At brown-bag today, Ronnie Jansson (NYU) gave a very nice talk about his work with Farrar (NYU) on the Milky Way magnetic field. They have made a multi-component model that obeys Maxwell's Equations (yes, that's a good thing) but also is maximum-likelihood against a set of rotation-measure and stokes Q and U data. They find an X-shaped field for the Milky Way viewed in projection by an external observer. This prediction is pretty hard to test directly (!) but it is consistent with observations of other nearby spirals. The biggest limitation of their work is the understanding of the Galactic high-energy electron density; their methods could be used to constrain both this and the magnetic field simultaneously; it sounds like that is in the plans. Great work.
In the afternoon, Foreman-Mackey and I teleconned with Brewer on our sampling-over-catalogs project. I argued for a descope to a minimal paper that gives a method that works, and leave all but the simplest applications to subsequent papers. I made this suggestion in part because I want to get things done and in part because it would be hard to describe the sampling over models of varying complexity and non-trivial scientific conclusions in the same abstract. During the call, we also discussed a novel way to do the sampling over varying complexity, and I noticed Brewer fork the code late in the day. The nice thing is that this project could generate some good idea in statistics (Brewer's home department when he starts his new job this year) as well as astronomy.
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