Cette thèse présente les avancées dans l'étude des étoiles naines blanches magnétiques. L'étude des étoiles naines blanches en général, le state final d'évolution de près de 95% des étoiles de notre galaxie, permet d'obtenir de l'information cruciale sur leurs progéniteurs. Se pencher sur les propriétés des champs magnétiques des étoiles naines blanches par opposition à celles de leur progéniteur, beaucoup plus difficiles à observer en partie à cause de la faible intensité du champ, est bien plus réalisable. Plusieurs hypothèses ont été formulées afin de décrire l'origine et l'évolution de ces objets atypiques. Que les champs soient d'origine fossile suite à l'évolution d'une étoile isolée et conservation du flux magnétique, ou créés lors de la rotation rapide de la fusion de deux étoiles, il nous faut bien comprendre leur résultat, les naines blanches magnétiques, avant de pouvoir retracer leur évolution. Toutefois, les modèles de naines blanches magnétiques d'aujourd'hui reposent sur un nombre d'approximation, qui ne sont valides jusqu'à une relativement faible intensité de champ. Ceci a été la motivation derrière ce projet de doctorat. Nous avons implémenté un traitement des raies d'absorption utilisant le calcul des énergies de transition de l'atome d'hydrogène et d'hélium sous champs magnétiques arbitraires. Ces calculs, fournis par le groupe de l'université de Tübingen en Allemagne, ont utilisé une approche numérique à la résolution de l'Hamiltonien de l'atome d'hydrogène et d'hélium en présence d'un champ magnétique d'intensité arbitraire. Cet ajout aux modèles d'atmosphères permet de modéliser la position et l'intensité des raies d'absorption dans le spectre des étoiles. Une procédure de discrétisation de la surface visible de l'étoile nous permet de modéliser des champs magnétiques avec une géométrie arbitraire, tel qu'un dipôle décentré et incliné par rapport à l'observateur. Ces nouveaux outils ont été utilisés afin d'étudier en premier lieu un ensemble des naines blanches magnétiques avec une atmosphère riche en hydrogène. De ces résultats, nous avons déterminé une distribution de masse de ces étoiles, avec une masse moyenne significativement plus élevée que leurs homologues non-magnétiques, tels qu'attendu par les théories d'évolution binaires. Les informations extraites des différentes caractéristiques des distributions obtenues suite à cette analyse ne nous permettent cependant pas de favoriser une hypothèse d'évolution plutôt qu'une autre. Suite à ceci, celles avec une atmosphère riche en hélium ont été les prochaines à être analysées. Nous avons ainsi déterminé rigoureusement, pour la première fois, les paramètres magnétiques de ces étoiles riches en hélium. / This thesis presents advances in the study of magnetic white dwarf stars. The study of white dwarf stars in general, the final state of evolution of nearly 95% of the stars in our galaxy, provides crucial information about their progenitors. It is much more feasible to study the magnetic field properties of white dwarf stars as opposed to their progenitor stars, which are much more difficult to observe in part because of the weak field strength. Several hypotheses have been formulated to describe the origin and evolution of these atypical objects. Whether the fields are of fossil origin following the evolution of an isolated star and conservation of magnetic flux, or created during the rapid rotation of the merger of two stars, we need to understand their result, the magnetic white dwarfs, before we can trace their evolution. However, today's models of magnetic white dwarfs rely on a number of approximations, which are only valid up to relatively low field strengths. This was the motivation behind this doctoral thesis. We have implemented a treatment of the absorption lines using the calculation of the transition energies of the hydrogen and helium atom under arbitrary magnetic fields. These calculations, provided by the group of the University of Tubingen in Germany, used a numerical approach to the resolution of the Hamiltonian of the hydrogen and helium atom in the presence of a magnetic field of arbitrary intensity. This addition to atmospheric models allows to model the position and intensity of absorption lines in the spectrum of stars. A discretization procedure of the visible surface of the star allows us to model magnetic fields with an arbitrary geometry, such as an offset and inclined dipole. These new tools have been used to study first a set of magnetic white dwarfs with a hydrogen-rich atmosphere. From these results, we have determined a mass distribution of these stars, with an average mass significantly higher than their non-magnetic counterparts, as expected by the binary evolution theories. The information extracted from the different characteristics of the distributions obtained from this analysis does not however allow us to favor one evolutionary hypothesis over another. Following this, those with a helium rich atmosphere were the next to be analyzed. We have thus determined rigorously, for the first time, the magnetic parameters of these helium-rich stars.

