He-like Ions as Practical Astrophysical Plasma Diagnostics: From Stellar Coronae to Active Galactic Nuclei
Abstract
We review X-ray plasma diagnostics based on the line ratios of He-like ions. Triplet/singlet line intensities can be used to determine electronic temperature and density, and were first developed for the study of the solar corona. Since the launches of the X-ray satellites Chandra and XMM-Newton, these diagnostics have been extended and used (from C v to Si xiii) for a wide variety of astrophysical plasmas such as stellar coronae, supernova remnants, solar system objects, active galactic nuclei, and X-ray binaries. Moreover, the intensities of He-like ions can be used to determine the ionization process(es) at work, as well as the distance between the X-ray plasma and the UV emission source for example in hot stars. In the near future thanks to the next generation of X-ray satellites (e.g., Astro-H and IXO), higher-Z He-like lines (e.g., iron) will be resolved, allowing plasmas with higher temperatures and densities to be probed. Moreover, the so-called satellite lines that are formed closed to parent He-like lines, will provide additional valuable diagnostics to determine electronic temperature, ionic fraction, departure from ionization equilibrium and/or from Maxwellian electron distribution.
- Publication:
-
Space Science Reviews
- Pub Date:
- December 2010
- DOI:
- 10.1007/s11214-010-9731-2
- arXiv:
- arXiv:1101.3184
- Bibcode:
- 2010SSRv..157..103P
- Keywords:
-
- Plasma diagnostics;
- Atomic processes;
- Line: formation;
- Radiation mechanisms: thermal;
- X-rays: general;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 36 pages, 16 figures. Invited Review talk at the "High-resolution X-ray spectroscopy: past, present, and future" conference, Utrecht, March 15-17 2010. Accepted for publication in Space Science Reviews (2010)