More than 80% of the stars in the Universe are expected to have initial masses below eight to ten times the mass of our sun. These low mass stars, including our sun, become cool red giants during one of the final evolutionary stages of their life: the Asymptotic Giant Branch (or AGB) phase. AGB stars are among the main producers of carbon and heavy (s-process) elements in the Universe. These elements are synthesized inside the star and mixed to the stellar atmosphere where stellar winds are responsible for the loss of more than 50% of the stellar mass, hence, AGB stars are strong polluters of the interstellar medium. The ejected material can clump together into dusty particles which may serve as ingredients for the birth of new stars and planets. When most of the AGB stellar envelope is lost, the AGB star stops releasing nuclear energy from interior processes and swaps its giant face for a planetary nebulae look, whereafter it fades away as a white dwarf.<p><p>The dredge-up of carbon and s-process elements into the AGB atmosphere causes an important chemical anomaly among them: initial oxygen-rich stars (M stars) are transformed into carbon-rich stars (C stars). As a consequence, a group of oxygen-rich AGB stars exists which makes the transition between M and C stars. These transition stars are classified as S.<p><p>Although AGB stars are identified as producers of heavy elements, their nucleosynthesis and mixing processes are weakly constrained due to large uncertainties on their estimated temperature, gravity and chemical composition. Stronger constraints on the atmospheric parameter space, hence interior processes, of AGB stars can be obtained by investigating the atmosphere of S stars. Since they are transition objects on the AGB, they trace the rise of the s-process. S stars are less numerous than C stars, but their optical spectra are brighter making it easier to identify atomic and molecular lines. Therefore, S stars belong to the most interesting objects along the AGB to perform this task.<p><p><p><p>From a practical point of view, the spectra of S stars are extremely difficult to study since they are dominated by different, overlapping molecular bands, and the spectral shape may vary strongly from star to star due to their transition status. Therefore, tailored model atmospheres for S stars are of utmost importance to understand the spectroscopic, and even photometric, changes in terms of variations in the atmospheric parameters. A comparison between the models and observations aims not only at constraining the atmospheric parameter space of S stars, it will also test the reliability of 1D state-of-the-art model atmospheres for such complex stars.<p><p><p><p>From an evolutionary point of view, the S-star family is contaminated with stars who gained their atmospheric enrichment in heavy elements from a companion star. Evidences were found that these binary S stars are not at all located on the AGB, hence, they are labelled as extrinsic S stars while S stars on the AGB are labelled as intrinsic. The difference in evolutionary stages between intrinsic and extrinsic S stars was already found 20 years ago, however, a separation in terms of surface temperature, gravity and chemical composition is not well-established due to the lack of S-star model atmospheres. Such a distinction in atmospheric parameters will facilitate the discovery of these intruders and even help to calibrate stellar evolutionary models of single and binary stars.<p>To achieve these goals, the first step consists in the construction of a grid of model atmospheres for S stars. The grid will be used to quantify the influence of atmospheric parameters on the model structure and emergent flux. These results will be analyzed to derive precise atmospheric parameters of observed S stars, using a set of well-defined photometric and spectroscopic indices. Once the best model atmosphere has been selected for all observed S stars, their atmospheric parameters will be discussed in view of their evolutionary stage. The best-fitting model atmosphere will also be used to derive abundances from spectral syntheses. The abundance profiles are compared with stellar evolution model prediction to constrain nucleosynthesis and mixing processes inside S stars. Derived abundances of unstable elements will be used to estimate, for the first time, the age of AGB stars. Finally, their abundance profile will be discussed as a function of their time spent on the AGB. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

Les petits corps du système solaire riches en volatiles incluent plusieurs populations d’objets : les astéroïdes de la ceinture principale, les astéroïdes troyens des planètes géantes, les objets trans-neptuniens (OTNs) et les comètes. Au cours de ces dernières années, l'’idée que leur position actuelle résulte de migrations orbitales plutôt qu’elle ne reflète leur région de formation a progressivement émergée. Spécifiquement, certains astéroïdes pourraient être des comètes, et certaines comètes pourraient être des OTNs. Je présente ici les travaux réalisés au cours de ma thèse pour contraindre la composition (minéralogie de surface et structure interne) de ces différentes populations afin i) de déterminer les liens qui les unissent, ii) comprendre leurs migrations passées et donc, iii) apporter de nouvelles contraintes aux modèles dynamiques décrivant la formation et l’évolution de notre système solaire. À cet effet, j’ai principalement utilisé comme méthode d’analyse l’observation spectroscopique, ainsi que la modélisation des données obtenues et leur comparaison aux données spectrales de météorites et poussières cosmiques étudiées en laboratoire. / The icy small bodies of our solar system encompass several populations of objects : the main belt asteroids, the giant planets Trojans, the Trans-Neptunian Objects (TNOs) and the comets. During recent years, the idea that their present location is the result of orbital migrations rather than their true formation location has progressively emerged. Specifically, some asteroids could be comets, and some comets could be TNOs. Here, I present the studies carried out along my PhD aiming to constrain the physical properties of all these populations in order ultimately i) to determine the link between these populations, ii) bring key constraints to their past orbital evolution and thus iii) key constraints to the formation and evolution models for our Solar System. For that purpose, I have used spectroscopy as a main tool, as well as data modelling using a radiative transfert code and comparison of our astronomical data to laboratory measurements of meteorites and cosmic dust.

