An unsupervised method for identifying $X$-enriched stars directly from spectra: Li in LAMOST

TL;DR

This paper introduces an unsupervised tangent space projection method to identify stars enriched with specific elements, like lithium, directly from spectra without requiring prior stellar labels, demonstrated on LAMOST data.

Contribution

The paper presents a novel unsupervised technique, tangent space projection, for detecting element-enriched stars directly from spectra, applicable to arbitrary elements and effective even with blended lines.

Findings

Identified 8,428 Li-enriched stars in LAMOST DR5.

Method works across different stellar evolutionary states.

Provides insights into mechanisms like planet accretion and stellar mixing.

Abstract

Stars with peculiar element abundances are important markers of chemical enrichment mechanisms. We present a simple method, tangent space projection (TSP), for the detection of $X$-enriched stars, for arbitrary elements $X$, even from blended lines. Our method does not require stellar labels, but instead directly estimates the counterfactual unrenriched spectrum from other unlabelled spectra. As a case study, we apply this method to the $6708~$\AA{} Li doublet in LAMOST DR5, identifying 8,428 Li-enriched stars seamlessly across evolutionary state. We comment on the explanation for Li-enrichement for different subpopulations, including planet accretion, nonstandard mixing, and youth.