On the origin of Microturbulence in hot stars

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On the origin of Microturbulencein hot stars

• Matteo Cantiello
• Utrecht University
• (N.Langer, A.de Koter, J.Vink, A.Voegler,
  S.N.Shore, I.Brott, S.C.Yoon)

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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
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Convection in hot stars
Matteo Cantiello On
the origin of Microturbulence in hot stars
Liège - July 2008
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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
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Opacity
Inside a massive star
Matteo Cantiello On
the origin of Microturbulence in hot stars
Liège - July 2008
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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
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Microturbulence in hot stars
Matteo Cantiello On
the origin of Microturbulence in hot stars
Liège - July 2008
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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
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Microturbulence vs Macroturbulence
L Size of line forming region D Scale on which
non-thermal velocity varies
D
L
D
D lt L Microturbulence
D gt L Macroturbulence non radial pulsation,
granules motion... ? See next talk
Matteo Cantiello On
the origin of Microturbulence in hot stars
Liège - July 2008
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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
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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
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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
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Results
Matteo Cantiello On
the origin of Microturbulence in hot stars
Liège - July 2008
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Results (LMC)
Models
FLAMES observations of microturbulence
Matteo Cantiello On
the origin of Microturbulence in hot stars
Liège - July 2008
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Results II(Metallicity)
Matteo Cantiello On
the origin of Microturbulence in hot stars
Liège - July 2008
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Wind clumping
Matteo Cantiello On
the origin of Microturbulence in hot stars
Liège - July 2008
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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
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Inner wind clumping
(Data from Puls et al. 06)
Matteo Cantiello On
the origin of Microturbulence in hot stars
Liège - July 2008
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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
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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
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The End
Thanks!
Matteo Cantiello On
the origin of Microturbulence in hot stars
Liège - July 2008
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Rotation and Microturbulence
Matteo Cantiello On
the origin of Microturbulence in hot stars
Liège - July 2008
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Small magellanic cloud
Matteo Cantiello On
the origin of Microturbulence in hot stars
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Milky Way
Matteo Cantiello On
the origin of Microturbulence in hot stars
Liège - July 2008