Stellar Loci. VIII. Photometric Metallicities for 100 Million Stars Based on Synthetic Gaia Colors

TL;DR

This paper presents a method to estimate stellar metallicities for 100 million stars using synthetic Gaia colors, achieving high precision and enabling new studies of the Milky Way's formation and evolution.

Contribution

The study introduces a novel application of the stellar locus method to synthetic Gaia colors, significantly improving metallicity estimates for a vast number of stars.

Findings

Metallicity estimates for 100 million stars with 0.05-0.1 dex precision at [Fe/H]=0

Achieved metallicity precision down to 0.4-0.5 dex for very metal-poor stars

Catalog publicly available for further astrophysical research

Abstract

We apply the stellar locus method to synthetic $(BP-RP)_{XPSP}$ and $(BP-G)_{XPSP}$ colors derived from corrected Gaia BP/RP (XP) spectra to obtain precise estimates of metallicity for about 100 million stars in the Milky Way (34 million giants in the color range $0.6 < (BP-RP)_0 < 1.75$ and 65 million dwarfs in the color range $0.2 < (BP-RP)_0 < 1.5$). The sub milli-magnitude precision of the derived synthetic stellar colors enables estimates of metallicity for stars as low as [Fe/H] $\sim -4$. Multiple validation tests indicate that the typical metallicity precision is between 0.05 -- 0.1 dex for both dwarfs and giants at [Fe/H] = 0 as faint as G $\sim$ 16, and decreases to 0.15 -- 0.25 dex at [Fe/H] = $-$2.0. For $-4.0 < $[Fe/H]$< -3.0$, the typical metallicity precision decreases to on the order of 0.4 -- 0.5 dex, based on the results from the reference sample. Our achieved precision is comparable to or better than previous efforts using the entire XP spectra, and about three times better than our previous work based on Gaia EDR3 colors. This opens up new opportunities for investigations of stellar populations, the formation and chemical evolution of the Milky Way, the chemistry of stars and star clusters, and the identification of candidate stars for subsequent high-resolution spectroscopic follow-up. The catalog is publicly available at https://doi.org/10.12149/101548.