Last modified: December 2023

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AHELP for CIAO 4.16 Sherpa


Context: models


Gaussian function for modeling absorption (equivalent width).




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.


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

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

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


The attributes for this object are:

Attribute Definition
fwhm The full-width half-maximum of the model in km/s.
pos The center of the gaussian, in Angstroms.
ewidth The equivalent width of the model, in Angstroms.
limit The model is only evaluated for points that lie within limit sigma of pos. It is a hidden parameter, with a value fixed at 4.


The functional form of the model for points is:

f(x) = 1 - ampl * exp(-0.5 * ((x - pos)/sigma)^2)

ampl = ewidth / sigma / 2.50662828

sigma = pos * fwhm / (2.354820044 * c)

and for integrated data sets the low-edge of the grid is used. The calculation is only done for those points that are in the range:

|x - pos| < limit * sigma

Outside this range the model is set to 1.


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

See Also

absorptionedge, absorptionlorentz, emissiongaussian, opticalgaussian