Galactic clusters with associated Cepheid variables. IV. C2128+488 (Anon. Platais) and V1726 Cygni

Abstract

New photoelectric UBV photometry of 32 stars, photographic UBV photometry of 120 stars, and spectroscopic observations of 8 stars are presented for C 2128+488 (Anon. Platais), the cluster associated with the 4[d over dot]237 s-Cepheid V1726 Cygni. The resulting photometry, spectral classifications, and radial velocities are used with spectroscopic and proper motion data previously published by Platais and others for the Cepheid and other stars in this field in a detailed cluster analysis. The newly obtained cluster distance modulus is V[subscript 0]-M[subscript V] = 10.98 [plus or minus] 0.02 s.e. (d = 1568 [plus or minus] 13 pc), and a value of R = A[subscript V]/E[subscript B-V = 3.07 [plus or minus] 0.27 s.e. is found to describe the dust extinction in the field. A space reddening of E[subscript B-V] = 0.43 [plus or minus] 0.02 is derived for V1726 Cyg from two late B-type companions which bracket the Cepheid, as well as from the reddenings of other stars in the field. Its resulting luminosity as a probable cluster member is [angled bracket]M[subscript V][angled bracket] = -3.42 [plus or minus] 0.07. A cluster radial velocity of -15.4 [plus or minus] 0.2 km s[superscript -1] and a cluster turnoff point at spectral type B7 are both consistent with the likely membership of V1726 Cyg, as are the available proper motion data. The small amplitude, sinusoidal light curve, and location of V1726 Cyg on the blue edge of the Cepheid instability strip are consistent with the properties expected for overtone pulsation, although such a possibility appears to imply an unrealistically small value ([Beta]=0.5 [plus or minus] 0.2) for the color coefficient in the PLC relation. A more reasonable value of [Beta]=2.1 [plus or minus] 0.2 is derived for the color term applicable to galactic cluster Cepheids in this program when V1726 Cyg is assumed to be pulsating in the fundamental mode.