Navegando por Autor "Souza, M. Gomes de"
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Artigo Debris disks among Kepler solar rotational analog stars(American Astronomical Society, 2018-12-21) Martins, Bruno Leonardo Canto; Silva Sobrinho, R.; Costa, A. D. da; Leão, Izan de Castro; Silva, D. Freire da; Teixeira, M. A.; Souza, M. Gomes de; Freitas, D. Freire da; Bravo, J. P.; Chagas, M. L. das; Medeiros, José Renan deObservations of circumstellar disks provide a powerful tool for our understanding of planetary system dynamics. Analogs to the solar system asteroid belts, debris disks result from the collision of the remaining solid material of the planet formation process. Even if the presence of disks is now reported for hundreds of stars, its detection around stars similar to the Sun is still very sparse. We report the results of a search for debris disks around Kepler stars with surface physical parameters close to solar values, including rotation period, using observations by the Wide-field infrared Survey Explorer. From the entire sample of Kepler stars, 881 targets were identified with these parameters and only six of them (KIC 1868785, 7267949, 7435796, 10533222, 11352643, and KIC 11666436) show unambiguous infrared excess, for which we determined as debris disk physical parameters. Interestingly, the present study reveals traces of debris disks much more massive and brighter than the solar system zodiacal dust, probably resulting from recent violent collisional events, orbiting stars with ages around the solar values.Artigo New suns in the cosmos. IV. The multifractal nature of stellar magnetic activity in kepler cool stars(The American Astronomical Society, 2017) Freitas, D. B. de; Nepomuceno, M. M. F.; Souza, M. Gomes de; Leão, Isan Castro; Chagas, M. L. das; Costa, A. D.; Martins, Bruno Leonardo Canto; Medeiros, José Renan deIn the present study, we investigate the multifractal nature of a long-cadence time series observed by the Kepler mission for a sample of 34 M dwarf stars and the Sun in its active phase. Using the Multifractal Detrending Moving Average algorithm, which enables the detection of multifractality in nonstationary time series, we define a set of multifractal indices based on the multifractal spectrum profile as a measure of the level of stellar magnetic activity. This set of indices is given by the (A, ${\rm{\Delta }}\alpha $, C, H)-quartet, where A, ${\rm{\Delta }}\alpha $, and C are related to geometric features from the multifractal spectrum and the global Hurst exponent H describes the global structure and memorability of time series dynamics. As a test, we measure these indices and compare them with a magnetic index defined as S ph and verify the degree of correlation among them. First, we apply the Poincaré plot method and find a strong correlation between the $\langle {S}_{\mathrm{ph}}\rangle $ index and one of the descriptors that emerges from this method. As a result, we find that this index is strongly correlated with long-term features of the signal. From the multifractal perspective, the $\langle {S}_{\mathrm{ph}}\rangle $ index is also strongly linked to the geometric properties of the multifractal spectrum except for the H index. Furthermore, our results emphasize that the rotation period of stars is scaled by the H index, which is consistent with Skumanich's relationship. Finally, our approach suggests that the H index may be related to the evolution of stellar angular momentum and a star's magnetic properties.