Young [$\alpha$/Fe]-enhanced stars discovered by CoRoT and APOGEE: What
  is their origin?
  We report the discovery of a group of apparently young CoRoT red-giant stars
exhibiting enhanced [alpha/Fe] abundance ratios (as determined from APOGEE
spectra) with respect to Solar values. Their existence is not explained by
standard chemical evolution models of the Milky Way, and shows that the
chemical-enrichment history of the Galactic disc is more complex. We find
similar stars in previously published samples for which isochrone-ages could be
robustly obtained, although in smaller relative numbers, which could explain
why these stars have not received prior attention. The young [alpha/Fe]-rich
stars are much more numerous in the CoRoT-APOGEE (CoRoGEE) inner-field sample
than in any other high-resolution sample available at present, as only CoRoGEE
can explore the inner-disc regions and provide ages for its field stars. The
kinematic properties of the young [$\alpha$/Fe]-rich stars are not clearly
thick-disc like, despite their rather large distances from the Galactic
mid-plane. Our tentative interpretation of these and previous intriguing
observations in the Milky Way is that these stars were formed close to the end
of the Galactic bar, near corotation -- a region where gas can be kept inert
for longer times, compared to other regions shocked more frequently by the
passage of spiral arms. Moreover, that is where the mass return from older
inner-disc stellar generations should be maximal (according to an inside-out
disc-formation scenario), further diluting the in-situ gas. Other possibilities
to explain these observations (e.g., a recent gas-accretion event) are also
discussed.
