Imaging the innermost circumstellar environment of the red supergiant WOH G64 in the Large Magellanic Cloud

Abstract

Significant mass loss in the red supergiant (RSG) phase has great influence on the evolution of massive stars and their final fate as supernovae. We present near-infrared interferometric imaging of the circumstellar environment of the dust-enshrouded RSG WOH G64 in the Large Magellanic Cloud. WOH G64 was observed with the GRAVITY instrument at ESO's Very Large Telescope Interferometer (VLTI) at 2.0--2.45 micron. We succeeded in imaging the innermost circumstellar environment of WOH G64 -- the first interferometric imaging of an RSG outside the Milky Way. The reconstructed image reveals elongated compact emission with a semimajor and semiminor axis of ~2 and ~1.5 mas (~13 and 9 stellar radii), respectively. The GRAVITY data show that the stellar flux contribution at 2.2 micron at the time of our observations in 2020 is much lower than predicted by the optically and geometrically thick dust torus model based on the VLTI/MIDI data taken in 2005 and 2007. We found a significant change in the near-infrared spectrum of WOH G64: while the (spectro)photometric data taken at 1--2.5 micron before 2003 show the spectrum of the central RSG with H2O absorption, the spectra and JHK' photometric data taken after 2016 are characterized by a monotonically rising continuum with very weak signatures of H2O. This spectral change likely took place between December 2009 and 2016. On the other hand, the mid-infrared spectrum obtained in 2022 with VLT/VISIR agrees well with the spectra obtained before 2007. The compact emission imaged with GRAVITY and the near-infrared spectral change suggest the formation of hot new dust close to the star, which gives rise to the monotonically rising near-infrared continuum and the high obscuration of the central star. The elongation of the emission may be due to the presence of a bipolar outflow or effects of an unseen companion.

10 pages, 8 figures, published in Astronomy and Astrophysics

References in corpus (14)

• Binary interaction dominates the evolution of massive stars
• An eclipsing binary distance to the Large Magellanic Cloud accurate to 2 per cent
• The High Angular Resolution Multiplicity of Massive Stars
• Confined Dense Circumstellar Material Surrounding a Regular Type II Supernova: The Unique Flash-Spectroscopy Event of SN 2013fs
• The wind speeds, dust content, and mass-loss rates of evolved AGB and RSG stars at varying metallicity
• The 3D Morphology of VY Canis Majoris. I The Kinematics of the Ejecta
• The Mass-Loss Return From Evolved Stars to the LMC: Empirical Relations for Excess Emission at 8 and 24 μm
• Efficient injection from large telescopes into single-mode fibres: Enabling the era of ultra-precision astronomy
• The X-Shooter Spectral Library (XSL): Data Release 2
• Spatially resolved dusty torus toward the red supergiant WOH G64 in the Large Magellanic Cloud
• ALMA Observations of Anisotropic Dust Mass-loss in the Inner Circumstellar Environment of the Red Supergiant VY Canis Majoris
• The Physical Properties of the Red Supergiant WOH G64: The Largest Star Known?
• Circumstellar Material Ejected Violently by A Massive Star Immediately before its Death
• The mass-loss rates of red supergiants at low metallicity: Detection of rotational CO emission from two red supergiants in the Large Magellanic Cloud