Caltech for a day

[On a research break this week; hence the lack of posts.]

I spent the day at Caltech Astronomy, with a dense schedule! Judy Cohen and I talked about RR Lyrae she is finding in the Milky Way halo and the challenge of getting a completeness function for statistical inferences. Pete Mao described to me the fiber positioners they are building for the Prime Focus Spectrograph multi-object spectrograph for Subaru. They have 50 seconds to get 2500 actuators in place (to a tolerance of 10-ish microns). Leslie Rogers and Ellen Price told me about Price's senior-thesis project to work out the composition constraints on short-period planets from tidal stress and the requirement that they not break up or mass-transfer. I was surprised to learn that there are some planets so close in that the tidal constraints rule out a range of compositions.

Nick Konidaris showed me new spectrographs being built in the high bay, and we talked about choices for spectral resolution. Adi Zitrin showed me amazing image of massive galaxy clusters he is using as telescopes to magnify very high-redshift galaxies; he has amazing examples, and also some nice techniques for building mass models. He does a great job of explaining arc multiplicity and morphology.

At lunch, students Rebecca Jensen-Clem and Michael Bottom told me about projects in high-contrast imaging, and Allison Strom and Sirio Belli told me about measuring the physical properties of galaxies in the redshift range 2 to 3. I tried to pitch my data-driven approaches at them: In the former area you might think about learning the actuator commands given the wavefront data directly from an optimization (with, presumably, the quality of the science image encapsulated in the objective function). In the latter, you might think about making a graph of galaxy spectra, where galaxies are joined by edges in the graph if their spectra are similar under any (reasonable) assumption about dust extinction. The students were (rightly) suspicious about both options!

Adam Miller and I discussed correct uses of machine learning in astronomy (since he is a great practitioner), and I once again pitched at him the possibility that we could try to replace their random-forest classifier in the time domain with a generative model of all stellar variable types. It would be hard, but exceedingly satisfying to do that. We discussed training-set imbalance and some clever ideas he has about combating it.

I asked Heather Knutson about how to get our (new) single transits we are finding in Kepler followed up with radial-velocity spectrographs. She made a great point about our future population inferences: Anything we infer from single transits makes a prediction for radial-velocity surveys and we should try to encourage the radial-velocity groups to confirm or deny in parallel. I discussed cadence and exposure-time issues for the Zwicky Transient Factory with Eric Bellm and visualization and interface for the LSST data with George Helou. I gave the Astrophysics Colloquium there about The Cannon and data-driven models (by my definition) and the day ended with a great dinner with Tom Soifer, Chuck Steidel, George Djorgovski, and Judy Cohen. It was a great trip!