Detection of the linearly polarised spectrum of the red supergiant star alpha Ori

TL;DR

This paper investigates the linear polarisation spectrum of the red supergiant star alpha Ori, proposing an analytical model to explain observed polarisation features that are difficult to detect due to spherical symmetry.

Contribution

The paper introduces an analytical model to explain the strong linear polarisation features observed in alpha Ori, a red supergiant star.

Findings

Identification of polarisation features in alpha Ori

Proposed analytical explanation for polarisation signatures

Insights into stellar atmosphere anisotropies

Abstract

In the solar limb, linear polarisation is due to anisotropy of the radiation field induced by limb darkening. It is maximal when it is seen parallel to the limb and it vanishes when it is integrated over the spherically-symmetric solar disk. Therefore for distant stars, that present spherical symmetry, linear polarisation signatures are very difficult to observe. However strong linear polarisation features have been reported in the prototypical red supergiant star alpha Ori (Betelgeuse). With an analytical model we propose to explain them.