Journal Article

Linear analyses for the stability of radial and non-radial oscillations of massive stars

Hideyuki Saio

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 412, issue 3, pages 1814-1822
Published in print April 2011 | ISSN: 0035-8711
Published online April 2011 | e-ISSN: 1365-2966 | DOI:
Linear analyses for the stability of radial and non-radial oscillations of massive stars

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In order to understand the periodic and semiperiodic variations of luminous OBA-type stars, linear non-adiabatic stability analyses for radial and non-radial oscillations have been performed for massive evolutionary models (8–90 M). In addition to radial and non-radial oscillations excited by the kappa-mechanism and strange mode instability, we discuss the importance of low-degree oscillatory convection (non-adiabatic g) modes. Although their kinetic energy is largely confined to the convection zone generated by the Fe-opacity peak near 2 × 105 K, the amplitude can emerge into the photosphere and should be observable in a certain effective temperature range. They have periods longer than those of the radial strange modes so that they seem to be responsible for some of the long-period microvariations of Luminous Blue Variables (LBVs; S Dor variables) and α Cyg variables. Moreover, monotonically unstable radial modes are found in some models whose initial masses are greater than or equal to 60 M with Z= 0.02. The monotonic instability probably corresponds to the presence of an optically thick wind. The instability boundary roughly coincides with the Humphreys–Davidson limit.

Keywords: stars: early-type; stars: evolution; stars: massive; stars: oscillations; supergiants

Journal Article.  6192 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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