Stellar Kinematics from Hipparcos Proper Motions

摘要

From Hipparcos proper motions, the authors analyze the local kinematics of the Milky Way from the young O-B5 stars, classical Cepheids, and the late-type K-M giants. Comparing the derived results, the kinematical discrepancies between each subset of stars are analyzed, and the possible reasons for the kinematical differences are discussed. The results of the solar motion relative to the stellar type are in good agreement with those given by Dehnen and Binney for the main sequence stars. The authors determined very stable solutions for the components u(sub 0) and w(sub 0). The component v(sub 0) varies in a wide range depending on stellar age. The Galactic rotation derived from the O-B5 stars (approx. 270 km s(exp -1)) is remarkably larger than the International Astronomical Union (IAU) recommended value. Analyzing Hipparcos proper motions from the O-B5 stars, they have identified a clear stellar warping motion that is an asystematic rotation of stars around the axis pointing to the Galactic center in the sense of increasing the inclination of the H I warp. The solution from the classical Cepheids seems to suggest a slight contracting motion of Cepheids along the direction of the Galactic rotation. The real feature of the contraction should be carefully investigated further.