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

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. 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. 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. 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. Importance of massive star winds
Meynet & Maeder
Townsley et al.

6. Mechanisms for x-ray emission
Magnetically channeled winds
Colliding winds
Okazaki et al.
Gagne et al. (model of Asif ud-Doula)

7. Mechanisms for x-ray emission
Intrinsic wind structure
(embedded wind shocks)
Feldmeier et al.

8. Mass loss rates of O stars
Fullerton et al. (2006)

9. Chandra and XMM

10. Soft x-ray spectra of ζ Puppis

11. Comparison with Capella

12. Comparison with Capella

13. Line shape is diagnostic of optical
depth

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. 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. Model x-ray profiles

17. Example: Fe XVII 15.014 Å

18. He-like triplet diagnostics
A ~ Z10

19. He-like triplet diagnostics

20. He-like triplet ratio and line profile
No additional free parameters!

21. Fit all lines to constrain mass loss

22. Fit all lines to constrain mass loss
κM ˙
τ*=
4 π v∞ R *

23. An unexpected problem

24. An unexpected problem

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 th
τ0= τ1=
v /r dv /dr

26. Sobolev theory
Velocity law Anisotropy factor
r dv
σ= −1
v dr

27. Angular distribution of emission

28. Effect of resonance scattering

29. Resonance scattering fits the data

30. Resonance scattering fits the data

31. Resonance scattering fits the data

32. Resonance scattering fits the data

33. Plausibility of resonance scattering

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. 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. Fe XVII line ratio problem
τ Sco

37. Fe XVII line ratio problem
ς Ori

38. Fe XVII line ratio problem
ς Pup

39. Inner shell absorption in Fe