#GaiaSprint, day 2

Oh yes it worked! Today Christina Eilers (MPIA) clearly got 10-percent parallax precision with her linear, data-driven spectroscopic parallax model, making use of APOGEE data and WISE and Gaia photometry. The model is literally a linear combination of inputs, with a hard regularization and cross-validation to protect against over-fitting. Because our outputs are the cross-validation predictions, every spectroscopic parallax we produce is technically independent of the Gaia training data (although there are some residual correlations etc if you really want to go deep). From Daniel Michalik (ESTEC) we learned a lot about both astrometric and photometric data-quality filtering for the Gaia data, which (we can see in the residuals) will further improve our results!

Because the model is purely linear, we can propagate uncertainties easily, and we can “run it both ways” as it were. We can definitely do better if we go to a nonlinear model, because linearity is such an absurdly difficult constraint. However, it is so beautiful to have a linear relationship, we might stay here for a few papers!

Many incredible results appeared today, but one that struck me is the following: Laura Inno (MPIA) looked at the Cepheid variables in the data, where she has ages and photometric distances and kinematics. She clearly sees a substantial warp in the outer disk. The question came up: Is this the same as the warp in the gas disk?

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