1999A&AS..135...57H

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 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 the literature) was made. A systematic trend for most of the program stars in a M_V vs. β (index of the Stroemgren uvbyβ system) diagram was detected leading to the conclusion that β is systematically influenced by the chemical peculiarity and/or magnetic field. Three roAp stars are outside the δ Scuti instability strip which implies that the driving mechanism of the two classes of pulsating star is different. This is also suggested by new pulsation models. No statistical difference between the galactic distribution of roAp and noAp stars was found.