The ability of animals to sense, interpret, and respond appropriately to social stimuli in their environment is essential for identifying and distinguishing between members of their own species. In mammals, social interactions both within and across species play a key role in determining if an animal will live to pass on its genes to the next generation or else be removed from the gene pool. The result of this selection pressure can be observed in specialized neural circuits that respond to social stimuli and orchestrate appropriate behavioral responses. This highly conserved network of brain structures is often referred to as the Social Behavior Network (SBN). The medial amygdala (MeA) is a central node in the SBN and has been shown to be involved in transforming information from olfactory sensory systems into social and defensive behavioral responses. Previous research has shown that individual neurons in the MeA of anesthetized mice respond selectively to different chemosensory social cues, a characteristic not observed in its upstream relay, the accessory olfactory bulb (AOB). However, the cause of this stimulus selectivity in the MeA is not yet understood. Here, I hypothesize that a subpopulation of neurons in the MeA that express the enzyme aromatase are involved in the sensory representation of social stimuli in awake, behaving animals. To test this hypothesis, I designed and built a novel behavioral apparatus that allows for discrete presentations of social stimuli in a highly controllable and reproducible environment. I then injected the adeno-associated virus (AAV) AAV-Syn-Flex-GCAMP6s into the MeA of Aromatase:Cre transgenic mice and implanted a fiber optic cannula slightly above the injection site. The combination of this transgenic mouse line and conditional AAV caused GCaMP6s expression to be exclusive to aromatase-expressing neurons. By coupling my novel behavioral apparatus to a fiber photometry system, I successfully recorded the moment-to-moment activity of aromatase neurons in the MeA of awake, behaving animals as they investigated various social stimuli. Aromatase neurons in the MeA of adult male mice respond strongly to conspecific social stimuli, including live adult mice, mouse pups, and mouse urine samples. Sniffing and investigative behaviors correlated strongly with increased GCaMP6s signal in aromatase neurons, reflecting increases in their neural activity. Interestingly, after repeated investigations of the same stimuli the activity of aromatase neurons gradually diminished. Presenting a novel stimulus following repeated investigations of a familiar stimulus reinstated some, but not all of the initial GCaMP6s signal. This points to the potential role that aromatase neurons may play in the habituation to social stimuli that are consistently present in their environment. Investigations of predator stimuli did not evoke significant responses from aromatase neurons, nor did investigations of non-social stimuli. These results demonstrate that aromatase expressing neurons in the MeA of awake, behaving animals encode the sensory representation of conspecific social stimuli, and their responses are highly selective to the type of stimulus presented.

The objects of research are low-molecular antioxidants, their mixtures and extracts of plant raw materials. Objective: To determine the antioxidant activity of tea and extracts of medicinal plant raw materials by potentiometric method using hexacyanoferrate (III) potassium as an oxidant model. The paper presents the causes of oxidative stress, exogenous antioxidants of natural origin, describes methods for determining the integral index of antioxidant activity. In the process of work, the antioxidant activity of low-molecular antioxidants was determined by potentiometric method using hexacyanoferrate (III) of potassium as an oxidizer model, potentiometric titration, photometric titration. As a result of the study, the antioxidant activity of extracts of various tea varieties and herbal plant raw materials was determined by the potentiometric method using potassium hexacyanoferrate (III) as an oxidant model. / Цель работы: определение антиоксидантной активности чая и экстрактов лекарственного растительного сырья потенциометрическим методом с использованием гексацианоферрата (III) калия в качестве модели окислителя. В работе представлены причины возникновения окислительного стресса, экзогенные антиоксиданты природного происхождения, описаны методы определения интегрального показателя антиоксидантной активности. В процессе работы определена антиоксидантная активность низкомолекулярных антиоксидантов потенциометрическим методом с использованием гексацианоферрата (III) калия в качестве модели окислителя, потенциометрическим титрованием, фотометрическим титрованием. В результате исследования определена антиоксидантная активность экстрактов различных сортов чая и лекарственного растительного сырья потенциометрическим методом с использованием гексацианоферрата (III) калия в качестве модели окислителя.

Due to the finite speed of light and a vast, expanding universe, telescopes are just now receiving the light emitted by galaxies as they were forming in the very early universe. The light from these galaxies has been redshifted (stretched to longer, redder wavelengths) as a result of its journey through expanding space. Using sophisticated techniques and exceptional multi-wavelength optical and infrared data, we isolate a population of 378 galaxies in the process of formation when the Universe was only two billion years old. By matching the distinctive properties of the light spectra of these galaxies to models, the redshift, age, dust content, star formation rate and total stellar mass of each galaxy are determined. Comparing our results to similar surveys of galaxy populations at other redshifts, a picture emerges of the growth and evolution of massive, star-forming galaxies over the course of billions of years.

