Last modified: December 2023

AHELP for CIAO 4.16 Sherpa


Context: models


The XSPEC vgnei model: collisional plasma, non-equilibrium, temperature evolution.



The xsvgnei model is an additive model component.


The model is described at [1] . The set_xsxset and get_xsxset functions are used to set and query the XSPEC XSET parameters, in particular the keyword "NEIVERS".

Deprecated in Sherpa 4.10.0

The kt_ave parameter has been renamed meankt to match the XSPEC definition. The name kt_ave can still be used to access the parameter, but this name will be removed in a future release.


>>> create_model_component("xsvgnei", "mdl")
>>> print(mdl)

Create a component of the xsvgnei model and display its default parameters. The output is:

   Param        Type          Value          Min          Max      Units
   -----        ----          -----          ---          ---      -----
   mdl.kT       thawed            1       0.0808         79.9        keV
   mdl.H        frozen            1            0            1           
   mdl.He       frozen            1            0        10000           
   mdl.C        frozen            1            0        10000           
   mdl.N        frozen            1            0        10000           
   mdl.O        frozen            1            0        10000           
   mdl.Ne       frozen            1            0        10000           
   mdl.Mg       frozen            1            0        10000           
   mdl.Si       frozen            1            0        10000           
   mdl.S        frozen            1            0        10000           
   mdl.Ar       frozen            1            0        10000           
   mdl.Ca       frozen            1            0        10000           
   mdl.Fe       frozen            1            0        10000           
   mdl.Ni       frozen            1            0        10000           
   mdl.Tau      thawed        1e+11        1e+08        5e+13     s/cm^3
   mdl.meankT   thawed            1       0.0808         79.9        keV
   mdl.redshift frozen            0       -0.999           10           
   mdl.norm     thawed            1            0        1e+24           


The attributes for this object are:

Attribute Definition
kT The temperature of the plasma, in keV.
H The H abundance: it should be set to 0 to switch on and 1 to switch off the free-free continuum.
He, C, N, O, Ne, Mg, Si, S, Ar, Ca, Fe, Ni The abundance of the element, with respect to Solar.
Tau The ionization timescale in units of s/cm^3.
meankT The ionization timescale averaged plasma temperature in keV.
redshift The redshift of the plasma.
norm The normalization of the model: see [1] for an explanation of the units.


XSPEC version

CIAO 4.16 comes with support for version 12.13.1e of the XSPEC models. This can be checked with the following:

% python -c 'from sherpa.astro import xspec;


See the bugs pages on the Sherpa website for an up-to-date listing of known bugs.

See Also

xsgnei, xsvvgnei