New radial velocity observations are presented for 24 Cepheids previously observed by others. All the available data are discussed; of the 18 stars for which observations are adequate one, S Mus, is certainly a binary; AH Vel and possibly V Car may be binaries. V 636 Sco, found to have a variable ?-velocity by Feast, is a long period binary. Re-examination of the literature on Cepheid radial velocities has revealed one new spectroscopic binary, AW Per, which was previously known to have a composite spectrum. At least 15 per cent of Cepheids are in spectroscopic binary systems of long period. There appears to be a deficiency of Cepheids in binary systems with periods of about one year. The confirmed and suspected Cepheid binaries have systematically smaller light amplitudes than Cepheids in general. Photometric criteria for the detection of hot companions to Cepheids are discussed and a list of possible examples found from UBV photometry is given. One, KN Cen, is found spectroscopically to be composite. The nature of the companions are examined. If the unseen companion of S Sge is a main sequence star, the Cepheid probably pulsates in the first harmonic.
- 1 - natural sciences ; 2 - physics & astronomy ; 3 - astronomy & astrophysics
- 1 - Physical Sciences ; 2 - Earth and Planetary Sciences ; 3 - Space and Planetary Science
- 1 - Physical Sciences ; 2 - Physics and Astronomy ; 3 - Astronomy and Astrophysics