Leonardo dos Santos (Geneva) "The high-energy environment and atmospheric escape of small exoplanets"
Abstract: Similarly to stars, planets also lose mass with time, even our own Earth. In particular, hot extrasolar planets orbiting close to their host stars are subject to large mass loss rates due to heating by high-energy irradiation and subsequent atmospheric escape. This process is so pervasive among hot planets that it imprints features in the population of transiting exoplanets, such as the hot-Neptune desert and the photoevaporation valley of super-Earths. Are small planets able to fight atmospheric escape and retain their primary atmospheres? If so, for how long? In this seminar, I will briefly go over some recent advances in observing the upper atmospheres of small transiting exoplanets aiming to constrain their rates of atmospheric escape and their high-energy environment. I will also present the main challenges of these observations, in particular the impact of stellar activity, and the preliminary results of a recent observation compaign to detect the upper atmosphere of a young transiting planet. Finally, I will discuss what are the best targets to observe atmospheric escape, and the future prospects for research.
Hila Glanz (Technion) "New perspectives on common envelope evolution"
Abstract: Common-envelope evolution (CEE) is the short-lived phase in the life of an interacting binary-system during which two stars orbit inside a single shared envelope.
Such evolution is thought to lead to the inspiral of the binary, the ejection of the extended envelope and the formation of a remnant short-period binary. However, detailed hydro-dynamical models of CEE encounter major di culties. They show that following the inspiral most of the envelope is not ejected; though it expands to larger separations, it remains bound to the binary. Here we propose that dust-driven winds can be produced following the CEE. These can evaporate the envelope following similar processes operating in the ejection of the envelopes of AGB stars. Pulsations in an AGB-star drives
the expansion of its envelope, allowing the material to cool down to low temperatures thus enabling dust condensation. Radiation pressure on the dust accelerates it, and through its coupling to the gas it drives winds which eventually completely erode the envelope. We show that the inspiral phase in CE-binaries can effectively replace the role of stellar pulsation and drive the CE expansion to scales comparable with those of AGB stars, and give rise to e cient mass-loss through dust-driven winds.
If time permits, I'll also discuss aspects of eccentric common envelope evolution and triple common envelope.