DIBs, and Gamma-Earth

I spent the day at the Institute for Advanced Study in Princeton, talking to Bovy (IAS), Menard (JHU), Zasowski (JHU), and Lan (JHU) about the possible use of diffuse interstellar bands observed in stellar spectra from SDSS-III APOGEE to measure the kinematics of the Milky Way disk. We came up with some first steps. The coolest thing we realized is that Bovy's MW disk models (built from stellar velocities) make zero-free-parameter predictions for the line-of-sight DIB velocities, under some "smooth model" assumptions. That is worth doing immediately. The team also gave me lots of good feedback on my work with Jeffrey Mei (NYUAD) on the mean (or really regression-created) spectrum of interstellar absorption from SDSS calibration stars.

Early in the day, Tremaine (IAS) gave me very valuable feedback and reactions to the exoplanet populations paper that Foreman-Mackey and I are finishing up. In particular, he and we agree completely that the thing we should be talking about (which Foreman-Mackey and I call "Gamma-Earth") should be the number of planets per star per unit natural-logarithmic radius per unit natural-logarithmic period, evaluated at the properties of Earth. This obviates atmospheric modeling and does not specify any "bin size". Great minds think alike!

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