Questions:

After fitting the spectra which may contain an emission line in addition
to a continuum you may want to perform simulations to determine whether
this line is significant.

1/ Protassov etal paper presents the statistical details of the problem.

"Statistics, Handle with Care: Detecting Multiple Model Components
with the Likelihood Ratio Test" by Protassov et al.
http://cxc.harvard.edu/xrayschool/analysis/protassov.pdf

2/ Use Sherpa and set up the simulations to perform the model comparison
tests.

3/ Follow the model comparison chart.
http://cxc.harvard.edu/xrayschool/analysis/model-selection.pdf

4/ Decide whether the emission line present in the spectrum.