<p> In this thesis we investigate the dynamical effect of a second generation of stellar formation in globular clusters in the context of the anomalous horizontal branch of NGC 2808. The horizontal branch of NGC 2808 is bifurcated in colour and exhibits an extended blue tail. This morphology can be explained if the blue tail stars have an enhanced helium content due to cluster self-enrichment. Specifically it has been proposed that NGC 2808 has experienced two distinct generations of star formation. The first generation has a top-heavy IMF, enhanced in 3 - 5Mo stars, and would produce many AGB stars within the first 200 Myrs of its life. The second generation then forms out of the helium-rich ejecta of the AGB stars and goes on to produce the blue tail in the horizontal branch that is currently observed in NGC 2808.</p> <p> We use three types of simulations to investigate this scenario. For a control model we run a simulation with a Salpeter IMF and a single generation. We then run models with a top-heavy IMF and a single generation and models with a top-heavy IMF and two generations. In the two generation models we also investigate the effect of concentration by examining simulations with two different length scales.</p> <p> We find that the models with the top-heavy IMF and a single generation are subject to extensive mass-loss in their early phases due to the large number of intermediate-mass stars and are less strongly affected by two-body relaxation than simulations with a Salpeter IMF. The models with two generations appear to be dynamically stable and long-lived objects, at least in their early stages. They seem to be observationally indistinguishable from single-generation clusters with Salpeter IMFs on the basis of their dynamics. The stellar populations of the two-generation clusters are found to have a much higher fraction of C-O white dwarfs than clusters with a Salpeter IMF. We find no evidence that these bodies will be preferentially scattered out of the system and they should remain part of the cluster until it dissolves after core collapse. The abundance of white dwarfs would provide an observational method of identifying two generation cluster candidates.</p> <p> Overall we find the two-generation scenario to be plausible on the basis of dynamics but due to the overabundance of white dwarfs produced by the top-heavy IMF and based on other studies of the chemistry of AGB stars we conclude that this scenario is unlikely to be the sole explanation for globular cluster self-enrichment.</p> / Thesis / Master of Science (MSc)

<p> The conditions ideally suited for blue straggler star formation are for the most part unknown, though there is mounting evidence to suggest that the preferred blue straggler formation pathway, whether it be via the coalescence of a primordial binary system or through the collision of two single main-sequence stars, depends largely on the cluster environment. In this thesis we are trying to isolate the preferred blue straggler formation mechanism(s) operating in various globular cluster environments by comparing relative blue straggler frequencies to global cluster properties.</p> <p> We define a series of selection rules to isolate the blue stragglers from main-sequence turn-off and extended horizontal branch stars in the colour-magnitude diagrams of 57 globular clusters taken from HST images of their central cores. The boundary conditions were defined using only the main-sequence turn-off as a point of reference, and are hence applied consistently from cluster to cluster. We chose to count only those stars found within one core radius of the cluster center in an effort to obtain a sample that is approximately representative of a uniform cluster environment where, ideally, a single blue straggler formation mechanism is predominantly operating. Relative frequencies of blue straggler stars are then found using the red giant branch for normalization and are subsequently analyzed. We confirm the anticorrelation between relative blue straggler frequency and total integrated cluster luminosity previously observed by Piotto et al. (2004), and find a new anticorrelation between relative blue straggler frequency and the central velocity dispersion, as well as a weak anticorrelation with the half-mass relaxation time. We find no other statistically significant trends. Observational implications pertaining to blue straggler formation mechanisms are then discussed.</p> <p> We present a very simple, semi-analytic model designed in an attempt to reproduce the observed trends in the core. Using estimates for the collisional timescales, we find that only a small percentage of the blue stragglers produced are a direct result of collisions. The majority of the blue stragglers created in our model are thus products of mass-transfer in tight, low-mass binary systems. We were surprised to find a reasonably good agreement between the data and our predictions, given the simplicity of our model. Our results suggest that the binary fraction could be a crucial parameter in shaping blue straggler populations, and hence better and more abundant observations of binary systems and their numbers could prove an important step in gaining a better understanding of blue straggler formation mechanisms.</p> / Thesis / Master of Science (MSc)

No description available.

