Weakened Magnetic Braking in the Exoplanet Host Star 51 Peg

Metcalfe, Travis S.; Strassmeier, Klaus G.; Ilyin, Ilya V.; Buzasi, Derek; Kochukhov, Oleg; Ayres, Thomas R.; Basu, Sarbani; Chontos, Ashley; Finley, Adam J.; See, Victor; Stassun, Keivan G.; van Saders, Jennifer L.; Sepulveda, Aldo G.; Ricker, George R.

doi:10.3847/2041-8213/ad0a95

Cited by 5 publications

(2 citation statements)

References 58 publications

(73 reference statements)

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“…We performed asteroseismic modeling for Luke and Leia and 47 stars from the Hall21 sample that fall within our desired mass range using version 2.0 of the Asteroseismic Modeling Portal (AMP; Metcalfe et al 2009;Woitaszek et al 2009;Metcalfe et al 2024). 10 This optimization method couples a parallel genetic algorithm (Metcalfe & Charbonneau 2003) with Modules for Experiments in Stellar Astrophysics (MESA) stellar evolution models (Paxton et al 2019) and the GYRE pulsation code (Townsend & Teitler 2013) to determine the stellar properties that most closely reproduce the observed oscillation frequencies and spectroscopic constraints for each star.…”

Section: Asteroseismic Samplementioning

confidence: 99%

Stellar Cruise Control: Weakened Magnetic Braking Leads to Sustained Rapid Rotation of Old Stars

Saunders,

van Saders,

Lyttle

et al. 2024

ApJ

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Despite a growing sample of precisely measured stellar rotation periods and ages, the strength of magnetic braking and the degree of departure from standard (Skumanich-like) spin-down have remained persistent questions, particularly for stars more evolved than the Sun. Rotation periods can be measured for stars older than the Sun by leveraging asteroseismology, enabling models to be tested against a larger sample of old field stars. Because asteroseismic measurements of rotation do not depend on starspot modulation, they avoid potential biases introduced by the need for a stellar dynamo to drive starspot production. Using a neural network trained on a grid of stellar evolution models and a hierarchical model-fitting approach, we constrain the onset of weakened magnetic braking (WMB). We find that a sample of stars with asteroseismically measured rotation periods and ages is consistent with models that depart from standard spin-down prior to reaching the evolutionary stage of the Sun. We test our approach using neural networks trained on model grids produced by separate stellar evolution codes with differing physical assumptions and find that the choices of grid physics can influence the inferred properties of the braking law. We identify the normalized critical Rossby number Rocrit/Ro⊙ = 0.91 ± 0.03 as the threshold for the departure from standard rotational evolution. This suggests that WMB poses challenges to gyrochronology for roughly half of the main-sequence lifetime of Sun-like stars.

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Section: Asteroseismic Samplementioning

confidence: 99%

Stellar Cruise Control: Weakened Magnetic Braking Leads to Sustained Rapid Rotation of Old Stars

Saunders,

van Saders,

Lyttle

et al. 2024

ApJ

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“…In solar analogs with slow rotation, such as 51 Peg, the activity cycle may be disrupted and lead to severely diminished Alfvén radii. Metcalfe et al (2024) has estimated the Alfvén radius of 51 Peg to be as low as R A = 4.7R star . It is important to note that defining the Alfvén surface by a single radius R A requires the underlying assumption that the stellar wind is a Parker wind (Schrijver et al 2003;Cohen et al 2011), i.e., radial, isothermal, and polytropic, resulting in a spherical Alfvén surface.…”

Section: Stellar Alfvén Surfacementioning

confidence: 99%

Exploring the Effects of Stellar Magnetism on the Potential Habitability of Exoplanets

Atkinson,

Alexander,

Farrish

2024

ApJ

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Considerable interest has centered on Earth-like planets orbiting in the circumstellar habitable zone (CHZ) of its star. However, the potential habitability of an exoplanet depends upon a number of additional factors, including the presence and strength of any planetary magnetic field and the interaction of this field with that of the host star. Not only must the exoplanet have a strong enough magnetic field to shield against stellar activity, but it must also orbit far enough from the star to avoid direct magnetic connectivity. We characterize stellar activity by the star’s Rossby number, Ro, the ratio of stellar rotation rate to convective turnover time. We employ a scaled model of the solar magnetic field to determine the star’s Alfvén radius, the distance at which the stellar wind becomes super-Alfvénic. Planets residing within the Alfvén surface may have a direct magnetic connection to the star and therefore not be the most viable candidates for habitability. Here, we determine the Rossby number of a sample of 1053 exoplanet-hosting stars for which the rotation rates have been observed and for which a convective turnover time can be calculated. We find that 84 exoplanets in our sample have orbits which lie inside the CHZ and that also lie outside the star’s Alfvén surface: 34 of these have been classified as terran (11) or superterran (23) planets. Applying the Alfvén surface habitability criterion yields a subset of the confirmed exoplanets that may be optimal targets for future observations in the search for signatures of life.

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Fine structure of the age–chromospheric activity relation in solar-type stars: II. Hα line

Souza dos Santos,

Porto de Mello,

Costa-Bhering

et al. 2024

Monthly Notices of the Royal Astronomical Society

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Excess chromospheric emissions within deep photospheric lines are effective proxies of stellar magnetism for FGK stars. This emission decays with stellar age and is a potential determinant of this important stellar quantity. We report absolutely calibrated H $\alpha$ chromospheric fluxes for 511 solar-type stars in a wide interval of precisely determined masses, [Fe/H], ages, and evolution states from high S/N, moderately high$-$resolution spectra. The comparison of H $\alpha$ and H + K chromospheric fluxes reveals a metallicity bias (absent from H $\alpha$) affecting Ca ii H + K fluxes thereby metal-rich stars with deep line profiles mimic low chromospheric flux levels, and vice versa for metal-poor stars. This bias blurs the age–activity relation, precluding age determinations for old, inactive stars unless mass and [Fe/H] are calibrated into the relation. The H + K lines being the most widely studied tool to quantify magnetic activity in FGK stars, care should be exercised in its use whenever wide ranges of mass and [Fe/H] are involved. The H $\alpha$ age–activity–mass–metallicity calibration appears to be in line with the theoretical expectation that (other parameters being equal) more massive stars possess narrower convective zones and are less active than less massive stars, while more metal-rich stars have deeper convective zones and appear more active than metal-poorer stars. If regarded statistically in tandem with other age diagnostics, H $\alpha$ chromospheric fluxes may be suitable to constrain ages for FGK stars with acceptable precision.

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Weakened Magnetic Braking in the Exoplanet Host Star 51 Peg

Cited by 5 publications

References 58 publications

Stellar Cruise Control: Weakened Magnetic Braking Leads to Sustained Rapid Rotation of Old Stars

Stellar Cruise Control: Weakened Magnetic Braking Leads to Sustained Rapid Rotation of Old Stars

Exploring the Effects of Stellar Magnetism on the Potential Habitability of Exoplanets

Fine structure of the age–chromospheric activity relation in solar-type stars: II. Hα line

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