Pulsation models for the roAp star HD 134214

TL;DR

This study models the pulsation frequencies of the roAp star HD 134214 using magnetic stellar models, identifying observed frequencies with deformed dipole and quadrupole modes, and discusses implications for atmospheric structure.

Contribution

First to fit observed pulsation frequencies of HD 134214 with magnetic stellar models, linking observed modes to specific deformed eigenmodes and analyzing their atmospheric properties.

Findings

Best-fit model has a 1.65 solar mass, log T_eff=3.858, 4.1kG magnetic field.

Observed frequencies correspond to deformed dipole and quadrupole modes.

Mode frequencies are above the acoustic cut-off, indicating damping.

Abstract

Precise time-series photometry with the MOST satellite has led to identification of 10 pulsation frequencies in the rapidly oscillating Ap (roAp) star HD 134214. We have fitted the observed frequencies with theoretical frequencies of axisymmetric modes in a grid of stellar models with dipole magnetic fields. We find that, among models with a standard composition of $(X,Z) = (0.70,0.02)$ and with suppressed convection, eigenfrequencies of a $1.65\,{\rm M}_\odot$ model with $\log T_{\rm eff} = 3.858$ and a polar magnetic field strength of 4.1kG agree best with the observed frequencies. We identify the observed pulsation frequency with the largest amplitude as a deformed dipole ($\ell = 1$) mode, and the four next-largest-amplitude frequencies as deformed $\ell = 2$ modes. These modes have a radial quasi-node in the outermost atmospheric layers ($\tau \sim 10^{-3}$). Although the model frequencies agree roughly with observed ones, they are all above the acoustic cut-off frequency for the model atmosphere and hence are predicted to be damped. The excitation mechanism for the pulsations of HD 134214 is not clear, but further investigation of these modes may be a probe of the atmospheric structure in this magnetic chemically peculiar star.