4.1.11. Dem: differential emission measure model

This model calculates a set of isothermal CIE spectra, that can be used later in one of the DEM analysis tools (see the “dem” commands of the syntax). The CIE spectra are evaluated for a logarithmic grid of temperatures between T_1 and T_2, with n bins.


For the DEM methods to work, the dem model is the only allowed additive component that can be present. No other additive components are allowed. But of course the spectrum of the dem model may be modified by applying any combination of multiplicative models (redshifts, absorptions, line broadening, etc.).


Because of the above, do not use the fit commands when you have a dem model. If you really need to fit, use the pdem model (Pdem: DEM models) instead.


In general, the spacing between the different temperature components should not be smaller than 0.10 in \log T. Smaller step sizes will produce unstable solutions.

The parameters of the model are:

t1 : Lower temperature T_1 in keV. Default value: 0.001 keV.
t2 : Upper temperature T_2 in keV. Default value: 100 keV.
nr : Number of temperature bins. Default value: 64.
The following parameters are the same as for the cie-model:
hden : Hydrogen density in 10^{20} \mathrm{m}^{-3}.
it : Ion temperature in keV.
vrms : RMS Velocity broadening in km/s (see Definition of the micro-turbulent velocity in SPEX).
ref : Reference element.
01...30 : Abundances of H to Zn.
file : Filename for the non-thermal electron distribution.

Recommended citation: Mewe et al. (1995)