Nearly uniform internal rotation of solar-like main-sequence stars revealed by space-based asteroseismology and spectroscopic measurements

Benomar, O.; Takata, Masasuke; Shibahashi, Hiromoto; Ceillier, T.; García, R. A.

doi:10.1093/mnras/stv1493

Cited by 108 publications

(149 citation statements)

References 87 publications

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“…This is justified, following the indications given by helio-and asteroseismology that low-mass and intermediate stars could be solid-body rotators on the main sequence (e.g. Kurtz et al 2014;Benomar et al 2015;Murphy et al 2016). In this case, the rotational mixing that develops beyond the Terminating Age Main Sequence (TAMS) in the radiative interior leads to a decrease of the surface lithium abundance prior to the FDU, and the predicted A(Li) for the secondary is smaller than the observed one.…”

Section: Lithium Abundance and Rotational Mixingmentioning

confidence: 83%

Seismic probing of the first dredge-up event through the eccentric red-giant and red-giant spectroscopic binary KIC 9163796

Beck

Kallinger

Pavlovski

et al. 2018

A&A

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Context. Binaries in double-lined spectroscopic systems (SB2) provide a homogeneous set of stars. Differences of parameters, such as age or initial conditions, which otherwise would have strong impact on the stellar evolution, can be neglected. The observed differences are determined by the difference in stellar mass between the two components. The mass ratio can be determined with much higher accuracy than the actual stellar mass. Aims. In this work, we aim to study the eccentric binary system KIC 9163796, whose two components are very close in mass and both are low-luminosity red-giant stars. Methods. We analyse four years of Kepler space photometry and we obtained high-resolution spectroscopy with the Hermes instrument. The orbital elements and the spectra of both components were determined using spectral disentangling methods. The effective temperatures, and metallicities were extracted from disentangled spectra of the two stars. Mass and radius of the primary were determined through asteroseismology. The surface rotation period of the primary is determined from the Kepler light curve. From representative theoretical models of the star, we derived the internal rotational gradient, while for a grid of models, the measured lithium abundance is compared with theoretical predictions. Results. From seismology the primary of KIC 9163796 is a star of 1.39±0.06 M ⊙ , while the spectroscopic mass ratio between both components can be determined with much higher precision by spectral disentangling to be 1.015±0.005. With such mass and a difference in effective temperature of 600 K from spectroscopy, the secondary and primary are, respectively, in the early and advanced stage of the first dredge-up event on the red-giant branch. The period of the primary's surface rotation resembles the orbital period within 10 days.The radial rotational gradient between the surface and core in KIC 9163796 is found to be 6.9 +2.0 −1.0 . This is a low value but not exceptional if compared to the sample of typical single field stars. The seismic average of the envelope's rotation agrees with the surface rotation rate. The lithium abundance is in agreement with quasi rigidly-rotating models. Conclusions. The agreement between the surface rotation with the seismic result indicates that the full convective envelope is rotating quasi-rigidly. The models of the lithium abundance are compatible with a rigid rotation in the radiative zone during the main sequence. Because of the many constraints offered by oscillating stars in binary systems, such objects are important test beds of stellar evolution.

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Section: Lithium Abundance and Rotational Mixingmentioning

confidence: 83%

Seismic probing of the first dredge-up event through the eccentric red-giant and red-giant spectroscopic binary KIC 9163796

Beck

Kallinger

Pavlovski

et al. 2018

A&A

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“…Previous analyses conducted on young open clusters did not find evidence of stellar-spin alignment 5 . Asteroseismology, the study of stellar oscillations, has proven to be a powerful tool to obtain model-independent information on the inclination angle of the stellar angular momentum vector, especially for red giant stars 7,8,10,11 . Red giants are typically low-and intermediate-mass stars that have evolved off the main sequence of the stellar evolution.…”

