The detailed observational analysis of three massive B- and O-type stars was carried out in this study in order to characterize their fundamental, magnetic, and variability properties. The bulk of the data acquired were obtained with the high-resolution ESPaDOnS spectropolarimeter at the Canada-France-Hawaii telescope, within the context of the Magnetism in Massive Stars (MiMeS) project. Two of these stars (HR5907 and HD57682) are newly detected magnetic stars, discovered from observations acquired as part of the broader survey component of the MiMeS program, while the last star, ω Ori, was previously reported as magnetic in the literature. The rotation periods of HR5907 and HD57682 were inferred from photometric, Hα emission and longitudinal field variations. A period of 0.508276 was inferred for HR5907, making this the shortest period, non-degenerate, magnetic massive star identified to date. Furthermore, ultraviolet and optical spectroscopy were combined to infer the fundamental properties of HR5907 and HD57682. Direct modelling of the Least-Squares Deconvolved line profiles and the longitudinal magnetic field measurements were used to infer the magnetic properties of HR5907, HD57682, and ω Ori. A detailed investigation of the newly obtained and archival polarimetric data of ω Ori revealed no convincing evidence for a magnetic field, despite evidence of variability in some emission quantities in this dataset, which had been previously attributed to a large-scale magnetic field. The strength and variability of the optical photospheric helium lines of HR5907 suggests that this star is He-rich, with a non-uniform distribution of its surface chemistry. Lastly, the emission variations in the hydrogen lines of HR5907 suggest this star hosts a highly-structured, rigidly-rotating, centrifugally supported magnetosphere. Similarly, line profile variations throughout the optical spectrum of HD57682 are attributed to emission variations caused by a rotationally-modulated, dynamical magnetosphere. As magnetism in massive stars is a relatively rare and poorly-studied phenomenon, these studies comprise the bulk of the detailed investigations of magnetic massive stars carried out to date. The results of these investigations are also discussed in the context of addressing the current outstanding issues related to magnetism in massive stars. / Thesis (Ph.D, Physics, Engineering Physics and Astronomy) -- Queen's University, 2012-09-28 17:22:35.115

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Nesta tese foi feito um estudo dos eventos cíclicos em Carinae em diversas faixas espectrais. A presença de um buraco na região polar do Homúnculo foi confirmada pelos mapas de velocidade da linha do [Fe II] 12567. A componente em emissão da linha do He I 10830, detectada na linha de visada do lóbulo NW e que apresenta velocidades negativas, foi mapeada e está contida no plano equatorial. Foi observado que durante um período de 206 dias, centrado na fase zero, a linha do He I 10830 apresenta um aumento na velocidade máxima da componente em absorção, atingindo 1800 km/s. Tal comportamento favorece orientações orbitais onde a passagem pelo periastro ocorre próximo à oposição. O Pequeno Homúnculo apresenta a mesma distribuição espacial da emissão em rádio e, considerando que esta seja proveniente principalmente da secundária, o fluxo de fótons no contínuo de Lyman é compatível com uma estrela de tipo espectral O5.5O7. A variabilidade das componentes largas e estreitas das linhas em diversas faixas espectrais apresenta um período bem definido (2022.1±0.6 dias) e extremamente estável ao longo dos últimos 60 anos, sendo que as variações observadas no período são devido aos erros nas medidas. Utilizando a componente estreita da linha do He I 6678 foi possível determinar a fase zero do ciclo #11 (T0=2452819.8). Os eventos espectroscópicos são compostos de dois regimes: um de variações lentas e outro de colapso. A primeira é revelada por variações lentas no nível de ionização do meio circunstelar ao longo de todo o ciclo e está associada a variações graduais