SPIRou reveals unusually strong magnetic fields of slowly rotating M dwarfs - Archive ouverte HAL
Article Dans Une Revue Monthly Notices of the Royal Astronomical Society Année : 2024

SPIRou reveals unusually strong magnetic fields of slowly rotating M dwarfs

Résumé

In this paper, we study six slowly rotating mid-to-late M~dwarfs (rotation period $P_{\mathrm{rot}} \approx 40-190\,\mathrm{dy}$) by analysing spectropolarimetric data collected with SPIRou at the Canada-France-Hawaii Telescope as part of the SPIRou Legacy Survey from 2019 to 2022. From $\approx$100--200 Least-Squares-Deconvolved (LSD) profiles of circularly polarised spectra of each star, we confirm the stellar rotation periods of the six M~dwarfs and explore their large-scale magnetic field topology and its evolution with time using both the method based on Principal Component Analysis (PCA) proposed recently and Zeeman-Doppler Imaging. All M~dwarfs show large-scale field variations on the time-scale of their rotation periods, directly seen from the circularly polarised LSD profiles using the PCA method. We detect a magnetic polarity reversal for the fully-convective M~dwarf GJ~1151, and a possible inversion in progress for Gl~905. The four fully-convective M~dwarfs of our small sample (Gl~905, GJ~1289, GJ~1151, GJ~1286) show a larger amount of temporal variations (mainly in field strength and axisymmetry) than the two partly-convective ones (Gl~617B, Gl~408). Surprisingly, the six M~dwarfs show large-scale field strengths in the range between 20 to 200\,G similar to those of M~dwarfs rotating significantly faster. Our findings imply that the large-scale fields of very slowly rotating M~dwarfs are likely generated through dynamo processes operating in a different regime than those of the faster rotators that have been magnetically characterized so far.
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hal-04287657 , version 1 (24-04-2024)

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L. Lehmann, J. -F. Donati, P. Fouque, C. Moutou, S. Bellotti, et al.. SPIRou reveals unusually strong magnetic fields of slowly rotating M dwarfs. Monthly Notices of the Royal Astronomical Society, 2024, 527, pp.4330-4352. ⟨10.1093/mnras/stad3472⟩. ⟨hal-04287657⟩
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