Parmi les méthodes qui permettent de détecter des exoplanètes, la photométrie des transits est celle qui a connu le plus grand essor ces dernières années grâce à l’arrivée des télescopes spatiaux CoRoT (en 2006) puis Kepler (en 2009). Ces deux satellites ont permis de détecter des milliers de transits potentiellement planétaires. Étant donnés leur nombre et l’effort nécessaire à la confirmation de leur nature, il est essentiel d’effectuer, à partir des données photométriques, un classement efficace permettant d’identifier les transits les plus prometteurs et qui soit réalisable en un temps raisonnable. Pour ma thèse, j’ai développé un outil logiciel, rapide et automatisé, appelé BART (Bayesian Analysis for the Ranking of Transits) qui permet de réaliser un tel classement grâce une estimation de la probabilité que chaque transit soit de nature planétaire. Pour cela, mon outil s’appuie notamment sur le formalisme bayésien des probabilités et l’exploration de l’espace des paramètres libres par méthode de Monte Carlo avec des chaînes de Markov (mcmc).Une fois les exoplanètes détectées, l’étape suivante consiste à les caractériser. L’étude du système solaire nous a démontré, si cela était nécessaire, que l’information spectrale est un point clé pour comprendre la physique et l’histoire d’une planète. L’interférométrie annulante est une solution technologique très prometteuse qui pourrait permettre cela. Pour ma thèse, j’ai travaillé sur le banc optique Nulltimate afin d’étudier la faisabilité de certains objectifs technologiques liés à cette technique. Au-delà de la performance d’un taux d’extinction de 3,7.10^-5 en monochromatique et de 6,3.10^-4 en polychromatique dans l’infrarouge proche, ainsi qu’une stabilité de σN30 ms = 3,7.10^-5 estimée sur 1 heure, mon travail a permis d’assainir la situation en réalisant un budget d’erreur détaillé, une simulation en optique gaussienne de la transmission du banc et une refonte complète de l’informatique de commande. Tout cela m’a finalement permis d’identifier les faiblesses de Nulltimate. / From all exoplanet detection methods, transit photometry went through the quickest growth over the last few years thanks to the two space telescopes, CoRoT (in 2006) and Kepler (in 2009). These two satellites have identified thousands of potentially planetary transits. Given the number of detected transits and the effort required to demonstrate their natures, it is essential to perform, from photometric data only, a ranking allowing to efficiently identify the most promising transits within a reasonable period of time. For my thesis, I have developed a quick and automated software called bart (Bayesian Analysis for the Ranking of Transits) which realizes such a ranking thanks to the estimation of the probability regarding the planetary nature of each transit. For this purpose, I am relying on the Bayesian framework and free parameter space exploration with Markov Chain Monte Carlo (mcmc) methods.Once you have detected exoplanets, the following step is to characterise them. The study of the solar system demonstrated, if it was necessary, that the spectral information is a crucial clue for the understanding of the physics and history of a planet. Nulling interferometry is a promising solution which could make this possible. For my thesis, I worked on the optical bench Nulltimate in order to study the feasibility of certain technological requirements associated with this technique. Beyond the obtention of a nulling ratio of 3,7.10^-5 in monochromatic light and 6,3.10^-4 in polychromatic light in the near infrared, as well as a stability of σN30 ms = 3,7.10^-5 estimated on 1 hour, my work allowed to clarify the situation thanks to a detailed error budget, a simulation of the transmission based on Gaussian beam optics and a complete overhaul of the computer control system. All of this finally resulted in the identification of the weaknesses of Nulltimate.

