The discovery of the Spite plateau in the abundances of 7Li for metal-poor stars led to the determination of an observationally deduced primordial lithium abundance. However, with the determination of the baryon density, Omega_B_h^2, from the Wilkinson Microwave Anisotropy Probe (WMAP) data, a discrepancy arose between observationally determined and theoretically determined abundances of 7Li. This is what has become known as the “lithium problem”. Of all the uncertain factors in determining a stellar Li abundance, the effective temperature is the most important. This thesis is concerned with determining an accurate effective temperature scale for metal-poor halo dwarfs, paying specific attention to eliminating any possible systematic errors. This is done by utilising the exponential term, Chi/T, of the Boltzmann equation. Two assumptions are adopted; firstly the simplifying assumptions of local thermodynamic equilibrium (LTE), and secondly the more sophisticated techniques of non-local thermodynamic equilibrium (NLTE). The temperature scales are compared to others derived using different techniques; a photometric scale, where I find comparable Teff in LTE and hotter temperatures by an average of ~ 150 K in NLTE; a scale derived using Balmer lines, for which I have comparable values in LTE and hotter Teff values, by typically 110 K – 160 K, in NLTE; and finally a scale derived using an infrared flux method (IRFM). Here I find their Teff values are hotter by ~ 250 K for LTE and ~ 190 K in NLTE. Lithium abundances are then calculated for the program stars and a mean Li abundance is derived. I find values ranging from A(Li) = 2.10 dex – 2.16 dex with the LTE scales and A(Li) = 2.19 dex – 2.21 dex for the NLTE scales. These mean Li abundances are compared to other observationally deduced abundances, for which I find comparable results in LTE and higher values in NLTE, and to the WMAP + big bang nucleosynthesis calculated Li abundance. I find that my new values are still considerably lower than the WMAP value and are therefore unable to reconcile the lithium problem. Second to this primary investigation, I use Ti as an independent test of the derived Teff values and log g’s. I find that Ti is not a useful constraint on the temperatures or, therefore, on the lithium problem. I also assess the impact of the new Teff scales on the different models of Galactic chemical evolution (GCE), comparing newly calculated abundances with GCE determined abundances. It was found that trends exist in several of the elements; however, these were not statistically relevant. Also a larger degree of scatter was found in the abundances compared to the Arnone et al. (2005). This scatter was not to the degree found in the Argast et al. (2000). Reasons for the differences have been discussed.

No description available.

O presente trabalho visa apresentar uma proposta e uma breve análise do potencial pedagógico do tema da Astrofísica Estelar, uma vez que a teoria da formação e da evolução das estrelas é uma fusão da Astronomia com a chamada Física Moderna. O assunto proposto está idealmente situado para iluminar e reforçar a base física do Ensino Médio (termodinâmica básica, propriedades da luz, gravitação newtoniana etc.) por meio dos conceitos da Astrofísica Estelar na escola, já que eles se relacionam com o conteúdo que os alunos estavam aprendendo naquele momento. O trabalho se desenvolveu a partir da realização de quatro aulas aplicadas em cinco turmas da 2.a série do Ensino Médio, que tinham, no total, 69 alunos, em uma escola pública da cidade de São Paulo. O tema das aulas se relacionou com a formação e a evolução estelar; porém, também discorreu-se sobre questões mais gerais da Astronomia, como as constelações e o conceito de galáxia, a fim de introduzir o assunto para os estudantes. Toda a atividade foi elaborada a partir de uma apresentação de slides enriquecida com imagens e simulações. Como fonte de dados, utilizou-se um Questionário Inicial e um Final, aplicados durante a atividade, além da gravação das aulas e de outras anotações, sendo a pesquisadora a própria professora da turma. Analisou-se o aprendizado do grupo como um todo e a evolução conceitual de alguns alunos ao longo das aulas. Identificou-se defasagem nos conteúdos de Física dos alunos. Nesse sentido, as aulas sobre estrelas contribuíram de alguma maneira para o aprendizado dos estudantes, conforme verificado. Os resultados mostraram um progresso significativo, destacando-se alguns conceitos físicos agora integrados, tais como a luz e a gravitação. / This study aims to present a proposal and a brief analysis on the pedagogic potential of Stellar Astrophysics, since the theory of formation and evolution of stars is a merger of astronomy and the so-called Modern Physics. The proposed theme is ideally posted to enlighten and enhance the high school basic physics (basic thermodynamics, properties of light, Newtonian gravity, etc.), addressing stellar astrophysics concepts at school, since they relate to the subjects the students are learning simultaneously. The work has been developed through the application of four lessons for five different second year high school groups of students, totaling 69 students from a public school in the city of São Paulo. The subject of the lessons was related on star formation and stellar evolution, although more general topics related to astronomy were also addressed, such as constellations and the concept of galaxy, in order to introduce the topics to the students. All activity was developed through a slide show enriched with images and simulations. For the data survey, initial and final questionnaires were used during the activity, in addition to the classes records and other notes, being the researcher the class teacher. An analysis of the learning of the group as a whole was made as well as a study of the conceptual evolution of some students throughout the classes. We identified a discrepancy in students\' physical contents. For that matter, the lessons about star contributed somehow to the students\' learning, as verified. The results showed a significant evolution, highlighting some physical concepts now integrated, such as light, gravitation and others.

