Journal Article

A 3D study of the photosphere of HD 99563 – I. Pulsation analysis*

L. M. Freyhammer, D. W. Kurtz, V. G. Elkin, G. Mathys, I. Savanov, W. Zima, H. Shibahashi and K. Sekiguchi

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 396, issue 1, pages 325-342
Published in print June 2009 | ISSN: 0035-8711
Published online June 2009 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2009.14538.x
A 3D study of the photosphere of HD 99563 – I. Pulsation analysis*

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We have used high-speed spectroscopy of the rapidly oscillating Ap (roAp) star HD 99563 to study the pulsation amplitude and phase behaviour of elements in its stratified atmosphere over one 2.91-d rotation cycle. We identify spectral features related to patches in the surface distribution of chemical elements and study the pulsation amplitudes and phases as the patches move across the stellar disc. The variations are consistent with a distorted non-radial dipole pulsation mode. We measure a 1.6 km s−1 rotational variation in the mean radial velocities of Hα and argue that this is the first observation of Hα abundance spots caused by He settling through suppression of convection by the magnetic field on an oblique rotator, in support of a prime theory for the excitation mechanism of roAp star pulsation. We demonstrate that HD 99563 is the second roAp star to show aspect dependence of blue-to-red running wave line profile variations in Nd iii spots.

Keywords: stars: atmospheres; stars: chemically peculiar; stars: individual: HD 99563; stars: magnetic fields

Journal Article.  13347 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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