Dipole low-order g mode instability of metal-poor low-mass main-sequence stars due to the $\varepsilon$-mechanism

We analyzed vibrational stability of metal-poor low-mass main-sequence stars due to the $\varepsilon$-mechanism. Since outer convection zones of the metal-poor stars is limited only to the very outer layers, the uncertainty in treatment of convection does not affect the result significantly. We found that the dipole g$_1$- and g$_2$-modes certainly become unstable due to the $\varepsilon$-mechanism for $Z\la 6\times 10^{-4}$. Besides that, we found that as the metallicity decreases the mass range of the $\varepsilon$-mechanism instability extends toward higher mass.