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

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 submillimagnitude precision of the derived synthetic stellar colors enables estimates of metallicity for stars as low as [Fe/H] ∼ −4. Multiple validation tests indicate that the typical metallicity precision is between 0.05 and 0.1 dex for both dwarfs and giants at [Fe/H] = 0, as faint as G  ∼ 16, and decreases to 0.15–0.25 dex at [Fe/H] = −2.0. For −4.0