Dear colleagues please find at the following link the preprint of a work accepted for publication in Astronomy & Astrophysics, showing the importance of updating the radiative losses on loop modeling, in particular on the very late phases of pulse-heated loop evolution:
http://arxiv.org/abs/1205.4553
This work may help to understand, for instance, why we see much fewer warm loops in active regions, than expected from a model of loop cooling from a hotter status. Special thanks to Peter Cargill for useful suggestions on the analytic part. Please contact me if you wish to have a 2-column version of the preprint. The abstract is below.
Best regards Fabio Reale
The role of radiative losses in the late evolution of pulse-heated coronal loops/strands F. Reale, E. Landi
Abstract: Radiative losses from optically thin plasma are an important ingredient for modeling plasma confined in the solar corona. Spectral models are continuously updated to include the emission from more spectral lines, with significant effects on radiative losses, especially around 1 MK. We investigate the effect of changing the radiative losses temperature dependence due to upgrading of spectral codes on predictions obtained from modeling plasma confined in the solar corona. The hydrodynamic simulation of a pulse-heated loop strand is revisited comparing results using an old and a recent radiative losses function. We find significant changes in the plasma evolution during the late phases of plasma cooling: when the recent radiative loss curve is used, the plasma cooling rate increases significantly when temperatures reach 1-2 MK. Such more rapid cooling occurs when the plasma density is larger than a threshold value, and therefore in impulsive heating models that cause the loop plasma to become overdense. The fast cooling has the effect of steepening the slope of the emission measure distribution of coronal plasmas with temperature at temperatures lower than ~2 MK. The effects of changes in the radiative losses curves can be important for modeling the late phases of the evolution of pulse-heated coronal loops, and, more in general, of thermally unstable optically thin plasmas.
loops@solar.physics.montana.edu