Modelling stellar structures and comparing them with observationsis a very important step when it comes to verifying our theories aboutstellar evolution. Three-dimensional reconstruction is therefore impor-tant and in the case of certain stellar types it makes for a large portionof the ongoing research.For this project, three dierent objects and their three-dimensionalmodels were selected for 3D-printing. The systems in question areEta Carinae, 1 Gruis and HD 101584 and the reason behind thischoice is the fact that each object showcases a dierent phase and/orprocess of stellar evolution approaching or during the planetary nebula(PN) stage. On top of that, these objects have been observed using atechnique that allows us to deduce their 3D structure.The three-dimensional models and prints allow us to nd features(such as axial symmetries) that give us more information about themovements inside the system and their consequences on how the stellarstructure has and will evolve.

We investigate binary hypotheses for the formation of bipolar nebulae using the smoothed particle hydrodynamics code Gadget-2. In the general case, we present a parameter study of mass loss from very simple common envelope models, which seems to show a strongly bipolar trend for sufficiently oblate envelopes and low enough spiral-in injection energy. The density profiles of the envelopes produce differing structure within the ejecta. We also investigate 3 specific bipolar mass loss events. In the case of the outer nebula of SN 1987A, we study the effects of fast polar jets interacting with a pre- existing progenitor wind and find that these are consistent with the observed light echoes from the nebula, in particular for the feature known as ’Napoleon’s Hat’. In the case of Cas A, we briefly study the effects of close binarity on supernova ejecta and suggest the influence of a close, compact companion may lead to at least one jet-like disturbance that may be observable in a supernova remnant. Finally, we study whether a fast bipolar wind, similar to that of Eta Car’s present wind, may inflate ejecta similar to that produced in the common envelope models to a shape consistent with that of Eta Car’s Homunculus Nebula.

O presente trabalho propõe uma abordagem abrangente para descrever a evolução da região central da Via Láctea, compreendendo-se aí o bojo, a barra e as interfaces dos mesmos com o limite interno do disco e com a região central do halo. Pretende-se investigar as propriedades químicas e cinemáticas destas estruturas, que são interconectadas, com o objetivo de separá-las e aplicar os resultados daí obtidos a um modelo de formação e evolução do bojo e da região interna do disco que descreva simultaneamente distintos aspectos da evolução da região central da Galáxia. Na primeira parte do trabalho, uma amostra de nebulosas planetárias (NPs) localizadas no disco interno e no bojo da Galáxia é utilizada para encontrar a distância galactocêntrica que melhor separa estas duas populações, do ponto de vista das abundâncias. Foram utilizadas escalas de distâncias estatísticas para o estudo da distribuição das abundâncias na interface bojo-disco. A aplicação do teste Kolmogorov-Smirnov mostrou que, em média, a população interna não segue o gradiente radial de abundâncias do disco na direção do centro galáctico. Baseado neste estudo, propõe-se uma distância galactocêntrica de 1.5 kpc para definir a interface bojo-disco. Na segunda parte do trabalho, foram realizadas observações espectrofotométricas de 21 NPs localizadas na direção do centro da Galáxia com o telescópio SOAR. Estes objetos estão localizados bem próximos ao plano galáctico na direção central da Via Láctea, onde não existem dados de NPs na literatura. Os resultados mostram que as NPs localizadas nesta região apresentam baixas abundâncias de oxigênio comparadas com as NPs do disco interno e de outras regiões do bojo. Os resultados indicam que o bojo apresenta uma complexa composição de populações estelares. Por um lado, a presença de nebulosas com baixas abundâncias mostra que o bojo pode ter se formado a partir de um disco galáctico antigo através de