Comment by Vincent Le Brun on 2023-08-24 09:41:16:
Didier Vibert wrote:

> when several elements are overlapping (eg Ha and NII) a unique wavelength offset and width (velocity dispersion) is fitted for the complex, whereas each element should have its own offset and width. Of course the fit has still to be done jointly.

is it true? If the overlap is only on the continuum the fit could be done independently . It is only if the lines overlap that a combined fit is to be done. But I'm not sure it will modify results

Comment by Didier Vibert on 2023-08-24 12:29:21:
Vincent Le Brun wrote in #note-1:
> Didier Vibert wrote:
>
> > when several elements are overlapping (eg Ha and NII) a unique wavelength offset and width (velocity dispersion) is fitted for the complex, whereas each element should have its own offset and width. Of course the fit has still to be done jointly.
>
> is it true? If the overlap is only on the continuum the fit could be done independently . It is only if the lines overlap that a combined fit is to be done. But I'm not sure it will modify results

the polynomial coefficients modelling the continuum have to be fitted jointly with the superposed lines: thus all lines parameters and the polynomial coeffs have to be fitted together