As my loyal reader knows, Christina Eilers (MPIA) and I have been working on a purely linear model for estimating parallax given APOGEE spectroscopy (and Gaia+2MASS+WISE photometry), for very luminous red giants. This model had some pathologies, which caused Hans-Walter Rix (MPIA) to disagree with us about various aspects of implementation. On my vacation, I figured out how to generalize this model to make it a linear predictor for absolute magnitude (or log luminosity or distance modulus) without breaking the nice properties of the model, to wit: We don't do any cuts on the Gaia parallaxes or parallax signal-to-noise, avoiding selection-induced biases. And we use the Gaia likelihood function correctly.
It worked! We are now predicting distance moduli with a distance precision of better than 10 percent for very luminous giants (more luminous than the red clump). We made some sweet maps of Milky Way disk kinematics (mean velocity and velocity dispersion as a function of location in the disk).
Late in the day, Matthias Samland (MPIA) re-booted our project with Jeroen Bouwman (MPIA) to apply technology like our Kepler CPM calibration to ground-based direct-imaging data from coronographs. We reminded ourselves where we are and made very short-term writing goals to write down what we think we are doing.