Interstellar Calcium Lines in the Spectra of Stars in Open Clusters.

Abstract

Distances of 31 open star clusters have been derived from the equivalent widths of the interstellar lines in the early-type stars. Velocities which have been obtained from both the interstellar and the stellar lines accord with dif- ferential galactic rotation. Tue distances have been derived by means of both stellar and interstellar velocities. Although the cor- relation of these distances with the corresponding equivalent widths is not especially good, it seems to be considerably better than the correlation of Trumpler's distances with equivalent width. The equivalent widths and both the stellar and the interstellar velocities seem, therefore, to provide a useful means of obtaining the distances of open clusters. Large systematic and accidental errors in the interstellar velocities of open clusters derived by Miss Phyllis Hayford probably explain why her observations were unsuited to a solution for galactic rotation. The stellar and interstellar velocities of 14 stars (Table 3) provide good evidence that they belong to the h and x Persei clusters