In Stars group meeting, Stephen Feeney (Flatiron) walked us through his very complete hierarchical model of the distance ladder, including supernova Hubble Constant measurements. He can self-calibrate and propagate all of the errors. The model is seriously complicated, but no more complicated than it needs to be to capture the covariances and systematics that we worry about. He doesn't resolve (yet) the tension between distance ladder and CMB (especially Planck).
Semyeong Oh (Princeton) and Adrian Price-Whelan (Princeton) reported on some of their follow-up spectroscopy of co-moving pairs of widely separated stars. They have a pair that is co-moving, moving at escape velocity in the halo, and separated by 5-ish pc! This could be a cold stellar stream detected with just two stars! How many of those will we find! Yet more evidence that Gaia changes the world.
Josh Winn (Princeton) dropped by and showed us a project that, by finding very precise stellar radii, gets more precise planet radii. That, in turn, shows that the super-Earths really split into two populations, super-Earths and mini-Neptunes, with a deficit between. Meaning: There are non-trivial features in the planet radius distribution. He showed some attempts to demonstrate that this is real, reminding me of the whole accuracy vs precision thing, once again.
In Cosmology group meeting, Dick Bond (CITA) corrected our use of “intensity mapping” to “line intensity mapping” and then talked about things that might be possible as we observe more and more lines in the same volume. There is a lot to say here, but some projects are going small and deep, and others are going wide and shallow; we learn complementary things from these approaches. One question is: How accurate do we need to be in our modeling of neutral and molecular gas, and the radiation fields that affect them, in order for us to do cosmology with these observables? I am hoping we can simultaneously learn things about the baryons, radiation, and large-scale structure.