RED GIANT STARS FROM SLOAN DIGITAL SKY SURVEY. I. THE GENERAL FIELD

摘要

We have obtained a sample of ~22,000 red giant branch (RGB) stars based on stellar parameters, provided by the ninth data release of the Sloan Digital Sky Survey, and the CH(G)/MgH indices, measured from the included spectra. The Galactic rest-frame velocity of V gsr versus longitude for the sample shows the existence of several groups of stars from globular clusters and known streams. Excluding these substructures, a sample of ~16,000 RGB stars from the general field is used to investigate the properties of the thick disk, the inner halo, and the outer halo of our Galaxy. The metallicity and rotational velocity distributions are investigated for stars at 0 kpc |Z| 10?kpc. It is found that the canonical thick disk dominates at 0 kpc |Z| 2?kpc and its contribution becomes negligible at |Z| 3?kpc. The MWTD is present and overlaps with the inner halo at 1 kpc |Z| 3?kpc. The inner halo starts at 2 kpc |Z| 3?kpc and becomes the dominated population for 4 kpc |Z| 10?kpc. For halo stars with |Z| 5?kpc, bimodal metallicity distributions are found for 20 kpc |Z| 25?kpc and 35 kpc RR 45?kpc, which suggests a dual halo, the inner and the outer halo, as reported in Carollo et al. at low |Z| values. The peak of metallicity for the inner halo is at [Fe/H] ~ –1.6 and appears to be at [Fe/H] ~ –2.3 for the outer halo. The transition point from the inner to the outer halo is located at |Z| ~ 20?kpc and RR ~ 35?kpc.