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confidence: 99%

Spin alignment of stars in old open clusters

et al. 2017

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Stellar clusters form by gravitational collapse of turbulent molecular clouds, with up to several thousand stars per cluster 1 . They are thought to be the birthplace of most stars and therefore play an important role in our understanding of star formation, a fundamental problem in astrophysics 2, 3 . The initial conditions of the molecular cloud establish its dynamical history until the stellar cluster is born. However, the evolution of the cloud's angular momentum during cluster formation is not well understood 4 . Current observations have suggested that turbulence scrambles the angular momentum of the cluster-forming cloud, preventing spin alignment amongst stars within a cluster 5 . Here we use asteroseismology [6][7][8] to measure the inclination angles of spin axes in 48 stars from the two old open clusters NGC 6791 and NGC 6819. The stars within each cluster show strong alignment. Threedimensional hydrodynamical simulations of proto-cluster formation show that at least 50% of the initial proto-cluster kinetic energy has to be rotational in order to obtain strong stellarspin alignment within a cluster. Our result indicates that the global angular momentum of the cluster-forming clouds was efficiently transferred to each star and that its imprint has survived after several gigayears since the clusters formed. About half of the overall star formation in the Milky Way is occurring in the 24 most massive giant molecular clouds 1 . The star forming regions are obscured by dust, hence direct observations are limited to the infrared and radio bands 2,3 . However, open clusters can be studied in a broad range of wavelengths because they contain small amounts of interstellar gas and dust. The great advantage of studying stars in a cluster -as opposed to field stars that often originate from dissolved small stellar systems -is that they can preserve the signature of the initial conditions of the progenitor molecular cloud.It is believed that molecular clouds satisfying the Jeans instability undergo gravitational fragmentation in which the internal motions are strongly influenced by turbulence 4,9 . This suggests that the angular momentum from the progenitor cloud cannot leave any significant imprint of its action on the stars born in the cluster. However, if the stars inherit the physical properties of the molecular cloud, they should to some extent reflect its average angular momentum. To investigate the angular momentum imprint, requires measurements of the space orientation of the stellar-spin axis. Previous analyses conducted on young open clusters did not find evidence of stellar-spin alignment 5 . Asteroseismology, the study of stellar oscillations, has proven to be a powerful tool to obtain model-independent information on the inclination angle of the stellar angular momentum vector, especially for red giant stars 7,8,10,11 . Red giants are typically low-and intermediate-mass stars that have evolved off the main sequence of the stellar evolution. Most red giants oscillate and their oscillations can be analyz...

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“…In solar-like stars, knowledge of magnetic field in radiative core is important even if it is buried under the dynamo field. Indeed it is a candidate for the transport of angular momentum in the stellar core that can explain the rotation profile observed by helio-and asterioseismology (Schou et al 1998;García et al 2007;Benomar et al 2015). These magnetic fields left by a convective zone in a stably stratified zone are called fossil fields.…”

Section: Stellar Evolution and Magnetismmentioning

confidence: 99%

Origin and Evolution of Magnetic Field in PMS Stars: Influence of Rotation and Structural Changes

Emeriau-Viard

Brun

2017

ApJ

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During stellar evolution, especially in the PMS, stellar structure and rotation evolve significantly causing major changes in the dynamics and global flows of the star. We wish to assess the consequences of these changes on stellar dynamo, internal magnetic field topology and activity level. To do so, we have performed a series of 3D HD and MHD simulations with the ASH code. We choose five different models characterized by the radius of their radiative zone following an evolutionary track computed by a 1D stellar evolution code. These models characterized stellar evolution from 1 Myr to 50 Myr. By introducing a seed magnetic field in the fully convective model and spreading its evolved state through all four remaining cases, we observe systematic variations in the dynamical properties and magnetic field amplitude and topology of the models. The five MHD simulations develop strong dynamo field that can reach equipartition state between the kinetic and magnetic energy and even superequipartition levels in the faster rotating cases. We find that the magnetic field amplitude increases as it evolves toward the ZAMS. Moreover the magnetic field topology becomes more complex, with a decreasing axisymmetric component and a non-axisymmetric one becoming predominant. The dipolar components decrease as the rotation rate and the size of the radiative core increase. The magnetic fields possess a mixed poloidal-toroidal topology with no obvious dominant component. Moreover the relaxation of the vestige dynamo magnetic field within the radiative core is found to satisfy MHD stability criteria. Hence it does not experience a global reconfiguration but slowly relaxes by retaining its mixed stable poloidal-toroidal topology.

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Nearly uniform internal rotation of solar-like main-sequence stars revealed by space-based asteroseismology and spectroscopic measurements

Cited by 108 publications

References 87 publications

Seismic probing of the first dredge-up event through the eccentric red-giant and red-giant spectroscopic binary KIC 9163796

Seismic probing of the first dredge-up event through the eccentric red-giant and red-giant spectroscopic binary KIC 9163796

Spin alignment of stars in old open clusters

Origin and Evolution of Magnetic Field in PMS Stars: Influence of Rotation and Structural Changes

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