Abstract

Context. Significant mass loss in the red supergiant (RSG) phase has great influence on the evolution of massive stars and their final fate as supernovae. Aims. We present near-infrared interferometric imaging of the circumstellar environment of the dust-enshrouded RSG WOH G64 in the Large Magellanic Cloud. Methods. WOH G64 was observed with the GRAVITY instrument at ESO's Very Large Telescope Interferometer (VLTI) at 2.0-2.45 mu m. We succeeded in imaging the innermost circumstellar environment of WOH G64 - the first interferometric imaging of an RSG outside the Milky Way. Results. The reconstructed image reveals elongated compact emission with a semimajor and semiminor axis of similar to 2 and similar to 1.5 mas (similar to 13 and 9 R-star), respectively. The GRAVITY data show that the stellar flux contribution at 2.2 mu m 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 mu m 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. Conclusions. 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.