The kinematics and white dwarf distribution have been studied for the Globular Cluster NGC 6397. The data was obtained from NASA’s Hubble Space Telescope in 2005. In particular, we used the images of a field 5’ Southeast of the core of NGC 6397 from Advanced Camera for Surveys to conduct our analyses. The first part of the study is about the kinematics of the globular cluster. Isotropy of velocity distribution and cluster rotation have been considered. As anticipated, this relaxed cluster exhibited no strong signs of anisotropy. However, there appears to be some level of rotation. The rotational motion turns out to be mu sub alpha cos(delta) = 3.88 ± 1.41 mas yr −1 and mu sub delta = −14.83 ± 0.58 mas yr −1. This result is not entirely expected and deserves further investigation in future studies. The second of the thesis is based on white dwarf populations in the globular cluster and the Galactic Bulge. As a first glance, there appears to be a lacking of white dwarfs at the age of approximately 0.6 Gyr. Further investigation reveals this to be statistically insignificant. Through this analysis, another pattern of white dwarf abundance is discovered. There appeared to be much more stars at the age between 0.9 − 2.0 Gyr. This could be a manifestation of modeling error. As the final consideration of this thesis, white dwarf candidates in the Galactic Bulge are illustrated. Approximately 10 candidates are found at the most probable location of stars in the Bulge. The analyses conducted in this thesis set stage for further development in understanding of globular clusters. In particular, the rotation analysis raises curiosity about the dynamics of NGC 6397 in the plane of the sky. Moreover, the velocity distribution analysis confirms properties and theories pertaining to globular clusters.

Nós apresentamos ajustes multicromáticos de isócronas ao diagrama cor-magnitude do aglomerado globular NGC 6366, baseados em dados fotométricos que obtivemos com o Southern Astrophysical Research (SOAR) Telescope e de arquivos do Hubble Space Telescope (HST) ACS/WFC. Nós corrigimos os dados por avermelhamento diferencial e calculamos a linha de tendência média dos diagramas cor-magnitude. Nós comparamos os dados com modelos de isócronas estelares de Dartmouth Stellar Evolution Database e PAdova and TRieste Stellar Evolution Code, ambos com a difusão microscópica começando na sequência principal. Considerando todas as determinações prévias de metalicidade desse aglomerado, nós testamos de metalicidades [Fe 111]=-1.00 até [Fe 111]=-0.50, e idades de 9 a 13 Ganos. Depois de determinar a extinção total para seletiva somente com estrelas pertencentes ao aglomerado, Rv=3.06 + 0.14, nós encontramos os parâmetros para esse aglomerado com sendo avermelhamento E (13 — V)= 0.69 ± 0.02(int) +0.04(ext), módulo de distância (m — M)v= 15.02 ± 0.07(int) ±0.13(ext), Idade= 11 ± 1.15 Ganos. Os modelos evolucionários falham em reproduzir a sequência de baixa Tef em diagramas cor-magnitude de multi-bandas, indicando que eles ainda tem uma descrição incompleta. Nós encontramos que as isócronas de Dartmouth Stellar Evolution Database ajustam melhor o ramo das sub gigantes e baixa sequência principal do que as isócronas de PAdova and TRieste Stellar Evolution Code. O uso de anãs brancas de aglomerados globulares em vez de anãs brancas do campo no estudo da formação, propriedades físicas e evolução estelar é justificado por vários fatores. Dentre eles o fato de que as anãs brancas mais frias de aglomerados globulares velhos são remanescentes das estrelas mais velhas que se formaram durante a formação do halo, ou seja, trazem informação da época em que a Galáxia estava se formando. Utilizamos as tabelas fotométricas de dados obtidos com o HST/ACS por Richer et al. (2008) e Bedin et al. (2009) dos aglomerados globulares NGC 6397 e M 4, respectivamente, que alcançam a volta para o azul da sequência de esfriamento das anãs brancas. Com a análise da sequência de esfriamento desses aglomerados, demonstramos que a cristalização de anãs brancas acontece através da