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