Beyond spectroscopy. II. Stellar parameters for over twenty million stars in the northern sky from SAGES DR1 and Gaia DR3

TL;DR

This paper provides precise photometric estimates of stellar parameters for nearly 26 million stars in the northern sky, utilizing SAGES DR1 and Gaia DR3 data, significantly enhancing our understanding of the Milky Way's formation and evolution.

Contribution

It introduces a new methodology for deriving stellar parameters from combined SAGES and Gaia data, enabling large-scale, accurate characterization of stars including metallicity and age.

Findings

Over five million metal-poor stars identified

Photometric metallicity estimates accurate to 0.1 dex for [Fe/H]>-1.0

Large dataset will improve models of Milky Way evolution

Abstract

We present precise photometric estimates of stellar parameters, including effective temperature, metallicity, luminosity classification, distance, and stellar age, for nearly 26 million stars using the methodology developed in the first paper of this series, based on the stellar colors from the Stellar Abundances and Galactic Evolution Survey (SAGES) DR1 and Gaia EDR3. The optimal design of stellar-parameter sensitive $uv$ filters by SAGES has enabled us to determine photometric-metallicity estimates down to $-3.5$, similar to our previous results with the SkyMapper Southern Survey (SMSS), yielding a large sample of over five million metal-poor (MP; [Fe/H]$\le -1.0$) stars and nearly one million very metal-poor (VMP; [Fe/H]$\le -2.0$) stars. The typical precision is around $0.1$ dex for both dwarf and giant stars with [Fe/H]$>-1.0$, and 0.15-0.25/0.3-0.4 dex for dwarf/giant stars with [Fe/H]$<-1.0$. Using the precise parallax measurements and stellar colors from Gaia, effective temperature, luminosity classification, distance and stellar age are further derived for our sample stars. This huge data set in the Northern sky from SAGES, together with similar data in the Southern sky from SMSS, will greatly advance our understanding of the Milky Way, in particular its formation and evolution.