First images of the Antares photosphere from spectropolarimetry

¹ Institut de Recherche en Astrophysique et Planétologie, Université de Toulouse, UPS, CNRS, IRAP/UMR 5277, 14 avenue Edouard Belin, 31400 Toulouse, France
² LUPM, UMR5299, CNRS and Université Montpellier, Place E.Bataillon, 34090 Montpellier, France
³ IRAP, Université de Toulouse, CNRS, UPS, CNES, 57 avenue d’Azereix, 65000 Tarbes, France

^★ Corresponding author.

Received: 12 May 2025
Accepted: 8 July 2025

Abstract

Aims. Antares is the closest red supergiant (RSG) to Earth. The discovery of linear polarization in the atomic lines of the star opens the path to producing direct images of the photosphere, and hence probing the dynamics at the surface.

Methods. We analyze this linear polarization signals following the same scheme as has been previously done for the RSG Betelgeuse, and find that they are comparable in all its details. This allows us to use the same models for the analysis of these polarization signals in both stars.

Results. We find that, as in Betelgeuse, the linear polarization signal of Antares is due to the depolarization of the continuum, combined with brightness inhomogeneities. This allows us to produce images of the photosphere of the star. We show that in Antares convective cells can last several months and that the largest ones can occupy roughly 30% of the stellar radius.