#GaiaSprint, day 3

(As usual, these blog notes are only biased, imperfect, personal highlights. They are not minutes of the meeting in any sense!) Anthony Brown (Leiden) kicked off the day by comparing the all-sky image of the Gaia TGAS catalog with the all-sky image of the stars that Gaia uses to set its attitude. This latter catalog is close to a random sampling of stars, so it makes a beautiful all-sky image.

Yesterday's check-in meeting continued this morning with Bovy showing the Oort constants. He claimed that he needed something to do while his data files unzipped, so he decided to measure the Oort constants, including constant C, which he claims has never really been measured before! This continues the theme of the awesomeness of the Gaia data: You measure things that have never before been possible while your files are unzipping. Bovy also gave us a tiny reminder of what the Oort constants are. Years ago, Bovy and I (more-or-less) failed to measure these constants in the SDSS data.

Daniel Michalik (Lund) came in by phone to tell us about the construction of the TGAS Catalog, and Alcione Mora (ESAC) told us about the Gaia Archive and how to use it. In Michalik's talk I was reminded that there are two small circles on the sky (small as in not great) where there will be close to 200 observations per star; these are great places to concentrate observing programs: Why wait to after Gaia to do the follow-up observing on the amazing time-domain astrophysics that will be discovered in those sky regions.

I spent my sprinting time working with Price-Whelan on the mid-plane of the Milky Way disk, with Bird on the age-velocity relationship, including a generative model for the ages, and with Ness on the causal relationships between metallicity, age, and vertical kinematics. On the latter, the quesion is: Is heating “caused” by age or by metallicity? (Or maybe some more sophisticated question than that.) The answer seems to be that in some parts of abundance space it is clearly age, and in others it is clearly metallicity. I hope this holds up!

At the evening check-in session, Ruth Angus (Columbia) showed that, of Semyeong Oh's comoving pairs of stars that both have gyrochronology ages, they seem (usually) to show the same-ish age. It is early, but it looks like a possible confirmation of the effectiveness of the gyrochronology, possibly in parts of the H-R diagram where it hasn't been well tested previously.

After that, Vasily Belokurov (Cambridge) blew us all away by punking the Gaia DR1 uncertainty model to find time-variable sources in the billion-star catalog. He then found a bridge of variable stars connecting the LMC to the SMC! That made me afraid, very afraid.

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