W Ursae Majoris-type (W UMa-type) variable stars are contact eclipsing binary stars whose evolution is unknown. Modelling to determine the physical parameters of as many W UMa-type variable stars as possible might provide some insight as to how these contact binaries form and evolve. The All Sky Automated Survey (ASAS) has discovered over ve thousand of these systems. Using data from the ASAS and from the Wide Angle Search for Planets (SuperWASP) project, models of selected ASAS contact binaries are being created to determine their physical parameters. Some W UMa-type variable stars are known to undergo changes in orbital period. For selected ASAS contact binaries, a period analysis has been performed using SuperWASP data to determine if the systems are undergoing changes in orbital period. Results of the modelling and period analyses of selected systems are presented. / Thesis (M. Sc. (Astronomy))

We will consider the scenario of the co-rotation of a fluid star (in specific, a neutron star) and a black hole. The neutron star (or primary)is assumed to have constant angular velocity. The tidal effects on the primary are investigated. First, the centrally condensed approximation is applied, where both bodies are considered as point sources. In the second treatment, the primary is treated as an incompressible and homogeneous fluid mass, which in addition to its own gravity is subject to centrifugal and Coriolis forces, derived from fluid motions. The black hole (or secondary) is treated as a rigid sphere and can be regarded as a point mass. The equilibrium figure is derived. The problem is then adapted to include vorticity and a pseudo-Newtonian potential. The coalescence of neutron star - black hole binaries and their importance to gravitational wave detection is also discussed. / Mathematical Sciences / M. Sc. (Applied Mathematics)

In this thesis I study the magnetic activity of young stars via observations of stellar prominences on single stars and by applying the Zeeman Doppler imaging (ZDI) technique to map the magnetic fields and measure differential rotation of a young binary system. Stellar prominences can be observed as absorption transients in the rotationally broadened chromospheric lines of rapidly rotating stars. Observations of Speedy Mic(K3V) reveal a densely packed prominence system at heights far above the stellar co-rotation radius. Further observations were used to estimate prominence column densities and masses. From very high signal-to-noise observations, loops of emission are found that trace the path of prominences seen transiting the stellar disc. I also present what appears to be the first observation of an erupting stellar prominence on AB Doradus (K0V). I modify an existing ZDI code so that it can recover the magnetic maps of a binary system. The new code is applied to observations of the pre-main sequence binary system HD 155555 (G5IV+K0IV). The radial magnetic maps reveal a complex surface magnetic topology with mixed polarities at all latitudes and rings of azimuthal field present on both stars. The evolution of the relative field strengths between observations in 2004 and 2007 could be indicative of a magnetic activity cycle. I adapt the sheared image technique for measuring differential rotation parameters to the binary case. Both stellar components of HD 155555 are found to have rates of differential rotation similar to those of the same spectral type main sequence single stars. This is in apparent conflict with previous work on evolved binary systems where low rates of differential rotation were found, leading to the suggestion of suppression by binary tidal forces. I find that the depth of convection zone alone can likely explain the differential rotation results without invoking tidal forces.

