Speaker: Margarida Cunha, Centro de Astrof?sica and Faculdade de Ciencias, Universidade do Porto, Porto, Portugal

Title: Modern ways to test old puzzles: the driving of oscillations in strongly magnetic, chemically peculiar stars

Abstract:
Chemically peculiar stars are stage to a wide variety of physical phenomena, including diffusion, convection, magnetism and pulsation. Progress in the understanding of these objects, through the study of their oscillations, can help us characterize these physical phenomena and better understand the way they are coupled in stars.

A number of chemically peculiar A-type stars, known as rapidly oscillating Ap (roAp) stars, have been known to exhibit high frequency oscillations since the early 80s. Despite this, the mechanism responsible for driving these oscillations is not fully understood. Currently, the most widely accepted theory states that oscillations in this class of pulsators are excited by the opacity mechanism acting on the hydrogen ionization region, in an envelope where convection has been suppressed by a strong magnetic field.  Nevertheless, this theory fails to correctly predict the observational red edge for this class of pulsators. Moreover, for a subset of these pulsators, the observed frequencies are significantly higher that what is predicted from non-adiabatic models with envelope convection suppressed.

In this talk I will present a study that is being conducted to test the predictions of non-adiabatic models of roAp stars. The principle is to use interferometry and computed bolometric fluxes to determine accurate global parameters for selected roAp stars and then use these as inputs  for the models. Model predictions for the frequency region of unstable modes is then compared with the frequency range of observed oscillations. I will discuss the dependence of the results on the input physics for the models and show that significant work is still required before we can confidently state that we fully understand the driving mechanism operating in roAp stars.