liberação de calor latente. Demonstramos também, pela primeira vez, o problema dos modelos de sequência de esfriamento de anãs brancas na volta para o azul e propormos que uma possível solução é, além de considerar o efeito da absorção induzida por colisão, é também necessário considerar que na atmosfera de anãs brancas mais frias de aglomerados globulares há uma mistura de H e He, em vez de uma atmosfera de II puro. / We present multichromatic isochrone fits to the colour-magnitude data of the globular cluster NGC 6366, based on photometric data obtained with Southern Astrophysical Research (SOAR) Telescope and archive data from Hubble Space Telescope (HST) ACS/WFC. We corrected the photometric data for differential reddening and calculated the mean ridge fine of the colour magnitude diagrams. We compared the isochrones of Dartmouth Stellar Evolution Database and PAdova and TRieste Stellar Evolution Code, both with microscopic diffusion starting on the main sequence. Bracketing all previous determinations of this cluster, we tested metallicities from [FelH]=- 1.00 to [Fe/H]=-0.50, and ages from 9 to 13 Gyrs. After determining the total to selective extinction ratio only from stars belonging to this cluster, obtaining Rv=3.06 + 0.14, we found the parameters for this cluster to be reddening E(B — V)=0.69 ± 0.02(int) ±0.04(ext), distance modulus (m — M)v= 15.02 ± 0.07(int) ±0.13(ext), Age= 11 ± 1.15 Gyr. Evolutionary models fail to reproduce the low-T eff main sequence in multi-band colour magnitude diagrams, indicating that they still have an incomplete physical description. We found that the Dartmouth Stellar Evolution Database isochrones fit better the sub giant branch and low main sequence than the PAdova and TRieste Stellar Evolution Code. The use of white dwarf stars from globular clusters instead of field white dwarf stars in the study of formation, physical properties and stellar evolution is justified by several factors. Among them is the fact that the coolest white dwarf stars in old globular clusters are remnants of the oldest stars that formed during the formation of the Galactic halo, i. e., bring us information about the time that the Galaxy was still forming. We use the photometric data obtained with the HST/ACS by Richer et al. (2008) and Bedin et al. (2009) of the globular clusters NGC 6397 and M 4, respectively, that reach the blue turn of the white dwarf cooling sequence.With the analysis of the cooling sequence of these clusters, we demonstrated that the crystallization of white dwarfs occurs with the release of latent heat. Also, we demonstrate, for the first time, the problem of the blue turn in the white dwarf cooling sequence and propose that a possible solution is, in addition to considering the effect of collision-induced absorption, it is necessary to consider that the atmosphere of cooler white dwarf stars is composed by a mixture of H and He, rather than an atmosphere of pure H.

Nós apresentamos ajustes multicromáticos de isócronas ao diagrama cor-magnitude do aglomerado globular NGC 6366, baseados em dados fotométricos que obtivemos com o Southern Astrophysical Research (SOAR) Telescope e de arquivos do Hubble Space Telescope (HST) ACS/WFC. Nós corrigimos os dados por avermelhamento diferencial e calculamos a linha de tendência média dos diagramas cor-magnitude. Nós comparamos os dados com modelos de isócronas estelares de Dartmouth Stellar Evolution Database e PAdova and TRieste Stellar Evolution Code, ambos com a difusão microscópica começando na sequência principal. Considerando todas as determinações prévias de metalicidade desse aglomerado, nós testamos de metalicidades [Fe 111]=-1.00 até [Fe 111]=-0.50, e idades de 9 a 13 Ganos. Depois de determinar a extinção total para seletiva somente com estrelas pertencentes ao aglomerado, Rv=3.06 + 0.14, nós encontramos os parâmetros para esse aglomerado com sendo avermelhamento E (13 — V)= 0.69 ± 0.02(int) +0.04(ext), módulo de distância (m — M)v= 15.02 ± 0.07(int) ±0.13(ext), Idade= 11 ± 1.15 Ganos. Os modelos evolucionários falham em reproduzir