uma evolução secular. Por outro lado, existem alguns objetos do bojo para os quais as abundâncias coincidem com o limite do gradiente radial do disco nesta região. Esta é uma evidência para um bojo composto por duas ou mais populações: uma originada do disco fino, e outra originada do disco espesso. Na última parte do trabalho propõe-se a inclusão de fluxos radiais de gás em um modelo de evolução química para simular os efeitos de uma barra localizada no centro da Galáxia nas distribuições de abundâncias, densidade de gás e taxa de formação estelar (SFR). Os resultados das simulações indicam que os modelos com fluxos de gás apresentam uma SFR mais alta no bojo e que os perfis da SFR e da densidade de gás na região central são melhor reproduzidos após a inclusão dos fluxos radiais no modelo. As simulações indicam ainda que o gradiente de abundâncias do disco é mais plano para o caso da inclusão da barra. Estes resultados indicam que a barra e os fluxos de gás exercem um importante papel na formação de estrelas no centro das galáxias espirais barradas. / This project proposes a comprehensive approach to describe the evolution of the central region of the Galaxy, comprising the bulge, the bar and their interfaces with the inner disk and the central region of the halo. We intend to investigate the chemical and kinematic properties of these structures, which are interconnected, aiming to separate them and apply these results to a model for the formation and evolution of the bulge and inner disk, capable to describe simultaneously distinct aspects of the evolution of the central region of the Galaxy. First, a sample of planetary nebulae (PNe) located in the inner-disk and bulge of the Galaxy is used in order to find the galactocentric distance that better separates these two populations, from the point of view of abundances. Statistical distance scales were used to study the distribution of abundances across the disk-bulge interface. A Kolmogorov-Smirnov test was used to find the distance in which the chemical properties of these regions better separates. The results of the statistical analysis indicate that, on the average, the inner population has lower abundances than the outer. Additionally, for the $\\alpha$-elements abundances, the inner population does not follow the disk radial gradient towards the galactic centre. Based on our results, we suggest a bulge-disk interface at 1.5 kpc, marking the transition between the bulge and inner-disk of the Galaxy, as defined by the intermediate mass population. Second, we present spectrophotometric observations for a sample of 21 PNe located towards the galactic centre of the Galaxy. The abundances are derived based on observations in the optical domain made at the SOAR telescope. Their location is interesting since there are no observations of PNe in this region. The data show lower oxygen abundances compared to those from PNe located in the inner disk and other bulge regions. The results show that the bulge has a complex composition of stellar populations. The presence of PNe with low abundances indicates that the bulge might be formed from an old galactic disk through secular evolution. On the other hand, other objects from our sample have abundances compared to those from inner disk PNe. This is evidence that two or more populations might compose the bulge: one originated from the thin disk, and the other from the thick disk. Last, we propose a chemical evolution model that includes radial gas flows. This is done in order to mimic the effects of the galactic bar on the chemical abundances distributions and the gas density profiles and the star formation rate (SFR). The results of the models with radial flows point to a high SFR in the bulge and, additionally, the SFR and gas density profiles in the inner Galaxy are better reproduced after the inclusion of radial gas flows in the model. After including a specific velocity pattern for the bar, the results show a flattening of the radial abundance gradient. Our results indicate that radial gas flows may play an important role in the star formation near the centre of barred spiral galaxies.

