PHOTOMETRY OF ASTROMETRIC REFERENCE STARS

We present, in the third in a series of papers, UBVRI, DDO, and uvby, H-beta photometry of astrometric reference stars. Spectral types and luminosity classifications made from the colors are used to determine their spectroscopic parallaxes. In this paper colors for 309 stars in 25 regions are given, and classifications for 210 stars have been made. These stars form reference frames in the Allegheny Observatory Multichannel Astrometric Photometer astrometric program, and in the Praesepe cluster reduced by Russell [Ph. D. thesis (1976)]. We find that our photometric spectral types are reliable to within 2.5 spectral subclasses.