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Last modified: December 2010

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AHELP for CIAO 4.3 Sherpa v1


Context: utilities


Calculate the equivalent width of an emission or absorption line.


eqwidth( src, combo, [lo, hi], [id], [bkg_id] )


The eqwidth command calculates the equivalent width of an emission or absorption line in the source or background data. The equivalent width is reported in the units of the analysis, either energy or wavelength.

An integral over the entire energy or wavelength range of the dataset - or a specified interval - is performed to evaluate the continuum model (src) and the continuum-plus-line model (combo) at each point. The integrand is then (combo-src)/src.

  • src - model expression that describes the continuum
  • combo - model expression that describes the continuum plus the line
  • lo - low energy/wavelength limit; default=None
  • hi - high energy/wavelength limit; default=None
  • id - the id of the dataset to use; if not given, uses the default dataset id (id=1 by default, see "ahelp get_default_id")
  • bkg_id - the id of the background to use; default is the first background dataset

The src and combo model expression components must be established, e.g. with set_source or set_model(), before they can be used by eqwidth.

Example 1

sherpa> set_model("powlaw1d.cont")
sherpa> set_model("gauss1d.eline")
sherpa> eqwidth(cont, cont+eline)

Define 1D gaussian and powerlaw models, then use them to find the equivalent width of the line.

Example 2

sherpa> set_bkg_model(2,"const1d.c1+gauss1d.line")
sherpa> eqwidth(c1, c1+line, lo=2., hi=10., id=2, bkg_id=1)

Define 1D constant and powerlaw models for background data set 1 associated with source data set 2, then use them to find the equivalent width of the line between 2.0 and 10.0 keV.

Example 3

sherpa> eqwidth(bb+pl, bb+pl+line1, "src")

Model components from the source model are used to calculate the equivalent width of a line in dataset "src".


See the bugs pages on the Sherpa website for an up-to-date listing of known bugs.

See Also

list_model_ids, show_bkg_model, show_bkg_source
add_model, add_user_pars, clean, create_model_component, delete_bkg_model, delete_model, delete_model_component, get_model, get_model_autoassign_func, get_model_component, get_model_component_image, get_model_component_plot, get_model_plot, get_num_par, get_order_plot, get_par, get_pileup_model, get_source, get_source_component_image, get_source_component_plot, image_model, image_model_component, image_source, image_source_component, integrate, link, load_table_model, load_user_model, reset, save_model, save_source, set_bkg_model, set_full_model, set_model_autoassign_func, set_pileup_model, set_source, set_xsabund, set_xscosmo, set_xsxsect, set_xsxset
plot_model, plot_model_component, plot_source, plot_source_component
delete_psf, load_conv
save_delchi, save_resid
calc_chisqr, calc_energy_flux, calc_model_sum, calc_photon_flux, calc_source_sum, calc_stat
contour_model, contour_ratio, contour_resid, get_ratio, get_resid

Last modified: December 2010
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