
1.0  the version from xspec v11.1 
1.1  as 1.0 but with updated ionization fractions using dielectronic recombination rates from Mazzotta et al (1998) 
2.0  same ionization fractions as 1.1 but uses AtomDB v2 to calculate the resulting spectrum 
3.x  ionization fractions and spectrum calculation uses AtomDB v3.x 
Note that versions 1.x have no emission from Ar. For versions 3.x and later additional xset options are available and are listed under the documentation for nei.
For the equil model the parameters are:
par1  plasma temperature (keV) 
par2  Metal abundances (He fixed at that defined by the abund command). The elements included are C, N, O, Ne, Mg, Si, S, Ar, Ca, Fe, Ni. Abundances are defined by the abund command 
par3  redshift 
norm  , where is the angular diameter distance to the source (cm), is the volume element (cm), and and are the electron and H densities (cm), respectively 
For the vequil model, the parameters are:
par1  plasma temperature (keV) 
par2–par13  Abundances for He, C, N, O, Ne, Mg, Si, S, Ar, Ca, Fe, Ni wrt Solar (defined by the abund command) 
par14  Redshift, z 
norm  , where is the angular diameter distance to the source (cm), is the volume element (cm), and and are the electron and H densities (cm), respectively 
For the bequil model the parameters are:
par1  plasma temperature (keV) 
par2  Metal abundances (He fixed at that defined by the abund command). The elements included are C, N, O, Ne, Mg, Si, S, Ar, Ca, Fe, Ni. Abundances are defined by the abund command 
par3  redshift 
par4  gaussian velocity broadening (sigma in km/s) 
norm  , where is the angular diameter distance to the source (cm), is the volume element (cm), and and are the electron and H densities (cm), respectively 
For the bvequil model, the parameters are:
par1  plasma temperature (keV) 
par2–par13  Abundances for He, C, N, O, Ne, Mg, Si, S, Ar, Ca, Fe, Ni wrt Solar (defined by the abund command) 
par14  Redshift, z 
par15  gaussian velocity broadening (sigma in km/s) 
norm  , where is the angular diameter distance to the source (cm), is the volume element (cm), and and are the electron and H densities (cm), respectively 
The references for this model are as follows:
Borkowski, Lyerly & Reynolds (2001)
Hamilton, Sarazin & Chevalier (1983)
Borkowski, Sarazin & Blondin (1994)
Liedahl, Osterheld & Goldstein (1995)
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