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IPAG
IRAP
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Présentation

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ANR Toupies : "TOwards Understanding the sPIn Evolution of Stars"

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IPAG (Grenoble), IRAP (Toulouse), AIM (Saclay), LUPM (Montpellier)

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01 Jan. 2012 - 31 Dec. 2016

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Objectives :

Understanding the angular momentum evolution of solar‐type stars is one of the toughest and most exciting 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.

Présentation

...

ANR Toupies : "TOwards Understanding the sPIn Evolution of Stars"

...

IPAG (Grenoble), IRAP (Toulouse), AIM (Saclay), LUPM (Montpellier)

...

01 Jan. 2012 - 31 Dec. 2016

...

Objectives :

Understanding the angular momentum evolution of solar‐type stars is one of the toughest and most exciting 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.

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