no cone de choque dos ventos (abertura angular e conteúdo). O regime de colapso é observado ao redor do mínimo e é causado por um colapso temporário do cone de choque. Os fenômenos de alta energia são sensíveis somente ao regime de colapso, enquanto os de baixa energia, ao de variação lenta. Os fenômenos que envolvem energias intermediárias, respondem aos dois regimes. Foi observado uma anti-correlação entre a linha do Fe II 6455 e a do He I 7065, indicando que a primeira é formada nas regiões mais externas do vento da primária e a segunda, na secundária ou no cone de choque dos ventos. A curva de luz do He II 4686 apresenta dois picos antes da fase zero e outro logo após. Os dois picos antes do mínimo apresentam uma correlação com os picos na faixa dos raios-X, porém estes ocorrem 16.5 dias antes daqueles. O mecanismo mais provável para explicar a luminosidade observada do He II 4686 é a produção de fótons com 1215 Å através do fluxo de fótons na faixa do ultra-violeta extremo/raios-X moles produzidos na região próxima ao ápex do cone de colisão dos ventos. Como este mecanismo é extremamente sensível à densidade do meio, a região mais favorável para produzir a luminosidade observada do He II 4686 é a região do cone de choque voltada para a primária. / In this thesis, a multi-wavelength study on the cyclic events of Eta Carinae was performed. The presence of a hole in the polar region of the Homunculus was confirmed by the velocity maps of the [Fe II] 12567 line. The blue-shifted component of the He I 10830, detected towards the NW lobe, was mapped and it is in the equatorial plane. It was observed that within a short period of 206 days, centered on phase zero, the He I 10830 line shows an increase in the maximum velocity of the absorption component, which reaches up to -1800 km/s. Such behavior favors orbital orientation with periastron passage around oposition. The Little Homunculus shows the same spatial distribution as the radio emission and considering that the radio flux comes mainly from the secondary, then the photon flux in the Lyman continuum is comparable to a star with spectral type in the range O5.5-O7. The variability of the narrow and broad lines from many spectral regions shows a well-defined period (2022.1+/-0.6 days), which is also extremely stable along the last 60 years, during which the observed variations in the period are due to measurement errors. Using the narrow component of the He I 6678 it was possible to determine the phase zero of the cycle #11 (T_0=2452819.8). The spectroscopic events are a combination of two components: slow variation and collapse. The former is revealed by slow changes in the ionization level of circunstellar matter across the whole cycle and is associated to gradual changes in the wind-wind collision shock-cone (angular opening and gaseous content). The collapse component is restricted to around the minimum and is caused by a temporary collapse of the wind-wind collision shock. High-energy phenomena are sensitive only to the collapse component, while low-energy only to the slow variation component. Intermediate-energy phenomena are sensitive to both components. It was observed an anti-correlation between the Fe II 6455 and He II 7065, suggesting that the former is formed in the outer parts of the primary\'s wind, while the latter is associated to the secondary or to the wind-wind shock cone. The lightcurve of He II 4686 shows two peaks before phase zero and another one short after it. The two peaks before phase zero are correlated to the peaks seen in the X-rays. However, the X-ray peaks occur 16.5 days before those seen in the He II 4686 lightcurve. The most likely mechanism to explain the observed peak luminosity of the He II 4686 is the creation of ~1215 Angstroms photons by the extreme ultra-violet/soft X-rays photons, which are produced near the apex of the wind-wind shock-cone. Since this mechanism is extremely sensitive to the density, the most likely region to form the observed peak luminosity of the He II 4686 is on the primary\'s side of the wind-wind shock-cone.