O presente trabalho visa apresentar uma proposta e uma breve análise do potencial pedagógico do tema da Astrofísica Estelar, uma vez que a teoria da formação e da evolução das estrelas é uma fusão da Astronomia com a chamada Física Moderna. O assunto proposto está idealmente situado para iluminar e reforçar a base física do Ensino Médio (termodinâmica básica, propriedades da luz, gravitação newtoniana etc.) por meio dos conceitos da Astrofísica Estelar na escola, já que eles se relacionam com o conteúdo que os alunos estavam aprendendo naquele momento. O trabalho se desenvolveu a partir da realização de quatro aulas aplicadas em cinco turmas da 2.a série do Ensino Médio, que tinham, no total, 69 alunos, em uma escola pública da cidade de São Paulo. O tema das aulas se relacionou com a formação e a evolução estelar; porém, também discorreu-se sobre questões mais gerais da Astronomia, como as constelações e o conceito de galáxia, a fim de introduzir o assunto para os estudantes. Toda a atividade foi elaborada a partir de uma apresentação de slides enriquecida com imagens e simulações. Como fonte de dados, utilizou-se um Questionário Inicial e um Final, aplicados durante a atividade, além da gravação das aulas e de outras anotações, sendo a pesquisadora a própria professora da turma. Analisou-se o aprendizado do grupo como um todo e a evolução conceitual de alguns alunos ao longo das aulas. Identificou-se defasagem nos conteúdos de Física dos alunos. Nesse sentido, as aulas sobre estrelas contribuíram de alguma maneira para o aprendizado dos estudantes, conforme verificado. Os resultados mostraram um progresso significativo, destacando-se alguns conceitos físicos agora integrados, tais como a luz e a gravitação. / This study aims to present a proposal and a brief analysis on the pedagogic potential of Stellar Astrophysics, since the theory of formation and evolution of stars is a merger of astronomy and the so-called Modern Physics. The proposed theme is ideally posted to enlighten and enhance the high school basic physics (basic thermodynamics, properties of light, Newtonian gravity, etc.), addressing stellar astrophysics concepts at school, since they relate to the subjects the students are learning simultaneously. The work has been developed through the application of four lessons for five different second year high school groups of students, totaling 69 students from a public school in the city of São Paulo. The subject of the lessons was related on star formation and stellar evolution, although more general topics related to astronomy were also addressed, such as constellations and the concept of galaxy, in order to introduce the topics to the students. All activity was developed through a slide show enriched with images and simulations. For the data survey, initial and final questionnaires were used during the activity, in addition to the classes records and other notes, being the researcher the class teacher. An analysis of the learning of the group as a whole was made as well as a study of the conceptual evolution of some students throughout the classes. We identified a discrepancy in students\' physical contents. For that matter, the lessons about star contributed somehow to the students\' learning, as verified. The results showed a significant evolution, highlighting some physical concepts now integrated, such as light, gravitation and others.

