Heidelberg, Universiẗat, Diss., 2001.

The strong mass loss of Luminous Blue Variables (LBVs) is thought to play a critical role in massive-star evolution, but their place in the evolutionary sequence remains debated. A key to understanding their peculiar instability is their high observed luminosities, which often depends on uncertain distances. Here we report direct distances and space motions of four canonical Milky Way LBVs-AG Car, HR. Car, HD. 168607, and (candidate) Hen. 3-519-from the Gaia first data release. Whereas the distances of HR. Car and HD. 168607 are consistent with previous literature estimates within the considerable uncertainties, Hen. 3-519 and AG Car, both at similar to 2 kpc, are much closer than the 6-8 kpc distances previously assumed. As a result, Hen. 3-519 moves far from the locus of LBVs on the Hertzsprung-Russell diagram, making it a much less luminous object. For AG Car, considered a defining example of a classical LBV, its lower luminosity would also move it off the S Dor instability strip. Lower luminosities allow both AG Car and Hen. 3-519 to have passed through a previous red supergiant phase, lower the mass estimates for their shell nebulae, and imply that binary evolution is needed to account for their peculiarities. These results may also impact our understanding of LBVs as potential supernova progenitors and their isolated environments. Improved distances will be provided in the Gaia second data release, which will include additional LBVs. AG Car and Hen. 3-519 hint that this new information may alter our traditional view of LBVs.

Three γ Doradus-type stars are analysed: HD139095, HD153580, and HD197541. Long-term observation campaigns have been conducted on each star, with over 300 spectra of each star being gathered for analysis using the HERCULES spectrograph at Mount John University Observatory. For each star, cross-correlation techniques were used to obtain representative line profiles for each spectrum. The analysis of these line profiles has resulted in frequency and pulsation mode identifications for these three stars. Abundance analysis has also been performed on HD139095 and HD197541, and their fundamental parameters are confirmed as being consistent with the γ Doradus class of stars. HD153580 and HD197541, previously only candidates for the class, can now be classified as bona fide γ Doradus type stars. The frequencies and modes identified in this thesis will be very useful in constraining future theoretical models, allowing us to better understand and model the interiors of γ Doradus stars.

Magíster en Ciencias de la Ingeniería, Mención Eléctrica. Ingeniero Civil Eléctrico. / Los sistemas cuasi-periódicos han sido estudiados en el contexto de sistemas dinámicos, como también en diversas áreas en las cuáles estos fenómenos son observables. Tal es el caso de la astronomía. El caso de estudio presentado en este trabajo corresponde a las estrellas Gamma Doradus, las que debido a sus características físicas poseen entre 1 a 5 períodos principales de pulsación, otorgándoles características periódicas y cuasi-periódicas al ser observadas en el espectro visible. En el estudio de estas estrellas, la correcta determinación de sus periodos y de la distancia entre ellos es de vital importancia, debido a que se relacionan con sus parámetros físicos, los cuales pueden llegar a ser inferidos. Por tal motivo se espera que estos modelos ayuden en la tarea de caracterización de la pulsación, mediante la descomposición de una curva de luz en señales de menor complejidad. La presente tesis se enfoca a la modelación y análisis de curvas de luz de estrellas Gamma Doradus mediante modelos de Neuropercolación. Neuropercolación es una familia de modelos estocásticos basados en la teoría de Autómata Celular Probabilístico en grillas y grafos aleatorios, inspirados en la dinámica de poblaciones neuronales. Estos modelos pueden ser utilizados para construir series de tiempo discretas, cuyos parámetros son las probabilidades que definen su dinámica. Se propone obtener tales parámetros para modelar una serie de tiempo mediante Optimización por Enjambre de Partículas (PSO), un método evolutivo de optimización basado en poblaciones. La metodología propuesta se aplicó tanto en señales sintéticas como a curvas de luz reales de estrellas Gamma Doradus. Dentro de la señales sintéticas se estudió la capacidad de modelación de una señal de Amplitud Modulada, tanto en presencia de datos perdidos como de ruido blanco aditivo en distintos niveles. Para todos los casos se obtuvieron modelos representativos de la dinámica del proceso. Posteriormente, con modelos de estrellas Gamma Doradus se observa que, con ciertos modelos, es posible recuperar todas la base de frecuencias con la que se construyen las curvas de luz. Esto entrega ventajas comparativas con la búsqueda de frecuencias directamente sobre la señal, además de mejorar la estimación del espaciamiento entre periodos. Al analizar ese método en curvas de estrellas Gamma Doradus obtenidas por el proyecto Kepler de la NASA es posible observar que si bien los modelos no obtienen ajustes perfectos de Error Cuadrático Medio, algunas de las curvas si llegan a ser modeladas con una alta precisión y bajos residuos. Otros casos, en señales con mayores componentes espectrales, la modelación no obtiene tan buenos resultados, y los residuos, aún en los mejores casos, presentan estructuras que podrían llegar a ser modeladas. Considerando la variabilidad intrínseca de resultados debido a la aleatoriedad de PSO y sus poblaciones iniciales, se concluye que es posible obtener modelos de señales cuasi-periódicas con gran exactitud, obteniendo las frecuencias principales del fenómeno. En los casos de modelos con menor ajuste la presencia de óptimos locales dificulta la convergencia hacia el óptimo global. Para los casos de estudio donde los errores fueron más altos, es posible que una mayor cantidad de datos ayude a la obtención de mejores modelos. Este trabajo presenta muchas opciones de extensiones, tales como la disminución de los tiempos de cómputo, mejoras del proceso de optimización, potencialidades en interpolación y predicción, y uso en series de tiempo con muestreos no-uniformes.