a sequência de baixa Tef em diagramas cor-magnitude de multi-bandas, indicando que eles ainda tem uma descrição incompleta. Nós encontramos que as isócronas de Dartmouth Stellar Evolution Database ajustam melhor o ramo das sub gigantes e baixa sequência principal do que as isócronas de PAdova and TRieste Stellar Evolution Code. O uso de anãs brancas de aglomerados globulares em vez de anãs brancas do campo no estudo da formação, propriedades físicas e evolução estelar é justificado por vários fatores. Dentre eles o fato de que as anãs brancas mais frias de aglomerados globulares velhos são remanescentes das estrelas mais velhas que se formaram durante a formação do halo, ou seja, trazem informação da época em que a Galáxia estava se formando. Utilizamos as tabelas fotométricas de dados obtidos com o HST/ACS por Richer et al. (2008) e Bedin et al. (2009) dos aglomerados globulares NGC 6397 e M 4, respectivamente, que alcançam a volta para o azul da sequência de esfriamento das anãs brancas. Com a análise da sequência de esfriamento desses aglomerados, demonstramos que a cristalização de anãs brancas acontece através da liberação de calor latente. Demonstramos também, pela primeira vez, o problema dos modelos de sequência de esfriamento de anãs brancas na volta para o azul e propormos que uma possível solução é, além de considerar o efeito da absorção induzida por colisão, é também necessário considerar que na atmosfera de anãs brancas mais frias de aglomerados globulares há uma mistura de H e He, em vez de uma atmosfera de II puro. / We present multichromatic isochrone fits to the colour-magnitude data of the globular cluster NGC 6366, based on photometric data obtained with Southern Astrophysical Research (SOAR) Telescope and archive data from Hubble Space Telescope (HST) ACS/WFC. We corrected the photometric data for differential reddening and calculated the mean ridge fine of the colour magnitude diagrams. We compared the isochrones of Dartmouth Stellar Evolution Database and PAdova and TRieste Stellar Evolution Code, both with microscopic diffusion starting on the main sequence. Bracketing all previous determinations of this cluster, we tested metallicities from [FelH]=- 1.00 to [Fe/H]=-0.50, and ages from 9 to 13 Gyrs. After determining the total to selective extinction ratio only from stars belonging to this cluster, obtaining Rv=3.06 + 0.14, we found the parameters for this cluster to be reddening E(B — V)=0.69 ± 0.02(int) ±0.04(ext), distance modulus (m — M)v= 15.02 ± 0.07(int) ±0.13(ext), Age= 11 ± 1.15 Gyr. Evolutionary models fail to reproduce the low-T eff main sequence in multi-band colour magnitude diagrams, indicating that they still have an incomplete physical description. We found that the Dartmouth Stellar Evolution Database isochrones fit better the sub giant branch and low main sequence than the PAdova and TRieste Stellar Evolution Code. The use of white dwarf stars from globular clusters instead of field white dwarf stars in the study of formation, physical properties and stellar evolution is justified by several factors. Among them is the fact that the coolest white dwarf stars in old globular clusters are remnants of the oldest stars that formed during the formation of the Galactic halo, i. e., bring us information about the time that the Galaxy was still forming. We use the photometric data obtained with the HST/ACS by Richer et al. (2008) and Bedin et al. (2009) of the globular clusters NGC 6397 and M 4, respectively, that reach the blue turn of the white dwarf cooling sequence.With the analysis of the cooling sequence of these clusters, we demonstrated that the crystallization of white dwarfs occurs with the release of latent heat. Also, we demonstrate, for the first time, the problem of the blue turn in the white dwarf cooling sequence and propose that a possible solution is, in addition to considering the effect of collision-induced absorption, it is necessary to consider that the atmosphere of cooler white dwarf stars is composed by a mixture of H and He, rather than an atmosphere of pure H.

