Spectroscopic studies of O-type stars. VII. Rotational velocities V sin i and evidence for macroturbulent motions.
Rotational velocities are derived from coude' spectrograms of 205 0-type stars in the northern and southern hemispheres. The velocity distribution for main-sequence stars is bimodal, containing a slow group with a V sin i peak near 100 km 1 and a fast group with a V sin i peak near 300 km s . The distribution of type III giants shows fewer of the high-velocity stars, and the type I supergiants are all distributed around a single peak near V sin i = 100 km s '. A number of Oe stars are found in the rapidly rotating group, by analogy with Be stars. The peak of the velocity distribution of the giants and supergiants does not shift as much to slower velocities as would have been expected from the peak for the main-sequence stars and stellar evolution leading to an increasing radius, with angular momentum conserved in shells. The detailed shapes of the distributions do not agree well with a purely rotational interpretation of the broadening, especially for the giants and supergiants. These facts, and the absence of any very sharp-lined supergiants, suggest that an additional parameter-turbulence-is probably necessary in evolved 0-type stars. Subject headings: stars: early-type - stars: rotation - turbulence