Last modified: December 2018

URL: http://cxc.harvard.edu/sherpa/ahelp/absorptionvoigt.html
AHELP for CIAO 4.11 Sherpa v1

absorptionvoigt

Context: models

Synopsis

Voigt function for modeling absorption (equivalent width).

Syntax

absorptionvoigt

Description

This model uses an AbsorptionGaussian component to model the core of the profile and an AbsorptionLorentz component to model the wings of the absorption feature. This model is intended to be used to modify another model (e.g. by multiplying the two together). It is for use when the independent axis is in Angstroms.


Example

>>> create_model_component("absorptionvoigt", "mdl")
>>> print(mdl)

Create a component of the absorptionvoigt model and display its default parameters. The output is:

mdl
   Param        Type          Value          Min          Max      Units
   -----        ----          -----          ---          ---      -----
   mdl.center   frozen         5000  1.17549e-38  3.40282e+38  angstroms
   mdl.ew       thawed            1  1.17549e-38  3.40282e+38  angstroms
   mdl.fwhm     thawed          100  1.17549e-38  3.40282e+38       km/s
   mdl.lg       thawed            1  1.17549e-38  3.40282e+38           

ATTRIBUTES

The attributes for this object are:

center

The center of the profile, in Angstroms.

ew

The equivalent width of the profile. The ewidth parameter of the Gaussian and Lorentz sub-components is set to half this value.

fwhm

The full-width half-maximum of the model in km/s.

lg

The fwhm parameters of the Gaussian and Lorentz components are set based on the fwhm and lg values: the Gaussian component has its fwhm parameter set equal to fwhm , and the Lorentz component has its fwhm parameter set to lg * fwhm .

Notes

The Voigt function is approximated by the sum of a Gaussian and a Lorentzian profile ( [1] ), which works best when the ratio between the FWHM of the Gaussian and Lorentzian sub-components is near unity. The flux value is always kept evenly divided in between each sub-component. The FWHM of each sub-component is related to that of the other sub-component via the lg parameter.

References


Bugs

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

See Also

models
absorptionedge, absorptiongaussian, opticalgaussian