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.


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 ...

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