A sismologia estelar oferece uma oportunidade única de sondar as propriedades internas das estrelas através do estudo de oscilações estelares. Essas oscilações são dependentes diretamente da física da cavidade onde são formadas. No entanto, a rotação da estrela introduz um eixo de simetria e levanta a degenerescência nas frequências, dificultando assim, a sua identificação. O objetivo deste trabalho foi estudar a dependência das frequências de oscilação estelar com a velocidade de rotação para modelos de massas intermediárias ao longo da sequência principal. Este estudo foi realizado através da modelagem de estrelas com uma grande variedade de massas e velocidades de rotação (2-8 Msol, 20-100km/s) com os códigos CESAM/FILOU. O comportamento do splitting rotacional e de sua assimetria nos modos g2, g1, p1 e p2 mostrou uma dependência com outros parâmetros físicos, além da rotação. A assimetria apresenta variações interessantes levando a um método de diagnóstico de evolução: quando vários modos são observados, as assimetrias levam a uma determinação precisa da fase evolutiva da estrela. Modelos representativos para a estrela HD50844 foram comparados com os dados observacionais. A falta da identificação dos modos (l,m) e o grande número de frequências não permite obter-se resultados precisos. / Asteroseismology provides a unique opportunity to probe the inner properties of stars through the study of stellar oscillations. These oscillations depend on the physics of the cavity where they are formed. However, the stellar rotation introduces an axis of symmetry and lifts the degeneracy of the frequencies, thus hindering the identification. The goal of this work was to study the dependence of the oscillation frequency on the stellar rotation velocities for models of intermediate mass along the main sequence. This study was performed through the modeling of stars with a wide range of masses and rotational velocities (2-8 Msun, 20-100km/s) with the codes CESAM/FILOU. The behavior of the rotational \\textit and its asymmetry for the modes g2, g1, p1 and p2 showed a dependence on other physical parameters, as well as rotation. The asymmetry presents interesting variations leading to a diagnostic method of evolution: when multiple modes are observed, the asymmetries lead to a precise determination of the evolution phase of the star. Representative models for the star HD50844 were compared with the observational data. The lack of identification of the modes (l,m) and the large number of frequencies does not allow to obtain accurate results.

No description available.

I developed a spectrum synthesis method to investigate the physical properties of hot OB main sequence (MS) stars, which are often rapid rotators. The code realistically simulates the surface conditions of rapidly rotating stars, considering the rotationally-deformed stellar shape and gravity darkening effect. Comparing the synthesized absorption line profiles with the observed spectra of the member stars of 19 young Galactic clusters, I determined the projected rotational velocities of 496 stars. The average surface temperature and gravity for most of these objects were then derived from H$\gamma$ line fits. The polar gravity of each star was estimated as a good indicator of the evolutionary status of the star. The derived parameters show that massive rotators spin down during their MS phase. The He abundance data (measured by fitting the He I lines) also favor the theoretical prediction that rotationally-induced mixing can gradually enrich the surface helium abundance through the MS phase. A quicker spin-down is evident in the lower mass star group where a large portion of helium peculiar stars are found. This correlation implies that strong stellar magnetic fields may exist on the surface of these lower mass stars. The same method is also applied to interferometric observations from the CHARA Array of a nearby rapid rotator, Regulus. By combining results from spectroscopic and interferometric analysis, the shape, space orientation, mass, and surface temperature distribution of Regulus are firmly determined. This analysis provides the first evidence of the gravity darkening phenomenon among stars that are not components of an eclipsing binary system. The surprisingly high luminosity determined for Regulus appears to agree with the theoretical prediction that rapid rotator can become more luminous as rotationally-induced mixing brings fresh hydrogen down to the core. Finally I present an extension of the model that simulates the shape, velocity, and temperature variations of a star experiencing nonradial pulsation. I simulated and analyzed the line profile variations in the spectra of $\epsilon$ Per, a B0.7~III star with strong evidence of nonradial pulsation (NRP). A comparison of the model simulations and observations indicates that the pulsations of $\epsilon$ Per have a corresponding local temperature variation that is out of phase with the radial oscillation (a non-adiabatic phase lag).

