Investigating mass loss from RSG and AGB stars using the new VLTI-MATISSE imaging instrument

It is currently an open question in stellar astrophysics which physical processes initiate the mass loss of red supergiants. Observations of Betelgeuse during its recent great dimming event in 2019/2020 suggested a discrete highly localised mass ejection event, possibly connected to photospheric motion caused by a stochastic occurence of an extreme convection cell and possibly enhanced by pulsation (Dupree et al. 2020, Harper et al. 2020, Montarges et al., submitted), which may also explain the mass-loss history of the red hypergiant VY CMa, and of RSGs in general (Humphreys et al. 2020). There is indication that corundum, metallic iron, or other large transparent grains auch as Ca-Al-rich silicates may be present as close as down to about 2 stellar radii, which may serve as seeds for Mg-Fe-rich silicates at larger radii (Gail 2020). Here, we image the extended molecular layers and inner dust shell of the red supergaint AH Scorpii (AH Sco), which is known to exhibit a strong and narrow classical 9.7 mu silicate feature. We use the newly available infrared beam combiner MATISSE at the Very Large Telescope Interferometer (VLTI) to image AH Sco in the L band with a spectral resolution of 506, focusing on the SiO (2-0) bandhead, as well as in the N band focusing on the silicate dust. Our spatial resolution ranges from 3 mas at 4 mu to 10 mas at 12.5 mu. We also provide an outlook on comparing the levitation of the atmospheres and the dust condensation sequence between RSG and AGB stars, using the same observational setup for the Mira star R Aqr