This thesis is a study of massive star formation: the environments in which they form and the effect that their radiation feedback has on their environments. We present high-performance supercomputer simulations of massive star formation inside molecular cloud clumps and cores. First, we present a novel radiative transfer code that hybridizes two previous approaches to radiative transfer (raytracing and flux-limited diffusion) and implements it in a Cartesian grid-based code with adaptive mesh refinement, representing the first of such implementations. This hybrid radiative transfer code allows for more accurate calculations of the radiation pressure and irradiated gas temperature that are the hallmark of massive star formation and which threaten to limit the mass which stars can ultimately obtain. Next, we apply this hybrid radiative transfer code in simulations of massive protostellar cores. We simulate their gravitational collapse and the formation of a massive protostar surrounded by a Keplerian accretion disk. These disks become gravitationally unstable, increasing the accretion rate onto the star, but do not fragment to form additional stars. We demonstrate that massive stars accrete material predominantly through their circumstellar disks, and via radiation pressure drive large outflow bubbles that appear stable to classic fluid instabilities. Finally, we present simulations of the larger context of star formation: turbulent, magnetised, filamentary cloud clumps. We study the magnetic field geometry and accretion flows. We find that in clouds where the turbulent and magnetic energies are approximately equal, the gravitational energy must dominate the kinetic energy for there to be a coherent magnetic field structure. Star cluster formation takes place inside the primary filament and the photoionisation feedback from a single massive star drives the creation of a bubble of hot, ionised gas that ultimately engulfs the star cluster and destroys the filament. / Thesis / Doctor of Philosophy (PhD)

京都大学 / 新制・課程博士 / 博士(理学) / 甲第24420号 / 理博第4919号 / 新制||理||1703(附属図書館) / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 前田 啓一, 講師 LEE Shiu Hang, 教授 太田 耕司 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

Tracing the element enrichment in the Universe requires to understand the element production in stellar models which is not well understood, in particular at low metallicity. In this thesis a variety of nucleosynthesis processes in stellar models across initial masses and metallicities is investigated and their relevance for chemical evolution explored. Stellar nucleosynthesis is investigated in asymptotic giant branch (AGB) models and massive star models with initial masses between 1 M⊙ and 25 M⊙ for metal fractions of Z = 0.02, 0.01, 0.006, 0.001, 0.0001. A yield grid with elements from H to Bi is calculated. It serves as an input for chemical evolution simulations. AGB models are computed towards the end of the AGB phase and massive star models are calculated until core collapse followed by explosive core-collapse nucleosynthesis. The simulations include convective boundary mixing in all AGB star models and feature efficient hot-bottom burning and hot dredge-up in AGB models as well the predictions of both heavy elements and CNO species under hot-bottom burning conditions. H-ingestion events in the low-mass low-Z AGB model with initial mass of 1M⊙ at Z = 0.0001 result in the production of large amounts of heavy elements. In super-AGB models H ingestion could potentially lead to the intermediate neutron-capture process. To model the chemical enrichment and feedback of simple stellar populations in hydrodynamic simulations and semi-analytic models of galaxy formation the SYGMA module is created and its functionality is verified through a comparison with a widely adopted code. A comparison of ejecta of simple stellar populations based on yields of this work with a commonly adopted yield set shows up to a factor of 3.5 and 4.8 less C and N enrichment from AGB stars at low metallicity which is attributed to complete stellar models, the modeling of the AGB stage and hot-bottom burning in super- AGB stars. Analysis of two different core-collapse supernova fallback prescriptions show that the total amount of Fe enrichment by massive stars differs by up to two at Z = 0.02. Insights into the chemical evolution at very low metallicity as motivated by the observations of extremely metal poor stars require to understand the H-ingestion events common in stellar models of low metallicity. The occurrence of H ingestion events in super-AGB stars is investigated and identified as a possible site for the production of heavy elements through the intermediate neutron capture process. The peculiar abundance of some C-Enhanced Metal Poor stars are explained with simple models of the intermediate neutron capture process. Initial efforts to model this heavy element production in 3D hydrodynamic simulations are presented. For the first time the nucleosynthesis of interacting convective O and C shells in massive star models is investigated in detail. 1D calculations based on input from 3D hydrodynamic simulations of the O shell show that such interactions can boost the production of odd-Z elements P, Cl, K and Sc if large entrainment rates associated with O-C shell merger are assumed. Such shell merger lead in stellar evolution models to overproduction factors beyond 1 dex and p-process overproduction factors above 1 dex for 130,132Ba and heavier isotopes. Chemical evolution models are able to reproduce the Galactic abundance trends of these odd-Z elements if O-C shell merger occur in more than 50% of all massive stars. / Graduate

