197,237 research outputs found
As populações de estrelas Wolf-Rayet em galáxias starburst de alta metalicidade
No full textTese (doutorado) - Universidade Federal de Santa Catarina, Centro de Ciências Físicas e Matemáticas. Programa de Pós-Graduação em FísicaNeste trabalho empregamos diferentes métodos de síntese de populações estelares para investigar as populações estelares de galáxias com formação estelar. Também estudamos como a morfologia e abundância do gás ditam os possíveis cenários de formação estelar -- contínuo ou instantâneo. Estamos particularmente interessados em estudar estrelas de alta massa e técnicas para detectá-las. Este trabalho é dividido em três partes. Na parte I discutimos o código Starburst99 e a nova biblioteca de estrelas de baixa metalicidade que adicionamos ao código. Esta nova biblioteca de baixa metalicidade (Z = ¼ Z#) extendeu o código Starburst99 ao regime de baixa metalicidade e verificamos que os ajustes sintéticos são melhorados pelo uso da nova biblioteca. Na parte II empregamos um código de síntese STARLIGHT, que desenvolvemos para o estudo de uma grande amostra de galáxias Starburst Nuclear e HII. Descobrimos que muitas das propriedades destas galáxias podem ser resumidas e melhor estudadas através do uso do vetor de populações X , cujas componentes representam a contribuição de diferentes elementos da base com idades e metalicidades conhecidas. Combinando componentes com idades semelhantes podemos simplificar ainda mais esta representação, escrevendo: X = (xY, xI, xO); onde xY, xI e xO são as componentes representando respectivamente as populações jovens, intermediárias e velhas. Propriamente combinando os diferentes componentes de idade podemos definir a idade média ponderada pela luz L. Verificamos que esta representação é uma maneira poderosa de descrever as propriedades desta amostra, pois as idades das galáxias descritas por L relacionam-se a várias outras propriedades. Em particular, relacionamos L à largura equivalente de H¸ Wobs(H¸). Encontramos que L atua como um ``relógio natural'' que corretamente descreve o comportamento da diluição da Wobs(H¸) com o tempo. Na parte III deste trabalho investigamos uma amostra de 32 galáxias starburst no ótico e no infra-vermelho para estudar a formação de estrelas massivas no regime de alta-metalicidade. Em particular, tentamos entender se a formação de estrelas Wolf-Rayet é favorecida de alguma forma em sistemas de alta metalicidade. Estudos anteriores encontram galáxias Wolf-Rayet em ambientes de baixa metalicidade e a questão é entender se estamos diante de um efeito de seleção ou diante de uma diferença natural entre os regimes de baixa e alta metalicidade. Estudamos as populações estelares da amostra utilizando tanto o código Starburst99 como o STARLIGHT. Também investigamos as propriedades da saliência Wolf-Rayet (uma clara indicação de estrelas com M > 25 M#) centrada em 4640 angstrons e calculamos o número de estrelas WR de Nitrogênio e de Carbono. Encontramos que grandes concentrações de estrelas WR são preferencialmente encontradas em galáxias muito jovens, indicando que a idade destes sistemas é um fator determinante na detecção destas estrelas
Optically thick clumps: not the solution to the Wolf-Rayet wind momentum problem?