Many uncertainties remain as to how the most massive stars are formed and how they interact with their environment via radiative and mechanical processes. This feedback may affect future generations of star formation -- triggering it by compressing gas, or hindering it by dispersing reservoirs. These scenarios can be simulated by solving the equations of hydrodynamics and radiative transfer. However, the latter is usually simplified due to its computational expense, despite its importance in determining the dynamics. In this thesis, I describe how I increased the efficiency of the radiation hydrodynamics code, TORUS, which uses a Monte Carlo approach to solving the radiative transfer. Tens of millions of energy packets are propagated through a domain split over hundreds of processors running in parallel with Message Passing Interface (MPI). By re-examining and improving communication algorithms, I lowered the radiation run time by about a factor of ten, making it tractable to run three-dimensional simulations of massive star feedback in clusters. This includes both the stellar and diffuse radiation fields, with multiple atomic species and silicate dust grains. The full ionization states and temperatures can then be fed in to produce self-consistent synthetic observations. I applied this to clouds of 1000 and 10,000 solar masses with surface density 0.01 g/cm^2, containing a 34 solar mass star, with photoionization and radiation pressure feedback. Photoionization is efficient at shaping and dispersing clouds. The expanding ionization front forms dense, spherical knots with pillars pointing away from the emitting star. These resemble the Pillars of Creation in the Eagle Nebula, and the proplyds observed in the Orion Nebula. In the lower-mass model, almost all material is removed from the (15.5 pc)^3 grid within 1.6 Myr; the higher mass cloud is somewhat more resistant, with 25 per cent remaining inside (32.3 pc)^3 after 4.3 Myr. Radiation pressure has a negligible effect, but will be more important for denser clouds or higher luminosities.

This is a spectroscopic and photometric study of suspected close binary systems among the massive stars. The stars studied here include stars with temperatures ranging from 45,000 Kelvin (K) to 15,000 K, corresponding to spectral types ranging from O3 V to B5 III, masses between 47 Solar Masses and 5 Solar Masses, and absolute V magnitudes from -6.28 to -2.0. I categorize 30 targets according to my spectroscopic observations into groups with no radial velocity variability, single-lined, and double-lined variability. My analysis of the 18 constant velocity stars results in estimates of stellar effective temperature, Teff, gravity, log g, projected rotational velocity, v sin i, and spectral classification. Analyzing single-lined systems, I find the same stellar parameters for five more systems, and also present the first orbits for these systems. I also explore the probable characteristics of the unseen companions in these systems. Three double-lined systems, two eclipsing and one with an ellipsoidal variation in the light curve, are fully analyzed, and I present important astrophysical parameters for each of these systems, including stellar masses, radii, ages, and distances to each system. The masses are accurate to 4.3% and 3.6% for the primary and secondary for LH 54-425, 2.1% and 1.6% for HI Mon, and 1.1% and 0.6% for HD 42401. Two more double-lined systems are studied, and preliminary results are presented. Photometric observations are analyzed for 56 targets from the All Sky Automated Survey in order to facilitate spectroscopic observations at key points in the binary orbit where spectral features of both components will be well separated. New spectroscopic observations of these eclipsing binaries with my computed ephemerides will allow us to obtain double-lined orbital elements and determine their masses, radii, ages, and distances. These computed parameters will then allow for comparison with theoretical stellar models, and a better understanding of the evolution of massive stars.

