Physical parameters of sdB stars from spectral energy distributions

The atmospheric parameters of 34 hot subdwarf B stars have been obtained us ing a combination of 61 short and long-wave IUE spectra, together with new and existing optical and infrared photometric data. Using a grid of high-gr avity helium-deficient model atmospheres and a chi (2)-minimization procedu re, 15 single sdB stars and 19 composite systems, containing a hot subdwarf B star and a cool main-sequence companion, were analyzed. From the (log L- log T-eff) diagram of our results, we conclude that the majority of the coo l companions to our sample of binary sdB stars are main sequence stars; in the range of 4000 < T-eff/K < 6000 and mass 0.8 < M/M-<circle dot> < 1.3. T he lower limit on detectability of cool stars in composite sdB of our sampl e is <similar to>3600 K, corresponding to a spectral type of M1 or later (L ang 1992).