Do Non-dipolar Magnetic Fields Contribute to Spin-down Torques?

See, Victor; Matt, Sean P.; Finley, Adam J.; Folsom, C. P.; Saikia, S. Boro; Donati, J.‐F.; Farès, R.; Hébrard, E.; Jardine, M.; Jeffers, S. V.; Marsden, S. C.; Mengel, M. W.; Morin, J.; Petit, P.; Vidotto, A. A.; Waite, I. A.

doi:10.3847/1538-4357/ab46b2

Cited by 69 publications

(91 citation statements)

References 77 publications

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“…). As these components are not expected to be capable of efficiently draining angular momentum via winds(See et al 2019), in compari-Age-Rotation diagram with model predictions for 0.97 M star using modified Kawaler wind-law and YaPSI tracks(Spada et al 2017). The red cross is HIP 102152, and the Sun is represented by its usual symbol.…”

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confidence: 79%

The ancient main-sequence solar proxy HIP 102152 unveils the activity and rotational fate of our Sun

Meléndez

Ponte

Galarza

2020

Monthly Notices of the Royal Astronomical Society: Letters

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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 analyzed 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 days (log B factor ∼ 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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confidence: 79%

The ancient main-sequence solar proxy HIP 102152 unveils the activity and rotational fate of our Sun

Meléndez

Ponte

Galarza

2020

Monthly Notices of the Royal Astronomical Society: Letters

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“…For mixed topologies (e.g., superpositions of dipoles and quadrupoles and/or octupoles), simulations of ISWs demonstrate that the stellar-wind torque is mainly determined by the lowest-order field topology (Finley & Matt 2017. However, supplementary analysis by See et al (2019) shows that higher-order fields (in mixed geometries) can have an effect on stellar-wind torques if the Alfvén surface is reached at a distance from the stellar surface where the higher-order field strengths have not declined enough to be considered negligible. Therefore, complex and more realistic field topologies should be considered in future SDI simulations to improve the accuracy of the current stellar-wind torque prescriptions.…”

Section: Discussionmentioning

confidence: 99%

Magnetic torques on T Tauri stars: Accreting versus non-accreting systems

Pantolmos

Zanni

Bouvier

2020

A&A

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Context. Classical T Tauri stars (CTTs) magnetically interact with their surrounding disks, a process that is thought to regulate their rotational evolution. Aims. We compute torques acting on the stellar surface of CTTs that arise from different accreting (accretion funnels) and ejecting (stellar winds and magnetospheric ejections) flow components. Furthermore, we compare the magnetic braking due to stellar winds in two different systems: isolated (i.e., weak-line T Tauri and main-sequence) and accreting (i.e., classical T Tauri) stars. Methods. We use 2.5D magnetohydrodynamic, time-dependent, axisymmetric simulations that were computed with the PLUTO code. For both systems, the stellar wind is thermally driven. In the star-disk-interaction (SDI) simulations, the accretion disk is Keplerian, viscous, and resistive, and is modeled with an alpha prescription. Two series of simulations are presented, one for each system (i.e., isolated and accreting stars). Results. In classical T Tauri systems, the presence of magnetospheric ejections confines the stellar-wind expansion, resulting in an hourglass-shaped geometry of the outflow, and the formation of the accretion columns modifies the amount of open magnetic flux exploited by the stellar wind. These effects have a strong impact on the stellar-wind properties, and we show that the stellar-wind braking is more efficient in the SDI systems than in the isolated ones. We further derive torque scalings over a wide range of magnetic field strengths for each flow component in an SDI system (i.e., magnetospheric accretion and ejections, and stellar winds), which directly applies a torque on the stellar surface. Conclusions. In all the performed SDI simulations, the stellar wind extracts less than 2% of the mass accretion rate and the disk is truncated by up to 66% of the corotation radius. All simulations show a net spin-up torque. We conclude that in order to achieve a stellar-spin equilibrium, we need either more massive stellar winds or disks that are truncated closer to the corotation radius, which increases the torque efficiency of the magnetospheric ejections.

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“…Solar symbols connected by the black vertical line shows the mass loss rate for the solar input magnetograms (l max = 10) during solar cycle minimum and maximum. resolution of the magnetogram might have a stronger impact for slowly rotating stars with Rossby number 2 (See et al 2019). Surprisingly, l max = 20 leads to a marginally higher mass loss and angular momentum loss rate when compared to l max = 150 during solar cycle maximum in CR 2159.…”

Section: Solar Wind Properties Determined From Our Two Grids Of Low-resolution Simulationsmentioning

confidence: 91%

The solar wind from a stellar perspective

Saikia

Jin

Johnstone

et al. 2020

A&A

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Context. Due to the effects that they can have on the atmospheres of exoplanets, stellar winds have recently received significant attention in the literature. Alfvén-wave-driven 3D magnetohydrodynamic models, which are increasingly used to predict stellar wind properties, contain unconstrained parameters and rely on low-resolution stellar magnetograms. Aims. In this paper, we explore the effects of the input Alfvén wave energy flux and the surface magnetogram on the wind properties predicted by the Alfvén Wave Solar Model (AWSoM) model for both the solar and stellar winds. Methods. We lowered the resolution of two solar magnetograms during solar cycle maximum and minimum using spherical harmonic decomposition. The Alfvén wave energy was altered based on non-thermal velocities determined from a far ultraviolet spectrum of the solar twin 18 Sco. Additionally, low-resolution magnetograms of three solar analogues, 18 Sco, HD 76151, and HN Peg, were obtained using Zeeman Doppler imaging and used as a proxy for the solar magnetogram. Finally, the simulated wind properties were compared to Advanced Composition Explorer (ACE) observations. Results. AWSoM simulations using well constrained input parameters taken from solar observations can reproduce the observed solar wind mass loss and angular momentum loss rates. The simulated wind velocity, proton density, and ram pressure differ from ACE observations by a factor of approximately two. The resolution of the magnetogram has a small impact on the wind properties and only during cycle maximum. However, variation in Alfvén wave energy influences the wind properties irrespective of the solar cycle activity level. Furthermore, solar wind simulations carried out using the low-resolution magnetogram of the three stars instead of the solar magnetogram could lead to an order of a magnitude difference in the simulated solar wind properties. Conclusions. The choice in Alfvén energy has a stronger influence on the wind output compared to the magnetogram resolution. The influence could be even stronger for stars whose input boundary conditions are not as well constrained as those of the Sun. Unsurprisingly, replacing the solar magnetogram with a stellar magnetogram could lead to completely inaccurate solar wind properties, and should be avoided in solar and stellar wind simulations. Further observational and theoretical work is needed to fully understand the complexity of solar and stellar winds.

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Do Non-dipolar Magnetic Fields Contribute to Spin-down Torques?

Cited by 69 publications

References 77 publications

The ancient main-sequence solar proxy HIP 102152 unveils the activity and rotational fate of our Sun

The ancient main-sequence solar proxy HIP 102152 unveils the activity and rotational fate of our Sun

Magnetic torques on T Tauri stars: Accreting versus non-accreting systems

The solar wind from a stellar perspective

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