Magnetic and Rotational Evolution of ρ CrB from Asteroseismology with TESS

ABSTRACT We present a detailed analysis of the possible future Sun’s rotational evolution scenario based on the 8-Gyr-old solar twin HIP 102152. Using HARPS high-cadence observations (and TESS light curves), we analysed the modulation of a variety of activity proxies (Ca ii , H i Balmer, and Na i lines), finding a strong rotational signal of 35.7 ± 1.4 d (log Bfactor ∼ 70, in the case of Ca ii K line). This value matches with the theoretical expectations regarding the smooth rotational evolution of the Sun towards the end of the main sequence, validating the use of gyrochronology after solar age.

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The impact of magnetism on tidal dynamics in the convective envelope of low-mass stars

Proceedings of the International Astronomical Union ◽

10.1017/s1743921319010020 ◽

2019 ◽

Vol 15 (S354) ◽

pp. 195-199

Author(s):

A. Astoul ◽

S. Mathis ◽

C. Baruteau ◽

F. Gallet ◽

A. Strugarek ◽

...

Keyword(s):

Magnetic Field ◽

Orbital Evolution ◽

Magnetic Contribution ◽

Low Mass Stars ◽

Convective Envelope ◽

Tidal Waves ◽

Tidal Interactions ◽

Rotational Evolution ◽

Low Mass ◽

The Impact

AbstractFor the shortest period exoplanets, star-planet tidal interactions are likely to have played a major role in the ultimate orbital evolution of the planets and on the spin evolution of the host stars. Although low-mass stars are magnetically active objects, the question of how the star’s magnetic field impacts the excitation, propagation and dissipation of tidal waves remains open. We have derived the magnetic contribution to the tidal interaction and estimated its amplitude throughout the structural and rotational evolution of low-mass stars (from K to F-type). We find that the star’s magnetic field has little influence on the excitation of tidal waves in nearly circular and coplanar Hot-Jupiter systems, but that it has a major impact on the way waves are dissipated.

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Stellar activity and rotation of the planet host Kepler-17 from long-term space-borne photometry

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833894 ◽

2019 ◽

Vol 626 ◽

pp. A38 ◽

Cited By ~ 4

Author(s):

A. F. Lanza ◽

Y. Netto ◽

A. S. Bonomo ◽

H. Parviainen ◽

A. Valio ◽

...

Keyword(s):

Maximum Entropy ◽

Differential Rotation ◽

Activity Cycle ◽

Magnetic Activity ◽

Model Parameters ◽

The Sun ◽

Level Of Activity ◽

Spot Model ◽

Rotational Evolution ◽

Solar Type

Context. The study of young Sun-like stars is fundamental to understanding the magnetic activity and rotational evolution of the Sun. Space-borne photometry by the Kepler telescope provides unprecedented datasets to investigate these phenomena in Sun-like stars. Aims. We present a new analysis of the entire Kepler photometric time series of the moderately young Sun-like star Kepler-17 accompanied by a transiting hot Jupiter. Methods. We applied a maximum-entropy spot model to the long-cadence out-of-transit photometry of the target to derive maps of the starspot filling factor versus the longitude and the time. These maps are compared to the spots occulted during transits to validate our reconstruction and derive information on the latitudes of the starspots. Results. We find two main active longitudes on the photosphere of Kepler-17, one of which has a lifetime of at least ∼1400 days although with a varying level of activity. The latitudinal differential rotation is of solar type, that is, with the equator rotating faster than the poles. We estimate a minimum relative amplitude ΔΩ/Ω between ∼0.08 ± 0.05 and 0.14 ± 0.05, our determination being affected by the finite lifetime of individual starspots and depending on the adopted spot model parameters. We find marginal evidence of a short-term intermittent activity cycle of ∼48 days and an indication of a longer cycle of 400−600 days characterized by an equatorward migration of the mean latitude of the spots as in the Sun. The rotation of Kepler-17 is likely to be significantly affected by the tides raised by its massive close-by planet. Conclusion. We confirm the reliability of maximum-entropy spot models to map starspots in young active stars and characterize the activity and differential rotation of this young Sun-like planetary host.

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Star-planet tidal interaction and the limits of gyrochronology

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834898 ◽

2019 ◽

Vol 626 ◽

pp. A120

Author(s):

F. Gallet ◽

P. Delorme

Keyword(s):

Angular Momentum ◽

Rotation Rate ◽

Age Determination ◽

Rotation Period ◽

Orbital Evolution ◽

Tidal Interaction ◽

Surface Rotation ◽

Rotational Evolution ◽

Forbidden Region ◽

The Impact

Context. Age estimation techniques such as gyrochronology and magnetochronology cannot be applied to stars that have exchanged angular momentum with their close environments. This is especially true for a massive close-in planetary companion (with a period of a few days or less) that could have been strongly impacted by the rotational evolution of the host star, throughout the stellar evolution, through the star-planet tidal interaction. Aims. In this article, we provide the community with a reliable region in which empirical techniques such as gyrochronology can be used with confidence. Methods. We combined a stellar angular momentum evolution code with a planetary orbital evolution code to study in detail the impact of star-planet tidal interaction on the evolution of the surface rotation rate of the star. Results. We show that the interaction of a close-in massive planet with its host star can strongly modify the surface rotation rate of this latter, in most of the cases associated with a planetary engulfment. A modification of the surface rotation period of more than 90% can survive a few hundred Myr after the event and a modification of 10% can last for a few Gyr. In such cases, a gyrochronology analysis of the star would incorrectly make it appear as rejuvenated, thus preventing us from using this method with confidence. To try overcome this issue, we proposed the proof of concept of a new age determination technique that we call the tidal-chronology method, which is based on the observed pair Prot, ⋆–Porb of a given star-planet system, where Prot, ⋆ is the stellar surface rotational period and Porb the planetary orbital period. Conclusions. The gyrochronology technique can only be applied to isolated stars or star-planet systems outside a specific range of Prot, ⋆–Porb. This region tends to expand for increasing stellar and planetary mass. In that forbidden region, or if any planetary engulfment is suspected, gyrochronology should be used with extreme caution, while tidal-chronology could be considered. This technique does not provide a precise age for the system yet; however, it is already an extension of gyrochronology and could be helpful to determine a more precise range of possible ages for planetary systems composed of a star between 0.3 and 1.2 M⊙ and a planet more massive than 1 Mjup initially located at a few hundredths of au from the host star.