Nesta tese é apresentado um catálogo fotométrico no infravermelho próximo de 35 Regiões HII, todas pertencentes ao disco Galáctico. Esta faixa espectral é útil uma vez que os comprimentos de onda são grandes o suficiente para se ter uma baixa extinção interestelar comparada ao visível, e são pequenos o suficiente para diagnosticar as fotosferas estelares. Foram obtidas imagens nas bandas J, H e K e imagens do Spitzer nos canais de 3,5, 5,8 e 8,0 m. Após a fotometria nas imagens JHK, foi possível construir diagramas cor-cor e cor-magnitude. Foram utilizadas imagens coloridas, compostas de uma combinação RGB das imagens nas três bandas, tanto para as imagens JHK quanto para as imagens do Spitzer. Estas imagens, junto com os diagramas, foram utilizadas para levantar candidatos a fontes ionizantes das regiões HII, assim como objetos ainda em estágios primordiais de evolução (CTTs e MYSOs). Estes dados também foram utilizados para associar à cada região HII um estágio evolutivo (de A até D, da região mais jovem à mais evoluída). Baseado na posição da Sequência Principal em diagramas cor-magnitude, foi possível comparar as distâncias cinemáticas com nossos dados. Além disso, quando possível, foram utilizadas distâncias de regiões HII determinadas por paralaxe espectrofotométrica (disponíveis na literatura) e utilizando duas leis de extinção interestelar extremas mostrou-se que estas distâncias são menores que suas contrapartidas cinemáticas, e estão em acordo com distâncias determinadas por outros métodos, como por paralaxe trigonométrica. Sabendo que estas regiões de formação estelar seguem a dinâmica do gás, o mapeamento da distribuição destas regiões permite checar a estrutura espiral da Via Láctea. / In this work, a near infrared photometric catalog of 35 HII regions that belongs to the Galactic plane is presented. This spectral range is useful since the wavelengths are long enough to have less influence of the interstellar extinction compared to the visible domain, and they are small enough to still show stellar photospheric features. Images of these HII regions in the J, H and K-band together with IRAC-Spitzer images (channels 4.5, 5.8 and 8.0 m) were used. After the photometry in the JHK images, color-color and color-magnitude diagrams were constructed. These two group of images (JHK and 4.5, 5.8 and 8.0 m) colored in a RGB combination were used, together with the diagrams, to identify the ionizing sources candidates, as well as objects still embedded in their natal cocoon (CTTs and MYSOs). An evolutionary stage to these regions (from A to D, from the younger region to the more evolved) was inferred based on the images and diagrams. These diagrams were also used to infer if the kinematic distance is correct, based on the Main Sequence location. Non-kinematic distances to several HII regions, when it was possible, were collected from the literature. Using two extreme interstellar extinction laws, it was possible to compare these distances with the kinematic results. These non-kinematic distances are lower than that from kinematic techniques. Also, these distance discrepancies are in agreement with distances derived by others methodologies, as trigonometric parallax. Since these star forming regions follow the gas dynamics, mapping their distribution along the Galaxy allows to check the spiral pattern of the Milky Way.

