A polarity reversal in the large-scale magnetic field of the rapidly rotating Sun HD 190771

TL;DR

This study tracks the magnetic field evolution of the rapidly rotating Sun-like star HD 190771, revealing a polarity reversal and changes in magnetic energy distribution over two years, providing insights into stellar dynamo processes.

Contribution

First detailed magnetic field evolution analysis of HD 190771, highlighting polarity reversal linked to rotation rate effects in solar-type stars.

Findings

Polarity reversal of the magnetic field occurred between 2007 and 2008.

A sharp decrease in the toroidal magnetic energy fraction was observed between 2008 and 2009.

No significant change in total magnetic energy was detected during the observed period.

Abstract

Aims. We investigate the long-term evolution of the large-scale photospheric magnetic field geometry of the solar-type star HD 190771. With fundamental parameters very close to those of the Sun except for a shorter rotation period of 8.8 d, HD 190771 provides us with a first insight into the specific impact of the rotation rate in the dynamo generation of magnetic fields in 1 $M_\odot$ stars. Methods. We use circularly polarized, high-resolution spectra obtained with the NARVAL spectropolarimeter (Observatoire du Pic du Midi, France) and compute cross-correlation line profiles with high signal-to-noise ratio to detect polarized Zeeman signatures. From three phase-resolved data sets collected during the summers of 2007, 2008, and 2009, we model the large-scale photospheric magnetic field of the star by means of Zeeman-Doppler imaging and follow its temporal evolution. Results. The comparison of the magnetic maps shows that a polarity reversal of the axisymmetric component of the large-scale magnetic field occurred between 2007 and 2008, this evolution being observed in both the poloidal and toroidal magnetic components. Between 2008 and 2009, another type of global evolution occured, characterized by a sharp decrease of the fraction of magnetic energy stored in the toroidal component. These changes were not accompanied by significant evolution in the total photospheric magnetic energy. Using our spectra to perform radial velocity measurements, we also detect a very low-mass stellar companion to HD 190771.