Tomography of Betelgeuse

These masks are cross-correlated with the observed spectra to recover the velocity field inside each atmospheric layer. We obtained about 2800 spectra during the past 15 years, observed with the STELLA robotic telescope in Tenerife. We analyzed the variability of 5 different layers of Betelgeuses photosphere.

We found phase shift between the layers, as well as between the variability of velocity and photometry. The time variations of the widths of the cross-correlation function reveal propagation of two shock waves during the Great Dimming. For about 2 years after the Dimming, the time scale of variability was different between the inner and outer photospheric layers.

By 2022, all the layers seemingly started to follow a similar behavior as before the Dimming, but pulsating with higher frequency corresponding with the first overtone. Combination of the extensive high-resolution spectroscopic data set with the tomographic method revealed the variable velocity fields in the photosphere of Betelgeuse, for the first time in such detail. We were also able to find new insights related to the Great Dimming event and its aftermath, namely the discovery of another shock wave and the subsequent rearrangement of the photosphere.