The efficiency of different spectroscopic techniques are examined through four different approaches: detailed analysis of IR spectra from the APOGEE database and examination of persistence, observing extremely metal-poor stars using the Plaskett telescope at the DAO, three analyses of various applications of machine learning in astronomy, and efficient transmission of light through optical fibres. Through the first study, the technical effects of persistence in the APOGEE's IR spectra are examined, and a new technique for removing the persistence is introduced. Most of the globular cluster Pal 1's spectra in the APOGEE database are affected by persistence. Therefore, the Pal 1 spectra are corrected for the persistence and their stellar abundances are determined independently from the APOGEE's pipeline, ASPCAP. Our results for the known members of Pal 1 were in a close agreement with the results from Sakari et al. (2011). Comparison between the results from the corrected and the original spectra suggest that the persistence could have a critical effect on the results. The second study of this thesis focused on observations of extremely metal-poor (EMP) stars from the Pristine survey. Through the DAO-Pristine project, we narrowed down the initial list of the Pristine survey by observing over 50 targets during 25 observing nights. The Ca II triplet absorption lines of the observed targets were examined and used for estimating the metallicity of the objects. Twelve candidate EMP stars with weak Ca II triplet lines are chosen from the observed targets. These candidate EMP stars will be observed with larger telescopes for more accurate determination of their metallicity. This thesis also presents the result of a threefold analysis for using machine learning techniques in astronomy. The supervised machine learning methods are used for determination of the stellar parameters of stars using their raw spectra, and unsupervised machine learning methods are used for classification of supernovae Type Ia from their calibrated spectra. The supervised analysis of the IR and optical spectra suggested that the StarNet neural network (Fabbro et al. 2017) can predict the stellar parameters of the APOGEE database and synthetic spectra, efficiently and accurately. The effect of persistence in the StarNet's results are examined, and we showed that the persistence does not have a critical effect on the overall performance of the StarNet. In addition, multiple unsupervised machine learning techniques such as K-mean and Self Organizing Maps (SOMs) are used for classification of the supernovae Type Ia spectra. The preliminary results suggest that a minimum of three subclasses of supernovae Type Ia can be found from our data, which are consistent with the previous studies. Finally, this thesis presents our final results for an optical system we designed for the MSE project. At UVic, we have used the standard collimated beam method, or "ring test," to measure the Focal Ratio Degradation (FRD) of MSE-like fibres. The FRD of the system is determined from the ratio of the Full Width Half Maximum (FWHM) to the radius of the ring. Early ring test results from a sample of MSE-like fibres show an FRD of 3.7%, which meets the MSE science requirement (i.e. FRD < 5% at f/2). Also, we have automated the ring test for fast, repeatable, and efficient measurements of an individual fibre in multi-fibre bundles. Our future tests will include automated non-static fibres in preparation for the MSE build phases. / Graduate

A major challenge in biology is to understand and predict the effect of mutations on protein structure, stability and function. Chapter 1 provides a general introduction on protein sequence-structure relationships and use of the CcdAB toxin-antitoxin system as a model to study molecular determinants of mutant phenotypes. In Chapter 2, we describe the use of saturation mutagenesis combined with deep sequencing to determine phenotypes for 1664 single-site mutants of the E. coli cytotoxin, CcdB. We examined multiple expression levels, effects of multiple chaperones and proteases and employed extensive in vitro characterization to understand how mutations affect these phenotypes. While general substitution preferences are known, eg polar residues preferred at exposed positions and non-polar ones at buried positions, we show that depth from the surface is important and that there are distinctly different energetic penalties for each specific polar, charged and aromatic amino acid introduced at buried positions. We also show that over-expression of ATP independent chaperones can rescue mutant phenotypes. Other studies have primarily looked at effects of ATP dependent chaperone expression on phenotype, where it is not