Seismic evidence for near solid-body rotation in two Kepler subgiants and implications for angular momentum transport

Autor: Jérôme Ballot, Federico Spada, S. Deheuvels, J. W. den Hartogh, A. Noll, Patrick Eggenberger
Přispěvatelé: Institut de recherche en astrophysique et planétologie (IRAP), Institut national des sciences de l'Univers (INSU - CNRS)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Observatoire Midi-Pyrénées (OMP), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS), Observatoire Astronomique de l'Université de Genève (ObsGE), Université de Genève (UNIGE), School of Chemical and Physical Sciences [Keele], Keele University [Keele], Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), Université de Genève = University of Geneva (UNIGE), ANR-18-CE31-0001,BEAMING,Mieux comprendre l'évolution du moment cinétique dans les géantes rouges(2018)
Rok vydání: 2020
Předmět:
Zdroj: Astronomy & Astrophysics
Astronomy and Astrophysics-A&A
Astronomy and Astrophysics-A&A, EDP Sciences, 2020, 641, pp.A117. ⟨10.1051/0004-6361/202038578⟩
Astronomy and Astrophysics-A&A, 2020, 641, pp.A117. ⟨10.1051/0004-6361/202038578⟩
ISSN: 1432-0746
0004-6361
DOI: 10.1051/0004-6361/202038578
Popis: Asteroseismic measurements of the internal rotation of subgiants and red giants all show the need for invoking a more efficient transport of angular momentum than theoretically predicted. Constraints on the core rotation rate are available starting from the base of the red giant branch (RGB) and we are still lacking information on the internal rotation of less evolved subgiants. We identified two young Kepler subgiants, KIC8524425 and KIC5955122, whose mixed modes are clearly split by rotation. Using the full Kepler data set, we extracted the mode frequencies and rotational splittings for the two stars using a Bayesian approach. We then performed a detailed seismic modeling of both targets and used the rotational kernels to invert their internal rotation profiles. We found that both stars are rotating nearly as solid bodies, with core-envelope contrasts of $\Omega_{\rm g}/\Omega_{\rm p}=0.68\pm0.47$ for KIC8524425 and $0.72\pm0.37$ for KIC5955122. This result shows that the internal transport of angular momentum has to occur faster than the timescale at which differential rotation is forced in these stars (between 300 Myr and 600 Myr). By modeling the additional transport of angular momentum as a diffusive process with a constant viscosity $\nu_{\rm add}$, we found that values of $\nu_{\rm add}>5\times10^4$~cm$^2$.s$^{-1}$ are required to account for the internal rotation of KIC8524425, and $\nu_{\rm add}>1.5\times10^5$~cm$^2$.s$^{-1}$ for KIC5955122. These values are lower than or comparable to the efficiency of the core-envelope coupling during the main sequence, as given by the surface rotation of stars in open clusters. On the other hand, they are higher than the viscosity needed to reproduce the rotation of subgiants near the base of the RGB. Our results yield further evidence that the efficiency of the internal redistribution of angular momentum decreases during the subgiant phase.
Comment: Accepted in A&A, 16 pages, 11 figures
Databáze: OpenAIRE
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