Les étoiles massives sont les principaux contributeurs à l'enrichissement du milieu interstellaire. Ce sont généralement des rotateurs rapides, dotés d'une enveloppe radiative dans laquelle l'interaction de la stratification et la rotation génère une rotation différentielle. Celle-ci peut alimenter divers phénomènes de transport et l'évolution rapide de l'étoile. Nombre de ces étoiles sont par ailleurs des pulsateurs classiques. Cette thèse s'intéresse en premier lieu à l'interaction entre la rotation différentielle et les pulsations à basse fréquence dans l'étoile : celles-ci sont des modes gravito-inertiels dont la force de rappel est une combinaison de la force de Coriolis et de la poussée d'Archimède. Ils sondent les couches profondes de l'étoile, et sont étudiés suivant deux méthodes : dans la limite non-dissipative par la méthode des caractéristiques, et dans le cas dissipatif par la résolution du problème complet par une méthode spectrale. Nous mettons en évidence différentes singularités (attracteurs, latitudes critiques, résonances de corotation, piégeage en coin) et des modes réguliers. Certains modes sont excités par des instabilités baroclines, qui, si des effets non-linéaires provoquent leur saturation, permettent l'existence d'un mécanisme d'excitation nouveau dû à la rotation différentielle. Dans un second temps, nous avons associé le code de structure ESTER au code de calcul d'oscillations TOP. Ces deux codes calculent les quantités dans une étoile en deux dimensions et les modes associés en tenant compte des effets de la rotation de façon complète. Nous utilisons visibilités et taux d'amortissement des modes pour sélectionner dans le spectre synthétique les meilleurs candidats à l'identification des modes observés. Nous présentons une application au rotateur rapide Rasalhague (aOph), pour lequel de nombreuses observations sont disponibles. Nous n'avons pas obtenu une identification des modes univoque, mais le problème est maintenant mieux cerné et diverses pistes de progrès ont été identifiées. / Massive stars are the main contributors of the interstellar medium enrichment. These stars are usually fast rotators, with a radiative envelope in which the interaction between stratification and rotation gives rise to a differential rotation. This can trigger transport phenomena in the star, and affect its fast evolution. Besides, many of these stars are classical pulsators. This work focuses first on the impact of a differential rotation on the low-frequency oscillation spectrum which contains gravito-inertial modes. These modes are restored by the combination of buoyancy and Coriolis force and probe deep layers of stars. Our study is twofold : we compute the paths of characteristics in the non-dissipative limit, and solve the fully-dissipative eigenvalue problem numerically using a spectral decomposition. We find various singularities (attractors, critical latitudes, corotation resonances, wedge-trapping) and regular modes. Some of these modes are excited by baroclinic instabilities that may saturate through non-linear effects. If so, we have discovered a new excitation mechanism for these modes, driven by differential rotation. Aside of this theoretical work ; we have considered the case of Rasalhague (aOph), which is a well-known fast rotator. We studied this star by associating the ESTER structure code with the TOP oscillation code. Both of these codes use a two-dimensional structure, taking rotation effects fully into account. We use the mode damping rates and visibilities to filter the best candidates for observed modes identification out of the synthetic spectra. Even though we could not reach a satisfactory identification of the observed frequencies, we improved our understanding of the problem and identified the next steps to be taken.

Made available in DSpace on 2017-07-21T19:25:56Z (GMT). No. of bitstreams: 1 TAIZAALISSUL.pdf: 1898582 bytes, checksum: 83c6ea30230ef658e8eedb8018b6d20d (MD5) Previous issue date: 2008-04-08 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / One of the main theories to explain the Be phenomenon is that they are hot stars with rotation speed close to the critical limit, ejecting matter and forming a gaseous disk around. Its geometry and kinematics is still a controversial subject. Those objects present H® line in emission among other phenomena. In this work are present observations of hot stars in young open clusters and the detection of Be stars. The study of Be stars in open clusters is a matter of interest because these objects keep the initial signatures of their initial formation. Most of Be stars known in open clusters were identified inside the Milky Way Galaxy, but not all were observed. Most of the observations concentrate on seeking the characteristics lines in emission for stars with low magnitude. As a consequence the complete scenario of incidence of Be stars in open clusters is still uncertain, what incentives its observation. In this work, we studied thirty two stars of the spectral type B, from NGC 4755 and NGC 6530 stellar clusters. As a first step we accomplished an analysis of the stars that present the Be phenomenon. Than, we estimate physical parameters of B and Be stars using the lines of HeI 4471 and MgII 4481 Å. We also accomplished a comparison among the vseni values calculated by several methods including the AMOEBA algorithm and other two methods elaborated using the IDL platform. For high-speeds (» 300 Km/s), there is a superestimative of the FWHM method for both clusters. But for low-speeds, there is consistence between values of vseni obtained with the FWHM method and AMOEBA. / Uma das principais teorias para explicar o fenômeno Be é que são estrelas quentes com velocidade de rotação próxima da velocidade crítica, ejetando matéria formando um disco gasoso ao seu redor. Sua geometria e cinemática ainda é um assunto calorosamente discutido. Esses objetos apresentam emissões nas linhas de Balmer, entre outros fenômenos. Neste trabalho são apresentadas observações de estrelas quentes em aglomerados jovens abertos e a detecção de Be nestes. O estudo de estrelas Be em aglomerados abertos é de particular interesse porque estes objetos guardam as assinaturas das condições iniciais de sua formação. A maioria das estrelas Be conhecidas em aglomerados abertos foram identificadas na Via Láctea, a maioria das observações concentra-se em procurar as linhas em emissão características nas estrelas de baixa magnitude. Como conseqüência a completeza de incidência de estrelas Be em aglomerados abertos é incerta, o que leva a um estímulo para o seu estudo. Nesse trabalho, foram estudadas trinta e duas estrelas do tipo espectral B, selecionadas dos aglomerados NGC 4755 e NGC 6530. Em uma primeira etapa, foi realizada uma análise das estrelas que apresentam o fenômeno Be. Depois, foram determinados os parâmetros físicos de estrelas B e Be utilizando as linhas de HeI 4471 e MgII 4481 Å. Foi realizada, ainda, uma comparação entre os valores de vseni calculados com o algoritmo AMOEBA e os valores obtidos com os programas elaborados no IDL. Para altas velocidades (» 300 Km/s), há superestimativas do método FWHM, para ambos os aglomerados. Mas para baixas velocidades, há consistência entre os valores de vseni obtidos com o método FWHM e AMOEBA.