No full textThe hot star wind momentum problem η = Mν∞/(L/c)» much greater than 1 is revisited, and it is shown that the conventional belief, that it can be solved by a combination of clumping of the wind and multiple scattering of photons, is not self-consistent for optically thick clumps. Clumping does reduce the mass loss rate M, and hence the momentum supply, required to generate a specified radio emission measure epsilon, while multiple scattering increases the delivery of momentum from a specified stellar luminosity L. However, in the case of thick clumps, when combined the two effects act in opposition rather than in unison since clumping reduces multiple scattering. From basic geometric considerations, it is shown that this reduction in momentum delivery by clumping more than offsets the reduction in momentum required, for a specified ε. Thus the ratio of momentum deliverable to momentum required is maximal for a smooth wind and the momentum problem remains for the thick clump case. In the case of thin clumps, all of the benefit of clumping in reducing η lies in reducing M for a given ε so that extremely small filling factors f ≈ 10-4 are needed. It is also shown that clumping affects the inference of M from radio ε not only by changing the emission measure per unit mass but also by changing the radio optical depth unity radius Rrad, and hence the observed wind volume, at radio wavelengths. In fact, for free-free opacity proportional to αn2, contrary to intuition, Rrad increases with increasing clumpiness
Obsèques de M. Rayet
No full textObsèques de M. Rayet. In: Bulletin astronomique, tome 23, 1906. pp. 273-277
Discours prononcé aux obsèques de M. Rayet
No full textStephan E. Discours prononcé aux obsèques de M. Rayet. In: Bulletin astronomique, tome 23, 1906. pp. 278-282
Histoire de la Faculté des sciences de Bordeaux (1838-1894) par M. G. Rayet, professeur à la Faculté
No full textArticle extrait des Actes de l'Académie nationale des Sciences, Belles-Lettres et Arts de Bordeaux. 3e série. 59e année. 1897. ISSN : 0242-6978Contient :
Première partie - Les bâtiments et les collections de la faculté
I. Fondation de la Faculté des Sciences
II. Bâtiments de la Faculté des Sciences
III. Budget
IV. Bibliothèque
Crédits spéciaux : achats des bibliothèques de MM. Baudrimont (décédé en 1880) et Hoüel (décédé en 1886)
V. Cabinet d'astronomie
VI. Cabinet de physique
VII. Cabinet de chimie
VIII. Cabinet de zoologie
IX. Cabinet de botanique
X. Cabinet de géologie et de minéralogie
Deuxième partie - Enseignement de la Faculté
I. Chaires. Personnel enseignant
II. Cours de la Faculté
III. Examens de Doctorat
IV. Examens de Licence
V. Examens des Baccalauréats
Troisième partie - Intervention de la Faculté dans les réformes des programmes d'examens et dans la création des universités
Quatrième partie - Les professeurs de la Faculté
I. Chaire de mathématiques : Le Besgue (V. A.) ; Hoüel (G.-J.) ; Brunel (G.-E.-A.) ; Saltel (L.) ; M. de Lagrandval (C.-S.-C.) ; Giraud (P.-J.-H.)
II. Chaire d'astronomie et mécanique rationnelle : Chenou (J.-C.-C.) ; Rollier (C.) ; Lespiault (F.-G.) ; Hadamard (J.-S.) ; Picart (T.-L.)
