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Title:
M-dwarf stellar winds: the effects of realistic magnetic geometry on rotational evolution and planets
Authors:
Vidotto, A. A.; Jardine, M.; Morin, J.; Donati, J. F.; Opher, M.; Gombosi, T. I.
Affiliation:
AA(SUPA, School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews KY16 9SS, UK; ), AB(SUPA, School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews KY16 9SS, UK), AC(Institut für Astrophysik, Georg-August-Universität, Friedrich-Hund-Platz 1, D-37077 Goettingen, Germany; LUPM-UMR5299, Université Montpellier II and CNRS, Place Eugène Bataillon, F-34095 Montpellier Cedex 05, France; Dublin Institute for Advanced Studies, School of Cosmic Physics, 31 Fitzwilliam Place, Dublin 2, Ireland), AD(LATT - CNRS/Université de Toulouse, 14 Av. E. Belin, F-31400 Toulouse, France), AE(Boston University, 725 Commonwealth Ave, Boston, MA 02215, USA), AF(University of Michigan, 1517 Space Research Building, Ann Arbor, MI 48109-2143, USA)
Publication:
Monthly Notices of the Royal Astronomical Society, Volume 438, Issue 2, p.1162-1175 (MNRAS Homepage)
Publication Date:
02/2014
Origin:
OUP
Astronomy Keywords:
MHD, methods: numerical, stars: low-mass, stars: magnetic field, planetary systems, stars: winds, outflows
Abstract Copyright:
2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society
DOI:
10.1093/mnras/stt2265
Bibliographic Code:
2014MNRAS.438.1162V

Abstract

We perform three-dimensional numerical simulations of stellar winds of early-M-dwarf stars. Our simulations incorporate observationally reconstructed large-scale surface magnetic maps, suggesting that the complexity of the magnetic field can play an important role in the angular momentum evolution of the star, possibly explaining the large distribution of periods in field dM stars, as reported in recent works. In spite of the diversity of the magnetic field topologies among the stars in our sample, we find that stellar wind flowing near the (rotational) equatorial plane carries most of the stellar angular momentum, but there is no preferred colatitude contributing to mass-loss, as the mass flux is maximum at different colatitudes for different stars. We find that more non-axisymmetric magnetic fields result in more asymmetric mass fluxes and wind total pressures ptot (defined as the sum of thermal, magnetic and ram pressures). Because planetary magnetospheric sizes are set by pressure equilibrium between the planet's magnetic field and ptot, variations of up to a factor of 3 in ptot (as found in the case of a planet orbiting at several stellar radii away from the star) lead to variations in magnetospheric radii of about 20 per cent along the planetary orbital path. In analogy to the flux of cosmic rays that impact the Earth, which is inversely modulated with the non-axisymmetric component of the total open solar magnetic flux, we conclude that planets orbiting M-dwarf stars like DT Vir, DS Leo and GJ 182, which have significant non-axisymmetric field components, should be the more efficiently shielded from galactic cosmic rays, even if the planets lack a protective thick atmosphere/large magnetosphere of their own.
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