As my loyal reader knows, I have opinions about spectroscopic extraction—the inference of the one-dimensional spectrum of an object as a function of wavelength, given the two-dimensional image of the spectrum in the spectrograph detector plane. The EXPRES team (I happen to know) and others have the issue with their spectrographs that the cross-dispersion direction (the direction precisely orthogonal to the wavelength direction) is not always perfectly aligned with the y direction on the detector. This is a problem because if it is aligned, there are very simple extraction methods available.
I spent parts of the day writing down not the general solution to this problem (which might possibly be Bolton & Schlegel's SpectroPerfectonism, although I have issues with that too), but rather with an expansion around the perfectly-aligned case, that leads to an iterative solution, but preserving the solutions that work at perfect alignment. It's so beautiful! As expansions usually are.
What to call this? I am building on Zechmeister et al's “flat-relative optimal extraction”. But I'm allowing tilts. So Froet? Is that a rude word in some language?
Hi. This is an exciting topic. Could you shortly elaborate on your issues with Bolton & Schlegel?
ReplyDeleteYes: It's a bit subtle; it is the point that B&S model the spectrum using an accurate LSF, which means that their model is effectively the infinite-resolution spectrum. Since this is being instantiated on a finite grid, but is supposed to be infinite resolution, ringing occurs. So then they smooth their result with a particular kernel (chosen wisely, but still). My guess is that there is a way to model the spectrum explicitly at finite resolution. Believe me, I am working on it!
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