Even though more than 4000 extra-solar planets are known today, only a small fraction of these has been captured in an image. To better understand the planet formation mechanisms in solar-like... Show moreEven though more than 4000 extra-solar planets are known today, only a small fraction of these has been captured in an image. To better understand the planet formation mechanisms in solar-like environments we started the Young Suns Exoplanet Survey (YSES). YSES targets a homogeneous sample of seventy young (~15Myr), Sun-like stars of the Scorpius-Centaurus association to search for sub-stellar companions. High-contrast imaging observations that were collected with the SPHERE instrument at the Very Large Telescope revealed (i) a shadowed transition disk around Wray 15-788 that shows significant signs of ongoing planet formation and (ii) one of the lowest-mass companions imaged to date: YSES 2b has a mass of 6.5 Jupiter masses and is orbiting its solar-mass primary at a separation of 110 au. Most intriguing, though, was (iii) the discovery of the first directly imaged multi-planet system around a Sun-like star. The detection of two gas-giant companions of 14±3 and 6±1 Jupiter masses that are orbiting YSES 1 at separations of 160 au and 320 au, respectively, provides important implications for the outer architecture of planetary systems and the underlying formation mechanisms. 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
This thesis describes the implementation and on-sky demonstration of high-resolution integral-field spectroscopy for extreme adaptive optics systems that are used to find and characterize... Show moreThis thesis describes the implementation and on-sky demonstration of high-resolution integral-field spectroscopy for extreme adaptive optics systems that are used to find and characterize exoplanets. For this work the Leiden EXoplanet Instrument (LEXI) was build, which is a visiting instrument for the William Herschel Telescope on La Palma. LEXI was used a pathfinder for testing new technology. The potential of these technqiues have been demonstrated with the observations of PDS 70 by the MUSE instruments, where we have characterized a proto-planet and found a second proto-planet in the same system. The proposed techniques in this thesis can be implemented on future instruments and telescopes for the characterization of exoplanets. Show less
This thesis describes the development and validation of new high-contrast imaging techniques, with the ultimate goal of enabling the next generation of instruments for ELT-class telescopes to... Show moreThis thesis describes the development and validation of new high-contrast imaging techniques, with the ultimate goal of enabling the next generation of instruments for ELT-class telescopes to directly image Earth-like extra-solar planets orbiting around nearby stars. In particular, we focus on developing new focal-plane wavefront sensing techniques and liquid crystal optics to achieve high-precision adaptive optics control which is capable of stabilising the entire instrument. We demonstrate that one such hybrid optical concept, the coronagraphic Modal Wavefront Sensor (cMWS), is capable of providing real-time, broadband (500-900 nm) control of non-common path aberrations during on-sky observation. We also demonstrate via both realistic simulations and laboratory testing that the focal-plane sensing technique of “Fast and Furious” phase diversity provides a robust, software-only solution to unforeseen, performance-limiting wavefront control issues such as the low-wind effect seen in the SPHERE instrument at the VLT. Lastly, we characterise the extinction profile of the VLT-SPHERE-IRDIS apodised Lyot coronagraph using observations of the minor planet Ceres, and use this to devise a calibration scheme which optimises the accuracy with which polarised signals from the innermost regions of protoplanetary disks may be retrieved. Show less
A remarkable population of short period transiting rocky exoplanets with equilibrium temperatures on the order of 2,000 K has recently been discovered. Their high temperatures make them very... Show moreA remarkable population of short period transiting rocky exoplanets with equilibrium temperatures on the order of 2,000 K has recently been discovered. Their high temperatures make them very different to the planets in our solar system. In particular, hot super-Earths are thought to have mineral atmospheres that are produced by the vaporisation of their surfaces, or large exospheres that are produced by sputtering of their exposed surfaces by intense stellar winds. Additionally, some smaller, low surface gravity hot rocky exoplanets have been found to be actively disintegrating and forming 'comet-like' dust tails that produce asymmetric transit light curves with forward scattering features. Since the gas and dust originates from the planetary surface, these planets offer the tantalising prospect of enabling us to probe the surface composition of rocky planets. The purpose of this thesis is to work towards this goal by searching for gas around hot rocky exoplanets with observational spectroscopy (Chapters 2 and 5), and by modelling the transit light curves produced by their 'comet-like' dust tails (Chapters 3 and 4). Show less
This thesis addresses the chemical processes that determine the compositions of giant planet atmospheres. Connecting the observed composition of exoplanets to their formation sites often involves... Show moreThis thesis addresses the chemical processes that determine the compositions of giant planet atmospheres. Connecting the observed composition of exoplanets to their formation sites often involves comparing the observed planetary atmospheric carbon-to-oxygen (C/O) ratio to a disk midplane model with a fixed chemical composition. In this scenario chemistry during the planet formation era is not considered, and the C/O ratios of gas and ice in disk midplane are simply defined by volatile icelines in a midplane of fixed chemical composition. However, kinetic chemical evolution during the lifetime of the gaseous disk can change the relative abundances of volatile species, thus altering the C/O ratios of planetary building blocks. In my chemical evolution models I utilize a large network of gas-phase, grain-surface and gas-grain interaction reactions, thus providing a comprehensive treatment of chemistry. In my talk I will show how chemical evolution can modify disk miplane chemistry and how this affects the C/O ratio of giant planet-forming material. I will argue that midplane chemical evolution needs to be addressed when predicting the chemical makeup of planets and their atmospheres. And as an extra, I will propose that chemical evolution can help constrain the formation histories of comets. Show less
