Could a change in magnetic field geometry cause the break in the wind-activity relation?

Vidotto, A. A. and Donati, J.-F. and Jardine, M. and See, V. and Petit, P. and Boisse, I. and Boro Saikia, S. and Hebrard, E. and Jeffers, S. V. and Marsden, S. C. and Morin, J. (2016) Could a change in magnetic field geometry cause the break in the wind-activity relation? Monthly Notices of the Royal Astronomical Society: Letters, 455 (1). L52-L56. ISSN 0035-8711

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Wood et al. suggested that mass-loss rate is a function of X-ray flux (M˙ ∝ F1.34 x ) for dwarf stars with Fx Fx,6 ≡ 106 erg cm−2 s−1. However, more active stars do not obey this relation. These authors suggested that the break at Fx,6 could be caused by significant changes in
magnetic field topology that would inhibit stellar wind generation. Here, we investigate this hypothesis by analysing the stars in Wood et al. sample that had their surface magnetic fields reconstructed through Zeeman–Doppler Imaging (ZDI). Although the solar-like outliers in the M˙ – Fx relation have higher fractional toroidal magnetic energy, we do not find evidence of a sharp transition in magnetic topology at Fx,6. To confirm this, further wind measurements and ZDI observations at both sides of the break are required. As active stars can jump between states with highly toroidal to highly poloidal fields, we expect significant scatter in magnetic
field topology to exist for stars with Fx Fx,6. This strengthens the importance of multi-epoch ZDI observations. Finally, we show that there is a correlation between Fx and magnetic energy, which implies that M˙ – magnetic energy relation has the same qualitative behaviour as the original M˙ – Fx relation. No break is seen in any of the Fx – magnetic energy relations.

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Item Type: Article (Commonwealth Reporting Category C)
Refereed: Yes
Item Status: Live Archive
Additional Information: Access to Published version in accordance with the copyright policy of the publisher.
Faculty / Department / School: Current - Faculty of Health, Engineering and Sciences - School of Agricultural, Computational and Environmental Sciences
Date Deposited: 10 Mar 2017 03:05
Last Modified: 19 Mar 2019 21:57
Uncontrolled Keywords: magnetic fields – stars: activity – stars: coronae – stars: low-mass – stars: winds, outflows.
Fields of Research : 02 Physical Sciences > 0201 Astronomical and Space Sciences > 020110 Stellar Astronomy and Planetary Systems
Socio-Economic Objective: E Expanding Knowledge > 97 Expanding Knowledge > 970102 Expanding Knowledge in the Physical Sciences
Identification Number or DOI: 10.1093/mnrasl/slv147

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