Io is the innermost Galilean moon of Jupiter and is considered the most volcanically active body in our solar system. With the help of the Hubble Space Telescope’s (HST) on-board Space Telescope Imaging Spectrograph (STIS), far-ultraviolet (FUV) images of Io have been captured for the past 20 years. The final goal of this project is to study the sulphur dioxide (SO2) distribution and volcanic activity on Io in FUV data taken in 1997/98 and 2013/14. The method used concerns the conversion of spectral Lyman-α intensity to SO2 density using algorithms implemented in MATLAB. As a result the SO2 distribution and volcanic activity on Io were determined and compared between the data collections. We found that the SO2 was higher in the images from 1997/98 compared to 2013/2014.

In my thesis I investigate the occurrence of mid-infrared excess around stars and their evolution. Since the launch of the first infrared satellite, IRAS, we have known that a large fraction of stars exhibit significant levels of infrared emission above their predicted photospheric level. Resolved optical and infrared images have revealed the majority of these excesses to arise from circumstellar disk structures, made up of distributions of planetesimals, rocks, and dust. These structures are descriptively called debris disks. The first part of my thesis analyzes the Spitzer Space Telescope Observations of δ Velorum. The 24 μm Spitzer images revealed a bow shock structure in front of the star. My analysis showed that this is a result of the star’s high speed interaction with the surrounding interstellar medium. We place this observation and model in context of debris disk detections and the origin of λ Boötis stars. The second part of my thesis summarizes our observational results on the open cluster Praesepe. Using 24 μm data, I investigated the fraction of stars with mid-infrared excess, likely to have debris disks. I also assembled all results from previous debris disk studies and followed the evolution of the fraction of stars with debris disks. The majority of debris disks systems are evolved, few hundred million or a Gyr old. Since the dissipation timescale for the emitting dust particles is less than the age of these systems, they have to be constantly replenished through collisional grinding of the larger bodies. The last two chapters of my thesis is a theoretical analysis of the collisional cascade in debris disks, the process that produces the constant level of dust particles detected. I introduce a numerical model that takes into account all types of destructive collisions in the systems and solves the full scattering equation. I show results of comparisons between my and other published models and extensive verification tests of my model. I also analyze the evolution of the particle size distribution as a function of the variables in my model and show that the model itself is quite robust against most variations.

The MIRI-MRS is a future space based Medium Resolution Spectrometer and one of four instruments to be integrated onto The James Webb Space Telescope. The Medium Resolution Spectrometer is designed to be diffraction limited across its entire passband of 5 - 28.3 microns. It achieves this through the spectral filtering of the passband into four channels with each one containing an integral field unit optimised for minimal diffraction losses. The integral field unit enables the simultaneous measurement of the spectral data across the entire field of view. The design of the Medium Resolution Spectrometer is outlined with particular reference to the choice of slice widths used for each channel to minimise the diffraction losses from the slicing mechanism. The slice widths are also used to derive the extent of the field of view and combined with the along slice plate scale at the detector the technique required for complete spatial sampling of the spectrometer is outlined. The operation of the Channel 1 image slicer component was tested cryogenically at 5 microns for diffraction losses due to the slicing of the point spread function. This was so that the actual diffraction losses could be measured and compared with the optical model. From the resulting analysis I concluded that the operation of the image slicers were well understood for diffraction losses. Performance tests were required on the instrument because of its novel design. This was the first implementation of an integral field unit operating between 5 - 28.3 microns and it was necessary to ensure that the operation of the image slicer did not induce unacceptable diffraction losses into the instrument. Tests were required on the assembled instrument to verify the optical design. A Verification Model of MIRI was built to enable test verification of the optical design. This testing was carried out in advance of the MIRI Flight Model assembly so that changes could be made to the Flight Model design if necessary. This testing phase was also designed to define the calibration process necessary to prepare the MIRI Flight Model for scientific operations. For the testing phase it was necessary to create an astronomical source simulator. This MIRI Telescope Simulator was constructed in Madrid where I spent two months ensuring the point source movement across the field of view would be sufficient to investigate the Medium Resolution Spectrometer. My contribution was to help assemble both the Verification and Flight Models. I also participated in the Verification Model testing phase from the test design phase to the test implementation and data analysis. My role in the analysis was to investigate the field of view of the Medium Resolution Spectrometer Verification Model and whether the field of view requirements for the spectrometer were met. During this analysis I also verified that the diffraction effects of the end-to-end instrument were well understood by the optical model. The Medium Resolution Spectrometer Verification Model field of view compromised the field of view requirement for the spectrometer. A similar analysis for the Flight Model showed that there would be a low probability that the field of view requirement would be met. As a result of the analysis I defined a new slit mask design that would align the field of view sampled by Channel 1 to increase the aligned field of view. As a result there is a high probability that the field of view requirement for the Flight Model will be exceeded. The test analysis discovered a magnification effect within the spectrometer which must be properly characterised to enable accurate field of view reconstruction. I designed a test necessary for the calibration phase of the Flight Model to enable full spatial alignment of the Medium Resolution Spectrometer. I also measured an excess flux level in the Channel 1 observations at the detector and there was a ghost detected in the Channel 1 images. Whilst the origin of either the excess flux or the ghost could not be completely determined I investigated the possibility that they will not be present in the Flight Model due to the slight design differences. If present however they will not increase the background level of an observation above the requirement outlined for Channel 1.

