In addition to the program written in ANSI C an IDL version is delivered.
This version is the predecessor of the presented program and is still the preferred
working version by the developers. Using the IDL version allows the user to
interactively process the fit results (as IDL is the Interactive Data
Language). Also, the graphic is more flexible in IDL than in pgplot and better
plots can be obtained without much trouble using IDL.
The IDL package contains the main program fit_main.pro, a file containing
all functions and routines fit_procs.pro, an include file fit.inc
that defines COMMON blocks and style settings, and a short script do.pro
customizing the application.
Before using the IDL routines, the include must be 'sourced' and the routines must be compiled:
IDL> @fit.inc IDL> .compile fit_procs IDL> .compile fit_main
For the case that the spectrum was prepared in IDL it can be written into a file with the correct format using the procedure writefile:
IDL> writefile,wave,sp,err,bkgd,bkgderr,fname,exp=exp,eff=eff,/unixwhere wave contains the wavelength vector, sp the spectrum, err the errors of the spectrum, bkgd the instrumental background, and bkgderr the errors of the background. All these vectors must have identical dimensions. In addition, the exposure time can be given (exp) and the effective areas (eff). The name of the resulting file, e.g., spectrum.dat, is indicated with the variable fname. If no full IDL version is available the keyword /unix can be used to still write the ASCII with the demo version of IDL. This takes longer than without the keyword.
A parameter file must be provided; it can be created with the GUI (cf.
Sec. 5.2.1) or the command-line program cora_inp
(Sect. 5.1.3). It follows the same format as the parameter file used by
the C program. The parameter file can be edited by hand or one can run the GUI
in parallel to the IDL session and use it just for editing the parameter file.
After compilation the program is started with
IDL> fit_main,[dtime=exposure time,]'spectrum.dat','fit.inp'[,psfile=psfile] .Terms in [..] can be omitted, the default names 'spectrum.dat', 'fit.inp' can be replaced by any name corresponding to correct and existing names of the spectrum and the parameter file.
The last two parameters, listed in the last line of the parameter file, can be
used to make IDL plot a graph of the likelihood curve in dependence of the
iterated variables. This is useful in order to get an impression of the shape
of each likelihood curve and thus the degree of the minimization problem. The
parameter nlik represents the number of points calculated for such a
graph, and with the second parameter, ispline, Spline interpolation
can be activated () or deactivated (). This function is
also carried out by the C-program for the first line, but is not supported
by the GUI.
Format parameters controlling line styles, character size etc. can be set in
fit.inc. Default values are given in the file fit.inc delivered
with the program, but can be ignored. If no specification is given, the
defaults are still used.
Fit results and other variables and vectors used by the program are stored in
COMMON blocks, listed in fit.inc, so after calling the fit routine, the
variables can be used for further processing. This feature was, e.g., used
by Ness, J.U., Mewe, R., Schmitt, J.H.M.M. et al. 2001 (A&A, 367, 282) to
disentangle first and third order of their Chandra LETGS spectrum of Capella.
The third dispersion order lines were modeled in their first order, and these
lines were then added to the instrumental background at the position of their
third order on the detector plate. This new spectrum with the manipulated
background spectrum was then used for the analysis of the remaining first order
lines, recognizing the third order lines as part of the instrumental
A short example session is delivered with the program do.pro, where compiling and executing is done. Note that closing the plot device is necessary after running the program. This is left to the user for the case that the user wants to add plotting elements not provided by the program like labels before closing the device. The program is called with