THE DETECTION OF BINARY COMPANIONS TO SUBDWARF B-STARS

Intermediate dispersion spectroscopy of a sample of 40 hot subdwarf B stars between 5500 and 9000 Angstrom has been obtained. The sample inc ludes a large fraction of targets which have been studied photometrica lly. Seven targets show strong lines arising from the infrared Can tri plet, the unequivocal signature of a cool companion. The positive Ca I I identifications include known photometric binaries and new targets; all are associated with a photometric red excess. Assuming a canonical value for the subdwarf luminosity, all of the detected companions are overluminous compared with the main sequence. The detection procedure indicates an improved and more secure method for the measurement of t he binary frequency of hot subdwarfs.