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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$^{28}$ erg s$^{-1}$. The ionization parameter at the inner edge of the cloud is log($\xi $)=5. The ionizing spectrum is a power law with energy index -1.

This input can be used to plot the T vs. $\xi $ 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 $\xi $. 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 $\sqrt{Ln}$ where $L$ is the input luminosity and $n$ 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 $\xi $ 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) [0] 
pressure (dyne/cm**2) (0.:1.) [0.03] 
density (cm**-3) (0.:1.e18) [1.e+4] 
spectrum type?[pow] 
radiation temperature or alpha?[-1.] 
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.) [1] 
nitrogen abundance (0.:100.) [1] 
oxygen abundance (0.:100.) [1] 
fluorine abundance (0.:100.) [1.0] 
neon abundance (0.:100.) [1] 
sodium abundance (0.:100.) [1.0] 
magnesium abundance (0.:100.) [1] 
aluminum abundance (0.:100.) [1.0] 
silicon abundance (0.:100.) [1] 
phosphorus abundance (0.:100.) [1.0] 
sulfur abundance (0.:100.) [1] 
chlorine abundance (0.:100.) [1.0] 
argon abundance (0.:100.) [1] 
potassium abundance (0.:100.) [1.0] 
calcium abundance (0.:100.) [1] 
scandium abundance (0.:100.) [1.0] 
titanium abundance (0.:100.) [1.0] 
vanadium abundance (0.:100.) [1] 
chromium abundance (0.:100.) [1.0] 
manganese abundance (0.:100.) [1.0] 
iron abundance (0.:100.) [1] 
cobalt abundance (0.:100.) [1.0] 
nickel abundance (0.:100.) [1] 
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' 
trad=-1. rlrad38=1.E-16  column=1.E+16   rlogxi=5.  lcpres=0 habund=1 heabund=1 
 liabund=0. beabund=0. babund=0. cabund=1. nabund=1 oabund=1 fabund=1 neabund=1 
naabund=1 mgabund=1 alabund=1 siabund=1 pabund=1 sabund=1 clabund=1 arabund=1 
kabund=1 caabund=1 scabund=1 tiabund=1 vabund=1 crabund=1 mnabund=1 feabund=1 
coabund=1 niabund=1 cuabund=1 znabund=1 modelname='filled sphere' niter=0  npass=1 
critf=1.E-07 nsteps=6 xeemin=0.04 emult=0.5 taumax=5. lprint=1  ncn2=999 
radexp=0 vturb=1.

next up previous contents
Next: xstar Model: H II Up: A Walkthrough of XSTAR Previous: A Walkthrough of XSTAR   Contents
Tim Kallman 2018-12-14