OBSERVATIONAL CONSEQUENCES OF TURBULENT PRESSURE IN THE ENVELOPES OF MASSIVE STARS

The major mass fraction of the envelope of hot luminous stars is radiatively stable. However, the partial ionization of hydrogen, helium, and iron gives rise to extended sub-surface convection zones in all of them. In this work, we investigate the effect of the pressure induced by the turbulent motion in these zones based on the mixing-length theory, and we search for observable consequences. We find that the turbulent pressure fraction can amount up to similar to 5% in OB supergiants and up to similar to 30% in cooler supergiants. The resulting structural changes are, however, not significantly affecting the evolutionary tracks compared to previous calculations. Instead, a comparison of macroturbulent velocities derived from high-quality spectra of OB stars with the turbulent pressure fraction obtained in corresponding stellar models reveals a strong correlation between these two quantities. We discuss a possible physical connection and conclude that turbulent pressure fluctuations may drive high-order oscillations, which-as conjectured earlier-manifest themselves as macroturbulence in the photospheres of hot luminous stars.