Navegando por Autor "Nepomuceno, M. M. F."
Agora exibindo 1 - 2 de 2
- Resultados por página
- Opções de Ordenação
Artigo New suns in the cosmos. iii. multifractal signature analysis(American Astronomical Society, 2016) Freitas, D. B. de; Nepomuceno, M. M. F.; Moraes Junior, P. R. V. de; Lopes, C. E. F.; Chagas, M. L. das; Bravo, J. P.; Costa, A. D.; Martins, B. L. Canto; Medeiros, José Renan de; Leão, I. C.In the present paper, we investigate the multifractality signatures in hourly time series extracted from the CoRoTspacecraft database. Our analysis is intended to highlight the possibility that astrophysical time series can be members of a particular class of complex and dynamic processes, which require several photometric variability diagnostics to characterize their structural and topological properties. To achieve this goal, we search for contributions due to a nonlinear temporal correlation and effects caused by heavier tails than the Gaussian distribution, using a detrending moving average algorithm for one-dimensional multifractal signals (MFDMA). We observe that the correlation structure is the main source of multifractality, while heavy-tailed distribution plays a minor role in generating the multifractal effects. Our work also reveals that the rotation period of stars is inherently scaled by the degree of multifractality. As a result, analyzing the multifractal degree of the referred series, we uncover an evolution of multifractality from shorter to larger periods.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.