THE DISCOVERY OF AN EXTREMELY LOW AMPLITUDE CEPHEID

Extremely low amplitude (200+/-20 m s-1) periodic radial velocity variations are found for HR 7796 (F8 Ib), thought to be a non-Cepheid in (or near) the instability strip. Two and one-half complete cycles have been monitored over three observing runs. The period is found to be 11.874+/-0.02 days. Observations of the reference star HR 509 (G8 V) taken on the same nights show no periodicities and a scatter of just 20 m s-1. A first-order approximation shows that HR 7796 does appear to follow the Cepheid period-luminosity relation. If HR 7796 is a Cepheid, it is the smallest amplitude Cepheid by more than an order of magnitude.