A Precision Velocity Study of Photometrically Stable Stars in the Cepheid Instability Strip

Results of a precision Doppler velocity survey of 15 stars that lie in or near the Cepheid instability strip are presented. Previous studies have shown that these stars are photometrically stable. Long-term radial velocity precision of 15 m s -1 has been achieved with the use of an iodine absorption cell and a high-resolution cross-dispersed echelle spectrometer. The stars show a variety of behavior from stability (at the level of 30 m s -1 ) to variability from 50 m s -1 to a few km s -1 . Periodograms of many of the program stars show significant peaks at 50-80 days that are not associated with radial pulsation. Previously undetected binary companions have been found around two of the stars. Line profiles are compared to δ Cep.