Radial pulsation of less-massive yellow supergiants
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Linear pulsation models of less-massive yellow supergiants withM=1M⊙ andL=3200L⊙ were investigated with the aim of understanding FG Sge's pulsation. We have found that the instability of the third overtone extends to at leastTe=8500 K, while the blue edge of the fundamental mode is nearTe=5500 K.
Nonlinear hydrodynamic simulations were performed for models withTe=6000 K and 5400 K with the same mass and luminosity as the linear models. We have found small limiting-amplitude pulsation due to the linearly unstable third overtone mode in the former model. In the latter model, we have found a limiting amplitude of pulsation with the period of the fundamental mode. However, the latter pulsation shows sub-structure which is caused by coupling between the fundamental and the third overtone modes and also possibly the second overtone mode.
It is suggested that the pulsation of FG Sge must have undergone mode-switching from the third overtone to the fundamental mode during its evolution toward later spectral types.
KeywordsLinear Model Fundamental Mode Spectral Type Radial Pulsation Hydrodynamic Simulation
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