Spectropolarimetric characterisation of exoplanet host stars in preparation of the Ariel mission

II. The magnetised wind environment of TOI-1860, DS Tuc A, and HD 63433

¹ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
² Institut de Recherche en Astrophysique et Planétologie, Université de Toulouse, CNRS, IRAP/UMR 5277, 14 avenue Edouard Belin, 31400 Toulouse, France
³ Centre for Planetary Habitability (PHAB), Department for Geosciences, University of Oslo, Oslo, Norway
⁴ INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
⁵ SRON, Netherlands Institute for Space Research, Niels Bohrweg 4, 2333 CA, Leiden, The Netherlands
⁶ Department of Physics and Astronomy, University College London, Gower Street, WC1E 6BT London, UK
⁷ Science Engagement and Oversight Office, Directorate of Science, European Space Research and Technology Centre (ESA/ESTEC), Keplerlaan 1, 2201 AZ, Noordwijk, The Netherlands
⁸ Laboratoire Univers et Particules de Montpellier, Université de Montpellier, CNRS, 34095 Montpellier, France
⁹ University of Vienna, Department of Astrophysics, Türkenschanzstrasse 17, 1180 Vienna, Austria
¹⁰ INAF – Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 7 October 2025
Accepted: 28 November 2025

Abstract

Aims. We update the status of the spectropolarimetric campaign dedicated to characterise the magnetic field properties of a sample of known exoplanet-hosting stars included in the current target list of the Ariel mission. The main aims are to inform observing strategies and subsequent analysis of the data of the Ariel mission, and to provide background information on the magnetic properties of the target and their variability on timescales of at least a few years.

Methods. We analysed spectropolarimetric data collected for 15 G-M type stars with Neo-Narval, HARPSpol, and SPIRou to assess the detectability of the large-scale magnetic field. For three stars we reconstructed the magnetic field topology and its temporal evolution via Zeeman-Doppler imaging (ZDI). Such reconstructions were then used to perform three-dimensional magnetohydrodynamical simulations of the stellar wind and environment impinging on the hosted exoplanets.

Results. We detected the magnetic field of six stars. Of these, we performed ZDI reconstructions for the first time of TOI-1860 and DS Tuc A, and for the second time of HD 63433, providing temporal information of its large-scale magnetic field. Consistently with previous results on young (~50–100 Myr) solar-like stars, the large-scale magnetic field is moderately strong (30–60 G on average) and complex, with a significant fraction of magnetic energy in the toroidal component and high-order poloidal components. From the simulations of the stellar wind, we found the orbit of TOI-1860 b to be almost completely sub-Alfvénic, the orbits of DS Tuc A b and HD 63433 d to be trans-Alfvénic, and the orbits of HD 63433 b and c to be super-Alfvénic. We obtained marginal detections of the magnetic field for TOI-836 and TOI-2076, and detections for TOI-1136, but the number of observations is not sufficient for magnetic mapping.

Conclusions. A magnetic star-planet connection can occur for most of TOI-1860 b’s orbit. This can happen more sporadically for DS Tuc A b and HD 63433 c given the lower fraction of their orbit in the sub-Alfvénic regime. The orbit of HD 63433 c is nevertheless more sub-Alfvénic than previously simulated owing to the temporal evolution of the stellar magnetic field. For HD 63433 b and c, we expect the formation of a bow shock between the stellar wind and the planet despite the evolution of the stellar magnetic field.