A Kinematical Study of 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 period-luminosity relation for classical cepheids is reexamined. Fitting the proper motion and radial velocity data via an axisymmetric model, the Oort constants and circular rotation velocity of the LSR are calculated to obtain the Galactocentric distance of the Sun, R 0 = 8.0 ± 0.8 kpc. From the rotation curve in solar neighborhood, the existence of weak ellipticity of the Galactic potential is found. Adopting a simple asymmetric model, we have obtained the ellipticity ∈(R 0) = 0.067 ± 0.036 at the Sun, while the minor axis points to φ b = 32° ± 15°.