Дисертації: "Star masses"

1

Randriamampandry, Solohery Mampionona. "Stellar masses of star forming galaxies in clusters." University of the Western Cape, 2010. http://hdl.handle.net/11394/3028.

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Magister Scientiae - MSc
We determine the stellar mass of star forming galaxies in the X-ray luminous cluster MS 0451.6-0305 at z ∼ 0.54. The stellar masses are estimated from fitting model spectral energy distributions (SEDs) to deep, optical UBRIz observations obtained from WIYN 3.5m telescope and public NIR K-band image from Palomar Observatory telescope. The model SEDs are based on the stellar population synthesis (SPS) model of Bruzual & Charlot (2003) and Conroy et al. (2009) that span a wide range of age, star formation history, Initial Mass Function (IMF), metallicity and dust content. We measure stellar masses for galaxies down to M∗∼2×10⁸M(.) We find a tight correlation between stellar masses derived from the two SPSs. We compare the derived stellar masses to the dynamical masses for a set of 25 star forming galaxies. The dynamical masses are derived from high resolution, spectroscopic observations of emission lines from the DEIMOS spectrograph on the Keck telescope. A strong correlation is seen between the dynamical and stellar mass for the galaxies; and the star forming galaxies show fairly constant ratio between stellar and dynamical mass. When comparing to the field sample of Guzm ́an et al. (2003) of luminous compact blue galaxies, we see an excess of low mass galaxies in the cluster.
South Africa

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2

Queiroz, Anna Bárbara de Andrade. "Star horse : a Bayesian tool for determining masses, ages, distances and extinction for field stars." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2018. http://hdl.handle.net/10183/180515.

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Nos encontramos em uma localização vantajosa para o estudo da formação e evolução de galáxias espirais. Situados no disco da Via-Láctea, somos capazes de fazer observações detalhadas sobre as estrelas individuais que a compõem. Com o avanço tecnológico das últimas décadas, foi possível coletar um grande conjunto de informações, (e.g. composição química, cinemática, astrometria e parâmetros atmosféricos), com alta resolução para uma vasta parte do volume Galáctico. Com o objetivo de compreender melhor a nossa Galáxia, desenvolvemos uma ferramenta, chamada StarHorse, que estima parâmetros como distâncias, idades, massas e avermelhamento utilizando informação disponível em levantamentos espectroscópicos, fotométricos e astrométricos. O código StarHorse estima os parâmetros através de um método Bayesiano, que constrói uma distribuição de probabilidade a partir do cálculo de verossimilhança entre observações e modelos de evolução teórica e a partir de priores Galácticos bem conhecidos. Os parâmetros que o StarHorse estima são cruciais para estudos de arqueologia Galáctica. Com eles é possível investigar a estrutura, o histórico de formação estelar, a função de massa inicial, o mapa tridimensional da nossa Galáxia e também adicionar vínculos a modelos quemodinâmicos da Via Láctea Neste trabalho, focaremos na descrição e validação do método, testando sua aplicabilidade em levantamentos recentes de espectroscópica, astrometria e fotometria. Também disponibilizamos catálogos com distâncias e extinção para comunidade astronômica. As nossas distâncias e extinções se tornaram referência dentro da colaboração APOGEE e foram liberadas junto com o seu Data Release 14. Ademais, catálogos foram liberados para os surveys RAVE, Gaia-ESO e GALAH. Neste trabalho, exploramos os resultados do StarHorse, especialmente os resultados APOGEE, em um contexto amplo de arqueologia Galáctica.
We are in an advantageous position to study the formation and evolution of disk galaxies. By being inside the Milky Way, we are able to make detailed observations about the individual stars that compose it. With the technological revolution of the latest years, it has been possible to collect a massive set of information, (e.g. chemical composition, kinematics, astrometry, and atmospheric parameters), with high resolution for a large portion of the Galactic volume. With the goal to understand better our Galaxy, we developed a tool, called StarHorse, that can estimate distances, ages, masses, and extinction from the available spectroscopic, astrometric, and photometric information. StarHorse makes these estimates through a Bayesian method, that builds a probability distribution over the models by calculating a likelihood function between observation and stellar evolution models, and by using common knowledge about our Galaxy as priors. The parameters that StarHorse estimates are crucial to Galactic archaeology studies. With them, we can investigate the structure, the star formation history, the initial mass function, the three-dimensional dust map of our Galaxy, and provide constraints to chemodynamical models of the Milky Way. In this work, we focus on the description and validation of the method, testing its applicability in recent spectroscopic and astrometric surveys. We also make available catalogs with distances and extinctions to the astronomy community. Our distances and extinctions became a reference inside the APOGEE-team and were released as part of the SDSS Data Release 14. Moreover, we made available catalogs also to other spectroscopic surveys such as Gaia-ESO, RAVE, and GALAH. In this work, we also explore these results, especially for APOGEE, in a broad Galactic archaeology context.

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3

Imara, Nia, Abraham Loeb, Benjamin D. Johnson, Charlie Conroy, and Peter Behroozi. "A Model Connecting Galaxy Masses, Star Formation Rates, and Dust Temperatures across Cosmic Time." IOP PUBLISHING LTD, 2018. http://hdl.handle.net/10150/627101.

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We investigate the evolution of dust content in galaxies from redshifts z = 0 to z = 9.5. Using empirically motivated prescriptions, we model galactic-scale properties-including halo mass, stellar mass, star formation rate, gas mass, and metallicity-to make predictions for the galactic evolution of dust mass and dust temperature in main-sequence galaxies. Our simple analytic model, which predicts that galaxies in the early universe had greater quantities of dust than their low-redshift counterparts, does a good job of reproducing observed trends between galaxy dust and stellar mass out to z approximate to 6. We find that for fixed galaxy stellar mass, the dust temperature increases from z = 0 to z = 6. Our model forecasts a population of low-mass, high-redshift galaxies with interstellar dust as hot as, or hotter than, their more massive counterparts; but this prediction needs to be constrained by observations. Finally, we make predictions for observing 1.1 mm flux density arising from interstellar dust emission with the Atacama Large Millimeter Array.

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4

Güver, Tolga, Feryal Özel, Herman Marshall, Dimitrios Psaltis, Matteo Guainazzi, and Maria Díaz-Trigo. "SYSTEMATIC UNCERTAINTIES IN THE SPECTROSCOPIC MEASUREMENTS OF NEUTRON STAR MASSES AND RADII FROM THERMONUCLEAR X-RAY BURSTS. III. ABSOLUTE FLUX CALIBRATION." IOP PUBLISHING LTD, 2016. http://hdl.handle.net/10150/621974.

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Many techniques for measuring neutron star radii rely on absolute flux measurements in the X-rays. As a result, one of the fundamental uncertainties in these spectroscopic measurements arises from the absolute flux calibrations of the detectors being used. Using the stable X-ray burster, GS 1826-238, and its simultaneous observations by Chandra HETG/ACIS-S and RXTE/PCA as well as by XMM-Newton EPIC-pn and RXTE/PCA, we quantify the degree of uncertainty in the flux calibration by assessing the differences between the measured fluxes during bursts. We find that the RXTE/PCA and the Chandra gratings measurements agree with each other within their formal uncertainties, increasing our confidence in these flux measurements. In contrast, XMM-Newton EPIC-pn measures 14.0 +/- 0.3% less flux than the RXTE/PCA. This is consistent with the previously reported discrepancy with the flux measurements of EPIC-pn, compared with EPIC MOS1, MOS2, and ACIS-S detectors. We also show that any intrinsic time-dependent systematic uncertainty that may exist in the calibration of the satellites has already been implicity taken into account in the neutron star radius measurements.

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5

Benbakoura, Mansour. "Evolution des étoiles de faible masse en interaction : observations multi-techniques et modélisation des systèmes multiples." Thesis, Université de Paris (2019-....), 2019. http://www.theses.fr/2019UNIP7027.

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Cette thèse est consacrée à l'étude des étoiles de faible masse ayant dans leur environnement proche d'autres étoiles ou des planètes. Nous nous sommes concentrés sur l'influence des interactions avec ces compagnons sur l'évolution stellaire ainsi que leurs conséquences observables.Dans la première partie, nous présentons le modèle d'évolution des systèmes étoile–planète que nous avons développé au cours de cette thèse, nommé ESPEM (Évolution des Systèmes Planétaires Et Magnétisme). Ce modèle prend en compte de façon ab-initio des effets du vent stellaire magnétisé et de la dissipation de marée sur la rotation stellaire et l'orbite planétaire, simultanément avec l'évolution structurelle de l'étoile. Premièrement, nous l'utilisons pour étudier l'évolution séculaire de la rotation des étoiles hôtes de systèmes planétaires et montrons notamment que cette évolution peut être significativement différente de celle des étoiles isolées. Ensuite, nous examinons les prédictions de ce modèle concernant l'architecture orbitale des systèmes étoile–planète. Nos résultats suggèrent une interprétation aux distributions de périodes orbitales et de de rotation stellaire observées.Dans la deuxième partie, nous montrons en quoi l'observation d'étoiles binaires évoluées permet de tester les théories astrophysiques, notamment l'astérosismologie et l'interaction de marée. Dans un premier temps, nous présentons les résultats d'un programme d'observations que nous avons mené pendant plus de deux ans et qui nous a permis de caractériser 16 systèmes binaires à éclipses. Ensuite, nous comparons ces résultats avec ceux que nous avons obtenus en analysant cet échantillon à l'aide d'outils astérosismiques dans le but de vérifier l'exactitude de ces derniers. Enfin, en élargissant l'échantillon étudié à 30 autres étoiles binaires évoluées, nous testons la théorie de l'évolution de marée. Ceci nous permet à la fois de valider la théorie et de comprendre l'évolution des systèmes observés dans ce travail.Ce travail met en avant deux aspects de la spécificité des systèmes multiples. Premièrement, il montre en quoi l'évolution des étoiles est impactée par la présence d'un compagnon stellaire ou planétaire. Deuxièmement, il met en avant l'intérêt des étoiles binaires pour tester les théories astrophysiques et renforce la compréhension actuelle de l'évolution stellaire
This thesis is devoted to the study of low-mass stars having other stars or planets in their immediate environment. We focused on the influence of interactions with these companions on stellar evolution and their observable consequences.In the first part, we present the model of evolution of star–planet systems that we developed during this thesis, called ESPEM (French acronym for Evolution of Planetary Systems and Magnetism). This model incorporates ab-initio prescriptions to quantify the effects of magnetized stellar wind and tidal dissipation on stellar rotation and planetary orbit, simultaneously with the star's structural evolution. First, we use it to study the secular evolution of the rotation of planet-host stars and show that this evolution can be significantly different from that of isolated stars. Next, we examine the predictions of this model regarding the orbital architecture of star–planet systems. Our results suggest an interpretation to the observed distributions of orbital and stellar rotation periods.In the second part of the manuscript, we show how the observation of advanced binary stars allows us to test astrophysical theories, in particular asteroseismology and tidal interaction. First, we present the results of an observation program that we conducted for more than two years and that allowed us to characterize 16 eclipsing binary systems. Then, we compare these results with those obtained by analyzing this sample using asteroseismic tools to verify the accuracy of the latter. Finally, by extending the studied sample to 30 other advanced binary stars including an evolved primary, we test the theory of tidal evolution. This allows us both to validate the theory and to understand the evolution of the systems observed in this work.This work highlights two aspects of the specificity of multiple systems. First, it shows how the evolution of stars is affected by the presence of a stellar or planetary companion. Second, it emphasizes the interest of binary stars in testing astrophysical theories and reinforces the current understanding of stellar evolution

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6

Gallet, Florian. "Modélisation de l'évolution du moment cinétique des étoiles de faible masse." Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENY055/document.

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En 1972, Skumanich découvre une relation empirique unique entre la période de rotation de surface des étoiles G et leur âge sur la séquence principale. Cette découverte ouvrit alors une nouvelle voie pour la datation stellaire : la gyrochronologie. Dès lors, bon nombre d'auteurs, entre la fin des années 80 et 90, se sont intéressés à l'évolution de la vitesse de rotation de surface des étoiles de faible masse ($M_*$ = 0.4 $M_{odot}$- 1.1 $M_{odot}$). Les premiers modèles phénoménologies sur le sujet été nés.L'évolution de la vitesse de rotation de ces étoiles commence à être raisonnablement bien reproduite par la classe de modèle paramétrique que je présente dans cette thèse. Par manque de descriptions théoriques satisfaisantes, seuls les effets globaux des mécanismes physiques impliqués sont ici décris. Le principal enjeu est d'étudier le cadre et la façon dont le moment cinétique stellaire est impacté par ces processus tout en contraignant leurs principales caractéristiques.Au cours de ma thèse, j'ai modélisé les trajets rotationnels des enveloppes externes et médianes des distributions de période de rotation de 18 amas stellaire entre 1 Myr et 1 Gyr. Ceci m'a permis d'analyser la dépendance temporelle des mécanismes physiques impliqués dans l'évolution du moment cinétique des étoiles de type solaire. Les résultats que j'ai obtenus montrent que l'évolution de la rotation différentielle interne impact fortement la convergence rotationnelle (relation empirique de Skumanich), l'évolution de l'abondance de surface en lithium, et les intensités du champ magnétique généré par effet dynamo. En plus de reproduire ces enveloppes externes, le modèle que j'ai développé fournit des contraintes sur les mécanismes de redistribution interne du moment cinétique et sur les durées de vie des disques circumstellaires, supposés responsables de la régulation rotationnelle observée durant les quelques premiers millions d'années de la pré-séquence principale. L'extension du modèle aux étoiles moins massives (0.5 et 0.8 $M_{odot}$) que j'ai réalisé, a également fournis la dépendance en masse de ces différents processus physiques.Cette étape à notamment ajoutée de fortes contraintes sur les temps caractéristiques associés au transport de moment cinétique entre le coeur et l'enveloppe, sur l'efficacité du freinage magnétique vraisemblablement reliée à un changement de topologie des étoiles de type solaire vers celles de 0.5 $M_{odot}$, et sur l'histoire rotationnelle, interne comme de surface, des étoiles entre 1 Myr à 1 Gyr
In 1972, Skumanich discovers a unique empirical relationship between the rotation period of the surface of G star and their age on the main sequence. This discovery then opened a new path for stellar dating: the gyrochronology. Therefore, many authors in the late 80's and the begenning 90's, were interested in the evolution of the surface angular velocity of low-mass stars ($M_*$ = 0.4 $M_{odot}$- 1.1 $M_{odot}$). The first phenomenological models on the subject were born.The angular velocity evolution of these stars begins to be reasonably well reproduced by the class of parametrical model that I present in this thesis. Because of the lack of adequate theoretical descriptions, only the overall effects of the physical mechanisms involved are described here. The main issue is to study the framework and how the stellar angular momentum is affected by these processes and to constrain their main characteristics.Over the course of my thesis, I modelled the rotational tracks of external and median envelopes and median of rotation period distributions of 18 stellar clusters between 1 Myr and 1 Gyr. This allowed me to analyse the time dependence of the physical mechanisms involved in the angular momentum evolution of solar-type stars. The results I obtained show that the evolution of the internal differential rotation significantly impact the rotational convergence (empirical Skumanich's relationship), the evolution of the surface lithium abundance, and the intensity of the magnetic field generated by dynamo effect. In addition to the reproduction of these external envelopes, the model I developed provides constraints on the mechanisms of internal redistribution of angular momentum and the lifetimes of circumstellar disks, that are held responsible for the rotational regulation observed during the first few million years of pre-main sequence. The extension of the model to less massive stars (0.5 et 0.8 $M_{odot}$) that I performed also provided the mass dependence of these physical processes. Most specifically, this step added strong constraints on the characteristic time associated to the transport of angular momentum between the core and the envelope, on the efficiency of magnetic braking likely related to a change of topology from solar-type stars to those of 0.5 $M_{odot}$, and on the internal and external rotational history of stars from 1 Myr to 1 Gyr

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7

Al, Muntafki Khudhair Abbas assaf. "Silicon monoxide masers and the magnetic field of R Cassiopeiae." Thesis, University of Manchester, 2012. https://www.research.manchester.ac.uk/portal/en/theses/silicon-monoxide-masers-and-the-magnetic-field-of-r-cassiopeiae(73264bdb-d77e-4182-8840-f6e94f6bebe8).html.