Made available in DSpace on 2015-03-03T15:15:22Z (GMT). No. of bitstreams: 1 SanziaAN.pdf: 964619 bytes, checksum: 25b161330259b5777dcaa8cf03c1242b (MD5) Previous issue date: 2008-04-22 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / ROTATION is one the most important aspects to be observed in stellar astrophysics. Here we investigate that particularly in stars with planets. This physical parameter supplies information about the distribution of angular momentum in the planetary system, as well as its role on the control of dierent phenomena, including coronal and cromospherical emission and on the ones due of tidal effects. In spite of the continuous solid advances made on the study of the characteristics and properties of planet host stars, the main features of their rotational behavior is are not well established yet. In this context, the present work brings an unprecedented study about the rotation and angular momentum of planet-harbouring stars, as well as the correlation between rotation and stellar and planetary physical properties. Our analysis is based on a sample of 232 extrasolar planets, orbiting 196 stars of dierent luminosity classes and spectral types. In addition to the study of their rotational behavior, the behavior of the physical properties of stars and their orbiting planets was also analyzed, including stellar mass and metallicity, as well as the planetary orbital parameters. As main results we can underline that the rotation of stars with planets present two clear features: stars with Tef lower than about 6000 K have slower rotations, while among stars with Tef > 6000 K we and moderate and fast rotations, though there are a few exceptions. We also show that stars with planets follow mostly the Krafts law, namely < J > / v rot. In this same idea we show that the rotation versus age relation of stars with planets follows, at least qualitatively, the Skumanich and Pace & Pasquini laws. The relation rotation versus orbital period also points for a very interesting result, with planet-harbouring stars with shorter orbital periods present rather enhanced rotation / ROTA??O ? um dos importantes aspectos a ser observado na astrof?sica estelar. Por isto, neste trabalho, investigamos este par?metro no estudo das estrelas hospedeiras de planetas. Par?metro f?sico este que fornece informa??o sobre a distribui??o do momentum angular dos sistemas planet?rios, bem como sobre o seu papel nos mais diferentes fen?menos, incluindo emiss?o cromosf?rica e coronal e sobre aqueles decorrentes de efeitos de mar?. Apesar dos cont?nuos avan?os feitos no estudo das caracter?sticas e das propriedades destes objetos, as principais caracter?sticas de seu comportamento rotat?rio ainda n?o est?o bem estabelecidas. Neste contexto, o presente trabalho traz um estudo pioneiro sobre a rota??o e o momentum angular das estrelas hospedeiras de planetas, bem como sobre a correla??o entre rota??o e par?metros f?sicos estelares e planet?rios. Nossa an?lise ? baseada em uma amostra de 232 planetas extrasolares, orbitando 196 estrelas de diferentes classes de luminosidade e tipos espectrais. Al?m do estudo do comportamento rotacional dessas estrelas, re-visitamos o comportamento das propriedades f?sicas destas estrelas e de seus planetas, incluindo a massa estelar e a metalicidade, bem como os par?metros orbitais planet?rios. Como resultados principais, podemos sublinhar que a rota??o das estrelas com planetas apresenta duas claras caracter?sticas: estrelas com Tef inferiores aproximadamente 6000 K possuem rota??es mais baixas, enquanto que entre aquelas com Tef > 6000 K encontramos rota??es modv eradas e altas, embora algumas exce??es. N?s mostramos tamb?m que as estrelas com planetas seguem, em sua maioria, a lei do Kraft, a saber < J > / v rot. Nesta mesma linha n?s mostramos que a rela??o rota??o versus idade das estrelas com planetas segue, ao menos qualitativamente, como qualquer outra estrela de campo ou de aglomerado, a lei de Skumanich e de Pace & Pasquini. Um resultado interessante a ser destacado ? a rela??o rota??o versus per?odo orbital, que aponta para uma tend?ncia de que as estrelas que abrigam planetas com per?odo orbital menores apresentam rota??es mais real?adas

No description available.