A nova is a cataclysmic variable star consisting of a white dwarf and a main sequence, subgiant or red giant companion. In a nova explosion, the white dwarf undergoes a thermonuclear runaway on its surface, as a result of build-up of accreted material from its companion. This leads to a large expulsion of matter from the WD surface, as well as a dramatic increase in the optical magnitude of the system. In this thesis, 5GHz C-band e-MERLIN observations of two novae (V959 Mon and V339 Del) and one symbiotic star (AG Pegasi) are presented. V959 Mon is a classical nova which was discovered in June 2012 by the Fermi Large Area Telescope as a gamma-ray source. High resolution e-MERLIN images of V959 Mon were made at six epochs following the June 2012 outburst, between 90 and 615 days after the Fermi discovery. The first four e-MERLIN observations revealed a morphology which was aspherical and expanding in the east-west direction. However, in the last two epochs, V959 Mon's ejecta morphology changed from being elongated east-west to being elongated north-south. Constant velocity models fit to measurements of V959 Mon's angular size at each epoch indicated that the expansion rate of the north-south component was significantly slower than that of the east-west component. The e-MERLIN observations of V339 Del and AG Pegasi were not as well resolved as the observations of V959 Mon, and only limited analysis of their ejecta structure was possible. In order to understand the complicated morphology seen in the e-MERLIN observations of V959 Mon, radio emission models of nova ejecta were constructed, and e-MERLIN observations of them were simulated. When constructing the models, two possible explanations for V959 Mon's morphology were explored. Firstly, the possibility was considered that the elongation observed in V959 Mon's ejecta, which changed over time from east- west to north-south, was spurious, resulting from incomplete sampling of the uv plane by e-MERLIN. To investigate this, an expanding spherical shell of ejecta was simulated, the extent to which its shape was distorted in simulated e-MERLIN images of it was investigated. Secondly, emission from an ejecta model featuring two components - one fast-moving component in the east-west direction, and another, more slow-moving component in the north-south direction - was simulated, in order to determine whether such an ejecta structure could result in the morphology seen in the e-MERLIN observations of V959 Mon. It was found that the spherical, Hubble flow model simulations were a reasonably good fit to V959 Mon's light curve, but could not explain the east-west elongation seen in V959 Mon's ejecta at the early epochs. Simulated observations of the two-component model were morphologically similar to V959 Mon, but produced light curves which were much fainter than V959 Mon's, indicating that a more in-depth analysis of two-component models of nova ejecta is necessary.

La structure des nuages sombres de la région Taurus-Auriga-perseus et les causes des différences chimiques observées sont etudiées à l'aide de données radio, IR et optique. Des observations millimétriques ont permis de réaliser des cartes détaillées enCO de ce complexe moléculaire interstellaire. De nouvelles molécules métalliques ont été détectées (CLNA,CLK,CLAL, et FAL) ainsi que des isotopes de SICC et HCCCH. Des travaux instrumentaux pour différents radiotélescopes sont aussi décrits.

Cette thèse développe les points suivants : Réactions d'échange de charge avec les ions multicharges dans le milieu interstellaire. Calcul de structure moléculaire. Développement d'une méthode de potentiel-modèle à un électron. Traitement collisionnel quantique de l'échange de charge des ions C(+2), Si(+2), N(+3) et C(+4) avec l'hydrogène atomique dans le milieu interstellaire.