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Silicon monoxide maser emission has been detected in many evolved stars in circumstellar envelopes in different vibrationally-excited rotational transitions. It is considered a good tracer to study the dynamics in a region close to the photosphere of the star. We present multi-epoch, total intensity, high-resolution images of 43 GHz, v=1, J=1-0 SiO maser emission toward the Mira variable R Cas. In total we have 23 epochs of data for R Cas at approximate monthly intervals over an optical pulsation phase range of φ = 0.158 to φ = 1.782. These maps show a ring-like distribution of the maser features in a shell, which is assumed to be centred on the star at average radius of 1.6 → 2.3 times the radius of star, R⋆. It is clear from these images that the maser emission is significantly extended around the star. At some epochs a faint outer arc can be seen at about 4 R⋆. The intensity of the emission waxes and wanes during the stellar phase. Some maser features are seen infalling as well as outflowing. We have made initial comparisons of our data with models by Gray et al. (2009). We have investigated the polarization morphology by mapping the linear and circular polarization of SiO masers in the v=1, J=1-0 transition. We found that some of the polarization vectors are either tangential or radial, which indicate a bimodal structure of the linear polarization morphology. Other angles can be seen as well. This is consistent with a radial, stellar-centred magnetic field in the SiO maser shell. We found in some isolated features the fractional linear polarization exceeds 100%. In other features, the polarization angle abruptly flips by 90◦. We found that our data are in the regime that the Zeeman splitting rate g is much greater than the stimulated emission rate R which in turn is greater than the decay rate , which indicates that the solution of Goldreich et al. (1973) can be applied.

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8

Thoroughgood, Timothy David. "The masses of cataclysmic variable stars." Thesis, University of Sheffield, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.419603.

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9

Booth, H. J. "Guide star lasers." Thesis, University of Oxford, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.300872.

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10

Avison, Adam Matthew. "Methanol masers and the environments of massive star formation." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/methanol-masers-and-the-environments-of-massive-star-formation(6387a264-f396-41a1-9c28-8dbd1a20be7f).html.

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This thesis presents an investigation into the environments of massive young stellar objects during the period of their evolution where 6.7GHz methanol masers form. Radio observations (both spectral line and continuum data) from the Methanol MultiBeam Survey (MMB) and multiple wavelength infrared data are used to characterise the physical conditions of environments associated with methanol masers. The velocity structures of methanol masers with velocity spreads spanning over 10km/s from the MMB-ATCA dataset are investigated. These sources are seen to have more structure than those with small velocity distributions, providing more information on the physical characteristics of the maser environments. A number of possible morphologies including potential disk, ring and outflow types are suggested for these source from both their velocity structure and position velocity distributions. The MMB-8GHz continuum dataset is used to define the size (e.g Hyper Compact, Ultra Compact or Compact) for Hii regions observed within the MMB-ATCA data. These Hii regions are found to be predominantly in the UCHii or HCHii size regime. Statistical testing to assess any difference in Hii region sizes between sources with maser/continuum source separation of > 0.2 parsecs and those of separation >0.2 parsecs, finds (at between the 80% and 93% significance level) that Hii sources with closely associated maser and continuum emission are smaller in size, suggesting that these sources are less evolved. MIPS 24 and 70µm data are used to define the colour magnitude space inhabited by MMB masers and Hii regions which are found to occupy a large region of log(F70 /F24 ) colour space between a lower limit value of 0.4 and up to 5. Kolmogorov-Smirnov testing of these data show statistically significant differences in the infrared (IR) environments between isolated masers and masers with associated Hii regions, indicating that isolated masers trace younger less evolved protostellar objects. Tests are conducted of 10 degree regions in galactic longitude of the Galactic Plane finding regions with statistically different IR environments indicating the relative ages of the star forming regions in the Galaxy. A null results was found for differing IR environments of masers based on the masers luminosity. An initial study of the IR environments of methanol masers using early data from the Hi-GAL survey, using the PACS and SPIRE instruments onboard the Herschel space telescope. With this investigation the colour-colour space characteristics and spectral energy distributions of the seven MMB masers in the PACS dataset are found and compared to non-maser Herschel sources, providing the basis for further investigation as more Herschel data becomes available.

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11

Bottinelli, Sandrine. "Hot corinos : molécules pré-biotiques autour des protoétoiles de type solaire." Grenoble 1, 2006. http://www.theses.fr/2006GRE10127.

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L'un des buts majeurs de l'astrophysique moderne est de comprendre la formation du Système Solaire. Puisque les protoétoiles de faible masse sont des soleils en formation, l'étude de ces objets est un des meilleurs moyens d'étudier le processus de formation du Soleil et de son système planétaire. Dans ma thèse, je me suis concentrée sur la chimie des premières phases d'évolution des protoétoiles de faible masse en étudiant les molécules organiques complexes dans des sources de Classe 0, qui représentent les phases les plus jeunes connues. De telles molécules ont été découvertes dans IRAS16293-2422, le prototype des sources de Classe 0, démontrant l'existence des ``hot corinos'', des régions où les manteaux des grains subliment. Certaines de ces molécules ont aussi été observées dans des comètes de notre Système Solaire, soulevant la question de savoir si (et auquel cas, comment) la chimie des Classes 0 affecte la composition chimique de la matière du disque protoplanétaire incorporée dans les comètes et autres corps planétaires. Cependant, il est d'abord nécessaire de déterminer si les hot corinos sont omniprésents dans les protoétoiles de faible masse, ou si IRAS16293-2422 est une exception. Ceci était le premier but de ma thèse. L'approche consistait principalement à observer trois sources de Classe 0 pour chercher des molécules organiques complexes. J'ai ainsi découvert et/ou confirmé trois hot corinos de plus. Le second but était de contraindre la taille de la région d'émission des molécules complexes au moyen d'observations interférométriques des deux hot corinos les plus brillants : cette émission est compacte (<150 AU), avec, dans l'un des cas, une composante étendue provenant de l'enveloppe externe. Le troisième but avait pour lieu de confronter les voies de formation possibles des molécules complexes avec les résultats de mes observations pour essayer de distinguer si ces molécules se forment en phase gazeuse ou à la surface des grains. Bien que mes données ne puissent éliminer aucun des deux cas, elles semblent favoriser le second type de formation. De plus, la comparaison entre hot corinos et leurs homologues massifs, les hot cores (qui montre que les molécules complexes sont relativement plus abondantes dans les hot corinos), soutient également la formation à la surface des grains
One of the major goals of modern astrophysics is to understand the formation of our Solar System. Since low-mass protostars are suns in the making, the study of these objects and their environment provides one of the best ways to investigate the Sun's formation process and to peek in the past history of our Solar System. In my thesis, I focused on the chemistry occuring in Class 0 sources (the earliest known phases in the evolutionary scenario of low-mass protostars) by studying complex organic molecules in their envelopes. Such molecules have been discovered in IRAS16293--2422, the prototype of Class 0 sources, proving the existence of hot corinos, the inner regions of the protostellar envelope where the icy grain mantles sublimate. Some of these molecules have also been observed in comets in our Solar System, raising the question of whether (and if so, how) the chemistry of Class 0 objects affects the chemical composition of the protoplanetary disk material from which comets and other planetary bodies form. However, it is first necessary to determine whether hot corinos are ubiquitous in low-mass protostars or if IRAS16293-2422 is an exception. This was the first goal of my thesis. The approach consisted mainly in observing three Class 0 sources to search for complex organic molecules. I thereby discovered and/or confirmed three more hot corinos. The second goal was then to constrain the size of emission of complex molecules. For this, I carried out interferometric observations of the two brightest hot corinos: this emission is compact (<150 AU) with, in one of the sources, an extended component originating from the cooler, less dense outer envelope. The third goal consisted in confronting the possible formation pathways with the results of my observations to try and discriminate whether complex organic molecules form via gas-phase or grain-surface reactions. Although it was not possible to arrive at a definite answer, my data seem to favor the later formation route. Moreover, the comparison of hot corinos and their high-mass analogs, the hot cores (showing that complex molecules are relatively more abundant in hot corinos), also support grain-surface synthesis of these molecules

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Sheehan, Patrick D., and Josh A. Eisner. "Disk Masses for Embedded Class I Protostars in the Taurus Molecular Cloud." IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/626418.

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Class I protostars are thought to represent an early stage in the lifetime of protoplanetary disks, when they are still embedded in their natal envelope. Here we measure the disk masses of 10 Class I protostars in the Taurus Molecular Cloud to constrain the initial mass budget for forming planets in disks. We use radiative transfer modeling to produce synthetic protostar observations and fit the models to a multi-wavelength data set using a Markov Chain Monte Carlo fitting procedure. We fit these models simultaneously to our new Combined Array for Research in Millimeter-wave Astronomy 1.3 mm observations that are sensitive to the wide range of spatial scales that are expected from protostellar disks and envelopes so as to be able to distinguish each component, as well as broadband spectral energy distributions compiled from the literature. We find a median disk mass of 0.018 M-circle dot on average, more massive than the Taurus Class II disks, which have median disk mass of similar to 0.0025 M-circle dot. This decrease in disk mass can be explained if dust grains have grown by a factor of 75 in grain size, indicating that by the Class II stage, at a few Myr, a significant amount of dust grain processing has occurred. However, there is evidence that significant dust processing has occurred even during the Class I stage, so it is likely that the initial mass budget is higher than the value quoted here.

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13

Nony, Thomas. "Formation d'étoiles massives en amas : conditions initiales, origine des masses stellaires et éjections protostellaires The unexpectedly large proportion of high-mass star-forming cores in a Galactic mini-starburst Detection of a high-mass prestellar core candidate in W43-MM1 Episodic accretion constrained by a rich cluster of outflows Molecular analysis of a high-mass prestellar core candidate in W43-MM1." Thesis, Université Grenoble Alpes (ComUE), 2019. http://www.theses.fr/2019GREAY054.

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Les recherches que j’ai menées durant ma thèse traitent de trois grands défis en formation stellaire : contraindre par les observations les phases précoces de la formation des étoiles massives – le stade préstellaire, déterminer l’origine des masses stellaires et caractériser les processus d’accrétion-éjection de la phase protostellaire.Dépasser les paradigmes actuels en formation stellaire nécessite d’étudier des régions de formations d’étoiles plus représentatives des processus typiques dans la Voie Lactée. C’est dans ce but que j’ai travaillé sur des observations ALMA de W43-MM1, un jeune proto-amas situé à 5500 pc du Soleil présentant un taux de formation stellaire élevé. J’ai d’abord identifié et caractérisé les cœurs sur la carte continuum. J’ai découvert 131 cœurs avec des tailles typiques de 2400 ua et des masses entre 1 et 100 Msol. La distribution en masse de ces cœurs (CMF) montre au-dessus de 1.6 Msol une pente de -0.96 +/- 0.13 significativement plus plate que celle de l’IMF de référence sur cet intervalle de masse, -1.35. Cela signifie une surabondance de cœurs massifs – et donc d’étoiles massives – par rapport au nombre attendu dans les modèles actuels de formation stellaire. Les explications possibles impliquent soit que la formation d’étoiles est atypique dans W43-MM1 (variabilité dans notre galaxie), soit que les étoiles massives se forment dans les amas sur des échelles de temps différentes des étoiles de type solaire (la formation d’étoiles ne serait pas un processus continu).J’ai ensuite caractérisé ces cœurs en utilisant les raies de CO(2-1) et SiO(5-4) et révélé un riche amas de flots protostellaires constitué de 46 lobes venant de 27 cœurs couvrant tout l’intervalle de masse et incluant 11 cœurs massifs (avec des masses supérieures à 16 Msol ). J’ai aussi utilisé la détection de molécules organiques complexes, des traceurs d’environnements chauds, comme un autre indicateur d’activité protostellaire. 12 des 13 cœurs massifs sont finalement apparus comme étant protostellaires, laissant un seul bon candidat cœur préstellaire massif. Ces statistiques interrogent sur l’universalité de la phase préstellaire pour les cœurs massifs et suggèrent que le modèle du cœur turbulent ne peux s’appliquer partout. Les flots protostellaires permettent aussi de reconstituer l’historique des processus d’accrétion/éjection. J’ai étudié la cinématique des nœuds constituant les jets moléculaires à haute vitesse en utilisant des diagrammes position-vitesse. J’ai montré que la complexité des structures en vitesse de ces nœuds cache une forte variabilité, et évalué le temps caractéristiques entre deux éjections à environ 500 ans. Ces échelles de temps sont similaires à celles mesurés entre deux sursauts d’accrétion pour les étoiles de type FU-Orionis
The research I have performed during my PhD addresses three major challenges of the star formation field: constraining, observationally, the earliest phases of high-mass star formation – the so-called prestellar stage, studying the origin of the stellar masses, and characterizing the process of protostellar accretion-ejection.Going beyond the current paradigms of star formation requires studying star-forming regions which are more representative of the general mode of star formation in the Milky Way. To this purpose I have used ALMA observations of W43-MM1, a young located at 5.5 kpc distance from the Sun, which presents a high star formation rate. The first step of my work has been to identify and characterize cores in the continuum image. I discovered 131 cores about 2400 AU in size which have mass between 1 and 100 Msun. I measured their mass distribution (CMF) and found a slope of -0.96 +/- 0.13 on 1.6 - 100 Msun that is markedly flatter than the reference Salpeter slope of the IMF on that range, -1.35. This means an overabundance of high-mass cores - and thus high-mass stars -compared to the number expected by the current models of star formation. Possible explanations imply either that star-formation is atypical in W43-MM1 (variably in the Milky Way) or that high-mass stars form at different time than low-mass stars in a cluster (star formation would not be a continuous process).I have characterized these cores using CO(2-1) and SiO(5-4) lines and revealed a rich cluster of 45 outflow lobes from 27 cores covering the whole mass range and including 11 high-mass cores (M>16 Msun). I have also used the detection of Complex Organic Molecules (COMs), typically detected in warm environments like hot cores, as indicator of the protostellar activity. 12 out of the 13 high-mass cores in W43-MM1 have eventually been characterized as protostellar, leaving one good high-mass prestellar core candidate. These statistics raises question about the universality of a prestellar phase for high-mass stars and suggests that the core-fed models for high-mass star formation cannot generally apply. The protostellar outflows also bring valuable information on the accretion/ejection history. I have studied the kinematics of high-velocity molecular jets that divide into knots using Position-Velocity diagrams. I have shown that the complex velocity structures of these knots hide a strong variability, and evaluated the associated timescale between two ejections to be about 500 yr. This is reminiscent of the values obtained between accretion burst in FU Orionis stars

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14

DeCocq, John D. "The impact of abundance variations on photometric luminosity indicators." Virtual Press, 1996. http://liblink.bsu.edu/uhtbin/catkey/1014853.

