Nearly 30,000 Late-type Main-sequence Stars with Stellar Age from LAMOST DR5

Abstract

We construct a sample of nearly 30,000 main-sequence stars with 4500 K < T_eff < 5000 K 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 a flare. A mild flare from R ∼ 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-υ_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 ∼1.0 Gyr.