possible to say whether mutational effects on folding kinetics or thermodynamic stability are the primary determinant of altered phenotypes, since there is energy input with these chaperones. The data suggest that mutational effects on folding rather than stability determine the in vivo phenotype of CcdB mutants. This has important implications for efforts to predict phenotypic effects of mutations and in protein design. While looking at the mutational landscape of a given gene from an evolutionary perspective, it is important to establish the genotype-phenotype relationships under physiologically relevant conditions. At the molecular level, the relationship between gene sequence and fitness has implications for understanding both evolutionary processes and functional constraints on the encoded proteins. Chapter 3 describes a methodology to test the fitness of individual CcdB mutants in E.coli over several generations by monitoring the rate of plasmid loss. We also propose a methodology for high throughput analysis of a pool of CcdB mutants using deep sequencing to quantitate the relative population of each mutant in a population of E.coli cells, grown for several generations and build the fitness landscape. While the F-plasmid based CcdAB system is known to be involved in plasmid maintenance through post-segregational killing, recent identification of ccdAB homologs on the chromosome, including in pathogenic strains of E.coli and other bacteria, has led to speculations on their functional role on the chromosome. In Chapter 4, we show that both the native ccd operon of the E.coli O157 strain as well as the ccd operon from the F- plasmid when inserted on the E.coli chromosome lead to protection from cell death under multiple antibiotic stress conditions through formation of persisters. Both the ccdF and ccdO157 operons may share common mechanisms for activation under stress conditions and also display weak cross activation. The chromosomal toxin shows weaker activity as compared to the plasmidic counterpart and is therefore less efficient in causing cell death. This has important implications in generation of potential therapeutics that target these TA systems. Chapter 5 describes the use of site-saturation mutagenesis coupled with deep sequencing to infer mutational sensitivity for the intrinsically disordered antitoxin, CcdA. The data allows us to make comparisons between overall as well as residue specific mutational sensitivity patterns with that of globular proteins, like CcdB (described in Chapter 2) and study toxin- antitoxin interaction and regulation through saturation suppressor mutagenesis. Interestingly, we found several examples of synonymous point mutations in CcdA that lead to loss of its activity. In Chapter 6 we attempt to explore the molecular bases for some of these synonymous mutations. In most cases the mutated codon has a similar overall codon preference to the WT one. Initial findings suggest a change in mRNA structure leading to change in CcdB: CcdA ratio, thereby causing cell death. These observations have important implications, because TA systems are ubiquitous, highly regulated and are known to be involved in multiple functions including drug tolerance. However a role for RNA structure in their regulation has not been shown previously. Appendix–I lists the mutational sensitivity scores for the CcdB mutants. Phenotypes for CcdA mutants obtained through deep sequencing have been tabulated in Appendix-II. Overall, we provide extensive datasets for mutational sensitivities of a globular (CcdB) and an intrinsically disordered protein (CcdA). Exploration of the molecular determinants of these mutant phenotypes not only provides interesting insights into CcdAB operon function but is also useful in understanding various aspects of protein stability, folding and activity as well as regulation of gene expression in bacteria.

O objetivo desta tese é analisar aspectos do sistema de satélites da Via Láctea de relevância cosmológica. Dentre estes aspectos destacam-se dois: o censo de satélites da Galáxia – onde constata-se que a quantidade destes objetos é muito inferior ao predito por modelos cosmológicos do tipo Matéria Escura Fria – e a frequência anômala de satélites luminosos, como a Pequena e Grande Nuvem de Magalhães (SMC e LMC respectivamente). Além disso, a determinação dos parâmetros estruturais da LMC pode impor vínculos a sua formação, histórico orbital e sobre a massa de nossa Galáxia. Neste trabalho é desenvolvida uma técnica de busca por satélites da Via Láctea. Esta técnica foi otimizada para utilizar dados da nova geração de grandes surveys de maneira eficiente. Este código, o FindSat, foi validado em uma amostra de galáxias anãs conhecidas e se mostrou