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

Abstract

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 ${\Omega }_{\mathrm{g}}/{\Omega }_{\mathrm{p}}=0.68\pm 0.47$ for KIC8524425 and $0.72\pm 0.37$ 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 ${\nu }_{\mathrm{add}}$, we found that values of ${\nu }_{\mathrm{add}}>5\times 10^4$~cm${}^2$.s${}^{-1}$ are required to account for the internal rotation of KIC8524425, and ${\nu }_{\mathrm{add}}>1.5\times 10^5$~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.

Accepted in A&A, 16 pages, 11 figures

References in corpus (28)

• ADIPLS -- the Aarhus adiabatic oscillation package
• Slowing the Spins of Stellar Cores
• The Mass-Dependence of Angular Momentum Evolution in Sun-Like Stars
• The connection between stellar granulation and oscillation as seen by the Kepler mission
• Asteroseismic measurement of surface-to-core rotation in a main sequence A star, KIC 11145123
• A new correction of stellar oscillation frequencies for near-surface effects
• YREC: The Yale Rotating Stellar Evolution Code
• Mixed modes in red giants: a window on stellar evolution
• Angular Momentum Transport via Internal Gravity Waves in Evolving Stars
• Asymptotic g modes: Evidence for a rapid rotation of the solar core
• Constraining the efficiency of angular momentum transport with asteroseismology of red giants: the effect of stellar mass
• Synthetic Stellar Photometry - II. Testing the bolometric flux scale, and tables of bolometric corrections for the Hipparcos/Tycho, Pan-STARRS1, SkyMapper and JWST systems
• Angular momentum redistribution by mixed modes in evolved low-mass stars. II. Spin-down of the core of red giants induced by mixed modes
• Asteroseismology of evolved stars to constrain the internal transport of angular momentum II. Test of a revised prescription for transport by the Tayler instability
• Can plume-induced internal gravity waves regulate the core rotation of subgiant stars?
• Asteroseismology of evolved stars to constrain the internal transport of angular momentum. I. Efficiency of transport during the subgiant phase
• Damping rates of solar-like oscillations across the HR diagram. Theoretical calculations confronted to CoRoT and Kepler observations
• The angular momentum transport by unstable toroidal magnetic fields
• Near-degeneracy effects on the frequencies of rotationally-split mixed modes in red giants
• Asteroseismology of 36 Kepler subgiants -- II: Determining ages from detailed modelling
• Asteroseismology of 36 \emph{Kepler} subgiants -- I. Oscillation frequencies, linewidths and amplitudes
• 3D evolution of magnetic fields in a differentially rotating stellar radiative zone
• Magnetic braking of stellar cores in red giants and supergiants
• Asteroseismology of evolved stars to constrain the internal transport of angular momentum. III. Using the rotation rates of intermediate-mass stars to test the Fuller-formalism
• Constraining transport of angular momentum in stars: Combining asteroseismic observations of core helium burning stars and white dwarfs
• Searching for g modes: Part II. Unconfirmed g-mode detection in the power spectrum of the time series of round-trip travel time
• Some glimpses from helioseismology at the dynamics of the deep solar interior
• Magnetic activity, differential rotation and dynamo action in the pulsating F9IV star KIC 5955122

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