Due to their violent stellar winds, ionising radiation and famous deaths as supernovae, massive stars play a key role in galactic evolution. A complete understanding of these objects has been hindered by both their rarity and by the relatively limited volume of the Universe that is accessible with existing facilities. Addressing the first of these limiting factors, the VLT-FLAMES Tarantula Survey (VFTS) has drawn from the 30 Doradus region an unprecedented sample of over 800 O and B-type stars. The survey is beginning to uncover a wide range of global properties such as the region’s binary fraction of massive stars and their dynamics, whilst also looking in detail at some of its more fascinating objects. This thesis documents the reduction of the VFTS data set, whilst also describing the analysis for one of the serendipitous discoveries: the massive binary R139. This high-mass binary will provide an excellent future calibration point for stellar models, in part as it seems to defy certain expectations about its evolution. Outwith the VFTS, a search for binary companions around a trio of B-type supergiants is presented. These stars are surrounded by nebulae that closely resemble the triple-ring structure associated with the poorly-understood SN1987A. Do these stars share a similar evolutionary fate? While strong evidence is found for periodic pulsations in one of the stars, there appears to be no indication of a short-period binary companion suggested in the literature. Gathering observations from a wide range of environments builds a fuller picture of massive stars, but the samples remain somewhat limited. The coming generation of extremely large telescopes will open new regions for studies like the VFTS. Fully utilising these remarkable telescopes will require many new technologies, and this thesis presents one such development project. For adaptive-optics corrected, multi-object instruments it will be necessary to position small pick-off mirrors in the telescope’s focal plane to select the sub-fields on the sky. This could be most efficiently achieved if the mirrors were self-propelled, which has led to a miniature robot project called MAPS - the Micro Autonomous Positioning System. A number of robots have been built with a footprint of only 30 x 30mm. These wirelessly-controlled robots draw their power from the floor on which they operate and have shown the potential to be positioned to an accuracy of tens of microns. This thesis details much of the early design work and testing of the robots, and also the development of the camera imaging system used to determine the position of the robots. The MAPS project is ongoing and a number of the potential future tests, and avenues for new research, are discussed. This is a thesis that brings together an area of active astronomical research with cutting-edge technological development, highlighting how tomorrow’s telescopes will be an essential tool to answer some of today’s most puzzling research questions

Nesta tese foi feito um estudo dos eventos cíclicos em Carinae em diversas faixas espectrais. A presença de um buraco na região polar do Homúnculo foi confirmada pelos mapas de velocidade da linha do [Fe II] 12567. A componente em emissão da linha do He I 10830, detectada na linha de visada do lóbulo NW e que apresenta velocidades negativas, foi mapeada e está contida no plano equatorial. Foi observado que durante um período de 206 dias, centrado na fase zero, a linha do He I 10830 apresenta um aumento na velocidade máxima da componente em absorção, atingindo 1800 km/s. Tal comportamento favorece orientações orbitais onde a passagem pelo periastro ocorre próximo à oposição. O Pequeno Homúnculo apresenta a mesma distribuição espacial da emissão em rádio e, considerando que esta seja proveniente principalmente da secundária, o fluxo de fótons no contínuo de Lyman é compatível com uma estrela de tipo espectral O5.5O7. A variabilidade das componentes largas e estreitas das linhas em diversas faixas espectrais apresenta um período bem definido (2022.1±0.6 dias) e extremamente estável ao longo dos últimos 60 anos, sendo que as variações observadas no período são devido aos erros nas medidas. Utilizando a componente estreita da linha do He I 6678 foi possível determinar a fase zero do ciclo #11 (T0=2452819.8). Os eventos espectroscópicos são compostos de dois regimes: um de variações lentas e outro de colapso. A primeira é revelada por variações lentas no nível de ionização do meio circunstelar ao longo de todo o ciclo e está associada a variações graduais no cone de choque dos ventos (abertura angular e conteúdo). O regime de colapso é observado ao redor do mínimo e é causado por um colapso temporário do cone de choque. Os fenômenos de alta energia são sensíveis somente ao regime de colapso, enquanto os de baixa energia, ao de variação lenta. Os fenômenos que envolvem energias intermediárias, respondem aos dois regimes. Foi observado uma anti-correlação entre a linha do Fe II 6455 e a do He I 7065, indicando que a primeira é formada nas regiões mais externas do vento da primária e a segunda, na secundária ou no cone de choque dos ventos. A curva de luz do He II 4686 apresenta dois picos antes da fase zero e outro logo após. Os dois picos antes do mínimo apresentam uma correlação