It was stream day today. We started with Bovy giving an impromptu lecture on a generative model for tidal streams based on actions and angles. It is almost identical to a model that I have been working on with / for Johnston and Price-Whelan, but angle-space makes it possible for Bovy to do one marginalization integral analytically that I have to do numerically. That huge benefit comes at a cost of course; the analytic marginalization requires a particular prior on stream disruption rate, and the action–angle formalism requires integrable potentials. All that said, the marginalization might be valuable computationally. During Bovy's disquisition, Robyn Sanderson pointed out that some of the ideas he was presenting might be in the Helmi & White paper from back in the day.
After this, Sanderson and I worked on our action-space clustering note. Sanderson debugged the use of KL-Divergence as a method to put uncertainties on parameter estimates; I worked on abstract and introduction text. One question I am interested in (and where Sanderson and I disagree) is whether what we are doing will work also for kinematically hot structures (thick disk, very old streams) or only kinematically cold ones. Since the method is based on information theory (or predictive value) I have an intuition that it will work for just about any situation (though obviously it will get less constraining as the structures get hotter).
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