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

The paper presents new photoelectric UBV photometry of 27 stars and spectroscopic observations of 12 stars for NGC 129, the cluster containing the 8.00-d Cepheid DL Cas. The photometry is used to restandardize previously published photoelectric and photographic observations of stars in NGC 129, including transformed Stromgren system data. A compilation of the best available photometric data for stars with V less than 15.3 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 11.11 +/-0.02 s.e., and a value of 3.20 +/-0.30 s.e. is found to describe the dust extinction in the field. A list of 94 candidate cluster members is presented, and a cluster radial velocity of -36.0 +/-1.8 km/s 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. (P.D.)