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Determination of Luminosity, Atmospheric Structure, and Magnetic Geometry from Studies of the Pulsation in roAp Stars

Published online by Cambridge University Press:  12 April 2016

D. W. Kurtz  and
Peter Martinez
D. W. Kurtz
Affiliation:
Department of Astronomy, University of Cape Town, Rondebosch 7700, South Africa
Peter Martinez
Affiliation:
Department of Astronomy, University of Cape Town, Rondebosch 7700, South Africa

Abstract

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For several of the rapidly oscillating Ap stars the best luminosity estimates available come from the asteroseismological interpretation of their pulsational frequency spectra. We give a list of the 23 currently known roAp stars along with their Strömgren photometric indices, Teff estimated from the Hβ index, and luminosity estimated asteroseismologically. In one case, ϒ Equ, we have an asteroseismological luminosity and a parallax luminosity which are in good agreement. Some of the roAp stars pulsate with frequencies greater than the critical frequency calculated for standard A-star models. This plus multi-colour high-speed photometry of HR 3831 indicate that the temperature gradients in the atmospheres of these stars are substantially steeper than in standard A-star models. We advocate a fine analysis of HR 3831 to see if there is consistency with the pulsational conclusions about T-τ in this star. Further fine analyses and multi-colour pulsational analyses on other roAp stars are then called for. The pulsation mode in HR 3831 can be decomposed into primarily an axisymmetric dipole mode with small radial, quadrupole and octupole perturbations. If the magnetic field is governing the distortion of this mode from a purely dipole mode, then the pulsation can be used to infer the magnetic field geometry. Comments on our current knowledge of all 23 roAp stars are made.

Type
VII. Photometric Variability and Evolutionary Status
Information
International Astronomical Union Colloquium , Volume 138: Peculiar versus Normal Phenomena in A-Type and Related Stars , 1993 , pp. 561 - 576
Copyright
Copyright © Astronomical Society of the Pacific 1993

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