Na literatura, a análise e a interpretação das linhas de emissão de H2 em nebulosas planetárias são feitas, em geral, considerando que a molécula somente seja produzida em ambientes neutros, como as regiões de fotodissociação ou com choques. No entanto, existem fortes evidências observacionais de que ao menos parte da emissão seja proveniente da região ionizada desses objetos. Em trabalhos anteriores mostramos que quantidades significativas de H2 podem sobreviver dentro dessa região hostil. No presente trabalho nosso objetivo é calcular e estudar a emissão de H2 em linhas no infravermelho produzidas na região ionizada de nebulosas planetárias, utilizando o código de fotoionização unidimensional Aangaba. Para isso, desenvolvemos diversas sub-rotinas que determinam o povoamento em níveis de energia da molécula e calculam a intensidade das linhas de emissão de H2. Obtivemos a intensidade de diversas linhas produzidas pela molécula H2 em nebulosas planetárias cujos parâmetros característicos (temperatura e luminosidade da estrela central, densidade do gás, tipo e tamanho dos grãos, etc.) estão na faixa de valores conhecidos para esses objetos. Como resultado de nosso trabalho, mostramos que a contribuição da região ionizada para a emissão de H2 de nebulosas planetárias pode ser significativa em diversas situações, particularmente quando a temperatura da estrela central é alta. Esse resultado pode explicar porque a detecção de linhas de H2 é mais provável em nebulosas planetárias bipolares, que têm estrelas tipicamente mais quentes. Além disso, verificamos que na região ionizada a excitação e a desexcitação colisional são mecanismos importantes de povoamento de todos os níveis rovibracionais do estado fundamental eletrônico de H2. Os mecanismos radiativos são também importantes, particularmente para os níveis de energia excitados. Os mecanismos de formação em estados excitados podem ter alguma influência no espectro de linhas produzidas pela desexcitação de níveis rotacionais bastante elevados, principalmente em ambientes densos. Em nossos modelos incluímos o efeito da molécula H2 no equilíbrio térmico do gás, verificando que a molécula H2 somente tem influência significativa na temperatura do gás em casos de temperatura da estrela central muito alta ou grande quantidade de grãos, principalmente através da desexcitação colisional. / The analysis and the interpretation of the H2 line emission of planetary nebulae have been done in the literature assuming that the molecule survives only in neutral environments, as in photodissociation or shocked regions. However, there is strong evidence that at least part of the H2 emission is produced inside the ionized region of such objects. In previous work we showed that significant amounts of H2 can survive inside the ionized region of planetary nebulae. The aim of the present work is to calculate and study the infrared line emission of H2 produced inside the ionized region of planetary nebulae using the one-dimensional photoionization code Aangaba. For this, we developed several numerical subroutines in order to calculate the statistical population of the H2 energy levels, as well as the intensity of the H2 infrared emission lines in physical conditions typical of planetary nebulae. We show that the contribution of the ionized region for the H2 emission can be significant, particularly in the case of nebulae with high temperature central stars. This result explains why H2 emission is more frequently observed in bipolar planetary nebulae (Gatley\'s rule), since this kind of object typically has hotter stars. We show that collisional excitation plays an important role on the H2 population of the rovibrational levels of the electronic ground state. Radiative mechanisms are also important, particularly for upper levels. Formation pumping may have some effects on the line intensities produced by de-excitation from very high rotational levels, specially in dense environments. We include the effects of H2 in the thermal equilibrium of the gas, concluding that H2 only contributes to the thermal equilibrium in the case of very high temperature of the central star or high grain to gas ratio, mainly through collisional de-excitation.

High mass loss rates in evolved stars make them the major contributors to recycling processed material back into the interstellar medium. This mass loss creates large circumstellar shells, rich in molecular material. This dissertation presents millimeter and submillimeter studies of the end stages of low mass and high mass stars in order to probe their molecular content in more detail. In low mass stars, the molecular material is carried on into the planetary nebula (PN) stage. Observations of CS, HCO⁺, and CO in planetary nebulae (PNe) of various post-asymptotic giant branch ages have shown that molecular abundances in these objects do not significantly vary with age, as previously thought. More detailed observations of the slightly oxygen-rich PN NGC 6537 resulted in the detection of CN, HCN, HNC, CCH, CS, SO, H₂CO, HCO⁺ and N₂H⁺, as well as numerous ¹³C isotopologues. Observations of the middle-aged PN M2-48 showed the presence of CN, HCN, HNC, CS, SO, SO₂, SiO, HCO⁺, N₂H⁺, and several ¹³C isotopologues. These observations represent the first detections of CS, SO, SO₂, and SiO in any planetary nebula. The implications of these observations are discussed. A 1 mm spectral survey of the supergiant star NML Cygni has been carried out with the Arizona Radio Observatory Submillimeter Telescope resulting in the observation of 102 emission features arising from 17 different molecules and 4 unidentified features. The line profiles observed in this circumstellar shell are asymmetric and vary between different molecules, akin to what has been seen in another supergiant, VY Canis Majoris. The non-LTE radiative transfer code ESCAPADE has been used to model molecular abundances in the various asymmetric outflows of VY Canis Majoris, showing just how chemically and kinematically complex these supergiant circumstellar envelopes really are.

