Seismic constraints on the radial dependence of the internal rotation profiles of six Kepler subgiants and young red giants

S. Deheuvels (1) , G. Doğan (2, 3) , M. J. Goupil (4) , T. Appourchaux (5) , O. Benomar (6) , H. Bruntt (3) , T. L. Campante (7) , L. Casagrande (8) , T. Ceillier (9) , G. R. Davies (3, 9, 7) , P. de Cat (10) , J. N. Fu (11) , R. A. García (9) , A. Lobel (10) , B. Mosser (12, 4) , D. R. Reese (13) , C. Regulo (12) , J. Schou (14) , T. Stahn (15) , A. O. Thygesen (16) , X. H. Yang (11) , W. J. Chaplin (3, 7) , J. Christensen-Dalsgaard (3) , P. Eggenberger (17) , Laurent Gizon (14, 15) , S. Mathis (9) , J. Molenda-Żakowicz (18) , M. Pinsonneault (19)

1 IRAP - Institut de recherche en astrophysique et planétologie
2 HAO - High Altitude Observatory
3 SAC - Stellar Astrophysics Centre [Aarhus]
4 LESIA - Laboratoire d'études spatiales et d'instrumentation en astrophysique
5 IAS - Institut d'astrophysique spatiale
6 SIfA - Sydney Institute for Astronomy
7 School of Physics and Astronomy [Birmingham]
8 RSAA - Research School of Astronomy and Astrophysics [Canberra]
9 AIM (UMR7158 / UMR_E_9005 / UM_112) - Astrophysique Interprétation Modélisation
10 ROB - Royal Observatory of Belgium = Observatoire Royal de Belgique
11 BNU - Beijing Normal University
12 IAC - Instituto de Astrofisica de Canarias
13 Institut d'Astrophysique et de Géophysique [Liège]
14 MPS - Max-Planck-Institut für Sonnensystemforschung = Max Planck Institute for Solar System Research
15 Institut für Astrophysik [Göttingen]
16 ZAH - Zentrum für Astronomie der Universität Heidelberg
17 ObsGE - Observatoire Astronomique de l'Université de Genève
18 Instytut Astronomiczny Uniwersytetu Wrocławskiego
19 Departments of Astronomy and Chemistry, The Ohio State University

Context. We still do not understand which physical mechanisms are responsible for the transport of angular momentum inside stars. The recent detection of mixed modes that contain the clear signature of rotation in the spectra of Kepler subgiants and red giants gives us the opportunity to make progress on this question.Aims. Our aim is to probe the radial dependence of the rotation profiles for a sample of Kepler targets. For this purpose, subgiants and early red giants are particularly interesting targets because their rotational splittings are more sensitive to the rotation outside the deeper core than is the case for their more evolved counterparts.Methods. We first extracted the rotational splittings and frequencies of the modes for six young Kepler red giants. We then performed a seismic modeling of these stars using the evolutionary codes Cesam2k and astec. By using the observed splittings and the rotational kernels of the optimal models, we inverted the internal rotation profiles of the six stars.Results. We obtain estimates of the core rotation rates for these stars, and upper limits to the rotation in their convective envelope. We show that the rotation contrast between the core and the envelope increases during the subgiant branch. Our results also suggest that the core of subgiants spins up with time, while their envelope spins down. For two of the stars, we show that a discontinuous rotation profile with a deep discontinuity reproduces the observed splittings significantly better than a smooth rotation profile. Interestingly, the depths that are found to be most probable for the discontinuities roughly coincide with the location of the H-burning shell, which separates the layers that contract from those that expand.Conclusions. We characterized the differential rotation pattern of six young giants with a range of metallicities, and with both radiative and convective cores on the main sequence. This will bring observational constraints to the scenarios of angular momentum transport in stars. Moreover, if the existence of sharp gradients in the rotation profiles of young red giants is confirmed, it is expected to help in distinguishing between the physical processes that could transport angular momentum in the subgiant and red giant branches.

Mots clés: asteroseismology; stars: evolution; stars: interiors; stars: rotation

Domaines: Astrophysique [astro-ph]

S. Deheuvels, G. Doğan, M. J. Goupil, T. Appourchaux, O. Benomar, et al.. Seismic constraints on the radial dependence of the internal rotation profiles of six Kepler subgiants and young red giants. Astronomy and Astrophysics - A&A, 2014, 564, pp.A27. ⟨10.1051/0004-6361/201322779⟩. ⟨cea-01236278⟩