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.Voegler, A.de Koter, J.Vink,
  S.N.Shore, I.Brott, S.C.Yoon)

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Outline of the talk

• Convection in hot stars
• Microturbulence in hot stars
• Methods
• Results
• Summary

Matteo Cantiello On
the origin of Microturbulence in hot stars
NAC - May 2008
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Convection in hot stars
Matteo Cantiello On
the origin of Microturbulence in hot stars
NAC - May 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
NAC - May 2008
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Opacity
Inside a massive star
Matteo Cantiello On
the origin of Microturbulence in hot stars
NAC - May 2008
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Subsurface convection
Matteo Cantiello On
the origin of Microturbulence in hot stars
NAC - May 2008
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Microturbulence in hot stars
Matteo Cantiello On
the origin of Microturbulence in hot stars
NAC - May 2008
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Microturbulence
Microturbulent velocity is the non thermal
component of the gas velocity in the region of
spectral line formation (Cowley 70)
Hunter et al. 2007
Matteo Cantiello On
the origin of Microturbulence in hot stars
NAC - May 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 want to check if subsurface convection is the
  cause of microturbulence

Matteo Cantiello On
the origin of Microturbulence in hot stars
NAC - May 2008
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The physical mechanism
Matteo Cantiello On
the origin of Microturbulence in hot stars
NAC - May 2008
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Methods

• 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 100 MSun at MW, LMC and
  SMC metallicities
• Observations of microturbulence in hot stars
  (VLT-Flames, Hunter et al. 2007)

Matteo Cantiello On
the origin of Microturbulence in hot stars
NAC - May 2008
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Results
Matteo Cantiello On
the origin of Microturbulence in hot stars
NAC - May 2008
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Results (LMC)
LMC
Models
observations (VLT-Flames)
Matteo Cantiello On
the origin of Microturbulence in hot stars
NAC - May 2008
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Results II(Metallicity)
SMC
Matteo Cantiello On
the origin of Microturbulence in hot stars
NAC - May 2008
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Summary

• Hot stars may have subsurface convection
• Subsurface convection is the cause of
  photospheric turbulence (Microturbulence)
• We predict
• Similar prediction for Wind Clumping

Matteo Cantiello On
the origin of Microturbulence in hot stars
NAC - May 2008
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The End
Thanks!
Matteo Cantiello On
the origin of Microturbulence in hot stars
NAC - May 2008
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Rotation and Microturbulence
Matteo Cantiello On
the origin of Microturbulence in hot stars
NAC - May 2008
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Small magellanic cloud
Matteo Cantiello On
the origin of Microturbulence in hot stars
NAC - May 2008
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Milky Way
Matteo Cantiello On
the origin of Microturbulence in hot stars
NAC - May 2008