Na literatura, a análise e a interpretação das linhas de emissão de H2 em nebulosas planetárias são feitas, em geral, considerando que a molécula somente seja produzida em ambientes neutros, como as regiões de fotodissociação ou com choques. No entanto, existem fortes evidências observacionais de que ao menos parte da emissão seja proveniente da região ionizada desses objetos. Em trabalhos anteriores mostramos que quantidades significativas de H2 podem sobreviver dentro dessa região hostil. No presente trabalho nosso objetivo é calcular e estudar a emissão de H2 em linhas no infravermelho produzidas na região ionizada de nebulosas planetárias, utilizando o código de fotoionização unidimensional Aangaba. Para isso, desenvolvemos diversas sub-rotinas que determinam o povoamento em níveis de energia da molécula e calculam a intensidade das linhas de emissão de H2. Obtivemos a intensidade de diversas linhas produzidas pela molécula H2 em nebulosas planetárias cujos parâmetros característicos (temperatura e luminosidade da estrela central, densidade do gás, tipo e tamanho dos grãos, etc.) estão na faixa de valores conhecidos para esses objetos. Como resultado de nosso trabalho, mostramos que a contribuição da região ionizada para a emissão de H2 de nebulosas planetárias pode ser significativa em diversas situações, particularmente quando a temperatura da estrela central é alta. Esse resultado pode explicar porque a detecção de linhas de H2 é mais provável em nebulosas planetárias bipolares, que têm estrelas tipicamente mais quentes. Além disso, verificamos que na região ionizada a excitação e a desexcitação colisional são mecanismos importantes de povoamento de todos os níveis rovibracionais do estado fundamental eletrônico de H2. Os mecanismos radiativos são também importantes, particularmente para os níveis de energia excitados. Os mecanismos de formação em estados excitados podem ter alguma influência no espectro de linhas produzidas pela desexcitação de níveis rotacionais bastante elevados, principalmente em ambientes densos. Em nossos modelos incluímos o efeito da molécula H2 no equilíbrio térmico do gás, verificando que a molécula H2 somente tem influência significativa na temperatura do gás em casos de temperatura da estrela central muito alta ou grande quantidade de grãos, principalmente através da desexcitação colisional. / The analysis and the interpretation of the H2 line emission of planetary nebulae have been done in the literature assuming that the molecule survives only in neutral environments, as in photodissociation or shocked regions. However, there is strong evidence that at least part of the H2 emission is produced inside the ionized region of such objects. In previous work we showed that significant amounts of H2 can survive inside the ionized region of planetary nebulae. The aim of the present work is to calculate and study the infrared line emission of H2 produced inside the ionized region of planetary nebulae using the one-dimensional photoionization code Aangaba. For this, we developed several numerical subroutines in order to calculate the statistical population of the H2 energy levels, as well as the intensity of the H2 infrared emission lines in physical conditions typical of planetary nebulae. We show that the contribution of the ionized region for the H2 emission can be significant, particularly in the case of nebulae with high temperature central stars. This result explains why H2 emission is more frequently observed in bipolar planetary nebulae (Gatley\'s rule), since this kind of object typically has hotter stars. We show that collisional excitation plays an important role on the H2 population of the rovibrational levels of the electronic ground state. Radiative mechanisms are also important, particularly for upper levels. Formation pumping may have some effects on the line intensities produced by de-excitation from very high rotational levels, specially in dense environments. We include the effects of H2 in the thermal equilibrium of the gas, concluding that H2 only contributes to the thermal equilibrium in the case of very high temperature of the central star or high grain to gas ratio, mainly through collisional de-excitation.

