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 18 of 18 for “"stellar wind"”.
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Studies of TeV Gamma-Ray Sources in the Hydrogen-Alpha Optical Line
… G18.7-2.2 is helping us to understand the interstellar medium (ISM) in multiple different wavebands (Voisin et al., 2016). G18.7-2.2 is observed in optical H𝛼, and has a spectral intensity ratio of ionised sulphur to H𝛼 [S II] / H𝛼 indicating that it is a SNR. There is a need to look for similar …
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Polarized Bow Shock Nebulae Reveal Features of the Winds and Environments of Massive Stars
… 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 a stellar wind bow shock …
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Gamma-ray bursts with MeerLICHT
… we found that a forward shock model within a stellar wind medium could explain all of our X-ray, optical and radio data, but not our 1.4 GHz upper limits. We suggested that a possible thermal electron population might explain the additional opacity at lower radio frequencies. The subject of …
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Multi-dimensional simulations of bow shocks of massive, high-velocity runaway stars
Stellar bow shocks result from the supersonic collision of stellar winds ejected by runaway stars and the interstellar medium (ISM). Studying their properties provides constraints on mass-loss rates, stellar wind velocities and the properties of the ISM. In this work, we study the formation of bow …
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Post-common-envelope binary central stars of Planetary Nebulae in the OGLE-IV survey
… (PNe) are defined as the ionized shells of circumstellar gas ejected through an intense stellar wind at the end of the star's life. PNe come in different shapes, from spherical to highly complex, non-spherical shapes. Mass loss in AGB stars is presumed as the shaping mechanism but how it results …
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Dust in circumstellar disks
… spatial distribution of dust particles in circumstellar disks. Using millimetre interferometric observations of optically thick disks around T Tauri stars, I provide conclusive evidence for the presence of millimetre- to centimetre-sized dust aggregates. These findings demonstrate that dust grain …
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Multiwavelength behaviour of Cygnus X-3 and related objects
… plasmons, strengthens the case for a dense stellar wind in the Cyg X-3 system. Further radio and sub(mm) observations of Cyg X-3 during outburst confirm previously observed phenomena such as quenched radio emission prior to outburst, and establish the importance of radiation loss mechanisms …
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A study of the long-term behavior of galactic X-ray sources with RXTE
… state. I show that absorption of X-rays by a stellar wind from the companion star can reproduce the observed modulations in the hard state. To explain the low orbital modulation in the soft-state data, a reduction of the wind density during the soft state would be required. In addition, I have …
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Multidimensional diffusive shock acceleration in the Winds from massive stars
Nonthermal radio emission has 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 …
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Mass transfer and accretion in the eccentric neutron-star binary Circinus X-1
… for transfer via Rochelobe overflow and from a stellar wind. I derive theoretical mass accretion profiles and compare them to the observed profile of the X-ray intensity. In order to explore the possible evolutionary history of Circinus X-1, I developed a binaryevolution computer code for a …
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A multi-frequency study of symbiotic stars
… line ratios as a primary indicator of interstellar extinction has been investigated and rejected. Estimates of 5-GHz optical depth, turnover frequency, angular diameter and mass-loss rate are calculated and an extinction-based method of distance determination is discussed. The ionized …
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Hydrogen-deficient central stars of planetary nebulae
… phase of their evolution. Such fluorescent circumstellar gas is called a "Planetary Nebula". About one-tenth of the Galactic central stars are hydrogen-deficient. Generally, the surface of these central stars is a mixture of helium, carbon, and oxygen resulting from partial helium burning. …
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Time Series Analysis of the A0 Supergiant HR 1040
… supergiants, HR 1040 has a highly variable stellar wind including High Velocity Absorption (HVA) events. The star was found to have an active phase with large variation in the physical characteristics of the windand with the potential for HVAs. During the active phase, correlation between …
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Meshless hydrodynamic simulations of young supernova remnants
… of their ejecta with the surrounding circumstellar medium results in the formation of supernova remnants that have been detected at all wavelengths, from radio to gamma-rays. For several dozen supernova remnants, very-long-baseline radio interferometers have spatially resolved the …
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Toward detection and characterization of exoplanetary magnetic fields via low frequency radio observation
… from the planet's ionosphere and/or the solar wind with the planet's magnetic field. The temporal and spectral characteristics and variability of planetary radio emission encode information about a planet's magnetic field strength and morphology, rotation, and interior. This thesis describes …
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Probes of pulsar emission physics: The double pulsar and the gamma-ray pulsar population
… of the symmetry of the beam.;The strong stellar wind produced by the high spin-down luminosity of the first born, recycled, 23 ms pulsar (pulsar A) of the double pulsar system distorts the magnetosphere of its companion pulsar B. The wind-magnetosphere interaction model determines a …
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Extragalactic Novae and Their Progenitors
… companion through Roche lobe overflow or via a stellar wind. As material is accreted, the pressure and temperature at the base of the accreted envelope increase until a thermonuclear runaway occurs. This causes a sudden increase in brightness (the outburst), which ranks among the most luminous …
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Magnetic braking in low-mass stars
… I also touch upon the working of the Cambridge stellar evolution code with which I evolve and model these stellar systems. In Chapter 2, I model the secular evolution of CVs with a double dynamo model wherein there is an interplay between two α-Ω dynamos, one in the convective envelope and the …