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
This thesis aims to demonstrate how the achromatic nature and design flexibility of liquid-crystal optics can be used to improve high-contrast imaging instruments to facilitate detailed exoplanet... Show moreThis thesis aims to demonstrate how the achromatic nature and design flexibility of liquid-crystal optics can be used to improve high-contrast imaging instruments to facilitate detailed exoplanet characterization.Chapter 2 discusses the design, performance, and future development of the liquid-crystal vector-apodizing phase plate (vAPP) coronagraph, five of which have been installed in different instruments on current generation telescopes since 2016. In chapter 3 we use the achromatic nature of the vAPP in combination with the LBT/ALES integral field spectrograph to obtain the first ever thermal infrared spectrum of the inner three HR 8799 planets. In Chapter 4 and 8 we show that by combining multiple grating patterns to reduce the influence of polarization leakage, we can improve the performance of liquid-crystal coronagraphs. In Chapter 5 and 6 we enhance sparse aperture masking, capable of detecting companions beyond the diffraction limit, by using liquid-crystal phase masks to enable low-resolution spectroscopy and improve throughput. In Chapter 7 we demonstrate that a liquid-crystal Zernike wavefront sensor can accurately and efficiently measure phase and amplitude aberrations simultaneously, facilitating extreme contrasts. Together, the concepts presented in this thesis can be used to improve high-contrast imaging instruments of both ground-based and space-based observatories. Show less
In this thesis we present multiple techniques to suppress starlight in order to better directly image planets around other stars. We propose a laboratory setup to test a new focal-plane... Show more In this thesis we present multiple techniques to suppress starlight in order to better directly image planets around other stars. We propose a laboratory setup to test a new focal-plane wavefront sensing technique. We also show an optical device that suppresses starlight using liquid crystals (the vector Apodizing Phase Plate or vAPP). A broadband prototype (500-900 nm) is tested in the optical lab and its properties are determined. We suggest an simple but effective adaptation called the grating-vAPP which is insensitive to one of the common manufacturing errors (retardance offset). Two versions are tested on-sky. One narrow-band prototype at the Large Binocular Telescope that shows that the concept of the grating vAPP works. A second at Magellan/Clay that shows that we can produce a single optic with a broadband behaviour from 2 to 5 microns bandwidth that suppresses both sides of the star simultaneously. The on-sky 5 sigma contrast is 8.3 magnitudes at 2 lambda/D and 12.2 magnitudes at 3.5 lambda/D which makes this coronagraph extremely suited for imaging and characterizing planets close to nearby bright stars. Show less
The Spectral Energy Distributions (SEDs) of star-forming regions and starburst galaxies are unique tracers of the star formation processes in these environments, since they contain information on... Show moreThe Spectral Energy Distributions (SEDs) of star-forming regions and starburst galaxies are unique tracers of the star formation processes in these environments, since they contain information on the escaping and processed photons emitted by newly formed massive stars. Understanding these internal processes is crucial in our physical interpretation of observations of unresolved star formation in the Universe. In the __rst part of this thesis, we study the physical conditions in resolved starburst regions using Bayesian __tting of their spatially integrated infrared SEDs, including both the thermal continuum and the atomic emission lines. We then apply the method to unresolved starburst to learn about their star formation physics. Our approach leads to robust constraints on physical parameters such as age, compactness, and amount of currently ongoing star formation in starburst, which are otherwise biased by model degeneracies, and allows us to link the resolved properties of giant H II regions to the star formation process at larger scales. In the second part of this thesis, we discuss the wavelength calibration of the next instrument to study the midinfrared spectral properties of starbursts, with improved resolution and sensitivity: the mid-infrared instrument (MIRI), which will __y onboard the James Webb Space Telescope in 2018. Show less
