Publications

Dear all, below are my papers published in physics and astrophysical journals.

Note: Click on the DOI or Link (ArXiv) of the paper to access the PDF file (free or not).

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• 2015

Title: Stellar cycles from photometric data: CoRoT stars

Author(s): Ferreira Lopes, C. E.; Leão, I. C.; de Freitas, D. B.; Canto Martins, B. L.; Catelan, M.; De Medeiros, J. R.

Title: The Rotational Behavior of Kepler Stars with Planets

Author(s): Paz-Chinchón, F.; Leão, I. C.; Bravo, J. P.; de Freitas, D. B.; Ferreira Lopes, C. E.; Alves, S.; Catelan, M.; Canto Martins, B. L.; De Medeiros, J. R.

Abstract: We analyzed the host stars of the present sample of confirmed planets detected by Kepler and Kepler Objects of Interest to compute new photometric rotation periods and to study the behavior of their angular momentum. Lomb–Scargle periodograms and wavelet maps were computed for 3807 stars. For 540 of these stars, we were able to detect rotational modulation of the light curves at a significance level of greater than 99%. For 63 of these 540 stars, no rotation measurements were previously available in the literature. According to the published masses and evolutionary tracks of the stars in this sample, the sample is composed of M- to F-type stars (with masses of 0.48–1.53 M ) with rotation periods that span a range of 2–89 days. These periods exhibit an excellent agreement with those previously reported (for the stars for which such values are available), and the observed rotational period distribution strongly agrees with theoretical predictions. Furthermore, for the 540 sources considered here, the stellar angular momentum provides an important test of Kraft’s relation based on the photometric rotation periods. Finally, this study directly contributes in a direct approach to our understanding of how angular momentum is distributed between the host star and its (detected) planetary system; the role of angular momentum exchange in such systems is an unavoidable piece of the stellar rotation puzzle.

Link: http://arxiv.org/abs/1502.05051

DOI:

10.1088/0004-637X/803/2/69

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Title: Nonextensivity at the Circum-Pacific subduction zones-Preliminary studies

Author(s): Scherrer, T. M.; França, G. S.; Silva, R.; de Freitas, D. B.; Vilar, C. S.

Abstract: Following the fragment-asperity interaction model introduced by Sotolongo-Costa and Posadas (2004) and revised by Silva et al. (2006), we try to explain the nonextensive effect in the context of the asperity model designed by Lay and Kanamori (1981). To address this issue, we used data from the NEIC catalog in the decade between 2001 and 2010, in order to investigate the so-called Circum-Pacific subduction zones. We propose a geophysical explanation to nonextensive parameter q. The results need further investigation however evidence of correlation between the nonextensive parameter and the asperity model is shown, i.e., we show that q-value is higher for areas with larger asperities and stronger coupling.

DOI:

10.1016/j.physa.2014.12.038

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Title: Analysis of four Brazilian seismic areas using a nonextensive approach

Author(s): Scherrer, T. M.; França, G. S.; Silva, R.; de Freitas, D. B.; Vilar, C. S.

Abstract: We analyse four seismic areas in Brazil using a nonextensive model and the data from the Brazilian Seismic Bulletin between 1720 and 2013. Two of those regions are contrasting zones, while the other two are dominated by seismic active faults. We notice that intraplate seismic zones present q-values similar to others fault zones, but the adjustment in contrast areas results in higher values for this parameter. The results reveal the nonextensive approach adjusts robustly also in case of intraplate earthquakes, showing that the Tsallis formalism is unquestionably a powerful tool to the analysis of this phenomenon.

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• 2014

Title: Strong evidences for a nonextensive behavior of the rotation period in open clusters

Author(s): de Freitas, D. B.; Nepomuceno, M. M. F.; Soares, B. B.; Silva, J. R. P.

