Jaques Kluska – Disks around evolved binaries: do they form second-generation planets? @ B18N, Salle Univers
Déc 3 @ 11 h 00 min – 12 h 00 min

Title: Disks around evolved binaries: do they form second-generation planets?
Speaker: Jaques Kluska (KU Leuven)


Most of the planets were formed around young stars. But can they also form around dying stars? 
The origin of the diversity and complexity of the detected exoplanetary systems stems from how they form in protoplanetary disks. These disks are intensively studied around young stars thanks to the high-angular resolution provided by recent instruments (VLT, ALMA). However, similar disks are also found around evolved stars, namely post-AGB binaries, raising the exciting but yet unanswered possibility of second-generation planet formation. Do planets form around evolved stars? While this question has only been tackled theoretically in the past, we have now the possibility to probe such second-generation planet formation by observations using high angular resolution instruments.
In this talk I will show the latest results of an extensive high angular resolution observing campaign of these disks using infrared interferometry at the VLTI (PIONIER, GRAVITY, MATISSE). I will show that these disks share many similarities with protoplanetary disks around young stars.
These disks are, therefore, a unique laboratory to test planet formation processes in a parameter space that is unmet around young stars (e.g., short disk lifetime, high stellar luminosity, lack of influence from the environment).
Whether or not planet formation is possible at the end of stellar evolution, studying it in a very different parameter space will provide an unprecedented test to current planet formation theories. 
Ileyk el Mellah – Circumbinary envelope and wind mass transfer: from cool evolved stars to high-mass X-ray binaries @ B18N, Salle Univers
Déc 14 @ 11 h 00 min – 12 h 00 min

Title: Circumbinary envelope and wind mass transfer: from cool evolved stars to high-mass X-ray binaries
Speaker: Ileyk el Mellah (IPAG)


Stellar multiplicity has been recognized as a ubiquitous feature: stars seldom live an effectively single life. In the late stellar evolutionary stages, mass loss plays a major role while interaction with an orbiting companion can leave remarkable imprints in the circumbinary envelope and influence the final fate of the system. In binaries, whether the outflows are line-driven from a blue supergiant or dust-driven from a red giant, the flow morphology shares common features which shed light on the launching mechanism. High spatial and spectral resolution instruments have identified arcs and spirals around cool evolved stars which suggest the presence of underlying (sub-)stellar companions. On the other hand, in high-mass X-ray binaries, time-resolved spectroscopy over multiple orbits reveals how the clumpy wind is disrupted and accreted by the compact object.

In this talk, I will present simulations of mass transfer mediated by dust and line-driven winds in binaries. With the mesh-based radiative magneto-hydrodynamics code MPI-AMRVAC, we designed a versatile 3D setup suitable to capture the wind dynamics. In high mass X-ray binaries, we can follow the wind over several orders of magnitude as it is accreted onto the compact object. I will show how the compact object can also be used as an orbiting X-ray backlight whose shimmering betrays the structure of the foreground absorbing material. Around cool evolved stars, these simulations are extended up to several 10 orbital separations at an affordable computational cost, thanks to adaptive mesh refinement. For different dust chemical content, they can reproduce the morpho-kinematics properties we extracted from ALMA’s multi-channel molecular line emission maps. In both cases, I will describe how mass transfer redistributes angular momentum and can lead to orbital inspiral.