@article{31e45e86f8f24a30930dc5b46404ad2b,
title = "Young [α/Fe]-enhanced stars discovered by CoRoT and APOGEE: What is their origin?",
abstract = "We report the discovery of a group of apparently young CoRoT red-giant stars exhibiting enhanced [α/Fe] abundance ratios (as determined from APOGEE spectra) with respect to solar values. Their existence is not explained bystandard 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 reliably obtained, although in smaller relative numbers. This might explain why these stars have not previously received attention. The young [α/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 because only CoRoGEE can explore the inner-disc regions and provide ages for its field stars. The kinematic properties of the young [α/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 than in other regions that are more frequently shocked by the passage of spiral arms. Moreover, this is where the mass return from older inner-disc stellar generations is expected to be highest (according to an inside-out disc-formation scenario), which additionally dilutes the in-situ gas. Other possibilities to explain these observations (e.g., a recent gas-accretion event) are also discussed.",
author = "C. Chiappini and F. Anders and Rodrigues, {T. S.} and A. Miglio and J. Montalb{\'a}n and B. Mosser and L. Girardi and M. Valentini and A. Noels and T. Morel and I. Minchev and M. Steinmetz and Santiago, {B. X.} and M. Schultheis and M. Martig and {Da Costa}, {L. N.} and Maia, {M. A.G.} and {Allende Prieto}, C. and {De Assis Peralta}, R. and S. Hekker and N. Theme{\ss}l and T. Kallinger and Garc{\'i}a, {R. A.} and S. Mathur and F. Baudin and Beers, {T. C.} and K. Cunha and P. Harding and J. Holtzman and S. Majewski and Sz M{\'e}sz{\'a}ros and D. Nidever and K. Pan and Schiavon, {R. P.} and Shetrone, {M. D.} and Schneider, {D. P.} and K. Stassun",
note = "Funding Information: The CoRoT space mission, launched on December 27 2006, was developed and operated by CNES, with the contribution of Austria, Belgium, Brazil, ESA (RSSD and Science Program), Germany and Spain. C.C. thanks A. Baglin, J. Storm and G. Cescutti for helpful discussions. T.S.R. acknowledges support from CNPq-Brazil. L.G. acknowledges support from PRIN INAF 2014. T.M. acknowledges financial support from Belspo for contract PRODEX Gaia-DPAC. S.M. acknowledges the support of the NASA grant NNX12AE17G. T.C.B. acknowledges partial support from grants PHY 08-22648; Physics Frontier Center/JINA, and PHY 14-30152; Physics Frontier Center/JINA Center for the Evolution of the Elements (JINA-CEE), awarded by the US National Science Foundation. The research leading to the presented results has received funding from the European Research Council under the European Community{\textquoteright}s Seventh Framework Programme (FP7/2007-2013) / ERC grant agreement No. 338251 (StellarAges). Funding for the SDSS-III Brazilian Participation Group has been provided by the Minist{\'e}rio de Ci{\^e}ncia e Tecnologia (MCT), Funda{\c c}{\~a}o Carlos Chagas Filho de Amparo {\`a} Pesquisa do Estado do Rio de Janeiro (FAPERJ), Conselho Nacional de Desenvolvimento Cient{\'i}fico e Tecnol{\'o}gico (CNPq), and Financiadora de Estudos e Projetos (FINEP). Funding for SDSS-III has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, and the US Department of Energy Office of Science. The SDSS-III web site is http://www.sdss3.org/ . SDSS-III is managed by the Astrophysical Research Consortium for the Participating Institutions of the SDSS-III Collaboration including the University of Arizona, the Brazilian Participation Group, Brookhaven National Laboratory, Carnegie Mellon University, University of Florida, the French Participation Group, the German Participation Group, Harvard University, the Instituto de Astrofisica de Canarias, the Michigan State/Notre Dame/JINA Participation Group, Johns Hopkins University, Lawrence Berkeley National Laboratory, Max Planck Institute for Astrophysics, Max Planck Institute for Extraterrestrial Physics, New Mexico State University, New York University, Ohio State University, Pennsylvania State University, University of Portsmouth, Princeton University, the Spanish Participation Group, University of Tokyo, University of Utah, Vanderbilt University, University of Virginia, University of Washington, and Yale University. Publisher Copyright: {\textcopyright} ESO, 2015.",
year = "2015",
month = apr,
day = "1",
doi = "10.1051/0004-6361/201525865",
language = "English (US)",
volume = "576",
journal = "Astronomy and Astrophysics",
issn = "0004-6361",
publisher = "EDP Sciences",
}