The Kinematics of B Stars, Cepheids, Galactic Clusters and Interstellar Gas in the Galaxy

Abstract

An analysis has been made of B star motions using all available stars with reliable radial velocities and distances. The radial velocities of the interstellar Ca II lines have also been studied. Recent work on cepheids and galactic clusters is discussed and in part re-analysed. The principal results are the following: 1. The K -term for the B stars (Table I and Section 4) varies with distance from the Sun, probably due to the effects of large stellar groupings. This effect conceals any dependence on spectral type and luminosity class except for the O stars where a significant positive K -term is probably chiefly due to a gravitational red shift (Section 4 (vii)). 2. The values of the Oort constant A in varibus sub-groups of OB star spectral types and luminosity classes are in good agreement showing that the adopted absolute magnitude calibration is self-consistent. 3. The small percentage of high velocity B stars can have a considerable effect on the K -term. The velocity dispersions of B stars, cepheids and galactic clusters are all about the same (∼ 11.5 km/sec). That for the interstellar Ca II is somewhat lower (6.9 km/sec). The observed distributions of the residuals are generally gaussian. The effect on the dispersions of observational errors is discussed. It is unlikely that the true dispersion for B stars is less than about 9 km/sec. 4. The solar motion for B stars nearer than 0.25 kpc is appreciably different from that obtained from more distant stars. This is probably chiefly due to the effects of the Sco–Cen association. 5. The distances of the B stars are corrected statistically for systematic errors (Section 8 and Appendix). The ω ( R ) curve for B stars and interstellar Ca II is then in much better agreement with the 21 cm observations than the uncorrected ω ( R ) curve. However the optical results suggest that the Leiden ω ( R ) curve has been drawn too high (Section 13). 6. The best values found for the components of the solar motion and the Oort constant are u0 = + 10 km/sec, v0 = + 13 km/sec, ( w0 = + 6 km/sec adopted) and A = + 14.3 ± 0.8 km/sec/kpc. 7. Distant B stars are used to derive a value of R0 , the distance to the galactic centre of 9.9 ± 0.9 kpc.