Building upon its success with the Hipparcos space astrometry mission launched in 1989, the European Space Agency has agreed to fund the construction of its successor, Gaia, and its launch in 2011. Despite the similarities between the two missions, Gaia will be orders of magnitude more powerful, more sensitive, but also more complex in terms of data processing. Growing from 120,000 stars with Hipparcos to about 120,000E4 stars with Gaia does not simply mean pushing the computing resources to their limits (1 second of processing per star yields 38 years for the whole Gaia-sky). It also means facing situations that did not occur with Hipparcos either by luck or because those cases were carefully removed from the Hipparcos Input Catalogue. This manuscript illustrates how some chunks of the foreseen Gaia data reduction pipeline can be trained and assessed using the Hipparcos observations. This is especially true for unresolved binaries because they pop up so far down in the Gaia pipeline that, by the time they get there, there is essentially no difference between Hipparcos and Gaia data. Only the number of such binaries is different, going from two thousand to ten million. Although the computing time clearly becomes an issue, one cannot sacrifice the robustness and correctness of the reduction pipeline for the sake of speed. However, owing to the requirement that everything must be Gaia-based (no help from ground-based results), the very robustness of the reduction has to be assessed as well. For instance, the underlying assumptions of some statistical tests used to assess the quality of the fits used in the Hipparcos pipeline might no longer hold with Gaia. That may not affect the fit itself but rather the quality indicators usually accompanying those fits. For the final catalogue to be a success, these issues must be addressed as soon as possible.

We present a multi-epoch Hubble Space Telescope (HST) study of stellar proper motions (PMs) for four fields along the Orphan Stream. We determine absolute PMs of several individual stars per target field using established techniques that utilize distant background galaxies to define a stationary reference frame. Five Orphan Stream stars are identified in one of the four fields based on combined color-magnitude and PM information. The average PM is consistent with the existing model of the Orphan Stream by Newberg et al. In addition to the Orphan Stream stars, we detect stars that likely belong to other stellar streams. To identify which stellar streams these stars belong to, we examine the 2d bulk motion of each group of stars on the sky by subtracting the PM contribution of the solar motion (which is a function of position on the sky and distance) from the observed PMs, and comparing the vector of net motion with the spatial extent of known stellar streams. By doing this, we identify candidate stars in the Sagittarius and Lethe streams, and a newly found stellar stream at a distance of similar to 17 kpc, which we tentatively name the "Parallel Stream." Together with our Sagittarius stream study, this work demonstrates that even in the Gaia era, HST will continue to be advantageous in measuring PMs of old stellar populations on a star-by-star basis, especially for distances beyond similar to 10 kpc.

This thesis demonstrates that any individual can provide relevant observational data to further research efforts within the Aerospace community, through the use of amateur telescopes. A Meade LX200 12 in. telescope and Lumenera Skynyx 2.0 camera were utilized to observe small LEO satellites, using a well-documented point-and-wait staring method. Over a period of three months, a total of 186 observation attempts were made resulting in 97 successful captures. From the gathered data, three possible aerospace applications were analyzed: validation of a satellite brightness prediction model, angles-only orbit determination including extended Kalman filtering, and temporal error growth in TLE-based orbit propagation. Further investigations include a preliminary optimization using MATLAB's fmincon function (informed by the previous analyses) to determine an optimal telescope size for performing LEO observations.