O mecanismo de formação de estrelas de alta massa é um dos problemas fundamentais em Astrofísica e um dos menos compreendidos. Duas teorias predizem a formação destes objetos, que se formariam via i) colisão de estrelas de baixa massa, ou ii) acreção por disco circunstelar. Atualmente, ambas as teorias carecem de testes observacionais críticos. Não obstante, o número de estrelas de alta massa jovens já identificadas na Galáxia corresponde a uma fração muito menor do que o esperado pela função de massa inicial. Este trabalho apresenta um estudo observacional de candidatos a MYSOs, selecionados a partir do levantamento Red MSX Source. Observações de 376 objetos nos filtros estreitos do H2 em 2.12 mícrons e num contínuo adjacente foram realizadas para identificar jatos moleculares colimados e 296 delas são apresentadas nesse trabalho. As observações do hemisfério Norte foram realizadas com o telescópio CFHT (Havaí) enquanto os objetos do hemisfério Sul, foram observados com o telescópio SOAR (Chile). A análise dos mapas de emissão em H2 permitiu concluir que 150 dos 296 objetos (51%) estão associados a emissões extensas em H2, e 62 delas foram classificadas como emissões polares. A análise da razão de aspecto das estruturas identificadas mostra que as emissões associadas a fontes com maior luminosidade apresentam baixo grau de colimação, tal como sugere o cenário de geração dos jatos a partir de ventos emanados pela pressão de radiação do disco circunstelar. A baixa fração de emissões polares (apenas 21% da amostra) indica que o tempo de vida dessas estruturas devem ser curtos. As evidências observacionais encontradas nesse trabalho corroboram o cenário de acreção via disco circunstelar e invalidam o modelo formação via coalescência de estrelas de baixa massa, que requer ambientes relativamente densos e não é capaz de produzir jatos colimados. / Very few massive stars in early formation stages were clearly identified in our Galaxy. The formation process of these objects is still unclear and two theories predict the formation of massive stars: i) by merging of low mass stars or ii) by an accretion disk. There are no critical observational evidences to choose between them. The lack of observational evidences combined with the small number of known massive stars in formation in our Galaxy does not allow us to choose between these scenarios. We present a near-infrared survey of MYSOs candidates selected from the Red MSX Source survey. Such catalog is based on an accurate revision of distances and luminosities, overcoming the limitations and failures in previous searches of this kind. 376 targets were observed through the H2 narrow-band filter at 2.12 microns and in the continuum to identify collimated molecular jets. 296 targets were successfully processed using the THELI pipeline and are presented. Observations in the Northern Hemisphere were carried at the CFHT telescope (Hawaii) while the Southern targets were observed with the Soar Telescope (Chile). The results show that 150 of the 296 sources display extended H2 emission and 62 of them are polar. The analysis of the aspect ratio of the structures indicates that emissions associated with higher luminosity sources have low degree of collimation. This is in agreement with the scenario of the radiation pressure-driven outflows from the circunstellar discs. The low fraction of sources associated with polar jets (21%) indicates a short timescale of such structures. The observational evidences found on this work support the accretion scenario and show that coalescence of low-mass stars (which may require relatively dense environments and is not expected to produce jet-like structures) is not likely to explain most of the studied MYSOs candidates.

The Chandra and XMM-Newton X-ray telescopes have led to numerous advances in the study and understanding of astrophysical X-ray sources. Particularly important has been the much increased spectral resolution of modern X-ray instrumentation. Wind-broadened emission lines have been spectroscopically resolved for many massive stars. This contribution reviews approaches to the modeling of X-ray emission line profile shapes from single stars, including smooth winds, winds with clumping, optically thin versus thick lines, and the effect of a radius-dependent photoabsorption coefficient.

Stellar winds play an important role for the evolution of massive stars and their cosmic environment. Multiple lines of evidence, coming from spectroscopy, polarimetry, variability, stellar ejecta, and hydrodynamic modeling, suggest that stellar winds are non-stationary and inhomogeneous. This is referred to as 'wind clumping'. The urgent need to understand this phenomenon is boosted by its far-reaching implications. Most importantly, all techniques to derive empirical mass-loss rates are more or less corrupted by wind clumping. Consequently, mass-loss rates are extremely uncertain. Within their range of uncertainty, completely different scenarios for the evolution of massive stars are obtained. Settling these questions for Galactic OB, LBV and Wolf-Rayet stars is prerequisite to understanding stellar clusters and galaxies, or predicting the properties of first-generation stars. In order to develop a consistent picture and understanding of clumped stellar winds, an international workshop on 'Clumping in Hot Star Winds' was held in Potsdam, Germany, from 18. - 22. June 2007. About 60 participants, comprising almost all leading experts in the field, gathered for one week of extensive exchange and discussion. The Scientific Organizing Committee (SOC) included John Brown (Glasgow), Joseph Cassinelli (Madison), Paul Crowther (Sheffield), Alex Fullerton (Baltimore), Wolf-Rainer Hamann (Potsdam, chair), Anthony Moffat (Montreal), Stan Owocki (Newark), and Joachim Puls (Munich). These proceedings contain the invited and contributed talks presented at the workshop, and document the extensive discussions.