eficiente em detectar as galáxias anãs mais tênues de que se tem registro. A aplicação desse código a uma região do Sloan Digital Sky Survey (SDSS) ainda não explorada nesse sentido revelou uma série de candidatos a novos satélites. Foram selecionados os candidatos mais promissores para observação de follow-up. Estas observações revelaram que um destes candidatos é de fato um novo satélite da Via Láctea. Este novo objeto é muito provavelmente um aglomerado globular do halo em estágio avançado de dissolução, porém, seu tamanho e magnitude integrada colocamno em um domínio limítrofe entre aglomerado e galáxia anã. Através da cuidadosa análise dos demais candidatos, constatou-se que nenhum outro é de fato um novo satélite da Galáxia. Além disso, foi realizado o estudo do perfil de densidade e geometria da LMC. Este estudo utilizou dados de verificação científica do Dark Energy Survey (DES). Constatase que o perfil de densidades para estrelas jovens (< 3 Gyr) possui um raio de escala cerca de 50% menor que o da população velha (> 3 Gyr), favorecendo o cenário de formação tipo outside-in. O estudo da extensão da componente estelar da LMC revela um raio de maré de cerca de 18 kpc, permitindo o cálculo da massa dinâmica total da LMC. O valor de massa obtido favorece a hipótese onde as Nuvens de Magalhães estariam por sua primeira passagem pelo perigaláctico. Além disso, a distância heliocêntrica e espessura do disco da LMC foram determinadas utilizando estrelas do Red Clump (RC). Notou-se que regiões no extremo norte da LMC estão sistematicamente mais próximas de nós do que o esperado, este efeito evidencia o warp no disco dessa galáxia. Observou-se que a espessura do disco aumenta na periferia da LMC, caracterizando o fenômeno de flare. O aumento na espessura juntamente com a maior extensão da população velha da LMC é interpretado como a presença de dois componentes discoidais. Esta é a primeira evidência desse tipo baseada apenas em métodos de contagem de estrelas. / The goal of this thesis is to analyse comologically relevant aspects of the Milky Way (MW) satellite system. Among these we may highlight two: the census of MW satellites – where the observed number of these objects is much less than what is expected by Cold Dark Matter (CDM) models – and the anomalous frequency of luminous satellites, such as the Small and Large Magellanic Clouds (SMC and LMC respectively). Besides the cosmological importance of the Clouds, the determination of its structural parameters may help to constraint models for their formation, orbital history, and ultimately the mass assembly in our Galaxy. In this work a technique to search newMWsatellites is developed. This technique was optimized to run efficiently on large datasets, such as the ones being generated by the new generation of surveys. The code, FindSat was validated in a sample of well known MW satellites and has proven to be well succeeded even for the most faint of these objects. The application of this code to an unexplored region of the Sloan Digital Sky Survey (SDSS) revealed a large amount of new dwarf galaxy candidates, some of which where selected for follow-up observation. These observations led to the discovery of a new MW satellite. This new object is most likely a globular cluster in an extreme stage of dissolution. However, its integrated magnitude and size makes it difficult to discern it from a dwarf galaxy. By a careful analysis of the remaining candidates, it was shown that no other new satellite was in the sample. The density profile and geometry of the LMC was also analysed. This study used the recent science verification data from the Dark Energy Survey (DES). It was found that the density profile for young stars (< 3 Gyr) has a scale radius 50% smaller when compared to the one obtained for older stars (> 3 Gyr). This result favours the outsidein galaxy formation scenario. The total extension of the LMC stellar component was measured, allowing the estimate of a truncation radius of about 18 kpc. Assuming that this truncation has tidal origins the dynamical mass of the LMC is inferred. The mass value found favours the case for the first perigalactic passage of the Clouds. Besides that, the heliocentric distance and thickness of the LMC disk was determined using Red Clump (RC) stars. Evidence for warp was found in the North edge of the LMC, in the sense that the disk is systematically more distance than expected. While the thickness of the disk increases towards the outer parts of the LMC, which is a phenomena known as flare. This effect joined with the fact that the older LMC stellar population is more extended, favours the presence of two disk components in this galaxy. This is the first evidence of this kind based only on star counts.

