Gaia Sprint continued today with Christina Eilers (MPIA) and I puzzling over the behavior of her code that is an extension of The Cannon to the case in which there are label uncertainties on the training-set stars. The behavior of the code is odd: As we give the code less freedom, the model of the stellar spectra gets better but the prediction gets worse. Makes no sense! The optimization is huge, and it relies on hand-typed analytic derivatives (I know, I know!), so we don't know whether we have conceptual issues or bugs.
Meanwhile, Andy Casey (Monash) and Ana Bonaca (Harvard) got excited about doing asteroseismology with the sparse photometric light curves that will be produced by Gaia. In particular, Casey got Stephen Feeney's (Flatiron) fake-data generator and likelihood function code (made for TESS-like data) working for Gaia-like data. He finds peaks in the likelihood function! Which means that maybe we can do asteroseismology without taking a Fourier Transform. His results, however, challenged both of our intuitions about the information about nu-max and delta-nu that ought to reside in any data stream. Inspired by all this, Bonaca and Donatas Narbutis (Lithuania) looked up large HST programs on stellar clusters and showed that it is plausible that we could do asteroseismology in HST too!
In other news, Mariangela Lisanti (Princeton) worked through recent results on dynamical friction in an ultralight-scalar dark-matter model (where the dark matter has a de Broglie wavelength that is kpc in scale!) and has plausible evidence that the timing argument (for the masses of local-group objects) might rule out or constrain ULS dark matter. And Anthony Brown (Leiden) and Olivier Burggraaff (Leiden) showed me an update of Jo Bovy and my (2009) extreme-deconvolution model of the local MW disk velocity field, and they find some structure in the vertical direction, which is cool and intriguing.