Tracing Kinematic and Chemical Properties of Sagittarius Stream by K-Giants, M-Giants, and BHB stars

Abstract

We characterize the kinematic and chemical properties of ∼3000 Sagittarius (Sgr) stream stars, including K-giants, M-giants, and blue horizontal branch stars (BHBs), selected from SEGUE-2, Large Sky Area Multi-Object Fibre Spectroscopic Telescope, and Sloan Digital Sky Survey separately in Integrals-of-Motion space. The orbit of the Sgr stream is quite clear from the velocity vector in the X-Z plane. Stars traced by K-giants and M-giants show that the apogalacticon of the trailing steam is ∼100 kpc. The metallicity distributions of Sgr K-giants, M-giants, and BHBs indicate that the M-giants are on average the most metal-rich population, followed by K-giants and BHBs. All of the K-giants, M-giants, and BHBs indicate that the trailing arm is on average more metal-rich than the leading arm, and the K-giants show that the Sgr debris is the most metal-poor part. The α-abundance of Sgr stars exhibits a similar trend with the Galactic halo stars at lower metallicity ([Fe/H] <∼ -1.0 dex), and then evolve down to lower [α/Fe] than disk stars at higher metallicity, which is close to the evolution pattern of the α-element of Milky Way dwarf galaxies. We find that V _Y and metallicity of K-giants have gradients along the direction of the line of sight from the Galactic center in the X-Z plane, and the K-giants show that V _Y increases with metallicity at [Fe/H] >∼ -1.5 dex. After dividing the Sgr stream into bright and faint streams according to their locations in equatorial coordinates, the K-giants and BHBs show that the bright and faint streams present different V _Y and metallicities, the bright stream is on average higher in V _Y and metallicity than the faint stream.