Abstract
Fifteen southern Cepheids with 3-7 day periods have been subjected to simultaneous radial velocity and UBV(RI)-KC photometric observations. A comparison of the resulting radial velocity curves with earlier data confirms the binary nature of V 350 Sgr, and indicates that RTrA, AP Sgr and V 496 Aql are binary as well. The lack of significant spectroscopic distinction between the binary and nonbinary Cepheids implies that the companion stars to the binary ones are neither very luminous nor able to alter Cepheid photometric properties. Doubts are raised concerning the reliability of the U-B versus B-V diagram open loop method results obtained for the case of small loop openings. The variable-gamma velocity method is more reliable for Cepheid binary searches.