Le but de ce mémoire est de poser les jalons qui permettront d'identifier les sources d'énergie et les mécanismes physiques qui sont responsables de l'activité manifestée par les étoiles T Tauri. Dans le contexte offert par l'étude de l'activité des étoiles de type solaire, il s'agit ici de déterminer dans quelle mesure l'analogie solaire peut être appliquée à l'activité manifestée par les étoiles T Tauri. Cette démarche qui consiste à différencier les sources d'énergie dont disposent ces étoiles constitue une première étape vers leur identification. Le Chapitre 1 constitue un rappel des propriétés des étoiles T Tauri (1.2), des modèles théoriques qui s'y rapportent (1.3), et des sources d'énergie dont elles peuvent bénéficier (104). L'existence de champs magnétiques à la surface des étoiles T Tauri est établie dans le Chapitre II : en premier lieu, la détection de variations périodiques dans les courbes de lumière de 11 étoiles T Tauri y est rapportée (II.2.1) ; les variations photométriques périodiques sont interprétées en terme d'une distribution de température hétérogène à la surface des étoiles (11.2.2, 11.2.3) ; le développement (II.2A) et l'application (II.2.5) d'un modèle théorique visant à reproduire les courbes de lumière observées permettent ensuite de déduire les propriétés physiques et géométriques de cette distribution; finalement, la présence de champs magnétiques photosphériques à la surface des étoiles T Tauri, premier indice de l'existence d'un processus dynamo, est déduite de la comparaison des propriétés de cette distribution avec celles des taches magnétiques couvrant la surface des systèmes RS CVn (II.2.6). Le rôle du processus dynamo dans le chauffage non-radiatif de l'atmosphère des étoiles T Tauri est étudié dans le Chapitre III : pour ce faire, après avoir discuté les paramètres qui semblent au mieux refléter le niveau d'activité stellaire et l'efficacité du processus dynamo (III.2), le comportement des étoiles T Tauri est analysé dans des diagrammes activité-rotation et comparé à celui des étoiles de type solaire (III.3) , L'existence du processus dynamo y est établie et ses limites cernées, Les implications de ces résultats sur la physique du processus dynamo dans les étoiles complétement convectives sont abordées (III.4.1) et, après une analyse détaillée des différences existant entre l'atmosphère des étoiles T Tauri et celle des étoiles de type solaire (III.4.2), les résultats obtenus sont confrontés aux prévisions des modèles théoriques (III.4.3) ; finalement, l'accrétion de matière circumstellaire à la surface des étoiles est présentée comme une source d'énergie susceptible de suppléer le processus dynamo (III.4.4). Deux appendices, présentés sous la forme de publications parues dans Astronomy and Astrophysics, complètent cette étude. L'appendice A décrit l'analyse et l'interprétation de la courbe de lumière périodique de l'étoile DN Tauri, un membre représentatif de la classe des étoiles T Tauri. Cette appendice se rapporte directement au Chapitre II. L'ensemble de l'étude présentée dans ce mémoire repose sur la détermination précise des taux de rotation d'un échantillon statistiquement significatif d'étoiles T Tauri. Cette détermination, qui fut notre première tache, est décrite dans l'appendice B. Le lecteur y trouvera un exposé détaillé des différentes méthodes utilisées pour mesurer les taux de rotation de ces étoiles peu lumineuses. En outre, les résultats obtenus y sont analysés dans le cadre du problème de l'évolution du moment angulaire durant les phases pré-séquence principale.

L'étoile beta Pictoris est à l'heure actuelle la seule étoile de la séquence principale autour de laquelle un disque de poussières a été visualise (1984). L'observation de son spectre visible et ultra-violet a révélé la présence de raies en absorption dues à la partie gazeuse du disque. L'étude de cette partie gazeuse a révélé que les raies observées variaient dans le temps: parfois, des composantes additionnelles en absorption, décalées par effet doppler vers les grandes longueurs d'onde y apparaissent. Ces phénomènes sporadiques ont été reliées à la chute vers l'étoile de petit corps de type comètaire vaporisant des éléments métalliques. La dynamique d'ions métalliques évaporés d'un corps parent a été ensuite etudiée, et une modélisation numerique du comportement d'un nuage de ces ions a été entreprise. La simulation a montré que les observations étaient reproduites par le modèle. De plus, la différence de comportement entre les raies visibles et uv a été expliquée. Des contraintes déduites de la simulation ont alors permis de formuler une hypothèse selon laquelle une planète située dans le disque pourrait par perturbations être responsable de la chute d'objets vers l'étoile. Un modèle fondé sur cette hypothèse a été ensuite développé. La simulation qui en a résulté a permis de montrer que si l'orbite de la planète est suffisamment elliptique, des perturbations sont capables d'envoyer un grand nombre de petits objets vers l'étoile. Il est ressorti de cette étude que l'évolution globale, constatée sur quelques années, des raies de beta Pictoris apparaissait comme une conséquence naturelle du modèle. En poursuivant l'étude théorique de ce disque, nous saurons peut-être s'il constitue le premier exemple de système planétaire découvert en dehors du système solaire

La première partie est une étude de l'évolution de la population des nuages HI en présence d'un milieu internuage de type coronal, entretenu par les explosions de supernova. La seconde partie concerne l'évolution d'un reste de supernova dans un milieu interstellaire hétérogene. La troisième partie propose un modèle dynamique de nébuleuse planétaire dont la morphologie et la dynamique doivent leur origine à une cavité centrale remplie de gaz coronal.