Galactic kinematics derived from classical cepheids

Abstract

On the basis of radial velocity and Hipparcos proper motion data, we have analyzed the galactic kinematics of classical Cepheids. Using the 3-D Ogorodnikov-Milne model we have determined the rotational velocity of the Galaxy to be V₀ = 240.5 ± 10.2 km/s, on assuming a glactocentric distance of the Sun of R₀ = 8.5 kpc. The results clearly indicate a contracting motion in the solar neighbourhood of (∂V _θ∂θ)/R = -2.60 ± 1.07 km s ^-1 kpc ^-1, along the direction of galactic rotation. Possible reason for this motion is discussed. The solar motion found here is S_⊙ = 18.78 ± 0.86 km/s in the direction l_⊙ = 54.4° ± 2.9° and b_⊙ = +26.6° ± 2.6°.