1. 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)

2. 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

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

4. 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

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

6. 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

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

8. 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

9. 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

10. 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

11. 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

12. 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

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

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

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

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

17. 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

18. 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

19. 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

20. 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

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

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

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

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