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Red dwarf stars are one proposed solution to the dark matter problem in the Milky Way Galaxy These cool, low luminosity stars are difficult to detect and segregate in surveys. This study utilizes photometric data obtained on the Kron-Cousins photometric system to develop criteria that classifies stars as red. Two of the color indices are then used to create a two-color diagram to allow separation of giant and dwarf stars. An algorithm based on calculated equations is provided to separate the giant and dwarf stars after detection. A third class of stars, subdwarfs, is addressed as a potential problem in future surveys. Some suggestions for detecting and removing these contaminating stars from the data are offered. Finally, a colormagnitude diagram is developed for red dwarf stars with KronCousins photometry. This curve allows for fairly accurate determination of photometric parallaxes for the red dwarf stars.An attempt was made to segregate the red dwarfs into velocity classes prior to calibrating the color-magnitude diagram. It was found that this approach offered no additional useful information.
Department of Physics and Astronomy

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15

Hypolite, Delphine. "Dynamique des étoiles de masse intermédiaire en rotation rapide et contraction gravitationnelle." Thesis, Toulouse 3, 2015. http://www.theses.fr/2015TOU30234/document.

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La rotation a un impact majeur sur la structure et l'évolution des étoiles. En particulier, elle est connue pour être responsable de processus de mélanges macroscopiques des éléments chimiques et de transport de moment cinétique au sein des zones radiatives des étoiles. Dans la première partie de cette thèse, nous montrons comment l'état actuel de la modélisation stellaire justifie une nouvelle approche bi-dimensionnelle qui ne repose pas sur les hypothèses usuelles de rotation faible ou de rotation différentielle sphérique. Nous développons, dans la deuxième partie, un modèle simplifié (approximation de Boussinesq) d'étoiles en rotation rapide, en deux dimensions, où la rotation différentielle qui s'instaure et la circulation méridienne associée sont calculées de manière cohérente. Nous y identifions les paramètres pertinents à la description de l'écoulement induit par une contraction gravitationnelle dans un environnement stratifié de manière stable. Dans la troisième partie, nous démontrons que cet écoulement de spin-up l'emporte sur l'écoulement barocline à l'issue d'un temps de Kelvin-Helmholtz. La rotation différentielle adopte un profil universel cylindrique et la circulation méridienne est celle d'un écoulement de spin-up. Une couche de Stewartson s'établit aussi sur le cylindre tangent au noyau du modèle et pourrait être la source d'un couplage efficace de la rotation du noyau et de celle de l'enveloppe d'une étoile en fin de Séquence Principale. Dans la dernière partie de cette thèse, nous étudions Achernar, étoile en rotation rapide de type Be à l'aide du code compressible ESTER. Les modèles obtenus tendent à montrer que l'étoile est en contraction gravitationnelle post-Séquence Principale. Pour en rendre compte, le code ESTER a été modifié afin de suivre l'évolution chimique de l'étoile sur une échelle de temps nucléaire
Rotation greatly impacts stellar structure and evolution. Particularly, it is known to be responsible of macroscopic mixings of chemical elements and transport of angular momentum within the radiative zones of stars. In the first part of this thesis, we show how the actual state of stellar modeling calls for a bi-dimensional approach going beyond usual assumptions of slow rotation and spherical differential rotation. We develop, in the second part of this thesis, a simplified model (Boussinesq approximation) of rapidly rotating stars in two dimensions, where the establishing differential rotation and associated meridional circulation are solved self-consistently. We describe the relevant parameters of the flow induced by a gravitational contraction in a stably stratified environment. In the third part, we demonstrate that this spin-up flow outweighs the baroclinic flow on a Kelvin-Helmholtz timescale. The differential rotation adopts an universal cylindrical profile and the meridional circulation is typical of the spin-up flow. A Stewartson layer appears too upon the tangent cylinder to the core and could explain an efficient coupling between the rotation of the core and the one of the envelope for stars at the end of the Main Sequence. In the last part of this thesis, we study Achernar, a rapidly rotating Be star, with the full-compressible ESTER code. Models we obtain tend to show that the star is undergoing a post Main Sequence gravitational contraction. To account this, the ESTER code has been modified to follow the chemical evolution of stars on a nuclear timescale

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16

Hindson, Luke Paul. "The G305 star forming complex : a panoramic view of the environment and star formation." Thesis, University of Hertfordshire, 2012. http://hdl.handle.net/2299/9197.

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This thesis presents molecular line and radio continuum observations of the giant molecular cloud (GMC) complex known as G305. The energy input from high-mass stars in the form of powerful winds and ionising radiation is one of the primary feedback mechanisms in GMCs. This feedback is thought to play a dual role both dispersing and destroying the natal environment but also sweeping up and compressing molecular gas and potentially triggering new episodes of star formation. Despite their importance to the evolution of GMCs and galaxies as a whole, the physical processes behind the formation and evolution of high-mass stars remains poorly understood. We therefore set out to obtain wide-field observations of the ionised and molecular environment to study the impact of high-mass stars on the evolution of G305. Observations conducted with the Mopra telescope of the molecular gas traced by NH3 in the (1,1), (2,2) and (3,3) transition and CO (12CO, 13CO and C18O J = 1–0) reveals the reservoir for future star formation in G305 and allows the physical properties and kinematics of the region to be studied. We identify 15 large molecular clouds and 57 smaller molecular clumps towards G305. The physical properties of the molecular gas are consistent with G305 being amongst the most massive a vigorous star forming regions in the Galaxy. We find a total molecular gas mass of 2:5–6:5 105M indicating that there is a large reservoir for future star formation. By considering virial equilibrium within the molecular clumps we discover that only 14% of the molecular clumps in G305 are gravitationally unstable, however these clumps contain > 30% of the molecular mass in G305 suggesting there is scope for considerable future star formation. To study the ionised environment towards G305 we have obtained some of the largest and most detailed wide-area mosaics with the Australia Telescope Compact Array to date. These radio continuum observations were performed simultaneously at 5.5 and 8.8 GHz and by applying two imaging techniques we are able to resolve HII regions from the ultra-compact to classical evolutionary phase. This has allowed high-mass star formation within G305 to be traced over the extent and lifetime of the complex. We discover that more than half of the observable total ionising flux in G305 is associated with embedded high-mass star formation around the periphery of a central cavity that has been driven into the molecular gas by a cluster of optically visible massive stars. By considering the contribution of embedded and visible massive stars to the observed radio continuum we suggest that more than 45 massive stars exist within G305. Combination of these two studies and recent and ongoing star formation provides the most in depth view of G305 to date and allows the star formation history and impact of high-mass stars to be investigated. We find compelling morphological evidence that suggests triggering is responsible for at least some of the observed high-mass star formation and construct a star formation history for the region.

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17

Dittmann, Jason. "Distances, Masses, Radii, and Metallicities of the Small Stars in the Solar Neighborhood." Thesis, Harvard University, 2016. http://nrs.harvard.edu/urn-3:HUL.InstRepos:33493314.

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Data from the NASA Kepler spacecraft indicate that small planets are common around the smallest main sequence stars (M dwarfs). Rocky planets transiting M dwarfs will be the best targets for atmospheric characterization with the next generation of scientific instruments. Ground based transit and radial velocity surveys, and the upcoming NASA TESS mission are expected to reveal the transiting terrestrial exoplanets that are nearest to the Sun. Understanding these worlds requires that we first understand their host stars. In this thesis, I present better estimates of the distances, masses, radii, and metallicities of these target stars. I used data from the MEarth-North transit survey to obtain trigonometric distances to 1507 mid-to-late M dwarfs with a precision of 5 milliarcseconds. I use these distance measurements to obtain better estimates of the masses and radii of these stars than available from photometry alone, and prioritize targets to monitor at high cadence for transiting planets. I find that the M dwarf census in the northern hemisphere is mostly complete to a distance of 25 parsecs for stars of spectral type M5.5V and earlier, and mostly complete for stars earlier than M7.0V out to 20 parsecs. I present calibrated MEarth optical photometry of 1844 MEarth-North targets with a typical precision of 1.5%. By combining these measurements with trigonometric distances, spectroscopic metallicities, and extant near infrared (NIR) magnitudes, I derive a color-magnitude-metallicity relation with a precision of 0.1 dex. I find that the median metallicity for Solar Neighborhood M dwarfs is [Fe/H] = -0.030 +/- 0.008, indistinguishable from the solar neighborhood G dwarfs. I present the MEarth-South discovery of LP 661-13, a low-mass double lined eclipsing binary system with an orbital period of 4.7 days. I determine the component masses to be 0.3050 +/- 0.0056 and 0.1937 +/- 0.0027 M_sun and the radii to be 0.3192 +/- 0.0037 and 0.2159 +/- 0.0061 R_sun. While each component is marginally consistent with stellar models, the sum of the radii is well constrained and is inflated 5% compared to stellar models, which cannot be ascribed to metallicity or age effects. LP 661-13 joins the small sample of low-mass stars with precisely measured masses and radii that serves as a robust test of models of fully convective dwarf stars. I present calibrated griz photometry of 150 of the MEarth-North target stars with a typical precision of 1%. I find that no combination of griz filters alone can reliably determine the metallicity of an M dwarf. However, interpolation in the (g-i, i-K) color plane can estimate the metallicity with a typical standard deviation of 0.1 dex. This precision is comparable to that from NIR spectroscopic methods that have been recently developed. Overlap between the upcoming Large Synoptic Survey Telescope (LSST) sources and the VISTA Hemisphere Survey sources will provide a sample of M dwarfs with estimated metallicities that can in turn be used as a chemical probe of the Milky Way Galaxy.
Astronomy

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18

Wong-McSweeney, Daniel B. C. "Masers and the Formation of Massive Stars." Thesis, University of Manchester, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.525985.

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19

Wright, Mark. "Probing the star-formed region W3(OH) with ground-state hydroxyl masers." Thesis, University of Bristol, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.340298.

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20

Ash, Timothy David Curtis. "The masses of the neutron stars in Cen X-3 and Vela X-1." Thesis, Open University, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.310006.

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21

Alvey, N. D. S. "Studies of the dusty environment of high-mass protostars." Thesis, University of Kent, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.365204.

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22

Sinukoff, Evan, Andrew W. Howard, Erik A. Petigura, Joshua E. Schlieder, Ian J. M. Crossfield, David R. Ciardi, Benjamin J. Fulton, et al. "ELEVEN MULTIPLANET SYSTEMS FROM K2 CAMPAIGNS 1 AND 2 AND THE MASSES OF TWO HOT SUPER-EARTHS." IOP PUBLISHING LTD, 2016. http://hdl.handle.net/10150/621388.

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We present a catalog of 11 multiplanet systems from Campaigns 1 and 2 of the K2 mission. We report the sizes and orbits of 26 planets split between seven two-planet systems and four three-planet systems. These planets stem from a systematic search of the K2 photometry for all dwarf stars observed by K2 in these fields. We precisely characterized the host stars with adaptive optics imaging and analysis of high-resolution optical spectra from Keck/HIRES and medium-resolution spectra from IRTF/SpeX. We confirm two planet candidates by mass detection and validate the remaining 24 candidates to >99% confidence. Thirteen planets were previously validated or confirmed by other studies, and 24 were previously identified as planet candidates. The planets are mostly smaller than Neptune (21/26 planets), as in the Kepler mission, and all have short periods (P < 50 days) due to the duration of the K2 photometry. The host stars are relatively bright (most have Kp < 12.5 mag) and are amenable to follow-up characterization. For K2-38, we measured precise radial velocities using Keck/HIRES and provide initial estimates of the planet masses. K2-38b is a short-period super-Earth with a radius of 1.55 +/- 0.16 R-circle plus, a mass of 12.0 +/- 2.9M(circle plus), and a high density consistent with an iron-rich composition. The outer planet K2-38c is a lower-density sub-Neptune-size planet with a radius of 2.42 +/- 0.29 R-circle plus and a mass of 9.9 +/- 4.6M(circle plus) that likely has a substantial envelope. This new planet sample demonstrates the capability of K2 to discover numerous planetary systems around bright stars.

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23

Brebner, G. C. "OH masers associated with molecular outflows." Thesis, University of Manchester, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.328268.

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24

Allain, Stéphanie. "L'évolution du moment cinétique des étoiles pré-séquence principale de faible masse." Grenoble 1, 1997. http://www.theses.fr/1997GRE10167.

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Cette thèse présente l'étude de la rotation des étoiles de faible masse (entre 0,5 et 1,2 m#+) pendant leurs phases pré-séquence principale, depuis les T Tauri âgées de quelques millions d'années, et séquence principale, à quelques milliards d'années. Deux approches complémentaires ont été utilisées : les observations apportent de nouvelles mesures de rotation de ces objets et la modélisation permet de comprendre les processus physiques mis en jeu. Les observations ont porté essentiellement sur les amas jeunes, IC4665, Alpha Persée et les Pléiades. Dans ces amas, les étoiles de type solaire sont à un âge charnière entre la phase pré-séquence principale et la séquence principale. Alors qu'un grand pourcentage d’étoiles tournent à des vitesses inferieures à 10 km. S#-#1, leurs vitesses de rotation exactes n'étaient pas connues à cause des limites de résolution instrumentales. Grace aux instruments CORAVEL et ELODIE de l'OHP, toutes les vitesses de rotation sont maintenant résolues dans Persée et les Pléiades pour les étoiles de masse comprise entre 0,6 et 1,1 m#+. Les distributions de vitesse équatoriales en fonction de la masse ont été construites dans les deux amas et sont comparées aux modèles. Un modèle d'évolution du moment cinétique a été développé, qui permet de prendre en compte l'évolution pré-séquence principale : les changements de structure interne, l'effet d'un disque d'accrétion, la perte de moment cinétique à la surface et le transfert de moment cinétique entre le cœur et l'enveloppe. Les nouvelles données apportent des contraintes fortes quant au transport de moment cinétique dans les intérieurs stellaires. Dans les étoiles en rotation rapide, un transfert très efficace du moment cinétique permet à l’étoile de garder une rotation quasi-solide pendant toute son évolution, de la phase T Tauri jusqu'à l’âge du soleil, en accord avec les observations de l'intérieur solaire. Par contre, l'existence même d'un grand nombre de rotateurs lents nécessite un découplage entre le cœur et l'enveloppe, avec un temps caractéristique de couplage de 100 millions d'années. L'évolution de la vitesse de ces rotateurs très lents au début de la séquence principale, pendant laquelle leur vitesse varie très peu, est également en accord avec un temps de couplage très long.

