Young [α/Fe]-enhanced stars discovered by CoRoT and APOGEE: What is their origin?

Author(s): C. Chiappini, F. Anders, T. S. Rodrigues, A. Miglio, J. Montalbán, B. Mosser, L. Girardi, M. Valentini, A. Noels, T. Morel, I. Minchev, M. Steinmetz, B. X. Santiago, M. Schultheis, M. Martig, L. N. da Costa, M. A. G. Maia, C. Allende Prieto, R. de Assis Peralta, S. Hekker, N. Themeßl, T. Kallinger, R. A. García, S. Mathur, F. Baudin, T. C. Beers, K. Cunha, P. Harding, J. Holtzman, S. Majewski, Sz. Mészáros, D. Nidever, K. Pan, R. P. Schiavon, M. D. Shetrone, D. P. Schneider, K. Stassun
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.
Appendix A is available in electronic form at www.aanda.org
Organisation(s): Department of Astrophysics
External organisation(s): Leibniz-Institut für Astrophysik Potsdam, Laboratório Interinstitucional de e-Astronomia (LIneA), Osservatorio Astronomico, University of Padova, University of Birmingham, Université de recherche Paris Sciences et Lettres, Université de Liège, Universidade Federal do Rio Grande do Sul, Laboratoire Joseph-Louis Lagrange , Max-Planck-Institut für Astronomie, Observatório Nacional/MCT, Institute of Astrophysics of the Canary Islands, University of La Laguna, Max Planck Institute for Solar System Research, Aarhus University, Université Paris VII - Paris-Diderot, Space Science Institute, Université Paris XI - Paris-Sud, University of Notre Dame, Case Western Reserve University, New Mexico State University, University of Virginia, Eötvös Loránd University Budapest, Indiana University Bloomington, University of Michigan, Apache Point Observatory, Liverpool John Moores University (LJMU), University of Texas, Austin, Pennsylvania State University, Vanderbilt University
Journal: Astronomy & Astrophysics
Volume: 576
No. of pages: 7
ISSN: 0004-6361
DOI: https://doi.org/10.1051/0004-6361/201525865
Publication date: 04-2015
Peer reviewed: Yes
Austrian Fields of Science 2012: 103003 Astronomy, 103004 Astrophysics
Keywords
ASJC Scopus subject areas: Astronomy and Astrophysics, Space and Planetary Science
Portal url: https://ucrisportal.univie.ac.at/en/publications/young-feenhanced-stars-discovered-by-corot-and-apogee-what-is-their-origin(75808eea-7f00-409a-b473-ab3ce00fbc68).html

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