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 5
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) [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.