Galactic archaeology: mapping and dating stellar populations with
  asteroseismology of red-giant stars
  Our understanding of how the Galaxy was formed and evolves is severely
hampered by the lack of precise constraints on basic stellar properties such as
distances, masses, and ages. Here, we show that solar-like pulsating red giants
represent a well-populated class of accurate distance indicators, spanning a
large age range, which can be used to map and date the Galactic disc in the
regions probed by observations made by the CoRoT and Kepler space telescopes.
When combined with photometric constraints, the pulsation spectra of such
evolved stars not only reveal their radii, and hence distances, but also
provide well-constrained estimates of their masses, which are reliable proxies
for the ages of the stars. As a first application we consider red giants
observed by CoRoT in two different parts of the Milky Way, and determine
precise distances for ~2000 stars spread across nearly 15,000 pc of the
Galactic disc, exploring regions which are a long way from the solar
neighbourhood. We find significant differences in the mass distributions of
these two samples which, by comparison with predictions of synthetic models of
the Milky Way, we interpret as mainly due to the vertical gradient in the
distribution of stellar masses (hence ages) in the disc. In the future, the
availability of spectroscopic constraints for this sample of stars will not
only improve the age determination, but also provide crucial constraints on
age-velocity and age-metallicity relations at different Galactocentric radii
and heights from the plane.
