A new determination from OB stars of the galactic rotation constants and the distance to the galactic centre

The overall kinematics of the OB stars has been rediscussed using a new calibration of H γ equivalent widths and MK luminosity classes by Balona & Crampton. As well as published material we have used data from new H γ equivalent width measurements in 590 southern OB stars. The principal results are A = 16.8 km s −1 kpc −1 , u0 = +7.4 km s −1 and v0 = +13.0 km s −1 . A distance, R0 , to the galactic centre of 9.0 kpc with a range of about 7.7−10.9 kpc is found. This is in satisfactory agreement with the determination of Rq from the distribution of RR Lyrae variables, especially if the latter is corrected for statistical effects.