The Kinematics and Chemistry of Red Horizontal Branch Stars in the
  Sagittarius Streams
  We have selelcted 556 Red Horizontal Branch (RHB) stars along the streams of
the Sagittarius dwarf galaxy (Sgr) from SDSS DR7 spectroscopic data using a
theoretical model. The metallicity and \alpha-elements distributions are
investigated for stars in the Sgr streams and for Galactic stars at the same
locations. We find that the Sgr stars have two peaks in the metallicity
distribution while the Galactic stars have a more prominent metal-poor peak.
Meanwhile, [\alpha/Fe] ratios of the Sgr stars are lower than those of the
Galactic stars. Among the Sgr stars, we find a difference in the metallicity
distribution between the leading and trailing arms of the Sgr tidal tails. The
metallicity and [\alpha/Fe] distribution of the leading arm is similar to that
of the Galaxy. The trailing arm is composed mainly of a metal rich component
and [\alpha/Fe] is obviously lower than that of the Galactic stars. The
metallicity gradient is -(1.8 \pm 0.3)\times10^{-3} dex degree^{-1} in the
first wrap of the trailing arm and -(1.5 \pm 0.4)\times10^{-3} dex degree^{-1}
in the first wrap of the leading arm. No significant gradient exists along the
second wraps of the leading or trailing arms. It seems that the Sgr dwarf
galaxy initially lost the metal poor component in the second wrap (older) arms
due to the tidal force of our Galaxy and then the metal rich component is
disrupted in the first wrap (younger) arms. Finally, we found that the velocity
dispersion of the trailing arm from 88^\circ<\Lambda_\odot<112^\circ is \sigma
= 9.808 \pm 1.0 km s^{-1}, which is consistent with previous work in the
literature.
