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Unkown stellar mass loss at low metallicityPowerPoint Presentation

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

Topics to be discussed

Predictions of properties of “normal” winds (Z~solar)

and comparison with observations

Predicted properties of low Z winds (Z~10-4 solar)

Extremely no Z winds (H and He only)

Net force in wind: gnet = - gN + ge + glines > 0

Gravity : gN = GM / R2

Rad pressure by electrons : ge = σe L / 4 π R2 c = Γe gN

Rad pressure by lines: gl = ge M(t)

Force multiplier: M(t) = k t-α (ne/W)δ

Solar Z : k ~ 1/30 α ~ 0.6 δ ~ 0.1

Castor, Abbott & Klein 1975, CAK

Predictions: scaling laws

Castor, Abbott, Klein 1975

v∞ ~ (2 to 3)v esc ~ √ (M/R)

Mdot ~ L 1/α M (α-1)/α

Predictions: scaling laws

Castor, Abbott, Klein 1975

v∞ ~ (2 to 3)v esc ~ √ (M/R)

Mdot ~ L 1/α M (α-1)/α

↓

Kudritzki et al 1989

П≡ Mdotv∞√ R ~L 1/α M 0.5-(1-α)/α ~ L 1/α

П = Modified wind momentum

Predicted mass loss rates

Vink et al. 2000

Problem:

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

“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

AV 83 and AV 69: very different winds!

Hillier et al. 2003

- Effects of rotation
- Flattening
- 2. Gravity = f( θ)
- 3. Teff = f(θ )
- 4. Mdot = f(θ)
- 5. Vwind = f(θ)
- 6. Spect type = f(sin i)

Meynet & Maeder 2002

The wind of a fast rotating hot supergiant

J. Bjorkman 2005

The problem of the winds of low luminosity SMC stars

Black = Gal

Red = LMC

Blue = SMC

П↔L relation breaks down at log L < 5.3 !!

Martins et al. 2004

Mass loss at very low metallicityZ/Zsun < 10-3

Predictions at low Zparameters k, α, δ vary with distance

Z/Zsun

1.0

0.2

10-2

10-3

10-4

П

Kudritzki 2002

Very low Z stars only have winds when they are close to Eddington limit !

grad = ge + glines > gN at some depth

glines = M(t) ge

Mmax ≈ 2000 Z/Zsun + M(H,He) from atomic physics

So maximumradiation pressure is

gradmax = (1+Mmax) ge = (1+Mmax) Γe gN > gN

Γe > (1+Mmax)-1

Zero metallicity stars Eddington limit !

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 >0 if

level populations are just right

but only in very small region of atmosphere.

Krticka & Kubat, 2005

g Eddington limit !eff > 0 only in very

small zone

Zero metallicity stars have NO line driven winds !!

Krticka & Kubat 2005

Conclusions Eddington limit !

A: 10-3 < Z/Zsun < 10 : Mdot ~ Z0.85

but : Mdot depends on (fast) rotation

B: 10-4 < Z/Zsun < 10-3 : Mdot ~only for large Γe

Γe > (1+Mmax)-1

Mmax ≈ 2000 Z/Zsun

C: Z/Zsun=0 : no line driven wind,

Mdot < 10 -10 Msun/yr

That’s all ! Eddington limit !

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