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The radii of M-dwarfs in the young open cluster NGC 2516

Authors

  • R. J. Jackson,

    Corresponding author
    1. Astrophysics Group, Research Institute for the Environment, Physical Sciences and Applied Mathematics, Keele University, Keele, Staffordshire ST5 5BG
      E-mail: rjj@astro.keele.ac.uk
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  • R. D. Jeffries,

    1. Astrophysics Group, Research Institute for the Environment, Physical Sciences and Applied Mathematics, Keele University, Keele, Staffordshire ST5 5BG
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  • P. F. L. Maxted

    1. Astrophysics Group, Research Institute for the Environment, Physical Sciences and Applied Mathematics, Keele University, Keele, Staffordshire ST5 5BG
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E-mail: rjj@astro.keele.ac.uk

ABSTRACT

Using a novel technique, which combines previously determined rotation periods with new spectroscopic determinations of projected rotation velocity, we have determined radii for fast-rotating, low-mass (0.2–0.7 M) M-dwarfs in the young, solar-metallicity open cluster, NGC 2516. The mean radii are larger than model predictions at a given absolute I or K magnitude and also larger than the measured radii of magnetically inactive M-dwarfs; the difference increases from a few per cent to 50 per cent for the lowest luminosity stars in our sample. We show that a simple two-temperature starspot model is broadly capable of explaining these observations, but requires spot coverage fractions of about 50 per cent in rapidly rotating M-dwarfs.

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