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Stellar population synthesis based modelling of the Milky Way using asteroseismology of 13000 Kepler red giants.
Sanjib Sharma (University Of Sydney), Dennis Stello (University Of Sydney), Joss Bland-Hawthorn (University Of Sydney), Daniel Huber (University Of Sydney), Tim Bedding (University Of Sydney)
With current space-based missions it is now possible to obtain age-sensitive asteroseismic information for tens of thousands of red giants. This provides a promising opportunity to study the Galactic structure and evolution. We use asteroseismic data of red giants, observed by Kepler, to test the current theoretical framework of modelling the Galaxy based on population synthesis modeling and the use of asteroseismic scaling relations for giants. We use the open source code Galaxia to model the Milky Way and find the distribution of the masses predicted by Galaxia to be systematically offset with respect to the seismically-inferred observed masses. The Galactic model overestimates the number of low mass stars, and these stars are predominantly old and of low metallicity. Using corrections to the Δν scaling relation suggested by stellar models significantly reduces the disagreement between predicted and observed masses. For a few cases where non-seismic mass estimates are available, the corrections to Δν also improve the agreement between seismic and non-seismic mass estimates. Altering the star formation rate in order to suppress stars older than 10 Gyr improves the agreement for mass but leads to inconsistent color distributions. We conclude that either the scaling relations and/or the Galactic models need to be revised to reconcile predictions of theory with asteroseismic observations.