Download - Massive star feedback – from the first stars to the present Jorick Vink (Keele University)
Outline
• Why predict Mass-loss rates?
(as a function of Z)
• Monte Carlo Method
• Results OB, B[e], LBV & WR winds
• Cosmological implications?
• Look into the Future
Progenitor for Collapsar model
• Rapidly rotating
• Hydrogen-free star (Wolf-Rayet star)
• But……
Woosley (1993)
Progenitor for Collapsar model
• Rapidly rotating
• Hydrogen-free star (Wolf-Rayet star)
• But……
Stars have winds…
Woosley (1993)
Why predict Mdot ?
• Energy & Momentum input into ISM
• Stellar Evolution– Explosions: SN, GRBs– Final product: Neutron star, Black hole
Why predict Mdot ?
• Energy & Momentum input into ISM
• Stellar Evolution– Explosions: SN, GRBs– Final product: Neutron star, Black hole– X-ray populations in galaxies
Why predict Mdot ?
• Energy & Momentum input into ISM
• Stellar Evolution
• Stellar Spectra – Analyses of starbursts
Why predict Mdot ?
• Energy & Momentum input into ISM
• Stellar Evolution
• Stellar Spectra – Analyses of starbursts– Ionizing Fluxes
Why predict Mdot ?
• Energy & Momentum input into ISM
• Stellar Evolution
• Stellar Spectra
• Stellar “Cosmology”
Why predict Mdot ?
• Energy & Momentum input into ISM
• Stellar Evolution
• Stellar spectra
• “Stellar cosmology”
Radiation-driven wind by Lines
dM/dt = f (Z, L, M, Teff)
STAR Fe
Lucy & Solomon (1970)Castor, Abbott & Klein (1975) = CAK
Wind
Approach:
• Assume a velocity law
• Compute model atmosphere, ionization stratification, level populations
• Monte Carlo to compute radiative force
The bi-stability Jump
HOT
Fe IV
low dM/dt
high Vinf
Low density
COOL
Fe III
high dM/dt
low Vinf
High density
Stars should pass the bistable limit
• During evolution from O B• LBVs on timescales of years
Implications for circumstellar medium (CSM) Mass-loss rate up ~ 2 wind velocity down ~ 2CSM density variations ~ 4
Success of Monte Carlo at solar Z
• O-star Mass loss rates
• Prediction of the bi-stability jump
• Mass loss behaviour of LBVs like AG Car
Monte Carlo mass-loss used in stellar models in Galaxy
Which element drives WR winds?
- C WR mass loss not Z(Fe)-dependent
- Fe WR mass loss depends on Z host
Corollary of lower WR mass loss:
less angular momentum loss
favouring the collapse of WR stars to produce GRBs
Long-duration GRBs favoured at low Z
Conclusions
• Successful MC Models at solar Z
• O star winds are Z-dependent (Fe)• WR winds are Z-dependent (Fe) GRBs• Low-Z WC models: flattening of this dependence• Below log(Z/Zsun) = -3 “Plateau”
Mass loss may play a role in early Universe
Future Work
• Solving momentum equation
• Wind Clumping
• Compute Mdot close to Eddington limit
• Compute Mdot at subsolar and Z = 0
Two O-star approaches
1. CAK-type Line force approximated
v(r) predicted CAK, Pauldrach (1986), Kudritzki (2002)
2. Monte Carlo V(r) adopted
Line force computed – for all radii multiple scatterings included
Abbott & Lucy (1985) Vink, de Koter & Lamers (2000,2001)
Advantages of our method
• Non-LTE
• Unified treatment (no core-halo)
• Monte Carlo line force at all radii
• Multiple scatterings
O stars at solar Z & low Z
LBV variability & WR as a function of Z
The bi-stability Jump
HOT
Fe IV
low dM/dt
high V(inf)
Low density
COOL
Fe III
dM/dt = 5 dM/dt HOT
V(inf) = ½ vinf HOT
High density = 10 HOT
The reason for the bi-stability jump
• Temperature drops
Fe recombines from Fe IV to Fe III Line force increases dM/dt up density up V(inf) drops
“Runaway”
Can we use our approach for WR stars?
• Potential problems:– Are these winds radiatively driven?– Is Beta = 1 a good velocity law?– Do we miss any relevant opacities?– What about wind clumping?
New Developments:
• Hot Iron Bump Fe X --- Fe XVI
• Graefener & Hamann (2005) can “drive”
a WC5 star self-consistently
Use Monte Carlo approach for a differential study of Mass loss versus Z