The boundbound and freefree radiative losses for the nonthermal distributions in solar and stellar coronae
Abstract
Context. The radiativeloss function is an important ingredient in the physics of the solar corona, transition region, and flares.
Aims: We investigate the radiative losses due to the boundbound transitions and bremsstrahlung for nonthermal κ and ndistributions.
Methods: The boundbound radiative losses are computed by integrating synthetic spectra. An analytical expression is derived for nonthermal bremsstrahlung. The bremsstrahlung is computed numerically using accurate values of the freefree Gaunt factor.
Results: We find that the changes in radiativeloss functions due to nonthermal distributions are several times greater than the errors due to the missing contribution of the freebound continuum or errors in atomic data. For κdistributions, the radiativeloss functions are in general weaker than for Maxwellian distribution, with a few exceptions caused by the behavior of Fe. The peaks of the radiativeloss functions are in general flatter. The situation is opposite for ndistributions, for which the radiativeloss functions have higher and narrower peaks. Local minima and maxima of the radiativeloss functions may also be shifted. The contribution from bremsstrahlung only changes by a few percent except in the extreme nonthermal case of κ = 2. Stability analysis reveals that the Xray loops are stable against the radiativelydriven thermal instability.
The calculated radiative losses for nonthermal distributions are available as two electronic tables at the CDS via anonymous ftp to cdsarc.ustrasbg.fr (130.79.128.5) or via http://cdsarc.ustrasbg.fr/vizbin/qcat?J/A+A/529/A103
 Publication:

Astronomy and Astrophysics
 Pub Date:
 May 2011
 DOI:
 10.1051/00046361/201016329
 Bibcode:
 2011A&A...529A.103D
 Keywords:

 atomic processes;
 radiation mechanisms: nonthermal;
 Sun: corona;
 Sun: Xrays;
 gamma rays;
 instabilities