Kinematics and Velocity Ellipsoid of the K Giants

Abstract

To study the kinematics of the K giant stars (luminosity class III) use is made of proper motions taken from van Leeuwen's new reduction of the Hipparcos catalog. 11,372 stars, of which 880 have radial velocities, were used in the final study. Semi-denite programming solves for the kinematical parameters such as the Oort constants and simultaneously for the coefficients of the velocity ellipsoid. The condition that both the solution for the solar velocity calculated from the kinematical parameters and from the velocity ellipsoid calculation be the same is enforced. The solution gives: solar velocity of 21:83±0:26 km s-1; Oort's constant's, in units of km s-1 kpc-1, A = 13:08 ± 1:72 and B = -10:21 ± 1:47, implying a rotational velocity of 197:94 ± 44:73 km s-1 if we take the distance to the Galactic center as 8:2±1:1 kpc; velocity dispersions, in units of km s-1, of: σx = 50:58±0:99,
σy = 42:42 ± 1:13, σz = 32:92 ± 0:56 with a vertex deviation of -7.º53 ± 3.º97.