#GaiaDR1 zero-day

Today (at 06:30 New York time) Gaia released it's DR1 data, and in particular the T-GAS sample of stars with five-parameter solutions and photometry. What a great day it was! I assembled with Kathryn Johnston (Columbia), David Spergel (Princeton), Adrian Price-Whelan (Princeton), Ruth Angus (Columbia), Keith Hawkins (Columbia), and others to get, play with, and make figures from the new data. Many amusing things happened, and this blog post will not capture them all.

Hawkins immediately plotted the velocity distribution of disk stars in the U-V plane, using the overlap between T-GAS and RAVE. He confirms the velocity structure Bovy, Roweis, and I predicted based on (clever, if I say so myself) de-projections of the Hipparcos data. Right as we were looking at this, Bovy tweeted the same thing. Hawkins has access to our RAVE-on data with detailed abundances, so he can show that the velocity structures are chemically inhomogeneous; the questions that are easy to ask are: Are they all inhomogeneous in the same ways, or are there differences? And can we see any spatial dependence within T-GAS of the velocity structure? He moved on to looking at the candle-standardness of the red clump.

Andy Casey (Cambridge), working remotely, made temperature-magnitude diagrams for the RAVE-on sample. I asked him to show what happens as you harden the cut on the parallax signal-to-noise (parallax over parallax uncertainty). He tweeted the answer. It really looks like we might be able to use Gaia to build a completely data-driven model of all aspects of stars.

Price-Whelan and I looked at various things. We started by trying to see if there is vertical velocity structure in the nearby disk that might show evidence for disk warping, or horizontal velocity structure that might look like spiral arm perturbations. The figures are confusing! There seems to be a very cold bubble around the Sun in the Galactocentric U velocity, which is odd. After spending lots of time confused about that, we looked for very wide separation binary stars, and we see lots! Indeed, it looks like we have evidence for binaries with separations larger than 1 pc! That's worth following up, especially if we have any overlapping spectra. Finally, Price-Whelan also showed that the Kepler-identified transiting exoplanet host stars are all on disk orbits; that is, we don't have (yet) any halo exoplanets. But these are early days!

That's just a tiny slice of the things we started to think about and play with. It is the beginning of a new era. Thank you to the Gaia Mission and all the people who gave years of their professional and scientific lives to this project.

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