Gravity modes present in gamma Doradus stars probe the deep stellar interiors and are thus of particular interest in asteroseismology. Mode identification will improve the knowledge of these stars considerably and allow an understanding of the issues with current pulsational models. The methods used in this thesis are also applied to a low degree pressure mode pulsator as a check for their validity. A frequency analysis followed by a mode identification were done based on the high resolution spectroscopic data of one β Cephei star, PT Puppis, and two γ Doradus stars, HD 189631 and AC Lepus. Extensive spectroscopic data sets are obtained by three instruments: HARPS, FEROS and HERCULES. We obtained 161 spectra for PT Puppis, 422 spectra for HD 189631 and 248 spectra for AC Lepus. The pulsational frequencies were determined by four methods: analysis of the variations in equivalent width, radial velocity, asymmetry of the line profile and by using the pixel-by-pixel frequency analysis. The mode identification was done using the recently developed Fourier Parameter Fit method. Without achieving the same degree of confidence for all results, we report the identification of two pulsational modes in PT Puppis: (l = 0 ; m = 0) at f₁ = 6.07 d⁻¹ and (2 ; 0) or (1 ; +1) at f₂ = 5.99 d⁻¹, four modes in HD 189631: (1 ; +1) at f₁ = 1.67 d⁻¹, (3 ; -2) at f₂ = 1.42 d⁻¹, (2 ; -2) at f₃ = 0.07 d⁻¹ and (4 ; +1) at f₄ = 1.82 d⁻¹ and two modes in AC Lepus: (2 ; -1) at f₁ = 0.75 d⁻¹ and (3 ; -3) at f₂ = 1.09 d⁻¹. This study provides the first pulsational analysis based on spectroscopy of PT Puppis, HD 189631 and AC Lepus. We discuss the performance of current methods of analysis, outline the difficulties presented by γ Doradus stars, and compare our results with other published pulsational mode identifications.

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

This thesis has analysed spectroscopic data for three stars in detail, the β Cephei star V2052 Ophiuchus, the γ Doradus star QW Puppis and the γ Doradus candidate star HD139095. Twelve other candidate γ Doradus stars have had their Vrotsin i, binary status and, where possible, the presence of line profile variation determined. A new technique utilising scaled delta functions has been developed to allow the extraction of a single, high S/N line profile from a high resolution and large wavelength range spectrum. This procedure has performed well in the γ Doradus stars examined. The application of the new mode identification technique, the Fourier Parameter Fit method, to the three stars examined in detail has been very successful. For each of the three stars constraints have been placed on the degree (l) and the azimuthal order (m) of the non-radial pulsation modes detected.

We present a spectral analysis of the spectrum from the Hubble Space Telescope Cosmic Origins Spectrograph (HST/COS) of the southern VY Scl nova-like variable BB Doradus, obtained as part of a Cycle 20 HST/COS survey of accreting white dwarfs (WDs) in cataclysmic variables. BB Dor was observed with COS during an intermediate state with a low mass accretion rate, thereby allowing an estimate of the WD temperature. The results of our spectral analysis show that the WD is a significant far-ultraviolet (FUV) component of the spectrum with a temperature of about 35,000-50,000 K, assuming a WD mass of 0.80 M-circle dot (log(g) = 8.4). The disk, with a mass accretion rate of approximate to 10(-10) M-circle dot yr(-1), contributes about 1/5 to 1/2 of the FUV flux.

We present the modes identified for frequencies found in spectroscopic observations of the Doradus stars HD 189631, QW Puppis, and IR Draconis. A cross-correlation tech- nique was used to create mean line profiles for HD 189631. Four frequencies and modes were identified for this star: 1.6774±0.0002 d⁻¹, 1.4174±0.0002 d⁻¹, 0.0714±0.0002 d⁻¹, and 1.8228 ± 0.0002 d⁻¹ which were identified with the modes (l,m) = (1, +1), (1, +1), (2,−2), and (1, +1) respectively. A least-squares deconvolution method was implemented for line profile generation in the study of QW Puppis and IR Draconis. Three frequen- cies were identified for QW Puppis: 0.055972 ± 0.000004 d⁻¹, 0.064846 ± 0.000004, and 5.219398±0.000002 d⁻¹. These frequencies were identified with the modes (l,m) = (1,−1), (4,−1), (4, +1). Two frequencies were identified in spectra of the rapidly rotating star IR Draconis: 0.00515 ± 0.00003 d⁻¹ and 2.35538 ± 0.00004 d⁻¹; which were identified with (l,m) = (1,−1), and (1, +1) modes respectively. These mode identifications will assist in modelling the structure and interior conditions of these main sequence, non-radially pulsating stars.

This thesis has analysed spectroscopic data for three stars in detail, the β Cephei star V2052 Ophiuchus, the γ Doradus star QW Puppis and the γ Doradus candidate star HD139095. Twelve other candidate γ Doradus stars have had their Vrotsin i, binary status and, where possible, the presence of line profile variation determined. A new technique utilising scaled delta functions has been developed to allow the extraction of a single, high S/N line profile from a high resolution and large wavelength range spectrum. This procedure has performed well in the γ Doradus stars examined. The application of the new mode identification technique, the Fourier Parameter Fit method, to the three stars examined in detail has been very successful. For each of the three stars constraints have been placed on the degree (l) and the azimuthal order (m) of the non-radial pulsation modes detected.