Jeremy Drake (CfA)
“Stellar Coronal Mass Ejections: Coming soon to an exoplanet near you”
Are recent superflares observed on Proxima Centauri and other stars harbingers of massive and energetic coronal mass ejections (CMEs)? Such CMEs would create extreme space weather environments for exoplanets and could severely erode planetary atmospheres. CMEs have not yet been definitively detected on stars other than the Sun, but if we use the Sun as a guide nearly all large stellar flares should be associated with CMEs. This presents a quandary: active stars are constantly flaring and extrapolation from the Sun suggests associated CMEs would require an unrealistically large energy budget. One potential answer is magnetic suppression of CMEs, in which the strong large-scale fields of active stars trap and prevent most CMEs from escaping. Monster CMEs will probably still exist, and have the potential to ravage planetary atmospheres. Their detection and understanding are of primary importance for stellar and planetary physics.
Tomasz Kaminski (CfA)
“Molecular dust precursors in envelopes of oxygen-rich AGB stars and red supergiants”
Condensation of circumstellar dust begins with formation of molecular clusters close to the stellar photosphere. These clusters are predicted to act as condensation cores at lower temperatures, i.e. allow efficient dust formation farther away from the star. The condensation process is poorly understood, particularly in oxygen-rich stars. Recent observations of exotic metal oxides, such as AlO, AlOH, TiO, and TiO2, whose emission can be traced at high angular resolutions with ALMA, have allowed first observational studies of the condensation process in oxygen-rich stars. We are now in the era when depletion of gas-phase species into dust can be observed directly. I am going to present the most recent observations that allow us to identify the species that initiate the formation of inorganic dust close to photospheres of AGB stars and red supergiants. I am also going to discuss challenges one has to face in interpreting the observations, especially these related to non-equilibrium chemistry, non-LTE gas excitation, and high complexity of stellar atmospheres in the dust-formation zone.