Grillmair stream

Koposov may have evidence that the velocity of the Grillmair stream is not exactly parallel to the configuration direction of the stream. Since the stream is cold and very near pericenter (by any reasonable model), this could have important implications for either the potential of the Milky Way or else how the stream formed. Unfortunately, it is hard to tell which. Had many confusing conversations about this today, but Bovy worked out that there are large classes of potentials in which the misalignment can't happen unless there is either a strong action gradient in the stream or else a time-dependence (or other nastiness) in the potential.

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