Turbulence-supported Massive Star Envelopes

Abstract The outer envelopes of massive ( M ≳ 10 ⊙ ) stars exhibit large increases in opacities from forests lines and ionization transitions (particularly iron helium) that trigger near-surface convection zones. One-dimensional (1D) models predict density inversions supersonic motions must be resolved with computationally intensive three-dimensional (3D) radiation hydrodynamic (RHD) modeling. Only the last decade have computational tools advanced to point where ab initio 3D these turbulent can calculated, enabling us present five RHD Athena++ (four previously published one new 13 model). When convective are subsonic, we find excellent agreement between 1D velocity magnitudes, stellar structure, photospheric quantities. However, when velocities approach sound speed, hydrostatic balance fails as pressure account for 80% force balance. As predicted by Henyey, show this additional support leads a modified temperature gradient, which reduces superadiabaticity is occurring. In addition, all display significant overshooting Fe zone. result, at surface indicative those There no confined zones seen models. particular, helium significantly modified. Stochastic low-frequency brightness variability also model comparable amplitude characteristic frequency observed stars.