The Curious Case of Betelgeuse

Since more than a decade, the AIP is monitoring $\alpha$ Ori with its robotic spectroscopic facility STELLA/SES in Teide observatory, Tenerife along with its automated photoelectric telescope T7 in Fairborn observatory, Az. Additionally, we got access with exclusive two-band photometric data on Betelgeuse from the BRITE satellite consortium, covering the last seven seasons. In late 2019, Betelgeuse showed a rapid brightness decline, reaching an all-time low in Feb. 2020, followed by a quick re-brightening. This poster  shows radial velocity data together with the photometry. The radial velocity follows the photometry in general, but sometimes shows a time-shift, which was particularly visible in the grand dimming event. Interesting is the time-frequency analysis of the different data set: All three show similar features at split-periods around the known P=420d.