don't calibrate your data!

Ben Johnson (UCSC) showed up in Heidelberg today and we discussed his project to obviate spectrophotometric calibration. He said, however, that we are not permitted to give the paper the same title as this blog post. However, I think it is apt, because he has a working system that suggests that inferences on spectra can proceed with a tiny bit of photometric data and no serious spectrophotometric calibration just as well as they can proceed when fully calibrated. Really the no-calibration method is better, in fact, because it models the spectrograph simultaneously with the spectral information; that is, it is makes less rigid assumptions about the hardware in general. The idea is to fit the calibration "vector" along with the parameters of interest, and take up the fiddly bits with a Gaussian Process. It seems to work. We spent part of the day moving a bit of furniture, to make the GP contribute multiplicatively (rather than additively) to the signal.