlight that the neutron-capture elements contain information that is distinct from that of the lighter elements and thus add at least one dimension to Milky Way abundance space. This work illustrates the importance of considering the neutron-capture elements when chemically characterizing stars and motivates ongoing work to improve their atomic data and measurements in spectroscopic surveys.