The detection of the rich p-mode spectrum and asteroseismology of Przybylski's star

Abstract

Aims. We investigate the oscillation spectrum of the most chemically-peculiar star in the sky, the rapidly-oscillating magnetic (roAp) star HD 101065. Methods. High-precision radial velocity (RV) measurements, spanning four consecutive nights on 3–6 March, 2004, were obtained with the HARPS echelle-spectrometer at the ESO 3.6-m telescope, and photometric data were acquired during 6 nights of observations at the 24-inch telescope of Siding Spring Observatory. The RVs were measured using all spectral lines in the wavelength range 4400–5100 A. Results. We detected a rich spectrum of oscillation modes with semi-amplitudes ranging between 217 m s −1 and 1.6 m s −1 .T hese belong to the complete spectrum of high-order, low � = 0–2 modes, having a large spacing of Δν = 64.07 ± 0.9 μHz. We calculated the nonadiabatic frequencies of axisymmetric high-order p-modes for main-sequence models with dipole magnetic fields of two chemical compositions (X,Z) = (0.7, 0.02) and (X,Z) = (0.695, 0.025). The former composition provided the best fit model and yielded stellar parameters of mass, M = 1.525 ± 0.025 M� ,a ge= (1.5 ± 0.1) × 10 9 yr, effective temperature log Te = 3.821 ± 0.006, luminosity logL/L� = 0.797 ± 0.026, surface gravity log g = 4.06 ± 0.04, and polar magnetic field strength, Bp = 8.7 ± 0. 3k G. We are able to identify the modes of all detected oscillation frequencies. The photometric U and B light curves have maxima that precede the RV maximum by 0.16–0.19 in phase.