On the basis of a recently derived color-metallicity relation and stellar parameters from the Sloan Digital Sky Survey Data Release 7 spectroscopic survey, a large sample of red horizontal-branch (RHB) candidates have been selected to serve as standard candles. The metallicity and kinematic distributions of these stars indicate that they mainly originate from the thick-disk and the halo populations. The typical thick disk is characterized by the first group peaking at [Fe/H] ∼ -0.6, Vrot∼ 170 km/s with a vertical scale height around|Z| ∼ 1.2 kpc, while stars with [Fe/H] < -0.9 are dominated by the halo population. Two sub-populations of the halo are suggested by the RHB stars peaking at [Fe/H] ∼ -1.3: one component with Vrot> 0 km/s (Halo I) shows a sign of metallicity gradient in the [Fe/H] versus |Z| diagram, while the other with Vrot< 0 km/s (Halo II) does not. The Halo I mainly clumps at the inner halo with R < 10 kpc and the Halo II comes both from the inner halo with R < 10 kpc and the outer halo with R > 10 kpc based on the star distribution in the R versus|Z| diagram.
Galaxy: disk - Galaxy: halo - Galaxy: kinematics and dynamics - stars: horizontal-branch
VizieR on-line data:
<Available at CDS (J/AJ/140/500): table1.dat>