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

In 1995 we initiated a Northern Hemisphere survey for rapidly oscillating A p stars. This paper presents the results including one new roAp star (HD 12 2970), the confirmation of rapid oscillations of HD 99563 and apparent null results for other stars. Using Hipparcos data a statistical analysis of the absolute magnitudes and galactic distributions of all known roAp and noAp stars (also taken from th e literature) was made. A systematic trend for most of the program stars in a M-V vs. beta (index o f the Stromgren uvby beta system) diagram was detected leading to the concl usion that beta is systematically influenced by the chemical peculiarity an d/or magnetic field. Three roAp stars are outside the delta Scuti instability strip which implie s that the driving mechanism of the two classes of pulsating star is differ ent. This is also suggested by new pulsation models. No statistical differe nce between the galactic distribution of roAp and noAp stars was found.