El brillo solar varía en escalas de tiempo de minutos a décadas. En particular, la variabilidad fotométrica observada puede relacionarse directamente con el período de rotación. Nuestro conocimiento de este vínculo permite extrapolaciones desde el Sol a otras estrellas. Incluso después de los exitosos estudios estelares logrados por las misiones Kepler o TESS, todavía hay una falta de información en los registros fotométricos de los períodos de rotación de estrellas similares al Sol. Los perfiles de curvas de luz no periódicas, la amplitud de modulación baja (los generados por la aparición aleatoria de características magnéticas y su rápida evolución, en comparación con la escala de tiempo de rotación) son las principales razones poco confiable estimación de la periodicidad en el Sol y sus análogos estelares. Esto indica que las estrellas con un perfil de brillo solar similar también podrían enfrentar un problema de detectabilidad del período de rotación. Lo que implica que solo una fracción de los sistemas similares a los solares se han analizado adecuadamente. Propongo en esta Tesis que una señal clara y optimizada del período de rotación puede ser determinada de manera confiable a partir del perfil del gradiente en el espectro de potencia (GPS) de las series de tiempo de brillo, también denominadas curvas de luz. El GPS es un método novedoso destinado a determinar los períodos de rotación de estrellas como el Sol (es decir, con un perfil de variabilidad de brillo similar). Adicionalmente, el método nos da valiosa información sobre la relación entre fáculas y manchas, lo que, en consecuencia, podría ayudarnos a interpretar la superficie estelar. Este trabajo se basa en el análisis de series de tiempo fotométricas de alta calidad adquiridas por el telescopio Kepler, mediciones de alta estabilidad y alta precisión de la misión SOHO / VIRGO y modelos detallados de variaciones de brillo solar. El método GPS se propone, se desarrolla y prueba con éxito en esta tesis.

Because luminance is the only value to which our sight responds, its measurement becomes important in terms of ensuring the proper function of vision. Nowadays luminance measuring can be made by conventional methods, such as direct using of luminance meter. However an entirely new method of measuring luminance levels is coming. This method is based on using luminance analyzers which work using a digital photography for the analysis of luminance. This thesis deals with these issues and is divided into several chapters, which form the two main parts of the thesis, the theoretical and the practical one. The theoretical part of the thesis deals with the basics of lighting technology, as well as the principles of measuring the luminance using conventional methods. New methods of measurement, i.e. using luminance analyzers, are discussed in two chapters which analyse both the principle and characteristics of analyzers available today. In the practical part is a comparative measurement carried out – in the laboratory and in terrain – using both methods.

La majorité des exoplanètes connues à ce jour ont été découvertes par la méthode du transit, qui infère indirectement l’existence de tels objets, si l’alignement le permet, en mesurant la baisse temporaire et répétée de la brillance d’une étoile lors du passage d’une exoplanète devant celle-ci. La recherche de biosignatures, donc de vie, dans l’atmosphère d’une exoplanète est désormais le principal objectif dans ce domaine d’études, et pour maintes raisons, celles de taille de moins d’approximativement deux rayons terrestres autour d’étoiles naines rouges sont particulièrement convoitées. Afin de connaître davantage de tels systèmes dans le voisinage solaire et dans toutes les régions du ciel, le Transiting Exoplanet Survey Satellite (TESS) fut lancé en avril 2018. Le grand échantillonnage de 21'' par pixel des caméras à bord de TESS résulte fréquemment à une contamination des données des étoiles d’intérêt montrant un signal prometteur de transit, par le flux d’autres étoiles à proximité. Lorsque l’une de ces sources contaminantes est une étoile binaire à éclipses, phénomène astrophysique pouvant mimer un transit, la détection constitue très souvent un événement faux positif. Ainsi, de nouvelles observations photométriques et spectroscopiques sont généralement requises pour identifier les véritables exoplanètes. Ce mémoire présente les résultats du suivi photométrique de neuf candidates exoplanètes identifiées par TESS à l’Observatoire du Mont-Mégantic avec la caméra Planètes Extra-Solaires en Transit et Occultations (PESTO). Une routine d’ajustement de courbe de transit développée durant cette maîtrise procure une estimation de certains paramètres physiques (rayons, demi-grand axe et inclinaison) des candidates. Parmi celles-ci, TOI 1452.01 ressort du lot, car cette probable exoplanète