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XSTAR Model: Spherical cloud

In this example we model a spherical, constant density cloud with a source at its center. The cloud is optically thin. The source luminosity is 10 erg s . The ionization parameter at the inner edge of the cloud is log( )=5. The ionizing spectrum is a power law with energy index -1.

This input can be used to plot the T vs. equilibrium for an optically thin gas. This is because it spans a large range in radius while keeping the density fixed. So it therefore spans a large range in ionization parameter. The output can be plotted directly (see chapter on output) in order to get temperature or abundances vs . It can be run with your choice of input spectrum. In doing this, it is important that the gas be truly optically thin. The optical depth scales as where is the input luminosity and is the density; this can lead to somewhat unrealistic choices for these parameters. Plus, this procedure does not capture all the branches in a truly multi-valued T vs curve. A more flexible and robust way to do this, which avoids these shortcomings, is given in chapter 7 on xstar2xspec.

We show how this model can be run in two ways: first by invoking XSTAR with no parameter values and utilizing the prompting for parameter values from XPI, and second by entering parameter values directly on the command line. In the former case, the prompt strings are more descriptive than the parameter values themselves, but the net result is the same in both cases.

Using prompting:

unix > xstar
xstar version 2.2.0
covering fraction (0.:1.) [1.]
temperature (/10**4K) (0.:1.e4) [10000.]
constant pressure switch (1=yes, 0=no) (0:1) 
pressure (dyne/cm**2) (0.:1.) [0.03]
density (cm**-3) (0.:1.e18) [1.e+4]
spectrum type?[pow]
luminosity (/10**38 erg/s) (0.:1.e10) [1.e-6]
column density (cm**-2) (0.:1.e25) [1.E17]
log(ionization parameter) (erg cm/s) (-10.:+10.) [5.]
hydrogen abundance (0.:100.) [1.]
helium abundance (0.:100.) [1.]
carbon abundance (0.:100.) 
nitrogen abundance (0.:100.) 
oxygen abundance (0.:100.) 
fluorine abundance (0.:100.) [1.0]
neon abundance (0.:100.) 
sodium abundance (0.:100.) [1.0]
magnesium abundance (0.:100.) 
aluminum abundance (0.:100.) [1.0]
silicon abundance (0.:100.) 
phosphorus abundance (0.:100.) [1.0]
sulfur abundance (0.:100.) 
chlorine abundance (0.:100.) [1.0]
argon abundance (0.:100.) 
potassium abundance (0.:100.) [1.0]
calcium abundance (0.:100.) 
scandium abundance (0.:100.) [1.0]
titanium abundance (0.:100.) [1.0]
chromium abundance (0.:100.) [1.0]
manganese abundance (0.:100.) [1.0]
iron abundance (0.:100.) 
cobalt abundance (0.:100.) [1.0]
nickel abundance (0.:100.) 
copper abundance (0.:100.) [1.0]
zinc abundance (0.:100.) [1.0]
model name[filled sphere]


Using the command line:

xstar cfrac=1 temperature=1000. pressure=0.03 density=1.E+4 spectrum='pow'    