I had great Gaia DR1 and Gaia Sprint brain-storming sessions today with Adrian Price-Whelan and Dan Foreman-Mackey. Price-Whelan proposed that we “run back the clock” on the TGAS stars to see if any pairs emerge from disruption events in the past. I commented that if we go to short times in the past, you need neither distances nor radial velocities: The angular motions suffice. It must be that as the time scale gets longer, distances and radial velocities matter more and more; it would be nice to see this come in continuously. We left that as a conceptual to-do, but we worked out a plan that ought to work in general. This project has a lot in common with the Kinematic Consensus projects that Hans-Walter Rix (MPIA) and I have worked on in the past.
I described to Foreman-Mackey some of my ideas about a data-driven model of the color-magnitude diagram. I have this idea of transforming the space to one in which the noise model is Gaussian, but that kind of thing always makes me feel dirty. We discussed the possibility that I could make my model only one-dimensional (in the parallax direction) by cutting the data into tiny color boxes. That's crazy, but the Gaia Sprint is a hack week, where experiments reign and we want to make things work. So maybe I will write that down this weekend.