Understanding the formation and evolution of planetary systems is one of the most fundamental challenges in astronomy. To directly image and study young exoplanets and the circumstellar disks they... Show moreUnderstanding the formation and evolution of planetary systems is one of the most fundamental challenges in astronomy. To directly image and study young exoplanets and the circumstellar disks they form from, dedicated high-contrast imaging instruments are built. Several of these instruments have polarimetric modes that are particularly powerful to reach the large contrasts required to directly image these objects as well as to characterize them. This thesis aims to improve the polarimetric sensitivity, accuracy, and capabilities of high-contrast imaging polarimeters for the detection and characterization of exoplanets and circumstellar disks. In addition, this thesis presents the first direct detections of linear polarization from self-luminous planetary mass companions. The focus of this thesis is mostly on ground-based high-contrast imaging, in particular with the instrument SPHERE-IRDIS at the Very Large Telescope. This thesis covers many aspects of high-contrast imaging polarimetry, ranging from theoretical work, calibrations, and the development of new observing techniques to actual scientific polarimetric measurements and astrophysical interpretation. Show less
One of the key limitations of the direct imaging of exoplanets at small angular separations are quasi-static speckles that originate from evolving non-common path aberrations (NCPA) to which the... Show moreOne of the key limitations of the direct imaging of exoplanets at small angular separations are quasi-static speckles that originate from evolving non-common path aberrations (NCPA) to which the primary adaptive optics system is inherently blind. The main focus of this thesis is the development and (on-sky) testing of integrated coronagraph and focal-plane wavefront-sensing solutions to deal with NCPA. First, we enable focal-plane wavefront sensing with vector-Apodizing Phase Plate coronagraph by integrating a pupil-plane amplitude asymmetry into the design. Low-order wavefront sensing is then demonstrated with a non-linear model-based algorithm and high-order wavefront with spatial Linear Dark Field Control. We introduce the polarization-encoded self-coherent camera, which is a new and more powerful variant of the self-coherent camera. Furthermore, we show through on-sky tests that the “Fast and Furious” focal-plane wavefront sensing algorithm is capable of measured and controlling the low-wind effect. Lastly, the vector speckle grid is presented and dramatically increases the signal-to-noise ration of exoplanet variability measurements. The ultimate goal of this thesis is to enable the direct imaging and characterization of rocky exoplanets with future extremely large telescopes. Show less
To study how planetary systems come into existence we study much younger systems still in formation. Gas and dust rich disks surrounding young stars are thought to be the precursors of... Show moreTo study how planetary systems come into existence we study much younger systems still in formation. Gas and dust rich disks surrounding young stars are thought to be the precursors of planetary systems and therefore known as protoplanetary disks. In this thesis, I study large-scale structures in protoplanetary disks through high-contrast imaging of the scattering surfaces of these disks; and I calibrated two high-contrast imagers. To observe these disks at optical wavelengths, we need to take into account that the central star is much brighter than the (star)light reflected by the disk surface: i.e., high contrast between star and disk. Additionally, light coming from the star & disk is disturbed by the Earth’s atmosphere. Therefore, specialized high-contrast imaging instruments are required to correct for atmospheric disturbance of the stellar light in order to allow the highest possible spatial resolution and contrast between the star and its nearby surroundings. Improving our understanding of these high-contrast imagers will allow for a better interpretation of the data recorded with these instruments, while the interpretation of disk structures detected at high spatial resolution forms a crucial step in our understanding of the general principles that govern disk evolution and planet formation. Show less
