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The aim of this work is to determine the deviation of the value of magnetic braking index $q$ from Skumanich $q=3$ canonical value for giant and main-sequence stars. In this context, the present work attempts to analytically calculate the braking index based on the balance of gravitational and centrifugal forces, a determining factor for understanding the delicate mechanisms that control the spin-down of stars in these evolutionary phases. In the present study, we used a wide sample of stellar targets from the \textit{Kepler} mission with well-defined mass, radius, and rotation period. As a result, \textit{Kepler} stellar parameters provide rather precise values of $q$ index limited in the range $1\leq q\leq 3$, which is consistent with the predictions of the model of magnetic stellar wind. Our results show conclusively that, within the model used in this work, any significant deviation of the braking index away from the value $q=3$ occurs at masses higher than the Kraft break., 7 pages, 5 figures (submitted to EPL)

We analyze the data from the 6 gravitational waves signals detected by LIGO through the lens of multifractal formalism using the MFDMA method, as well as shuffled and surrogate procedures. We identified two regimes of multifractality in the strain measure of the time series by examining long memory and the presence of nonlinearities. The moment used to divide the series into two parts separates these two regimes and can be interpreted as the moment of collision between the black holes. An empirical relationship between the variation in left side diversity and the chirp mass of each event was also determined.

Resumo O presente artigo é uma homenagem ao legado deixado pelo maior experimento astronômico do século XX. Os eclipses e suas multifaces são o alvo principal desse artigo. Veremos que os eclipses não somente revelam os segredos das estrelas, mas também aqueles da natureza humana. A inspiração e fascínio pelos eclipses nos tornaram capazes de prever o futuro e imaginar tais fenômenos em outros sistemas solares. Para mergulhar nesse mundo fascinante, iremos percorrer os caminhos que levaram uma espécie de primatas nômades, munidos de lascas de pedra e ossos, a criar maravilhosas máquinas que nos levaram a lugares jamais pensados. Nesse percurso, faremos uma reflexão sobre como cientistas e pensadores se empenharam em manter acessa a chama da liberdade e do livre pensamento. O artigo segue apresentando o pano de fundo histórico que culminou na comprovação da Teoria da Relatividade de Einstein no céu sobralense. Os dois tópicos seguintes apontam as questões abertas na astrofísica que são resultados da investigação de eclipses: o problema da coroa solar e a descoberta de exoplanetas através da técnica de trânsito planetário. For fim, um retrato geral sobre a onda de obscurantismo que questionam as leis da física e, em particular, os eclipses é apresentado. Abstract The present paper is a tribute to the legacy left by the largest astronomical experiment of the twentieth century. Eclipses and their multifaces are the main target of this paper. We will see that eclipses not only reveal the secrets of the stars, but also those of human nature. Inspiration and fascination with eclipses have enabled us to predict the future and imagine such phenomena in other solar systems. To immerse ourselves in this fascinating world, we will walk the paths that led a kind of nomadic primate with splinters of stone and bone to create wonderful machines that took us to places never thought of. Along the way, we will reflect on how scientists and thinkers have endeavored to maintain the flame of freedom and free thought. The paper goes on to present the historical background that led to the proof of Einstein's Theory of Relativity in the Sobral's sky. The next two topics point to the open questions in astrophysics that are the result of eclipse research: the solar corona problem and the discovery of exoplanets through the planetary transit technique. Finally, a general picture of the wave of obscurantism that questions the laws of physics and, in particular, the eclipses is presented.

In the present paper, we analyze the signatures of long-range persistence in seismic sequences along Circum-Pacific subduction zones, from Chile to Kermadec, extracted from the National Earthquake Information Center (NEIC) catalog. This region, known as the Pacific Ring of Fire, is the world's most active fault line, containing about 90$\%$ of the world's earthquakes. We used the classical rescaled range ($R/S$) analysis to estimate the long-term persistence signals derived from a scaling parameter called the Hurst exponent, $H$. We measured the referred exponent and obtained values of $H>0.5$, indicating that a long-term memory effect exists. We found a possible fractal relationship between $H$ and the $b_{s}(q)$-index, which emerges from the non-extensive Gutenberg-Richter law as a function of the asperity. Therefore, $H$ can be associated with a mechanism that controls the level of seismic activity. Finally, we concluded that the dynamics associated with fragment-asperity interactions can be classified as a self-affine fractal phenomenon., 14 pages, 5 figures, accepted to RBGf. arXiv admin note: substantial text overlap with arXiv:1707.09018

the present paper, we propose that the stellar initial mass distributions as known as IMF are best fitted by $q$-Weibulls that emerge within nonextensive statistical mechanics. As a result, we show that the Salpeter's slope of $\sim$2.35 is replaced when a $q$-Weibull distribution is used. Our results point out that the nonextensive entropic index $q$ represents a new approach for understanding the process of the star-forming and evolution of massive stars., 5 pages, 2 figures, Accepted to EPL

