Volume 595, November 2016
|Number of page(s)||10|
|Section||Galactic structure, stellar clusters and populations|
|Published online||28 October 2016|
Cannibals in the thick disk: the young α-rich stars as evolved blue stragglers
1 Institute of Astronomy, University of Cambridge, Madingley Road, CB3 0HA, Cambridge, UK
2 Núcleo de Astronomía, Facultad de Ingeniería, Universidad Diego Portales, Av. Ejército 441, Santiago, Chile
3 Institut d’Astronomie et d’Astrophysique, Université Libre de Bruxelles, Campus Plaine CP 226, Boulevard du Triomphe, 1050 Bruxelles, Belgium
4 Institute of Astronomy, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
5 Observatoire de Genève, Université de Genève, 1290 Versoix, Switzerland
Received: 20 July 2016
Accepted: 20 September 2016
Spectro-seismic measurements of red giants enabled the recent discovery of stars in the thick disk that are more massive than 1.4 M⊙. While it has been claimed that most of these stars are younger than the rest of the typical thick disk stars, we show evidence that they might be products of mass transfer in binary evolution, notably evolved blue stragglers. We took new measurements of the radial velocities in a sample of 26 stars from APOKASC, including 13 “young” stars and 13 “old” stars with similar stellar parameters but with masses below 1.2 M⊙ and found that more of the young starsappear to be in binary systems with respect to the old stars.Furthermore, we show that the young stars do not follow the expected trend of [C/H] ratios versus mass for individual stars. However, with a population synthesis of low-mass stars including binary evolution and mass transfer, we can reproduce the observed [C/N] ratios versus mass. Our study shows how asteroseismology of solar-type red giants provides us with a unique opportunity to study the evolution of field blue stragglers after they have left the main-sequence.
Key words: stars: evolution / blue stragglers / Galaxy: stellar content / binaries: general / binaries: spectroscopic
© ESO, 2016
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