Atomic physics of shocked plasma in the winds of massive stars

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Talk given by Maurice A. Leutenegger (NASA-GSFC) at the 17th APiP, 19-22 July 2011, Queen's University, Belfast, UK.

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Atomic physics of shocked plasma in the winds of massive stars

  1. 1. 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)
  2. 2. 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
  3. 3. 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 2 -3● ½Ṁv ∞ ~ 10 Lbol ; Lx ~ 10-7 Lbol● TMS ~ few 10 Myr
  4. 4. 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
  5. 5. Importance of massive star winds Meynet & Maeder Townsley et al.
  6. 6. Mechanisms for x-ray emission Magnetically channeled winds Colliding winds Okazaki et al. Gagne et al. (model of Asif ud-Doula)
  7. 7. Mechanisms for x-ray emissionIntrinsic wind structure(embedded wind shocks) Feldmeier et al.
  8. 8. Mass loss rates of O stars Fullerton et al. (2006)
  9. 9. Chandra and XMM
  10. 10. Soft x-ray spectra of ζ Puppis
  11. 11. Comparison with Capella
  12. 12. Comparison with Capella
  13. 13. Line shape is diagnostic of optical depth
  14. 14. Profile formation Approximate wind as two component fluid Lλ =4 π ∫ dV ηλ e −τ ∞τ( p , z)=∫ κ(λ )ρ(r ) dz z
  15. 15. Profile formation ∞ M˙τ( p , z)=∫ κ(λ )ρ(r ) dz ρ= 2 z 4 π r v (r) κM ˙τ( p , z)=τ* t ( p , z ) τ*= 4 π v∞ R *
  16. 16. Model x-ray profiles
  17. 17. Example: Fe XVII 15.014 Å
  18. 18. He-like triplet diagnostics A ~ Z10
  19. 19. He-like triplet diagnostics
  20. 20. He-like triplet ratio and line profile No additional free parameters!
  21. 21. Fit all lines to constrain mass loss
  22. 22. Fit all lines to constrain mass loss κM ˙ τ*= 4 π v∞ R *
  23. 23. An unexpected problem
  24. 24. An unexpected problem
  25. 25. Sobolev theory: radiative transfer in a supersonic, accelerating wind ( ) −1 dv z L sob=v th dz τ sob=χ L sob χ v th χ v thτ0= τ1= v /r dv /dr
  26. 26. Sobolev theoryVelocity law Anisotropy factor r dv σ= −1 v dr
  27. 27. Angular distribution of emission
  28. 28. Effect of resonance scattering
  29. 29. Resonance scattering fits the data
  30. 30. Resonance scattering fits the data
  31. 31. Resonance scattering fits the data
  32. 32. Resonance scattering fits the data
  33. 33. Plausibility of resonance scattering
  34. 34. 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
  35. 35. 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!)
  36. 36. Fe XVII line ratio problem τ Sco
  37. 37. Fe XVII line ratio problem ς Ori
  38. 38. Fe XVII line ratio problem ς Pup
  39. 39. Inner shell absorption in Fe

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