Apresentamos fotometria profunda (V ~ 25,5) nas bandas V e I obtidas com a Wide Field and Planetary Camera 2 a bordo do telesc opio espacial Hubble para 7 campos distantes ~5º do centro da Grande Nuvem de Magalhães. Ajustamos isócronas aos diagramas cor-magnitude a fim de identficar diferentes populaões estelares nestes campos. Uma população velha (τ > 10¹º anos) foi encontrada em todos os campos. Alguns eventos de elevada formação estelar, com idades entre 2 x 109 e 4 x 109 anos, foram também encontrados em alguns campos localizados na região N/NO. Funções de luminosidade de estrelas de baixa massa (m ≤ 1; 1msol) foram obtidas para todos os campos. Aparentemente não há diferenças na mistura de populações entre os campos como sugerido através do teste Kolmogorov-Smirnov aplicados as funções de luminosidade. Finalmente, derivamos perfis de densidade para estrelas velhas e de idade intermediária. O primeiro apresenta uma inclinação levemente maior quando comparado com o último.

With the Hubble Space Telescope and its near-infrared capabilities, it is now possible to probe deep into the epoch of reionization, improving our understanding of galaxy evolution through cosmic history. Whether it is via colour-selection or fitting the spectral energy distribution, it has now become routine to amass large samples of galaxies as distant as redshift z = 8, with the current frontier of observations at z = 9 - 10. The new Hubble Frontier Fields (HFF) programme provides the potential to study the most distant, intrinsically faint background galaxies through the gravitational lensing provided by a foreground galaxy cluster. This thesis presents a study of the galaxy population at z = 9 - 10 that exploits this phenomenon. In an initial search of the first two HFF cluster+parallel pointings, Abell 2744 and MACS J0416.1-240, we unveil twelve candidate high-redshift galaxies at 8:4 < z < 9:5, and are thus able to place constraints on the galaxy UV luminosity function at z = 9. For this study, we employ the "blank-field" method, whereby we confine attention to only the homogeneously deep, relatively low-magnification regions of the imaging. We are able to demonstrate evidence for a smooth decline in UV luminosity density between z ≃ 8 and z ≃ 9, in contrast to reports in the recent literature of a steep drop-off at these redshifts. We extend this study to include the new MACS J0717.5+3745 and MACS J1149+2223 cluster+parallel pointings, and supplement the search for z ≃ 9-10 galaxies with twenty CLASH cluster pointings. From a search over an area ≃ 130 sq. arcmin, we are able to present 33 galaxy candidates with photometric redshift solutions in the range 8:4 < zphot < 11:2. Our new results reinforce the argument for a smoothly-evolving LF between z ≃ 8 and z ≃ 9, which can be equally well modelled by a factor ≃ 2 drop in Φ* or a dimming of ≃ 0:5 mag in M*. We also find evidence that this smooth decline in the UV luminosity function, and hence UV luminosity density, continues to z ≃ 10. As well as considering the galaxy population at z = 9 - 10, this thesis presents a study of the stellar populations of galaxies at z ≥ 5. We are able to extend the luminosity baseline and measure the colour-magnitude relation at z = 5 - 8, through a combination of probing intrinsically faint galaxies behind cluster fields, in conjunction with both ultra-deep, pencil beam imaging such as the Hubble Ultra Deep Field (HUDF) and wider, shallower imaging from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS). This allows us to make inferences about the underlying stellar populations of galaxies at these epochs, and provides a unique insight into the colours of intrinsically faint, lensed galaxies as faint as M1500 ~ -14. We find that the data is consistent with an essentially unchanged average UV slope (β) for a given luminosity across the redshift range z = 5-8. We also find that the data favours a mild flattening of the colour-magnitude relation with redshift between z = 5 and z = 8.

