H. Saio, M. Gruberbauer, W. W. Weiss, J. M. Matthews, T. Ryabchikova
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.
View original:
http://arxiv.org/abs/1110.4186
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