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Previous issue date: 2016-07-14 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior (CAPES) / Ap?s a descoberta pioneira de um planeta gigante orbitando 51 Peg por Mayor $\& $ Queloz (1995), cerca de duas d?cadas atr?s, j? forma descobertos descobertos de mais de 3434 planetas, em cerca de 2568 sistemas planet?rios. A grande maioria desses exoplanetas orbitam estrelas de campo da sequ?ncia principal com massas solares. As observa??es destas estrelas oferecem v?rias vantagens, incluindo brilho e uma grande variedade de caracter?sticas estelares, como a massa, idade, composi??o qu?mica e estado evolutivo. No entanto, as caracter?sticas muito diferentes das estrelas de campo tamb?m representa uma desvantagem para a nossa capacidade de tirar conclus?es precisas a perguntas muito b?sicas, incluindo o papel do ambiente estelar na forma??o do planeta. N?o h? uma resposta clara para o fato de que estrelas da sequ?ncia principal, que hospedagem planetas gigantes, s?o ricas em metal (Gonzalez 1997; Santos et al., 2004), enquanto que as estrelas evolu?das, que hospedagem planetas gigantes, n?o s?o (Pasquini et al 2007). De fato, diferentes fen?menos t?m sido propostos para explicar esta discrep?ncia em metalicidade, incluindo a polui??o estelar em estrelas da sequ?ncia principal (Laughlin $ \ & $ Adams 1997), ou um mecanismo de forma??o de planetas favorecendo o nascimento de planetas em torno de estrelas ricas em metal (Pollack al., 1996), como tamb?m o meio ambiente estelar (Haywood 2009). A observa??o das estrelas em aglomerados abertos oferece a possibilidade de controlar rigorosamente as caracter?sticas estelares, pois cada aglomerado representa um conjunto homog?neo de estrelas. Al?m disso, estrelas pertencentes a aglomerados abertos foram formadas ao mesmo tempo e nas mesmas condi??es e, portanto, espera-se que tem a mesma idade, metalicidade, e dist?ncia galatoc?ntrica. A partir do trabalho de Mermilliod $\& $ Mayor 2008, escolhemos aglomerados que abrigam estrelas gigantes para serem inclu?dos na nossa pesquisa. Utilizamos o banco de dados de aglomerados WEBDA (Mermilliod 1995) para obter informa??es sobre a nossa amostra. Os principais crit?rios que foram a idade do aglomerado (entre 0,02 e alguns Ganos, com massas do TO > 1,5 M$_{\ bigodot}$) e a magnitude de suas estrelas gigantes (mais brilhante do que V = 13,5). Em seguida, rejeitamos estrelas com ?ndice de cor (B - V) maiores que 1,4, porque gigantes frias brilhantes s?o conhecidas por terem VR inst?vel. As observa??es foram realizadas utilizando HARPS (Mayor et al., 2003), o ca?ador de planetas no telesc?pio ESO de 3,6 m. No modo de alta precis?o (HAM), temos uma abertura no c?u de um segundo de arco e um poder de resolu??o de 115.000. A faixa espectral coberta ? de 380-680 nm. Nossa an?lise espectral ? baseada nos modelos de atmosfera MARCS e na ferramentas espectrosc?picas Turbospectrum. N?s determinamos par?metros estelares e metalicidade de an?lise LTE de linhas Fe I e Fe II. Uma vez que temos a alta resolu??o e alta S/R espectral, n?s tamb?m computamos as abund?ncias de Li, usando a linha em 6.707,78 {\ AA}, Si I, Na I, Mg I, Al I, Ca I, Ti I, Co I, Ni I, Zr I, II e La Cr I. Apresentamos uma caracteriza??o espectrosc?pica de 42 estrelas gigantes, em 12 aglomerados estelares abertos, usando espectroscopia de alta resolu??o. Todos esses aglomerados s?o parte de uma busca por planetas gigantes que orbitam estrelas gigantes de massa intermediaria e os nossos resultados mostram que todos os aglomerados estudados tem $[Fe/H]$ com valores pr?ximos ao solar e que concordam com os resultados encontrados na literatura, apenas com uma pequena dispers?o. Estas abund?ncias nos permitir? realizar uma an?lise comparativa das abund?ncias de estrelas com e sem planetas, a partir do qual ser? poss?vel detectar diferen?as, anomalias e determinar o n?vel de intera??es planeta-estrela. O objetivo deste trabalho ? estudar a forma??o de planetas gigantes em aglomerados abertos. Desta forma, poderemos melhor compreender se um ambiente estelar pode afetar o processo de forma??o, a frequ?ncia e a evolu??o dos sistemas planet?rios em rela??o ?s estrelas de campo. / After the pioneering discovery of a giant planet orbiting 51 Peg by Mayor & Queloz
(1995), about two decades ago, the literature reports the discovery of more than 3434 confirmed