Due to the finite speed of light and a vast, expanding universe, telescopes are just now receiving the light emitted by galaxies as they were forming in the very early universe. The light from these galaxies has been redshifted (stretched to longer, redder wavelengths) as a result of its journey through expanding space. Using sophisticated techniques and exceptional multi-wavelength optical and infrared data, we isolate a population of 378 galaxies in the process of formation when the Universe was only two billion years old. By matching the distinctive properties of the light spectra of these galaxies to models, the redshift, age, dust content, star formation rate and total stellar mass of each galaxy are determined. Comparing our results to similar surveys of galaxy populations at other redshifts, a picture emerges of the growth and evolution of massive, star-forming galaxies over the course of billions of years.

Due to the finite speed of light and a vast, expanding universe, telescopes are just now receiving the light emitted by galaxies as they were forming in the very early universe. The light from these galaxies has been redshifted (stretched to longer, redder wavelengths) as a result of its journey through expanding space. Using sophisticated techniques and exceptional multi-wavelength optical and infrared data, we isolate a population of 378 galaxies in the process of formation when the Universe was only two billion years old. By matching the distinctive properties of the light spectra of these galaxies to models, the redshift, age, dust content, star formation rate and total stellar mass of each galaxy are determined. Comparing our results to similar surveys of galaxy populations at other redshifts, a picture emerges of the growth and evolution of massive, star-forming galaxies over the course of billions of years.

Due to the finite speed of light and a vast, expanding universe, telescopes are just now receiving the light emitted by galaxies as they were forming in the very early universe. The light from these galaxies has been redshifted (stretched to longer, redder wavelengths) as a result of its journey through expanding space. Using sophisticated techniques and exceptional multi-wavelength optical and infrared data, we isolate a population of 378 galaxies in the process of formation when the Universe was only two billion years old. By matching the distinctive properties of the light spectra of these galaxies to models, the redshift, age, dust content, star formation rate and total stellar mass of each galaxy are determined. Comparing our results to similar surveys of galaxy populations at other redshifts, a picture emerges of the growth and evolution of massive, star-forming galaxies over the course of billions of years.

This thesis is concerned with various aspects of the detection and characterisation of transiting extra-solar planets. The noise properties of photometric data from SuperWASP, a wide-field survey instrument designed to detect exoplanets, are investigated. There has been a large shortfall in the number of planets such transit surveys have detected, compared to previous predictions of the planet catch. It has been suggested that correlated, or red, noise in the photometry is responsible for this; here it is confirmed that red noise is present in the SuperWASP photometry, and its effects on planet discovery are quantified. Examples are given of follow-up photometry of candidate transiting planets, confirming that modestly-sized telescopes can rule out some candidates photometrically. A Markov-chain Monte Carlo code is developed to fit transit lightcurves and determine the depth of such lightcurves in different passbands. Tests of this code with transit data of WASP-3 b are reported. The results of a search for additional transiting planets in known transiting planetary systems are presented. SuperWASP photometry of 24 such systems is searched for additional transits. No further planets are discovered, but a strong periodic signal is detected in the photometry of WASP-10. This is ascribed to stellar rotational variation, the period of which is determined to be 11.91 ± 0.05 days. Monte Carlo modelling is performed to quantify the ability of SuperWASP to detect additional transiting planets; it is determined that there is a good (> 50 per cent) chance of detecting additional, Saturn-sized planets in P ~ 10 day orbits. Finally, the first-ever attempt to detect the secondary eclipse of a transiting extra-solar planet at radio wavelengths is made. Although no eclipse is conclusively detected, upper limits to the flux density from HD 189733 b are established, and compared to theoretical predictions of the flux due to electron-cyclotron maser emission.

