Fitting Equivalent Widths

Define the equivalent width (eqw) fit-function with the number of components you need to calculate the eqw of:

 eqwFit_init(1);

Set the model with the underlying continuum given as first parameter to the eqwFit fit-function and the components as further parameters, e.g.:

fit_fun("eqwFit(1, powerlaw, egauss)*tbnew_simple");

This will renormalize the egauss to match the corresponding eqw-parameter (see below) based on an unabsorbed power-law continuum, which is absorbed afterwards. Then, you should set appropriate parameter ranges for the eqw-parameter, e.g. allow only negative values in case of an absorption feature:

set_par("eqwFit(1).width1"; min = -1000, max = 0);

If you want to calculate the eqw of two components, you first need to initialize the eqw fit-function in a new (!) Isis-shell:

  eqwFit_init(2);
  fit_fun("eqwFit(1, powerla, egauss(1), egauss(2))*tbnew_simple");