The bound-bound and free-free radiative losses for the nonthermal distributions in solar and stellar coronae

Abstract

Context. The radiative-loss 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 bound-bound transitions and bremsstrahlung for nonthermal κ-and n-distributions. Methods. The bound-bound 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 free-free Gaunt factor. Results. We find that the changes in radiative-loss functions due to nonthermal distributions are several times greater than the errors due to the missing contribution of the free-bound continuum or errors in atomic data. For κ-distributions, the radiative-loss 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 n-distributions, for which the radiative-loss functions have higher and narrower peaks. Local minima and maxima of the radiative-loss 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 X-ray loops are stable against the radiatively-driven thermal instability.

INVESTIGATING THE DIFFERENTIAL EMISSION MEASURE AND ENERGETICS OF MICROFLARES WITH COMBINEDSDO/AIA ANDRHESSIOBSERVATIONS

“…In this equation, DEM(T ) is the amount of emission multiplied by event area A and hence in units of cm −3 K −1 , and Λ(T ) represents the radiative loss function, which has been investigated by many authors (e.g., Rosner et al 1978;Mewe & Gronenschild 1981;Cook et al 1989;Martens et al 2000;Klimchuk et al 2008;Dudík et al 2011). …”

H TO Zn IONIZATION EQUILIBRIUM FOR THE NON-MAXWELLIAN ELECTRON κ-DISTRIBUTIONS: UPDATED CALCULATIONS

“…The Fe xii and Fe xiii ions are shifted to higher T (up to 0.1-0.15 dex). We note that the changes in the ionization equilibria due to the updated atomic data will reflect on, e.g., changes in the total radiative losses (Dudík et al 2011) and will also modify the proposed diagnostic methods for κ-distributions (Dzifčáková & Kulinová 2010;Mackovjak et al 2013).…”

“…In this paper, we present up-to-date calculations of the ionization and recombination rates (Section 3) and ionization equilibria (Section 4) for κ-distributions for elements from H to Zn. Such calculations are necessary for diagnostics of the κ-distributions in both the solar transition region and the corona as well as subsequent calculations of the radiative losses (Dudík et al 2011) or responses of various extreme ultraviolet or X-ray filters (Dudík et al 2009) used both to model and observe these portions of the solar atmosphere with potential applications to other astrophysical environments.…”

Nonequilibrium Processes in the Solar Corona, Transition Region, Flares, and Solar Wind (Invited Review)

“…The synthesis of the Fe, Ca and Si helium-like line spectra during flares were performed for n-distributions by Dzifčáková (2006) and Kulinová et al (2011). The influence on the total radiative losses and continua was subsequently studied by Dudík et al (2011Dudík et al ( , 2012. proposed the use of changes in the ionization and excitation equilibria with n-distributions for diagnostics from the flare X-ray line spectra observed at 5-6Å by the RESIK spectrometer.…”