The morning started with Bedell and Foreman-Mackey and me devising a self-calibration approach to combining the individual-order radial velocities we are getting for the different orders at the different epochs for a particular star in the HARPS archive. We need inverse variances for weighting in the fit, so we got those too. The velocity-combination model is just like the uber-calibration of the SDSS imaging we did so many years ago. We discussed optimization vs marginalization of nuisances, and decided that the data are going to be good enough that probably it doesn't matter which we do. I have to think about whether we have a think-o there.
After that, I worked with Anderson and Belokurov on finding kinematic (phase-space) halo substructure in fake data, in SDSS, and in Gaia DR2. We have been looking at proper motions, because for halo stars, these are better measured than parallaxes! Anderson made some great visualizations of the proper-motion distribution in sky (celestial-coordinate) pixels. Today she made some visualizations of celestial-coordinate distribution in proper-motion pixels. I am betting this latter approach will be more productive. However, Belokurov and I switched roles today, with me arguing for “visualize first, think later” and him arguing for making sensible metrics or models for measuring overdensity significances.
Andy Casey (Monash) is in town! I had a speedy conversation with him about calibration, classification, asteroseismology, and The Cannon.