When Galactic microlensing events of stars are observed, one usually measures a symmetric light curve corresponding to a single lens, or an asymmetric light curve, often with caustic crossings, in the case of a binary lens system. In principle, the fraction of binary stars at a certain separation range can be estimated based on the number of measured microlensing events. However, a binary system may produce a light curve which can be fitted well as a single lens light curve, in particullary if the data sampling is poor and the errorbars are large. We investigate what fraction of microlensing events produced by binary stars for different separations may be well fitted by and hence misinterpreted as single lens events for various observational conditions. We find that this fraction strongly depends on the separation of the binary components, reaching its minimum at between 0.6 and 1.0 Einstein radius, where it is still of the order of 5% The Einstein radius is corresponding to few A.U. for typical Galactic microlensing scenarios. The rate for misinterpretation is higher for short microlensing events lasting up to few months and events with smaller maximum amplification. For fixed separation it increases for binaries with more extreme mass ratios.<br><br> Problem of degeneracy in photometric light curve solution between binary lens and binary source microlensing events was studied on simulated data, and data observed by the PLANET collaboration. The fitting code BISCO using the PIKAIA genetic algorithm optimizing routine was written for optimizing binary-source microlensing light curves observed at different sites, in I, R and V photometric bands. Tests on simulated microlensing light curves show that BISCO is successful in finding the solution to a binary-source event in a very wide parameter space. Flux ratio method is suggested in this work for breaking degeneracy between binary-lens and binary-source photometric light curves. Models show that only a few additional data points in photometric V band, together with a full light curve in I band, will enable breaking the degeneracy. Very good data quality and dense data sampling, combined with accurate binary lens and binary source modeling, yielded the discovery of the lowest-mass planet discovered outside of the Solar System so far, OGLE-2005-BLG-390Lb, having only 5.5 Earth masses. This was the first observed microlensing event in which the degeneracy between a planetary binary-lens and an extreme flux ratio binary-source model has been successfully broken. For events OGLE-2003-BLG-222 and OGLE-2004-BLG-347, the degeneracy was encountered despite of very dense data sampling. From light curve modeling and stellar evolution theory, there was a slight preference to explain OGLE-2003-BLG-222 as a binary source event, and OGLE-2004-BLG-347 as a binary lens event. However, without spectra, this degeneracy cannot be fully broken.<br><br> No planet was found so far around a white dwarf, though it is believed that Jovian planets should survive the late stages of stellar evolution, and that white dwarfs will retain planetary systems in wide orbits. We want to perform high precision astrometric observations of nearby white dwarfs in wide binary systems with red dwarfs in order to find planets around white dwarfs. We selected a sample of observing targets (WD-RD binary systems, not published yet), which can possibly have planets around the WD component, and modeled synthetic astrometric orbits which can be observed for these targets using existing and future astrometric facilities. Modeling was performed for the astrometric accuracy of 0.01, 0.1, and 1.0 mas, separation between WD and planet of 3 and 5 A.U., binary system separation of 30 A.U., planet masses of 10 Earth masses, 1 and 10 Jupiter masses, WD mass of 0.5M and 1.0 Solar masses, and distances to the system of 10, 20 and 30 pc. It was found that the PRIMA facility at the VLTI will be able to detect planets around white dwarfs once it is operating, by measuring the astrometric wobble of the WD due to a planet companion, down to 1 Jupiter mass. We show for the simulated observations that it is possible to model the orbits and find the parameters describing the potential planetary systems. / Bei von Sternen verursachten Mikrolinsen-Ereignissen beobachtet man meist symmetrische Lichtkurven einer einzelnen Linse oder asymmetrische Lichtkurven (oftmals