The Io UV footprint (IFP) is one of the most spectacular signatures of the Io-Jupiter interaction. It consists of several auroral spots and an extended tail which are located close to the feet of the magnetic field lines passing through Io in each hemisphere. The purpose of the present study is to demonstrate that a careful analysis of the Io UV footprint based on observations acquired with the STIS and ACS high resolution and high sensitivity FUV cameras on board the Hubble Space Telescope can provide us with essential information on the ongoing physical processes. The thesis is organized around basic questions: What is the Io footprint?, Where is the Io footprint?, How high is the Io footprint?, How big is the Io footprint? and finally: How bright is the Io footprint? The answers to these questions have profound implications for the understanding of the phenomenon. Among the most important results of this work is the unexpected finding of a faint auroral spot appearing upstream of the main Io spot in one hemisphere while only downstream spots are seen in the opposite hemisphere. The detailed study of the evolution of the inter-spot distances puts previous models describing the footprint morphology under question. We propose a new interpretation which involves that some spots are caused by electrons accelerated away from the planet along the field lines in one hemisphere, crossing the equatorial plane in the form of electron beams and precipitating in the opposite hemisphere, creating the so-called Trans-hemispheric Electron Beam (TEB) spots. The information provided by the position of the satellite footprints is not restricted to the interaction between the moon and the Jovian magnetosphere. The analysis of the footpaths of Io, Europa and Ganymede helped us to further constrain the magnetic field models, notably through the identification of a large magnetic anomaly in the northern hemisphere. Additionally, the study of the speed of the Io footprint along its reference contour suggests that a second anomaly regions may also exist in the North. In this work, we present a new and direct method to measure the altitude of the different footprint features. The main spot and the tail emissions have a peak altitude of 900 km while the peak altitude of the Trans-hemispheric Electron Beam spot is 700 km. These results suggest that the main spot and tail emissions are caused by the precipitation of electrons with a mean energy around 1 keV, far lower than the 55 keV value previously derived from spectral measurements. The vertical extent of these emissions is surprisingly broad (scale height ~400 km) and is best fitted with an incoming kappa electron energy distribution (spectral index ~2.3). This suggests that the electron acceleration is supplied by processes related to inertial Alfvén waves rather than by quasi-static potentials as proposed by some theoretical models. The size of the main footprint spot is carefully estimated on a much larger image sample than before: its length along the footpath is ~900 km while its width perpendicular to the footpath is <200 km. Larger lengths are sometimes observed but in that case, they are attributed to the mix of individual spots. The spot length is larger than the projected diameter of Io around the magnetic field lines but is consistent with recent simulations. As far as the Io footprint brightness is concerned, variations on two timescales have been studied. On timescales of minutes, systematic brightness fluctuation on the order of 30% (and going up to 50%) are observed. Additionally, cases of simultaneous variations of the main and the TEB spots are reported, which suggests that the process that triggers these fast variations is located close to the planet. Variations of the main spot brightness with the System III longitude of Io are also analyzed. Our new measurement method fully considering the multi-spot structure of the IFP and the real geometry of the observations provides more accurate estimates for the precipitating energy flux (between 100 and 500 mW/m for the main spot). The main spot brightness peaks at 110° and 290° longitude, which could be attributed either to an enhanced interaction strength when Io is near the dense torus center or to spots merging which is also observed to occur in these sector. Nevertheless, strong North-South asymmetries are also observed, which suggests that the surface magnetic field strength also influences the spots brightness. ---------------------------------------------------------------------- L'empreinte aurorale d'Io est l'une des signatures les plus impressionnantes de l'interaction Io-Jupiter. Présente dans chaque hémisphère, elle se situe à proximité des pieds des lignes de champ magnétique qui interceptent Io et se compose de plusieurs taches suivies d'une longue trainée. Cette étude