disk heating

At Milky Way group meeting, Price-Whelan talked about chaotic streams, Gail Zasowski (JHU) talked about the SDSS demographics survey, and Jonathan Bird (Vanderbilt) talked about the age–velocity relationship in the Milky Way Disk. This latter project started yesterday, with Bird asking Ness and me for the ages for red-clump stars, which Bovy had previously matched up to proper motion measurements. The age–velocity relation has only been precisely measured previously using ages (as opposed to chemical abundance proxies) in the Hipparcos sample (that is, very locally at the Solar position), so if our ages are good, this will become the best measurement of the disk heating mechanisms ever.

In the afternoon, Rix and I worked with Bird to turn his empirical velocity dispersion (measured as a function of age and Galactocentric radius) method into a probabilistic method with a likelihood function. With a few severe assumptions, we got a very simple form. The plan is to try to run some MCMC tomrrow. We encouraged Bird to spend an extra week in Heidelberg if he can!