Young alpha-rich stars in the Galaxy from K2

We investigated young {alpha}-rich stars in different parts of the Galaxy and we find that the fraction of young {alpha}-rich stars remains constant with respect to the number of high-{alpha} stars at ~10%. Furthermore, young {alpha}-rich stars have kinematic and chemical properties similar to high-{alpha} stars, except for [C/N] ratios. Thanks to our new K2 sample, we conclude that young {alpha}-rich stars have similar occurrence rates in different parts of the Galaxy, and that they share properties similar to the normal high-{alpha} population, except for [C/N] ratios.

This suggests that these stars are not genuinely young, but are products of binary evolution, and mergers or mass accretion. Under that assumption, we find the fraction of these stars in the field to be similar to that found recently in clusters. This suggests that ~10% of the low-{alpha} field stars could also have their ages underestimated by asteroseismology.

This should be kept in mind when using asteroseismic ages to interpret results in Galactic archaeology.