Carbon-Enhanced Metal-Poor star candidates from BP/RP Spectra in $Gaia$ DR3

TL;DR

This study uses Gaia DR3 BP/RP spectra and machine learning to identify nearly 59,000 candidate carbon-enhanced metal-poor stars across the Milky Way, expanding the known sample and enabling future detailed analyses.

Contribution

It presents the first large-scale all-sky catalog of CEMP star candidates identified through Gaia spectra using XGBoost, with validation against high-resolution data.

Findings

Identified 58,872 CEMP candidates with 12% estimated contamination.

Validated 60-68% of candidates against high-resolution catalogs.

Candidates span from 0.8 to over 30 kpc from the Galactic center.

Abstract

Carbon-enhanced metal-poor (CEMP) stars comprise almost a third of stars with [Fe/H] < --2, although their origins are still poorly understood. It is highly likely that one sub-class (CEMP-$s$ stars) is tied to mass-transfer events in binary stars, while another sub-class (CEMP-no stars) are enriched by the nucleosynthetic yields of the first generations of stars. Previous studies of CEMP stars have primarily concentrated on the Galactic halo, but more recently they have also been detected in the thick disk and bulge components of the Milky Way. $Gaia$ DR3 has provided an unprecedented sample of over 200 million low-resolution ($R\approx$ 50) spectra from the BP and RP photometers. Training on the CEMP catalog from the SDSS/SEGUE database, we use XGBoost to identify the largest all-sky sample of CEMP candidate stars to date. In total, we find 58,872 CEMP star candidates, with an estimated contamination rate of 12%. When comparing to literature high-resolution catalogs, we positively identify 60-68% of the CEMP stars in the data, validating our results and indicating a high completeness rate. Our final catalog of CEMP candidates spans from the inner to outer Milky Way, with distances as close as $r \sim$ 0.8 kpc from the Galactic center, and as far as $r >$ 30 kpc. Future higher-resolution spectroscopic follow-up of these candidates will provide validations of their classification and enable investigations of the frequency of CEMP-$s$ and CEMP-no stars throughout the Galaxy, to further constrain the nature of their progenitors.