Oral Presentation
THE STELLAR KINEMATICS IN THE SOLAR NEIGHBORHOOD FROM LAMOST DATA
We use about 200,000 FGK main-sequence stars from the LAMOST DR1 data to map the local stellar kinematics. With the velocity de-projection method, we are able to derive the 3 dimensional velocity and velocity ellipsoid for the stars using only the line-of-sight velocity. The geometric distortion of the de-projection in the velocity ellipsoid is well addressed and a calibration approach is developed to correct it. Then, we apply the de-projection method with calibration to the LAMOST data and obtain the mean velocity components and the velocity ellipsoids in various bins of the stellar effective temperature at 100 < |z| < 300, 200 < |z| < 400, and 300 < |z| < 500 pc. We find that the stars with Teff > 6000 K show a net asymmetric motion in all three orientations. Specifically, they are moving in toward the Galactic center and up toward the north Galactic pole compared with the cooler stars. Their azimuthal velocity increases with |z|, which is an opposite trend as the cooler stars. It is noted that these warmer stars are very young with mean age of only ~2 Gyr. There are a few possible scenarios may explain the asymmetric motion: (1) the young stars are not yet completely relaxed; (2) they are excited by the resonance induced by the central rotating bar or the spiral structures; or (3) they are perturbed by a merging dwarf galaxy. Neither of the scenarios can be easily ruled out with the current data. Using the mean velocities of the cool and old stars, which are staying in equilibrium, we derive the solar motion of (U⊙, V⊙, W⊙)=(9.58±1.44, 13.77±0.68, 7.01±0.62) km/s with respect to the local standard of the rest. The velocity dispersions and the cross terms determined with the LAMOST data are compared with other literatures and approximately consistent with the previous studies.
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