d’environ deux rayons terrestres orbite dans la zone habitable de son hôte naine rouge, c’est-à-dire à une distance permettant la présence d’eau liquide à sa surface. / The majority of the exoplanets known to date have been discovered using the transit method, which indirectly infers the existence of such objects by measuring a temporary and repeated drop in the brightness of a star when, for the right alignement, an exoplanet passes in front of it. The search for biosignatures, thus life, in an exoplanet atmosphere is now the main objective in this field of study, and for several reasons, planets with a radius less than approximately two Earth radii around red dwarfs are particularly targeted. With the goal of finding more such systems in the solar neighbourhood and in all regions of the sky, the Transiting Exoplanet Survey Satellite (TESS) was launched in April 2018. The large image sampling of 21'' per pixel of the cameras on board TESS often results in data contamination of stars showing promising transit signal, by the flux of nearby stars. If one of these contaminating sources happens to be an eclipsing binary, an astrophysical phenomenon able to mimic a transit, the detection is most likely a false positive event. Thus, follow-up observations in photometry and in spectroscopy are generally required to identify the genuine exoplanets. This thesis presents the results of a photometric monitoring campaign at the Observatoire du Mont-Mégantic with the Planètes Extra-Solaires en Transit et Occultations (PESTO) camera of nine exoplanet candidates identified by TESS. A transit curve fitting routine developed during this master’s provides an estimation for certain physical parameters (radius, semi-major axis and inclination) of these candidates. Among them, TOI 1452.01 stands out, because this probable exoplanet has an estimated radius close to two Earth radii, in addition to being located within the habitable zone of its red dwarf host, i.e. at a distance allowing the presence of liquid water on its surface.

The significant increase of astronomical data necessitates new strategies and developments to analyse a large amount of information, which no longer is efficient if done by hand. Supervised machine learning is an example of one such modern strategy. In this work, we apply the classification technique on Gaia+2MASS+WISE data to explore the usage of supervised machine learning on large astronomical archives. The idea is to create an algorithm that recognises entries with unusual infrared properties which could be interesting for follow-up observations. The programming is executed in MATLAB and the training of the algorithms in the classification learner application of MATLAB. Each catalogue; Gaia+2MASS+WISE contains ~109, 5×108 and 7×108 (The European Space Agency 2019, Skrutskie et al. 2006, R. M. Cutri IPAC/Caltech) entries respectively. The algorithms searches through a sample from these archives consisting of 765266 entries, corresponding to objects within a &lt;500 pc range. The project resulted in a list of 57 entries with unusual infrared properties, out of which 8 targets showed none of the four common features that provide a natural physical explanation to the unconventional energy distribution. After more comprehensive studies of the aforementioned targets, we deem it necessary for further studies and observations on 2 out of the 8 targets (Nr.1 and Nr.8 in table 3) to establish their true nature. The results demonstrate the applicability of machine learning in astronomy as well as suggesting a sample of intriguing targets for further studies. / Inom astronomi samlas stora mängder data in kontinuerligt och dess tillväxt ökar snabbt för varje år. Detta medför att manuella analyser av datan blir mindre och mindre lönsama och kräver istället nya strategier och metoder där stora datamängder snabbare kan analyseras. Ett exempel på en sådan strategi är vägledd maskininlärning. I detta arbete utnyttjar vi en vägled maskininlärnings teknik kallad klassificering. Vi använder klassificerings tekniken på data från de tre stora astronomiska katalogerna Gaia+2MASS+WISE för att undersöka användningen av denna teknik på just stora astronomiska arkiv. Idén är att skapa en algorithm som identifierar objekt med okontroversiella infraröda egenskaper som kan vara intressanta för vidare observationer och analyser. Dessa ovanliga objekt är förväntade att ha en lägre emission i det optiska våglängdsområdet och en högre emission i det infraröda än vad vanligtvis är observerad för en stjärna. Programmeringen sker i MATLAB och träningsprocessen av algoritmerna i MATLABs applikation classification learner. Algoritmerna söker igenom en samling data bestående av 765266 objekt, från katalogerna Gaia+2MASS+WISE. Dessa kataloger innehåller totalt ~109, 5×108 och 7×108 (The European Space Agency 2019, Skrutskie et al. 