Thesis (M.Sc. (Physics & Electronics)) - Rhodes University, 2008.

Nebulosas planetárias são o resultado do processo de evolução estelar de estrelas com massas que vão de 0.8 a 8 massas solares; seu estudo possibilita uma melhor compreensão dos mecanismos de enriquecimento do meio interestelar por parte destas estrelas e a sua influência direta na evolução química da Galáxia. O uso da espectroscopia de campo integral possibilita o estudo da distribuição angular de propriedades como a densidade, as abundâncias iônicas, o perfil de ionização entre outras; já a espectroscopia de alta dispersão permite um estudo detalhado do campo de velocidades destes objetos, com velocidades típicas de expansão de 25km/s. Este trabalho é baseado nestas duas técnicas, com o objetivo de se obter a distribuição de diversos parâmetros físicos, apresentados aqui na forma de mapas e de diagramas, para uma amostra de nebulosas planetárias austrais. Os dados foram adquiridos utilizando a instrumentação do Observatório do Pico dos Dias (MCT/LNA), em duas missões realizadas em 2011 e 2012, usando respectivamente os espectrógrafos Eucalyptus e Coudé. Os resultados mostram a distribuição angular da densidade eletrônica, do fluxo das linhas do [SIII](6311A) e H, e também a distribuição da razão [SIII](6311A)/[SII](6717+6731A). Estes resultados salientam as regiões com maior grau de ionização, gradientes de ionização e inomogeneidades. Diagramas de diagnóstico são também mostrados a fim de complementar a análise e classificar os objetos. Os perfis cinemáticos também obtidos permitiram o estudo morfológico da amostra, detalhando suas estruturas. Os campos de velocidades foram usados para o cálculo da idade cinemática assim como a distância de uma das nebulosas da amostra. Os resultados obtidos são bons dados de entrada para futuras simulações morfo-cinemáticas que podem ser feitas utilizando softwares como o SHAPE, além de também serem possíveis simulações com códigos de fotoionização para a obtenção de modelos complementares. Os resultados em si são importantes tendo em vista a falta de informações a respeito da estrutura de planetárias austrais, já que não há nenhum grande levantamento morfológico como os existentes para as nebulosas boreais. / Planetary nebulae are the result of the stellar evolution process for stars from 0.8 to 8 solar masses; their study allows a better understanding of the enrichment mechanisms of interstellar medium by these stars, and their influence to the chemical evolution of the Galaxy. The use of integral field spectroscopy allows the study of the angular distribution of properties like density, chemical abundances and ionization profiles among others; on the other hand, high dispersion spectroscopy allows a detailed study of the velocity fields of these objects, with typical expansion velocity of 25km/s. This work is based on these two techniques; and aims to obtain the distribution of several physical parameters, presented here in the format of maps and diagrams. Data were acquired using the instrumentation from Pico dos Dias Observatory (MCT/LNA), in two missions performed in 2011 and 2012, using respectively the Eucalyptus and Coudé spectrographs. The results show the angular distribution of the electronic density, the flux of [SIII](6311A) and H alpha lines, and the distribution of the [SIII](6311A)/[SII](6717+ 6731A) ratio. These results highlight the regions with higher degree of ionization, ionization gradients and inhomogeneities. Diagnostics diagrams are shown too, aiming to complement the analysis and classify the objects. Kinematic profiles were also obtained and allowed the morphological study of the sample, detailing the structure of the objects. The velocity fields were used to calculate the kinematical age as well as the distance of one nebula of the sample. These results are a good start for future morpho-kinematic simulations. They can be used in softwares like SHAPE, and also in simulations with photoionization codes to obtain additional models. The results are also important in view of the rarity of information about structure of southern planetary nebulae, since there is no large survey such as those existing to the northern planetary nebulae.

