(R-I) colors of cepheids and yellow supergiants in open clusters.

Abstract

The (R-I) and (b-y) observations of nine Cepheids which are members of open clusters, 14 field Cepheids, and 34 nonvariable yellow giants in or near open clusters are presented. Color-color relations for the Cepheids are found to differ significantly from star to star. Additionally, the nonvariables may differ from the Cepheid color-color relation. Pulsational masses are determined for the Cepheids using both (R-I) and (B-V) colors as temperature indicators. For some of the shorter period stars the (R-I) masses agree with evolutionary masses, which is not the case for the (B-V) masses. A small increase (about 0.1 mag) in the absolute magnitudes of the short-period Cepheids is sufficient to bring agreement between the (R-I) masses and the evolutionary masses for the bulk of the stars, but the long-period stars still have low masses. However, it is suggested that this may be due to systematic errors in the color excesses. The cluster NGC 129 is found to have a nonvariable star within the instability strip in addition to the Cepheid DL Cas. Because the absolute magnitude and intrinsic color are all determined from the cluster, this is the best established case of a nonvariable in the Cepheid strip. Several other clustersmore » contain a number of yellow giants, and they are compared with evolutionary tracks. (AIP)« less