Ages and masses of million Galactic disk main sequence turn-off and sub-giant stars from the LAMOST Galactic spectroscopic surveys

TL;DR

This study estimates ages and masses for nearly one million Galactic disk stars using LAMOST spectra, revealing detailed stellar population structures and disk evolution patterns.

Contribution

It provides the first large-scale, robust age and mass estimates for a vast sample of disk stars, utilizing Bayesian isochrone matching with spectroscopic data.

Findings

Median age error is 34%, with better accuracy for stars older than 2 Gyr.

Clear correlations among age, metallicity, and alpha-element abundance.

Discovery of double sequence features in age--[$ mf extalpha$/Fe] and age--[Fe/H] spaces.

Abstract

We present estimates of stellar age and mass for 0.93 million Galactic disk main sequence turn-off and sub-giant stars from the LAMOST Galactic Spectroscopic Surveys. The ages and masses are determined by matching with stellar isochrones using Bayesian algorithm, utilizing effective temperature $T_{\rm eff}$, absolute magnitude ${\rm M}_V$, metallicity [Fe/H] and $\alpha$-element to iron abundance ratio [$\alpha$/Fe] deduced from the LAMOST spectra. Extensive examinations suggest the age and mass estimates are robust. The overall sample stars have a median error of 34 per cent for the age estimates, and half of the stars older than 2\,Gyr have age uncertainties of only 20--30 per cent. Median error for the mass estimates of the whole sample stars is $\sim8$ per cent. The huge dataset demonstrates good correlations among stellar age, [Fe/H] ([$\alpha$/H]) and [$\alpha$/Fe]. Particularly, double sequence features are revealed in the both the age--[$\alpha$/Fe] and age--[Fe/H]([$\alpha$/H]) spaces. In the [Fe/H]--[$\alpha$/Fe] space, stars of 8--10\,Gyr exhibit both the thin and thick disk sequences, while younger (older) stars show only the thin (thick) disk sequence, indicating that the thin disk became prominent 8--10\,Gyr ago, while the thick disk formed earlier and almost quenched 8\,Gyr ago. Stellar ages exhibit positive vertical and negative radial gradients across the disk, and the outer disk of $R\gtrsim$\,9\,kpc exhibits a strong flare in stellar age distribution.