SPEX Reference manual (PDF) - SRON

2.31 Var: various settings for the plasma models 45
2.31 Var: various settings for the plasma models
2.31.1 Overview
For the plasma models, there are several quantities that have useful default values but can be adjusted
manually for specific purposes. We list them below.
Free-bound emission
Usually the freebound emission takes most of the computing time for the plasma models. This is because
it needs to be evaluated for all energies, ions and atomic sublevels that are relevant. In rder to reduce the
computational burden, there is a parameter gfbacc in SPEX that is approximately the accuracy level for
the free-bound calculation. The default value is 10 −3 . If this quantity is higher, less shells are taken into
account and the computation proceeds faster (but less accurate). The users are advised not to change
this parameter unless they are knowing what they do!
Line emission contributions
By default, all possible line emission processes are taken into account in the plasma models. For testing
purposes, it is possible to include or exclude specific contributions. These are listed below in Table 2.6.
Table 2.6: Possible line emission processes
Abbrevation Process
ex electron excitation
rr radiative recombination
dr dielectronic recombination
ds dielectronic recombination satellites
ii inner shell ionisation
Doppler broadening
By default, thermal Doppler broadening is taken into account. However, the user can put this off for
testing purposes.
Atomic data
The user can choose between the ”old” Mekal code (the current default) and updated calculations for
the ions for which this is possible.
Warning: The updated atomic database that can be used through the command ”var calc new” is still
being developed and incomplete. Using this database is therefore not yet recommended.
Mekal code
We have made several minor improvements to the original Mekal plasma model. These improvements
are included by default. However, it is possible to discard some of these improvements by going back to
the old code. The improvements are classified as follows (with the appropriate syntax word added here).
Wav: wavelength corrections according to the work of Phillips et al. 1999, based upon Solar flare spectra;
in addition, the 1s-np wavelengths of Ni XXVII and Ni XXVIII have been improved.
Fe17: The strongest Fe XVII lines are corrected in order to agree with the rates as calculated by Doron
& Behar (2002).