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

Abstract

Previous studies have related surface temperature maps, obtained with the Doppler imaging (DI) technique, of LQ Hya with long-term photometry. We compare surface magnetic field maps, obtained with the Zeeman Doppler imaging (ZDI) technique, with contemporaneous photometry, with the aim of quantifying the star's magnetic cycle characteristics. We inverted Stokes IV spectropolarimetry into magnetic field and surface brightness maps using a tomographic inversion code that models high signal-to-noise ratio mean line profiles produced by the least squares deconvolution (LSD) technique. The magnetic field and surface brightness maps reveal similar patterns to previous DI and ZDI studies: non-axisymmetric polar magnetic field structure, void of fields at mid-latitudes, and a complex structure in the equatorial regions. There is a weak but clear tendency of the polar structures to be linked with strong radial field and the equatorial ones with the azimuthal. We find a polarity 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 with the retrieved field complexity. Comparing to global magnetoconvection models for rapidly rotating young Suns, this field topology and dominance of the poloidal field component could be explained by a turbulent dynamo, where differential rotation does not play a major role (so called alpha^2 Omega or alpha^2 dynamos), and axi- and non-axisymmetric modes are excited simultaneously. The complex equatorial magnetic field structure could arise from the twisted (helical) wreaths often seen in these simulations, while the polar feature would be connected to the mostly poloidal non-axisymmetric component having a smooth spatial structure.

arXiv comment13 pages, 8 figures, 7 tables

References in corpus (34)

• Least squares deconvolution of the stellar intensity and polarization spectra
• A catalogue of young runaway Hipparcos stars within 3kpc from the Sun
• Patterns of photometric and chromospheric variation among Sun-like stars: A 20-year perspective
• Magnetic activity in the HARPS M-dwarf sample. The rotation-activity relationship for very low-mass stars through R'HK
• Magnetic cycles of the planet-hosting star tauBootis
• Magnetic cycles of the planet-hosting star Tau Bootis: II. a second magnetic polarity reversal
• Multiple and changing cycles of active stars II. Results
• High-Dispersion Optical Spectra of Nearby Stars Younger Than The Sun
• Temporal fluctuations in the differential rotation of cool active stars
• Dipolar versus multipolar dynamos: the influence of the background density stratification
• Magnetic field topology of the unique chemically peculiar star CU Virginis
• A solar-like magnetic cycle on the mature K-dwarf 61 Cyg A (HD 201091)
• Activity trends in young solar-type stars
• The Evolving Magnetic Topology of $\tau$ Boötis
• Estimating activity cycles with probabilistic methods II. The Mount Wilson Ca H&K data
• Transition from axi- to nonaxisymmetric dynamo modes in spherical convection models of solar-like stars
• Direct observation of magnetic cycles in Sun-like stars
• Magnetic fields on young, moderately rotating Sun-like stars - I: HD~35296 and HD~29615
• Magnetic fields of young solar twins
• A polarity reversal in the large-scale magnetic field of the rapidly rotating Sun HD 190771
• Magnetic field topology of the RS CVn star II Pegasi
• The relation between stellar magnetic field geometry and chromospheric activity cycles II: The rapid 120 day magnetic cycle of Tau Bootis
• Direct evidence of a full dipole flip during the magnetic cycle of a sun-like star
• Spectroscopic parameters for solar-type stars with moderate/high rotation. New parameters for 10 planet-hosts
• Spot activity of LQ Hya from photometry between 1988 and 2011
• The continuous period search method and its application to the young solar analogue HD 116956
• How reliable is Zeeman Doppler Imaging without simultaneous temperature reconstruction?
• Zeeman-Doppler imaging of active young solar type stars
• Strong variable linear polarization in the cool active star II Peg
• Starspot activity of HD 199178. Doppler images from 1994--2017
• Short-term evolution and coexistence of spots, plages and flare activity on LQ Hydrae
• Doppler Imaging of LQ Hya for 1998-2002
• Spot evolution on LQ Hya during 2006--2017: temperature maps based on SOFIN and FIES data
• Chromospheric emission of solar-type stars with asteroseismic ages

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