Cool Under the Spotlight: Inferring the Photospheric Temperature of Betelgeuse from Spectra

Betelgeuse, the bright red supergiant in the constellation Orion, is one of the most recognizable stars in the night sky. Beginning in late 2019, the crimson star adorning Orion’s shoulder began to dim drastically, attracting worldwide attention. By February 2020, it had become historically faint, reaching a minimum of about 35% of its usual brightness. Over the next few months, the brightness rapidly returned to normal. Two years later, several scenarios have been presented to explain this phenomenon, which has since been dubbed the Great Dimming Event. The most prominent explanations include dust occultation, changes in the effective temperature of the star, or some combination of the two. Here, we present five epochs of low-resolution spectroscopy of Betelgeuse obtained using the 40-inch reflecting telescope at Mount Laguna Observatory that sample the object immediately before, during, and well after the historic minimum. Through direct comparison between these spectra and PHOENIX stellar atmosphere models, we investigate whether the change in effective temperature inferred from the spectral comparison alone can explain the decrease in brightness observed during the Great Dimming Event.