O presente trabalho propõe uma abordagem abrangente para descrever a evolução da região central da Via Láctea, compreendendo-se aí o bojo, a barra e as interfaces dos mesmos com o limite interno do disco e com a região central do halo. Pretende-se investigar as propriedades químicas e cinemáticas destas estruturas, que são interconectadas, com o objetivo de separá-las e aplicar os resultados daí obtidos a um modelo de formação e evolução do bojo e da região interna do disco que descreva simultaneamente distintos aspectos da evolução da região central da Galáxia. Na primeira parte do trabalho, uma amostra de nebulosas planetárias (NPs) localizadas no disco interno e no bojo da Galáxia é utilizada para encontrar a distância galactocêntrica que melhor separa estas duas populações, do ponto de vista das abundâncias. Foram utilizadas escalas de distâncias estatísticas para o estudo da distribuição das abundâncias na interface bojo-disco. A aplicação do teste Kolmogorov-Smirnov mostrou que, em média, a população interna não segue o gradiente radial de abundâncias do disco na direção do centro galáctico. Baseado neste estudo, propõe-se uma distância galactocêntrica de 1.5 kpc para definir a interface bojo-disco. Na segunda parte do trabalho, foram realizadas observações espectrofotométricas de 21 NPs localizadas na direção do centro da Galáxia com o telescópio SOAR. Estes objetos estão localizados bem próximos ao plano galáctico na direção central da Via Láctea, onde não existem dados de NPs na literatura. Os resultados mostram que as NPs localizadas nesta região apresentam baixas abundâncias de oxigênio comparadas com as NPs do disco interno e de outras regiões do bojo. Os resultados indicam que o bojo apresenta uma complexa composição de populações estelares. Por um lado, a presença de nebulosas com baixas abundâncias mostra que o bojo pode ter se formado a partir de um disco galáctico antigo através de uma evolução secular. Por outro lado, existem alguns objetos do bojo para os quais as abundâncias coincidem com o limite do gradiente radial do disco nesta região. Esta é uma evidência para um bojo composto por duas ou mais populações: uma originada do disco fino, e outra originada do disco espesso. Na última parte do trabalho propõe-se a inclusão de fluxos radiais de gás em um modelo de evolução química para simular os efeitos de uma barra localizada no centro da Galáxia nas distribuições de abundâncias, densidade de gás e taxa de formação estelar (SFR). Os resultados das simulações indicam que os modelos com fluxos de gás apresentam uma SFR mais alta no bojo e que os perfis da SFR e da densidade de gás na região central são melhor reproduzidos após a inclusão dos fluxos radiais no modelo. As simulações indicam ainda que o gradiente de abundâncias do disco é mais plano para o caso da inclusão da barra. Estes resultados indicam que a barra e os fluxos de gás exercem um importante papel na formação de estrelas no centro das galáxias espirais barradas. / This project proposes a comprehensive approach to describe the evolution of the central region of the Galaxy, comprising the bulge, the bar and their interfaces with the inner disk and the central region of the halo. We intend to investigate the chemical and kinematic properties of these structures, which are interconnected, aiming to separate them and apply these results to a model for the formation and evolution of the bulge and inner disk, capable to describe simultaneously distinct aspects of the evolution of the central region of the Galaxy. First, a sample of planetary nebulae (PNe) located in the inner-disk and bulge of the Galaxy is used in order to find the galactocentric distance that better separates these two populations, from the point of view of abundances. Statistical distance scales were used to study the distribution of abundances across the disk-bulge interface. A Kolmogorov-Smirnov test was used to find the distance in which the chemical properties of these regions better separates. The results of the statistical analysis indicate that, on the average, the inner population has lower abundances than the outer. Additionally, for the $\\alpha$-elements abundances, the inner population does not follow the disk radial gradient towards the galactic centre. Based on our results, we suggest a bulge-disk interface at 1.5 kpc, marking the transition between the bulge and inner-disk of the Galaxy, as defined by the intermediate mass population. Second, we present spectrophotometric observations for a sample of 21 PNe located towards the galactic centre of the Galaxy. The abundances are derived based on observations in the optical domain made at the SOAR telescope. Their location is interesting since there are no observations of PNe in this region. The data show lower oxygen abundances compared to those from PNe located in the inner disk and other bulge regions. The results show that the bulge has a complex composition of stellar populations. The presence of PNe with low abundances indicates that the bulge might be formed from an old galactic disk through secular evolution. On the other hand, other objects from our sample have abundances compared to those from inner disk PNe. This is evidence that two or more populations might compose the bulge: one originated from the thin disk, and the other from the thick disk. Last, we propose a chemical evolution model that includes radial gas flows. This is done in order to mimic the effects of the galactic bar on the chemical abundances distributions and the gas density profiles and the star formation rate (SFR). The results of the models with radial flows point to a high SFR in the bulge and, additionally, the SFR and gas density profiles in the inner Galaxy are better reproduced after the inclusion of radial gas flows in the model. After including a specific velocity pattern for the bar, the results show a flattening of the radial abundance gradient. Our results indicate that radial gas flows may play an important role in the star formation near the centre of barred spiral galaxies.

