Constraints on Magnetic Braking from the G8 Dwarf Stars 61 UMa and τ Cet
Article
Metcalfe, Travis S., Strassmeie, Klaus G., Ilyin, Ilya V., van Saders, Jennifer L., Ayres, Thomas R., Finley, Adam J., Kochukhov, Oleg, Petit, Pascal, See, Victor, Stassun, Keivan G., Jeffers, Sandra V., Marsden, Stephen C., Morin, Julien and Vidotto, Aline A.. 2023. "Constraints on Magnetic Braking from the G8 Dwarf Stars 61 UMa and τ Cet
." The Astrophysical Journal Letters. 948 (1). https://doi.org/10.3847/2041-8213/acce38
Article Title | Constraints on Magnetic Braking from the G8 Dwarf Stars 61 UMa and τ Cet |
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ERA Journal ID | 45091 |
Article Category | Article |
Authors | Metcalfe, Travis S., Strassmeie, Klaus G., Ilyin, Ilya V., van Saders, Jennifer L., Ayres, Thomas R., Finley, Adam J., Kochukhov, Oleg, Petit, Pascal, See, Victor, Stassun, Keivan G., Jeffers, Sandra V., Marsden, Stephen C., Morin, Julien and Vidotto, Aline A. |
Journal Title | The Astrophysical Journal Letters |
Journal Citation | 948 (1) |
Article Number | L6 |
Number of Pages | 5 |
Year | 2023 |
Publisher | IOP Publishing |
Place of Publication | United Kingdom |
ISSN | 2041-8205 |
2041-8213 | |
Digital Object Identifier (DOI) | https://doi.org/10.3847/2041-8213/acce38 |
Web Address (URL) | https://iopscience.iop.org/article/10.3847/2041-8213/acce38 |
Abstract | During the first half of their main-sequence lifetimes, stars rapidly lose angular momentum to their magnetized winds, a process known as magnetic braking. Recent observations suggest a substantial decrease in the magnetic braking efficiency when stars reach a critical value of the Rossby number, the stellar rotation period normalized by the convective overturn timescale. Cooler stars have deeper convection zones with longer overturn times, reaching this critical Rossby number at slower rotation rates. The nature and timing of the transition to weakened magnetic braking have previously been constrained by several solar analogs and two slightly hotter stars. In this Letter, we derive the first direct constraints from stars cooler than the Sun. We present new spectropolarimetry of the old G8 dwarf τ Cet from the Large Binocular Telescope, and we reanalyze a published Zeeman Doppler image of the younger G8 star 61 UMa, yielding the large-scale magnetic field strengths and morphologies. We estimate mass-loss rates using archival X-ray observations and inferences from Lyα measurements, and we adopt other stellar properties from asteroseismology and spectral energy distribution fitting. The resulting calculations of the wind braking torque demonstrate that the rate of angular momentum loss drops by a factor of 300 between the ages of these two stars (1.4–9 Gyr), well above theoretical expectations. We summarize the available data to help constrain the value of the critical Rossby number, and we identify a new signature of the long-period detection edge in recent measurements from the Kepler mission. |
Keywords | Spectropolarimetry ; Stellar evolution; Stellar magnetic fields; Stellar rotation; Stellar winds |
ANZSRC Field of Research 2020 | 510109. Stellar astronomy and planetary systems |
Byline Affiliations | White Dwarf Research Corporation, United States |
Leibniz Institute for Astrophysics Potsdam, Germany | |
University of Hawaii, United States | |
University of Colorado Boulder, United States | |
Paris-Saclay University, France | |
University of Paris, France | |
Uppsala University, Sweden | |
University of Toulouse, France | |
European Space Research and Technology Centre (ESTEC), Netherlands | |
Vanderbilt University, United States | |
Max Planck Institute for Solar System Research, Germany | |
Centre for Astrophysics | |
University of Montpellier, France | |
Leiden Observatory, Netherlands |
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