THREE MOVING GROUPS DETECTED IN THE LAMOST DR1 ARCHIVE

Abstract

We analyze the kinematics of thick disk and halo stars observed by the Large sky Area Multi-Object Fiber Spectroscopic Telescope. We have constructed a sample of 7,993 F, G and K nearby main-sequence stars (\textit{d} $<$ 2 kpc) with estimates of position (x, y, z) and space velocity ($U$, $V$, $W$) based on color and proper motion from the SDSS DR9 catalog. Three `phase-space overdensities' are identified in [\textit{V}, $\sqrt{U^{2}+2V^{2}}$] with significance levels of $\sigma$ $>$ 3. %[L$_{Z}$, eccentricity], [L$_{Z}$, L$_{\bot}$], and [V$_{az}$, V$_{\triangle}E$]. Two of them (Hyades-Pleiades stream, Arcturus-AF06 stream) have been identified previously. We also find evidence for a new stream (centered at \textit{V} $\sim$ -180 km s$^{-1}$) in the halo. The formation mechanisms of these three streams are analyzed. Our results support the hypothesis the Arcturus-AF06 stream and the new stream originated from the debris of a disrupted satellite, while Hyades-Pleiades stream has a dynamical origin.