Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 53 for “"Massive stars"”.
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Massive stars in low metallicity environments
The evolution of massive stars has been a key field of research for many decades, as it has significant effects on a variety of astrophysical disciplines. Nonetheless, it is still widely uncertain due to a deficit of observational evidence to verify theoretical models. Recent surveys of the galaxy …
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Rotation and magnetism in massive stars
… number of important effects on the evolution of stars. Apart from structural changes because of the centrifugal force, turbulent mixing and meridional circulation can dramatically affect a star's chemical evolution. This leads to changes in the surface temperature and luminosity as well as …
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Massive stars in 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 …
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The Formation Of Massive Stars: A 30 Mo Case Study
… the manner in which a convective core develops. Stars more massive than {dollar}sim{dollar}30 Mo can develop convective cores before the onset of central hydrogen burning. It is estimated that stars more massive than {dollar}sim{dollar}95 Mo will have a convective core throughout the whole of …
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Multidimensional diffusive shock acceleration in the Winds from massive stars
… been seen in the winds around a quarter of all O-stars. The emission is attributed to shock accelerated cosmic rays. The shocks thought to be causing the acceleration are either wind-embedded shocks due to radiative line driving instabilities in the stellar wind, or shocks due to the colliding …
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The Evolution of Massive Stars: The Influence of Initial Composition and Mass Loss
… the evolution of 15, 30, and 40 M(,(CIRCLE)) stars with compositions Y = 0.28 and Z = 0.02, 0.01, 0.001 and 0.0002, and of 50 M(,(CIRCLE)) stars with Y = 0.28, Z = 0.0002. These models have been evolved through core helium burning up to the point of carbon ignition. All models were evolved …
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Polarized Bow Shock Nebulae Reveal Features of the Winds and Environments of Massive Stars
<p>Massive stars strongly affect their surroundings through their energetic stellar winds during their lifetime and through their energetic deaths as supernovae. When a stellar wind interacts with the local interstellar medium (ISM), if the relative velocity between wind and ISM is supersonic, then …
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Study of supernovae and massive stars and prospects with the 4m International Liquid Mirror Telescope
Massive stars are the progenitors of the most energetic explosions in the Universe such as core-collapse supernovae (CCSNe) and gamma ray bursts. During their life time they follow various evolutionary phases (e.g. supergiant, luminous blue variable and Wolf-Rayet). They strongly influence their …
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Comprehensive analyses of massive binaries and implications on stellar evolution
… stellar winds, and supernova explosions, massive stars (Mini & 8 M☉) bear a tremendous impact on galactic evolution. It became clear in recent decades that the majority of massive stars reside in binary systems. This thesis sets as a goal to quantify the impact of binarity (i.e., the …
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Exploring the Environment of Young Stars: Disks, Companions and Clusters
… FU Ori phenomenon and the formation of massive stars. The main results are the following: 1. By applying the novel method of polarimetric differential imaging and the NACO/VLT instrument we probe one of the closest circumstellar disks in the planet-forming age at scales of our inner …
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The impact of star cluster environments on planet formation
It is thought that most stars, including our Sun, form within clusters alongside many other stars. Planet formation and star formation occur simultaneously, and therefore the birth environment of stars will shape the formation of planets. Properties of the present day Solar System hint to a past in …
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Multi-wavelength study of neutron stars in the Magellanic Clouds
Massive stars are essential drivers of galaxy evolution, as well as the synthesis of heavier elements, enriching the interstellar and intergalactic medium with metals through every cycle of star formation. Thus to understand the evolving universe, it is essential to quantify the formation and …
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Rare Stellar Populations in the Magellanic Clouds: Identification of Super-Asymptotic Giant Branch Star and Yellow Supergiant Binary Candidates
… and characterize multiple new populations of massive stars in rare or elusive phases of stellar evolution---thereby demonstrating the power of large surveys and systematic observation campaigns to constrain models of massive star evolution. First, I investigate the true nature of the peculiar …
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The environmental impact of high- and low-mass stars: from formation to main sequence
… two different physical phenomena associated with stars: (1) the interplay of magnetic fields and collapsing clouds, and (2) the effects of radiation from massive stars. We first compare polarization measurements of 52 Galactic star-forming regions with their locations in the Galaxy. In particular, …
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Nitrogen Abundances in Early-Type Be Stars
A sample of 26 Be stars from the Magnetism in Massive Stars (MiMeS) spectroscopic survey are analyzed for their photospheric nitrogen abundances in an effort to detect rotational mixing in the Be stars. Be stars are massive stars, between 3 and 20 times the mass of the Sun, that are surrounded by a …
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Star Formation in OB Associations and Clusters
… need to be examined. We used the resolved massive stars and young stellar objects (YSOs) in N 44 to study star formation at both levels with extended coverage in space and time. Our study of massive stars showed that the present-day mass functions (PDMFs) of four star formation regions do …
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The influence of stellar birth environment on protoplanetary disc dispersal
… which discs evolving in close proximity to other stars might be truncated and dispersed by their neighbours. These are tidal truncation by star-disc encounters and external photoevaporation due to irradiation by massive stars. I make the distinction between encounters that occur in multiple …
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Dynamics of dense gas-star systems : Black holes and their precursors
… subject, but we set about an analysis on super-massive stars. How these stars could power the quasar activity by star accretion and energy flows is one of the questions that arises. We undertake other questions, such as the uncertain evolution of such an object and its interaction with the …
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Precursors in Gamma-ray Bursts Observed by Fermi
… universe. They come from the core collapses of massive stars and the mergers of compact objects, and are observed as bright flashes of gamma rays (prompt emission) followed by long-lived, fading emission (afterglow) across the electromagnetic spectrum. The instruments on the Fermi Gamma-ray …
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