SPECTROSCOPY OF THE ROAP STAR-ALPHA CIR - I - VELOCITIES OF H-ALPHA AND METAL LINES

We present radial velocity measurements of the rapidly oscillating Ap (roAp) star alpha Cir, obtained from dual-site observations with mediu m-dispersion spectrographs. The amplitude and phase of the principal p ulsation mode vary significantly, depending on which line is being mea sured. The amplitude is observed to be as high as 1000 m s(-1) in some wavelength bands, despite a previous upper limit of 36 m s(-1). Furth ermore, some lines are apparently pulsating in anti-phase with others. We suggest this indicates a high-overtone standing wave with a veloci ty node in the atmosphere of the star.