planets (exoplanet.eu), in about 2568 planetary systems. Solar mass main sequence field stars host
the vast majority of these exoplanets. The observation of these stars offers several advantages,
including brightness and a large variety of stellar characteristics, such as mass, age, chemical composition
and evolutionary status. However, the widely differing characteristics of field stars also
represents a drawback for our capability to derive precise conclusions to very basic questions, including
the role of stellar environment on planet formation. There is no clear answer for the fact that
main-sequence stars hosting giant planets are metal rich (Gonzalez 1997; Santos et al. 2004), while
evolved stars hosting giant planets are not (Pasquini et al. 2007). Indeed, different phenomena
have been proposed to explain this discrepancy in metallicity, including stellar pollution acting on
main-sequence stars (Laughlin & Adams 1997, e.g.), a planet formation mechanism favouring the
birth of planets around metal rich stars (Pollack al. 1996) and the stellar environment (Haywood
2009). The observation of stars in open cluster offers the possibility to strictly control the stellar
characteristics, because each cluster represents a homogeneous set of stars. Besides, open cluster
stars were formed at the same time and in the same circumstances and thus are expected to have the
same age, metallicity, and galactocentric distance. From the work of Mermilliod & Mayor 2008 we
choose clusters harbouring giants stars to be included in our survey. We used the WEBDA cluster
database (Mermilliod 1995) to get information about our sample. The main criteria we focused
on were the age of the cluster (between 0.02 and a few Gyr, with TO masses > 1,5 MJ) and the
magnitude of its giant stars (brighter than V = 13.5). Then we rejected stars with colour index (B -
V) larger than 1.4, because cool, bright giants are known to be RV unstable. The observations were
performed using HARPS (Mayor et al. 2003), the planet hunter at the ESO 3.6 m telescope. In high
accuracy mode (HAM), it has an aperture on the sky of one arcsecond, and a resolving power of
115000. The spectral range covered is 380 - 680 nm. Our spectral analysis is based on the MARCS
models of atmospheres and Turbospectrum spectroscopic tool. We determined stellar parameters
and metallicity from LTE analysis of Fe I and Fe II lines. Once we get the high resolution and high
S/N spectra, we also computed Li abundances that was obtained using the line at 6707.78 ?, Si I,
Na I, Mg I, Al I, Ca I, Ti I, Co I, Ni I, Zr I, La II and Cr I. We presented a spectroscopic characterisation of 42 giants, in 12 open clusters, using high resolution spectroscopy. All these clusters
are part of a survey for giant planets orbiting intermediate-mass giant stars and the results show
that all the clusters studied have [Fe=H] values close to solar, results that agree with the literature
with a small dispersion. These abundances will enable us to perform a comparative analysis of the
abundances of stars with and without planets, from which it will be possible to detect differences,
anomalies and determine the level of planet-star interactions. The goal of this campaign is to study
the formation of giant planets in OCs to understand whether a different environment might affect
the planet formation process, the frequency, and the evolution of planetary systems with respect to
field stars. In addition, searching for planets in OCs enables us to study the dependency of planet
formation on stellar mass and to compare the chemical composition of stars with and without
planets in detail.
| Identifer | oai:union.ndltd.org:IBICT/oai:repositorio.ufrn.br:123456789/21830 |
| Date | 14 July 2016 |
| Creators | Oliveira, Gislana Pereira de |
| Contributors | 96670193491, Miranda, Antonio Carlos da Silva, 12857645449, Angel, Cristian Andres Cortes, 01578836476, Freitas, Daniel Brito de, 57947139334, Medeiros, Jos? Renan de, 08896135400, Martins, Bruno Leonardo Canto |
| Publisher | PROGRAMA DE P?S-GRADUA??O EM F?SICA, UFRN, Brasil |
| Source Sets | IBICT Brazilian ETDs |
| Language | Portuguese |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, info:eu-repo/semantics/doctoralThesis |
| Source | reponame:Repositório Institucional da UFRN, instname:Universidade Federal do Rio Grande do Norte, instacron:UFRN |
| Rights | info:eu-repo/semantics/openAccess |
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