Membership of Cepheids and Red Giants in 8 Open Clusters: Ngc 129, 6067, 6649, 6664, IC 4725, Ly 6, RU 79

摘要

The membership of 8 cluster Cepheids, DL Cas, Ev Sct, V367 Set, S Nor, TW Nor, V340 Nor, USgr and CS Vel, were examined by comparing their systemic radial velocity with that observed for the red giants in the same clusters. The membership is very probable in seven cases, the exception being CS Vel. Additional observations of main sequence stars are necessary to confirm conclusions. One spectroscopic binary was discovered among the Cepheids (DL Cas) and at least four were among the red giants. Orbits for two red giants, in NGC 129 and IC 4725 were determined. The position within the instability strip of the nonvariable F5Ib star in NGC 129 is due to its probable composite (gK+dB) character. The ratio of the number of Cepheids to the number of red giants is less than 1, in good agreement with the prediction of evolutionary models with core overshooting.