asteroseismological estimators; and Dr Hahn!

Because of the availability of Dan Huber (Hawaii) in the city today, we moved Stars group meeting to Thursday! He didn't disappoint, telling us about asteroseismology projects in the Kepler and K2 data. He likes to emphasize that the >20,000 stars in the Kepler field that have measured nu-max and delta-nu have—every one of them—been looked at by (human) eye. That is, there is no fully safe automated method for measuring these. My loyal reader knows that this is a constant subject of conversation in group meeting, and has been for years now. We discussed developing better methods than what is done now.

In my mind, this is all about constructing estimators, which is something I know almost nothing about. I proposed to Stephen Feeney (Flatiron) that we simulate some data and play around with it. Sometimes good estimators can be inspired by fully Bayesian procedures. We could also go fully Bayes on this problem! We have the technology (now, with new Gaussian-Process stuff). But we anticipate serious slowness: We need methods that will work for TESS, which means they have to run on hundreds of thousands to millions of light curves.

In the afternoon, Chang Hoon Hahn (NYU) defended his PhD, which is on methods for making large-scale structure measurements. We have joked for many years that my cosmology group meeting is always and only about fiber collisions. (Fiber collisions: Hardware-induced configurational constraints on taking spectra or getting redshifts of galaxies that are close to one another on the sky.) This has usually been Hahn's fault, and he didn't let us down in his defense. Fiber collisions is a problem that seems like it should be easy and really, really is not. It is an easy problem to solve if you have an accurate cosmological model at small scales! But the whole point is that we don't. And in the future, when surveys use extremely complicated fiber positioners (instead of just drilling holes), the fiber-collision problem could become very severe. Very. As in: It might require knowing (accurately) very high-point functions of the galaxy distribution. More on this at some point: This problem has legs. But, in the meantime: Congratulations Dr Hahn!