Betelgeuse Just Isn’t That Cool: Effective Temperature Alone Cannot Explain the Recent Dimming of Betelgeuse suggests that the recent dimming might be caused by increased optical absorption by dust around the star, based on a spectral analysis.

Question: The images below show absorption features assigned to titanium oxide (TiO). Why are these features saw-tooth shaped? When I think of absorption edges the transmitted light drops when crossing from lower to higher energy photons, but here the measured light increases from lower to higher energy.

Fig. 1.— Optical spectrophotometry of Betelgeuse from 2020 (black) and 2004 (red).

Fig. 2.— Normalized and continuum-flattened spectra of Betelgeuse from 2020 (black) and 2004 (red dashed), illustrating the relative depths of the T_eff-sensitive TiO bands (labeled) in both spectra.