There is growing evidence that Ness, Rix, and I can determine stellar masses (and therefore ages) on the red-giant branch using The Cannon, trained on asteroseismology results from Kepler and spectra from APOGEE. I am stoked. There is some debate among our team about what is going to be the spectral signature that is delivering the mass/age information. Last week, Ness showed me that at least some of the information is coming from very weak emission lines. The Cannon has discovered chromospheric activity! Today, Ness and I worked on visualizing the spectral regions that are delivering label information. We came up with a pretty novel plot, one draft example of which is below.
Also today Andrew Gordon Wilson (CMU) showed up to school us on Gaussian Processes. He said that he would have no trouble computing the determinant of the covariance matrix for the CMB real-space likelihood function even for Planck-sized data; he said the determinant would take seconds! His methods involve a regular grid of inducing points and interpolation to the irregular grid. So we threw down the challenge; now Foreman-Mackey and I have to get the problem set up for him. We'll see!