This thesis reports the calibration, imaging and analysis of one epoch of VLBA observations of the 1612 MHz OH maser emission from the protoplanetary nebula OH 0.9+1.3. These are the first polarisation VLBI observations of this source and the spatial morphology of the OH emission is resolved on this scale. Proto-planetary nebulae represent the transition phase in the evolution of stars between the asymptotic giant branch (AGB) phase and their emergence as planetary nebulae. A long-standing astronomical question is how the predominantly spherical circumstellar envelopes of AGB stars evolve into the bipolar and axisymmetric structures that are commonly observed in planetary nebula. Proto-planetary nebulae offer a unique opportunity to study this transformation process. The high-resolution VLBI maps produced in this thesis were used to investigate the morphology and kinematics of OH 0.9+1.3 with a view to gaining insight into the development of asymmetries in the circumstellar material. The OH maser emission of OH 0.9+1.3 has a double-peaked profile with one peak blue-shifted and the other red-shifted with respect to the stellar velocity. The total intensity maser maps demonstrate a considerable degree of asymmetry with the blue- and red-shifted emission located in spatially distinct regions of the envelope. The blue-shifted emission is distributed preferentially along an axis at a projected position angle of » 135± ( North through East). The morphology of this source is not consistent with the standard symmetric thin-shell model and an attempt to fit the traditional OH/IR kinematic model of a simple expanding shell to the maser components was found to be unsatisfactory. No definitive evidence of a bipolar outflow was observed either. The high degree of asymmetry observed in the source is consistent with its status as a proto-planetary nebula. The source was imaged in all four Stokes parameters and the fractional linear and circular polarisations of the maser components were derived from the Stokes parameter maps. In all except one of the components the total fractional polarisation was found to be low ( < 15%). The mean fractional linear and circular polarisation were calculated to be 5.54% and 7.11% respectively. The absence of an identifiable Zeeman pair in the Stokes V map prohibited the estimation of the magnetic field in the circumstellar envelope of this source.

Central star binarity is often invoked as the main driver behind the shaping of aspherical planetary nebulae, however observational support for this hypothesis is lacking. This work presented in this thesis attempts to observationally test this theory by investigating the relationship between central star binarity and nebular morphology for several planetary nebulae. The discovery of six new binary central star systems is also reported. A detailed spatio-kinematical analysis of Abell 41 was performed, showing the nebula to have a bipolar morphology waisted by a toroidal structure, the symmetry axis of which is found to be perpendicular to the plane of the central binary. This alignment is exactly as predicted, indicating that the central binary, MT Ser, has played a significant role in shaping Abell 41. This is only the second planetary nebulae to have had this link, between binary and nebular inclination, explicitly shown. A spatio-kinematic model has been developed for ETHOS 1, indicating that its spectacular polar outflows are kinematically older than the central region of the nebula. This finding is discussed in the context of binary evolution, and it is concluded that the polar outflows in these nebulae are probably formed before their central binaries have entered the common-envelope phase. The central star of ETHOS 1 has yet to be the subject of detailed study, and as such, the orientation of the nebula could not be compared to that of its central binary. A spatio-kinematical analysis of SuWt 2 is presented, proving that the nebular ring is in fact at the waist of a much larger, extended bipolar structure. SuWt 2 is not known to contain a post-main sequence central star, required to eject and ionise the nebular shell, but rather a double A-type binary. The results of the analysis are discussed with relation to possible formation scenarios for SuWt 2. It is concluded that, while neither component of the double A-type binary could be the nebular progenitor, the presence of a third component to the system, which would have been the progenitor, cannot be ruled out. However, as there is no evidence that the central star of SuWt 2 is a binary alone, it is suggested that SuWt 2 should be removed from future lists of planetary nebulae known to host a binary central star. A sample of sixteen central stars of planetary nebulae, displaying morphological traits believed to be typical of central star binarity, were monitored for signs of periodic photometric variability associated with binarity. Six new photometrically variable close-binary stars were discovered, representing a ~15% increase on the previously known figure. The binary detection success rate from this investigation is compared to that of other surveys, and it is concluded that, while the results are promising, a more rigorous test is required to fully assess the extent to which specific morphological traits can be used as indicators of central star binarity.

New detections of CCH have been made toward nine planetary nebulae (PNe), including K4-47, K3-58, K3-17, M3-28, and M4-14. Measurements of the N = 1 -> 0 and N = 3 -> 2 transitions of this radical near 87 and 262 GHz were carried out using the new 12 m and the Sub-Millimeter Telescope (SMT) of the Arizona Radio Observatory (ARO). The presence of fine and/or hyperfine structure in the spectra aided in the identification. CCH was not observed in two PNe which are sources of C-60. The planetary nebulae with positive detections represent a wide range of ages and morphologies, and all had previously been observed in HCN and HNC. Column densities for CCH in the PNe, determined from radiative transfer modeling, were N-tot(CCH) similar to 0.2-3.3 x 10(15) cm(-2), corresponding to fractional abundances with respect to H-2 of f similar to 0.2-47 x 10(-7). The abundance of CCH was found to not vary significantly with kinematic age across a time span of similar to 10,000 years, in contrast to predictions of chemical models. CCH appears to be a fairly common constituent of PNe that are carbon-rich, and its distribution may anti-correlate with that of C-60. These results suggest that CCH may be a product of C-60 photodestruction, which is known to create C-2 units. The molecule may subsequently survive the PN stage and populate diffuse clouds. The distinct, double-horned line profiles for CCH observed in K3-45 and M3-28 indicate the possible presence of a bipolar flow oriented at least partially toward the line of sight.

