Thesis (Ph. D.)--University of Canterbury, 2006. / Typescript (photocopy). Includes bibliographical references (p. 195-204). Also available via the World Wide Web.

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Thesis (Ph. D.)--University of Canterbury, 2009. / Typescript (photocopy). "December 18, 2009." Includes bibliographical references (p. 251-255). Also available via the World Wide Web.

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Study determined if 2MASS photometric data are reliable for luminosity classification using JHK plots of Reid and Hawley (2001). Effects of interstellar reddening on the placement of giant and dwarf data on the JIIK plot were analyzed. Dwarfs (N=54) were selected from Hipparchos and the 2MASS data reduced to an H-K range of 0.14-0.40. A disk dwarf region was identified using linear regression on the low space velocity stars. Giants selected from Volume 5 of the Michigan Catalogue of HD stars and SAG stars classified at Ball State University. They yielded 304 individual giants and 13 matches in the 0.14-0.40 H-K range respectively. The 2MASS data was reliable for luminosity classification of the SAGBSU giants. The classification of the Michigan giants was not possible due to interstellar reddening and the likely presence of faint giant companions. / Department of Physics and Astronomy

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Made available in DSpace on 2014-12-17T15:15:04Z (GMT). No. of bitstreams: 1 BrunoLM_DISSERT.pdf: 7166646 bytes, checksum: f3020f244ae15650c85072127bcd05e2 (MD5) Previous issue date: 2014-04-24 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / Lithium (Li) is a chemical element with atomic number 3 and it is among the lightest known elements in the universe. In general, the Lithium is found in the nature under the form of two stable isotopes, the 6Li and 7Li. This last one is the most dominant and responds for about 93% of the Li found in the Universe. Due to its fragileness this element is largely used in the astrophysics, especially in what refers to the understanding of the physical process that has occurred since the Big Bang going through the evolution of the galaxies and stars. In the primordial nucleosynthesis in the Big Bang moment (BBN), the theoretical calculation forecasts a Li production along with all the light elements such as Deuterium and Beryllium. To the Li the BNB theory reviews a primordial abundance of Log log ǫ(Li) =2.72 dex in a logarithmic scale related to the H. The abundance of Li found on the poor metal stars, or pop II stars type, is called as being the abundance of Li primordial and is the measure as being log ǫ(Li) =2.27 dex. In the ISM (Interstellar medium), that reflects the current value, the abundance of Lithium is log ǫ(Li) = 3.2 dex. This value has great importance for our comprehension on the chemical evolution of the galaxy. The process responsible for the increasing of the primordial value present in the Li is not clearly understood until nowadays. In fact there is a real contribution of Li from the giant stars of little mass and this contribution needs to be well streamed if we want to understand our galaxy. The main objection in this logical sequence is the appearing of some giant stars with little mass of G and K spectral types which atmosphere is highly enriched with Li. Such elevated values are exactly the opposite of what could happen with the typical abundance of giant low mass stars, where convective envelops pass through a mass deepening in which all the Li should be diluted and present abundances around log ǫ(Li) ∼1.4 dex following the model of stellar evolution. In the Literature three suggestions are found that try to reconcile the values of the abundance of Li theoretical and observed in these rich in Li giants, but any of them bring conclusive answers. In the present work, we propose a qualitative study of the evolutionary state of the rich in Li stars in the literature along with the recent discovery of the first star rich in Li observed by the Kepler Satellite. The main objective of this work is to promote a solid discussion about the evolutionary state based on the characteristic obtained from the seismic analysis of the object observed by Kepler. We used evolutionary traces and simulation done with the population synthesis code TRILEGAL intending to evaluate as precisely as possible the evolutionary state of the internal structure of these groups of stars. The results indicate a very short characteristic time when compared to the evolutionary scale related to the enrichment of these stars / O L?tio (Li) ? um elemento qu?mico com n??mero at?mico 3 e est? entre os elementos mais leves conhecidos no Universo. De forma geral, o L?tio ? encontrado na natureza sob a forma de dois is?topos est?veis, o 6Li e o 7Li. Este ?ltimo ? o mais dominante e responde por cerca de 93% do Li encontrado no Universo. Devido a sua caracter?stica de fragilidade, esse elemento ? largamente utilizado na astrof?sica, sobretudo no que diz respeito ao entendimento dos processos f?sicos que ocorrem desde o Big Bang, passando pela evolu??o de gal?xias e estrelas. Na nucleoss?ntese primordial no momento do Big Bang (BBN), os c?lculos te?ricos preveem uma produ??o de Li juntamente com outros elementos leves tais como o Deut?rio e o Ber?lio. Para o Li, a teoria do BBN rev? uma abund?ncia primordial de log ǫ(Li) = 2.72 dex, numa escala logar?tmica relativa ao H. A abund?ncia de Li encontrada nas estrelas pobres em metal ou estrelas de Popula??o II, ? assim clamado como sendo a abund?ncia de Li primordial e ? medida como sendo log ǫ(Li) = 2.27 dex. J? no ISM (interestellar medium), que reflete o valor atual, a abund?ncia de L?tio ? de log ǫ(Li) = 3.2 dex. Este valor ? de grande import?ncia para a nossa compreens?o da evolu??o qu?mica da Gal?xia. Os processos respons?veis pelo aumento do valor primordial para o valor presente do Li n?o s?o claramente compreendidos nos dias de hoje. O fato ? que existe uma contribui??o real de Li provenientes das estrelas gigantes de pouca massa, e esta contribui??o precisa ser bem estimada se quisermos entender a evolu??o qu?mica da nossa Gal?xia. O principal entrave desta sequ?ncia l?gica, ? o aparecimento de algumas estrelas gigantes de baixa massa, de tipos espectrais G e K, cuja atmosfera ? altamente enriquecida com Li. Tais valores elevados s?o exatamente ao contr?rio do que se poderia esperar como abund?ncia t?pica para as estrelas gigantes de baixa massa, onde envelopes convectivos passam por um aprofundamento em massa (dredge-up) nos quais todo o Li deveria ser dilu?do e apresentar abund?ncias em torno de log ǫ(Li) ∼ 1.4 dex, seguindo o modelo padr?o de evolu??o estelar. Na literatura, encontram-se tr?s sugest?es que tentam reconciliar os valores da abund?ncia de Li de forma te?rica e observada nessas gigantes ricas em Li; no entanto, nenhuma dessas traz respostas conclusivas. No presente trabalho, propomos um estudo qualitativo do estado evolutivo das estrelas ricas em Li presentes na literatura. Neste sentido, foi coletado uma amostra de estrelas ricas em Li juntamente com a recente descoberta da primeira estrela rica em Li observada pelo sat?lite Kepler. O objetivo principal deste trabalho ? de promover uma s?lida discuss?o sobre o estado evolutivo baseado nas caracter?sticas obtidas a partir da an?lise s?smica do objeto observado pelo sat?lite Kepler. Utilizamos tra?ados evolutivos e simula??es feitas com o c?digo de s?ntese de popula??o TRILEGAL com o intuito de avaliar t?o preciso quanto poss?vel o estado evolutivo e a estrutura interna deste grupo de estrelas. Os resultados apontam para um tempo caracter?stico muito curto, quando comparado com a escala evolutiva, referente ao enriquecimento destas estrelas

