I broke my own rules and left #AstroHackWeek to catch up with #LennartFest. The reason for the rule infraction is that the latter meeting is the retirement celebration of Lennart Lindegren (Lund) who is one of the true pioneers in astrometry, and especially astrometry in space and at scale. My loyal reader knows his influence on me!
Talks today were somewhat obscured by my travel exhaustion. But I learned some things! Francois Mignard (Côte d'Azur) gave a nice talk on the reference frame. He started with an argument that we need a frame. I agree that we want inertial proper motions, but I don't agree that they have to be on a coordinate grid. If there is one thing that contemporary physics teaches us it is that you don't need a coordinate system. But the work being done to validate the inertial-ness of the frame is heroic, and important.
Floor van Leewen (Cambridge) spoke about star clusters. He hypothesized—and then showed—that proper motions can be as informative about distance as parallaxes, especially for nearby clusters. This meshes with things Boris Leistedt (NYU) and I have been talking about, and I think we can lay down a solid probabilistic method for combining these kinds of information responsibly.
Letizia Capitanio (Paris) reminded us (I guess, but it was new to me) that the Gaia RVS instrument captures a diffuse interstellar band line. This opens up the possibility that we could do kinematic dust mapping with Gaia! She also showed some competitive dust maps based on Gaussian Process inferences.
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