Les naines brunes sont, en termes de masse, les objets astrophysiques intermédiaires entre les planètes géantes gazeuses et les étoiles de faible masse. Elles se forment de la même manière que les étoiles, par contraction gravitationnelle d’un fragment de nuage de gaz moléculaire ayant atteint la limite de Jeans, mais se différencient par leur incapa- cité à produire les réactions de fusion de l’hydrogène dans leur cœur. Les naines brunes sont par conséquent des objets qui se refroidissent graduellement, et dont les propriétés spectrales évoluent au cours du temps. Ce mémoire présente la recherche de nouvelles candidates de type spectral T tardif et Y, dans le but de compléter le relevé des naines brunes du voisinage solaire. Cette recherche est motivée par deux objectifs principaux. Premièrement, un échantillon com- plet des objets de faible masse est nécessaire pour contraindre correctement la limite aux faibles masses de la fonction de masse initiale des nuages interstellaires, problème clé en astrophysique actuellement. Deuxièmement, les naines brunes de types spectraux tardifs sont les objets stellaires dont les propriétés atmosphériques sont les plus semblables à celles des planètes géantes gazeuses. Par conséquent, la recherche de nouvelles naines brunes permet indirectement d’améliorer nos connaissances des exoplanètes, sans être contraints par la proximité d’étoiles brillantes. À partir du WISE All-Sky Source Catalog, nous avons établi un échantillon de 55 candidates naines brunes répondant aux critères photométriques attendus. Parmi ces can- didates, 17 ont fait l’objet d’un suivi photométrique en bande J à l’Observatoire du Mont-Mégantic, et 9 ont pu être détectées. De ces 9 détections, 4 objets présentent des mouvements propres cohérents avec ceux de naines brunes. / In terms of mass, brown dwarfs are the objects that bridge the gap between giant gaseous planets and low-mass stars. They form in the same way as stars, by gravita- tional collapse of a molecular cloud fragment that reached the Jeans limit, but differ by their inability to produce hydrogen nuclear fusion in their core. As a consequence, brown dwarfs are objects gradually cooling, and their spectral properties evolve over time. This thesis presents the search for new late T and Y dwarf candidates, in order to complete the sample of known brown dwarfs in the solar vicinity. This pursues two main objectives. First, a complete sample of low-mass objects will allow to better con- strain the low-mass edge of the initial mass function of interstellar clouds, currently one of the key problems in astrophysics. Second, late-type brown dwarfs are the stellar ob- jects that have spectral properties most similar to those of giant gaseous planets. As a consequence, the search for new brown dwarfs also aims to increase our knowledge on exoplanets, without being hindered by the glare of a host star. From the WISE All-Sky Source Catalog, we established a sample of 55 brown dwarf candidates having the expected photometric properties. We have been performing a J band follow-up of 17 of these candidates at the Observatoire du Mont-Mégantic, and we detected 9 of them. 4 of these 9 detections present a proper motion that is consistent with those of brown dwarfs.

Les naines brunes sont des objets astronomiques de faible masse ( 0.012 - 0.075 M_Sun ) et de basse température ( T < 3,500 K ). Bien qu’elles se forment comme des étoiles, c’est-à-dire par l’effondrement d’un nuage de gaz moléculaire, les naines brunes n’ont pas une masse suffisante pour entretenir des réactions de fusion nucléaire en leur coeur. Les naines brunes relativement chaudes (type L) sont recouvertes de nuages de poussière mais ces derniers disparaissent progressivement de l’atmosphère lorsque la température chute sous les 1,500 K (type T). Les naines brunes près de la transition L/T devraient donc être partiellement recouvertes de nuages. De par leur rotation relativement rapide (2 h - 12 h), le couvert nuageux inhomogène des naines brunes devrait produire une variabilité photométrique observable en bande J (1.2 um), la longueur d’onde à laquelle les nuages ont la plus forte opacité. Ce mémoire présente les résultats d’une recherche de variabilité photométrique infrarouge pour une dizaine de naines brunes de type spectral près de la transition L/T. Les observations, obtenues à l’Observatoire du Mont-Mégantic, ont permis le suivi photométrique en bande J de neuf cibles. Une seule d’entre elles, SDSS J105213.51+442255.7 (T0.5), montre des variations périodiques sur une période d’environ 3 heures avec une amplitude pic-à-pic variant entre 40 et 80 mmag. Pour les huit autres cibles, on peut imposer des limites (3 sigma) de variabilité périodique à moins de 15 mmag pour des périodes entre 1 et 6 heures. Ces résultats supportent l’hypothèse qu’un couvert nuageux partiel existe pour des naines brunes près de la transition L/T mais ce phénomène demeure relativement peu fréquent. / Brown dwarfs are astronomical objects of low mass ( 0.012 - 0.075 M_Sun ) and low temperature ( T < 3,500 K ). While they do form like stars through gravitational collapse of a molecular gas cloud, they do not have sufficient mass to sustain nuclear fusion reactions in their core. Relatively hot brown dwarfs (type L) are covered by an homogeneous dust cloud cover that progressively disappears from their atmosphere when the temperature falls below 1,500 K (type T). Therefore, brown dwarfs near the L/T transition should be partially covered with clouds. Due to the fast rotation of brown dwarfs (2 h - 12 h), this inhomogeneous cloud cover should produce photometric variability observable in the J band (1.2 um), the wavelength at which the clouds have the strongest opacity. This thesis presents the results of a search for infrared photometric variability in brown dwarfs near the L/T transition. The observations, obtained at the Observatoire du Mont-Mégantic, have allowed the photometric follow-up of nine targets in the J band. Only one of them, SDSS J105213.51+442255.7 (T0.5), showed periodic variations with a period of about 3 hours with a peak-to-peak amplitude ranging from 40 to 80 mmag. For the remaining eight targets, we can place upper limits (3 sigma) of 15 mmag for the amplitude of periodic variability over a period range betwen 1 and 6 hours. While these results support the hypothesis that partial dust cloud covers do exist among L/T dwarfs, this phenomenon is by no means ubiquitous.