GALACTIC CLUSTERS WITH ASSOCIATED CEPHEID VARIABLES .4. C2128+488 (ANON PLATAIS) AND V1726 CYGNI

New photoelectric UBV photometry of 32 stars, photographic UBV photome try of 120 stars, and spectroscopic observations of 8 stars are presen ted for C 2128+488 (Anon. Platais), the cluster associated with the 4. 237d s-Cepheid V1726 Cygni. The resulting photometry, spectral classif ications, and radial velocities are used with spectroscopic and proper motion data previously published by Platais and others for the Cephei d and other stars in this field in a detailed cluster analysis. The ne wly obtained cluster distance modulus is V0-Mv=10.98 +/- 0.02s.e. (d=1 568 +/- 13 pc), and a value of R = A(V)/E(B-V) = 3.07 +/- 0.27 s.e. is found to describe the dust extinction in the field. A space reddening of E(B-V) = 0.43 +/- 0.02 is derived for V1726 Cyg from two late B-ty pe companions which bracket the Cepheid, as well as from the reddening s of other stars in the field. Its resulting luminosity as a probable cluster member is [M(V)] = -3.42 +/- 0.07. A cluster radial velocity o f -15.4 +/- 0.2 km s-1 and a cluster turnoff point at spectral type B7 are both consistent with the likely membership of V1726 Cyg, as are t he available proper motion data. The small amplitude, sinusoidal light curve, and location of V1726 Cyg on the blue edge of the Cepheid inst ability strip are consistent with the properties expected for overtone pulsation, although such a possibility appears to imply an unrealisti cally small value (beta = 0.5 +/- 0.2) for the color coefficient in th e PLC relation. A more reasonable value of beta = 2.1 +/- 0.2 is deriv ed for the color term applicable to galactic cluster Cepheids in this program when V1726 Cyg is assumed to be pulsating in the fundamental m ode.