Longitudinal Analysis of Sudden Behavioral Changes in Red Supergiants Betelgeuse and RW Cephei

Music City Center 

The extreme dimming events observed in Betelgeuse in 2019-20 and RW Cephei in 2022 occurred suddenly following long periods of stable behavior. After these events, the stars have increased in brightness but have not returned to earlier behavior. Unobserved Components Models (UCM) provide a statistical method for analyzing changes in baseline characteristics such as these. UCM separates a light curve into periodic, baseline level, regression trend, and irregular components. This enables qualification and comparison of a star's behavior before, during, and after events such as those recently seen in Betelgeuse and RW Cephei. This analysis finds Betelgeuse has brightened since the dimming event, with a shorter period and an upward trend in brightness exceeding the previous baseline level. As of May 2023, Betelgeuse is found to have a V of 0.2 and a period of about 310 - 360 days, lower than the period of 400 - 425 days before the dimming event. The irregular variable RW Cephei is found to have a historical baseline magnitude of 7.01 ± 0.12. RW Cephei also has increased in brightness since its dimming event, from 7.75 at its faintest in early 2023 to 7.38 two months later. Source code for UCM analysis of variable stars is given in Python, R, and SAS.