Galactic clusters with associated Cepheid variables. II. NGC 129 AND DL Cassiopeiae

Abstract

New photoelectric UBV photometry of 27 stars and spectroscopic observations of 12 stars are presented for NGC 129, the cluster containing the 8[d over dot]00 Cepheid DL Cas. The photometry is used to restandardize previously published photoelectric and photographic observations of stars in NGC 129, including transformed Strömgren system data. A compilation of the best available photometric data for stars with V [less than] 15.3 (the limit for reliable observations) is used in conjunction with published proper motion data and spectroscopic observations of the brighter stars for a detailed cluster analysis. The newly obtained distance modulus of NGC 129 is V[subscript 0]—M[subscript V]=11.11 [plus or minus] 0.02 s.e. (d = 1.670 [plus or minus] 0.013 kpc), and a value of R = A[subscript V]/E[subscript B-V]=3.20 [plus or minus] 0.30 s.e. is found to describe the dust extinction in the field. A space reddening of E[subscript B-V]=0.47 [plus or minus] 0.01 is derived for DL Cas from consideration of a possible circumstellar reddening effect for cluster B stars, and its resulting luminosity is [angled bracket]M[subscript V][angled bracket] = -3.80 [plus or minus] 0.05. A list of 94 candidate cluster members is presented, and a cluster radial velocity of -36.0 [plus or minus] 1.8 km s[superscript -1] is derived using the supergiants and bright B stars. The membership status of the supergiants is discussed in connection with other available information for cluster stars.