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.
Results
Showing 1 to 19 of 19 for “"stellar surface"”.
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The solution of two dimensional problems in astrophysics
… companion will heat some of the matter near the stellar surface enough to cause mass ablation to occur. Finally, some of the matter in the supernova shell will stick to the star. The results of this calculation are compared to the results of previous attempts to solve the problem analytically by …
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The magnetospheres of accreting neutron stars
… pressure outside and the pressure of the stellar field inside. We illustrate the way the shape differs for different scalings of confining pressure with radius, and show that cusps form in the polar magnetosphere if the scale of the magnetosphere is much larger than the star's radius. When …
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Exoplanetary system WASP-3 : measurement of the projected spin-orbit angle and evidence for stellar activity
… angle between the planetary orbital axis and the stellar rotation axis, ... degrees. I use the new photometric data to refine the system parameters. Additionally, I present evidence for stellar activity, as the spectra obtained on UT June 19, 2008 reveal an increase in radial velocity to a peak …
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Shear instabilities between accretion disks and nova objects
… novae are thermonuclear explosions on the surface of white dwarfs caused by accretion from a companion star. Most studies focus on modelling the explosive phase (thermonuclear runaway), while this thesis, instead, focuses on the pre-explosion stage, investigating how shear instabilities and …
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Millisecond oscillations during thermonuclear X-ray bursts
… suggest that they originate from patterns in the stellar surface brightness that drift in the direction opposite the rotation of the neutron star, yielding oscillation frequencies lower than that of the spin. The patterns produce oscillations that are very sinusoidal - harmonic components have …
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Hot planetary nebulae nuclei and related objects
… Our approach is to use analyses of nebular and stellar spectral features as diagnostics of the physical conditions that prevail in and around these objects. We obtain stellar magnitudes, Zanstra temperatures, extinction constants, abundances, and other diagnostics. By placing the central stars …
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Disk-magnetosphere interaction in X-ray binaries
… corotation with the neutron star well above the stellar surface. We report the results of a detailed numerical study of the interaction of a slim Keplerian accretion disk with the magnetic field of an aligned rotator. We show that the accretion flow generally exhibits a sonic point because of the …
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Heartbeat Stars and the Ringing of Tidal Pulsations
… area and temperature variations over the stellar surface. In the precise Kepler data, these changes cause a notable variation in the light curve in the form of a tidal pulse. In this work I present novel modelling tools produced specifically to model heartbeat stars. These include the …
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Magnetospheres of neutron stars accreting from disks
… configurations. In one, the disk extends to the stellar surface while in the other, there is a gap between the inner edge of the disk and the surface of the star. The solutions determine the poloidal and toroidal components of the magnetic field as a function of position within the magnetosphere. …
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The star formation and dynamics of nearby galaxies
A scaling relation between the surface density of star formation and gas in the disks of galaxies has become the basis of our understanding of extragalactic star formation on scales of hundreds of parsecs and larger. This is an empirical law but star formation is a complex process - the presence of …
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Star formation and disk stability in nearby galaxies
… Survey Explorer (WISE) were used to derive the stellar disk and star formation properties. In the case of the single-fluid thin gas-disk model, we find that the star forming disks show typical values of 3 - 15, much higher than the theoretical threshold value of 1. The high values can be …
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The Structure and Polarization Properties of the SiO Masers in the Extended Atmosphere of R Aquarii
… the silicate dust formation point close to the surface of the star. Very Long Baseline Interferometry (VLBI) has shown that these masers do indeed lie close to the stellar surface at a distance of a few stellar radii. This extended atmosphere is a complex region dominated by stellar pulsations …
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Unearth: Revealing the Effects of Stellar Activity on Exoplanet Host Stars
… thesis, I investigate the effect activity has on stellar spectra, using HARPS data of the well observed K1 V star α Centauri B. I compare spectra from high- and low-activity periods (as traced by log R′HK) of α Cen B. I produce ‘relative spectra’ by dividing the high-activity spectra by a …
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PROBING THE NATURE OF COMPACT OBJECTS: SCATTERING, TIDES AND QUASINORMAL MODES
… conditions for the metric perturbations at the stellar surface, that are determined by numerically solving the metric- and matter-perturbation equations inside the NS. This allows us to roughly quantify the impact of tidal heating on the GW phase during the inspiral across different equations of …
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Correcting the rotation curve of spiral galaxies for the non-circular motions induced by a bar
… of the azimuthally averaged rotation curve, the stellar surface brightness, and the gas surface density. The parameters posterior distribution functions (PDFs) combine with the disc stability parameters PDFs are used as criterion to select the model parameters. The velocities of the gas particles …
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Understand thy star, understand thy planet
… Earth-analogue planets. However, it is now stellar activity that poses a critical challenge on the pathway to detect habitable Earth-like worlds. This thesis is therefore dedicated to understanding the effect stellar activity has on spectroscopically observed radial-velocity (RV) variations …
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X and UV radiation from accreting non-magnetic degenerate dwarfs
… by the impact of accreting matter with the stellar surface. The resulting X-ray and UV spectrum gives vital clues about the nature of the underlying star and the extreme conditions of temperature and magnetic field strength that may exist in the emission region. While the X-ray spectra of …
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The binary system containing the pulsar PSR 1913+16 and ultra-violet and x-radiation from accreting magnetic white dwarfs
… and is also. a challenge for theories of stellar evolution. However, proposed uses of the system rely on assumptions about the nature of the pulsar's unobserved companion. I discuss ways of determining the nature of the companion from observation of the pulsar. Geometrical constraints on …
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Robotic telescopes & Doppler imaging : measuring differential rotation on long-period active stars
Auf der Sonne sind viele Phänomene zu sehen die mit der solaren magnetischen Aktivität zusammenhängen. Das dafür zuständige Magnetfeld wird durch einen Dynamo erzeugt, der sich vermutlich am Boden der Konvektionszone in der sogenannten Tachocline befindet. Angetrieben wird der Dynamo teils von der …