The metallicity of K giant stars along the Sagittarius streams

The Large Sky-Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) Data Release 3 provided 341 691 K giant stars with stellar parameters. Based on the models of Law and Majewski, we identified 252 K giant stars in the leading stream associated with the Sagittarius (Sgr) dwarf galaxy. We obtained 132 K giant stars belonging to the trailing arm of Sgr using the model of Belokurov et al. We studied the metallicity distribution of member stars along the streams and found a flat gradient in the first wrap of the leading stream, $-(0.88\pm 0.3)\times {10}^{-3}dex/({}^{\circ })$ in the second wrap of the leading stream and $-(1.2\pm 0.3)\times {10}^{-3}dex/({}^{\circ })$ in the first wrap of the trailing stream. Moreover, we obtained a combined metallicity gradient with our sample and data from the literature. We also analyzed the properties of an overdensity, which is located in the leading stream of the Sgr. (paper)