# # Program information file # PROGRAM_ID 2021A100 PROGRAM_TITLE Taking Betelgeuse's Temperature--Using water absorption features in Red Supergiants to investigate the cause of the Great Dimming of 2019/2020 PROGRAM_INV1 Amanda Townsend PROGRAM_INV2 Matthew Richter PROGRAM_INV3 PROGRAM_INV4 PROGRAM_INV5 PROGRAM_SCICAT stellar PROGRAM_ABSTRACT_BEG Betelgeuse's naked-eye-visible dimming has captured the attention of the public and astronomers alike. While there are two leading hypotheses to explain the cause -- circumstellar dust, and a drop in the star's effective temperature -- there is no conclusive evidence in favor of either one. During the Great Dimming of 2019/2020, where Betelgeuse decreased significantly in optical brightness, SOFIA-EXES obtained observations of Betelgeuse at two different mid-infrared wavelength locations: 25.99 microns and 25.25 microns. New, complementary follow-up observations to this pre-existing data with both EXES and TEXES will allow us to discriminate between the two ideas. The EXES Great Dimming observations match previous pre-dimming observations of the iron and sulfur emission lines, respectively, from 2015 and 2017. This unique mid-infrared dataset also shows photospheric water absorption features which are sensitive to temperature. Along with follow-up observations of Betelgeuse, we propose to observe a set of template M-supergiant stars with different temperatures at these same wavelengths with EXES as well as in order to fully contextualize the relationship between these water lines and the star's photospheric temperature using theoretical models. TEXES observations at three extra wavelength settings near 12 microns and 18 microns of Betelgeuse and our other RSG template stars will supplement existing and future EXES observations to give a wider perspective on the photospheric temperatures of these stars. This will allow us to determine Betelgeuse's effective temperature during the Great Dimming and assess whether this played a role in the star's observed behavior. PROGRAM_ABSTRACT_END