A Kinematical Study for the Galaxy Based on the Revised Hipparcos Astrometric Data

Abstract

On the basis of the revised Hipparcos data recently released, the zero-point of the PL relation for classical cepheids was reexamined. Fitting proper motion and radial velocity data via an axis symmetric model, Oort constants and circular rotation velocity of the LSR were calculated to obtain Galactocentric distance of the sun, R0 = 8.0±0.8 kpc. From the rotation curve in solar neighborhood, the existence of weak ellipticity of the Galactic potential was found. Adopting a simple asymmetric model, we obtained the ellipticity ɛ (R0) = 0.067±0.036 at the sun, while the minor axis pointing to φb = 320 + 150.