From the main sequence onwards, stars of intermediate masses (1-8 Solar masses) eject a large portion of their mass with rates as high as 0.0001 Solar masses per year during their transition through the Asymptotical Giant Branch (AGB) stage. The outflows are shaped by the same mechanisms that shape the ejecta, which in turn appear to depart from spherical symmetry as early as the AGB stage. The ejecta are then evolving into asymmetrical structures. Stars like that are giant factories of dust, responsible for the enrichment of their surrounding Galactic medium in metals heavier than helium. Depending on their abundances during the AGB stage, the stars are either oxygen-rich or carbon-rich, and as such, the dust produced in their atmospheres is either O-rich or C-rich. The chemical composition of the ejecta, indicates the stellar chemistry at the moment of ejection. The disruption of the spherical symmetry of the mass loss can be caused by fast rotation, stellar magnetic fields or binarity, the latter being the most efficient and favourable mechanism. Such mechanisms can lead to the creation of circumstellar, equatorial, dusty structures, like discs, torii or spirals. Due to their small relative sizes, compared to their surrounding nebulae, they can be studied at best with the use of infrared interferometric techniques. We report the discovery of three such structures in sources at three different evolutionary stages, respectively, with the use of single- and multi-aperture interferometry. In the C-rich AGB star V Hya we imaged via aperture masking in the near-infrared, a complex and possibly orbiting structure, which is embedded within the star's molecular torus. Our MIDI observations in the mid-infrared have revealed, a silicate disc within the symbiotic nebula M2-9 that is currently being shaped by the central binary system within its core, and a C-rich disc-like structure in the born-again star Sakurai's Object, that is also aligned to an asymmetry found in its surrounding planetary nebula. Finally, we compare the properties of the structures found here with those found in the literature in order to establish a relation between late stellar evolution and the existence of dusty structures.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Sciences, 1980. / Microfiche copy available in Archives and Science. / Bibliography: leaves 152-168. / by Melvin Bruce Fegley, Jr. / Ph.D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Sciences, 1981. / Microfiche copy available in Archives and Science. / Bibliography: leaves 52-55. / by Guyton Hampton Watkins, Jr. / M.S.

Estrelas centrais de nebulosas planetárias (ECNPs) têm um intervalo de massa relativamente grande na fase da sequência principal, por isso espera-se que elas também tenham diferentes idades, tipicamente acima de 1 Gano. Além de necessárias para o conhecimento das propriedades das ECNPs, a determinação das idades é também importante no contexto da evolução química da Galáxia, como no estudo da variação temporal dos gradientes radiais de abundâncias químicas. Entretanto, não há um método único e confiável que possa ser aplicado para estimar a idade de todos os tipos de estrelas. Neste projeto, desenvolvemos dois métodos de idades cinemáticas baseados na relação idade-dispersão de velocidade do disco da Galáxia encontrada pelo recente levantamento Geneva-Copenhagen. O primeiro método compara a velocidade de rotação esperada da ECNP com a velocidade predita pela curva de rotação da Galáxia em sua posição, e interpreta a diferença entre elas como a dispersão de velocidade do objeto, relacionada com a idade. O segundo método consiste em calcular as componentes da velocidade espacial, com algumas hipóteses, e estimar diretamente as dispersões das velocidades, inferindo uma idade pela relação adotada. Duas amostras foram escolhidas, contendo 234 e 866 nebulosas planetárias, para as quais velocidades radiais precisas estão disponíveis na literatura. Os resultados sugerem que a maioria das ECNPs no disco Galáctico tem idade abaixo de 5 Gano, e um pico ente 0 e 3 Gano. Esses resultados são comparados com algumas distribuições recentes de idades baseadas em correlações independentes envolvendo as abundâncias químicas das nebulosas planetárias. / Central stars of planetary nebulae (CSPN) have a relatively large mass interval on the main sequence, so that it is expected that these stars also have different ages, typically above 1 Gyr. Apart from the properties of the CSPN themselves, the problem of age determination is also important in the context of the chemical evolution of the Galaxy, as in the understanding of the time variation of chemical abundance gradients. However, there are no unique and reliable methods that can be applied to estimate the age of all types of stars. In this work, we developed two methods of kinematic ages based on the age-velocity dispersion relation of the Galactic disk derived by the recent Geneva-Copenhagen survey. The first method compares the expected rotation velocity of CSPN with the predicted velocity by the Galactic rotation curve at its position, and interprets the difference between them as the velocity dispersion of the star, which is related to the stellar age. The second method consists in calculating the U, V, W velocity components of CSPN, with some hypotheses, and estimating directly the velocity dispersions, so that the age can be derived. Two samples were chosen, containing 234 and 866 nebulae, for which accurate radial velocities are available in the literature. The results suggest the most CSPN in the Galactic disk have ages under 5 Gyr with a distribution peaked between 0 and 3 Gyr. These results are also compared with some recent age distributions based on independent correlations involving the nebular chemical abundances.

