STUDIES OF HOT B-SUBDWARFS .9. COUSINS BVRI PHOTOMETRY AND THE BINARYFRACTION OF HOT, HYDROGEN-RICH SUBDWARFS IN THE PALOMAR-GREEN SURVEY

Cousins BVRI photometry is presented for a sample of 100 hot, hydrogen -rich subdwarf candidates selected principally from the Palomar-Green and Kitt Peak-Downes colorimetric surveys. The combination of these da ta with existing Stromgren photometry permits the construction of ener gy distributions in the range lambdalambda3500-7900. With the help of flux-ratio diagrams, we have isolated 31 objects with flat energy dist ributions indicative of a composite nature. Approximate effective temp eratures and spectral types are derived for the primary and secondary stars, respectively. We present evidence, based on the absolute visual magnitudes determined for the primary components, that the secondary stars in most systems are likely to be overluminous compared to normal main-sequence stars. Because of selection effects, the spectral types of the secondary stars are restricted to the range late G to early M. When allowance is made for these selection effects, the fraction of h ot hydrogen-rich subdwarfs with main-sequence companions in the PG sur vey can be inferred, and is estimated to be approximately 54%-66%.