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Cited by 882Stellar, planetary, and galactic studiesSolar and Space Plasma DynamicsAstrophysics and Star Formation Studies

The stellar-activity-rotation relationship and the evolution of stellar dynamos

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Wright, Nicholas J., Drake, Jeremy J., Mamajek, Eric E., Henry, Gregory W.·2011·The Astrophysical Journal
DOI 10.1088/0004-637x/743/1/48
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Abstract

We present a sample of 824 solar and late-type stars with X-ray luminosities and rotation periods. This is used to study the relationship between rotation and stellar activity and derive a new estimate of the convective turnover time. From an unbiased subset of this sample the power-law slope of the unsaturated regime, L X / L bol ∝Ro β , is fit as β = −2.70 ± 0.13. This is inconsistent with the canonical β = −2 slope to a confidence of 5σ, and argues for an additional term in the dynamo number equation. From a simple scaling analysis this implies ΔΩ/Ω∝Ω 0.7 , i.e., the differential rotation of solar-type stars gradually declines as they spin down. Supersaturation is observed for the fastest rotators in our sample and its parametric dependencies are explored. Significant correlations are found with both the corotation radius and the excess polar updraft, the latter theory providing a stronger dependence and being supported by other observations. We estimate mass-dependent empirical thresholds for saturation and supersaturation and map out three regimes of coronal emission. Late F-type stars are shown never to pass through the saturated regime, passing straight from supersaturated to unsaturated X-ray emission. The theoretical threshold for coronal stripping is shown to be significantly different from the empirical saturation threshold (Ro < 0.13), suggesting it is not responsible. Instead we suggest that a different dynamo configuration is at work in stars with saturated coronal emission. This is supported by a correlation between the empirical saturation threshold and the time when stars transition between convective and interface sequences in rotational spin-down models.

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  • A star's rotation determines its XUV luminosity, with rapid rotators being more luminous than slow rotators.

    “Rotation is important since it determines a star's XUV luminosity, with rapid rotators being more luminous than slow rotators (Wright et al. 2011).”

    From The young Sun's XUV-activity as a constraint for lower CO2-limits in the Earth's Archean atmosphere (2021) · cites this paper as Wright et al. 2011

    Section 3, “X-ray Emission Versus Stellar Rotation” (page unavailable), reports that the X-ray-to-bolometric luminosity ratio generally rises with rotation rate, supporting the rapid-versus-slow comparison for X-rays. The paper does not establish the broader claim about XUV luminosity, and it notes that X-ray emission saturates at high rotation rates rather than continuing to rise. (LLM, conf=0.88)

    Experimental — accuracy not yet measured

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Research works printed but not linked: 3

  1. Brandenburg, A., Käpylä, P. J., & Korpi, M. J. 2011, arXiv:1103.5475 · arXiv
  2. Henry, G. W. 1995a, in ASP Conf. Ser. 79, Robotic Telescopes. Current Capabilities, Present Developments, and Future Prospects for Automated Astronomy, ed. G. W. Henry & J. A. Eaton (San Francisco, CA: ASP), 44
  3. Henry, G. W. 1995b, in ASP Conf. Ser. 79, Robotic Telescopes. Current Capabilities, Present Developments, and Future Prospects for Automated Astronomy, ed. G. W. Henry & J. A. Eaton (San Francisco, CA: ASP), 37

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Authors
Wright, N. J., Drake, J. J., Mamajek, E. E., & Henry, G. W.
Affiliations
  • Center for Astrophysics Harvard & Smithsonian (US)
  • University of Rochester (US)
  • Tennessee State University (US)
Corresponding author
Wright, Nicholas J.
ORCID
Venue
The Astrophysical Journal
Publisher
American Astronomical Society
Published
2011-11-21
Volume
743
Issue
1
Pages
48
ISSN
  • 0004-637X (ISSN-L)
  • 1538-4357
DOI
10.1088/0004-637x/743/1/48
OpenAlex
W2127400668
Cited by
882
References
154
Citations by year
2026: 56 · 2025: 75 · 2024: 91 · 2023: 79 · 2022: 67 · 2021: 83 · 2020: 83 · 2019: 74 · 2018: 51 · 2017: 58 · 2016: 55 · 2015: 28 · 2014: 35 · 2013: 26 · 2012: 20
FWCI
13.68
Type
journal article
Language
en
Open access
Locations
  • The Astrophysical Journal (publishedVersion)
  • arXiv (Cornell University) (submittedVersion)
  • University of Hertfordshire Research Archive (University of Hertfordshire) (submittedVersion)
  • arXiv (Cornell University)
Funders
  • National Science Foundation
  • National Aeronautics and Space Administration (NAS8-39073)
Topics
  • Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Stellar, planetary, and galactic studies
  • Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Solar and Space Plasma Dynamics
  • Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Astrophysics and Star Formation Studies
Keywords
stellar activity, stellar rotation, stellar dynamo, X-ray emission, convective turnover time, differential rotation, supersaturation, saturation threshold, corotation radius, late-type stars, F-type stars, spin-down

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