The thesis "Spinning Worlds" is about the characterisation of two types of gas-giant exoplanets: Hot Jupiters, with orbital periods of fewer than five days, and young, wide-orbit gas giants,... Show moreThe thesis "Spinning Worlds" is about the characterisation of two types of gas-giant exoplanets: Hot Jupiters, with orbital periods of fewer than five days, and young, wide-orbit gas giants, with orbital periods as long as thousands of years. The thesis is based on near-infrared observations of 1 hot Jupiter and 3 wide-orbit gas giants at high spectral resolution. The observing strategies and the analyses are unique for the two types. For the hot Jupiter, HD 209458 b, the focus is the vertical temperature structure of the atmosphere. This particular hot Jupiter was previously thought to have an atmospheric layer where the temperature increases with altitude, but we found evidence against the existence of such a layer. The three wide-orbit gas giants are all in the early stages of their lives, and we measured their rotation and found a correlation with age: The very youngest objects rotate more slowly than the slightly older (20 million years) objects. We interpret this as the initially hot and bloated exoplanets cooling down and contracting, causing them to spin-up, until the contraction slows down as they approach a radius comparable to that of Jupiter. 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
This thesis presents observations of exoplanets orbiting very close to their parent star, with a particular focus on a novel technique for characterizing their atmospheres. This is based on the use... Show moreThis thesis presents observations of exoplanets orbiting very close to their parent star, with a particular focus on a novel technique for characterizing their atmospheres. This is based on the use of high-resolution spectroscopy from the ground. The first detection of the atmosphere of a non-transiting planet is presented, together with the determination of its mass and orbital inclination. Moreover, it is shown that high-dispersion spectroscopy is very effective in recognizing molecular species, measuring their relative abundances, and determining whether temperature increases or decreases with altitude in the observed planetary atmospheres. The method also led to the measurement of the rotational period of a transiting exoplanet, which was found to be tidally locked, in line with theoretical predictions. Finally, the evidence for the disintegration of a small, rocky planet candidate in the Kepler database is presented. This result was obtained by fitting the light curve of the object with a model of a trailing tail of dust. Show less
The study of exoplanets and the protoplanetary discs in which they form is a very challenging task. In this thesis we present several studies in which we investigate the potential of imaging... Show moreThe study of exoplanets and the protoplanetary discs in which they form is a very challenging task. In this thesis we present several studies in which we investigate the potential of imaging polarimetry at visible and near-infrared wavelengths to reveal the characteristics of these objects and overcome the scientific and technical challenges involved. Show less
It is less than 20 years since astronomers discovered the first exoplanet orbiting a Sun-like star. In this short period more than 770 confirmed exoplanets have been detected. With so many... Show moreIt is less than 20 years since astronomers discovered the first exoplanet orbiting a Sun-like star. In this short period more than 770 confirmed exoplanets have been detected. With so many exoplanets the next step is their characterization. What is their atmosphere made of? Does it contain water clouds? Is there water on the planetary surface? Could there be life on these planets? To answer all these questions good and reliable models are necessary for interpreting the signal we observe from the detected exoplanets. In this thesis, Karalidi works with a numerical code to model the flux and polarization properties of starlight reflected by exoplanets with various forms of inhomogeneities. She shows that the rainbow, created by water clouds in the planetary atmosphere, is a powerful ally in our search for water clouds on other planets. In the upcoming years the detection of giant planets will be easier than the detection of terrestrial planets. For this reason Karalidi also describes the influence that various formations, such as zones, spots and polar hazes, have on the signal of Jupiter-like exoplanets. Show less
The different chapters cover studies in which the physical structures of the gas such as temperature, densities and movements of the gas are estimated. In addition chemical characteristics of the... Show moreThe different chapters cover studies in which the physical structures of the gas such as temperature, densities and movements of the gas are estimated. In addition chemical characteristics of the gas such as different molecular abundances and their spatial distribution are defined. This information is discussed in the context of how the chemical evolution of the gas in the planet-forming region progress and how this affects which type of planets that can form there. The results are mainly based on infrared observations and radiative transfer disk models. Show less
