Is AD Leo entering a polarity reversal? Long-term monitoring of the large-scale magnetic field with ESPaDOnS, NARVAL and SPIRou Stefano Bellotti1,3, Julien Morin2, Lisa Lehmann1, Pascal Petit1, Gaitee Hussain3 and the SLS consortium 1: IRAP, Toulouse (FR), 2: LUPM, Montpellier (FR), 3: ESA/ESTEC, Noordwijk (NL) stefano.bellotti@irap.omp.eu Acknowledgements: Based on observations obtained at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council (NRC) of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique (CNRS) of France, and the University of Hawaii. The observations at the CFHT were performed with care and respect from the summit of Maunakea which is a significant cultural and historic site. We gratefully acknowledge the CFHT QSO observers who made this project possible. We acknowledge funding from ANR of France (SPlaSH), with PI Xavier Delfosse. Fig 1. Evolution of Bl. Left: optical (circles) and near-infrared (squares) time series between 2006 and 2020. Right: near-infrared time series phase-folded at the stellar rotation period. FWHM of Stokes I ●FWHM useful activity tracer sensitive to Zeeman eﬀect → high Landé factor (geﬀ) lines can reveal activity signal ●Full vs high-geﬀ mask [12]: all FWHM values are larger in the latter case ●Constant vs sine ﬁt: the variations of the 2020b epoch are better described by sinusoid ﬁt (22% decrease in residual RMS) Longitudinal magnetic ﬁeld ●Disk-integrated, line-of-sight component of the magnetic ﬁeld (Bl) ●Stellar north pole is dominated by negative dipole all the time ●Global decrease in ﬁeld strength over 14 years ●Reduced axisymmetry indicated by varying amplitude in the phase-folded time series Fig 2. Phase-folded FWHM curves using full and high-geff masks for near-infrared epochs: 2019a (top), 2019b2020a (middle), 2020b (bottom) ●Increased FWHM variations imply lower degree of axisymmetry ●FWHM phase variations are reﬂected by ZDI maps Principal Component Analysis ●Apply PCA to mean-subtracted near-infrared Stokes V (2019-2020) to infer details on non-axisymmetric ﬁeld [13, see also poster of L. T. Lehmann] Zeeman-Doppler Imaging ●Reconstruction of the large-scale magnetic ﬁeld topology by means of a maximum-entropy algorithm Stellar magnetic cycles With a long-term monitoring of the large-scale magnetic ﬁeld, we can search for temporal evolution of the topology and uncover stellar dynamo theories. The Sun is an important benchmark: the magnetic cycle is characterised by a 11-yr variation in sunspot number, size and latitude of emergence, and magnetic polarity reversal [1,2]. Spectropolarimetric observations revealed analogous polarity ﬂips also on other stars [3,4]. At the lower end of the main sequence, M dwarfs represent excellent laboratories to study non-solar dynamo mechanisms underlying the generation and preservation of magnetic ﬁelds. Conclusions ●Variations in the coeﬃcients are more sinusoidal and ampliﬁed → large-scale ﬁeld is dipolar and its axisymmetry decreases over time Fig 3. Evolution of PCA coefficients for the first three eigenvectors over the near-infrared epochs: 2019a (top), 2019b2020a (middle) and 2020b (bottom). ●First three eigenvectors have signals → on average ﬁeld is non-axisymmetric Fig 4. Evolution of ZDI map over near-infrared epochs: 2019a (left), 2019b2020a (middle) and 2020b (right). The magnetic maps are in flat polar view, with the north pole at the center and the equator marked by a solid line ●The geometry is poloidal (magnetic energy fraction >90%) and dipolar (>70%), as in 2006-2016 observations ●Axisymmetry decreases from >85% to 48% in 2020b and tilt angle increases from 15o to 56o accordingly ●Decreasing axisymmetry of the large-scale ﬁeld conﬁrmed by diﬀerent techniques ●Global evolution of the large-scale ﬁeld of AD Leo possibly suggesting a magnetic cycle, in the strong aligned dipole category ●Diﬀerence of longitudinal and ZDI ﬁeld streng