The presented thesis describes the observations of the Galactic center Quintuplet cluster, the spectral analysis of the cluster Wolf-Rayet stars of the nitrogen sequence to determine their fundamental stellar parameters, and discusses the obtained results in a general context. The Quintuplet cluster was discovered in one of the first infrared surveys of the Galactic center region (Okuda et al. 1987, 1989) and was observed for this project with the ESO-VLT near-infrared integral field instrument SINFONI-SPIFFI. The subsequent data reduction was performed in parts with a self-written pipeline to obtain flux-calibrated spectra of all objects detected in the imaged field of view. First results of the observation were compiled and published in a spectral catalog of 160 flux-calibrated $K$-band spectra in the range of 1.95 to 2.45,$mu$m, containing 85 early-type (OB) stars, 62 late-type (KM) stars, and 13 Wolf-Rayet stars. About 100 of these stars are cataloged for the first time. The main part of the thesis project was concentrated on the analysis of the WR stars of the nitrogen sequence and one further identified emission line star (Of/WN) with tailored Potsdam Wolf-Rayet (PoWR) models for expanding atmospheres (Hamann et al. 1995) that are applied to derive the stellar parameters of these stars. For this purpose, the atomic input data of the PoWR models had to be extended by further line transitions in the near-infrared spectral range to enable adaequate model spectra to be calculated. These models were then fitted to the observed spectra, revealing typical paramters for this class of stars. A significant amount of hydrogen of up to $X_text{H} sim 0.2$ by mass fraction is still present in their stellar atmospheres. The stars are also found to be very luminous ($log{(L/L_odot)} > 6.0$) and show mass-loss rates and wind characteristics typical for radiation-driven winds. By comparison with stellar evolutionary models (Meynet & Maeder 2003a; Langer et al. 1994), the initial masses were estimated and indicate that the Quintuplet WN stars are descendants from the most massive O stars with $M_text{init} > 60 M_odot$ and their ages correspond to a cluster age of 3-5,million years. The analysis of the individual WN stars revealed an average extinction of $A_K =3.1 pm 0.5$,mag ($A_V = 27 pm 4$) towards the Quintuplet cluster. This extinction was applied to derive the stellar luminosities of the remaining early-type and late-type stars in the catalog and a Hertzsprung-Russell diagram could be compiled. Surprisingly, two stellar populations are found, a group of main sequence OB stars and a group of evolved late-type stars, i.e. red supergiants (RSG). The main sequence stars indicate a cluster age of 4 million years, which would be too young for red supergiants to be already present. A star formation event lasting for a few million years might possibly explain the Quintuplet's population and the cluster would still be considered coeval. However, the unexpected and simultaneous presence of red supergiants and Wolf-Rayet stars in the cluster points out that the details of star formation and cluster evolution are not yet well understood for the Quintuplet cluster. / Die vorgelegte Arbeit befasst sich mit der Spektralanalyse der massereichen Sterne, speziell der Wolf-Rayet Sterne der Stickstoffsequenz, des Quintuplet-Sternhaufens im Galaktischen Zentrum, welches durch Staubwolken vor visuellen Beobachtungen verborgen ist. Der Sternhaufen wurde in einer der ersten Infrarot-Durchmusterungen entdeckt (Okuda et al. 1987, 1989) und f"ur dieses Projekt mit dem Grossteleskop ESO-VLT und dem Infrarotinstrument SINFONI-SPIFFI beobachtet. Die Daten wurden aufbereitet und die flusskalibrierten Spektren in einem Katalog ver"offentlicht. Darin enthalten sind 85 Sterne fr"uhen Spektraltyps (O- und B-Sterne), 62 Sterne sp"aten Spektraltyps (K- und M-Sterne), sowie 13 Wolf-Rayet Sterne. Etwa 100 Sterne sind zum ersten mal detektiert und katalogisiert worden. Die flusskalibrierten Spektren der Wolf-Rayet Sterne der Stickstoffsequenz (WN) wurden mit den Potsdam Wolf-Rayet Modellen f"ur expandierende Sternatmosph"aren (Hamann et al. 1995) untersucht, wozu zun"achst Atomdaten der Modelle f"ur den Infrarotbereich erg"anzt werden mussten. Verschiedene Modellspektren und -energieverteilungen wurden mit den Beobachtungen verglichen, um die Sternparameter Temperatur, Radius, Leuchtkraft und die Charakteristik des Sternwinds Geschwindigkeit, chemische Zusammensetzung und Massenverlustrate zu bestimmen. Der ermittelte hohe Wasserstoffgehalt der Winde der WN-Sterne zeigt, dass sie Abk"ommlinge von massereichen O-Sternen sind, die die Hauptreihe verlassen haben. Desweiteren sind die Sterne sehr leuchtkr"aftig ($log(L/L_odot) > 6$) und zeigen Massenverlustraten, die typisch sind f"ur strahlungsgetriebenen Sternwinde. Im Vergleich mit Sternentwicklungsmodellen (Meynet & Maeder 2003a; Langer et al. 1994) ergeben sich Anfangsmassen von $M_text{init}>60,M_odot$, sowie ungef"ahre Sternalter von 3-5 Millionen Jahren f"ur die WN-Sterne, was dem angenommenen Altern des Quintuplet-Haufens entspricht. Durch die Analyse der spektralen Energieverteilungen der einzelnen WN-Sterne konnte eine mittlere interstellare Extinktion von $A_K =3.1 pm 0.5$,mag ($A_V = 27 pm 4$,mag) in der Richtung des Quintuplet-Haufens ermittelt und f"ur die Bestimmung der Leuchtkr"afte der verbleibenden Sterne des Katalog verwendet werden. Die anschliess ende vorl"aufige Analyse ergab eine Dichotomie der Sternpopulation von fr"uhen und sp"aten Sternen im Hertzsprung-Russell-Diagramm. W"ahrend die OB-Sterne entsprechend der Entwicklungstheorie auf der Hauptreihe des Haufens liegen, befinden sich die KM-Sterne im entwickelten Stadium der Roten Riesen, welches f"ur Sterne diesen Typs fr"uhestens nach 7 Millionen Jahren erwartet wird. Somit steht die zeitgleiche Entstehung aller Sterne des Sternhaufens in Frage. Sie wird im Rahmen von Haufenzugeh"origkeit und einer Phase ausgedehnter Sternentstehung diskutiert. Es bleibt anzuerkennen, dass die Sternentstehung und -entwicklung auch im speziellen Fall des Quintuplet-Haufens noch nicht hinreichend gut verstanden sind.