Abstract: Time-dependent nonextensivity in a stellar astrophysical scenario combines nonextensive entropic indices q_K derived from the modified Kawaler’s parametrization, and q, obtained from rotational velocity distribution. These q’s are related through a heuristic single relation given by q≈ q₀(1-Delta t/q_K) , where t is the cluster age. In a nonextensive scenario, these indices are quantities that measure the degree of nonextensivity present in the system. Recent studies reveal that the index q is correlated to the formation rate of high-energy tails present in the distribution of rotation velocity. On the other hand, the index q_K is determined by the stellar rotation-age relationship. This depends on the magnetic-field configuration through the expression q_K=1+4aN/3 , where a and N denote the saturation level of the star magnetic field and its topology, respectively. In the present study, we show that the connection q-q_K is also consistent with 548 rotation period data for single main-sequence stars in 11 open clusters aged less than 1 Gyr. The value of q_K ~2.5 from our unsaturated model shows that the mean magnetic-field topology of these stars is slightly more complex than a purely radial field. Our results also suggest that stellar rotational braking behavior affects the degree of anti-correlation between q and cluster age t. Finally, we suggest that stellar magnetic braking can be scaled by the entropic index q.

Link: http://arxiv.org/abs/1408.0657

DOI:

10.1209/0295-5075/108/39001

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Title: Chandrasekhar’s Relation and Stellar Rotation in the Kepler Field

Author(s): Silva, J. R. P.; Soares, B. B.; de Freitas, D. B.

Abstract: According to the statistical law of large numbers, the expected mean of identically distributed random variables of a sample tends toward the actual mean as the sample increases. Under this law, it is possible to test the Chandrasekhar’s relation (CR), <V> = (pi/4)^-1<Vsin i>, using a large amount of Vsin i and V data from different samples of similar stars. In this context, we conducted a statistical test to check the consistency of the CR in the Kepler field. In order to achieve this, we use three large samples of V obtained from Kepler rotation periods and a homogeneous control sample of Vsin i to overcome the scarcity of Vsin i data for stars in the Kepler field. We used the bootstrap-resampling method to estimate the mean rotations (<V> and <Vsin i>) and their corresponding confidence intervals for the stars segregated by effective temperature. Then, we compared the estimated means to check the consistency of CR, and analyzed the influence of the uncertainties in radii measurements, and possible selection effects. We found that the CR with <sin i> = pi/4 is consistent with the behavior of the <V> as a function of <Vsin i> for stars from the Kepler field as there is a very good agreement between such a relation and the data.

Link: http://arxiv.org/abs/1410.8048

DOI:

10.1088/0004-637X/796/1/69

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Chapters and Forewords

Wavelet Analysis of Stellar Rotation and Other Periodicities:. from the Sun to Corot

ASTRONOMY AND RELATIVISTIC ASTROPHYSICS New Phenomena and New States of Matter in the Universe. Proceedings of the Third Workshop (IWARA07). Held 3 – 6 October 2007 in João Pessoa, Paraíba, Brazil. Edited by César A Zen Vasconcellos (Federal University of Rio Grande do Sul, Brazil), Bardo E J Bodmann (Federal University of Rio Grande do Sul, Brazil), Horst Stoecker (Johann Wolfgang Goethe University, Germany), Marcelo J Reboucas (Centro Brasileiro de Pesquisas Físicas, Brazi), Valdir B Bezerra (Federal University of Paraíba, Brazil) & Walter Greiner (Johann Wolfgang Goethe University, Germany) . Published by World Scientific Publishing Co. Pte. Ltd., 2010. ISBN #9789814304887, pp. 147-151

By de Freitas, D. B.; C. de Leao, I.; Martins, B. L. Canto; Do Nascimento, J. D.; de Medeiros, J. R.

The Role of Magnetic Braking Effects on the Rotation of Subgiant and Giant Stars

ASTRONOMY AND RELATIVISTIC ASTROPHYSICS New Phenomena and New States of Matter in the Universe. Proceedings of the Third Workshop (IWARA07). Held 3 – 6 October 2007 in João Pessoa, Paraíba, Brazil. Edited by César A Zen Vasconcellos (Federal University of Rio Grande do Sul, Brazil), Bardo E J Bodmann (Federal University of Rio Grande do Sul, Brazil), Horst Stoecker (Johann Wolfgang Goethe University, Germany), Marcelo J Reboucas (Centro Brasileiro de Pesquisas Físicas, Brazi), Valdir B Bezerra (Federal University of Paraíba, Brazil) & Walter Greiner (Johann Wolfgang Goethe University, Germany) . Published by World Scientific Publishing Co. Pte. Ltd., 2010. ISBN #9789814304887, pp. 245-250

By Maciel, S. C.; de Freitas, D. B.; de Medeiros, J. R.