APEC: collisional ionisation equilibrium model (External)¶
This model calculates the spectrum of a plasma in collisional ionisation equilibrium (CIE), based on the APEC table model from ATOMDB. Despite of the similarity between this model and the XSPEC implementation, the underlying algorithm to interpolate the APEC table model is unlikely to be identical. This design allows direct comparison between SPEX CIE and XSPEC APEC implementations, providing insight into the systematic uncertainties introduced by interpolation.
The SPEX evaluation of APEC may differ slightly from the XSPEC implementation due to differences in the interpolation algorithms. In addition, the normalization follows the SPEX convention. This means that a SPEX-APEC model, at its default distance and with a normalization of \(4\pi\), corresponds to an XSPEC-APEC model evaluated at zero redshift.
Note
The current apec model cannot be used to read the APEC-NEI fits table.
Install¶
Before the APEC model in SPEX can be used, ATOMDB should be installed on your machine. If you do not have an ATOMDB installation yet, please download ATOMDB here.
Before loading SPEX, please make sure to set the APECROOT environment
variable to the location of your ATOMDB installation, more specifically
the path to the apec_coco.fits and apec_line.fits files. For example:
export APECROOT=/home/user/atomdb/atomdb_v3.1.2
or in C-type shells:
setenv APECROOT /home/user/atomdb/atomdb_v3.1.2
When the variable is set correctly, SPEX can find the table models automatically.
Abundances¶
The SPEX implemenatation of APEC does use the SPEX abundance setting. Please take care to set the abundance to a similar set if you want to compare APEC with the original XSPEC implementation.
Parameter description¶
The parameters of the model are:
norm : the normalisation, which is the emission measure
\(Y \equiv n_{\mathrm H} n_{\mathrm e} V\) in units of
\(10^{64}\) \(\mathrm{m}^{-3}\), where
\(n_{\mathrm e}\) and \(n_{\mathrm H}\) are the electron and
Hydrogen densities and \(V\) the volume of the source.
At the default SPEX distance and with a normalization of \(4\pi\),
this model corresponds to an XSPEC-APEC model evaluated at zero redshift.
Default value: 1.t : the electron temperature \(T_{\mathrm e}\) in keV. Default
value: 1.vrms : RMS Velocity broadening in km/s (see Definition of the micro-turbulent velocity in SPEX)01 : Abundance of hydrogen (H, Z=1) in Solar units. Default 1.02 : Abundance of helium (He, Z=2) in Solar units. Default 1.30 : Abundance of zinc (Zn, Z=30) in Solar units.
Default 1.vrms : RMS Velocity broadening in km/s (see Definition of the micro-turbulent velocity in SPEX)Recommended citation: Smith et al. (2001) and Foster et al. (2012)