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##

equil, vequil: collisional plasma, ionization equilibrium

Ionization equilibrium collisional plasma model. This is the
equilibrium version of Kazik Borkowski's NEI models. Several versions
are available. To switch between them use the xset **neivers**
command. The versions available are:

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 |

3.0 |
ionization fractions and spectrum calculation uses AtomDB v3 |

Note that versions 1.x have no emission from Ar. The default is
version 3.0. The vequil variant allows the user to set the
abundances for the model. For versions 3 and above the abundances of
the trace elements (ie Li, Be, B, F, Na, P, Cl, K, Sc, Ti, V, Cr, Mn,
Co, Cu, Zn) can be set using xset **APEC_TRACE_ABUND**. These
trace element abundances can be set either to the abundance of one of
the main elements or to a numerical value (relative to Solar). For
instance,

XSPEC12> xset APEC_TRACE_ABUND Fe

sets trace element abundances to that of iron while
XSPEC12> xset APEC_TRACE_ABUND 1.0

sets them to Solar. The default value for APEC_TRACE_ABUND is 1.0.
For the equil model the parameters are:

par1 |
plasma temperature (keV) |

par2 |
Metal abundances (He fixed at cosmic). 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
electron density (cm), and is the hydrogen density
(cm). |

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
electron density (cm), and is the hydrogen density
(cm). |

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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