mit Kaustik-Crossing), die durch Doppel-Linsen hervorgerufen werden. Im Prinzip kann aus der Zahl der gemessenen unsymmetrischen Ereignisse der Anteil der Doppelstern-Systeme in Abhängigkeit vom Winkelabstand abgeschätzt werden. Allerdings kann auch ein Doppelsystem Lichtkurven erzeugen, die gut mit einer Einzellinsen-Lichtkurve gefittet werden können. Die gilt insbesondere bei lückenhafter Messung oder grossen Messfehlern. In dieser Arbeit wird für verschiedene Beobachtungsbedingungen untersucht, wie häufig Lichtkurven, die von Doppellinsen mit unterschiedlichen Abständen erzeugt werden, gut mit Einzellinsen-Lichtkurven gefittet werden können und damit fehlinterpretiert werden. Es wurde herausgefunden, dass der Anteil fehlinterpretierter Lichtkurven stark von der Separation der Komponenten abhängig ist: das Minimum liegt zwischen 2 A.E. and 5 A.E. / wobei der Anteil immer noch 5% beträgt. Die Rate der Fehlinterpretationen ist höher für kurze Mikrolinsen-Ereignisse (bis zu wenigen Monaten) und für Ereignisse mit geringer Maximalverstärkung. Bei gleicher Separation steigt die Rate mit extremeren Massenverhältnissen an.<br><br> Das Problem der Degenerierung zwischen den Lichtkurven für doppelte Linsensysteme und doppelte Hintergrund-Quellen wurde anhand simulierter Daten und mit Beobachtungsdaten des PLANET Projekts untersucht. Der Fit-Code BISCO, der den genetischen Algorithmus PIKAIA nutzt, wurde geschrieben, um Doppel-Linsen Lichtkurven, die von verschiedenen Observatorien in den photometrischen Bändern I, B, und V gemessen wurden, zu modellieren. Tests mit simulierten Daten haben gezeigt, dass BISCO in der Lage ist, in einem sehr weiten Parameterbereich die korrekte Lösung für die Lichtkurve einer Doppel-Linsen zu finden. In dieser Arbeit wird die Flussverhältnis-Methode empfohlen, um die Degenerierung zwischen Doppel-Linse und Doppel-Quelle aufzulösen. Modellierungen zeigen, dass nur wenige zusätzliche Datenpunkte im V-Band genügen, um zusammen mit einer vollständigen Lichtkurve im I-Band die Degenerierung aufzubrechen. Mit sehr guter Datenqualität und zeitlich dichten Messungen, kombiniert mit genauer Modellierung von Doppel-Linsen und Doppel-Quellen, gelang die Entdeckung des bisher masseärmsten Planeten ausserhalb des Sonnensystems: OGLE-2005-BLG-390Lb, mit nur 5.5 Erdmassen. Dies war das erste Mikrolinsen-Ereignis, bei dem die Degenerierung zwischen plantarer Doppel-Linse und einer Doppel-Quelle mit extremem Flussverhältnis erfolgreich aufgelöst wurde. Für die Ereignisse OGLE-2003-BLG-222 und OGLE-2004-BLG-347 besteht die Degenerierung trotz sehr dichter Messungen. Aufgrund der Lichtkurvenmodellierung und Argumenten aus der Theorie der Sternentwicklung ist die Erklärung von OGLE-2003-BLG-222 als Doppel-Quelle und OGLE-2004-BLG-347 als Doppel-Linsen Ereignis vorzuziehen. Allerdings kann die Degenerierung ohne spektrale Daten nicht vollständig aufgelöst werden.<br><br> Bisher wurde kein Planet als Begleiter eines Weissen Zwerges gefunden, obwohl es möglich sein sollte, dass jupiterähnliche Planeten die Spätstadien der Sternentwicklung überleben und dass sich Weisse Zwerge Planetensysteme mit weiten Umlaufbahnen erhalten können. Wir planen hochgenaue astrometrische Beobachtungen von nahen Weissen Zwergen in weiten Doppelsystemen, um Planeten um Weisse Zwerge zu finden. Wir haben eine Stichprobe von Systemen zusammengestellt, in denen möglicherweise Planeten gefunden werden könnten. Wir haben synthetische astrometrische Orbits modelliert, die für diese Systeme mit existierenden und zukünftigen astrometrischen Instrumenten beobachtbar sind. Die Modellierungen wurden für astrometrische Genauigkeiten von 0.01, 0.1, 1.0 Mikrobogensekunden gerechnet. Als Abstände zwischen weissem Zwerg und Planet wurden 3, 5 und 10 Astronomische Einheiten angenommen, für den Abstand zwischen den Doppelsternkomponenten 30 A.E. Als Planetenmassen wurden 10 Erdmassen, bzw. 1 und 10 Jupitermassen gewählt, als Masse für den weissen Zwerg 0.5 und 1.0 Sonnenmassen. Die Distanzen zum System betragen 10 und 20 parsec. Als Resultat dieser Untersuchung wurde herausgefunden, dass das PRIMA Instrument am VLTI in der Lage sein wird, die astrometrischen Oszillationen, die ein Planet ab einer Jupitermasse verursacht, zu detektieren. Wir zeigen, dass es möglich sein wird, die Umlaufbahnen solcher Planeten zu modellieren und damit die Parameter dieser Planetensysteme zu bestimmen.

