The Spectra and Radial Velocities of Stars in the Orion Nebula Cluster.

Radial velocity and spectral type are known for forty-five stars within 24' of Ol Orionis, most of them from new data in this paper. The kinematics and spectral peculiarities of the Orion Nebula cluster are discussed in terms of these stars, with reference also to astrometric data. Various parameters are determined, including the distance of the cluster, mean radial velocity and significant departures from it, the dispersion of the velocities, and the distinction between atmospheric and mass components of the velocity. The data are consistent with a uniform expansion of the cluster, but do not establish it. There are notable atmospheric motions in some member stars.