THE STELLAR KINEMATICS IN THE SOLAR NEIGHBORHOOD FROM LAMOST DATA

Abstract

We use about 200,000 FGK-type main-sequence stars from the LAMOST DR1 data to map the local stellar kinematics. With the velocity deprojection technique, we are able to derive the averaged three-dimensional velocity and velocity ellipsoids using only the line-of-sight velocity for the stars with various effective temperatures within pc. Using the mean velocities of the cool stars, we derive the solar motion of (, , ) = (9.58 ± 2.39, 10.52 ± 1.96, 7.01 ± 1.67) with respect to the local standard of rest. Moreover, we find that the stars with K show a net asymmetric motion of ∼3 in compared to the stars with K. And their azimuthal velocity increases when increases. This peculiar motion in the warmer stars is likely because they are young and not completely relaxed, although other reasons, such as the resonance induced by the central rotating bar or the spiral structures and the perturbation of the merging dwarf galaxies, cannot be ruled out. The derived velocity dispersions and cross-terms for the data are approximately consistent with previous studies. We also find that the vertical gradients of and are larger than that of . And the vertical gradient of shows a clear correlation with , while the other two do not. Finally, our sample shows a vertex deviation of about at pc, but roughly zero at pc.