Summary: Mon. Not. R. Astron. Soc. 000, 000--000 (0000) Printed 18 February 1998 (MN L A T E X style file v1.4)
The detection of binary companions to subdwarf B stars ?
C. Simon Jeffery 1 and Don L. Pollacco 2
1 Armagh Observatory, College Hill, Armagh BT61 9DG, Northern Ireland
2 Isaac Newton Group, La Palma
Accepted . Received ; .
Intermediate dispersion spectroscopy of a sample of 40 hot subdwarf B stars between
5500 A and 9000 A has been obtained. The sample includes a large fraction of targets
which have been studied photometrically. Seven targets show strong lines due to the
infrared Ca ii triplet, the unequivocal signature of a cool companion. The positive
Ca ii identifications include known photometric binaries and new targets; all are as
sociated 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 the binary frequency of hot subdwarfs.
Key words: Stars: earlytype, subdwarfs, binaries: spectroscopic.
Hot subdwarfs are O and Btype stars which may be found,
on an HertzsprungRussell diagram, below the upper main