Pulsation models for the roAp star HD 134214

Abstract

Precise time series photometry with the MOST satellite has led to identification of 10 pulsation frequencies in the rapidly oscillating Ap (roAp) star HD134214. 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 1.65M_☉ model with log T_eff =3.858 and a polar magnetic field strength of 4.1 kG agree best with the observed frequencies. We identify the observed pulsation frequency with the largest amplitude as a deformed dipole (𝓁 = 1) mode, and the four next largest amplitude frequencies as deformed 𝓁 = 2 modes. These modes have a radial quasi-node in the outermost atmospheric layers (τ ∼ 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 HD134214 is not clear, but further investigation of these modes may be a probe of the atmospheric structure in this magnetic chemically peculiar star.