A SEARCH FOR RAPID RADIAL-VELOCITY VARIATIONS IN ALPHA-CIRCINI

We present rapid radial velocity measurements (sigma approximately 55 m s-1) for the roAp star alpha Cir made using a molecular iodine gas absorption cell. A period analysis places an upper limit of 60 m s-1 for the peak-to-peak amplitude of any radial velocity variations in the frequency range 20 to 375 days-1. Phasing the measurements to the known photometric period of 6.83 minutes results in an upper limit of 36 m s-1 (peak-to-peak) for the radial velocity amplitude of the pulsations. This yields an upper limit to the ratio of radial velocity amplitude to photometric amplitude (2K/DELTAm(B)) of about 10 km s-1 mag-1, substantially less than was found for two other roAp stars by other investigators.