The government has included biological technology industries among the priorities of development program for ¡§challenge 2008--national development plan¡¨ and ¡§Two Trillions Double Stars Industries Development Plan¡¨. As the labor cost rising and many industries moving to Mainland China, several traditional industries in Taiwan have successfully transformed into biological technology industries for surviving, while some pharmaceutical industries seems not to do well as above. So the author would like to dip out intensively why non-pharmaceutical industries could convert the investment into biological technology sectors successfully than the pharmaceutical counterparts. It would collect some relevant data and get interviews from respective company and literature review, and then apply SWOT (Strength, Weakness, Opportunity and Threats) analysis to understand what kinds of impediments those companies have encountered, how they resolved the problems and what results they yielded. May this study provide feasible advises about the optimal routes and approaches for Taiwan industries to transform into biological technology sectors by analyzing and comparing different cases of converted investment. The results that have been found are as follows: the converted investments which non-pharmaceutical industries embarked upon could divided into two approaches--- one for those companies that had adequately understand their own merits and felt they should convert the investment into biological technology sectors; another one is that the transformed company only hoped to facilitate the opportunity which government prioritized to market their products well. In near future, we would see the biological technology industries come to merger, vertical integration and strategic alliance due to research & development, marketing access and acquirements of capitals. According to this survey, most pharmaceutical companies wouldn¡¦t like to transform into biological technology industries because of some state policies, such as cGMP system, health insurance bureau lowering the payment for pharmaceutical companies, domestic markets having been liberated and new labor retirement pension fund systems. Besides, the pharmaceutical industries have been stepping up the speed of merger and shakeout, certainly would they not to transform into biological technology industries. Therefore, if the domestic industries hope to convert their investments, they should layout short-term and long-term strategies, which the former ought to take priority of creating the profits so as to facilitate the development of the latter which would focus on building up marketing accesses, cultivating R&D talents and their competences, as well as expanding strategic alliance actively with international enterprises for biological technology. To conclude, this study would provide Taiwan industries who tried to transform some advises, such as to consider merger, develop healthy food, beef up the integrated supply chains, loosen the conditions of becoming a listed company or OTC(over-the-counter) company, value the intellectual property right and open overseas markets.

We will consider the scenario of the co-rotation of a fluid star (in specific, a neutron star) and a black hole. The neutron star (or primary)is assumed to have constant angular velocity. The tidal effects on the primary are investigated. First, the centrally condensed approximation is applied, where both bodies are considered as point sources. In the second treatment, the primary is treated as an incompressible and homogeneous fluid mass, which in addition to its own gravity is subject to centrifugal and Coriolis forces, derived from fluid motions. The black hole (or secondary) is treated as a rigid sphere and can be regarded as a point mass. The equilibrium figure is derived. The problem is then adapted to include vorticity and a pseudo-Newtonian potential. The coalescence of neutron star - black hole binaries and their importance to gravitational wave detection is also discussed. / Mathematical Sciences / M. Sc. (Applied Mathematics)

Despite being observed since the XVIIIth century, Algol systems and related objects are<p>still rather poorly understood. We know that they are composed by a generally B-A main sequence<p>star and a lighter but more evolved companion star. This paradox is explained by the transfer of mass<p>between the two stars, but new problems arose. In particular, I studied the mass-transfer driven spin-<p>up of the accreting star that drives the star to critical rotation and the puzzling, indirectly observed, non-conservative evolution. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

Si l'évolution des étoiles simples est relativement bien comprise, l'étude des étoiles binaires, qui représentent la majorité des étoiles, nécessite encore des progrès majeurs, particulièrement en ce qui concerne leurs différents modes d'interactions. Dans ces systèmes, la composition de surface d'une étoile peut être altérée non seulement par l'accrétion d'éléments synthétisés au sein de l'étoile compagnon, mais également par des processus de mélanges internes induits par les forces de marées et d'un transport du moment angulaire. Plusieurs classes d'étoiles post-transfert de masse (les étoiles à baryum, CH et S) possèdent effectivement des compositions de surface caractérisées par la présence d'éléments lourds, tel que le baryum. Ces systèmes sont présumés se former au sein de systèmes binaires incluant une étoile de la branche asymptotique des géantes (appelé étoile AGB). Ces dernières sont des étoiles remarquables qui représentent l'unique site d'une nucléosynthèse particulière. En effet, elles constituent les contributeurs essentiels de la production de fluor ou de baryum. Les étoiles AGB sont également caractérisées par une importante perte de masse par vent qui éjecte progressivement leur enveloppe enrichie en ces éléments. Au sein d'un système binaire, une partie de ce vent est accréditée par l'étoile compagnon et pollue ainsi sa surface, laissant une signature spectrale distincte qui subsistera longtemps après que l'étoile AGB ait disparu. Ce scénario est suggéré comme étant responsable de la formation d'une grande variété d'étoiles chimiquement particulières, tels que les étoiles à baryum.<p>Cependant, plusieurs propriétés clés de ces systèmes, en particulier leurs distributions de périodes orbitales et d'excentricités, demeurent inexpliquées depuis des décennies. L'incapacité de nos modèles à reproduire ces propriétés orbitales met en évidence notre compréhension limitée des mécanismes d'interaction qui gouvernent l'évolution des systèmes binaires. Plus particulièrement, des mécanismes qui génèrent des orbites excentriques au sein des étoiles à baryum et des systèmes analogues sont requis. Nous examinons ainsi la possibilité qu'à sa naissance l'étoile naine blanche subisse un kick ou que la présence d'un disque entourant le système binaire soit à l'origine des fortes excentricités observées chez les étoiles à baryum. Ces deux mécanismes permettent pour la première fois depuis l'étude de ces systèmes d'apporter une solution à ces problèmes. Il est montré comment comprendre les signatures induites par un compagnon étoile AGB et les corréler avec les propriétés orbitales du système binaire est essentiel pour tester et améliorer notre connaissance de l'évolution des étoiles binaires; l'objectif de ce travail.<p> / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

