Long-term spectropolarimetric monitoring of the cool supergiant Betelgeuse

TL;DR

This study presents a long-term spectropolarimetric monitoring of Betelgeuse, revealing insights into its magnetic activity, convection, and temperature variations over two years using high-resolution instruments.

Contribution

It provides the first extensive spectropolarimetric dataset of Betelgeuse, analyzing magnetic and photospheric changes over time with simultaneous multi-parameter measurements.

Findings

Detection of temporal magnetic field variations.

Correlation between magnetic activity and photospheric indicators.

Insights into convection and temperature dynamics in Betelgeuse.

Abstract

We report on a long-term monitoring of the cool supergiant Betelgeuse, using the NARVAL and ESPaDOnS high-resolution spectropolarimeters, respectively installed at Telescope Bernard Lyot (Pic du Midi Observatory, France) and at the Canada-France-Hawaii Telescope (Mauna Kea Observatory, Hawaii). The data set, constituted of circularly polarized (Stokes V) and intensity (Stokes I) spectra, was collected between 2010 and 2012. We investigate here the temporal evolution of magnetic field, convection and temperature at photospheric level, using simultaneous measurements of the longitudinal magnetic field component, the core emission of the Ca II infrared triplet, the line-depth ratio of selected photospheric lines and the radial velocity of the star.