BDTD - Biblioteca Digital de Teses e Dissertações
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Doctoral Thesis Evolução do índice de freio magnético para estrelas do tipo solar(2017-05-26) Cavalcante, Francisco Jânio; Freitas, Daniel Brito de; http://lattes.cnpq.br/2709876077692695; Martins, Bruno Leonardo Canto; Medeiros, José Renan de; http://lattes.cnpq.br/9151590034650501; Pacheco, Eduardo Janot; Nepomuceno, Mackson Matheus França; http://lattes.cnpq.br/1388531008519499The present work is based on the effects of the magnetic brake for the evolution of the loss of angular momentum and, consequently, the relation between stellar rotation and age. In general, this loss rate defined by dJ=dt depends on the angular velocity in the form dJ=dt / q, where q is a parameter of non-extensive statistical mechanics. In the context of stellar rotation, this parameter is directly related to the brake index. For q equal to unity, the magnetic field saturation scenario is recovered. Such an approach was proposed and investigated by de Freitas and De Medeiros for unsaturated field stars. We propose a new non-extensive approach to the evolution of stellar rotation based on the Reiners and Mohanty model. We have developed a non-extensive version of the Reiners and Mohanty torque, and compared with the model proposed by de Freitas and De Medeiros, using a velocity sample v sin i for ~ 16000 F and G field stars. As a result, we show that the Kawaler and Reiners-Mohanty models exhibit strong discrepancies in relation to the domain of validity of the entropic index q. These discrepancies are mainly due to the sensitivity of the stellar rotation on the stellar radius . Our results also showed that the modified Kawaler model is consistent within a wide mass range, while the Reiners and Mohanty model is restricted to masses smaller than that of a G6 Main Sequence star. We also devoted part of this thesis to studying the evolutionary behavior of the magnetic brake index for stars outside the Main Sequence. In this approach, we consider that the brake index undergoes a variation along the evolution of the star, that is, it is not a constant, but depends on the effect of I_. Thus, we justify the fact that G-type giant stars are governed by the same Skumanich law. However, they must be corrected by one factor. In this thesis, we show that this factor is due to the non-conservation of the volume of the star, which becomes more evident in later evolutionary stages, as is the case of the giants. We find that the effect of the variation of the moment of inertia (dI=dt) is more important when the volume of the star is not conserved.Master Thesis Um estudo sobre a interação estrela-planeta a partir da relação massa-período planetário com a atividade estelar(Universidade Federal do Rio Grande do Norte, 2012-03-30) Cavalcante, Francisco Jânio; Martins, Bruno Leonardo Canto; ; http://lattes.cnpq.br/2673267660389058; ; http://lattes.cnpq.br/2200207631918632; Medeiros, José Renan de; ; http://lattes.cnpq.br/9151590034650501; Miranda, Antônio Carlos da Silva; ; http://lattes.cnpq.br/3236324734090101n this work, we analyze the behavior of the chromospheric and coronal activities as a function of the mass and the orbital period of extrasolar planets which were detected by transit technique. So we look for possible effects of the planet on the star s chromosphere and corona. For this study we selected a sample of 48 stars with chromospheric activity indicator and 23 with coronal activity indicator. Our work is based on the work from Pont et al. (2011) in order to study stars with planets which were obtained by transit technique. Furthermore, we studied the relationship between planetary mass and orbital period with the chromospheric and coronal activity in order to better understand which influences the planets cause in the outer layers of stellar atmosphere. In our analysis we can observe that the mass of the planets exerts no influence in the stellar activity. However, we observed that the stellar coronal and chromospheric activities decrease with the increase of the orbital period of the planetMaster Thesis Um estudo sobre a interação estrela-planeta a partirda relação massa-período planetário com a atividade estelar(Universidade Federal do Rio Grande do Norte, 2012-03-30) Cavalcante, Francisco Jânio; Martins, Bruno Leonardo Canto; ; http://lattes.cnpq.br/2673267660389058; ; http://lattes.cnpq.br/2200207631918632; Medeiros, José Renan de; ; http://lattes.cnpq.br/9151590034650501; Miranda, Antônio Carlos da Silva; ; http://lattes.cnpq.br/3236324734090101In this work, we analyze the behavior of the chromospheric and coronal activities as a function of the mass and the orbital period of extrasolar planets which were detected by transit technique. So we look for possible effects of the planet on the star s chromosphere and corona. For this study we selected a sample of 48 stars with chromospheric activity indicator and 23 with coronal activity indicator. Our work is based on the work from Pont et al. (2011) in order to study stars with planets which were obtained by transit technique. Furthermore, we studied the relationship between planetary mass and orbital period with the chromospheric and coronal activity in order to better understand which influences the planets cause in the outer layers of stellar atmosphere. In our analysis we can observe that the mass of the planets exerts no influence in the stellar activity. However, we observed that the stellar coronal and chromospheric activities decrease with the increase of the orbital period of the planet