Since the first successful measurements of stellar trigonometric parallax in the 1830s, the study of nearby stars has focused on the highest proper motion stars (mu > 0.18"/yr). Those high proper motion stars have formed the backbone of the last 150 years of study of the Solar Neighborhood and the composition of the Galaxy. Statistically speaking, though, there is a population of stars that will have low proper motions when their space motions have been projected onto the sky. At the same time, over the last twenty years, populations of relatively young stars (less than ~100 Myr), most of them with low proper motions, have been revealed near (<100 >pc) the Sun. This dissertation is the result of two related projects: A photometric search for nearby (<25 >pc) southern-hemisphere M dwarf stars with low proper motions (mu < 0.18"/yr), and a search for nearby (

Dans cette thèse, la recherche se concentre sur le re-calibrage des observations historiques de Phoebe, le 9ème satellite de Saturne, et l'amélioration de son orbite sur la base des données re-calibrés. La précision de calcul de l'orbite dépend de la qualité du modèle théorique (erreur interne) et de la précision des observations utilisées pour ajuster le modèle (erreur externe). Phoebe est loin de sa planète et des satellites majeurs. Le modèle théorique n'est pas très compliqué et l'erreur interne est bien connu et généralement bonne. Toutefois, l'erreur externe est en général inconnue et est la principale cause de l'erreur globale. Comme la luminosité de Phoebe est faible (Vmag = 16,5), il n'y a pas beaucoup d'observations faites dans le temps passé. La précision de son orbite n'est pas aussi bonne que celles des autres grands satellites de Saturne. Un modèle plus adéquat du mouvement du satellite devrait être construit non seulement sur la base des observations de haute-précision, mais aussi sur des données couvrant une période aussi longue que possible. Les observations de Phoebe sur plus de cent ans ont été calibré avec différents catalogues. Il y a quelques incohérences dans les données d'observation obtenues à partir de différents auteurs à différentes époques. De nombreuses observations ont été publiées dans différents formats; elles ne peuvent pas être utilisées directement pour ajuster le modèle dynamique; elles doivent être converties dans un format de données unifié et être corrigées pour des erreurs systématiques, avec les dernières constantes astronomiques dans le système de référence. Les premières observations de Phoebe ont une mauvaise précision et ne collent pas bien aux modèles. A cette époque, les catalogues utilisés ne contenaient pas assez d'étoiles avec une précision suffisante, donc il n'y avait pas beaucoup de étoiles du catalogue sur la plaque. En raison de la précision insatisfaisante des catalogues à l'époque, les positions des étoiles de référence ne sont pas très précises. Cela influe sur la position de Phoebe. Dans le présent travail, nous introduisons une méthode permettant, même si nous ne disposons pas des vraies plaques, de réduire les positions des satellites naturels avec des catalogues astrométriques modernes, tels que UCAC ou GAIA dans le futur. Après la re-calibration des données d'observation historiques, la réduction des observations a été effectuée et la nouvelle éphéméride de Phoebe on a été dérivée. La représentation synthétique au mouvement orbital de Phoebe à partir des éphémérides a été réalisée. / In this thesis, the research focuses on the recalibration of historical observations of Phoebe, the 9th satellite of Saturn, and its orbit improvement based on the re-calibrated data. The accuracy of orbit predictions depends on the theoretical model's quality (internal error) and on the quantity and accuracy of the observations used to fit the model (external error). Phoebe is far away from its planet and other major satellites, so that the theoretical model is not very complicated and the internal error is well known and generally good. However, the external error is generally unknown and is the main cause of the global error. Since the brightness of Phoebe is faint (Vmag=16.5), not so many observations have been made in the past time. The accuracy of its ephemeris is not as good as those of other major satellites of Saturn. A most adequate model of satellite motion should be built not only based on high-accurate recent observations but also on data over a period of time as long as possible. The observations of Phoebe over one hundred years have been calibrated with different catalogs. There are some inconsistencies in observational data obtained from different authors at different epochs. Many observations have been published in different formats; they cannot be used directly to fit the dynamical model, should be re-input into unified data format, and be corrected for systematic differences, with the latest astronomical constants and reference frame. The earliest observations of Phoebe have bad accuracy and not fit the models very well. At that time, the catalogues they used did not contain enough stars with a precise accuracy, so there were not many catalogue stars on the plate. Because of the unsatisfactory precision of the old catalogues at the epoch, the positions of the reference stars were not very precise. This brings today inaccuracy on the position of Phoebe. In the present work, we introduce a method, even if we do not have real plates, to reduce the positions of the natural satellites with modern astrometric catalogues, such as UCAC or GAIA in the future. After the re-calibration of historical observation data, reduction of observations has been completed and the new ephemeris Phoebe was derived. Then the synthetic representation of Phoebe's orbital motion from the ephemeris was provided.

A principal scientific goal of the Gemini Planet Imager (GPI) is obtaining milliarcsecond astrometry to constrain exoplanet orbits. However, astrometry of directly imaged exoplanets is subject to biases, systematic errors, and speckle noise. Here, we describe an analytical procedure to forward model the signal of an exoplanet that accounts for both the observing strategy (angular and spectral differential imaging) and the data reduction method (Karhunen-Loeve Image Projection algorithm). We use this forward model to measure the position of an exoplanet in a Bayesian framework employing Gaussian processes and Markov-chain Monte Carlo to account for correlated noise. In the case of GPI data on beta Pic b, this technique, which we call Bayesian KLIP-FM Astrometry (BKA), outperforms previous techniques and yields 1 sigma errors at or below the one milliarcsecond level. We validate BKA by fitting a Keplerian orbit to 12 GPI observations along with previous astrometry from other instruments. The statistical properties of the residuals confirm that BKA is accurate and correctly estimates astrometric errors. Our constraints on the orbit of beta Pic b firmly rule out the possibility of a transit of the planet at 10-sigma significance. However, we confirm that the Hill sphere of beta Pic b will transit, giving us a rare chance to probe the circumplanetary environment of a young, evolving exoplanet. We provide an ephemeris for photometric monitoring of the Hill sphere transit event, which will begin at the start of April in 2017 and finish at the end of January in 2018.

