%0 Journal Article
%T The large-scale magnetic field of Proxima Centauri near activity maximum
%+ Institut de recherche en astrophysique et planétologie (IRAP)
%+ Laboratoire Univers et Particules de Montpellier (LUPM)
%+ Institut de Planétologie et d'Astrophysique de Grenoble (IPAG)
%A Klein, Baptiste
%A Donati, Jean-François
%A Hébrard, Élodie M.
%A Zaire, Bonnie
%A Folsom, Colin P.
%A Morin, Julien
%A Delfosse, Xavier
%A Bonfils, Xavier
%Z 7 pages, 5 figures, accepted to MNRAS
%< avec comité de lecture
%@ 0035-8711
%J Monthly Notices of the Royal Astronomical Society
%I Oxford University Press (OUP): Policy P - Oxford Open Option A
%V 500
%N 2
%P 1844–1850
%8 2021-01
%D 2021
%Z 2010.14311
%R 10.1093/mnras/staa3396
%K Techniques: polarimetric
%K Stars: individual
%K Proxima Centauri
%K Stars: low-mass
%K Stars: magnetic field
%K Stars: rotation
%Z Physics [physics]/Astrophysics [astro-ph]/Solar and Stellar Astrophysics [astro-ph.SR]
%Z Physics [physics]/Astrophysics [astro-ph]/Earth and Planetary Astrophysics [astro-ph.EP]Journal articles
%X We report the detection of a large-scale magnetic field at the surface of the slowly-rotating fully-convective M dwarf Proxima Centauri. Ten circular polarization spectra, collected from April to July 2017 with the HARPS-Pol spectropolarimeter, exhibit rotationally-modulated Zeeman signatures suggesting a stellar rotation period of $89.8 \pm 4.0$ d. Using Zeeman-Doppler Imaging, we invert the circular polarization spectra into a surface distribution of the large-scale magnetic field. We find that Proxima Cen hosts a large-scale magnetic field of typical strength 200 G, whose topology is mainly poloidal, and moderately axisymmetric, featuring, in particular, a dipole component of 135 G tilted at 51$^{\circ}$ to the rotation axis. The large-scale magnetic flux is roughly 3 times smaller than the flux measured from the Zeeman broadening of unpolarized lines, which suggests that the underlying dynamo is efficient at generating a magnetic field at the largest spatial scales. Our observations occur $\sim$1 yr after the maximum of the reported 7 yr-activity cycle of Proxima Cen, which opens the door for the first long-term study of how the large-scale field evolves with the magnetic cycle in a fully-convective very-low-mass star. Finally, we find that Proxima Cen's habitable zone planet, Proxima-b, is likely orbiting outside the Alfv\`en surface, where no direct magnetic star-planet interactions occur.
%G English
%2 https://hal.science/hal-02996801/document
%2 https://hal.science/hal-02996801/file/2010.14311.pdf
%L hal-02996801
%U https://hal.science/hal-02996801
%~ IN2P3
%~ IRD
%~ INSU
%~ METEO
%~ UNIV-SAVOIE
%~ UNIV-TLSE3
%~ UGA
%~ CNRS
%~ CNES
%~ OSUG
%~ OMP
%~ OMP-IRAP
%~ LUPM
%~ IPAG
%~ UNIV-MONTPELLIER
%~ LUPM_AS
%~ INRAE
%~ UGA-EPE
%~ UNIV-UT3
%~ UT3-INP
%~ UT3-TOULOUSEINP
%~ UM-2015-2021
%~ INEE-CNRS