Central stars of planetary nebulae are low-mass stars on the brink of their final evolution towards white dwarfs. Because of their surface temperature of above 25,000 K their UV radiation ionizes the surrounding material, which was ejected in an earlier 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. Moreover, most of them have a strong stellar wind, similar to massive Pop-I Wolf-Rayet stars, and are in analogy classified as [WC]. The brackets distinguish the special type from the massive WC stars. Qualitative spectral analyses of [WC] stars lead to the assumption of an evolutionary sequence from the cooler, so-called late-type [WCL] stars to the very hot, early-type [WCE] stars. Quantitative analyses of the winds of [WC] stars became possible by means of computer programs that solve the radiative transfer in the co-moving frame, together with the statistical equilibrium equations for the population numbers. First analyses employing models without iron-line blanketing resulted in systematically different abundances for [WCL] and [WCE] stars. While the mass ratio of He:C is roughly 40:50 for [WCL] stars, it is 60:30 in average for [WCE] stars. The postulated evolution from [WCL] to [WCE] however could only lead to an increase of carbon, since heavier elements are built up by nuclear fusion. In the present work, improved models are used to re-analyze the [WCE] stars and to confirm their He:C abundance ratio. Refined models, calculated with the Potsdam WR model atmosphere code (PoWR), account now for line-blanketing due to iron group elements, small scale wind inhomogeneities, and complex model atoms for He, C, O, H, P, N, and Ne. Referring to stellar evolutionary models for the hydrogen-deficient [WC] stars, Ne and N abundances are of particular interest. Only one out of three different evolutionary channels, the VLTP scenario, leads to a Ne and N overabundance of a few percent by mass. A VLTP, a very late thermal pulse, is a rapid increase of the energy production of the helium-burning shell, while hydrogen burning has already ceased. Subsequently, the hydrogen envelope is mixed with deeper layers and completely burnt in the presence of C, He, and O. This results in the formation of N and Ne. A sample of eleven [WCE] stars has been analyzed. For three of them, PB 6, NGC 5189, and [S71d]3, a N overabundance of 1.5% has been found, while for three other [WCE] stars such high abundances of N can be excluded. In the case of NGC 5189, strong spectral lines of Ne can be reproduced qualitatively by our models. At present, the Ne mass fraction can only be roughly estimated from the Ne emission lines and seems to be in the order of a few percent by mass. Furthermore, using a diagnostic He-C line pair, the He:C abundance ratio of 60:30 for [WCE] stars is confirmed. Within the framework of the analysis, a new class of hydrogen-deficient central stars has been discovered, with PB 8 as its first member. Its atmospheric mixture resembles rather that of the massive WNL stars than of the [WC] stars. The determined mass fractions H:He:C:N:O are 40:55:1.3:2:1.3. As the wind of PB 8 contains significant amounts of O and C, in contrast to WN stars, a classification as [WN/WC] is suggested. / Zentralsterne Planetarischer Nebel sind massearme Sterne kurz vor ihrer finalen Entwicklung zu Weißen Zwergen. Aufgrund ihrer Oberflächentemperatur von über 25 000 K sind sie in der Lage, durch Abstrahlung von UV-Licht das sie umgebende Material, welches in einer vorigen Phase ihrer Entwicklung abgestoßen wurde, zu ionisieren. Das solchermaßen zum Leuchten angeregte Gas bezeichnet man als