III. Chaire d'astronomie physique : Rayet (G.)
IV. Chaire de physique : Abria (J.-J.-B.) ; Pionchon (J.-E.-N.) ; Morisot (J.-A.-F.)
V. Chaire de chimie : Laurent (A.) ; Baudrimont (A.-E.) ; Gayon (L.- U.) ; Sabatier (A.-M. P.) ; Forquignon (L.-J.-B.)
VI. Chaire de chimie industrielle : Joannis (J.-A.)
VII. Chaire de zoologie : Bazin (P.- F.- A.) ; Bert (Paul) ; Pérez (J.)
VIII. Chaire de géologie et minéralogie : De Collegno (G.-P.) ; Raulin (V.) ; Fallot (J.-E.) ; Goguel (P.-H.)
IX. Chaire de botanique : Millardet (P.-M.-A.) ; Costantin (J.-N.) ; Rodier (E.-G.-P.) ; Devaux (H.-E.
Violet absorption edges of C IV lines in Wolf-Rayet spectra: possible superposition with diffuse interstellar bands at 5780Å and 5797Å
No full textIt is shown that the violet edges normally seen in Wolf-Rayet stars around 5800Å are principally due to displaced C IV absorption. The diffuse interstellar bands are seldom of comparable strength and can be seen separately if the absorption characteristics of the envelope of the Wolf-Rayet stars are such as to avoid an overlap between the two
Violet absorption edges of C IV lines in Wolf-Rayet spectra: possible superposition with diffuse interstellar bands at 5780Å and 5797Å
No full textIt is shown that the violet edges normally seen in Wolf-Rayet stars around 5800Å are principally due to displaced C IV absorption. The diffuse interstellar bands are seldom of comparable strength and can be seen separately if the absorption characteristics of the envelope of the Wolf-Rayet stars are such as to avoid an overlap between the two
On the bipolarity of Wolf-Rayet nebulae
No full textWolf-Rayet stars are amongst the rarest but also most intriguing massive stars. Their extreme stellar winds induce famous multiwavelength circumstellar gas nebulae of various morphologies, spanning from circles and rings to bipolar shapes. This study is devoted to the investigation of the formation of young, asymmetric Wolf-Rayet gas nebulae and we present a 2.5-dimensional magneto-hydrodynamical toy model for the simulation of Wolf-Rayet gas nebulae generated by wind-wind interaction. Our method accounts for stellar wind asymmetries, rotation, magnetization, evolution, and mixing of materials. It is found that the morphology of the Wolf-Rayet nebulae of blue supergiant ancestors is tightly related to the wind geometry and to the stellar phase transition time interval, generating either a broadened peanut-like or a collimated jet-like gas nebula. Radiative transfer calculations of our Wolf-Rayet nebulae for dust infrared emission at 24 mu m show that the projected diffuse emission can appear as oblate, bipolar, ellipsoidal, or ring structures. Important projection effects are at work in shaping observed Wolf-Rayet nebulae. This might call a revision of the various classifications of Wolf-Rayet shells, which are mostly based on their observed shape. Particularly, our models question the possibility of producing pre-Wolf-Rayet wind asymmetries, responsible for bipolar nebulae like NGC 6888, within the single red supergiant evolution channel scenario. We propose that bipolar Wolf-Rayet nebulae can only be formed within the red supergiant scenario by multiple/merged massive stellar systems, or by single high-mass stars undergoing additional, e.g. blue supergiant, evolutionary stages prior to the Wolf-Rayet phase
On the bipolarity of Wolf-Rayet nebulae
No full textWolf-Rayet stars are amongst the rarest but also most intriguing massive stars. Their extreme stellar winds induce famous multiwavelength circumstellar gas nebulae of various morphologies, spanning from circles and rings to bipolar shapes. This study is devoted to the investigation of the formation of young, asymmetric Wolf-Rayet gas nebulae and we present a 2.5-dimensional magneto-hydrodynamical toy model for the simulation of Wolf-Rayet gas nebulae generated by wind-wind interaction. Our method accounts for stellar wind asymmetries, rotation, magnetization, evolution, and mixing of materials. It is found that the morphology of the Wolf-Rayet nebulae of blue supergiant ancestors is tightly related to the wind geometry and to the stellar phase transition time interval, generating either a broadened peanut-like or a collimated jet-like gas nebula. Radiative transfer calculations of our Wolf-Rayet nebulae for dust infrared emission at 24 mu m show that the projected diffuse emission can appear as oblate, bipolar, ellipsoidal, or ring structures. Important projection effects are at work in shaping observed Wolf-Rayet nebulae. This might call a revision of the various classifications of Wolf-Rayet shells, which are mostly based on their observed shape. Particularly, our models question the possibility of producing pre-Wolf-Rayet wind asymmetries, responsible for bipolar nebulae like NGC 6888, within the single red supergiant evolution channel scenario. We propose that bipolar Wolf-Rayet nebulae can only be formed within the red supergiant scenario by multiple/merged massive stellar systems, or by single high-mass stars undergoing additional, e.g. blue supergiant, evolutionary stages prior to the Wolf-Rayet phase
Gaston Lespiault / par M. G. Rayet
No full textExtrait des Annales de l'Observatoire de Bordeaux, Tome XII, 1906
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