Towards a theory of rapidly oscillating Ap stars

TL;DR

This paper explores the magnetic suppression of convection and pulsation mechanisms in rapidly oscillating Ap stars, proposing a theoretical framework for understanding their unique atmospheric peculiarities and oscillation behaviors.

Contribution

It introduces a theoretical perspective on the magnetic and pulsation phenomena in Ap stars, addressing their atmospheric peculiarities and oscillation alignment.

Findings

Magnetic spots inhibit convection in Ap stars.

Pulsations are nonradial and axisymmetric, aligned with magnetic spots.

Discussion of excitation mechanisms and unresolved issues.

Abstract

Peculiar A stars are so named because they exhibit abundance peculiarities in their atmospheres. It is believed that these arise as a result of differentiation of chemical species in large magnetic spots in which convective mixing is inhibited: there might be just two antipodal spots, whose axis is inclined to the axis of rotation. Many of the Ap stars that are rotating slowly also pulsate, with periods substantially shorter than the period of the fundamental radial mode. The pulsations appear to be nonradial, but axisymmetric, with their common axis usually aligned with the axis of the spots. In this lecture I shall first discuss the magnetic suppression of convection in the spots, and then I shall try to explain the pulsation phenomenon, reviewing some of the suggestions that have been made to explain the alignment and the excitation mechanism, and finally raising some issues that need to be addressed.