Atomic physics of shocked plasma in winds of massive stars
Abstract
High resolution diffraction grating spectra of X-ray emission from massive stars obtained with Chandra and XMM-Newton have revolutionized our understanding of their powerful, radiation-driven winds. Emission line shapes and line ratios provide diagnostics on a number of key wind parameters. Modeling of resolved emission line velocity profiles allows us to derive independent constraints on stellar mass-loss rates, leading to downward revisions of a factor of a few from previous measurements. Line ratios in He-like ions strongly constrain the spatial distribution of Xray emitting plasma, confirming the expectations of radiation hydrodynamic simulations that X-ray emission begins moderately close to the stellar surface and extends throughout the wind. Some outstanding questions remain, including the possibility of large optical depths in resonance lines, which is hinted at by differences in line shapes of resonance and intercombination lines from the same ion. Resonance scattering leads to nontrivial radiative transfer effects, and modeling it allows us to place constraints on shock size, density, and velocity structure.
- Publication:
-
The 17th International Conference on Atomic Processes in Plasmas (ICAPIP)
- Pub Date:
- May 2012
- DOI:
- 10.1063/1.4707864
- Bibcode:
- 2012AIPC.1438..111L
- Keywords:
-
- astrophysical plasma;
- plasma diagnostics;
- radiative transfer;
- stellar radiation;
- stellar spectra;
- stellar winds;
- X-ray emission spectra;
- X-ray sources (astronomical);
- 52.25.Os;
- 52.70.La;
- 95.30.Qd;
- 97.10.Me;
- 97.10.Ri;
- Emission absorption and scattering of electromagnetic radiation;
- X-ray and gamma-ray measurements;
- Magnetohydrodynamics and plasmas;
- Mass loss and stellar winds;
- Luminosities;
- magnitudes;
- effective temperatures colors and spectral classification