Magnetic fields in M dwarfs: rapid magnetic field variability in EV Lac

Abstract

We report here our spectropolarimetric observations obtained using the Espadons/CFHT high resolution spectrograph of two M dwarf stars which standard models suggest are fully convective: EV Lac (M3.5) and HH And (M5.5). The difference in their rotational velocity makes them good targets to study the dependence of the magnetic field topology in M dwarfs on rotation. Our results reveal some aspects of the field topology in EV Lac and HH And. We measured mean longitudinal magnetic field strengths (Bz) in EV Lac ranging from 18+-3 G to -40+-3 G. The Bz variations are seen to occur in a timescale of less than 50 minutes, significantly shorter than the rotation period, and are not due to a flaring event. We discuss some formation scenarios of the Zeeman signatures found in EV Lac. For HH And we could not detect circular polarization and thus we place an upper limit to Bz of 5 G.

Accepted by ApJ Letters

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• Discovery of Radio Emission from the Tight M8 Binary: LP 349-25
• Simulations of Winds of Weak-Lined T Tauri Stars: The Magnetic Field Geometry and The Influence of the Wind on Giant Planet Migration
• Nonlinear regimes in mean-field full-sphere dynamo
• X-ray Flares of EV Lac: Statistics, Spectra, Diagnostics
• Kepler Observations of Very Low-Mass Stars
• Correlating Intrinsic Stellar Parameters with Mg II Self-Reversal Depths