OBSERVATIONAL CONSEQUENCES OF TURBULENT PRESSURE IN THE ENVELOPES OF MASSIVE STARS
Luca Grassitelli(1), Luca Fossati(1),Sergio Simon-Diaz(2,3), Norbert Langer(1),Norberto Castro(1),Debashis Sanyal(1)
(1) Argelander Institute for Astronomy, University of Bonn
(2) Instituto de Astrofısica de Canarias, Tenerife
(3) Departamento de Astrofisica, Universidad de La Laguna
The major mass fraction of the envelope of hot luminous stars is radiatively stable. However, the partial ionisation 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 search for observable consequences. We find that the turbulent pressure fraction can amount up to 5% in OB supergiants, and 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 of 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.
Reference: ApJ Letters
Status: Manuscript has been accepted