vise à démontrer qu'une analyse minutieuse de l'empreinte UV d'Io basée sur les observations des instruments STIS et ACS du Télescope Spatial Hubble peut apporter des informations cruciales sur les processus physiques qui sont en jeu. Cette thèse est organisée autour de questions relativement basiques: Qu'est-ce que l'empreinte d'Io?, Où se trouve-t-elle?, A quelle altitude se trouve-t-elle?, Quelle est sa taille? et enfin Quelle est sa brillance?. Les réponses à ces questions ont de profondes implications pour la compréhension du phénomène. Parmi les résultats principaux de ce travail, il y a la découverte inattendue d'une faible tache aurorale apparaissant en amont de la tache principale dans un hémisphère alors que les seules taches observées dans l'hémisphère opposé sont situées en aval. L'étude détaillée de la distance inter-taches remet en question les précédents modèles décrivant la morphologie de l'empreinte. Nous proposons ici une nouvelle interprétation de certaines de ces taches: elles seraient causées par des électrons initialement accélérés le long des lignes de champ dans la direction opposée à Jupiter, qui ensuite traverseraient le plan équatorial sous la forme de faisceaux d'électrons et qui précipiteraient finalement dans l'hémisphère opposé en générant la tache du Faisceau d'Electrons Trans-hemisphérique (FET). Les informations fournies par la position des empreintes de satellites ne se limitent pas à l'interaction entre Io et la magnétosphère de Jupiter. L'analyse des contours parcourus par les empreintes d'Io, d'Europe et de Ganymède permet de mieux contraindre les modèles de champ magnétique joviens, entre autre à travers l'identification d'une importante anomalie magnétique dans l'hémisphère nord. De plus, l'étude de la vitesse de l'empreinte d'Io le long du contour de référence suggère qu'elle pourrait être accompagnée d'une deuxième anomalie dans cet hémisphère. Dans cette étude, nous présentons une méthode directe pour mesurer l'altitude des différentes sous-structures qui forment l'empreinte. Le pic d'émissions de la tache principale et de la trainée est situé à 900 km d'altitude alors que celui de la tache FET est à 700 km. Ces résultats suggèrent que la tache principale et la trainée sont la conséquence de la précipitation d'électrons ayant une énergie moyenne d'approximativement 1 keV, une valeur largement inférieure aux 55 keV déduits à partir de précédentes mesures spectrales. L'extension verticale de ces émissions est étonnamment large (hauteur d'échelle: ~400 km) et la distribution d'énergie des électrons incidents qui reproduit au mieux les observations est une distribution kappa d'indice spectral ~2.3. Cela suggère que l'accélération des électrons est liée à des ondes d'Alfvén inertielles plutôt qu'aux potentiels quasi-statiques proposés par certains modèles théoriques. La taille de la tache principale a été mesurée sur un ensemble d'images beaucoup plus étendu qu'auparavant: sa longueur le long du contour est de ~900 km alors que sa largeur telle que mesurée perpendiculairement à celui-ci est de <200 km. Des longueurs plus importants sont parfois observées mais elles résultent de la superposition partielle de plusieurs taches individuelles. La longueur des taches est plus grande que la projection du diamètre d'Io le long des lignes de champ, ce qui était prévu par des simulations récentes. En ce qui concerne la brillance des taches, deux échelles de temps ont été étudiées en particulier. A l'échelle de la minute, nous avons mis en évidence des fluctuations de l'ordre de 30% de la brillance moyenne et pouvant atteindre jusqu'à 50 % de celle-ci. Dans certains cas, on observe des variations corrélées de la tache principale et de la tache FET, ce qui suggère que le processus qui induit ces variations rapides se situe près de la surface de Jupiter. Les variations de la brillance de la tache principale en fonction de la longitude Système III d'Io ont également été analysées. Notre nouvelle méthode de mesure prend pleinement en compte la géométrie de l'observation ainsi que le fait que l'empreinte est composée de différentes taches, ce qui permet une estimation plus précise du flux d'énergie incident (entre 100 et 500 mW/m pour la tache principale). La brillance de la tache principale possède deux maxima, un à 110° et un autre à 290° de longitude. Ces augmentations de brillance peuvent avoir deux origines: soit elles sont dues à l'augmentation de l'intensité de l'interaction entre Io et le plasma quand Io est proche du centre du tore, soit elles sont liées à la superposition des taches principales et FET qui se produit également dans ces secteurs. Néanmoins, de fortes asymétries Nord-Sud sont aussi observées, ce qui semble indiquer que l'intensité du champ magnétique de surface joue aussi un rôle en ce qui concerne la brillance des spots.

