Near- and mid-infrared spectrum of WOH G64. a: spectrophotometric and photometric data taken at 1–4 μm before 2010. The light blue, pink, and violet lines represent the spectra taken with ISO/PHT in 1996, ISO/SWS in 1998, and SOFI in 2003, respectively. The red triangles and open squares correspond to the photometric data from Whitelock et al. (2003) and Wood et al. (1992), respectively. The bars show the (peak-to-peak) variability amplitudes, not the measurement errors. The gray diamond and blue triangle represent the photometric data taken with WISE in 2009–2010 and Spitzer in 2005–2006, respectively. The H₂O absorption features in the RSG spectrum are also indicated. b: spectra of WOH G64 taken more recently. The green and orange lines represent the spectra taken with X-shooter in 2016 and GRAVITY in 2020, respectively. The blue diamonds show the JHK′ photometric data taken in 2024 with REM/REMIR. The GRAVITY and X-shooter data are scaled to the REM/REMIR K′-band flux. The spikes in the X-shooter spectrum as well as the very tiny peak at ∼2.16 μm in the GRAVITY spectrum are the residual of the correction for the absorption lines in the spectrum of the calibrator. c: mid-infrared spectra of WOH G64 showing the 10 μm silicate feature in absorption. The blue and black lines represent the spectra obtained with MIDI in 2005 and 2007, respectively, by Ohnaka et al. (2008). The dotted green line shows the Spitzer/IRS spectrum taken in 2004, while the orange line corresponds to the VISIR spectrum taken in 2022. The wavelength range between 9.3 and 9.8 μm is severely affected by the telluric absorption.