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25

Schwarz-Tatrin, Anja [Verfasser], and Jochen [Akademischer Betreuer] Stark. "Wirkmechanismen anorganischer Sekundärrohstoffe in silicatkeramischen Massen / Anja Schwarz-Tatrin ; Betreuer: Jochen Stark." Weimar : F. A. Finger-Institut für Baustoffkunde, 2009. http://d-nb.info/1115342088/34.

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26

Wainwright, C. L. "The effects of spin-orbit coupling on gravitational wave uncertainties." Pomona College, 2007. http://ccdl.libraries.claremont.edu/u?/stc,20.

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Paper discusses the expected uncertainty of orbital parameters of binary stars as measured by the space-based gravitational wave observatory LISA (Laser Interferometer Space Antenna) and how the inclusion of spin in the model of the binary stars affects the uncertainty. The uncertainties are found by calculating the received gravitational wave from a binary pair and then performing a linear least-squares parameter estimation. The case of a 1500 solar mass black hole that is 20 years from coalescing with a 1000 solar mass black hole--both of which are 50 x 10^6 light years away--is analyzed, and the results show that the inclusion of spin has a negligible effect upon the angular resolution of LISA but can increase the accuracy in mass and distance measurements by factors of 15 and 65, respectively.

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27

Ospina-Zamudio, Juan David. "Complexité chimique des protoétoiles de masse intermédiaire : une étude de Cep E-mm." Thesis, Université Grenoble Alpes (ComUE), 2019. http://www.theses.fr/2019GREAY013/document.

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Les étoiles de masse intermédiaire (2M⊙ ≤ M ≤ 10M⊙) sont parmi les sources dominantes du champ interstellaire FUV dans la Galaxie. Elles régulent les phases du milieu interstellaire et l’ensemble des processus de formation stellaire galactique. Alors que les protoétoiles de type solaire et massives ont été et continuent à faire l’objet de nombreuses études, la formation des étoiles intermédiaires a été relativement peu étudiée. Leur structure physique, composition chimique et leur richesse moléculaire sont un domaine à explorer.L’objectif de ma thèse est d’obtenir un recensement détaillé et aussi complète que possible des propriétés physico-chimiques d’une protoétoile isolée de masse intermédiaire. Notre choix s’est porté sur Cep E-mm (100 L⊙).J’ai pour cela complété un relevé spectral de l’émission moléculaire dans les bandes (sub)millimétriques entre 72 et 350 GHz avec le télescope de 30m de l’IRAM. La sensibilité des observations a permis d’identifier la présence de nombreuses molécules complexes organiques (COMs) dans l’enveloppe de la protoétoile, mais aussi, plusieurs espèces moléculaires inhabituelles dans le jet généré par la protoétoile. Des observations complémentaires avec le télescope de 30m ont permis de cartographier l’émission moléculaire à grande échelle (20’’ à 11’’ ; 15000 à 8000 UA). En parallèle, des cartes interférométriques de l’émission moléculaire entre 86 – 90 GHz et 216 – 220 GHz ont été obtenues avec l’interféromètre de l’IRAM (NOEMA) à 1.4’’ (1000 UA) de résolution angulaire. Ces observations m’ont permis d’obtenir une première description de la distribution de l’émission moléculaire au sein de l’enveloppe, des grandes échelles, dans les parties extérieures de l’enveloppe étendue, aux petites échelles dans la région d’un hot corino. Les études présentées ici ont suivi un travail méticuleux de réduction et d’analyse des données, single-dish et interférométriques. Plus précisément, j’ai identifié et séparé les contributions à l’émission détectée dans le lobe du télescope de 30m de l’IRAM des différentes régions physiques du cœur protostellaire. De ce fait, j’ai identifié et caractérisé quatre composantes physiques qui diffèrent par leurs propriétés spectroscopiques et leurs conditions d’excitation : l’enveloppe étendue, le hot corino, le flot bipolaire basse vitesse et le jet à haute vitesse. Enfin, l’anisotropie de la distribution de brillance du flot et du jet bipolaire ne peut pas être modélisée par l’approche ‘’classique’’ d’une source gaussienne. J’ai développé des outils spécifiques semi-analytiques pour calculer de manière approchée, et plus raisonnable, le couplage entre le lobe du télescope et la source
Intermediate-mass stars (2 M⊙ ≤ M ≤ 10 M⊙) are among the dominant sources of FUV interstellar field in the Galaxy. They regulate the phases of interstellar medium and the whole process of galactic star formation. While solar-type and massive protostars have been and continue to be the subject of many studies, the formation of intermediate stars has been relatively little studied. Their physical structure, chemical composition and molecular richness are still a subject to explore.The aim of my thesis is to obtain a detailed census, as complete as possible ,of the physical and chemical structure of an isolated intermediate-mass protostar: Cep E-mm (100 L⊙).I have completed a spectral survey of the molecular emission in the (sub)millimetre bands between 72 and 350 GHz with IRAM 30m telescope. The sensitivity of the observations made it possible to identify the presence of numerous complex organic molecules (COMs) in the protostar envelope, but also several unusual molecular species in the protostellar jet. Additionally, further observations with the IRAM 30m telescope made it possible to map the molecular emission at large scale (20’’ to 11’’; 15000 to 8000 AU). In parallel, interferometric maps of the molecular emission between 86 – 90 GHz and 216 – 220 GHz were obtained with NOEMA, the IRAM interferometer, at 1.4’’ (1000 AU) of angular resolution. These observations allowed me to obtain the distribution of molecular emission within the source, from large scales in the outer parts of the extended envelope, to the small scales in the hot corino region. The single-dish and interferometric observations were reduced and analysed in a meticulous manner. More precisely, I identified and separated the molecular emission contribution from the different physical regions as observed with the IRAM 30m telescope. I have identified and characterized fours physical components that differ in their spectroscopic properties and excitation conditions: the extended envelope, the hot corino, the bipolar outflow and the high-velocity jet. Finally, the anisotropy of the brightness distribution from the outflow system cannot be modelled by the “classical” Gaussian approach. I have developed specific tools to estimate, in a semi-analytical manner, the coupling between the telescope lobe and the source

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28

Gaurat, Mathieu. "Stabilité des configurations magnétiques dans les étoiles de masse intermédiaire." Thesis, Toulouse 3, 2016. http://www.theses.fr/2016TOU30336/document.

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L'origine de certains champs magnétiques stellaires observés et leur impact sur l'évolution des étoiles sont mal compris. C'est particulièrement vrai dans le cas des étoiles de masse intermédiaire de la séquence principale. Des relevés spectropolarimétriques récents ont en effet révélé l'existence d'une dichotomie magnétique inexpliquée, de 2 ordres de grandeur en terme de champ longitudinal, entre le fort champ des étoiles Ap/Bp et le faible champ des étoiles Vega-like. Le but de cette thèse est de tester la possibilité que cette dichotomie magnétique soit liée, comme proposé par Aurière el al. (2007), au développement d'instabilités magnétohydrodynamiques (MHD) dans la zone radiative des étoiles de masse intermédiaire. Pour cela, j'ai réalisé des simulations numériques MHD 2D et 3D qui permettent de suivre l'évolution d'un champ magnétique axisymétrique soumis initialement à une rotation différentielle dans une zone stratifiée de façon stable puis de considérer le développement d'instabilités MHD non-axisymétriques. L'influence de différents paramètres physiques des simulations, comme l'intensité initiale du champ magnétique poloïdal, le profil de rotation différentielle, la valeur des coefficients de diffusion ou encore l'importance de la stratification stable, a été testée. L'analyse des résultats des simulations montre que des instabilités MHD comme l'instabilité magnétorotationnelle et celle de Tayler peuvent se déclencher dans une zone radiative en rotation différentielle. En accord avec le scénario de Aurière et al. (2007), ces instabilités se développent assez pour modifier la structure spatiale à grande échelle d'un champ magnétique si l'intensité initiale du champ poloïdal est suffisamment faible par rapport à l'intensité initiale de la rotation différentielle. Le champ longitudinal calculé pour nos simulations les plus instables est diminué de 15% par rapport à un cas stable. Ce travail de thèse montre donc que les instabilités MHD sont des possibles candidats pour expliquer le désert magnétique des étoiles de masse intermédiaire de la séquence principale
The origin of some of the observed stellar magnetic fields and their impact on stellar evolution are not well understood. This is particularly true for the main sequence intermediate-mass stars. Recent spectropolarimetric surveys have indeed exhibited an unexplained magnetic dichotomy, of 2 orders of magnitude in term of the longitudinal field, between the strong field of Ap/Bp stars and the weak field of Vega-like stars. This thesis aims to test the possibility that this magnetic dichotomy is linked to the development of magnetohydrodynamic (MHD) instabilities in the radiative zone of intermediate-mass stars, as proposed by Aurière et al. (2007). To do that, I have performed 2D and 3D MHD numerical simulations that allow to follow the evolution of an axisymetric magnetic field which is initially submitted to a differential rotation in a stably stratified zone and then to consider the development of non-axisymetric MHD instabilities. The influence of different physical parameters of the simulations, as the initial strength of the poloidal magnetic field, the differentially rotating profile, the diffusion coefficient values or the effect of the stable stratification, has been tested. The analysis of the simulation results show that MHD instabilities as the magneto-rotational instability or the Tayler instability can be triggered in a differentially rotating radiative zone. In agreement with the scenario of Aurière et al. (2007), these instabilities are enough developed to modify the large scale spatial structure of a magnetic field if the initial strength of the poloidal field is sufficiently weak with respect to the initial strength of the differentially rotation. The computed longitudinal field in our most unstable simulations is reduced by 15% with respect to a stable case. Therefore, this thesis work shows that the magnetic instabilities are possible candidates to explain the magnetic desert of the main sequence intermediate-mass stars

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29

Gallaway, Mark John. "Rubies in the dust : tracing high mass star formation throughout the Milky Way." Thesis, University of Hertfordshire, 2012. http://hdl.handle.net/2299/7671.

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Over the last decade a number of potential tracers of massive star (M > 8M ) formation have been put forward. In this thesis I attempt to understand how these tracers relate to one another and attempt to identify the most suitable tracer for future surveys for massive star formation sites. In this thesis we examine a number of these tracers; the Methanol Maser Multi- Beam Survey (MMB), the Red MSX Survey (RMS), the Boston University Five Colleges Radio Astronomical Observatory (BU-FCRAO) Galactic Ring Survey (GRS), the BOLOCAM Galactic Plane Survey (BGPS) and the Perretto & Fuller (P&F) Infrared Dark Cloud (IRDC) Catalogue, in addition to the Cyganowski Extended Green Objects Catalogue. This work employs a bespoke non-circular aperture photometry technique, K=1 Nearest Neighbour Analysis and Minimum Spanning Trees (MSTs) in multi-dimensional parameter space with oversampling, edge weighing, mean edge fracturing and convex hull tting. Additional, new 13CO observations were made of the young infrared cluster BDS[2003] 107 (Bica 107) and its environs. We see that despite not being contained within the GLIMPSE Point Source Archive the bulk of masers have an infrared bright counterpart. Photometry of the counterparts shows that they occupy the same colour spaces as that previously determined in Ellingsen (2006); [3.6]-[4.5]>1 and [8.0]<1. We show that the bulk of RMS MYSOs do not exhibit masing and that a signi cant fraction of MYSOs are not found within the RMS . Additionally, we see that the EGO RMS association rate is higher than expected. The BGPS, GRS and P&F IRDC exhibit clustering and elongating, with a common characteristic clustering scale of the order of 6 8 pc. We see that the BGPS is more strongly associated with massive star formation than the GRS. Additionally, we see that although in general all three hull types occupy similar co-located spatial positions they also appear as isolated hulls. The analysis of Bica 107 shows that it is part of a larger star forming region containing Bica 108 and the ultra compact HII region, G5.89. The maser associated with Bica 107 appears to lie on the edge of the cluster's expanding CO shell. The observation that the IRAC colour-magnitude occupied by the masers from the Ellingsen sample is consistent with the MMB, sample suggest that these objects have broadly consistent colours during their masing phase. This can be attributed to the dust and gas envelope being radiatively dominant. The cross matching results indicate that the majority of MYSOs do not exhibit masing. The RMS appears to be missing MYSOs due to missing sources in the MSX catalogue and a photospheric bluing due to MSX large beam width, moving candidates outside the RMS colour cut. The RMS EGO relationship appears to be inconsistent with observed MYSO evolution and may be indicative of multiple EGO generation mechanism as suggested by De Buizer and Vacca (2010). The BPGS and GRS objects and IRDCs do not appear to form a star formation sequence and their existence is not necessarily an indicator of on-going star formation; rather they are an indication of the potential for star formation. All three species types showing signs of clustering and elongation. The shared characteristic scale is suggestive that there may be a processes acting below the scale of the GMC but above that of a single star forming region. The maser associated with Bica 107 appears to be either an example of triggered star formation or late onset star formation within the region and is not an example of continuing star formation within Bica 107. We conclude that a GLIMPSE based colour-selected survey, with follow-up observation to reduce contamination, would be the most appropriate method for identifying MYSOs, given the reliability of the tracers examined in this thesis.

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30

Christiansen, Jessie L., Andrew Vanderburg, Jennifer Burt, B. J. Fulton, Konstantin Batygin, Björn Benneke, John M. Brewer, et al. "Three’s Company: An Additional Non-transiting Super-Earth in the Bright HD 3167 System, and Masses for All Three Planets." IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/625817.

