On the origin of Microturbulence in hot stars Matteo Cantiello Utrecht University (N.Langer, A.de Koter, J.Vink, A.Voegler, S.N.Shore, I.Brott, S.C.Yoon)

Outline of the talk Convection in hot stars Microturbulence in hot stars Implications for wind clumping Matteo Cantiello On the origin of Microturbulence in hot stars Liège - July 2008

Convection in hot stars Matteo Cantiello On the origin of Microturbulence in hot stars Liège - July 2008

Stellar structure Low Mass stars Massive stars e.g 1MSun e.g 20 MSun Radiative core Convective envelope Convective core Radiative envelope Matteo Cantiello On the origin of Microturbulence in hot stars Liège - July 2008

Opacity Inside a massive star Matteo Cantiello On the origin of Microturbulence in hot stars Liège - July 2008

Subsurface convection (e.g. Cantiello et al. ’08, Maeder et al. ‘08) Matteo Cantiello On the origin of Microturbulence in hot stars Liège - July 2008

Microturbulence in hot stars Matteo Cantiello On the origin of Microturbulence in hot stars Liège - July 2008

Microturbulence Is the additional broadening coming from nonthermal motions varying on a small scale in the region of line formation. Observed line profile Intrinsic line profile Matteo Cantiello On the origin of Microturbulence in hot stars Liège - July 2008

Microturbulence vs Macroturbulence L = Size of line forming region D= Scale on which non-thermal velocity varies D L D D < L Microturbulence D > L Macroturbulence non radial pulsation, granules motion... ? See next talk Matteo Cantiello On the origin of Microturbulence in hot stars Liège - July 2008

Origin of microturbulence? To fit stellar spectra of hot stars microturbulence (~0-20 km/s) is needed Used as a free parameter. Unknown physical origin We look for a correlation between subsurface convection and microturbulence Convection microturbulence clumping ? Matteo Cantiello On the origin of Microturbulence in hot stars Liège - July 2008

The physical mechanism (e.g. Lighthill ‘52, Stein ‘67, Edmunds ’78, de Jager et al. ’91) Matteo Cantiello On the origin of Microturbulence in hot stars Liège - July 2008

Method We use a 1D-hydrodynamic stellar evolution code (Langer et al., Heger et al.) Convection: Ledoux criterion and Mixing length theory (Bohm-Vitense ‘58) Opacity: OPAL ‘96 (Rogers & Iglesias ‘96) Grids of models from 5 to 120 MSun at MW, LMC and SMC metallicities Observations of microturbulence in hot stars (ESO Flames, Hunter et al. 2007, Trundle et al. 2007) Matteo Cantiello On the origin of Microturbulence in hot stars Liège - July 2008

Results Matteo Cantiello On the origin of Microturbulence in hot stars Liège - July 2008

Results (LMC) Models + FLAMES observations of microturbulence Matteo Cantiello On the origin of Microturbulence in hot stars Liège - July 2008

Results II (Metallicity) Matteo Cantiello On the origin of Microturbulence in hot stars Liège - July 2008

Wind clumping Matteo Cantiello On the origin of Microturbulence in hot stars Liège - July 2008

Wind clumping Evidences that winds of massive stars are clumped (e.g. Puls at al. ‘06) Inner wind seems to be more clumped (Puls at al. ‘06) Line-driven instability prediction not confirmed (Runacres & Owocki ’02,’05) Correlation between clumping at the base of the wind and subsurface convection (hence microturbulence)? Matteo Cantiello On the origin of Microturbulence in hot stars Liège - July 2008

Inner wind clumping in ~ 1.05...2 R* (Data from Puls et al. ’06) Matteo Cantiello On the origin of Microturbulence in hot stars Liège - July 2008

Summary Most hot stars have subsurface convection Convection increases with Z , T, L Subsurface convection correlates with microturbulent velocities Similar prediction for wind clumping Matteo Cantiello On the origin of Microturbulence in hot stars Liège - July 2008

The future ? Microturbulence, once a fudge factor, could become a physical phenomenon which plays an important role in the evolution of massive stars! Need for hydro simulations of the atmosphere of hot stars. Magnetic fields: dynamo from subsurface convection? Matteo Cantiello On the origin of Microturbulence in hot stars Liège - July 2008

The End Thanks! Matteo Cantiello On the origin of Microturbulence in hot stars Liège - July 2008

Rotation and Microturbulence Matteo Cantiello On the origin of Microturbulence in hot stars Liège - July 2008

Small magellanic cloud Matteo Cantiello On the origin of Microturbulence in hot stars Liège - July 2008

Milky Way Matteo Cantiello On the origin of Microturbulence in hot stars Liège - July 2008