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Spectral wavelengths usually are defined as vacuum wavelength. The index of refraction of the medium influences the wavelength, and as such 'in vacuum' is both easier to define and measure: You'd need to define and specify composition, pressure and temperature in addition to the wavelength for each measurement in air - all of which is unnecessary if you ...


If you're looking explicitly for radio-loud quasars, I'd recommend looking at a catalog of (mainly extragalactic) radio sources, rather than a catalog of quasars, given that only a small fraction of quasars are radio-loud. The Third Cambridge Catalogue of Radio Sources (VizieR link) might be a nice starting point, particularly given how many objects are ...


The answer turned out to be that I was pushing the models package too far with the data that I was giving it. More careful background subtraction and much more localised fitting helped greatly.

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