Today was my last day in Heidelberg for 2014. Sad day! I spent most of my research time working with Ness on our data-driven models of stars. We got the code to go from first-order (linear) linear fitting to second-order (quadratic) linear fitting, and vowed that we would never go to third order! We will use a Gaussian Process before we do that. We discussed outliers—both outlier stars and outlier pixels—and how to deal with them while still retaining computational tractability, good probability of convergence to a good optimum (or good sampling prospects), and the likelihood principle. We don't have a good solution yet, although I have ideas in my old document on fitting a line. We also discussed next steps on the path to paper 1, including especially making figures that demonstrate the properties and qualities of the individual-wavelength least-square fits we are doing.
At the end of the day, I was noticing that this project is a perfect example of the new discipline of "Data Science", about which I am supposed to have opinions: It was an idea we both had, but I didn't know enough about the spectroscopy, and Ness didn't know enough about the methods available. Neither of us could have done this project without the collaboration (nor without significant amounts of computation).