[AstroPy] Specutils: use of Gaussians and estimators

[Peter Dzwig]

I am running the "simple example" from specutils as a precursor to doing
some line-fitting.

The demo code is here:

 https://specutils.readthedocs.io/en/stable/fitting.html

This runs and does pretty much what it says.


However I want to use estimate_line_parameters to get an approximation
to the parameters in the Gaussian, because I am interested in looking at
a number of long spectra with a lot of lines in.

So I modify the specutils.fitting import to

from specutils.fitting import fit_lines, estimate_line_parameters


and add in

e1 = estimate_line_parameters(spectrum, models.Gaussian1D())
a = round(e1.amplitude.value,2)
b = round(e1.fwhm.value,2)
c = round(e1.stddev.value,2)

This gives meaningful values and I replace the call to the Gaussian  and
the plot by:

g_init = models.Gaussian1D(amplitude=a*u.Jy, mean=b*u.um, stddev=c*u.um)

then

g_fit = fit_lines(spectrum, g_init)
y_fit = g_fit(x*u.um)

The initial values are:

initial amplitude= 3.35  initial fwhm =  2.41  initial stddev= 1.02

But on looking at the output parameters using g_fit.amplitude.value etc,
I get:

final amplitude= -0.24 Jy  final fwhm =  0.0 um  final stddev= 0.0 um

for the output values!! Surely it should be possible to use estimators
in this way. Am I mistaken?

FWIW I am running matplotlib 3.2.2, specutils 1.0, pyspeckit 0.1.23,
numpy 1.19, python 3.6 over Ubuntu 19.10

Anyone any thoughts?

Peter Dzwig
-- 

Dr. Peter Dzwig