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arXiv · 1404.2733

Stellar magnetism: empirical trends with age and rotation

A. A. Vidotto·S. G. Gregory·M. Jardine·J. -F. Donati·P. Petit·J. Morin·C. P. Folsom·J. Bouvier·A. C. Cameron·G. Hussain·S. Marsden·I. A. Waite·R. Fares·S. Jeffers·J. D. do Nascimento Jr
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Abstract

We investigate how the observed large-scale surface magnetic fields of low-mass stars (~0.1 -- 2 Msun), reconstructed through Zeeman-Doppler imaging (ZDI), vary with age t, rotation and X-ray emission. Our sample consists of 104 magnetic maps of 73 stars, from accreting pre-main sequence to main-sequence objects (1 Myr < t < 10 Gyr). For non-accreting dwarfs we empirically find that the unsigned average large-scale surface field <|Bv|> is related to age as $t^{-0.655 \pm 0.045}$. This relation has a similar dependence to that identified by Skumanich (1972), used as the basis for gyrochronology. Likewise, our relation could be used as an age-dating method ("magnetochronology"). The trends with rotation we find for the large-scale stellar magnetism are consistent with the trends found from Zeeman broadening measurements (sensitive to large- and small-scale fields). These similarities indicate that the fields recovered from both techniques are coupled to each other, suggesting that small- and large-scale fields could share the same dynamo field generation processes. For the accreting objects, fewer statistically significant relations are found, with one being a correlation between the unsigned magnetic flux and rotation period. We attribute this to a signature of star-disc interaction, rather than being driven by the dynamo.

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A. A. Vidotto, S. G. Gregory, M. Jardine, J. -F. Donati, P. Petit, J. Morin, C. P. Folsom, J. Bouvier, A. C. Cameron, G. Hussain, S. Marsden, I. A. Waite, R. Fares, S. Jeffers, J. D. do Nascimento Jr. 2014-04-10. Stellar magnetism: empirical trends with age and rotation. https://doi.org/10.1093/mnras/stu728

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