Atomic physics of shocked plasma in the winds of massive stars
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Atomic physics of shocked plasma in the winds of massive stars Maurice Leutenegger (NASA/GSFC/CRESST/UMBC) David Cohen (Swarthmore College) Stan Owocki (Bartol Research Institute)
description
Talk given by Maurice A. Leutenegger (NASA-GSFC) at the 17th APiP, 19-22 July 2011, Queen's University, Belfast, UK.
Transcript of Atomic physics of shocked plasma in the winds of massive stars
Atomic physics of shocked plasma in the winds of massive stars
Maurice Leutenegger (NASA/GSFC/CRESST/UMBC)
David Cohen (Swarthmore College)
Stan Owocki (Bartol Research Institute)
Outline
● Background on winds of massive stars● Mechanisms for x-ray emission● Mass loss rate problem● Background on x-ray observatories● Doppler profile diagnostics● He-like triplet diagnostics● Special bonus problems: optically thick x-ray
radiative transfer in a supersonic flow; Fe XVII line ratios
Massive stars
● Spectral type O, early B; T ~ 30-50 kK
● M ~ 30-120 Mʘ
; L bol
~ 105 – 106 Lʘ
● Mass loss rates 10-7 – 10-5 Mʘ/year (compare to
sun at 10-14 Mʘ/year); v
∞ ~ 2000 km/s
● ½ Ṁ v∞
2 ~ 10-3 Lbol
; Lx ~ 10-7 Lbol
● TMS
~ few 10 Myr
Theory of radiatively driven winds
● Radiation pressure in spectral lines becomes much more effective due to deshadowing of optically thick lines in a supersonic flow
Importance of massive star winds
Meynet & Maeder
Townsley et al.
Mechanisms for x-ray emission
Okazaki et al.
Gagne et al. (model of Asif ud-Doula)
Colliding winds
Magnetically channeled winds
Mechanisms for x-ray emission
Feldmeier et al.
Intrinsic wind structure(embedded wind shocks)
Mass loss rates of O stars
Fullerton et al. (2006)
Chandra and XMM
Soft x-ray spectra of ζ Puppis
Comparison with Capella
Comparison with Capella
Line shape is diagnostic of optical depth
Profile formation
Lλ=4π∫dV ηλ e−τ
τ( p , z)=∫z
∞
κ(λ)ρ(r' )dz '
Approximate wind as two component fluid
Profile formation
τ*=κ M
4 π v∞R*
ρ= M
4π r2v (r)
τ( p , z)=τ* t ( p , z )
τ( p , z)=∫z
∞
κ(λ)ρ(r' )dz '
Model x-ray profiles
Example: Fe XVII 15.014 Å
He-like triplet diagnostics
A ~ Z10
He-like triplet diagnostics
He-like triplet ratio and line profile
No additional free parameters!
Fit all lines to constrain mass loss
Fit all lines to constrain mass loss
τ*=κ M
4 π v∞R*
An unexpected problem
An unexpected problem
Sobolev theory: radiative transfer in a supersonic, accelerating wind
Lsob=v th(dv zdz )−1
τ sob=χ Lsob
τ0=χ v thv /r τ1=
χ v thdv /dr
Sobolev theory
Velocity law Anisotropy factor
σ= rvdvdr
−1
Angular distribution of emission
Effect of resonance scattering
Resonance scattering fits the data
Resonance scattering fits the data
Resonance scattering fits the data
Resonance scattering fits the data
Plausibility of resonance scattering
Summary
● X-ray emission from single O star winds can be understood in terms of the embedded wind shock paradigm
● Independent constraints can be placed on mass loss rates by x-ray line shapes, leading to downward revisions factors of 2-4 from recombination/free-free diagnostics
● He-like triplet diagnostics constrain plasma location and confirm the EWS paradigm
Summary
● Resonance scattering can symmetrize line profile shapes; we know it is important from comparisons of resonance and intercombination lines from the same ion
● (If there is time, ask me about Fe XVII line ratios!)
Fe XVII line ratio problem
τ Sco
Fe XVII line ratio problem
ς Ori
Fe XVII line ratio problem
ς Pup
Inner shell absorption in Fe