Planetarischen Nebel. Etwa ein Zehntel der galaktischen Zentralsterne sind wasserstoffarm. Im Allgemeinen besteht die Oberfläche dieser Zentralsterne aus einer Mischung der Elemente Helium, Kohlenstoff und Sauerstoff, welche z.T. durch Heliumbrennen erzeugt wurden. Die meisten dieser Sterne haben darüberhinaus einen starken Sternwind, ähnlich den massereichen Pop-I-Wolf-Rayet-Sternen und werden in Analogie zu diesen als [WC] klassifiziert, wobei die eckigen Klammern der Unterscheidung von den massereichen WC-Sternen dienen. Qualitative Analysen der Spektren von [WC]-Sternen lassen eine Entwicklungssequenz dieser Sterne von kühleren sogenannten late-type [WC]-Sternen (kurz [WCL]) zu sehr heißen, early-type [WC]-Sternen (kurz [WCE]) vermuten. Mithilfe von Computerprogrammen, die den Strahlungstransport im mitbewegten Beobachtersystem zusammen mit den statistischen Gleichungen der Besetzungszahlen der Ionen im Sternwind rechnen können, wurden quantitative Untersuchungen der Winde von [WC]-Sternen möglich. Erste Analysen mit Modellen ohne Eisenlinien ergaben dabei systematisch unterschiedliche Häufigkeiten für [WCL]- und [WCE]-Sterne. Während sich für [WCL]-Sterne ein Verhältnis der Massenanteile von He:C von etwas 40:50 ergab, fand man für die [WCE]-Sterne ein mittleres Verhältnis von 60:30 für die He:C-Massenanteile. Dabei sollte die Entwicklung von [WCL] nach [WCE] innerhalb einer sehr kurzen Zeit durch Aufheizung infolge der Kontraktion der Hülle erfolgen und nicht mit einer wesentlichen Abnahme der Kohlenstoffhäufigkeit bei gleichzeitiger Zunahme der Heliumhäufigkeit an der Oberfläche einhergehen. Im Rahmen der vorgelegten Arbeit wird untersucht, ob sich mittels verbesserter Modelle für die Atmosphären von [WC]-Sternen das He:C-Häufigkeitsverhältnis der [WCE]-Sterne bestätigt. Elaboriertere Modelle, welche vom Potsdamer WR-Modelatmosphären-Code (PoWR) berechnet werden können, berücksichtigen Line-Blanketing aufgrund von Elementen der Eisengruppe, kleinskalige Windinhomogenitäten und die Elemente He, C, O, H, P, N und Ne. Unter Bezug auf Sternentwicklungsmodelle, die die Ursache der Wasserstoffunterhäufigkeit von [WC]-Sternen erklären, sind insbesondere die Neon- und Stickstoff-Häufigkeiten interessant. Von den drei möglichen Entwicklungskanälen für [WC]-Sterne führt lediglich das VLTP-Szenario zu einer Stickstoff-Überhäufigkeit von einigen Prozent bezogen auf die Masse. Bei einem VLTP, einem very late thermal pulse, handelt es sich um einen plötzlichen, starken Anstieg der Energieproduktion in der helium-brennenden Schale, während das Wasserstoffbrennen bereits zum Erliegen gekommen ist. Infolge eines VLTPs wird sämtlicher Wasserstoff kurz nach dem thermischen Puls in tiefere Schichten gemischt und in Anwesenheit von C, He und O verbrannt. Infolgedessen wird N und auch Ne erzeugt. Bei der Analyse von elf [WCE]-Sternen wurden für drei von ihnen, PB 6, NGC 5189 und [S71d]3, Stickststoffmassenanteile von 1,5 % bestimmt, während für drei andere Sterne solche hohen Stickstoffhäufigkeiten ausgeschlossen werden können. Für NGC 5189 gelang außerdem die qualitative Reproduktion der beobachteten, starken Ne-Spektrallinien mittels unserer Modelle. Zur Zeit lässt sich aus der Stärke der Ne-Emissionslinien der Ne-Massenanteil leider nur abschätzen, er scheint aber im Bereich einiger Prozent zu liegen. Mittels eines diagnostischen He-C-Linienpaares konnte das He:C-Massenverhältnis von 60:30 für [WCE]-Sterne bestätigt werden. Als Ergebnis der Analyse von PB 8 postulieren wir eine neue Klasse von wasserstoffarmen Zentralsternen, die in ihrer Elementzusammensetzung eher an massereiche WNL-Sterne als an [WC]-Sterne erinnern. Die ermittelten Massenanteile H:He:C:N:O betragen 40:55:1.3:2:1.3, der Wind von PB 8 enthält daher im Unterschied zu WN-Sternen signifikante Mengen von O und C. Es wird daher eine Klassifizierung als [WN/WC] vorgeschlagen.

