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 2 -3● ½Ṁv ∞ ~ 10 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 Magnetically channeled winds Colliding winds Okazaki et al. Gagne et al. (model of Asif ud-Doula)
Mechanisms for x-ray emissionIntrinsic wind structure(embedded wind shocks) Feldmeier et al.
Mass loss rates of O stars Fullerton et al. (2006)
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!)