Ah, back to work again. It is my incredible privilege to work in Heidelberg every summer. Today I spoke with Sara Rezaei Kh (MPIA) and Christina Eilers (MPIA) about projects to use Gaia DR2 to constrain properties of the Milky-Way disk, especially the rotation curve and the dust density as a function of position. That connected to a longer conversation with Lauren Anderson (Flatiron) and Hans-Walter Rix (MPIA) about measuring the properties of stellar populations in boxels of the Milky Way. Boxels in position, or in velocity, or in actions. It also led to some work in which Eilers and I looked at external validation (using open clusters) of our spectroscopic parallaxes.
I also re-started projects on M-type dwarf stars with Jessica Birky (UCSD) who is in HD for the summer. She will write up her results using The Cannon to transfer labels from a small training set fit by Andrew Mann (Columbia) to all of APOGEE if all goes well.
And into town came Daniel Stern (JPL), who gave an incredibly impressive talk about HabEx, the NASA mission concept for the next decadal survey. It is an ambitious mission, but strongly cost controlled. If it is paired with a starshade (an idea I love), it could do amazing exoplanet science. And it really motivates me to get back to thinking about physical optics!
Finally, I spent a couple hours in the back of the room for #StellarHalos18, where I learned about Gaia DR2 projects on the Milky-Way halo. In particular, I learned about the Malhan method for finding streams. It puts high weight on stars with likely co-orbital neighbors, and then uses a by-hand or by-eye step to link them into stream discoveries. Very impressive. Very fast. Very high impact! But a bit too heuristic for my taste; let's automate all the things!