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An abrupt change in the stellar spin-down law at the fully convective boundary

Nature Astronomy volume 8, pages 223–229 (2024)Cite this article

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Abstract

Unlike partially convective stars such as the Sun, fully convective stars do not possess a radiative core. Whether a star needs this core to generate a solar-like magnetic dynamo is still unclear. Recent studies suggest fully and partially convective stars exhibit very similar period–activity relationships, hinting that dynamos generated by stars with and without radiative cores hold similar properties. Here, using kinematic ages, we discover an abrupt change in the stellar spin-down law across the fully convective boundary. We found that fully convective stars exhibit a higher angular momentum loss rate, corresponding to a torque that is ~1.51 times higher for a given angular velocity than partially convective stars around the fully convective boundary. Because stellar-wind torques depend primarily on large-scale magnetic fields and mass-loss rates, both of which are suggested to be similar for partially and fully convective stars, the observed abrupt change in spin-down law suggests that the dynamos of partially and fully convective stars may be fundamentally different.

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Fig. 1: Spin-down of stars and stellar models near the fully convective boundary.
Fig. 2: Spin-down sequences for fully and partially convective stars in narrow temperature bins.
Fig. 3: Period–mass diagrams plotted with Markov chain Monte Carlo best-fit models.

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Data availability

The data used are available in Supplementary Data 1.

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Acknowledgements

Y.L. acknowledges support from the the European Space Agency (ESA) through the Science Faculty of the European Space Research and Technology Centre (ESTEC). V.S. acknowledges support from the ESA as an ESA Research Fellow. R.A. acknowledges support from NSF AAG grant no. 2108251. S.P.M. acknowledges support as a visiting scholar from the Center for Computational Astrophysics at the Flatiron Institute, which is supported by the Simons Foundation. This work has made use of data from the ESA mission Gaia, processed by the Gaia Data Processing and Analysis Consortium (DPAC). Funding for the DPAC has been provided by national institutions, in particular, the institutions participating in the Gaia Multilateral Agreement. This research also made use of public auxiliary data provided by ESA/Gaia/DPAC/CU5 and prepared by Carine Babusiaux. This research was done using services provided by the OSG Consortium47,48, which is supported by the National Science Foundation award nos. 2030508 and 1836650. This research has also made use of NASA’s Astrophysics Data System and the VizieR49 and SIMBAD50 databases, operated at CDS, Strasbourg, France.

Author information

Authors and Affiliations

  1. Astronomy Department, Columbia University, New York, NY, USA

    Yuxi (Lucy) Lu & Ruth Angus

  2. Astrophysics Department, American Museum of Natural History, New York, NY, USA

    Yuxi (Lucy) Lu & Ruth Angus

  3. European Space Agency (ESA), European Space Research and Technology Centre (ESTEC), Noordwijk, the Netherlands

    Victor See

  4. AIM, CEA, CNRS, Université Paris-Saclay, Université de Paris, Sorbonne Paris Cité, Gif-sur-Yvette, France

    Louis Amard

  5. Center for Computational Astrophysics, Flatiron Institute, New York, NY, USA

    Ruth Angus

  6. Department of Physics and Astronomy, University of Exeter, Exeter, UK

    Sean P. Matt

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Contributions

Y.L. developed the initial idea and prepared the observational data. L.A. prepared the stellar evolution model. Y.L., V.S., L.A. and R.A. conducted the data analysis. Y.L., V.S., L.A., R.A. and S.P.M. interpreted the broader context and wrote the manuscript.

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Correspondence to Yuxi (Lucy) Lu.

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Nature Astronomy thanks Maarit Korpi-Lagg and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary Fig. 1.

Supplementary Data 1

The raw data used to generate the figures in the main text. The second row describes each column, and the units are in brackets

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Lu, Y.(., See, V., Amard, L. et al. An abrupt change in the stellar spin-down law at the fully convective boundary. Nat Astron 8, 223–229 (2024). https://doi.org/10.1038/s41550-023-02126-2

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