Today was the first day of the meeting Galactic Archaeology and Stellar Physics in honor of Ken Freeman (MSSSO). As per usual when I am at a meeting, this blog can't convey the full day of talks, so I will just put here very personal highlights.
Freeman opened the conference, giving his overview of what he wants to know about the Galaxy. He is excited about the revolution happening now in which we might have 6-d phase space and 30-ish chemical abundances for stars all over the Galaxy. He brought up two themes that would be very important in today's talks, the bimodality in the alpha/Fe distribution (and its connection to different disk components), and radial migration. On the former, he uses the bimodality to separate the thin and thick disks; he is so confident that he literally calls a chemically separated component the “thick disk”. On the latter, he showed some results I hadn't seen on velocities as a function of metallicity that he argued make the radial migration clear. I have to figure that out! Relevant to things we worked on in the Gaia Sprint, he asked whether the disk components are different heights because of heating or a big event. I think we now know that at small heights it is heating. But the alpha-rich component might be thick because of an event.
Hekker discussed the SAGE project to get a uniform catalog of masses and ages for stars out of non-uniform inputs. She referenced The Cannon but is taking an opposite tack: She is trying to homogenize the data by making all the data constrain the same physical model.
Ruiz-Dern discussed red-clump stars, and in particular building a data-driven model of the relationships between spectroscopic parameters and photometric colors. She showed very good evidence that we could do a lot of the science we do with spectroscopy with photometry instead! That was not her goal, but it got me thinking in a totally new way about my project with Lauren Anderson.
Bovy discussed his results of dissecting the Galaxy into narrow chemical-abundance slices. Where Freeman had used the differing amplitudes in the alpha/Fe bimodality as a function of position to show how different different parts of the Galaxy are, Bovy used the same data to show how similar different parts are! That's a great property of a good scientific result: It can be interpreted either way! He discussed in detail what aspects of his Galaxy decomposition results are consistent and inconsistent with ideas from radial migration.
Talks by Duong and Chiappini again used chemistry to investigate the thin and thick disks, and Chiappini explicitly warned the audience that we will get different results if we split the Galaxy on chemical or structural lines. This also mirrored comments by Bovy.
Toyouchi looked at explaining the alpha/Fe bimodality with an event in the Milky Way's past. This got me thinking about the question: How can we tell whether the bimodality is a fundamental property of the chemical enrichment of molecular clouds or whether it is just the result of some very specific event in the Milky Way's particular past?
Feuillet showed amazing age-abundance relationships for the 19-ish elements that APOGEE observes. It is a goldmine of empirical results. She finds a few highly problematic elements. Like us, she finds that alpha/Fe is strongly correlated with age, at all alpha/Fe values and at all ages.
Buder talked about the GALAH survey and what has been learned and improved with the Gaia DR1 TGAS release. He announced that GALAH is using The Cannon as part of its data analysis pipeline. He said (and I believe him) that they are using it to speed up the code. I like that; it's good for my brand!