Takafumi Sonoi, Hiromoto Shibahashi
We find that low-degree low-order g-modes become unstable in metal-poor
low-mass stars due to the $\varepsilon$-mechanism of the pp-chain. Since the
outer convection zone of these stars is limited only to the very outer layers,
the uncertainty in the treatment of convection does not affect the result
significantly. The decrease in metallicity leads to decrease in opacity and
hence increase in luminosity of a star. This makes the star compact and results
in decrease in the density contrast, which is favorable to the
$\varepsilon$-mechanism instability. We find also instability for high order
g-modes of metal-poor low-mass stars by the convective blocking mechanism.
Since the effective temperature and the luminosity of metal-poor stars are
significantly higher than those of Pop I stars, the stars showing $\gamma$
Dor-type pulsation are substantially less massive than in the case of Pop I
stars. We demonstrate that those modes are unstable for about $1\,M_\odot$
stars in the metal-poor case.
View original:
http://arxiv.org/abs/1202.5121
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