Kinematics and Velocity Ellipsoid of Halo Red Giants

Abstract

Here, we aim to determine the kinematical properties, velocity ellipsoid and Oort constants using a sample of halo red giants. The study is based mainly on the space and radial velocities of 1583 red giant stars collected from the SEGUE-1 and SEGUE-2 surveys. We divided the sample into three subsamples: the inner halo, the outer halo and the stars near the galactic plane. The fitting of the radial velocity equation gives a mean of Oort constants A = 15.6 ± 1.6 km s-1 kpc-1 and B = -13.9 ± 1.8 km s-1 kp-1 and angular velocity |A - B | = 29.5 ± 0.2 km s-1 kpc-1, which implies a rotational velocity of 221.25 ± 26.66 km s-1 if we take the distance to the galactic center as 7.5 kpc.