Topological changes in the magnetic field of LQ Hya during an activity minimum

Lehtinen, J. J.; Käpylä, Maarit J.; Hackman, T.; Kochukhov, O.; Willamo, T.; Marsden, S.C.; Jeffers, Sandra V.; Henry, G.W.; Jetsu, L.

doi:10.1051/0004-6361/201936780

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Topological changes in the magnetic field of LQ Hya during an activity minimum

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Käpylä, Maarit J.
Max Planck Research Group in Solar and Stellar Magnetic Activity, Max Planck Institute for Solar System Research, Max Planck Society;
Department Sun and Heliosphere, Max Planck Institute for Solar System Research, Max Planck Society;

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Jeffers, Sandra V.
Department Solar and Stellar Interiors, Max Planck Institute for Solar System Research, Max Planck Society;

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Citation

Lehtinen, J. J., Käpylä, M. J., Hackman, T., Kochukhov, O., Willamo, T., Marsden, S., et al. (2022). Topological changes in the magnetic field of LQ Hya during an activity minimum. Astronomy and Astrophysics, 660: A141. doi:10.1051/0004-6361/201936780.

Cite as: https://hdl.handle.net/21.11116/0000-000A-85BE-A

Abstract

Aims.Previous studies have related surface temperature maps, obtained with the Doppler imaging (DI) technique, of LQ Hya withlong-term photometry. Here, we will compare surface magnetic field maps, obtained with the Zeeman Doppler imaging (ZDI)tech-nique, with contemporaneous photometry, with the aim of quantifying the star’s magnetic cycle characteristics.Methods.We inverted StokesIVspectropolarimetry, obtained with the HARPSpol and ESPaDOnS instruments, into magnetic fieldand surface brightness maps using a tomographic inversion code that models high signal-to-noise ratio mean line profiles produced bythe least squares deconvolution (LSD) technique. The maps were compared against long-term ground based photometry which offersa proxy for the spot cycle of the star.Results.The magnetic field and surface brightness maps reveal similar patterns to previous DI and ZDI studies: non-axisymmetricpolar magnetic field structure, void of fields at mid-latitudes, and a complex structure in the equatorial regions. Thereis a weak butclear tendency of the polar structures to be linked with strong radial field and the equatorial ones with the azimuthal. Wefind apolarity reversal in the radial field between 2016 and 2017 coincident with an activity minimum seen in the long-term photometry.The inverted field strengths cannot easily be related with the observed spottedness, but we find that they are partially connected withthe retrieved field complexity.Conclusions.Comparing to global magnetoconvection models for rapidly rotating young Suns, this field topology and dominanceof the poloidal field component could be explained by a turbulent dynamo, where differential rotation does not play a major role (socalledα2Ωorα2dynamos), and axi- and non-axisymmetric modes are excited simultaneously. The complex equatorial magnetic fieldstructure could arise from the twisted (helical) wreaths often seen in these simulations, while the polar feature wouldbe connected tothe mostly poloidal non-axisymmetric component having a smooth spatial structure.