Long-term magnetic field stability of Vega

TL;DR

This study presents new spectropolarimetric data of Vega, confirming the stability of its surface magnetic field over multiple years and showing minimal distortion by large-scale surface flows.

Contribution

The paper provides the first long-term spectropolarimetric monitoring of Vega's magnetic field, demonstrating its stability and consistency over several years.

Findings

Magnetic signatures of Vega are stable over multiple years.

Surface magnetic geometry shows minimal distortion by surface flows.

Consistent Zeeman-Doppler Imaging maps across observations.

Abstract

We present new spectropolarimetric observations of the normal A-type star Vega, obtained during the summer of 2010 with NARVAL at T\'elescope Bernard Lyot (Pic du Midi Observatory). This new time-series is constituted of 615 spectra collected over 6 different nights. We use the Least-Square-Deconvolution technique to compute, from each spectrum, a mean line profile with a signal-to-noise ratio close to 20,000. After averaging all 615 polarized observations, we detect a circularly polarized Zeeman signature consistent in shape and amplitude with the signatures previously reported from our observations of 2008 and 2009. The surface magnetic geometry of the star, reconstructed using the technique of Zeeman-Doppler Imaging, agrees with the maps obtained in 2008 and 2009, showing that most recognizable features of the photospheric field of Vega are only weakly distorted by large-scale surface flows (differential rotation or meridional circulation).