GD-1 and chemical tangents

Tuesdays and Thursdays are lower on the research this semester! But I did get in two excellent discussions. The first was with Bonaca (Harvard) who has made an absolutely great visualization that compares the Gaia data on GD-1 and her model for GD-1. I think this figure might get featured in a lot of talks! We are still checking things, but it looks great. We discussed what would be the final scope of her paper, because—as with all projects—there is a huge possible scope but we need to finish a paper soon! I'm happy with the scope and it seems achievable and sensible. The big issue is that the constraints we have on the perturber than interacted with GD-1 come from a model that has toy aspects to it, while the full generative stream model is expensive enough that we don't want to go there for inference just yet. Soon, but not for this paper.

Over a late lunch I discussed many things with Price-Whelan (Princeton), both about GD-1 and about our chemical tangents project. On the latter, we discussed (for approximately the millionth time) how to describe the project most compactly. This project is strange enough for the typical astronomer, that we have to think carefully about how we present it. There are a lot of things that sound right but are wrong. And I am a huge believer in repeatedly re-describing projects. I think every time you go through it, you learn something new, and improve your presentation. This is a huge benefit of fully Open Science.

In that spirit: We are trying to find the surfaces in phase space along which the distribution of stars in abundance space is constant. Not the abundance is constant, but the distribution in abundances. Those surfaces contain the orbits! In some sense it comes down to the point that the joint distribution in actions and abundances is not separable, so the abundances can inform you about the actions! But that description is too terse. And Rix likes to say: Stars don't change their abundances as they orbit! So if you have drawn orbits through phase space that would require abundance changes, either your population isn't mixed or else you are wrong about those orbits.