2006, R. M. Cutri IPAC/Caltech) objekt vardera. Det begränsade dataset som algoritmerna söker igenom motsvarar objekt inom en radie av &lt;500 pc. Många av de objekt som algoritmerna identifierade som ”ovanliga” tycks i själva verket vara nebulösa objekt. Den naturliga förklaringen för dess infraröda överskott är det omslutande stoft som ger upphov till värmestrålning i det infraröda. För att eliminera denna typ av objekt och fokusera sökningen på mer okonventionella objekt gjordes modifieringar av programmen. En av de huvudsakliga ändringarna var att introducera en tredje klass bestående av stjärnor inneslutna av stoft som vi kallar "YSO"-klassen. Ytterligare en ändring som medförde förbättrade resultat var att introducera koordninaterna i träningen samt vid den slutgiltiga klassificeringen och på så vis, identifiering av intressanta kandidater. Dessa justeringar resulterade i en minskad andelen nebulösa objekt i klassen av ”ovanliga” objekt som algoritmerna identifierade. Projektet resulterade i en lista av 57 objekt med ovanliga infraröda egenskaper. 8 av dessa objekt påvisade ingen av det fyra vanligt förekommande egenskaperna som kan ge en naturlig förklaring på dess överflöd av infraröd strålning. Dessa egenskaper är; nebulös omgivning eller påvisad stoft, variabilitet, Hα emission eller maser strålning. Efter vidare undersökning av de 8 tidigare nämnda objekt anser vi att 2 av dessa behöver vidare observationer och analys för att kunna fastslå dess sanna natur (Nr.1 och Nr.8 i tabell 3). Den infraröda strålningen är alltså inte enkelt förklarad för dessa 2 objekt. Resultaten av intressanta objekt samt övriga resultat från maskininlärningen, visar på att klassificeringstekniken inom maskininlärning är användbart på stora astronomiska datamängder.

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Bacterial DNA replication can stall at DNA lesions, leading to cell death if the damage fails to be repaired. To circumvent this, bacteria possess a mechanism called translesion DNA synthesis (TLS) to allow DNA damage bypass. The ImuABC TLS mutasome comprises the RecA domain-containing protein ImuA, the inactive polymerase ImuB, and the error-prone polymerase ImuC. ImuA and ImuB are necessary for the mutational function of ImuC that can lead to antimicrobial resistance (AMR) as seen in high-priority pathogens Pseudomonas aeruginosa and Mycobacterium tuberculosis. Understanding how ImuA and ImuB contribute to this function can lead to new targets for antimicrobial development. This research aims to discover the molecular functions of ImuA and ImuB homologs from Myxococcus xanthus through structural modelling and biochemical analyses. ImuA was discovered to be an ATPase whose activity is enhanced by DNA. Based on predicted structural models of the ATPase active site, I identified the critical residues needed for ATP hydrolysis, and found that the ImuA C-terminus regulates ATPase activity. Further, ImuA and ImuBNΔ34 (a soluble truncation of ImuB) display a preference for longer single-stranded DNA and overhang DNA substrates, and their affinity for DNA was quantified in vitro. To better understand how ImuA and ImuB assemble in the TLS mutasome, bacterial two-hybrid assays determined that ImuA and ImuB can self-interact and bind one another. Mass photometry revealed that ImuA is a monomer and ImuBNΔ34 is a trimer in vitro. ImuA and ImuBNΔ34 binding affinity was quantified in vitro at 1.69 μM ± 0.21 by microscale thermophoresis, and removal of the ImuA C-terminus weakens this interaction. Lastly, ImuA and ImuBNΔ34 secondary structures were quantified using circular dichroism spectroscopy, and ImuA was modified to enable crystallization for future structural studies. Together, this research provides a better understanding of ImuABC-mediated TLS, potentially leading to novel antibiotics to reduce the clinical burden of AMR. / Thesis / Master of Science (MSc) / The antimicrobial resistance (AMR) crisis is fueled by the emergence of multi-drug resistant microbes, posing a major threat to global health and disease treatment. Bacteria can develop resistance to antibiotics through mutations in the genome. When the genome becomes damaged, bacteria can acquire these mutations by an error-prone replication mechanism called translesion DNA synthesis (TLS). In some bacteria, TLS involves a specialized enzyme complex, consisting of proteins ImuA, ImuB and ImuC, allowing replication past bulky DNA damage and lesions. The goal of this thesis is to investigate how the ImuA and ImuB proteins contribute to the functioning of this mistake-making machinery. I used biochemical and biophysical methods to identify ImuA and ImuB interactions with each other and themselves. I discovered that ImuA is an enzyme that uses energy to enhance its binding to DNA, and determined the specific amino acids involved in this function.