Nós apresentamos ajustes multicromáticos de isócronas ao diagrama cor-magnitude do aglomerado globular NGC 6366, baseados em dados fotométricos que obtivemos com o Southern Astrophysical Research (SOAR) Telescope e de arquivos do Hubble Space Telescope (HST) ACS/WFC. Nós corrigimos os dados por avermelhamento diferencial e calculamos a linha de tendência média dos diagramas cor-magnitude. Nós comparamos os dados com modelos de isócronas estelares de Dartmouth Stellar Evolution Database e PAdova and TRieste Stellar Evolution Code, ambos com a difusão microscópica começando na sequência principal. Considerando todas as determinações prévias de metalicidade desse aglomerado, nós testamos de metalicidades [Fe 111]=-1.00 até [Fe 111]=-0.50, e idades de 9 a 13 Ganos. Depois de determinar a extinção total para seletiva somente com estrelas pertencentes ao aglomerado, Rv=3.06 + 0.14, nós encontramos os parâmetros para esse aglomerado com sendo avermelhamento E (13 — V)= 0.69 ± 0.02(int) +0.04(ext), módulo de distância (m — M)v= 15.02 ± 0.07(int) ±0.13(ext), Idade= 11 ± 1.15 Ganos. Os modelos evolucionários falham em reproduzir a sequência de baixa Tef em diagramas cor-magnitude de multi-bandas, indicando que eles ainda tem uma descrição incompleta. Nós encontramos que as isócronas de Dartmouth Stellar Evolution Database ajustam melhor o ramo das sub gigantes e baixa sequência principal do que as isócronas de PAdova and TRieste Stellar Evolution Code. O uso de anãs brancas de aglomerados globulares em vez de anãs brancas do campo no estudo da formação, propriedades físicas e evolução estelar é justificado por vários fatores. Dentre eles o fato de que as anãs brancas mais frias de aglomerados globulares velhos são remanescentes das estrelas mais velhas que se formaram durante a formação do halo, ou seja, trazem informação da época em que a Galáxia estava se formando. Utilizamos as tabelas fotométricas de dados obtidos com o HST/ACS por Richer et al. (2008) e Bedin et al. (2009) dos aglomerados globulares NGC 6397 e M 4, respectivamente, que alcançam a volta para o azul da sequência de esfriamento das anãs brancas. Com a análise da sequência de esfriamento desses aglomerados, demonstramos que a cristalização de anãs brancas acontece através da liberação de calor latente. Demonstramos também, pela primeira vez, o problema dos modelos de sequência de esfriamento de anãs brancas na volta para o azul e propormos que uma possível solução é, além de considerar o efeito da absorção induzida por colisão, é também necessário considerar que na atmosfera de anãs brancas mais frias de aglomerados globulares há uma mistura de H e He, em vez de uma atmosfera de II puro. / We present multichromatic isochrone fits to the colour-magnitude data of the globular cluster NGC 6366, based on photometric data obtained with Southern Astrophysical Research (SOAR) Telescope and archive data from Hubble Space Telescope (HST) ACS/WFC. We corrected the photometric data for differential reddening and calculated the mean ridge fine of the colour magnitude diagrams. We compared the isochrones of Dartmouth Stellar Evolution Database and PAdova and TRieste Stellar Evolution Code, both with microscopic diffusion starting on the main sequence. Bracketing all previous determinations of this cluster, we tested metallicities from [FelH]=- 1.00 to [Fe/H]=-0.50, and ages from 9 to 13 Gyrs. After determining the total to selective extinction ratio only from stars belonging to this cluster, obtaining Rv=3.06 + 0.14, we found the parameters for this cluster to be reddening E(B — V)=0.69 ± 0.02(int) ±0.04(ext), distance modulus (m — M)v= 15.02 ± 0.07(int) ±0.13(ext), Age= 11 ± 1.15 Gyr. Evolutionary models fail to reproduce the low-T eff main sequence in multi-band colour magnitude diagrams, indicating that they still have an incomplete physical description. We found that the Dartmouth Stellar Evolution Database isochrones fit better the sub giant branch and low main sequence than the PAdova and TRieste Stellar Evolution Code. The use of white dwarf stars from globular clusters instead of field white dwarf stars in the study of formation, physical properties and stellar evolution is justified by several factors. Among them is the fact that the coolest white dwarf stars in old globular clusters are remnants of the oldest stars that formed during the formation of the Galactic halo, i. e., bring us information about the time that the Galaxy was still forming. We use the photometric data obtained with the HST/ACS by Richer et al. (2008) and Bedin et al. (2009) of the globular clusters NGC 6397 and M 4, respectively, that reach the blue turn of the white dwarf cooling sequence.With the analysis of the cooling sequence of these clusters, we demonstrated that the crystallization of white dwarfs occurs with the release of latent heat. Also, we demonstrate, for the first time, the problem of the blue turn in the white dwarf cooling sequence and propose that a possible solution is, in addition to considering the effect of collision-induced absorption, it is necessary to consider that the atmosphere of cooler white dwarf stars is composed by a mixture of H and He, rather than an atmosphere of pure H.