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HD 3167 is a bright (V = 8.9), nearby KO star observed by the NASA K2 mission (EPIC 220383386), hosting two small, short-period transiting planets. Here we present the results of a multi-site, multi-instrument radial-velocity campaign to characterize the HD 3167 system. The masses of the transiting planets are 5.02 +/- 0.38 M-circle plus for HD 3167 b, a hot super-Earth with a likely rocky composition (rho(b) = 5.6(-1.43)(+2.15) g cm(-3)), and 9.80(-1.24)(+1.30) M-circle plus for HD 3167 c, a warm sub-Neptune with a likely substantial volatile complement (rho(c) = 1.97(-0.59)(+0.94) g cm(-3)). We explore the possibility of atmospheric composition analysis and determine that planet c is amenable to transmission spectroscopy measurements, and planet b is a potential thermal emission target. We detect a third, non-transiting planet, HD 3167 d, with a period of 8.509 +/- 0.045 d (between planets b and c) and a minimum mass of 6.90 +/- 0.71 M-circle plus. We are able to constrain the mutual inclination of planet d with planets b and c: we rule out mutual inclinations below 1.degrees 3 because we do not observe transits of planet d. From 1.degrees 3 to 40 degrees, there are viewing geometries invoking special nodal configurations, which result in planet d not transiting some fraction of the time.

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31

Amard, Louis. "Évolution de la rotation des étoiles jeunes de faible masse." Thesis, Montpellier, 2016. http://www.theses.fr/2016MONTT258/document.

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Le moment cinétique d’une étoile, comme sa masse ou sa composition chimique, est l’une de ses propriétés fondamentales, l’un de celles qui varient à cours du temps et influent sur la structure de l’étoile. Celui-ci peut être global, on l’observe alors à travers la vitesse de rotation de surface d’une étoile, ou local, auquel cas il nous faut sonder l’intérieur stellaire et étudier les processus de redistribution au sein des régions internes du moment cinétique. Au cours de cette thèse dans le cadre du projet ToUpiES, nous nous sommes intéressés en particulier à l’évolution du moment cinétique des étoiles de faible masse au cours de leur jeunesse, qui est une période critique de leur vie en ce qui concerne l’impact et l’évolution du moment cinétique. Nous avons d’abord inclus au sein du code d’évolution STAREVOL les prescriptions les plus à jour pour l’extraction du moment cinétique par les vents magnétisés. L’étude systématique des combinaisons de ce freinage avec différentes prescriptions existantes pour le traitement de la turbulence horizontale et verticale dans la zone radiative des étoiles, nous a permis de sélectionner un jeu de prescriptions capable de reproduire, les périodes de rotation dans les amas ouverts pour une étoile de type solaire. Nous comparons ensuite l’application de ces processus de transport et d’extraction du moment cinétique à un modèle de 1, 2 masse solaire, aux autres processus jugés potentiellement efficaces pour transport le moment cinétique à ce jour (ondes internes de gravités, instabilité MHD de Tayler-Spruit, modes de gravités). Cela nous a permis de présenter dans chacun des cas les spécificités du profil de rotation prédit par ces différents modes de transport. Puis, nous avons mis en place un modèle rotationnel fonctionnel adapté à l’ensemble des étoiles de faible masse, permettant entre autre de reproduire les périodes de rotation observées dans les amas jeunes pour les étoiles de faible masse (avec une masse comprise entre 0, 2 et 1, 1 M⊙). Ceci a donné lieu à une grille de modèle d’évolution unique à ce jour. Enfin, cette grille a été utilisée dans le cadre de travaux dans différents domaines, tels que l’impact de l’évolution stellaire sur l’habitabilité d’un système, la caractérisation d’étoiles-hôte ou encore l’étude de l’évolution de la topologie magnétique au cours des phases jeunes
The angular momentum content of a star, as its mass or its chemical composition is one of the fundamental properties of a star, one of those that evolves with time and modify the stellar structure. The angular momentum can be studied as a global property, we can then observe it through the surface rotation velocity, or a local property that vary inside the star, we therefore have to probe the stellar radiation zone and study the secular angular momentum redistribution processes that happen in this region. During this PhD, in the frame of the ToUpiES project, we have been especially interested in the evolution of the young low-mass stars angular momentum, since this phase of evolution is critical regarding the evolution of extraction and redistribution angular momentum processes. First, we included in the STAREVOL evolution code the most up-to-date prescription for the wind-driven angular momentum extraction. We led a systematic study of the various combination of this braking with the different existing prescriptions for the treatment of horizontal and vertical turbulent motions in stellar radiative zones. This allows us to select a set of prescription able to reproduce the observed rotation periods in young open clusters for a broad mass-range. Next, we analysed how these prescriptions for extraction and transport of angular momentum behave when applied to a 1.2M⊙ model. We compared the result to what is obtained with other processes estimated as potentially very efficient to redistribute angular momentum (internal gravity waves, MHD Tayler-Spruit instability, gravity modes). This allows us to derive in each case, the specificity of the rotation profiles predicted by the different transport processes. Then, we set up a functional rotational model adapted to almost the entire range low-mass stars, allowing to reproduce the observed low-mass stars rotation periods in young open clusters (with 0, 2M⊙ ≤M≤ 1, 1M⊙). This models can also predict the rotational evolution at different metallicities. Eventually, these models have been used in the frame of various works in different domains such as the characterisation of planet host-stars, the evolution of the magnetic topology during the young stellar phases or even the impact of stellar evolution on the habitability of a planetary system

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32

Quinn, Lyshia Jane. "Maser hunting in the galactic plane." Thesis, University of Manchester, 2010. https://www.research.manchester.ac.uk/portal/en/theses/maser-hunting-in-the-galactic-plane(efee9222-ec4e-4153-aa6a-4047c08430f9).html.

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The process of massive star formation greatly influences its surroundings through their outflows, vast UV output and shocks from their supernova death. They form at great distances from the Earth, enshrouded by dust and gas and have relatively short lifetimes. Astrophysical masers which form in these environments may act as locators of the star forming regions. The aim of this thesis is to study massive star formation using masers to probe these regions. The three main masers used in this thesis are the Class I and Class II methanol masers and the 6035 MHz ex-OH maser. The methanol masers are divided into two groups, Class I and Class II, based on their distance from a central source. The Class I masers are separated 1-2 pc from a central source, the central source is the star forming region. The Class II masers are associated close to a star forming source. They are often associated with a 6035 MHz ex-OH maser. The 6035 MHz ex-OH masers are less common than the 6668 MHz Class I methanol masers. They are often found at sites of the 6668 MHz Class I masers and 1665/7 MHz OH masers. This thesis presents two maser surveys, the Methanol Multibeam (MMB) survey and the Class I survey. The MMB survey is currently surveying the entire Galactic Plane for the 6668 MHz Class II methanol maser and the 6035 MHz ex-OH maser. Over 60\% of the survey in the Southern hemisphere is now complete using the Parkes telescope. Over 900 6668 MHz Class I methanol masers and 110 6035 MHz ex-OH masers have been detected, with all of these masers pinpoint the location of newly forming high mass stars. Follow up observations to determine the precise locations of the 6668 MHz methanol and 6035 MHz ex-OH masers are currently underway. The first ever unbiased Class I survey has observed 1 sq degree of the Galactic Plane for the 44 GHz Class I methanol masers using the Mopra telescope in Australia. The 44 GHz Class II methanol masers are hypothesised to be associated with the outflows of high mass stellar objects. The Class I survey has detected 25 44 GHz methanol masers, with 23 being new detections. A smaller survey for 36 GHz Class I masers was also conducted using the Mopra telescope centered on the region with the highest population of 44 GHz Class I masers.

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33

Karovicova, Iva. "Multiepoch infrared interferometric observations of evolved stars at the VLTI." Nice, 2011. http://www.theses.fr/2011NICE4037.

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Cette thèse exploite des mesures interférométriques multi-époques d’étoiles évoluées de la branche horizontale asymptotique (AGB) du diagramme HR. Il s’agit d’étoiles de masses petites à intermédiaires (0. 6 – 10 Mo) en phase finale de leur évolution. Ces étoiles pulsantes subissent une perte de masse très importante via un vent stellaire dense et poussiéreux qui enrichit l’environnement stellaire de gaz et de poussières. Ces processus de perte de masse sont encore mal compris et font l’objet de beaucoup d’investigations. Grâce à leur luminosité et diamètre très importants, ces étoiles sont des cibles privilégiées d’observations à Haute Résolution Angulaire. Les étoiles AGB étudiées ici ont été mesurées pendant plusieurs cycles d’oscillation au moyen des deux interféromètres AMBER et MIDI du VLTI, donc en proche et moyen infrarouge. Le but de cette investigation est la connexion entre le mécanisme de pulsation, la condensation et la chimie des poussières dans le but de mieux comprendre leur perte de masse. J’ai étudié un échantillon de quatre étoiles évoluées, les variables de type Mira riches en oxygène RR Aql, S Ori, Gx Mon et R Cnc, au moyen de donnée MIDI multi-époque et de données AMBER individuelles. Ces données sont modélisées par des modèles standards de disques uniformes ou gaussiens. Les données AMBER sont modélisées par une atmosphère auto-excitée libre de poussière incluant les couches moléculaires juste supérieures responsables du continuum spectral (modèles de série P et M, Ireland et al. 2004a,b). Les données MIDI permettent de rajouter à ce modèle l’enveloppe gazeuse radiative. Le transfert radiatif de l’enveloppe utilise le code mcsim_mpi (Ohnaka et al. , 2006) et prolonge le travail de Wittkowski et al. (2007). Deux types de poussière sont envisagés, silicate et Al₂O₃. Les modèles ont été simulés à différentes phases et avec différents paramètres de l’enveloppe de poussière pour étudier la variabilité de la photométrie et de la dimension interférométrique en infrarouge moyen. Les visibilité spectrales n’ont pas permis, pour aucune de nos étoiles, de mettre en évidence de variation significative intra-cycle ou d’un cycle à l’autre, dans nos barres d’erreur de 5 à 20%. Notre étude montre que les spectres de visibilité et de photométrie des quatre étoiles sont bien décrits par le modèle d’enveloppe radiative au-dessus d’une source centrale décrite par un modèle d’atmosphère dynamique. L’enveloppe de poussière optiquement mince de RR Aql est bien modélisée par des grains de silicate. L’addition de grains de Al₂O₃ n’améliore pas l’ajustement du modèle, mais n’exclut pas la présence d’une enveloppe interne optiquement plus mince que celle de silicate. GX Mon est bien modélisé par une combinaison de A Al₂O₃ et de silicates, alors que les enveloppes d nS Ori et R Cncn sont modélisables par des grains de Al₂O₃ seul sans contribution de silicate. Les rayons inférieurs des enveloppes sont de l’ordre de 2 à 2. 5 rayons photosphériques pour Al₂O₃ et de 4 à 5 pour le silicate. Les modélisations effectuées dans ce travail de thèse confirment que les variations inter et intra-cycle attendues ne sont pas détectables dans la précision de nos mesures. Cette étude est la première comparaison entre des mesures interférométriques couvrant plusieurs cycles d’oscillation et des modèles couvrant une large gamme de phases des oscillations
This thesis presents multi-epoch interferometric observations of evolved stars on the Asymptotic Giant Branch (AGB). The Asymptotic Giant Branch is populated by low to intermediate mass stars (0. 6 – 10 Mo) in the final stage of their stellar evolution. Pulsating AGB stars suffer from strong mass loss via a dense and dusty outflow from an extended stellar atmosphere returning gas and dust to the interstellar medium. The processes leading to the violent mass loss are not well understood and are therefore under intense investigations. Due to the AGB stars’ large diameters and high luminosities, evolved stars are ideal targets for high angular resolution observations. The AGB stars presented in this thesis were observed over several pulsation cycles using the near-infrared AMBER and mid-infrared MIDI instruments at the Very Large Telescope Interferometer (VLTI). The goal of this study is to investigate the connection between the pulsation mechanism, the dust chemistry of AGB stars, and the condensation sequence in order to better understand the mass loss process. The thesis studies a sample of four evolved stars, the oxygen-rich Mira variables RR Aql, S Ori, GX Mon, and R Cnc. We obtained multi-epoch MIDI observations and individual AMBER observations. The presented data are modelled using basic models of uniform disks and Gaussian profiles. The AMBER data, along with the basic models, are modelled using dust-free self-excited dynamic model atmospheres (P and M series). These modeles represent the stellar atrmosphere including the continuum forming atmosphere and overlying molecular layers (Ireland et al. , 2004b,a). In addition to the basic models, the MIDI data are fitted by a radioactive transfer model of the circumstellar dust shell where the central stellar intensity profile is described by the previously mentioned series of dust-free dynamic model atmospheres, which are based on self-excited pulsation model. The radiative transfer model is computed using the radiative transfer code mcsim_mpi (Ohnaka et al. , 2006). The modelling approach follows the work presented by Wittkowski et al. (2007). For all stars, two dust species of silicate and Al₂O₃ grains were examined. In order to investigate the expected variability of our mid-infrared photometric and interferometric data, model simulations using variations of model phase and dust shell parameters were performed. The observed visibility spectra for all studied stars do not show indications of variations as a function of pulsation phase and cycle within our investigated phases and uncertainties (5%-20%). The observed photometry spectra may indicate intra-cycle and cycle-to-cycle variations with a significance of 1-5σ. However, the photometry variations cannot be confirmed within our uncertainties. Our study shows that the photometric and visibility spectra for all stars can be well described by the radiative transfer model of the dust shell that uses a dynamic model atmosphere describing the central source. For all epochs, we found the best fitting models consisting of a dynamic model atmosphere, and dust shells parameters including the optical depth of the dust shell, the inner radii, the power-law index of the density distribution, and the photospheric aangular diameter. The optically thin dust shell did not improve the model fit. However, the model simulations indicate that the presence of an inner Al₂O₃ dust shell with low optical depth compared to the silicate dust shell can not be excluded. GX Mon can be modelled with a combination of Al₂O₃ and silicate grains. The dust shell of S Ori and R Cnc can be well modelled using only Al₂O₃ dust grains without a contribution of silicates. The inner boundary radii of Al₂O₃ appears around 2-2. 5 photospheric radii and the inner moundary radii of silicate appears around 4-5 photospheric radii. The modelling simulations performed in this thesis confirmed that significant intra-cycle and cycle-to-cycle visibility variations are not expected at mid-infrared flux and visibility values are expected to be less that 25% and 20% respectively, and are too low to be detected within the measurement uncertainties. The study represents the first comparison between interferometric observation and a combination of a radiative transfer modelling with dynamic atmosphere models over and extended range of pulsation phases covering several cycles

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34

Johanson, Adam. "Radio Emission Toward Regions of Massive Star Formation in the Large Magellanic Cloud." BYU ScholarsArchive, 2015. https://scholarsarchive.byu.edu/etd/4419.

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Four regions of massive star formation in the Large Magellanic Cloud (LMC) were observed for water and methanol maser emission and radio continuum emission. A total of 42 radio detections were made including 27 new radio sources, four water masers, and eight compact HII regions. The lobes of a radio galaxy were resolved for the first time, and the host galaxy identified. Seven sources were associated with known massive young stellar objects (YSOs). A multi-wavelength analysis using both the infrared and radio spectrum was used to characterize the sources. Mid-infrared color-magnitude selection criteria for ultracompact HII (UCHII) regions in the LMC are presented, yielding 136 UCHII region candidates throughout that galaxy. New maser detections identified two previously unknown massive YSOs. No methanol masers were detected, consistent with previous studies and supporting the hypothesis that the LMC may be deficient in these molecules. These discoveries contribute to the history of star formation in the LMC, which will lead to a better understanding of star formation in the Milky Way and throughout the universe.

