The stability of massive main-sequence stars as a function of metallicity

We investigate the pulsational stability of massive (M≳ 120M_⊙) main-sequence stars of a range of metallicities, including primordial, Population III stars. We include a formulation of convective damping motivated by numerical simulations of the interaction between convection and periodic shear flows. We find that convective viscosity is likely strong enough to stabilize radial pulsations whenever nuclear burning (the ε-mechanism) is the dominant source of driving. This suggests that massive main-sequence stars with Z≲ 2 × 10^-3 are pulsationally stable and are unlikely to experience pulsation-driven mass loss on the main sequence. These conclusions are, however, sensitive to the form of the convective viscosity and highlight the need for further high-resolution simulations of the convection-oscillation interaction. For more metal-rich stars (Z≳ 2 × 10^-3), the dominant pulsational driving arises due to the κ-mechanism arising from the iron-bump in opacity and is strong enough to overcome convective damping. Our results highlight that even for oscillations with periods a few orders of magnitude shorter than the outer convective turnover time, the 'frozen-in' approximation for the convection-oscillation interaction is inappropriate, and convective damping should be taken into account when assessing mode stability.