Soutenance de thèse de Nicholas Scott le 30 octobre 2015

Titre de la thèse

First science with JouFLU

Directeurs de thèse

Vincent Coudé du Foresto (LESIA, Observatoire de Paris) et Harold McAlister (CHARA, Georgia State University)

Résumé

Jouvence of FLUOR (JouFLU) is a major overhaul of the FLUOR (Fiber Linked Unit for Optical Recombination) beam combiner built by the Laboratoire d’Etudes Spatiales et d’Instumentation en Astrophysique (LESIA) and installed at the CHARA array. These upgrades improve the precision, observing efficiency, throughput, and integration of FLUOR with the CHARA Array as well as introduce new modes of operation to this high-precision instrument for interferometry. Such high precision observations with FLUOR has provided the first unambiguous resolved detections of hot dust around main sequence stars (Absil et al. 2006), showing an unexpectedly dense population of (sub)micrometer dust grains close to their sublimation temperature (1400K). Competing models exist to explain the persistence of this dust ; some of which suggest that dust production is a punctuated and chaotic process fueled by asteroid collisions and comet infall that would show variability on timescales of a few years (Wya ! tt 2008) . By re-observing stars from the Absil et al. (2013) exozodiacal disks survey surveys we have searched for variations in the detected disks. We have found evidence that for some stars the amount of circumstellar flux from these previously detected exozodis has varied. The flux from some exozodis has increased, for some the flux has decreased, and for a few the amount has remained constant. These results are intriguing and will be no doubt useful for future modeling of this phenomenon. Furthermore, long-term monitoring is suggested for some of these objects to determine the rate of variation.