Kronos–Krios; photometric redshifts without training

In the early morning, Ana Bonaca (Harvard) and I discussed our information-theory project on cold stellar streams. We talked about generalizing our likelihood model or form, and what that would mean for the lower bound (on the variance of any unbiased estimator; the Cramér–Rao bound). I have homework.

At the Flatiron, instead of group meeting (which we moved to tomorrow), we had a meeting on the strange pair of stars that Semyeong Oh (Princeton) and collaborators have found, with very odd chemical differences. We worked through the figures for the paper, and all the alternative explanations for their formation, sharpening up the arguments. In a clever move, David Spergel (Flatiron) named them Kronos and Krios. More on why that, soon.

In the afternoon, in cosmology group meeting, Boris Leistedt (NYU) talked about his grand photometric-redshift plan, in which the templates and the redshifts are all estimated together in a beautiful hierarchical model. He plans to get photometric redshifts with no training redshifts whatsoever, and also no use of pre-set or known spectral templates (though he will compose the data-driven templates out of sensible spectral components). There was much discussion of the structure of the graphical model (in particular about selection effects). There was also discussion about doing low-level integrals fast or analytically.

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