Seismic Evidence for a Rapidly Rotating Core in a Lower-giant-branch Star Observed with Kepler
Sébastien Deheuvels
(1, 2, 3)
,
Rafael A. Garcia
(4, 5)
,
William J. Chaplin
(4)
,
Sarbani Basu
(1)
,
H. M. Antia
(6)
,
Thierry Appourchaux
(7)
,
Othman Benomar
(8)
,
Guy R. Davies
(5)
,
Yvonne P. Elsworth
(9)
,
Laurent Gizon
(10)
,
Marie-José Goupil
(2, 3)
,
Daniel Reese
(11, 2, 3)
,
Clara Regulo
(12)
,
Jesper Schou
(13)
,
T. Stahn
(10)
,
Luca Casagrande
(14)
,
Jörgen Christensen-Dalsgaard
(15)
,
D. Fischer
(1)
,
Saskia Hekker
(16)
,
Hans Kjeldsen
(15)
,
Savita Mathur
(17)
,
Benoît Mosser
(2, 3)
,
Marc H. Pinsonneault
(4)
,
J. Valenti
(18)
,
Jessie L. Christiansen
(19)
,
Karen Kinemuchi
(20)
,
Fergal Mullally
(19)
1
Department of Astronomy, Yale University
2 LESIA - Laboratoire d'études spatiales et d'instrumentation en astrophysique
3 Etoile
4 Kavli Institute for Theoretical Physics and Department of Physics, University of California
5 CEA - Commissariat à l'énergie atomique et aux énergies alternatives
6 TIFR - Tata Institute of Fundamental Research
7 IAS - Institut d'astrophysique spatiale
8 SIfA - Sydney Institute for Astronomy
9 School of Physics and Astronomy, University of Birmingham
10 Georg-August-University = Georg-August-Universität Göttingen
11 Institut d'Astrophysique, Géophysique et Océanographie, Université de Liège
12 IAC - Instituto de Astrofisica de Canarias
13 W.W. Hansen Experimental Physics Laboratory, Stanford University
14 Mount Stromlo Observatory, Australian National University
15 DASC - Danish AsteroSeismology Centre
16 AI PANNEKOEK - Astronomical Institute Anton Pannekoek
17 High Altitude Observatory, National Center for Atmospheric Research
18 STScI - Space Telescope Science Institute
19 SETI Institute, NASA Ames Research Center, Moffett Field
20 BAER - Bay Area Environmental Research Institute
2 LESIA - Laboratoire d'études spatiales et d'instrumentation en astrophysique
3 Etoile
4 Kavli Institute for Theoretical Physics and Department of Physics, University of California
5 CEA - Commissariat à l'énergie atomique et aux énergies alternatives
6 TIFR - Tata Institute of Fundamental Research
7 IAS - Institut d'astrophysique spatiale
8 SIfA - Sydney Institute for Astronomy
9 School of Physics and Astronomy, University of Birmingham
10 Georg-August-University = Georg-August-Universität Göttingen
11 Institut d'Astrophysique, Géophysique et Océanographie, Université de Liège
12 IAC - Instituto de Astrofisica de Canarias
13 W.W. Hansen Experimental Physics Laboratory, Stanford University
14 Mount Stromlo Observatory, Australian National University
15 DASC - Danish AsteroSeismology Centre
16 AI PANNEKOEK - Astronomical Institute Anton Pannekoek
17 High Altitude Observatory, National Center for Atmospheric Research
18 STScI - Space Telescope Science Institute
19 SETI Institute, NASA Ames Research Center, Moffett Field
20 BAER - Bay Area Environmental Research Institute
Résumé
Rotation is expected to have an important influence on the structure and the evolution of stars. However, the mechanisms of angular momentum transport in stars remain theoretically uncertain and very complex to take into account in stellar models. To achieve a better understanding of these processes, we desperately need observational constraints on the internal rotation of stars, which until very recently was restricted to the Sun. In this paper, we report the detection of mixed modes---i.e., modes that behave both as g modes in the core and as p modes in the envelope---in the spectrum of the early red giant KIC 7341231, which was observed during one year with the Kepler spacecraft. By performing an analysis of the oscillation spectrum of the star, we show that its non-radial modes are clearly split by stellar rotation and we are able to determine precisely the rotational splittings of 18 modes. We then find a stellar model that reproduces very well the observed atmospheric and seismic properties of the star. We use this model to perform inversions of the internal rotation profile of the star, which enables us to show that the core of the star is rotating at least five times faster than the envelope. This will shed new light on the processes of transport of angular momentum in stars. In particular, this result can be used to place constraints on the angular momentum coupling between the core and the envelope of early red giants, which could help us discriminate between the theories that have been proposed over the last few decades.