Field linkage and magnetic helicity density

Lund, K. and Jardine, M. and Russell, A. J. B. and Donati, J.-F. and Fares, R. and Folsom, C. P. and Jeffers, S. V. and Marsden, S. C. ORCID: and Morin, J. and Petit, P. and See, V. (2021) Field linkage and magnetic helicity density. Monthly Notices of the Royal Astronomical Society, 502 (4). pp. 4903-4910. ISSN 0035-8711

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The helicity of a magnetic field is a fundamental property that is conserved in ideal MHD. It can be explored in the stellar context by mapping large-scale magnetic fields across stellar surfaces using Zeeman-Doppler imaging. A recent study of 51 stars in the mass range 0.1-1.34 M⊙ showed that the photospheric magnetic helicity density follows a single power law when plotted against the toroidal field energy, but splits into two branches when plotted against the poloidal field energy. These two branches divide stars above and below ∼0.5 M⊙. We present here a novel method of visualizing the helicity density in terms of the linkage of the toroidal and poloidal fields that are mapped across the stellar surface. This approach allows us to classify the field linkages that provide the helicity density for stars of different masses and rotation rates. We find that stars on the lower mass branch tend to have toroidal fields that are non-axisymmetric and so link through regions of positive and negative poloidal field. A lower mass star may have the same helicity density as a higher mass star, despite having a stronger poloidal field. Lower mass stars are therefore less efficient at generating large-scale helicity.

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Item Type: Article (Commonwealth Reporting Category C)
Refereed: Yes
Item Status: Live Archive
Faculty/School / Institute/Centre: Current - Institute for Advanced Engineering and Space Sciences - Centre for Astrophysics (1 Aug 2018 -)
Faculty/School / Institute/Centre: Historic - Faculty of Health, Engineering and Sciences - School of Sciences (6 Sep 2019 - 31 Dec 2021)
Date Deposited: 14 Apr 2022 01:55
Last Modified: 31 May 2022 00:45
Uncontrolled Keywords: methods: analytical; stars: magnetic field
Fields of Research (2020): 51 PHYSICAL SCIENCES > 5101 Astronomical sciences > 510109 Stellar astronomy and planetary systems
Socio-Economic Objectives (2020): 28 EXPANDING KNOWLEDGE > 2801 Expanding knowledge > 280120 Expanding knowledge in the physical sciences
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