Unkown stellar mass loss at low metallicity

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Unkown stellar mass loss at low metallicity

• Henny Lamers
• Astronomical Institute and
• SRON Laboratory for Space Research
• Utrecht University

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Topics to be discussed

• Predictions of properties of normal winds
  (Zsolar)
• and comparison with observations
• Predicted properties of low Z winds (Z10-4
  solar)
• Extremely no Z winds (H and He only)

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Net force in wind gnet - gN ge glines
gt 0
Gravity gN GM / R2
Rad pressure by electrons ge se L / 4 p R2
c Ge gN
Rad pressure by lines gl ge M(t)
Force multiplier M(t) k t-a (ne/W)d
Solar Z k 1/30 a 0.6
d 0.1
Castor, Abbott Klein 1975, CAK
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Predictions scaling laws
Castor, Abbott, Klein 1975

• v8 (2 to 3) v esc v (M/R)
• Mdot L 1/a M (a-1)/a

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Predictions scaling laws
Castor, Abbott, Klein 1975

• v8 (2 to 3) v esc v (M/R)
• Mdot L 1/a M (a-1)/a

?
Kudritzki et al 1989
? Mdot v8 v R L 1/a M 0.5-(1-a)/a
L 1/a ? Modified wind momentum
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Predicted mass loss rates
Vink et al. 2000
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Modified wind momentum ? ? L
predictions
Log ?
observations
Vink et al. 2000
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New study with improved mass loss rates
Galactic stars
Markova et al. 2004
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Problem

• Some stars with very similar stellar
  parameters show a large difference in mass loss
  rate and wind properties !!

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Tale of two stars
AV 83 AV 69 Type
O7 Iaf O7.5 III L/Lsun 3.5 105
4.1 105 Teff 32800 33900 R/Rsun
18.5 18.6 He/H 0.2
0.1 C/N 0.15 15

Hillier et al. 2003
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AV 83 and AV 69 very different winds!
Hillier et al. 2003
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AV 83 AV 69 Mdot 7 10-7 9
10-7 V8 940 1800 ß 2.0
1.0 fclump 0.1 1
ROTATION !!!
Hillier et al. 2003
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• Effects of rotation
• Flattening
• 2. Gravity f( ?)
• 3. Teff f(? )
• 4. Mdot f(?)
• 5. Vwind f(?)
• 6. Spect type f(sin i)

Meynet Maeder 2002
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The wind of a fast rotating hot supergiant
J. Bjorkman 2005
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Mass loss and metallicity
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Predictions for line driven winds
10-2 lt Z/Zsun lt101
Mdot Z 0.85
Vink et al. 2001
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Observations ? Predictions
LMC SMC
Vink et al. 2001
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The problem of the winds of low luminosity SMC
stars
Black Gal Red LMC Blue SMC
??L relation breaks down at log L lt 5.3 !!
Martins et al. 2004
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Mass loss at very low metallicityZ/Zsun lt 10-3
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Predictions at low Zparameters k, a, d vary
with distance
Z/Zsun 1.0 0.2 10-2 10-3 10-4
?
Kudritzki 2002
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Very low Z stars only have winds when they are
close to Eddington limit !

• grad ge glines gt gN at some depth
• glines M(t) ge
• Mmax 2000 Z/Zsun M(H,He) from atomic
  physics
• So maximum radiation pressure is
• gradmax (1Mmax) ge (1Mmax) Ge gN gt gN
  
• Ge gt (1Mmax)-1

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Dependence of mass loss on Ge
? Mdot 10-8
Msun/yr
Kudritzki 2002
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Zero metallicity stars
1. Radiation pressure only due to H and He
lines 2. H lines alone are never strong enough 3.
HeII lines can produce grad-gN gt0 if level
populations are just right but only in very
small region of atmosphere.
Krticka Kubat, 2005
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geff gt 0 only in very
small zone
Zero metallicity stars have NO line driven winds
!!
Krticka Kubat 2005
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Conclusions

• A 10-3 lt Z/Zsun lt 10 Mdot Z0.85
• but
  Mdot depends on (fast) rotation
• B 10-4 lt Z/Zsun lt 10-3 Mdot only for
  large Ge
• Ge gt
  (1Mmax)-1
• Mmax
  2000 Z/Zsun
• C Z/Zsun0 no line driven
  wind,
• Mdot lt
  10 -10 Msun/yr

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Thats all !
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