A kinematic study of the Galaxy

Abstract

Using the proper motion and parallax data for 1011 O-B stars in the Hipparcos Catalogue we have derived the Oort constants, A = 17.60 ± 0.21 (km/s)/kpc, B = -14.62 ± 0.20 (km/s)/kpc, and a solar velocity V_⊙ = 16.7 ± 0.10 km/s in the direction l_⊙ = 45.3° ± 2.8°, b_⊙ = 21.0° ± 2.3°. For a galactocentric distance of the sun of R₀ = 8.5 kpc, we then get a galactic rotational velocity of the solar neighbourhood of V_lsr = 273.9 km/s, obviously much higher than the IAU published value of 220 km/s. We have investigated the cause for this difference.