In this section we run through a couple of fictitious interactive XSTAR sessions to illustrate how to use XSTAR's interface. First of all, it is important that the environment variables are set in a manner similar to that required by FTOOLS. This is described in more detail in Chapter 14. Once XSTAR is installed and configured, at the unix prompt, type:
By invoking XSTAR with this simple command, you will be prompted for a series of physical and control parameters for the simulation.
The input parameters are: The model covering fraction, temperature, pressure or density, spectrum shape and ionizing luminosity, column density, ionization parameter, and element abundances relative to their cosmic abundances. Definitions for these and the units assumed are described in detail in chapter 4. All input parameters have default values, selected by pressing return at the prompt, thus it is possible to simply start XSTAR as above to invoke the default model.
Input of these parameters is handled through an IRAF-style interface, XPI, developed for the FTOOLS suite of programs. This has several features which may prove convenient to the user: (i) Parameter values from an invocation of XSTAR are stored and available as default values for the next XSTAR run. These are shown in square brackets when the user is prompted for values. (ii) Default values of input parameters are stored in the file xstar.par which is stored in the directory specified by the PFILES environment variable. (iii) Each parameter has an allowed range of values, shown in parentheses during the prompting. Input values outside of this range will result in exiting the program. (iv) Input parameters can be hidden from the prompting process. Such parameters, in the default xstar.par, are those which are expected to be unneeded for simple problems. Manipulation of these parameters requires a slightly more advanced familiarity with the code. (v) Parameter values can be input from the command line rather than by prompting. The value of this scripting capability will be seen in Chapter 7 which discusses building table models for the XSPEC spectral analysis program. All these features are described in more detail in the documentation for FTOOLS
It is also possible to run a model at a fixed temperature, i.e. to disable the thermal equilibrium condition. In order to do this the ordinarily hidden parameter niter must be set to 0, and then the temperature parameter must be set to the desired value (in units of 10 K).
In the sections that follow are a few XSTAR sessions to illustrate using the program. We illustrate both the prompted and the command line invocation of XSTAR with only the required parameters specified.