Nearly 30,000 late-type main-sequence stars with stellar age from LAMOST DR5

TL;DR

This study analyzes nearly 30,000 main-sequence stars from LAMOST DR5 to explore the Galaxy's age distribution, disk flare, and vertical perturbations, revealing age-related structural and kinematic features in the Milky Way.

Contribution

It provides a large stellar sample with age estimates to study Galactic structure, flare, and vertical perturbations, highlighting recent disk perturbation effects.

Findings

Older stars are more prevalent at higher |Z|.

A mild flare in stellar age distribution from R ~ 8.0 to 9.0 kpc.

Spiral structures in Z-velocity phase space indicate recent vertical perturbations.

Abstract

We construct a sample of nearly 30,000 main-sequence stars with 4500K $<T\rm_{eff}<$ 5000K and stellar ages estimated by the chromospheric activity$-$age relation. This sample is used to determine the age distribution in the $R-Z$ plane of the Galaxy, where $R$ is the projected Galactocentric distance in the disk midplane and $Z$ is the height above the disk midplane. As $|Z|$ increases, the percentage of old stars becomes larger. It is known that scale-height of Galactic disk increases as $R$ increases, which is called flare. A mild flare from $R$ $\sim$ 8.0 to 9.0 kpc in stellar age distribution is found. We also find that the velocity dispersion increases with age as confirmed by previous studies. Finally we present spiral-shaped structures in $Z-\upsilon_{Z}$ phase space in three stellar age bins. The spiral is clearly seen in the age bin of [0, 1] Gyr, which suggests that a vertical perturbation to the disk probably took place within the last $\sim$ 1.0 Gyr.