<p> The globular cluster system of a nearby giant elliptical galaxy, NGC 5128 is studied to place constraints on the formation history of the galaxy. In this thesis, we have identified 190 new globular clusters via radial velocity measurements, bringing the total known population of globular clusters to 605 within this galaxy. We have examined the colour and spatial distributions of the globular cluster system and find it is bimodal in colour, with both a red and blue globular cluster population. The blue population is more spatially extended than the red, and both populations fall off in number density with radius as a power-law. There is a clear lack of globular clusters along the isophotal minor axis of the galaxy beyond a galactocentric radius of 15' warranting further search. With this new dataset, we have measured the ages, metallicities, and formation timescales for 72 globular clusters. The spectroscopic metallicity distribution function is bimodal indicating there is a metal-rich and metal-poor globular cluster population that corresponds to the red and blue globular clusters, respectively. We find the majority of both metal-rich (56%) and metal-poor (92%) globular clusters are older than 8 Gyr, comparable to the Milky Way globular cluster system. We do find a smaller fraction, 18% of our sample, are metal-rich globular clusters with ages younger than 5 Gyr, while the remaining globular clusters have intermediate ages between 5 -8 Gyr. The formation times of these globular clusters, estimated by their alpha-to-iron abundance ratios, indicate they formed quickly, on a timescale similar to globular clusters in most spiral galaxies, but on slower timescales than those in some other giant elliptical galaxies. The kinematics of the full globular cluster system is analyzed, as well as for the metal-rich and metal-poor globular clusters separately, as a function of galactocentric radius. We find the metal-poor globular cluster system has a small rotation signature of 17±14 km s-1 around no clearly defined axis and its dynamics are dominated by dispersion. The metal-rich globular cluster system has a mild rotation of 41 ± 15 km s-1 about the galaxy's isophotal major axis, following the rotation of a representative field star population, the planetary nebulae. The motion of the metal-rich globular cluster system is also dominated by random motion. We estimate the mass of the galaxy to be (5.5 ± 1.9) x 1011 with a mass-to-light ratio of 15.35 M0 /L80 using the globular cluster M0 population out to 20'. This estimate places NGC 5128 on a mass scale similar to other giant elliptical galaxies. The evidence collected suggests that NGC 5128 formed in a hierarchical scenario, gradually building up larger structure from smaller protogalaxies at early times in the history of the Universe. The group environment of NGC 5128 may have prolonged star formation within the galaxy as well, enabling a small spread in the old ages of globular clusters and also slowing the formation timescales compared to globular clusters in other giant elliptical galaxies. Results from this thesis also support more recent accretions in the history of NGC 5128, building up the more metal-rich and young globular clusters, which have a different rotation axis than the rest of the population. </p> / Thesis / Doctor of Philosophy (PhD)