Context. Theoretical studies predict that the length scale of convection in stellar atmospheres isproportional to the pressure scale height, which implies that giant and supergiant stars should have convection granules of sizes comparable to their radii. Numerical simulations and the observation of anisotropies on stellar discs agree well with this prediction. Aims. To measure the characteristic sizes of convection structures of models simulated with the CO5BOLD code, to look at how they vary between models and to study their limitations due to numerical resolution. Methods. Fourier analyses are performed to frames from the models to achieve spatial spectral power distributions which are averaged over time. The position of the main peak and the averagevalue of the wavevector are taken as indicators of these sizes. The general shape of the intensity map of the disc in the frame is fitted and subtracted so that it does not contaminate the Fourier analysis. Results. A general relationship of the convection granule size being more or less ten times larger than the pressure length scale is found. The expected wavevector value of the time-averaged spectral power distributions is higher than the position of the main peak. Loose increasing trends with the characteristic sizes by the pressure scale height increasing against stellar mass, radius, luminosity,temperature and gravity are found, while a decreasing trends are found with the radius and modelresolution. Bad resolution subtracts signals on the slope at the side of the main peak towards larger wavevector values and in extreme cases it creates spurious signal towards the end of the spectrum due to artifacts appearing on the frames. Conclusions. The wavevector position of the absolute maximum in the time-averaged spectral power distribution is the best measure of the most prominent sizes in the stellar surfaces. The proportionality constant between granule size and pressure length scale is of the same order ofmagnitude as the one in the literature, however, models present sizes larger than the ones expected, likely because the of prominent features do not correspond to convection granules but to larger features hovering above them. Further studies on models with higher resolution will help in drawing more conclusive results. Appendix. The SIA pipeline takes a set of time-dependent pictures of stellar disks and uses a Fourier Analysis to measure the characteristic sizes of their features and other useful quantities, such as standard deviations or the spatial power distributions of features. The main core of the pipeline consists in identifying the stellar disc in the frames and subtracting their signal from the spatial power distributions through a general fit of the disc intensity. To analyze a time sequence, the SIA pipeline requires at least two commands from the user. The first commandorders the SIA pipeline to read the .sav IDL data structure file where the frame sequence is stored and to produce another .sav file with information on the spectral power distributions, the second command orders the reading of such file to produce two more .sav files, one containing time-averaged size measurements and their deviations while the other breaking down time-dependant information and other arrays used for the calculations. The SIA pipeline has been entirely written in Interactive Data Language (IDL). Most of the procedures used here are original from the SIA pipeline, but a small handfull like ima3_distancetransform.pro, power2d1d.pro, extremum.pro and smooth2d.pro from Bernd Freytag and peaks.pro and compile opt.pro amongst others are actually external. / <p>The report consists in two parts:</p><p>1.- The main project, where we apply our pipeline and get scientific results.</p><p>2.- The appendix, where a technical description of the pipeline is given.</p>