Evolving magnetic lives of Sun-like stars. I. Characterisation of the large-scale magnetic field with Zeeman-Doppler imaging

Planets orbiting young, solar-type stars are embedded in a more energetic environment than that of the solar neighbourhood. They experience harsher conditions due to enhanced stellar magnetic activity and wind shaping the secular evolution of a planetary atmosphere. This study is dedicated to the characterisation of the magnetic activity of eleven Sun-like stars, with ages between 0.2 and 6.1 Gyr and rotation periods between 4.6 and 28.7 d. Based on a sub-sample of six stars, we aim to study the large-scale magnetic field, which we then use to simulate the associated stellar wind and environment. Finally, we want to determine the conditions during the early evolution of planetary habitability. We analysed high-resolution spectropolarimetric data collected in 2018 and 2019 with Narval. We computed activity diagnostics from chromospheric lines such as CaII H&K, H$α$, and the CaII infrared triplet, as well as the longitudinal magnetic field from circularly polarised least-squares deconvolution profiles. For six stars exhibiting detectable circular polarisation signals, we reconstructed the large-scale magnetic field at the photospheric level by means of Zeeman-Doppler imaging (ZDI). In agreement with previous studies, we found a global decrease in the activity indices and longitudinal field with increasing age and rotation period. The large-scale magnetic field of the six sub-sample stars displays a strength between 1 and 25 G and reveals substantial contributions from different components such as poloidal (40-90 %), toroidal (10-60 %), dipolar (30-80 %), and quadrupolar (10-40 %), with distinct levels of axisymmetry (6-84 %) and short-term variability of the order of months. Ultimately, this implies that exoplanets tend to experience a broad variety of stellar magnetic environments after their formation.