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35

Huang, Xuan. "Monolithically integrated quantum confined stark effect tuned semiconductor lasers." Thesis, University College London (University of London), 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.368167.

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36

Svoboda, Brian E., Yancy L. Shirley, Cara Battersby, Erik W. Rosolowsky, Adam G. Ginsburg, Timothy P. Ellsworth-Bowers, Michele R. Pestalozzi, et al. "THE BOLOCAM GALACTIC PLANE SURVEY. XIV. PHYSICAL PROPERTIES OF MASSIVE STARLESS AND STAR-FORMING CLUMPS." IOP PUBLISHING LTD, 2016. http://hdl.handle.net/10150/621258.

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We sort 4683 molecular clouds between 10 degrees < l < 65 degrees from the Bolocam Galactic Plane Survey based on observational diagnostics of star formation activity: compact 70 mu m sources, mid-IR color-selected YSOs, H2O and CH3OH masers, and UCH II. regions. We also present a combined NH3-derived gas kinetic temperature and H2O maser catalog for 1788 clumps from our own GBT 100 m observations and from the literature. We identify a subsample of 2223 (47.5%) starless clump candidates (SCCs), the largest and most robust sample identified from a blind survey to date. Distributions of flux density, flux concentration, solid angle, kinetic temperature, column density, radius, and mass show strong (>1 dex) progressions when sorted by star formation indicator. The median SCC is marginally subvirial (alpha similar to 0.7) with >75% of clumps with known distance being gravitationally bound (alpha < 2). These samples show a statistically significant increase in the median clump mass of Delta M similar to 170-370 M-circle dot from the starless candidates to clumps associated with protostars. This trend could be due to (i) mass growth of the clumps at (M) over dot similar to 200-440 M-circle dot Myr(-1) for an average freefall 0.8 Myr timescale, (ii) a systematic factor of two increase in dust opacity from starless to protostellar phases, and/or (iii). a variation in the ratio of starless to protostellar clump lifetime that scales as similar to M-0.4. By comparing to the observed number of CH3OH maser containing clumps, we estimate the phase. lifetime of massive (M > 10(3) M-circle dot) starless clumps to be 0.37 +/- 0.08 Myr (M/10(3) M-circle dot)(-1); the majority (M < 450 M-circle dot) have phase. lifetimes longer than their average freefall time.

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37

Guenel, Mathieu. "Dissipation de marée dans les étoiles de faible masse et les planètes géantes : ondes inertielles, structure interne et rotation différentielle." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLS307/document.

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Cette thèse étudie les mécanismes de dissipation de marée dans les étoiles de faible masse, possédant comme notre Soleil une enveloppe convective externe (i.e. de types M à F), ainsi que dans les planètes géantes gazeuses similaires à Jupiter et Saturne. En particulier, nous cherchons à comprendre et à caractériser l’influence de la structure et de la dynamique internes de ces corps sur les différents mécanismes physiques à l’origine de cette dissipation afin d’évaluer leur importance relative.Dans le cas des planètes géantes, nous utilisons des modèles semi-analytiques préexistants et nous montrons que la dissipation induite par la présence éventuelle d’un cœur solide viscoélastique n’est pas négligeable par rapport à celle induite par les ondes inertielles (dont la force de rappel est l’accélération de Coriolis) dans l’enveloppe convective. Pour les étoiles de faible masse, nous développons de nouvelles méthodes semi-analytiques ainsi que des simulations numériques d’ondes inertielles de marée se propageant dans l’enveloppe convective externe, dont nous calculons et caractérisons la dissipation d’énergie associée. Pour la première fois, nous prenons en compte les effets d’une rotation différentielle latitudinale telle qu’observée dans le Soleil et prédite par de nombreuses simulations numériques de convection dans les étoiles de faible masse. Nous mettons en évidence l’existence de nouvelles familles de modes inertiels ainsi que l’importance des résonances de corotation pour la dissipation de marée. Enfin, nous dérivons une nouvelle prescription pour la viscosité turbulente appliquée à ces ondes de marées en prenant en compte l’influence de la rotation sur les propriétés de la convection le long de l’évolution des étoiles
This thesis studies the tidal dissipation mechanisms in low-mass stars that have an external convective envelope like the Sun (i.e. from M- to F-type stars), as well as in Jupiter- and Saturn-like gaseous giant planets. We particularly focus on understanding and characterizing the influence of the internal structure and dynamics of these bodies on the various physical mechanisms that cause this tidal dissipation, in order to assess their relative strength.In the case of giant planets, we use preexisting semi-analytical models and we show that the dissipation induced by the possible presence of a viscoelastic solid core is not negligible compared to the one induced by inertial waves (whose restoring force is the Coriolis acceleration) in the convective envelope. For low-mass stars, we perform a new semi-analytic study as well as numerical simulations of tidal inertial waves propagating in the external convective envelope, and we compute the associated energy dissipation. For the first time, the effects of a background latitudinal differential rotation, as observed in the Sun and predicted by various numerical simulations of convection in low-mass stars, is taken into account. We highlight the existence of new families of inertial modes as well as the importance of corotation resonances for tidal dissipation. Finally, we derive a new prescription for the turbulent viscosity applied to these tidal waves that takes into account the influence of rotation on the properties of convective flows along the evolution of stars

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38

Blazère, Aurore. "Étude des champs magnétiques dans les étoiles massives et de masse intermédiaire." Thesis, Paris Sciences et Lettres (ComUE), 2016. http://www.theses.fr/2016PSLEO009/document.

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Les champs magnétiques jouent un rôle important dans l'évolution stellaire, mais les propriétés magnétiques des étoiles massives et de masse intermédiaire sont mal connues. Seul une petite fraction (7%) des étoiles massives et de masse intermédiaire possèdent un champ magnétique et la force de leur champ dipolaire est supérieure à ~300 Gauss. La théorie pour expliquer l'origine de ces champs, la théorie des champs fossiles, n'explique pas pourquoi seulement une petite partie des étoiles chaudes ont un champ magnétique. Récemment, un champ magnétique ultra-faible (moins de 1 Gauss) a été découvert sur deux étoiles de masse intermédiaire (Vega et Sirius). Ce sont peut être les premières détections d'un nouveau type de champ magnétique faible. Deux familles d'étoiles magnétiques chaudes pourraient donc exister, avec des champs forts ou ultra-faibles, séparées par ce qu'on appelle le désert magnétique. Ma thèse consiste à analyser des données spectropolarimétriques prises avec des spectropolarimètres haute résolution, principalement avec Narval installé au télescope de 2 mètres à l'Observatoire du Pic du Midi. Une partie de ma thèse été dédiée à l'étude des champs magnétiques les plus faibles, parmi les champs forts. J'ai analysé les observations de l'étoiles O massive zeta Ori A. Peu d'étoiles O sont connues pour être magnétiques et zeta Ori A possède le plus faible champ magnétique. J'ai aussi participé à un programme observationnel pour déterminer la limite supérieure du désert magnétique grâce aux étoiles Ap/Bp. Le but de ces études est de tester la dépendance de la limite supérieure du désert magnétique par rapport à la rotation et à la masse. Une deuxième partie de ma thèse est consacrée à la recherche des champs ultra-faibles pour fournir des contraintes aux divers scenarios qui expliquent la dichotomie entre les champs forts et faibles et améliorer notre connaissance des propriétés ce type de champ magnétique. Je présente les résultats d'étude d'étoiles normales, UZ Lyn et Vega, ainsi que celles de plusieurs d'étoiles chimiquement particulières (Am et HgMn). Les études présentées dans ma thèse apportent une lumière nouvelle sur le magnétisme des étoiles chaudes et des contraintes pour la physique stellaire en général, en particulier pour l'évolution stellaire
Magnetic fields are known to play a fundamental role in stellar evolution but the magnetic properties of massive and intermediate-mass stars are not well understood. Only a small (7%) fraction of massive and intermediate-mass stars are found to be magnetic and their dipolar magnetic field strength is above ~300 Gauss. The current paradigm, the fossil field theory, describes this magnetism as remnant of an early phase of the star-life, but leaves many basic questions unanswered, such as the small fraction of magnetic stars, and in practice provides no constraint to stellar evolution theory. Recently, an ultra weak magnetic field (less than 1 Gauss) has been discovered in two intermediate mass stars (Vega and Sirius). They may be the first detections of a new type of weak magnetic fields. Two families of magnetic stars may thus exist: with strong or ultra-weak fields, separated by the so-called magnetic desert. My PhD thesis consists in analyzing observational data taken with high-resolution spectropolarimeters, mainly with Narval installed on the 2-meter telescope at the Pic du Midi Observatory, to detect magnetic fields. One part of my thesis is dedicated to the study of the weakest end of strong magnetic fields. I analyzed the observations of a massive O star, zeta Ori A. Only a few O stars are known to be magnetic and zeta Ori A has the weakest field. I was also involved in a project to determine the upper limit of the magnetic desert thanks to observations of Ap/Bp stars. The goal of these studies is to test the dependence of the upper limit with rotation and mass. The other part of my thesis is dedicated to the search for ultra-weak fields in hot stars to provide constraints to the various scenarios that explain the strong vs weak field dichotomy and improve our understanding of the properties of this kind of weak field. I present the result of the studies of normal stars, UZ Lyn and Vega, and of several chemically peculiar (Am and HgMn) stars. The studies presented in my PhD thesis provide new clues about magnetism in hot stars and constraint for stellar physics in general, in particular for stellar evolution

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39

Fantina, Anthea Francesca. "Supernovae theory : study of electro-weak processes during gravitational collapse of massive stars." Paris 11, 2010. http://www.theses.fr/2010PA112225.

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Dans le cadre de la théorie des Supernovae de type II, la plus part des simulations numériques échouent de reproduire l'explosion observée, à cause de phénomènes hydrodynamiques et des processus nucléaires pas encore bien connus. Le but de ce travail est d'étudier certains processus microphysiques et d'évaluer leur impact parmi des simulations hydrodynamiques. Parmi les processus électro-faibles intervenant pendant l'effondrement, le plus important est la capture électronique, crucial pour déterminer l'évolution de la fraction leptonique dans la phase de neutronization. Elle a un impact sur l'efficacité du rebond et l'énergie de l'onde du choc. De plus, l'équation d'état de la matière et les taux de capture électronique dans les noyaux sont modifiés par la masse effective des nucléons dans les noyaux, dûe aux corrélations à multi-corps, et à sa dépendance de la température. On présente un modèle nucléaire avec le but d'étudier la masse effective nucléaire. On a inclus dans une approche de la fonctionnelle de la densité une masse effective piquée en surface pour reproduire des effets au delà de Hartree-Fock. On présente aussi les modèles de supernova sur lesquels j'ai travaillé, dans une approximation à une zone et à une dimension en symétrie sphérique, newtonienne et en relativité générale. On montre que, en introduisant une masse effective dépendante de la température dans un code à une zone et newtonien en symétrie sphérique avec transport des neutrinos, la deleptonization est réduite : cela a un impact non-negligeable sur la formation de l'onde du choc. On présente aussi les résultats obtenus avec un code en relativité générale avec un traitement muIti-groupe des neutrinos
Ln the framework of type II Supernovae theory, most of numerical simulations of the supernova core collapse and shock wave propagation fail to reproduce the observed explosion, because of both hydrodynamical phenomena and to some microphysical processes involved in the picture and not yet completely understood. The aim of this work is to investigate some microphysical aspects and to analyze their effects through hydrodynamical simulations. Among electro-weak processes occuring in core-collapse supernova, the most important one is the electron capture, crucial to determine the evolution of lepton fraction during the neutronization phase. It affects the efficiency of the bounce and the strength of the shock wave. Moreover, both the equation of state of supernova matter and electron capture rates in nuclei are modified by the nuclear effective mass in nuclei, induced by many-body correlations, and its temperature dependence. I will present a nuclear model aimed at studying the nuclear effective mass. We have included in a energy density functional approach a surface-peaked nuclear effective mass to mimic some effects beyond Hartree-Fock. I will then present the supernova models I have worked on, in a one-zone approximation, and in spherically symmetric one-dimensional approximation, Newtonian and General Relativistic. We will show that, introducing a temperature dependent effective mass into a one-zone and a one dimensional Newtonian code with neutrino transport, the deleptonization is reduced and has a non-negligible effect on the shock wave energetics. We will also present results obtained with the General Relativistic code with a multi-group treatment of neutrinos

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40

Richter, Laura. "A comparative polarimetric study of the 43 GHz and 86 GHz SiO masers toward the supergiant star VY CMa." Thesis, Rhodes University, 2012. http://hdl.handle.net/10962/d1005239.

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The aim of this thesis is to perform observational tests of SiO maser polarisation and excitation models, using component-level comparisons of multiple SiO maser transitions in the 43 GHz and 86 GHz bands at milliarcsecond resolution. These observations reqwre very long baseline interferometric imaging with very accurate polarimetric calibration. The supergiant star VY CMa was chosen as the object of this study due to its high SiO maser luminosity, many detected SiO maser lines, and intrinsic scientific interest. Two epochs of full-polarisation VLBA observations of VY CMa were performed. The Epoch 2 observations were reduced using several new data reduction methods developed as part of this work, and designed specifically to improve the accuracy of circular polarisation calibration of spectral-line VLBI observations at millimetre wavelengths. The accuracy is estimated to be better than 1% using these methods. The Epoch 2 images show a concentration of v= l and v=2 J= 1-0 SiO masers to the east and northeast of the assumed stellar position. The v=l J=2-1 masers were more evenly distributed around the star, with a notable lack of emission in the northeast. There is appreciable spatial overlap between these three lines. The nature of the overlap is generally consistent with the predictions of hydrodynamical circumstellar SiO maser simulations. Where the v=l J = 1-0 and J =2-1 features overlap, the v=l J = 2-1 emission is usually considerably weaker. This is not predicted by current hydrodynamical models, but can be explained in the context of collisional pumping in a low density environment. Six observational tests of weak-splitting maser polarisation models were performed, including intercomparisons of linear polarisation in the v=l J=1-0 and J=2-1lines, linear polarisation versus saturation level, linear polarisation versus distance from the star, circular polarisation in the v= l J = 1-0 and J=2-1 lines, circular versus linear polarisation and modeling of ~ 900 electric-vector position angle rotations. The polarisation model tests generally do not support non-Zeeman circular polarisation mechanisms. For the linear polarisation tests, the results are more consistent with models that predict similar linear polarisation across transitions. The scientific importance of these tests is described in detail and avenues for future work are described.