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Rotational evolution of solar-type protostars during the star-disk interaction phase

Astronomy and Astrophysics ◽

10.1051/0004-6361/201935432 ◽

2019 ◽

Vol 632 ◽

pp. A6 ◽

Cited By ~ 3

Author(s):

F. Gallet ◽

C. Zanni ◽

L. Amard

Keyword(s):

Stellar Wind ◽

Main Sequence ◽

Stellar Winds ◽

Stellar Rotation ◽

Solar Mass ◽

Stellar Envelope ◽

Spin Evolution ◽

Rotational Evolution ◽

Solar Type ◽

The Impact

Context. The early pre-main sequence phase during which solar-mass stars are still likely surrounded by an accretion disk represents a puzzling stage of their rotational evolution. While solar-mass stars are accreting and contracting, they do not seem to spin up substantially. Aims. It is usually assumed that the magnetospheric star-disk interaction tends to maintain the stellar rotation period constant (“disk-locking”), but this hypothesis has never been thoroughly verified. Our aim is to investigate the impact of the star-disk interaction mechanism on the stellar spin evolution during the accreting pre-main sequence phases. Methods. We devised a model for the torques acting on the stellar envelope based on studies of stellar winds, and we developed a new prescription for the star-disk coupling founded on numerical simulations of star-disk interaction and magnetospheric ejections. We then used this torque model to follow the long-term evolution of the stellar rotation. Results. Strong dipolar magnetic field components up to a few kG are required to extract enough angular momentum so as to keep the surface rotation rate of solar-type stars approximately constant for a few Myr. Furthermore an efficient enough spin-down torque can be provided by either one of the following: a stellar wind with a mass outflow rate corresponding to ≈10% of the accretion rate, or a lighter stellar wind combined with a disk that is truncated around the corotation radius entering a propeller regime. Conclusions. Magnetospheric ejections and accretion powered stellar winds play an important role in the spin evolution of solar-type stars. However, kG dipolar magnetic fields are neither uncommon or ubiquitous. Besides, it is unclear how massive stellar winds can be powered while numerical models of the propeller regime display a strong variability that has no observational confirmation. Better observational statistics and more realistic models could contribute to help lessen our calculations’ requirements.

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The accelerating rotation of the magnetic He-weak star HD 142990

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz1129 ◽

2019 ◽

Vol 486 (4) ◽

pp. 5558-5566 ◽

Cited By ~ 4

Author(s):

M Shultz ◽

Th Rivinius ◽

B Das ◽

G A Wade ◽

P Chandra

Keyword(s):

Rotation Period ◽

Photometric Data ◽

Data Sets ◽

Surface Magnetic Field ◽

Short Rotation ◽

Magnetic Stars ◽

Weak Star ◽

Rotational Evolution ◽

Strong Surface ◽

Rapid Rotator

ABSTRACT HD 142990 (V 913 Sco; B5 V) is a He-weak star with a strong surface magnetic field and a short rotation period (Prot ∼ 1 d). Whilst it is clearly a rapid rotator, recent determinations of Prot are in formal disagreement. In this paper, we collect magnetic and photometric data with a combined 40-yr baseline in order to re-evaluate Prot and examine its stability. Both period analysis of individual data sets and O − C analysis of the photometric data demonstrate that Prot has decreased over the past 30 yr, violating expectations from magnetospheric braking models, but consistent with behaviour reported for 2 other hot, rapidly rotating magnetic stars, CU Vir and HD 37776. The available magnetic and photometric time series for HD 142990 can be coherently phased assuming a spin-up rate $\dot{P}$ of approximately −0.6 s yr−1, although there is some indication that $\dot{P}$ may have slowed in recent years, possibly indicating an irregular or cyclic rotational evolution.

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The rotational evolution of young low mass stars

Proceedings of the International Astronomical Union ◽

10.1017/s1743921307009593 ◽

2007 ◽

Vol 3 (S243) ◽

pp. 231-240 ◽

Cited By ~ 9

Author(s):

Jérôme Bouvier

Keyword(s):

Angular Momentum ◽

Accretion Disk ◽

Main Sequence ◽

Young Stars ◽

Sequence Evolution ◽

Main Sequence Stars ◽

Low Mass Stars ◽

Rotational Evolution ◽

Low Mass

AbstractStar-disk interaction is thought to drive the angular momentum evolution of young stars. In this review, I present the latest results obtained on the rotational properties of low mass and very low mass pre-main sequence stars. I discuss the evidence for extremely efficient angular momentum removal over the first few Myr of pre-main sequence evolution and describe recent results that support an accretion-driven braking mechanism. Angular momentum evolution models are presented and their implication for accretion disk lifetimes discussed.

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