Building upon its success with the Hipparcos space astrometry mission launched in 1989, the European Space Agency has agreed to fund the construction of its successor, Gaia, and its launch in 2011. Despite the similarities between the two missions, Gaia will be orders of magnitude more powerful, more sensitive, but also more complex in terms of data processing. Growing from 120,000 stars with Hipparcos to about 120,000E4 stars with Gaia does not simply mean pushing the computing resources to their limits (1 second of processing per star yields 38 years for the whole Gaia-sky). It also means facing situations that did not occur with Hipparcos either by luck or because those cases were carefully removed from the Hipparcos Input Catalogue.<p><p>This manuscript illustrates how some chunks of the foreseen Gaia data reduction pipeline can be trained and assessed using the Hipparcos observations. This is especially true for unresolved binaries because they pop up so far down in the Gaia pipeline that, by the time they get there, there is essentially no difference between Hipparcos and Gaia data. Only the number of such binaries is different, going from two thousand to ten million.<p><p>Although the computing time clearly becomes an issue, one cannot sacrifice the robustness and correctness of the reduction pipeline for the sake of speed. However, owing to the requirement that everything must be Gaia-based (no help from ground-based results), the very robustness of the reduction has to be assessed as well. For instance, the underlying assumptions of some statistical tests used to assess the quality of the fits used in the Hipparcos pipeline might no longer hold with Gaia. That may not affect the fit itself but rather the quality indicators usually accompanying those fits. For the final catalogue to be a success, these issues must be addressed as soon as possible.<p> / Agrégation de l'enseignement supérieur, Orientation sciences / info:eu-repo/semantics/nonPublished

This MSc report discusses the attributes of W Ursae Majoris (W UMa) stars and an investigation into the Minimum Entropy (ME) method, a digital technique applied to the determination of their periods of variability. A Python code programme was written to apply the ME method to photometric data collected on W UMa stars by the All Sky Automated Survey (ASAS). Starting with the orbital period of the binaries estimated by ASAS, this programme systematically searches around this period for the period which corresponds to the lowest value of entropy. Low entropy here means low scatter (or spread) of data across the phase-magnitude plane. The ME method divides the light curve plot area into a number of elements of the investigators choosing. When a particular orbital period is applied to this photometric data, the resulting distribution of this data in the light curve plane corresponds to a speci c number of data points in each element into which this plane has been divided. This data spread is measured and calculated in terms of entropy and the lowest value of entropy corresponds to the lowest spread of data across the light curve plane. This should correspond to the best light curve shape available from the data and therefore the most accurate orbital period available. Subsequent to the testing of this Python code on perfect sine waves, it was applied, and its results compared, to the 62 ASAS eclipsing binary stars which were investigated by Deb and Singh (2011). The method was then applied to selected stars from the ASAS data base. / Environmental Sciences / M. Sc. (Astronomy)

