Pulsational Radial Velocity Studies of Roap Stars

Abstract

The magnetic Ap stars are characterized by their strong (~kilogauss) fields whose axis is inclined with respect to the rotation axis as well as anomalous abundances of elements that are distributed inhomogeneously on the stellar surface. (Some elements are concentrated near the magnetic poles and others are concentrated near the magnetic equator.) The rapidly oscillating Ap stars (roAp) are a pulsating subclass of these objects that oscillate in nonradial modes of high radial order (n ~ 30), low degree (ι = 1–3, m = 0) and with periods of 4–15 minutes (Kurtz, 1990). The axis of pulsations is aligned with the magnetic axis and the photometric amplitudes of individual modes are less then 5 mmag. Most of our knowledge of roAp star have come from photometric measurements, but radial velocity (RV) studies, which have been few until recently, can provide valuable insights into the nature of the roAp phenomenon. We have begun a program to study the oscillations in these stars using precise stellar radial velocity (RV) measurements, Here we present results for 5 roAp stars: γ Equ, 33 Lib, HD 134214, and HR 1217, and HD 122970.