O objetivo deste trabalho é o estudo das condições de existência e a determinação da concentração da molécula H2 em diferentes condições típicas de nebulosas planetárias, dentro da região ionizada. Para este cálculo, desenvolvemos sub-rotinas computacionais que se acoplam ao código de fotoionização unidimensional Aangaba que, até agora, somente considerava espécies atômicas (H, He, C, N, O, Mg, Ne, Si, S, Ar, Cl e Fe) e seus íons. Inserimos nesse código os equilíbrios químico e de ionização envolvendo a molécula H2 e os demais compostos de hidrogênio, H-, H2+, H3+, além do H, H+ e dos elétrons que o código de fotoionização Aangaba já considerava em sua forma original. A molécula H3 não é considerada por ser instável. Levamos em conta 41 diferentes mecanismos de formação e destruição desses compostos do hidrogênio. Destacamos particularmente o efeito da reação de formação de H2 na superfície de grãos na produção global dessa molécula em nebulosas planetárias, considerada na literatura como a rota mais importante de formação dessa molécula no meio interestelar. Para isso, estudamos a possibilidade da sobrevivência de grãos dentro da região ionizada da nebulosa planetária. Analisamos também a influência das propriedades da estrela central e da densidade do gás, assim como das propriedades dos grãos astrofísicos, na concentração de H2. Demonstramos que quantidades significativas de H2 podem sobreviver dentro da região ionizada de nebulosas planetárias, principalmente na região de recombinação do hidrogênio. A concentração de H2 relativa à densidade total de H alcança valores de até 1E-4 e a razão entre a massa de H2 e a massa total de H da NP chega a valores de 4E-4. Verificamos que a razão entre a massa de H2 e a massa de H total da nebulosa aumenta significativamente com o aumento da temperatura de estrela central. Essa maior quantidade de H2 em nebulosas planetárias com estrela central mais quente pode explicar porque é mais comum encontrar emissão da molécula H2 em nebulosas planetárias com estrutura bipolar (regra de Gatley), já que nebulosas com esse tipo morfológico têm estrela central tipicamente mais quente. Na literatura, o valor 6,9E-5 é obtido para a razão entre a massa de H2 e a massa de H total da nebulosa planetária NGC 6720, a partir de dados observacionais. Usando os mesmos parâmetros deste artigo, calculamos com o código de fotoionização Aangaba o valor de 3,3E-5, que está razoavelmente próximo do valor da literatura. / The goal of this work is the study of the H2 molecule survival and the determination of its abundance in different typical planetary nebulae conditions inside the ionized region. In order to do these calculations, we developed Fortran subroutines for the Aangaba one-dimensional photoionization code that, until this work, only took into account the atomic species (H, He, C, N, O, Mg, Ne, Si, S, Ar, Cl, and Fe) and their ions. Ionization and chemical equilibria of H, H+, H-, H2, H2+, and H3+ are assumed. The H3 molecule is not included because it is unstable. Fortyone different reactions that could form and destroy these species are taken into account. Reaction on grain surfaces, the most important mechanism for the production of H2 molecules in the interstellar medium, is analyzed in detail in the conditions of planetary nebulae ionized regions. We make a careful analysis of the grain survival in these regions. We also study the influence of the central star properties and gas density, as well as the astrophysical grain properties in the obtained H2 concentration. It is shown that a significant concentration of H2 can exist inside the ionized region of planetary nebulae, mostly in the recombination zone. The H2 concentration relative to the total hydrogen concentration reaches values as high as 1E-4 and the H2 mass to total hydrogen mass ratio inside the ionized region reaches values as high as 4E-4. The ratio increases with increasing temperature. This fact can explain why the H2 emission is more often observed in bipolar planetary nebulae (Gatley?s rule), since this kind of object has typically hotter stars. In the literature a H2 mass to total hydrogen mass ratio equal to 6.9E-5 is estimated from observations for the planetary nebula NGC6720. With the same input parameters for the gas density and the stellar spectrum, we calculated a ratio equal to 3.3E-5, close to the observed value.