We present optical spectrophotometry of the red supergiant Betelgeuse from 2020 February 15 , during its recent unprecedented dimming episode .
By comparing this spectrum to stellar atmosphere models for cool supergiants , as well as spectrophotometry of other Milky Way red supergiants , we conclude that Betelgeuse has a current effective temperature of 3600 \pm 25 K. While this is slightly cooler than previous measurements taken prior to Betelgeuse ’ s recent lightcurve evolution , this drop in effective temperature is insufficient to explain Betelgeuse ’ s recent optical dimming .
We propose that episodic mass loss and an increase in the amount of large-grain circumstellar dust along our sightline to Betelgeuse is the most likely explanation for its recent photometric evolution .