Linear analyses for the stability of radial and nonradial oscillations of massive stars

Details Linear analyses for the stability of radial and nonradial oscillations of massive stars Linear analyses for the stability of radial and nonradial oscillations of massive stars

2010-11-22

arxiv.org/abs/1011.4729v1

Astronomy and Astrophysics

Astrophysics

Solar and Stellar Astrophysics

10 pages, 14 figures, accepted for publication in MNRAS

Scientific paper

In order to understand the periodic and semi-periodic variations of luminous O- B- A-type stars, linear nonadiabatic stability analyses for radial and nonradial oscillations have been performed for massive evolutionary models ($8M_\odot - 90M_\odot$). In addition to radial and nonradial oscillations excited by the kappa-mechanism and strange-mode instability, we discuss the importance of low-degree oscillatory convection (nonadiabatic g$^-$) modes. Although their kinetic energy is largely confined to the convection zone generated by the Fe opacity peak near $2\times10^5$K, the amplitude can emerge to 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 LBVs (S Dor variables) and $\alpha$ Cyg variables. Moreover, monotonously unstable radial modes are found in some models whose initial masses are greater than or equal to $60M_\odot$ with $Z=0.02$. The monotonous instability probably corresponds to the presence of an optically thick wind. The instability boundary roughly coincides with the Humphreys-Davidson limit.

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