Dr Kate Storey-Fisher

Kate Storey-Fisher (NYU) defended her PhD here at NYU today. She killed it! She talked about emulating cosmological simulations (at the level of statistics, not maps), making invariant scalars that encode the shapes and dynamics of dark-matter halos, and her awesome 1.2 million all-sky quasar catalog from ESA Gaia and NASA WISE. It was all things my loyal reader knows lots about but I loved it. It has been an honor and a privilege to work with KSF these years, and I will miss her very very much.

exoplanet transit science

I have had a good day finishing up my reading of the PhD dissertation of Emily Sandford (Columbia), who has a great collection of results on transit measurements of planets and stars. She makes use of Bayesian methods and also classic optimization or signal-processing methods to make challenging inferences, and she shows the limits and capabilities of current and future data. One thing I liked was that she works on what are called “single transits” where only one transit is found in the whole survey duration; what can you infer from that? A lot! (I have also worked on this problem long ago.) In the dissertation she busts a myth that the multiplicity distribution requires that there be a mixture of two qualitatively different kinds of planetary systems. I enjoyed that, and it leads to a lot of other science. Plus some creative work on understanding the detailed properties of multi-planet systems, treating them like sequence data. It's a great thesis and I am very much looking forward to tomorrow's defense.

preparing for defense

My only real research today was a session with Dun Wang (NYU) in preparation for his PhD defense. I encouraged him to talk about less, not more: The defense (at least here) doesn't need to be about everything (that would take hours, anyway); it should be about what you learned, and what was most fun.

Dr. Adrian Price-Whelan

It was my great pleasure to sit on the PhD defense committee for Adrian Price-Whelan (Columbia) today. He spoke about using phase-space structures, especially streams of stars, to constrain the gravitational field in the Milky Way. He pointed out that we should call it the “gravitational field” not the “gravitational potential” because the latter is only known up to a constant. (I think the argument is deeper: The potential exists only to be differentiated, never observed!)

Two important ideas that were under heavy discussion both in Price-Whelan's talk and in the discussion afterwards were the following: Price-Whelan may have the first ever empirical evidence for dynamical chaos outside of planetary systems. His evidence is in the form of morphological predictions for stellar streams. This argument is weak at present, but if the evidence grows stronger, he will be responsible for a new kind of fundamental measurement.

The other idea is that we might be making big mistakes interpreting the Milky Way entirely in terms of simple, integrable models. As my loyal reader knows, I have ranted about this for years, but my rants have been vapor-ware. Price-Whelan (along with Pearson at Columbia and Bonaca at Yale, I should add) is close to being able to address this point directly and quantitatively.

In addition to all of these things, Price-Whelan has delivered some great probabilistic methods and code, contributed heavily to important open-source astronomy projects, and led our community in education regarding code, data analysis, and research practice. It has been a great pleasure and opportunity for me to be involved in his work for (what his thesis points out is) the last decade!

dissertation transits

Schölkopf, Foreman-Mackey, and I discussed the single-transit project, in which we are using standard machine learning and a lot of signal injections into real data to find single transits in the Kepler light curves. This is the third chapter of Foreman-Mackey's thesis, so the scope of the project is limited by the time available! Foreman-Mackey had a breakthrough on how to split the data (for each star) into train, validate, and test such that he could just do three independent trainings for each star and still capture the full variability. False positives remain dominated by rare events in individual light curves.

With Dun Wang, we discussed the GALEX photon project; his job is to see what about the photons is available at MAST, if anything, especially anything about the focal-plane coordinates at which they were detected (as opposed to celestial-sphere coordinates). This was followed by lunch at facebook with Yann LeCun.

galaxy sources and sinks

In a low-research day, Jiang and I discussed the idea of using continuity to understand galaxy evolution. That is, changes in the number density of any population of galaxies should be quantitatively explained by sources of galaxies in that population, sinks, and evolution within the population. We can measure each of these terms for some galaxy populations, so there is a rich set of projects here.