Direct Ultraviolet Imaging and Spectroscopy of Betelgeuse

TL;DR

This study presents four years of ultraviolet imaging and spectroscopy of Betelgeuse, revealing its extended UV emission, surface features, pulsations, chromospheric activity, and localized flows that may drive mass loss.

Contribution

First direct UV imaging and spectroscopy of Betelgeuse over multiple years, showing surface variability, chromospheric extension, and dynamic flows.

Findings

Extended UV emission about twice the optical diameter

Surface features change over months or less

Localized flows may initiate mass outflow

Abstract

Direct images of Betelgeuse were obtained over a span of 4 years with the Faint Object Camera on the Hubble Space Telescope. These images reveal the extended ultraviolet continuum emission (about 2 times the optical diameter), the varying overall ultraviolet flux levels and a pattern of bright surface continuum features that change in position and appearance over several months or less. Concurrent photometry and radial velocity measures support the model of a pulsating star, first discovered in the ultraviolet from IUE. Spatially resolved HST spectroscopy reveals a larger extention in chromospheric emissions of Mg II as well as the rotation of the supergiant. Changing localized subsonic flows occur in the low chromosphere that can cover a substantial fraction of the stellar disk and may initiate the mass outflow.