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41

Felli, Derek Sean. "The Morphology and Uniformity of Circumstellar OH/H₂O Masers around OH/IR Stars." BYU ScholarsArchive, 2017. https://scholarsarchive.byu.edu/etd/6633.

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Even though low mass stars (< 8 solar masses) vastly outnumber high mass stars (< 8 solar masses), the more massive stars drive the chemical evolution of galaxies from which the next generation of stars and planets can form. Understanding mass loss of asymptotic giant branch stars contributes to our understanding of the chemical evolution of the galaxy, stellar populations, and star formation history. Stars with mass < 8 solar masses form planetary nebulae, while those with mass < 8 solar masses go supernova. In both cases, these stars enrich their environments with elements heavier than simple hydrogen and helium molecules. While some general info about how stars die and form planetary nebulae are known, specific details are missing due to a lack of high-resolution observations and analysis of the intermediate stages. For example, we know that mass loss in stars creates morphologically diverse planetary nebulae, but we do not know the uniformity of these processes, and therefore lack detailed models to better predict how spherically symmetric stars form asymmetric nebulae. We have selected a specific group of late-stage stars and observed them at different scales to reveal the uniformity of mass loss through different layers close to the star. This includes observing nearby masers that trace the molecular shell structure around these stars. This study revealed detailed structure that was analyzed for uniformity to place constraints on how the mass loss processes behave in models. These results will feed into our ability to create more detailed models to better predict the chemical evolution of the next generation of stars and planets.

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42

Lannier, Justine. "Formation des planètes géantes autour des étoiles de faibles masses : contraintes observationnelles en imagerie (optique adaptative)." Thesis, Université Grenoble Alpes (ComUE), 2016. http://www.theses.fr/2016GREAY041/document.

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L'étude des exoplanètes, et en particulier celle des planètes géantes gazeuses, est une branche jeune et florissante de l'astrophysique moderne. Les grandes problématiques qui ont émergé des études sur cette population de planètes consistent à comprendre comment elles se sont formées, comment elles ont spatialement et temporellement évolué, et comment elles influencent d'éventuelles autres planètes au sein des systèmes stellaires. Afin d'apporter des réponses à ces questions, il a été nécessaire de développer des techniques d'observation et des outils d'analyse des données les plus performants possibles. C'est dans ce cadre que j'ai effectué mon travail de thèse, qui s'est articulé autour de trois projets.En premier lieu, je me suis intéressée à étudier le taux d'occurrence des planètes géantes gazeuses en orbite autour des naines M. Pour réaliser cette étude statistique, j'ai utilisé des données de deux relevés NaCo, le premier étant consacré aux naines M, et le second étant constitué d'étoiles AF et ayant été précédemment étudié par des membres de notre équipe. J'ai développé un code Monte Carlo, et me suis servie de la logique de la contraposition pour mener une étude comparative des résultats de ces deux relevés. J'ai également associé des gammes de rapports de masses entre la planète et son étoile à des mécanismes de formation privilégiés. J'en ai conclu que la formation des planètes géantes gazeuses formée par accrétion sur coeur était favorisée si ces planètes se situaient autour d'étoiles AF plutôt que des naines M, pour des séparations allant de 8 à 400 unités astronomiques. La fréquence des planètes géantes gazeuses reste toutefois faible quelque soit la masse de l'étoile considérée (typiquement <20%).Je me suis par la suite intéressée à développer un outil statistique capable de combiner des données de vitesses radiales et d'imagerie directe afin d'apporter des contraintes supplémentaires sur la population de planètes géantes situées à toutes les séparations, pour des systèmes particuliers. Le code que j'ai écrit repose sur une génération Monte Carlo de planètes synthétiques. Je l'ai appliqué sur les données de vitesses radiales et d'imagerie d'étoiles jeunes et proches : AUMic, ßPictoris, HD113337, et HD95086. Les futures applications pourront être nombreuses à la fois parce que les données de vitesses radiales sont de plus en plus abondantes, et parce que les instruments de haut contraste et haute résolution angulaire permettent de sonder des séparations toujours plus courtes.Grâce à ces deux premiers projets de ma thèse, j'ai pris en main les outils de réduction de données développés à l'IPAG, et j'ai développé des outils statistiques me permettant de commencer à mener mon dernier projet. Cet ultime projet consiste en l'observation, la réduction et l'analyse de données de vitesses radiales HARPS et d'imagerie SPHERE obtenues conjointement pour un set de naines K5-M5, proches et jeunes. L'analyse de l'ensemble des données va permettre d'apporter de fortes contraintes sur les populations de planètes géantes gazeuses en orbite autour des étoiles de faible masse, depuis les très courtes jusqu'aux plus longues séparations
Studying exoplanets, and in particular gaseous giant planets, is a new field of modern astrophysics. Understanding how the giant planets form, dynamically evolve, evolve with time, and have an impact on potential other planets within a stellar system are part of the biggest challenges of this science. The development of the most efficient observational technics and optimal analysis tools have been necessary to bring answers to these problematics. This is the context in which I realized my PhD thesis. I present in this manuscript the three projects that I led during these last three years.First, I studied the occurrence rate of the giant planets that orbit around M dwarfs. To realize this statistical study, I used NaCo data from two surveys. The first survey was composed of M dwarfs, the second was made of AF stars that were already studied by members of our team. I developed a Monte Carlo code, and used the contrapositive logic to lead a comparative analysis of these two surveys. I also associated stellar to planet mass ratios to planetary formation scenarios. My conclusions are that giant planets can more easily be formed by core accretion around AF stars than around M dwarfs, for separations between 8 and 400 astronomical units. Wide-orbit giant planets are rare whatever the stellar mass (basically <20%).Then, I developed a statistical tool that combines radial velocity and direct imaging data of specific stars, to better constrain the giant planet population at all separations. The code that I wrote is based on a Monte Carlo generation of synthetic planet populations. I applied this code on radial velocity and direct imaging data from young and nearby stars: AUMic, ßPictoris, HD113337, and HD95086. The future applications will be numerous thanks to the increase of the time baseline of radial velocity data and thanks to new high contrast and high resolution instruments able to probe shorter regions.These first two projects have allowed me to understand how to reduce and analyse data, and to develop statistical tools useful for my last project. This last project consists of observing, reducing and analyzing radial velocity and direct imaging data of a sample of K5-M5 young and nearby dwarfs. This project will bring strong constraints on the gaseous giant planet population that orbits around low mass stars, from short to wider separations

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43

Miret, Roig Núria. "COSMIC-DANCE : A comprehensive census of nearby star forming regions." Thesis, Bordeaux, 2020. http://www.theses.fr/2020BORD0327.

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Comprendre comment se forment les étoiles est l’une des questions fondamentales auxquelles l’astronomie entend répondre. Malheureusement, nous ne pouvons pas étudier la formation stellaire en temps réel et différentes méthodes indirectes doivent être utilisées pour faire la lumière sur ce sujet. L’objectif principal de cette thèse est de déterminer la fonction de masse initiale, la distribution de masse des étoiles à leur naissance, dans différentes associations et régions de formation d’étoiles. La fonction de masse est le produit direct de la formation stellaire et constitue donc un paramètre d’observation fondamental pour contraindre les théories de formation stellaire et sous-estellaire. Nous nous sommes concentrés sur l’amas ouvert de 30 Ma IC 4665 et la région de formation d’étoiles de 1 - 10 Ma de Upper Scorpius (USC) et r Ophiuchi (r Oph). Nous avons combiné l’astrométrie et la photométrie de Gaia Data Release 2 avec nos observations au sol pour préparer un catalogue profond et étendu de chaque région. Ensuite, nous avons calculé les probabilités d’appartenance en utilisanttoute l’astrométrie et la photométrie disponibles et identifié les membres à haute probabilité. Nous avons utilisé la liste finale des membres pour estimer la distribution de magnitude, et les fonctions de luminosité et masse de ces associations. Alors que la première a l’avantage d’être indépendante des modèles d’évolution, tandis que les fonctions de luminosité et de masse peuvent être utilisées pour contraindre les mécanismes de formation d’étoiles. L’étude d’IC 4556 nous a permis d’identifier des objets sous-stellaires, sans pour autant pouvoir fournir un recensement complet dans ce domaine de masse. Dans USC et r Oph, nous avons identifié une population très riche d’objets sous-stellaires, significativement plus nombreux que les prédictions des modèles de formation par effondrement de coeurs moléculaires, suggérant que la formation de naines brunes et d’objets de masses planétaires isolés par des phénomènes d’éjection dans des systèmes planétaires a une contribution importante et du même ordre que l’effondrement des coeurs moléculaires à la population finale d’objets dans un amas. L’âge est un paramètre fondamental pour étudier la formation et l’évolution des étoiles pour plusieurs raisons: premièrement puisqu’il établit une échelle de temps sur laquelle placer les observations. Deuxièmement car il est essentiel pour convertir les luminosités en masses, avec l’aide de modèles d’évolution stellaire. Les incertitudes sur l’age de USC et r Oph se traduisant en erreurs importantes dans notre estimation de la fonction de masse, j’ai développé une stratégie d’étude de "l’âge dynamique" au moyen d’une analyse orbitale de traçage des mouvements des membres d’associations jeunes. J’ai ainsi mis au point une stratégie incluant i) les observations et la recherche de données dans les archives publiques, ii) la réduction et l’analyse des spectres échelles obtenus; iii) et l’analyse dynamique, pour déterminer l’âge d’une association. La méthodologie, développée avec l’association b Pictoris (b Pic), est prête à être appliquée à d’autres régions et en particulier à USC et r Oph. Les membres que nous avons identifiés sont par ailleurs d’excellentes cibles pour des études complémentaires telles que la recherche de disques (produit également fondamental de la formation stellaire), d’exoplanètes, de système multiples, mais aussi pour la caractérisation des atmosphères et propriétés physiques des naines brunes et des planètes errantes. [...]
Understanding how stars form is one of the fundamental questions which astronomy aims to answer. Currently, it is well accepted that the majority of stars form in groups and that their predominant mechanism of formation is the core-collapse. However, several mechanisms have been suggested to explain the formation of substellar objects, and their contribution is still under debate. The main goal of this thesis is to determine the initial mass function, the mass distribution of stars at birth time, in different associations and star-forming regions. The mass function constitutes a fundamental observational parameter to constrain stellar and substellar formation theories since different formation mechanisms predict different fraction of stellar and substellar objects. We used the Gaia Data Release 2 catalogue together with ground-based observations from the COSMIC-DANCe project to look for high probability members via a probabilistic model of the distribution of the observable quantities in both the cluster and background populations. We applied this method to the 30 Myr open cluster IC 4665 and the 1 - 10 Myr star-forming region Upper Scorpius (USC) and r Ophiuchi (r Oph). We found very rich populations of substellar objects which largely exceed the numbers predicted by core-collapse models. In USC, where our sensitivity is best, we found a large number of free-floating planets and we suggest that ejection from planetary systems must have a similar contribution than core-collapse in their formation. The age is a fundamental parameter to study the formation and evolution of stars and is essential to accurately convert luminosities to masses. For that, we also presented a strategy to study the dynamical traceback age of young local associations through an orbital traceback analysis. We applied this method to determine the age of the b Pictoris moving group and in the future, we plan to apply it to other regions such as USC. The members we identified with the membership analysis are excellent targets for follow-up studies such as a search for discs, exoplanets, characterisation of brown dwarfs and free-floating planets. I this thesis, we presented a search for discs hosted by members of IC 4665 and we found six excellent candidates to be imaged with ALMA or the JWST. The tools we developed, are ready to be used in other regions such as USC and r Oph, where we expect to find a larger number of disc-host stars

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44

Langa, Mihloti Christina. "An investigation into the variability of methanol and hydroxyl masers in the star-forming region G12.89+0.49 / Mihloti Christina Langa." Thesis, North-West University, 2006. http://hdl.handle.net/10394/1700.

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45

Jenness, Timothy. "A molecular line and continuum study of water maser sources." Thesis, University of Cambridge, 1996. https://www.repository.cam.ac.uk/handle/1810/245081.

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Recent observations at the James Clerk Maxwell Telescope (JCMT) and elsewhere have identified a class of very deeply embedded, possibly protostellar, sources which are not associated with any of the traditional indicators of star formation, such as HII regions and near-infrared emission, but which do lie close to otherwise isolated H2O masers. This thesis describes a search, based on catalogues of known water maser positions, for new deeply embedded cores similar to those found in S106 and M17. In addition to millimetre molecular line and submillimetre continuum observations, 22 GHz and 8 GHz radio observations have been made of a number of the sources in order to obtain more accurate maser positions and to search for any associated compact HII regions. Observing sources such as these in less active star forming regions provides a cleaner environment in which to examine the maser excitation and the ongoing process of star formation. A sample of 44 water maser sources was observed from which submillimetre continuum emission was detected from 40 (91 per cent). The most striking feature of the data is the close association of the masers with the submillimetre cores: the data are consistent with masers occurring within 6000 AU of the embedded core. The results can be summarised as follows: o High temperature gas has been detected, and most of the submillimetre cores have mean densities greater than 10^6 /cm^3. o The masers have low velocities with respect to the molecular cloud and are uniformly distributed within 6600 AU of the submillimetre core. o The isotropic maser luminosity is proportional to the far-infrared luminosity over more than 5 orders of magnitude. o There is no obvious correlation between the near-infrared spectral class and the maser emission. o Where a radio spectral index is known the majority of sources are optically thin HII regions. The bulk of the remainder are undetected and have a flux density less than 1 mJy. o Masers not associated directly with a submillimetre core show explicit evidence for shocks. Embedded cores \emph{have} been detected with this survey and the maser emission is consistent with collisionally excited pump models.

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46

Montarges, Miguel. "Perte de masse des étoiles massives évoluées : l'environnement circumstellaire à haute résolution angulaire." Thesis, Paris 6, 2014. http://www.theses.fr/2014PA066364/document.

