A value-added catalogue of neural network-based europium abundances for GALAH DR4

TL;DR

This paper introduces a neural network-based method to produce a high-quality, homogeneous catalogue of europium abundances for nearly 120,000 GALAH DR4 stars, improving precision and coverage, especially at low metallicities.

Contribution

It develops a CNN-based label transfer technique to enhance europium abundance measurements in GALAH DR4, creating a large, high-confidence, publicly available catalogue.

Findings

Achieved high-precision europium abundances for over 54,000 giants.

Reproduced known Galactic chemical evolution trends.

Provided europium abundances for metal-poor stars using spectral synthesis.

Abstract

The rapid neutron-capture ($r$-process) element europium (Eu) is a valuable tracer of neutron star mergers and other rare nucleosynthetic events. The stellar spectroscopic survey GALAH's unique wavelength range and setup include the Eu absorption feature at $\sim6645$ \r{A} for almost a million stars in the most recent Data Release 4 (DR4). However, DR4 also saw a decreased precision in reported Eu measurements compared to previous data releases. In this work, we use a convolutional neural network (CNN) to perform label transfer, wherein we use the GALAH DR4 spectra and stellar parameters to infer DR3 [Eu/H] abundances. This CNN is then applied to DR4 spectra without corresponding DR3 Eu abundances to develop a new, publicly available catalogue of [Eu/H] values for high signal-to-noise targets. We include [Eu/H] predictions for $118\,946$ stars, out of which $54\,068$ giants constitute our "golden sample" of high-confidence predictions, which pass stricter quality cuts and have a reported precision $\lesssim0.1$. To overcome the scarcity of training data in the low metallicity regime, we provide an additional catalogue of [Eu/H] abundances for metal poor ($\mathrm{[Fe/H]}<-1$) stars derived from synthesis of the Eu feature. Our "golden sample" can be combined with [Eu/H] values from GALAH DR3 to create a catalogue of over $100\,000$ vetted, high-quality abundances on a homogeneous scale. Moreover, we are able to reproduce known science results, including the elevated Eu abundances of accreted stars and previously observed Galactic chemical evolution trends. This catalogue represents one of the largest available samples of [Eu/H] abundances for high signal-to-noise targets.