Galactic clusters with associated Cepheid variables. VII. Berkeley 58 and CG Cassiopeiae

TL;DR

This study investigates the open cluster Berkeley 58 and its potential association with the Cepheid variable CG Cas, providing detailed photometric and spectroscopic data to determine cluster parameters and the Cepheid's membership.

Contribution

The paper offers new photometric, spectroscopic, and star count data for Berkeley 58, establishing its parameters and confirming CG Cas as a likely cluster member, which aids in understanding Cepheid-cluster associations.

Findings

Berkeley 58 has an age of ~100 million years and is located 3.03 kpc away.

CG Cas is a probable cluster member with a period increase indicating third crossing of the instability strip.

The cluster's parameters and the Cepheid's properties support their physical association.

Abstract

Photoelectric, photographic, and CCD UBV photometry, spectroscopic observations, and star counts are presented for the open cluster Berkeley 58 to examine a possible association with the 4.37d Cepheid CG Cas. The cluster is difficult to separate from the early-type stars belonging to the Perseus spiral arm, in which it is located, but has reasonably well-defined parameters: an evolutionary age of ~10^8 years, a mean reddening of E(B-V)_(B0)=0.70+-0.03 s.e., and a distance of 3.03+-0.17 kpc (V_0-M_V=12.40+-0.12 s.d.). CG Cas is a likely cluster coronal member on the basis of radial velocity, and its period increase of +0.170+-0.014 s yr^(-1) and large light amplitude describe a Cepheid in the third crossing of the instability strip lying slightly blueward of strip centre. Its inferred reddening and luminosity are E(B-V)=0.64+-0.02 s.e. and <M_V> =-3.06+-0.12. A possible K supergiant may also be a cluster member.