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Les mécanismes physiques de la perte de masse des étoiles évoluées sont encore largement inconnus. Ce processus essentiel est pourtant le moteur principal de l'évolution chimique du milieu interstellaire. Pour les supergéantes rouges (SGR), le déclenchement de l'éjection de la matière et les mécanismes de condensation de la poussière demeurent mal compris. La façon dont les géantes rouges parviennent à former des nébuleuses planétaires non-Sphériques est aussi inconnue. Au cours de ma thèse j'ai étudié des étoiles évoluées grâce à des techniques de haute résolution angulaire permettant de détailler leur surface et leur environnement proche où se trouve l'origine de la perte de masse. À partir d'observations interférométriques en infrarouge (IR), j'ai caractérisé l'enveloppe de vapeur d'eau et de monoxyde de carbone de la SGR Bételgeuse. J'ai également suivi l'évolution d'un point chaud à sa surface et analysé la structure de sa convection ainsi que celle d'Antarès (une autre SGR très proche) grâce à des simulations hydrodynamiques radiatives. L'imagerie à la limite de diffraction (optique adaptative en IR, télescope spatial en ultraviolet) m'a permis d'étudier l'évolution des inhomogénéités de l'enveloppe circumstellaire de Bételgeuse et découvrir un disque circumstellaire autour de L2 Puppis, une étoile de la branche asymptotique des géantes. Ces observations multi-Longueurs d'onde, répétées à plusieurs époques, m'ont permis d'initier un suivi temporel et d'apporter des informations sur la dynamique en jeu. Renouvelé sur un plus grand échantillon d'étoiles dans les années à venir, ce programme permettra de mieux appréhender la perte de masse des étoiles évoluées
Mass loss of evolved stars is still largely mysterious, despite its importance as the main evolution engine for the chemical composition of the interstellar medium. For red supergiants (RSG), the triggering of the outflow and the mechanism of dust condensation remain unknown. Concerning red giant stars, we still do not know how their mass loss is able to form a bipolar planetary nebula. During my PhD thesis, I observed evolved stars with high angular resolution techniques. They allowed us to study the surface and the close environment of these stars, from where mass loss originates. With near-Infrared interferometric observations, I characterized the water vapor and carbon monoxide envelope of the nearby RSG Betelgeuse. I also monitored a hot spot on its surface and analyzed the structure of its convection, as well as that of Antares (another very nearby supergiant) thanks to radiative hydrodynamical simulations. Diffraction-Limited imaging techniques (near-Infrared adaptive optics, ultraviolet space telescope) allowed me to observe the evolution of inhomogeneities in the circumstellar envelope of Betelgeuse and to discover a circumstellar disk around L2 Puppis, an asymptotic giant branch star. These multi-Scale and multi-Wavelength observations obtained at several epochs allowed us to monitor the evolution of the structures and to derive information on the dynamics of the stellar environment. With a wider stellar sample expected in the next few years, this observing program will allow a better understanding of the mass loss of evolved stars

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47

Yung, Hong-kiu Bosco, and 容康喬. "Identification of oxygen-rich evolved stars by maser surveys and statistical studies on infrared data." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2013. http://hdl.handle.net/10722/193506.

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The post-asymptotic giant branch (post-AGB) phase is a short episode in the life of a star with mass between 0.8 to 8 M⊙. It comes after the AGB phase, and before the planetary nebula phase. A rapid change in many physical properties of a star is suggested to happen in this phase, for example the onset of jets. However, a lot of details are still unknown. In this thesis, three major problems are addressed: insufficient samples of post-AGB stars, identification of post-AGB stars, and the true status of a special class of objects called the “water fountains (WFs)”. WFs are evolved stars associated with high velocity collimated bipolar jets that can be traced by H2O maser emissions. For the first two problems, new searching criteria are introduced with two new maser surveys on oxygen-rich post-AGB stars. It is necessary to collect more samples of post-AGB stars for further studies. Nonetheless, there has been no systematic searching method because most of the post-AGB stars are dim in optical and near-infrared wavelengths, which increases the difficulty in identification. Maser thus becomes a good alternative tool. In the first survey which focused only on H2O masers, over 200 AGB or post-AGB star candidates have been selected and observed. Those candidates were mainly chosen by new colour criteria with the far-infrared AKARI data. In particular, four characteristic maser sources were found, and they are currently suggested as possible very young post-AGB stars. In the second survey, another 100 objects were observed in OH and/or H2O masers. Three possible high velocity objects were discovered, including a new rare member of WFs. The colour criteria are proved to be quite sensitive in distinguishing post-AGB stars from AGB stars or other types of objects, even though there are still some contamination from young stellar objects. A follow-up study shows that the Q-parameters are effective in isolating objects with spherical or aspherical envelopes, which are also useful in finding post-AGB stars. Regarding the third problem, one-dimensional radiative transfer models have been used to study the spectral energy distributions (SEDs) of all known WFs. Owing to the young dynamical ages of the WF jets, it has been suggested that WFs represent the very early post-AGB phase, when the circumstellar envelopes started to depart from spherical symmetry. However, it is shown from the present SED study that WFs in fact could have various form of morphologies, some of them are even spherical which resemble the AGB stars. It implies that WFs do not necessary belong to the very early post-AGB phase, and the present interpretation on the WF status may not be entirely correct.
published_or_final_version
Physics
Doctoral
Doctor of Philosophy

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48

Lima, Rodolfo Valentim da Costa. "Análise Bayesiana de dois problemas em Astrofísica Relativística: neutrinos do colapso gravitacional e massas das estrelas de nêutrons." Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/14/14131/tde-26062013-162012/.

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O evento estraordinário de SN1987A vem sendo investigado há mais de vinte e cinco anos. O fascínio que cerca tal evento astronômico está relacionado com a observação em tempo real da explosão à luz da Física de neutrinos. Detectores espalhados pelo mundo observaram um surto neutrinos que dias mais tarde foi confirmado como sendo a SN1987A. Kamiokande, IMB e Baksan apresentaram os eventos detectados que permitiu o estudo de modelos para a explosão e resfriamento da hipotética estrela de nêutrons remanescente. Até hoje não há um consenso a origem do progenitor e a natureza do objeto compacto remanescente. O trabalho se divide em duas partes: estudo dos neutrinos de SN1987A através de Análise Estatística Bayesiana através de um modelo proposto com duas temperaturas que evidenciam dois surtos de neutrinos. A motivação está na hipótese do segundo surto como resultado da formação de matéria estranha no objeto compacto. A metodologia empregada foi a desenvolvida por um trabalho interessante de Loredo (2002) que permite modelar e testar hipóteses sobre os modelos via Bayesian Information Criterion (BIC). A segunda parte do trabalho, a mesma metodologia estatística é usada no estudo da distribuição de massas das estrelas de nêutrons usando a base de dados disponível (http://stellarcollapse.org). A base de dados foi analisada utilizando somente o valor do objeto e seu desvio padrão. Construindo uma função de verossimilhança e utilizando distribuições ``a priori\'\' com hipótese de bimodalidade da distribuição das massas contra uma distribuição unimodal sobre todas as massas dos objetos. O teste BIC indica forte tendência favorável à existência da bimodalidade com valores centrados em 1.37M para objetos de baixa massa e 1.73M para objetos de alta massa e a confirmação da fraca evidência de um terceiro pico esperado em 1.25M.
The extraordinary event of supernova has been investigated twenty five years ago. The fascination surrounds such astronomical event is on the real time observation the explosion at light to neutrino Physics. Detectors spread for the world had observed one burst neutrinos that days later it was confirmed as being of SN1987A. Kamiokande, IMB and Baksan had presented the detected events that allowed to the study of models for the explosion and cooling of hypothetical neutron star remain. Until today it does not have a consensus the origin of the progenitor and the nature of the remaining compact object. The work is divided in two parts: study of the neutrinos of SN1987A through Analysis Bayesiana Statistics through a model considered with two temperatures that two evidence bursts of neutrinos. The motivation is in the hypothesis of as burst as resulted of the formation of strange matter in the compact object. The employed methodology was developed for an interesting work of Loredo & Lamb (2002) that it allows shape and to test hypotheses on the models saw Bayesian Information Criterion (BIC). The second part of the work, the same methodology statistics is used in the study of the distribution of masses of the neutron stars using the available database http://stellarcollapse.org/. The database was analyzed only using the value of the object and its shunting line standard. Constructing to a a priori function likelihood and using distributions with hypothesis of bimodal distribution of the masses against a unimodal distribution on all the masses of objects. Test BIC indicates fort favorable trend the existence of the bimodality with values centered in 1.37M for objects of low mass and 1.73M for objects of high mass and week evidence of one third peak around 1.25M.

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49

Peralta, Carlos Andrés. "Superfluid spherical Couette flow and rotational irregularities in pulsars /." Connect to thesis, 2006. http://eprints.unimelb.edu.au/archive/00003176.

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50

Bonne, Lars. "La formation du gaz dense à l'origine des étoiles de faible et de haute masse." Thesis, Bordeaux, 2020. http://www.theses.fr/2020BORD0121.

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Pour comprendre la formation des étoiles, il faut étudier les processus physiques qui forment le gaz froid et dense dans le milieu interstellaire. Le télescope spatial Herschel a récemment démontré que la majorité du gaz froid et dense est formée de structures filamentaires (des filaments).Dans cette thèse, plusieurs raies de CO ont été observées avec le télescope APEX autour du filament de Musca. Ces observations ont été complémentées par des observations [CII] et [OI] avec le télescope SOFIA. La non-détection de [CII] démontre que le nuage de Musca est situé dans un champ de radiation UV faible (1 G0). Par contre, les observations de CO(4-3) avec APEX montrent qu'il y a du gaz CO chauffé (> 50 K) autour du filament que l'irradiation UV ne peut pas expliquer. La comparaison avec des modèles de chocs indique que l'émission CO(4-3) doit alors être le résultat d'un choc J à basse vitesse (< 4 km/s). L'analyse du spectre CO(4-3) montre aussi que l'émission venant du choc ressemble à une signature de choc d'accrétion. Cette observation suggère qu'un choc à basse vitesse, dû à une accrétion continue, est responsable de la formation du gaz dense et froid du filament de Musca.Ce scénario d'accrétion du filament de Musca est de plus étudié à grandes échelles dans les raies CO(2-1) et CO(1-0) obtenues avec les télescopes APEX et NANTEN2. Ces observations montrent un gradient de vitesse sur la crête de Musca qui est correlé avec le champ de vitesse autour du filament. L'analyse globale des observations de Musca montre une asymétrie à la fois spatiale et cinématique. Cette asymétrie est vue comme une forme en V dans le diagramme position-vitesse perpendiculaire au filament. L'inclusion d'observations du gaz neutre HI dans l'analyse confirme que Musca fait partie d'un nuage HI plus grand, le complex Chamaeleon-Musca. Le HI montre aussi que l'asymétrie cinématique est présente des grandes échelles du nuage HI jusqu'aux petites échelles de la crête du filament de Musca. En comparant le HI avec les vitesses CO de Cha I, Cha II et Cha III, on constate que l'asymétrie cinématique est présente pour toutes les régions denses du complexe de Chamaeleon-Musca. Ce scénario d'accrétion asymétrique, qui est observé, est reproduit dans des simulations d'une collision de nuages magnétisés. Dans ce scénario, c'est la déformation du champ magnétique qui est responsable de l'accrétion asymétrique. La formation du filament Musca serait ainsi due à la convergence de deux flots de matière guidée par la courbure du champ magnétique provoquée par la collision des nuages HI à grande échelle.Dans la dernière partie, la cinématique du nuage massif DR21, qui forme des étoiles massives, est étudiée pour comparer la formation des étoiles massives à celle des étoiles de faible masse. Le nuage DR21 montre une asymétrie en V similaire à celle de Musca, ce qui indique que le nuage DR21 est aussi formé par une collision de nuages moléculaires mais avec une vitesse de collision plus importante que pour Musca. Les observations indiquent de plus que la formation des étoiles massives dans le nuage DR21 serait la conséquence directe de la prédominance de la gravité à grande échelle (> 1 pc) du gaz dense en contraste avec Musca pour lequel la gravité ne dominerait qu'aux plus petites échelles (< 0.1-0.2 pc). L'analyse cinématique globale de toute la région du Cygne montre que toute la région résulte de la même collision de nuages. Cette observation indique que c'est une collision de nuages à grande vitesse (> 10 km/s) qui pourrait expliquer la formation d'une association d'étoiles OB de plusieurs milliers d'étoiles. Dans ce scénario, les étoiles massives (OB) se formeraient dans les structures denses et massives (hubs et ridges) formées aux convergences dues à la collision à grande vitesse de nuages, et où la gravité à grande échelles domine la cinématique et l'évolution du gaz dense
To understand how stars can form in the interstellar medium (ISM), it has to be understood how cold (~ 10 K) and dense gas (> 10^{4} cm^{-3}) can emerge during the evolution of the ISM. With the Herschel telescope it was found that most of this dense star forming gas is organised in filamentary structures.To understand how this dense filamentary gas forms, multiple CO transitions were observed towards the Musca filament, which can form low-mass stars, using the APEX telescope. These observations were complemented with [CII] and [OI] observations by the SOFIA telescope. The non-detection of [CII] demonstrates that the Musca cloud is embedded in a weak FUV field (< 1 G0). However, the observed CO(4-3) line with APEX demonstrates the presence of warm (> 50 K) CO gas around the Musca filament which cannot be explained with heating by the FUV radiation field. A comparison of the observed CO(4-3) emission with shock models shows that the emission can be the result of a low-velocity (< 4 km/s) J-type shock. Further analysis of this emission demonstrates that this shock emission resembles the signature of a shock responsible for mass accretion on a filament. This suggests that a low-velocity shock as a result of continuous mass accretion is responsible for the formation of cold and dense gas that can form stars in the Musca filament.The accretion scenario for Musca is further analysed with low-J CO observations from APEX and NANTEN2 to study the large scale gas kinematics. These observations unveil a velocity gradient over the Musca filament crest which is correlated with the velocity field of the nearby ambient gas. This suggests that the velocity gradient is the result of mass accretion from the ambient cloud. Analysing the full Musca cloud demonstrates a spatial and kinematic asymmetry from low- to high-density gas. This asymmetry is seen as a V-shape in the position-velocity (PV) diagram perpendicular to the Musca filament. Including atomic hydrogen (HI) observations in the analysis first of all confirms that Musca is part of a larger HI cloud, the Chamaeleon-Musca complex. It also demontrates that the kinematic asymmetry is seen from the HI cloud down to the filament crest. Furthermore, the CO-HI asymmetry is found for basically all dense regions (Cha I, Cha II, Cha III and Musca) with archival data of Chamaeleon-Musca, while HI shows indications of more than one velocity component. This asymmetric accretion scenario is predicted by magnetised cloud-cloud collision simulations, where the bending of the magnetic field is responsible the observed asymmetric accretion scenario. The filament formation in Musca is thus the result of two intersecting converging flows which are driven by the magnetic field bending due to a large-scale colliding HI flow that triggered the observed star formation in the full Chamaeleon-Musca complex.Finally, the kinematics of the high-mass star forming ridge DR21 and its surrounding gas are studied to compare low- and high-mass star formation. This shows a similar spatial and kinematic asymmetry as in Musca, which suggests that DR21 is formed by a giant molecular cloud (GMC) collision. However, it is also found for high-mass star formation in the DR21 cloud that gravity plays an important role on large scales (> 1 pc) while for Musca gravity only starts to dominate locally (r < 0.1-0.2 pc). So, due to the high density in the DR21 cloud after the GMC collision, gravity eventually drives the evolution of the compressed cloud for high-mass star forming regions. Kinematic observations of the full Cygnus-X north region show further indications of two interacting velocity components over the entire region, which indicates that a high-velocity (> 10 km/s) GMC collision can result in the formation of an OB association similar to OB2. These OB stars then form in gravitationally collapsing hubs and ridges due to the compression by the GMC collision

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