While I was on vacation, Jessica Birky (UCSD) used Gaia DR2 to identify many M-type dwarfs among the APOGEE spectroscopy, and type them using our data-driven models. The effective temperatures and metallicities that she finds vary beautifully along and across (respectively) the main sequence. It looks great. There are also many stars way above the main sequence, and we think these may be very young stars that are falling onto the main sequence. If that's true, it looks like we will have age indicators too. But we might postpone that to a second paper.
Megan Bedell (Flatiron) and I discussed the regularization scheme in her wobble code to measure precise radial velocities of stars, and also deliver extremely precise telluric and micro-telluric models. We decided to revisit all of the regularization and try to set it sensibly. The problem we are facing is that there are more regularization parameters and choices than we can comfortably cross-validate. So we have to do something more greedy for now. We discussed and Bedell started to implement. We also discussed the new scope for our note on information-theory bounds on radial-velocity precision; my job is to write that up tonight or tomorrow.
Christina Eilers (MPIA) and I made many improvements to her code to map the Milky-Way disk with red-giant stars, including changing slightly the absolute-magnitude model, estimating uncertainties on kinematic quantities through proper (nonlinear) error-propagation, switching to cylindrical coordinates, and working out (with the enormous help of Hans-Walter Rix and Ortwin Gerhard) a Jeans approach to getting the rotation curve in the face of asymmetric drift. At the end of the day I became convinced that the simplicity of our data-driven model for stellar luminosities will permit us to infer a dust map from our results; as my loyal reader knows, this is why I love linear models! I hope I'm right.