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  LBT/PEPSI Spectropolarimetry of a Magnetic Morphology Shift in Old Solar-type Stars

Metcalfe, T. S., Kochukhov, O., Ilyin, I. V., Strassmeier, K. G., Godoy-Rivera, D., & Pinsonneault, M. H. (2020). LBT/PEPSI Spectropolarimetry of a Magnetic Morphology Shift in Old Solar-type Stars. Astrophysical Journal, Letters, 887(2): L38. doi:10.3847/2041-8213/ab5e48.

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Item Permalink: http://hdl.handle.net/21.11116/0000-0006-71F8-3 Version Permalink: http://hdl.handle.net/21.11116/0000-0006-71F9-2
Genre: Journal Article

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 Creators:
Metcalfe, T. S.1, Author
Kochukhov, O., Author
Ilyin, I. V., Author
Strassmeier, K. G., Author
Godoy-Rivera, D., Author
Pinsonneault, M. H., Author
Affiliations:
1Department Solar and Stellar Interiors, Max Planck Institute for Solar System Research, Max Planck Society, Justus-von-Liebig-Weg 3, 37077 Göttingen, DE, ou_1832287              

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 Abstract: Solar-type stars are born with relatively rapid rotation and strong magnetic fields. Through a process known as magnetic braking, the rotation slows over time as stellar winds gradually remove angular momentum from the system. The rate of angular momentum loss depends sensitively on the magnetic morphology, with the dipole field exerting the largest torque on the star. Recent observations suggest that the efficiency of magnetic braking may decrease dramatically in stars near the middle of their main-sequence lifetimes. One hypothesis to explain this reduction in efficiency is a shift in magnetic morphology from predominantly larger to smaller spatial scales. We aim to test this hypothesis with spectropolarimetric measurements of two stars that sample chromospheric activity levels on opposite sides of the proposed magnetic transition. As predicted, the more active star (HD 100180) exhibits a significant circular polarization signature due to a nonaxisymmetric large-scale magnetic field, while the less active star (HD 143761) shows no significant signal. We identify analogs of the two stars among a sample of well-characterized Kepler targets, and we predict that the asteroseismic age of HD 143761 from future Transiting Exoplanet Survey Satellite observations will substantially exceed the age expected from gyrochronology. We conclude that a shift in magnetic morphology likely contributes to the loss of magnetic braking in middle-aged stars, which appears to coincide with the shutdown of their global dynamos.

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Language(s): eng - English
 Dates: 2020
 Publication Status: Published in print
 Pages: -
 Publishing info: -
 Table of Contents: -
 Rev. Method: Peer
 Identifiers: DOI: 10.3847/2041-8213/ab5e48
 Degree: -

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Title: Astrophysical Journal, Letters
  Other : ApJL
Source Genre: Journal
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Publ. Info: Bristol, UK : Institute of Physics Publishing (IOP)
Pages: - Volume / Issue: 887 (2) Sequence Number: L38 Start / End Page: - Identifier: ISSN: 0004-637X
CoNE: https://pure.mpg.de/cone/journals/resource/954922828215_1