eqwidth

sherpa.astro.utils.eqwidth(data, model, combo, lo=None, hi=None) → float[source] [edit on github]

Calculate the equilavent width of combo.

The equivalent width (EW) is calculated following George & Fabian (1991) as “(combo - model) / src”. As combo is assumed to be the continuum model (model) combined with the source model, e.g. “model + line”, then this is equivalent to “line / model”. This means that emission lines have a positive EW and absorption lines a negative EW.

Parameters:

  • data – The data object used to define the grid on which the model is evaluated.

  • model – The continuum model (this may contain multiple components).

  • combo – The continuum plus line (absorption or emission) model.

  • lo (optional) – The lower limit for the calculation. The default value of None means that the lower range of the data set is used.

  • hi (optional) – The upper limit for the calculation. The default value of None means that the lower range of the data set is used.