In a long conversation, Lily Zhao (Yale), Megan Bedell (Flatiron), and I looked at a possible re-scope of our new paper on spectrograph calibration. Zhao is finishing one paper that builds a hierarchical, non-parametric wavelength solution. It does better than fitting polynomials independently for different exposure groups, even in the full end-to-end test of measuring and fitting stellar radial-velocities. But the paper we were discussing today is about the fact that the same distortions to the spectrograph that affect the wavelength solution also (to the same order) affect the positions of the spectroscopic traces on the device. That is, the relationship between (say) x position on the detector and wavelength can be inferred (given good training data) from the y position on the detector of the spectral traces. We have been struggling with how to implemnent and use this but then we realized that we could instead write a paper showing that it is true, and defer implementations to the pipeline teams. Implementation isn't trivial! But the result is nice. And kind-of obvious in retrospect.
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