Abstract
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 (8-90M⊙). 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 × 105K, 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 60M⊙ 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.
Original language | English |
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Pages (from-to) | 1814-1822 |
Number of pages | 9 |
Journal | Monthly Notices of the Royal Astronomical Society |
Volume | 412 |
Issue number | 3 |
DOIs | |
Publication status | Published - 2011 Apr |
Externally published | Yes |
Keywords
- Stars: early-type
- Stars: evolution
- Stars: massive
- Stars: oscillations
- Supergiants
ASJC Scopus subject areas
- Astronomy and Astrophysics
- Space and Planetary Science