observing and fitting streams of stars

I spent the day up at Columbia, visiting Johnston's group and also Geha and Bonaca came down from Yale. We discussed all things tidal streams, including recent papers by Sanders and by Bovy (streams are the new exoplanets?). We noticed that some things in those papers might be in one or two old papers by Johnston and by Helmi. Will do due diligence on that soon. One thing I don't like about these recent papers is that they are very tied to the action–angle formalism, which requires integrable potentials, which puts incredibly strong, unrealistic, global constraints on what can be fit.

We made a more concrete, more specific outline for Price-Whelan's current paper, which is the first in the business to do (what I consider) proper treatment of individual-star uncertainties, and also which is not tied to integrability. We also looked at some likelihood issues coming from Bonaca and Küpper. One thing that remains puzzling to me after all the discussion is why some tidal-disruption stream models make something that looks like a "feathered" (or zig-zagging) stream and some don't. This issue might be partially resolved by whether the outputs are shown as a collection of points or a density distribution, since the latter de-emphasizes the feathering. We started the discussion about what it would take to observe that feathering in full detail; Geha has lots of telescope time!

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