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

O mecanismo de formação de estrelas de alta massa é um dos problemas fundamentais em Astrofísica e um dos menos compreendidos. Duas teorias predizem a formação destes objetos, que se formariam via i) colisão de estrelas de baixa massa, ou ii) acreção por disco circunstelar. Atualmente, ambas as teorias carecem de testes observacionais críticos. Não obstante, o número de estrelas de alta massa jovens já identificadas na Galáxia corresponde a uma fração muito menor do que o esperado pela função de massa inicial. Este trabalho apresenta um estudo observacional de candidatos a MYSOs, selecionados a partir do levantamento Red MSX Source. Observações de 376 objetos nos filtros estreitos do H2 em 2.12 mícrons e num contínuo adjacente foram realizadas para identificar jatos moleculares colimados e 296 delas são apresentadas nesse trabalho. As observações do hemisfério Norte foram realizadas com o telescópio CFHT (Havaí) enquanto os objetos do hemisfério Sul, foram observados com o telescópio SOAR (Chile). A análise dos mapas de emissão em H2 permitiu concluir que 150 dos 296 objetos (51%) estão associados a emissões extensas em H2, e 62 delas foram classificadas como emissões polares. A análise da razão de aspecto das estruturas identificadas mostra que as emissões associadas a fontes com maior luminosidade apresentam baixo grau de colimação, tal como sugere o cenário de geração dos jatos a partir de ventos emanados pela pressão de radiação do disco circunstelar. A baixa fração de emissões polares (apenas 21% da amostra) indica que o tempo de vida dessas estruturas devem ser curtos. As evidências observacionais encontradas nesse trabalho corroboram o cenário de acreção via disco circunstelar e invalidam o modelo formação via coalescência de estrelas de baixa massa, que requer ambientes relativamente densos e não é capaz de produzir jatos colimados. / Very few massive stars in early formation stages were clearly identified in our Galaxy. The formation process of these objects is still unclear and two theories predict the formation of massive stars: i) by merging of low mass stars or ii) by an accretion disk. There are no critical observational evidences to choose between them. The lack of observational evidences combined with the small number of known massive stars in formation in our Galaxy does not allow us to choose between these scenarios. We present a near-infrared survey of MYSOs candidates selected from the Red MSX Source survey. Such catalog is based on an accurate revision of distances and luminosities, overcoming the limitations and failures in previous searches of this kind. 376 targets were observed through the H2 narrow-band filter at 2.12 microns and in the continuum to identify collimated molecular jets. 296 targets were successfully processed using the THELI pipeline and are presented. Observations in the Northern Hemisphere were carried at the CFHT telescope (Hawaii) while the Southern targets were observed with the Soar Telescope (Chile). The results show that 150 of the 296 sources display extended H2 emission and 62 of them are polar. The analysis of the aspect ratio of the structures indicates that emissions associated with higher luminosity sources have low degree of collimation. This is in agreement with the scenario of the radiation pressure-driven outflows from the circunstellar discs. The low fraction of sources associated with polar jets (21%) indicates a short timescale of such structures. The observational evidences found on this work support the accretion scenario and show that coalescence of low-mass stars (which may require relatively dense environments and is not expected to produce jet-like structures) is not likely to explain most of the studied MYSOs candidates.