A New Asteroseismic Kepler Benchmark Constrains the Onset of Weakened Magnetic Braking in Mature Sun-like Stars

Creators: Bhalotia, Vanshree^{1, 2}; Huber, Daniel^{1, 3}; van Saders, Jennifer L.¹; Metcalfe, Travis S.⁴; Stassun, Keivan G.⁵; White, Timothy R.³; Aguirre Børsen-Koch, Víctor⁶; Ball, Warrick H.⁷; Basu, Sarbani⁸; Serenelli, Aldo M.^{9, 10}; Sawczynec, Erica¹¹; Guzik, Joyce A.¹²; Howard, Andrew W.¹³; Isaacson, Howard¹⁴

1. University of Hawaii at Manoa
2. National Radio Astronomy Observatory
3. University of Sydney
4. White Dwarf Research Corporation
5. Vanderbilt University
6. University of Copenhagen
7. University of Birmingham
8. Yale University
9. Institute of Space Sciences
10. Institut d'Estudis Espacials de Catalunya
11. The University of Texas at Austin
12. Los Alamos National Laboratory
13. California Institute of Technology
14. University of California, Berkeley

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Abstract

Stellar spin down is a critical yet poorly understood component of stellar evolution. In particular, results from the Kepler Mission imply that mature age, solar-type stars have inefficient magnetic braking, resulting in a stalled spin-down rate. However, a large number of precise asteroseismic ages are needed for mature (≥3 Gyr) stars in order to probe the regime where traditional and stalled spin-down models differ. In this paper, we present a new asteroseismic benchmark star for gyrochronology discovered using reprocessed Kepler short cadence data. KIC 11029516 (Papayu) is a bright (Kp = 9.6 mag) solar-type star with a well-measured rotation period (21.1 ± 0.8 days) from spot modulation using 4 yr of Kepler long-cadence data. We combine asteroseismology and spectroscopy to obtain T_eff = 5888 ± 100 K, [Fe/H] = 0.30 ± 0.06 dex, M = 1.24 ± 0.05 M_⊙, R = 1.34 ± 0.02 R_⊙, and age of 4.0 ± 0.4 Gyr, making Papayu one of the most similar stars to the Sun in terms of temperature and radius with an asteroseismic age and a rotation period measured from spot modulation. We find that Papayu sits at the transition of where traditional and weakened spin-down models diverge. A comparison with stars of similar zero-age main-sequence temperatures supports previous findings that weakened spin-down models are required to explain the ages and rotation periods of old solar-type stars.

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Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

Acknowledgement

We gratefully acknowledge everyone involved in the Kepler mission, the W. M. Keck Observatory and STScI for their efforts, which have made this paper possible. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. The primary author wishes to greet Maunakea with , offering utmost reverence to the piko ho'okahi and her Kānaka Maoli descendants. These astronomical observations would not have been possible without Maunakea's ha'awina. Guided by pono and our , we use the discovery of , to malama this 'āina and her kānaka. V.B. thanks her parents, siblings, mentors, and for their during this project that has culminated in her first first-author scientific publication.

V.B. and D.H. acknowledge support from the National Aeronautics and Space Administration (80NSSC19K0597). D.H. also acknowledges support from the Alfred P. Sloan Foundation and the Australian Research Council (FT200100871). J.L.v.S. acknowledges support from the National Aeronautics and Space Administration (80NSSC19K0597). S.B. acknowledges NSF grant AST-2205026. T.S.M. acknowledges NASA grant 80NSSC22K0475. Computational time at the Texas Advanced Computing Center was provided through XSEDE allocation TG-AST090107. A.M.S. acknowledges grants PID2019-108709GB-I00 from Ministry of Science and Innovation (MICINN, Spain), Spanish program Unidad de Excelencia María de Maeztu CEX2020-001058-M, 2021-SGR-1526 (Generalitat de Catalunya), and support from ChETEC-INFRA (EU project No. 101008324). The Kepler data presented in this paper were obtained from the Mikulski Archive for Space Telescopes (MAST) at the Space Telescope Science Institute. The specific observations analyzed can be accessed via doi:10.17909/nkrv-hp53. STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. Support for MAST for non-HST data is provided by the NASA Office of Space Science via grant NNX13AC07G and by other grants and contracts. The spectral data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

Software References

lightkurve (Barentsen et al. 2020), echelle (Hey & Ball 2020), DIAMONDS (Corsaro & De Ridder 2014), kiauhoku (Claytor et al. 2020), MESA (Paxton et al. 2011, 2013, 2015, 2018, 2019), Astropy (Astropy Collaboration et al. 2018), Matplotlib (Hunter 2007), NumPy (Oliphant 2006; Van Der Walt et al. 2011), and Pandas (pandas development team 2020)

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