In November 2012, the European Space Agency (ESA) is planning to launch Gaia, a mission designed to measure with microarcsecond accuracy the astrometric properties of over a billion stars. Microarcsecond astrometry requires extremely accurate positional measurements of individual stellar transits on the focal plane, which can be disrupted by radiation-induced Charge Transfer Inefficiency (CTI). Gaia will suffer radiation damage, impacting on the science performance, which has led to a series of Radiation Campaigns (RCs) being carried out by industry to investigate these issues. The goal of this thesis is to rigorously assess these campaigns and facilitate how to deal with CTI in the data processing. We begin in Chapter 1 by giving an overview of astrometry and photometry, introducing the concept of stellar parallax, and establishing why observing from space is paramount for performing global, absolute astrometry. As demonstrated by Hipparcos, the concept is sound. After reviewing the Gaia payload and discussing how astrometric and photometric parameters are determined in practice, we introduce the issue of radiation-induced CTI and how it may be dealt with. The on board mitigating strategies are investigated in detail in Chapter 2. Here we analyse the effects of radiation damage as a function of magnitude with and without a diffuse optical background, charge injection and the use of gates, and also discover a number of calibration issues. Some of these issues are expected to be removed during flight testing, others will have to be dealt with as part of the data processing, e.g. CCD stitches and the charge injection tail. In Chapter 3 we turn to look at the physical properties of a Gaia CCD. Using data from RC2 we probe the density of traps (i.e. damaged sites) in each pixel and, for the first time, measure the Full Well Capacity of the Supplementary Buried Channel, a part of every Gaia pixel that constrains the passage of faint signals away from the bulk of traps throughout the rest of the pixel. The Data Processing and Analysis Consortium (DPAC) is currently adopting a 'forward modelling' approach to calibrate radiation damage in the data processing. This incorporates a Charge Distortion Model (CDM), which is investigated in Chapter 4. We find that although the CDM performs well there are a number of degeneracies in the model parameters, which may be probed further by better experimental data and a more realistic model. Another way of assessing the performance of a CDM is explored in Chapter 5. Using a Monte Carlo approach we test how well the CDM can extract accurate image parameters. It is found that the CDM must be highly robust to achieve a moderate degree of accuracyand that the fitting is limited by assigning finite window sizes to the image shapes. Finally, in Chapter 6 we summarise our findings on the campaign analyses, the on-board mitigating strategies and on how well we are currently able to handle radiation damage in the data processing.

AutoCAD, Zemax Optic Studio 15, and Interactive Data Language (IDL) with the Proper Library are used to computationally model and test a diffractive mask (DiM) suitable for use in the Gemini Multi-Conjugate Adaptive Optics System (GeMS) on the Gemini South Telescope. Systematic errors in telescope imagery are produced when the light travels through the adaptive optics system of the telescope. DiM is a transparent, flat optic with a pattern of miniscule dots lithographically applied to it. It is added ahead of the adaptive optics system in the telescope in order to produce diffraction spots that will encode systematic errors in the optics after it. Once these errors are encoded, they can be corrected for. DiM will allow for more accurate measurements in astrometry and thus improve exoplanet detection. The mechanics and physical attributes of the DiM are modeled in AutoCAD. Zemax models the ray propagation of point sources of light through the telescope. IDL and Proper simulate the wavefront and image results of the telescope. Aberrations are added to the Zemax and IDL models to test how the diffraction spots from the DiM change in the final images. Based on the Zemax and IDL results, the diffraction spots are able to encode the systematic aberrations.

Velmi přesná následná astrometrie je nezbytným předpokladem sledování blízkozemních objektů, které mohou představovat riziko srážky se Zemí. Tato práce přináší ucelený přehled přesné astrometrie, obsahuje potřebnou matematickou teorii, postup předzpracování snímků v astronomii, a nastiňuje použití filtrů. Navrhuje nové metody pro vyrovnání pozadí snímků před provedením astrometrického měření pro případ, kdy nejsou dostupné kalibrační snímky. Tyto metody jsou založeny na vytvoření syntetického flatfieldu pomocí aplikování filtru na snímek a následné užití tohoto flatfieldu pro odstranění pozadí snímku. Metody byly otestovány na vzorových snímcích a vzápětí použity k získání astrometrických pozic prvního mezihvězdného objektu 1I/2017 U1 ('Oumuamua).