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apec, vapec, vvapec: APEC emission spectrum

An emission spectrum from collisionally-ionized diffuse gas calculated from the AtomDB atomic database. More information can be found at http://atomdb.org/ which should be consulted by anyone running this model. This default version number can be changed by modifying the ATOMDB_VERSION string in your Xspec.init file.

By default this model reads atomic physics continuum and line data from the files apec_v[version]_coco.fits and apec_v[version]_line.fits in the $HEADAS/../spectral/modelData directory. Different files can be specified by using the command xset APECROOT. There are several options. APECROOT can be set to a version number (eg 1.10, 1.2.0, 1.3.1, 2.0.1, 2.0.2, 3.0.2, 3.0.3). In this case the value of APECROOT will be used to replace the default version number in the name of the standard files and the resulting files will be assumed to be in the modelData directory. Alternatively, a filename root (eg apec_v1.2.0) can be given. This root will be used as a prefix for the _coco.fits and _line.fits files. Finally, if neither of these work then the model will assume that the APECROOT value gives the complete directory path, e.g.

XSPEC12> xset APECROOT /foo/bar/apec_v1.2.0

will use the input files

/foo/bar/apec_v1.2.0_coco.fits 
/foo/bar/apec_v1.2.0_line.fits.

Thermal broadening of lines can be included by using: xset APECTHERMAL yes. This runs significantly slower than the option without thermal broadening so you should only use this when necessary. Velocity broadening of lines can be included by using: xset APECVELOCITY <velocity>, where <velocity> is sigma in km/s. This is added in Gaussian quadrature with any thermal broadening in use.

A continuum-only spectrum can be obtained by using xset APECNOLINES yes. This will turn off lines for all models using the apec files. To get a line-free version of a single apec model use nlapec.

The apec model uses abundances set by the abund command. The vapec and vvapec variants allow the user to set the abundance using additional parameters. For apec and vapec 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. Note that this means that the apec and vapec models will show emission lines even if the abundance parameters are set to zero.

For the apec model the parameters are:

par1 plasma temperature, keV
par2 Metal abundances (He fixed at cosmic). The elements included are C, N, O, Ne, Mg, Al, Si, S, Ar, Ca, Fe, Ni. Relative abundances are set by the abund command. The trace element abundances are from xset APEC_TRACE_ABUND, the default is 1.0.
par3 Redshift, z
norm ${10^{-14}\over{4\pi[D_A(1+z)]^2}}\int n_en_HdV$, where $D_A$ is the angular diameter distance to the source (cm), $n_e$ and $n_H$ are the electron and H densities (cm$^{-3}$), respectively

For the vapec variant the parameters are as follows.

par1 plasma temperature, keV
par2-par14 Abundances for He, C, N, O, Ne, Mg,Al, Si, S, Ar, Ca, Fe, Ni wrt Solar (defined by the abund command). The trace element abundances are from xset APEC_TRACE_ABUND, the default is 1.0.
par15 redshift, z
norm ${10^{-14}\over{4\pi[D_A(1+z)]^2}}\int n_en_HdV$, where $D_A$ is the angular diameter distance to the source (cm), $n_e$ and $n_H$ are the electron and H densities (cm$^{-3}$), respectively

For the vvapec variant the parameters are as follows.

par1 plasma temperature, keV
par2-par31 Abundances for H, He, Li, Be, B, C, N, O, F, Ne, Na, Mg, Al, Si, P, S, Cl, Ar, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn wrt Solar (defined by the abund command)
Par32 redshift, z
norm ${10^{-14}\over{4\pi[D_A(1+z)]^2}}\int n_en_HdV$, where $D_A$ is the angular diameter distance to the source (cm), $n_e$ and $n_H$ are the electron and H densities (cm$^{-3}$), respectively


next up previous contents
Next: atable: tabulated additive model Up: Additive Model Components Previous: agauss, zagauss: gaussian line