Magnetic Field of the Active Planet-hosting M Dwarf AU Mic

Abstract

AU Mic is a young, very active M dwarf star with a debris disk and at least one transiting Neptune-size planet. Here we present detailed analysis of the magnetic field of AU Mic based on previously unpublished high-resolution optical and near-infrared spectropolarimetric observations. We report a systematic detection of circular and linear polarization signatures in the stellar photospheric lines. Tentative Zeeman Doppler imaging modeling of the former data suggests a non-axisymmetric global field with a surface-averaged strength of about 90 G. At the same time, linear polarization observations indicate the presence of a much stronger $\approx$2 kG axisymmetric dipolar field, which contributes no circular polarization signal due to the equator-on orientation of AU Mic. A separate Zeeman broadening and intensification analysis allowed us to determine a mean field modulus of 2.3 and 2.1 kG from the Y- and K-band atomic lines respectively. These magnetic field measurements are essential for understanding environmental conditions within the AU Mic planetary system.

13 pages, 8 figures; accepted for publication in ApJ

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• The magnetic field and multiple planets of the young dwarf AU~Mic
• AU Microscopii in the FUV: Observations in Quiescence, During Flares, and Implications for AU Mic b and c
• Simulating the Space Weather in the AU Mic System: Stellar Winds and Extreme Coronal Mass Ejections
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• A Seven-Day Multi-Wavelength Flare Campaign on AU Mic I: High-Time Resolution Light Curves and the Thermal Empirical Neupert Effect
• Company for the ultra-high density, ultra-short period sub-Earth GJ 367 b: discovery of two additional low-mass planets at 11.5 and 34 days
• Searching for flaring star-planet interactions in AU Mic TESS observations
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• Multiwavelength Vertical Structure in the AU Mic Debris Disk: Characterizing the Collisional Cascade
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