Rapidly oscillating Ap stars have proved to be extremely interesting objects, for they combine in a unique way different physical properties, like stellar magnetism and abnormal chemical abundances, with important physical phenomena, like acoustic oscillations. In this paper we will discuss how the indirect effect of the magnetic field and the presence of chemical peculiarities may influence different aspects of the pulsations in roAp stars and will try to discuss their implications to our understanding of the latter.

Introduction

Rapidly oscillating Ap stars (hereafter roAp stars) have now been known for a couple of decades (Kurtz 1982). They are located in the main-sequence part of the classical instability strip, close to the δ Scuti stars, but unlike the latter, roAp stars are small-period pulsators, oscillating with periods that vary typically from 5 to 15 minutes. They are found among the coolest subgroup of classical Ap stars, and, thus, not only are they chemically peculiar, but also they have strong large scale magnetic fields, with typical intensities of a few kG. This combination of properties makes roAp stars extremely interesting targets for asteroseismology. Moreover, the oscillations they exhibit are interpreted as high-order, low-degree modes, opening the possibility of applying asymptotic techniques.

The magnetic fields present in roAp stars influence the oscillations both directly and indirectly.