next previous
Up: A search for rapid


1 Introduction

Among the magnetic chemically peculiar A-type stars, the rapidly oscillating Ap (roAp) stars are quite outstanding. This group exhibits rapid photometric and spectroscopic variations with periods of minutes and very small amplitudes (A B$\leq$10mmag). These oscillations are probably low spherical degree, high overtone p-modes. Using the (in general) rich oscillation spectra, several important astrophysical parameters such as the (asteroseismological) luminosity, the rotational period, the magnetic field strength and the atmospheric structure can be inferred.

Since the early eighties, the South African working group has spent a lot of time in detecting new roAp stars. They discovered more than twenty new roAps (e.g. see Martinez & Kurtz 1995) and published also an extensive list of null results (Martinez & Kurtz 1994). Several surveys in the Northern Hemisphere were also devoted to find new members of this group (e.g. Heller & Kramer 1988; Nelson & Kreidl 1993). Unfortunately, only one new roAp star (HD 176232, 10 Aql) was detected. Recently, Dorokhova & Dorokhov (1998) announced the discovery of a second roAp star (HD 99563) discovered at a Northern Hemisphere observatory.

This situation leads to a dilemma when trying to make a statistically sound analysis for this group. Two main problems arise:

Since only one observatory (Mt. Dushak-Erekdag, Central Asia; Dorokhova & Dorokhov 1998) regularly searches for new roAp stars, we decided to initiate a Northern Hemisphere survey for roAp stars in 1995. Observations are carried out with one of the twin 0.75 m Austrian Automatic Photoelectric Telescopes at Fairborn Observatory and at McDonald Observatory.

In this paper we report the discovery of one new equatorial roAp star (HD 122970), the confirmation that HD 99563 shows rapid oscillations and the apparent null results of our survey. With the help of Hipparcos data we examine the absolute magnitudes and galactic distribution of all investigated stars.


next previous
Up: A search for rapid

Copyright The European Southern Observatory (ESO)