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Title: New suns in the cosmos. IV. The multifractal nature of stellar magnetic activity in kepler cool stars
Authors: 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 de
Keywords: Data analysis – stars;Activity – stars;Stars - rotation;Solar- type - Sun
Issue Date: 2017
Publisher: The American Astronomical Society
Citation: FREITAS, D. B. de ; NEPOMUCENO, M. M. F. ; GOMES DE SOUZA, M. ; LEÃO, I. C. ; CHAGAS, M. L. das ; COSTA, A. D. ; CANTO MARTINS, B. L. ; MEDEIROS, J. R. de. New Suns in the Cosmos. IV. The Multifractal Nature of Stellar Magnetic Activity in Kepler Cool Stars. The Astrophysical Journal, v. 843, p. 103, 2017. Disponívelem: Acesso em: 20 Maio 2020.
Portuguese Abstract: In 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.
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