nei, vnei, vvnei: collisional plasma, non-equilibrium, constant temperature

Non-equilibrium ionization collisional plasma model. This assumes a
constant temperature and single ionization parameter. It provides a
characterization of the spectrum but is not a physical model. The
references for this model can be found under the description of the
equil model. 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 vnei variant allows the user to set the
abundances for the more common elements. 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 Fesets trace element abundances to that of iron while

XSPEC12> xset APEC_TRACE_ABUND 1.0sets them to Solar. The default value for APEC_TRACE_ABUND is 1.0. Full control over all the elemental abundances is available in the vvnei model.

For the nei 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 | Ionization timescale in units of s/cm. |

par4 | 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 vnei model, the parameters are:

par1 | plasma temperature (keV) |

par2 | H abundance (set to 0 for no free-free continuum, otherwise 1) |

par3-par14 | Abundances for He, C, N, O, Ne, Mg, Si, S, Ar, Ca, Fe, Ni wrt Solar (defined by the abund command) |

par15 | Ionization timescale in units of s/cm. |

par16 | Redshift, z |

norm | , where is the angular diameter distance to the source (cm), is the electron density (cm), and is the hydrogen density (cm). |

Finally, for the vvnei model, the parameters are:

par1 | plasma temperature (keV) |

par2 | H abundance (set to 0 for no free-free continuum, otherwise 1) |

par3-par31 | Abundances for all elements with 2 Z 30 wrt Solar (defined by the abund command) |

par32 | Ionization timescale in units of s/cm. |

par33 | Redshift, z |

norm | , where is the angular diameter distance to the source (cm), is the electron density (cm), and is the hydrogen density (cm). |