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TOwards Understanding the sPIn Evolution of Stars – TOUPIES

TOUPIES: TOwards Understanding the sPIn Evolution fo Stars

The goal of the TOUPIES project is to characterize and model the evolution of the rotation rates of solar-type and low-mass stars from birth to maturity.

Measuring and modeling the evolution of spin rates in low-mass stars

While the major physical processes impacting on the rotational evolution of solar-type stars are probably identified (magnetized winds, star-disk interaction, internal transport of angular momentum), none is fully understood yet, and few are properly included in stellar evolutionary models. The goal of the present project is to gain a better understanding of the physical processes at play in the rotational evolution of solar-type stars (stellar dynamos, disk accretion, magnetic winds, angular momentum transport, chemical mixing, etc.) and to include them in a new generation of stellar models whose predictions can be tested against accurate observational constraints. The latter will be obtained in the course of the project, by measuring the rotation rates of hundreds of low-mass stars at various stages of evolution, from birth to the age of the Sun. Because magnetic field is a central ingredient to many of the physical processes that control rotational evolution (stellar winds, star-disk interaction, core-envelope coupling), a major effort will be devoted to measure the surface magnetic field of solar-type stars at all stages of evolution. Finally, lithium content provides a unique window to internal angular momentum transport processes, such as chemical mixing resulting from hydro-dynamical instabilities. The derivation of rotation rates, magnetic properties, and lithium abundances will provide the most complete and stringent set of observational constraints that will be used to confront the predictions of a new generation of angular momentum evolution models.

We will perform long-term photometric monitoring of several young open clusters in order to derive the distribution of rotation rates of their low-mass members. In parallel, long-term spectropolarimetric monitoring of young Suns will provide clues to their magnetic properties, while their lithium content will be derived from high resolution spectroscopy. On the modeling part, the goal is to include in a new generation of rotating stellar models all the important physical processes, namely magnetic braking by stellar winds, star-disk magnetic interaction, internalangular momentum trasnport by instabilities and gravity waves.

The first distributions of rotation in young clusters were obtained, as well as the characterization of the magnetic fields of several young Suns. The semi-empirical models today can reproduce all the observations and more physical models begin to include the transport of angular momentum by gravity waves.

The goal remains to include all relevant physical processes into rotating stellar models. Additional observations of rotation and magnetism will help constraint these models. As internal gravity waves start to be included, we shall also focus o the physics of the star-disk interaction that drvies the angular momentum evolution of very young stars.


Part of 2013 Publication (see ipag.osug.fr/Anr_Toupies/ for a complete list)


Ferreira, J.\ 2013.\ Braking down an accreting protostar : disc-locking, disc winds, stellar winds, X-winds and Magnetospheric Ejecta.\ EAS Publications Series 62, 169-225.

Bouvier, J., Matt, S. P., Mohanty, S., Scholz, A., Stassun, K. G., Zanni, C.\ 2013.\ Angular momentum evolution of young low-mass stars and brown dwarfs : observations and theory.\ ArXiv e-prints arXiv:1309.7851.

Bouvier, J.\ 2013.\ Observational studies of stellar rotation.\ EAS Publications Series 62, 143-168.

Palacios, A.\ 2013.\ Influence of Rotation on Stellar Evolution.\ EAS Publications Series 62, 227-287.

Moraux, E., and 11 colleagues 2013.\ The Monitor Project : Stellar rotation at 13\ Myr : I. A photometric monitoring survey of the young open cluster h\ Per.\ ArXive-prints arXiv:1306.6351.

Gallet, F., Bouvier, J.\ 2013.\ Improved angular momentum evolution model for solar-like stars.\ Astronomy and Astrophysics 556, A36.

Pinto, R. F., Brun, A. S.\ 2013.\ Flux Emergence in a Magnetized Convection Zone.\ The Astrophysical Journal 772, 55.

Charbonnel, C., Decressin, T., Amard, L., Palacios, A., Talon, S.\ 2013.\ Impact of internal gravity waves on the rotation profile inside pre-main sequence low-mass stars.\ Astronomy and Astrophysics 554, A40.

Affer, L., Micela, G., Favata, F., Flaccomio, E., Bouvier, J.\ 2013.\ Rotation in NGC 2264 : a study based on CoRoT photometric observations.\ Monthly Notices of the Royal Astronomical Society 430, 1433-1446.

Strugarek, A., Brun, A. S., Mathis, S., Sarazin, Y.\ 2013.\ Magnetic Energy Cascade in Spherical Geometry. I. The Stellar Convective Dynamo Case.\ The Astrophysical Journal 764, 189.


Zanni, C., Ferreira, J.\ 2013.\ MHD simulations of accretion onto a dipolar magnetosphere. II. Magnetospheric ejections and stellar spin-down.\ Astronomy and Astrophysics 550, A99.

Understanding the angular momentum evolution of solar-type stars is one of the toughest remaining challenges of modern stellar astrophysics. During birth, from pre-stellar cores to proto-stars, the angular momentum is reduced by 4 orders of magnitude, probably evacuated by powerful magnetically-driven jets and outflows. During pre-main sequence evolution, the magnetic interaction between the young star and its accretion disk appears to dictate its rotational evolution, preventing it from spinning up, even though the star contracts toward the main sequence and gains angular momentum from disk accretion. At the arrival on the main sequence, the largest dispersion is observed in the rotation rates of solar-type stars, with rotational velocities ranging from less than 10 km/s to more than 200 km/s. A few billions years later, by the age of the Sun, rotational velocities rarely exceed a few km/s, and the initial dispersion has decreased to a mere few percent. The rotational spin down experienced by low mass stars on the main sequence is thought to result from the braking effect of magnetically-driven winds. While the major physical processes impacting on the rotational evolution of solar-type stars are probably identified (magnetized winds, star-disk interaction, internal transport of angular momentum), none is fully understood yet, and few are properly included in stellar evolutionary models. The goal of the present project is to gain a better understanding of the physical processes at play in the rotational evolution of solar-type stars (stellar dynamos, disk accretion, magnetic winds, angular momentum transport, chemical mixing, etc.) and to include them in a new generation of stellar models whose predictions can be tested against accurate observational constraints. The latter will be obtained in the course of the project, by measuring the rotation rates of hundreds of low-mass stars at various stages of evolution, from birth to the age of the Sun. Because magnetic field is a central ingredient to many of the physical processes that control rotational evolution (stellar winds, star-disk interaction, core-envelope coupling), a major effort will be devoted to measure the surface magnetic field of solar-type stars at all stages of evolution. Finally, lithium content provides a unique window to internal angular momentum transport processes, such as chemical mixing resulting from hydro-dynamical instabilities. The derivation of rotation rates, magnetic properties, and lithium abundances will provide the most complete and stringent set of observational constraints that will be used to confront the predictions of a new generation of angular momentum evolution models.

Project coordination

Jérome BOUVIER (CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE - DELEGATION REGIONALE RHONE-ALPES SECTEUR ALPES) – Jerome.Bouvier@univ-grenoble-alpes.fr

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

LUPM CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE - DELEGATION REGIONALE LANGUEDOC-ROUSSILLON
IPAG CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE - DELEGATION REGIONALE RHONE-ALPES SECTEUR ALPES
IRAP UNIVERSITE TOULOUSE III [PAUL SABATIER]
CEA/IRFU/AIM COMMISSARIAT A L'ENERGIE ATOMIQUE ET AUX ENERGIES ALTERNATIVES - CENTRE D'ETUDES NUCLEAIRES SACLAY

Help of the ANR 469,946 euros
Beginning and duration of the scientific project: December 2011 - 48 Months

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