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What will Gaia tell us about the Galactic disk?

Published online by Cambridge University Press:  01 June 2008

Coryn A. L. Bailer-Jones
Coryn A. L. Bailer-Jones*
Affiliation:
Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany email: calj@mpia.de
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Abstract

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Gaia will provide parallaxes and proper motions with accuracy ranging from 10 to 1000 microarcsecond on up to one billion stars. Most of these will be disk stars: for an unreddened K giant at 6 kpc, it will measure the distance accurate to 2% and the transverse velocity to an accuracy of about 1 km/s. Gaia will observe tracers of Galactic structure, kinematics, star formation and chemical evolution across the whole HR diagram, including Cepheids, RR Lyrae, white dwarfs, F dwarfs and HB stars. Onboard low resolution spectrophotometry will permit – in addition to an effective temperature estimate – dwarf/giant discrimination, metallicity measurement and extinction determination. For the first time, then, Gaia will provide us with a three-dimensional spatial/properties map and at least a two-dimensional velocity map of these tracers. (3D velocities will be obatined for the brighter sources from the onboard RV spectrograph). This will be a goldmine of information from which to learn about the origin and evolution of the Galactic disk. I briefly review the Gaia mission, and then show how the expected astrometric accuracies translate into distance and velocity accuracies and statistics. I then briefly examine the impact Gaia should have on a few scientific areas relevant to the Galactic disk, specifically disk structure and formation, the age–metallicity–velocity relation, the mass–luminosity relation, stellar clusters and spiral structure. Concerning spiral arms, I note how a better determination of their locations and pattern speed from their OB star population, plus a better reconstruction of the Sun's orbit over the past billion years (from integration through the Gaia-measured gravitational potential) will allow us to assess the possible role of spiral arm crossings in ice ages and mass extinctions on the Earth.

Keywords

space vehiclestelescopesastrometrystars: generalGalaxy: structurestellar contentspiral armsice ages and mass extinctions
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 4 , Issue S254: The Galaxy Disk in Cosmological Context , June 2008 , pp. 475 - 482
Copyright
Copyright © International Astronomical Union 2009

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