Radial velocity study of the roAp star α Circinus

We present results of 548 high-dispersion spectra of the roAp star alpha Circinus over a five-night period. The pulsational radial velocities measured from the rare-earth elements, Nd III, Halpha and Hbeta are easily measured and occur at the photometric period. The amplitude is largest in Nd III and Halpha, is lower in the rare earths and Hbeta, and cannot be measured in other metal lines. This behaviour can be understood in terms of an increase of pulsational amplitude with height in the atmosphere coupled with abundance stratification. The radial velocities show a significant variation at the rotational period of 4.463 d and a marginally significant periodicity at a frequency of 8.16 cycle d(-1). The latter may be a very low-amplitude delta Scuti pulsation.