SPEX User's Manual - SRON

3.4 Cf: isobaric cooling flow differential emission measure model 51
3.4 Cf: isobaric cooling flow differential emission measure model
This model calculates the spectrum of a standard isobaric cooling flow. The differential emission measure
distribution dY (T)/dT for the isobaric cooling flow model can be written as
D(T) ≡ dY (T)/dT =
5Ṁk
2µm H Λ(T),
(3.4)
where Ṁ is the mass deposition rate, k is Boltzmann’s constant, µ the mean molecular weight (0.618
for a plasma with 0.5 times solar abundances), m H is the mass of a hydrogen atom, and Λ(T) is the
cooling function. We have calculated the cooling function Λ using our own SPEX code for a grid of
temperatures and for 0.5 times solar abundances. The spectrum is evaluated by integrating the above
differential emission measure distribution between a lower temperature boundary T 1 and a high temperature
boundary T n . We do this by creating a temperature grid with n bins and calculating the spectrum
for each temperature.
Warning: Take care that n is not too small in case the relevant temperature is large; on the other hand
if n is large, the computational time increases. Usually a spacing with temperature differences between
adjacent bins of 0.1 (in log) is sufficient and optimal.
Warning: The physical relevance of this model is a matter of debate
The parameters of the model are:
norm - The mass deposition rate Ṁ in M ⊙ yr −1
t1 - Lower temperature cut-off temperature T 1 . Default: 0.1 keV.
tn - Upper temperature cut-off temperature T n . Default: 1 keV.
nr - Number of temperature bins n used in the integration. Default value: 16
p - Slope p = 1/α. Default: 0.25 (α = 4).
cut - Lower temperature cut-off, in units of T max . Default value: 0.1.
The following parameters are the same as for the cie-model:
ed - Electron density in 10 20 m −3
it - Ion temperature in keV
vmic - Micro turbulent velocity in km/s
ref - Reference element
01. . .30 - Abundances of H to Zn
file - Filename for the nonthermal electron distribution
3.5 Cie: collisional ionisation equilibrium model
This model calculates the spectrum of a plasma in collisional ionisation equilibrium (CIE). It consists
essentially of two steps, first a calculation of the ionisation balance and then the calculation of the X-ray
spectrum. The basis for this model is formed by the mekal model, but several updates have been included.
3.5.1 Temperatures
Some remarks should be made about the temperatures. SPEX knows three temperatures that are used
for this model.
First there is the electron temperature T e . This is usually referrred to as ”the” temperature of the plasma.
It determines the continuum shape and line emissivities and the resulting spectrum is most sensitive to
this.
Secondly, there is the ion temperature T i . This is only important for determining the line broadening,
since this depends upon the thermal velocity of the ions (which is determined both by T i and the atomic
mass of the ion). Only in high resolution spectra the effects of the ion temperature can be seen.