How galaxies form and evolve is one of the primary outstanding problems in extragalactic astronomy. I conduct a quantitative census of the relative importance of the major structural components (flattened and dynamically cold disk-dominated components versus puffy and dynamically hot spheroidal or triaxial bulges/ellipticals) in massive galaxies over cosmic time and across different environments in order to explore how galaxies evolve under the action of the various assembly mechanisms (major mergers, minor mergers, gas accretion, and internal secular processes) in these different regimes. I perform three inter-related analyses focusing on massive galaxies from z ~ 0 - 3 in both field and rich cluster environments. Important strengths of this thesis include the use of high-resolution, panchromatic imaging from some of the largest and deepest galaxy surveys with the Hubble Space Telescope (HST), Spitzer, and Chandra space telescopes, and also the inclusion of detailed comparisons between the empirical data and hierarchical ΛCDM-based models of galaxy evolution. / text

White dwarf stars are the burnt out remnants that remain after a star like the Sun has completed its nuclear evolution. In such a star there are no remaining nuclear energy sources, so the star evolves by simply radiating its stored thermal energy out into space. This may seem rather uninteresting, but in fact there is a wealth of physical phenomena that occur during this part of a star's life - from getting kicked at birth, to neutrino emission in early life, to some interesting high density physics, through to functioning as precise clocks that can provide an age for some of the oldest know stars in the Universe. Some of these phases will be illustrated with detailed observations taken recently with the Hubble Space Telescope.

The James Web Space telescope will replace the aging Hubble in 2012. One instrument onboard will be the Near Infrared Spectroscope which will require a reconfigurable slit mask to control light incident upon it. One design for this device is called the Mechanically Actuated Reconfigurable Slit mask (MARS). The MARS uses several electromagnetic clamps to move shutters though the focal plane. The goal of this thesis is to develop a system to characterise these clamps at cryogenic temperatures. FEA simulations predicted clamp performance and aided in the development of a test apparatus. An apparatus which utilises the Lorentz force to force the clamp jaws open was developed, built and tested. The device was built inside a cryostat which operated at 30 K. It was found that the test apparatus performed as intended. The clamps themselves proved to be problematic. Small perturbations or misalignments caused significant inconsistencies in experimental results.

The first stars in the Universe are thought to have formed in high dark matter density minihalos about 200 million years after the Big Bang. If these stars were able to contract dark matter into their stellar core while forming, some of them might have turned into dark stars (DSs) powered by the heat from dark matter annihilation. The possibilities for detection of DSs with the upcoming James Webb Space Telescope (JWST), scheduled for launch in 2021, is investigated in this work. With DS models generated in Spolyar et al. (2009) and atmosphere spectra from Gustafsson et al. (2008), spectral analysis has been carried out in MATLAB to find the unique colors of DSs compared to galaxies generated in Zackrisson et al. (2017) at z ≈ 7 − 11. It was found that lower temperature DSs (Teff ≤ 7800K) are distinguishable from galaxies and that they would be bright enough to be detected with the JWST provided a magnification factor of µ ≈ 160−1000 with the use of gravitational lensing. More recent DS models reveal that the DS of temperature Teff = 7800K is detectable even without the use of gravitational lensing. However, the probability of finding one today is really small due to DSs’ presumably short lifetime. The results of this work are hoped to give a better understanding of the properties of DSs and to increase the probability of finding one in the large imaging survey carried out by the JWST. / De första stjärnorna i universum antas ha bildats i minihalos med hög densitet av mörk materia omkring 200 miljoner år efter Big Bang. Om dessa stjärnor kunde dra till sig mörk materia under sitt bildande kan vissa av dem ha utvecklats till mörka stjärnor (s.k. dark stars) med mörk materia som energikälla. I detta arbete undersöks möjligheterna att upptäcka dem med det kommande James Webb Space Teleskopet (JWST) som planeras för uppskjutning år 2021. Med dark starmodeller genererade i Spolyar et al. (2009) och atmosfärspektra från Gustafsson et al. (2008) har spektralanalys utförts i MATLAB för att hitta vilka dark stars som går att urskilja från galaxer genererade i Zackrisson et al. (2017) vid z ≈ 7−11. Det visade sig att dark stars med låg temperatur (Teff ≤ 7800K) är urskiljbara och att de flesta av dessa dark stars, vid en förstoringsfaktor av µ ≈ 160−1000 vid användning av gravitationell linsning, är tillräckligt ljusstarka för att kunna detekteras. Jämfört med senare dark star-modeller skulle även Teff = 7800K DSs kunna detekteras utan användning av gravitaionell linsning. Sannolikheten att hitta en dark star är fortfarande väldigt liten på grund av dess förmodade korta livstid. Resultaten av detta arbete hoppas kunna ge en bättre förståelse för egenskaperna hos mörka stjärnor samt öka sannolikheten för detektion med JWST.