Gamma-ray binaries are extreme systems that produce non-thermal emission from radio to very-high-energy (above TeV) gamma rays, with the energy output in the spectral energy distribution (SED) dominated by the MeV–GeV photons. Their broadband emission is usually modulated by the orbital cycle of the system, which suggests that the physical conditions are also periodic and reproducible. The diversity of systems, together with the reproducibility of the conditions within each system, makes gamma-ray binaries excellent physical laboratories in which high energy particle acceleration, diffusion, absorption, and radiation mechanisms can be explored. Nevertheless, the number of known gamma-ray binaries is still very limited, and only a six binary systems have been classified as gamma-ray binaries. These systems produce outflows of relativistic particles emitting synchrotron radio emission that extend up to several astronomical units, which correspond to projected angular scales of a few milliarcseconds (mas) at typical distances of 2-3 kpc. Very Long Baseline Interferometry (VLBI) provide mas resolution and therefore can be used to directly see this radio outflow. In this thesis we present VLBI observations of five of the six gamma-ray binaries known. We have revealed for the first time the radio structure of two gamma-ray binaries, and found periodic changes in the structure of other two. Based on these results, we have established the basic properties and behaviour of the radio emission of gamma-ray binaries on AU scales, and we have contributed to find characteristics that are common to all of them. / En los últimos años se ha producido una mejora significativa de los instrumentos que permiten observar fenómenos astrofísicos en rayos gamma de alta y muy alta energía. Gracias a estos avances, se ha podido detectar emisión de rayos gamma en sistemas binarios. Tan sólo seis sistemas binarios han sido clasificados como estrellas binarias de rayos gamma (tres de ellos aún son candidatos). Estos sistemas producen chorros de material relativista que a su vez producen grandes cantidades de energía en todo el espectro electromagnético, desde ondas radio hasta emisión de rayos gamma hasta energías del teraelectronvolt (TeV). Estos chorros se desplazan a alta velocidad produciendo estructuras en escalas de varias unidades astronómicas (UA). Estas estructuras pueden ser observadas directamente mediante técnicas de interferometría radio de muy larga línea de base (VLBI). En esta tesis nos centramos en el estudio de las propiedades morfológicas y astrométricas de binarias de rayos gamma observadas mediante VLBI. De las seis binarias conocidas, se han observado cinco de ellas. Los resultados principales son los siguientes. Se ha detectado estructura extendida en escalas de 120 UA en el sistema binario PSR B1259-63. Esta ha sido la primera evidencia observacional de que púlsares jóvenes no acretantes interaccionando con estrellas jóvenes pueden producir emisión radio extendida. Se ha descubierto que la emisión del sistema LS 5039 muestra cambios periódicos en su morfología, que son estables en escalas de varios años. También se ha determinado el movimiento propio de este sistema y se ha obtenido su trayectoria galáctica en el pasado. Se ha confirmado que el sistema LS I +61 303 muestra variabilidad orbital periódica, aunque presenta cambios significativos en ciertas fases orbitales. Se ha encontrado un desplazamiento del pico de la emisión a varias frecuencias, así como un cambio en sus posiciones relativas. Se ha descubierto emisión extendida procedente de la fuente de rayos gamma HESS J0632+057, y se ha confirmado inequívocamente su asociación con el sistema binario MWC 148. Por último, no se ha encontrado contrapartida radio a la fuente de rayos gamma AGL 2241+4454, cuya contrapartida óptica ha sido propuesta en el sistema MWC 656. Estos resultados permiten sentar las bases de la estructura en escalas de varias UA de los sistemas binarios de rayos gamma, así como su comportamiento en función de la fase orbital. Las características comunes halladas en estos sistemas ha permitido encontrar enlaces observacionales entre estos sistemas, dando consistencia a este particular grupo de estrellas que presentan emisión en rayos gamma.