mercredi 11 septembre 2019
La soutenance aura lieu le mercredi 18 septembre 2019 à 14h00 dans la salle de conférence du Château (bâtiment 9) sur le site de Meudon.
"The 2017 conjunction of Beta Pictoris b : Life and Death of PicSat, followed by a VLTI/GRAVITY observation of the re-emergence"
Sylvestre Lacour
Beta Pictoris is arguably one of the best-known stellar system outside of our own. A rare combination of a bright star, the presence of an edge-on debris disk, and the young age of the system, all make Beta Pic a remarkable target to study the evolution of planetary systems. Thirty years of direct imaging and transit spectroscopy observations have revealed a highly structured disk, with rings, belts, and a giant planet : Beta Pic b. But very little is known about how the system came into being. In particular, the formation history of Beta Pic b and the way it interacts with the disk remain elusive. This thesis focuses on two new attempts made to observe the giant planet, at the time of its inferior conjunction, in 2017/2018. As part of the international observation campaign dedicated to the 2017 Beta Pic b Hill sphere transit, PicSat, a small three-unit CubeSat, was launched to Low Earth Orbit. The satellite carried a fibered photometer, whose objective was to monitor the brightness of the star Beta Pictoris, in order to detect and characterize the transit of the Hill sphere of Beta Pictoris b. The design, development, and tests of this instrument are detailed in the first part of this thesis. The satellite was successfully deployed in orbit, but a malfunction of its commercial attitude control system made it unable to produce any photometric data. The second part of this thesis introduces VLTI/GRAVITY spectro-interferometric observations of the giant planet Beta Pic b, made soon after the conjunction. The combined four 8.2 m telescopes of the VLTI were used to obtain a high signal to noise, medium resolution, K-band spectrum of the planet, from which the first estimate of the planetary carbon-to-oxygen ratio was be derived. The resulting substellar C/O ratio suggests that the giant planet is unlikely to have formed through gravitational instability, and that core-accretion is a more plausible scenario.
La thèse sera soutenue en anglais.
