Stellar magnetism : empirical trends with age and rotation
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We investigate how the observed large-scale surface magnetic fields of low-mass stars (~0.1-2M⊙), reconstructed through Zeeman-Doppler imaging, vary with age t, rotation and X-ray emission. Our sample consists of 104 magnetic maps of 73 stars, from accreting premain 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 is related to age as t−0.655 ± 0.045. This relation has a similar dependence to that identified by Skumanich, 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.
Vidotto , A A , Gregory , S G , Jardine , M , Donati , J F , Petit , P , Morin , J , Folsom , C P , Bouvier , J , Cameron , A C , Hussain , G , Marsden , S , Waite , I A , Fares , R , Jeffers , S & Do Nascimento Jr. , J D 2014 , ' Stellar magnetism : empirical trends with age and rotation ' Monthly Notices of the Royal Astronomical Society , vol 441 , no. 3 , pp. 2361-2374 . DOI: 10.1093/mnras/stu728
Monthly Notices of the Royal Astronomical Society
© 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society
AAV acknowledges support from a Royal Astronomical Society Fellowship and from the Swiss National Science Foundation via an Ambizione Fellowship. SGG acknowledges support from the Science and Technology Facilities Council (STFC) via an Ernest Rutherford Fellowship [ST/J003255/1] and RF via a consolidated grant [ST/J001651/1]. JB, PP and CPF acknowledge support from the ANR 2011 Blanc SIMI5-6 020 01 ‘Toupies: Towards understanding the spin evolution of stars’