Soutenance de Thèse : Chen Xie

« Development of advanced post-processing methods for the direct detection of exoplanets with ground-based high-contrast imagers »

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Thesis Abstract:
“Current high-contrast imaging techniques have limitations (i.e., self-subtraction and oversubtraction) at short angular separations (i.e., <0.3″), precisely where most exoplanets are situated. It is thus necessary to develop advanced post-processing techniques to overcome these limitations, further pushing the limit of current high-contrast imagers.  The goal of this thesis is to explore the potential of reference-star differential imaging (RDI) by using all the archival data for the detection and characterization of exoplanets and disks. The RDI technique I developed for SPHERE/IRDIS lays out the very fundamental framework in this thesis, and it enabled a wide range of applications and further developments. I show that RDI is a promising imaging technique for SPHERE, which can outperform angular differential imaging (ADI) at short angular separations. To expand the application to the SPHERE/IFS data, I further developed the RDI technique to include spectral diversities in the reference library without compromising sensitivity while reducing computational demands in post-processing. The concept of using archival data as references inspired the development of a new background subtraction for IRDIS. Combining RDI with data imputation using sequential nonnegative matrix factorization (DIsNMF), I demonstrate that RDI-DIsNMF is an optimized and model-free disk imaging technique that minimizes self-subtraction and oversubtraction. RDI-DIsNMF can accurately recover the disk morphology and preserve the disk flux with a throughput approaching 100%. At last, I apply the multiple techniques I developed in this thesis on IRDIS observations of HD 100453 as an astrophysical application. By recovering the spiral features via RDI-DIsNMF, I measure the spiral motion across 4 yr to perform dynamical motion analyses. The spiral pattern motion is consistent with the orbital motion of the eccentric companion. With this first observational evidence of a companion driving a spiral arm among protoplanetary disks, we directly and dynamically confirm the long-standing theory on the origin of spiral features in protoplanetary disks. ”

Jury members:

Remi SOUMMER                 Rapporteur
David MOUILLET                Rapporteur
Anne-Marie LAGRANGE     Examinatrice
Sasha HINKLEY                  Examinateur
Hervé Le COROLLER           Examinateur
Jean-Luc BEUZIT                Président du jury
Arthur VIGAN                    Directeur de thèse
Elodie CHOQUET               Co-directrice de thèse