stellar stream EM

Lang and I had discussed with Rix and Sergey Koposov (MPIA) the statistical detection of the proper motion of a cold stellar stream using the proper motions from comparison of the SDSS with the USNO-B imaging. This looks possible because although no star in the stream is measured at high signal-to-noise, and although no star is clearly in the stream or not, there is power in numbers. Unfortunately, just as Lang and I were getting ready to bust out some expectation-maximization, Koposov obtained the proper motion of the stream in question by a completely straightforward frequentist analysis. Nice work!

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