com os picos na faixa dos raios-X, porém estes ocorrem 16.5 dias antes daqueles. O mecanismo mais provável para explicar a luminosidade observada do He II 4686 é a produção de fótons com 1215 Å através do fluxo de fótons na faixa do ultra-violeta extremo/raios-X moles produzidos na região próxima ao ápex do cone de colisão dos ventos. Como este mecanismo é extremamente sensível à densidade do meio, a região mais favorável para produzir a luminosidade observada do He II 4686 é a região do cone de choque voltada para a primária. / In this thesis, a multi-wavelength study on the cyclic events of Eta Carinae was performed. The presence of a hole in the polar region of the Homunculus was confirmed by the velocity maps of the [Fe II] 12567 line. The blue-shifted component of the He I 10830, detected towards the NW lobe, was mapped and it is in the equatorial plane. It was observed that within a short period of 206 days, centered on phase zero, the He I 10830 line shows an increase in the maximum velocity of the absorption component, which reaches up to -1800 km/s. Such behavior favors orbital orientation with periastron passage around oposition. The Little Homunculus shows the same spatial distribution as the radio emission and considering that the radio flux comes mainly from the secondary, then the photon flux in the Lyman continuum is comparable to a star with spectral type in the range O5.5-O7. The variability of the narrow and broad lines from many spectral regions shows a well-defined period (2022.1+/-0.6 days), which is also extremely stable along the last 60 years, during which the observed variations in the period are due to measurement errors. Using the narrow component of the He I 6678 it was possible to determine the phase zero of the cycle #11 (T_0=2452819.8). The spectroscopic events are a combination of two components: slow variation and collapse. The former is revealed by slow changes in the ionization level of circunstellar matter across the whole cycle and is associated to gradual changes in the wind-wind collision shock-cone (angular opening and gaseous content). The collapse component is restricted to around the minimum and is caused by a temporary collapse of the wind-wind collision shock. High-energy phenomena are sensitive only to the collapse component, while low-energy only to the slow variation component. Intermediate-energy phenomena are sensitive to both components. It was observed an anti-correlation between the Fe II 6455 and He II 7065, suggesting that the former is formed in the outer parts of the primary\'s wind, while the latter is associated to the secondary or to the wind-wind shock cone. The lightcurve of He II 4686 shows two peaks before phase zero and another one short after it. The two peaks before phase zero are correlated to the peaks seen in the X-rays. However, the X-ray peaks occur 16.5 days before those seen in the He II 4686 lightcurve. The most likely mechanism to explain the observed peak luminosity of the He II 4686 is the creation of ~1215 Angstroms photons by the extreme ultra-violet/soft X-rays photons, which are produced near the apex of the wind-wind shock-cone. Since this mechanism is extremely sensitive to the density, the most likely region to form the observed peak luminosity of the He II 4686 is on the primary\'s side of the wind-wind shock-cone.

This thesis presents both a study of the cluster-scale environments in which massive stars form, investigating in particular how the ionized gas in these regions relates to the molecular star-forming material, as well as detailed studies of two luminous forming stars, AFGL 2591 and IRAS 20126+4104, to determine whether they are forming similarly to their low-mass counterparts. The results of this work include the identification of 35 HII regions (20 newly discovered) via a radio continuum survey of ionized gas towards 31 molecular cluster-forming clumps. The observed ionized gas was found to be preferentially associated with the clumps, which were shown to have a range of evolutionary stages. The massive star formation efficiency was determined for the clumps with associated ionized gas, and a relationship was found between the mass of the clumps and the mass of their embedded massive stars. By modelling the SEDs and images of AFGL 2591 and IRAS 20126+4104, it was found that the geometry of their circumstellar material was generally consistent with an envelope plus disk, similar to that expected for low-mass protostars. However, within the central ~1800 AU, the mid-IR images of IRAS 20126+4104 were better described by only a flattened envelope, suggesting that the radiation from IRAS 20126+4104 may be affecting the regions closest to the star. Observations of the ionized and molecular gas towards AFGL 2591 were carried out, and a photoionization code was developed to interpret these observations. The results showed that the observed 3.6 cm emission is likely to be produced by both a shock-ionized jet and a hypercompact HII region that does not appear to have disrupted the jet or the large-scale circumstellar environment. In addition, the C¹⁸O(1-0) emission observed towards AFGL2591 traces the densest parts of the outflow, with the blue-shifted emission exhibiting many of the properties of the outflows from low-mass protostars.