Mixed modes in red giants: a window on stellar evolution^⋆

¹ LESIA, CNRS, Université Pierre et Marie Curie, Université Denis Diderot, Observatoire de Paris, 92195 Meudon Cedex, France
e-mail: benoit.mosser@obspm.fr
² Department of Astronomy, The University of Tokyo, 113-033 Tokyo, Japan
³ School of Physics and Astronomy, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
⁴ GEPI, CNRS, Université Denis Diderot, Observatoire de Paris, 92195 Meudon Cedex, France
⁵ Sydney Institute for Astronomy, School of Physics, University of Sydney, Sydney NSW 2006, Australia
⁶ Université de Toulouse; UPS-OMP, CNRS, IRAP, 14 avenue Edouard Belin, 31400 Toulouse, France
⁷ Instituut voor Sterrenkunde, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
⁸ Institut d’Astrophysique et Géophysique de l’Université de Liège, Allée du six Août, 17, 4000 Liège, Belgium
⁹ Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, 8000 Aarhus C, Denmark
¹⁰ Institut für Astrophysik, Georg-August-Universität Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
¹¹ Institut de Physique de Rennes, Université de Rennes 1, CNRS (UMR 6251), 35042 Rennes, France
¹² Universita di Padova, Italy

Received: 22 September 2014
Accepted: 31 October 2014

Abstract

Context. The detection of oscillations with a mixed character in subgiants and red giants allows us to probe the physical conditions in their cores.

Aims. With these mixed modes, we aim at determining seismic markers of stellar evolution.

Methods. Kepler asteroseismic data were selected to map various evolutionary stages and stellar masses. Seismic evolutionary tracks were then drawn with the combination of the frequency and period spacings.

Results. We measured the asymptotic period spacing for 1178 stars at various evolutionary stages. This allows us to monitor stellar evolution from the main sequence to the asymptotic giant branch and draw seismic evolutionary tracks. We present clear quantified asteroseismic definitions that characterize the change in the evolutionary stages, in particular the transition from the subgiant stage to the early red giant branch, and the end of the horizontal branch.

Conclusions. The seismic information is so precise that clear conclusions can be drawn independently of evolution models. The quantitative seismic information can now be used for stellar modeling, especially for studying the energy transport in the helium-burning core or for specifying the inner properties of stars entering the red or asymptotic giant branches. Modeling will also allow us to study stars that are identified to be in the helium-subflash stage, high-mass stars either arriving or quitting the secondary clump, or stars that could be in the blue-loop stage.