A search for rapid oscillations in chemically peculiar A-type stars

Abstract. In 1995 we initiated a Northern Hemisphere survey for rapidly oscillating Ap stars. This paper presents the results including one new roAp star (HD 122970), the con rmation of rapid oscillations of HD 99563 and appar-ent null results for other stars. Using Hipparcos data a statistical analysis of the ab-solute magnitudes and galactic distributions of all known roAp and noAp stars (also taken from the literature) was made. A systematic trend for most of the program stars in a MV vs. (index of the Strömgren uvby system) dia-gram was detected leading to the conclusion that is sys-tematically influenced by the chemical peculiarity and/or magnetic eld. Three roAp stars are outside the Scuti instability strip which implies that the driving mechanism of the two classes of pulsating star is dierent. This is also sug-gested by new pulsation models. No statistical dierence between the galactic distribution of roAp and noAp stars was found