Using a generalized function of the stellar spin-down law, we investigate the age dependence of the magnetic braking index ($q$). Our survey includes 9 open clusters aged lower than 1 Gyr and ranged in mass from 0.7 to 1.1$M_{\odot}$. Our aim is to verify the time behavior of the nonextensive braking index $q$ which brings the cumulative distribution of the rotational velocities of the stars of the youngest cluster ($\alpha{\rm Per}$) taken at the future age of an older cluster. As a result, the $q$-index is calculated over time $t-t_{\alpha{\rm Per}}$, where $t$ is the age of older open cluster used to estimate the future cumulative distribution of the rotational velocity of the $\alpha{\rm Per}$ cluster with present-day age $t_{\alpha{\rm Per}}$. We find that the values of $q$ are slightly constant around 1.36 and 1.38 according to the mass bin. In conclusion, the results seem to indicate that the mechanism that controls the rotational decay of stars in open clusters does not depend on the increment of time., Comment: 6 pages, 3 figures, 2 tables, submit to the EPL journal. arXiv admin note: text overlap with arXiv:2003.01444, arXiv:2003.06287

Kepler-30 is a unique target to study stellar activity and rotation in a young solar-like star accompanied by a compact planetary system. We use about 4 years of high-precision photometry collected by the Kepler mission to investigate the fluctuations caused by photospheric convection, stellar rotation, and starspot evolution as a function of the timescale. Our main goal is to apply methods for the analysis of timeseries to find the timescales of the phenomena that affect the light variations. We correlate those timescales with periodicities in the star as well as in the planetary system. We model the flux rotational modulation induced by active regions using spot modelling and apply the MFDMA in standard and multiscale versions for analysing the behaviour of variability and light fluctuations that can be associated with stellar convection and the evolution of magnetic fields on timescales ranging from less than 1 day up to about 35 days. The light fluctuations produced by stellar activity can be described by the multifractal Hurst index that provides a measure of their persistence. The spot modeling indicates a lower limit to the relative surface differential rotation of $\Delta \Omega/\Omega\sim 0.02\pm 0.01$ and suggests a short-term cyclic variation in the starspot area with a period of $\sim 34$ days, virtually close to the synodic period of 35.2 days of the planet Kepler-30b. By subtracting the two timeseries of the SAP and PDC Kepler pipelines, we reduce the rotational modulation and find a 23.1-day period close to the synodic period of Kepler-30c. This period also appears in the multifractal analysis as a crossover of the fluctuation functions associated with the characteristic evolutionary timescales of the active regions in Kepler-30 as confirmed by spot modelling. These procedures and methods may be greatly useful for analysing current TESS and future PLATO data., Comment: 27 pages and 27 figures; Accepted to the A&A Journal

This work brings a wavelet analysis for 14 Kepler white dwarf stars, in order to confirm their photometric variability behavior and to search for periodicities in these targets. From the observed Kepler light curves we obtained the wavelet local and global power spectra. Through this procedure, one can perform an analysis in time-frequency domain rich in details, and so to obtain a new perspective on the time evolution of the periodicities present in these stars. We identified a photometric variability behavior in ten white dwarfs, corresponding to period variations of ~ 2 h to 18 days: among these stars, three are new candidates and seven, earlier identified from other studies, are confirmed., 7 pages, 5 figures, accepted for publication in MNRAS

A multifractal formalism is employed to analyse high-precision time-series data of \textit{Kepler} stars with surface differential rotation traces. The multifractal detrended moving average analysis (MFDMA) algorithm has been explored to characterize the multi-scale behaviour of the observed time series from a sample of 662 stars selected with parameters close to those of the Sun, e.g., effective temperature, mass, effective gravity and rotation period. Among these stars, 141 have surface differential rotation traces, whereas 521 have no detected differential rotation signatures. In our sample, we also include the Sun in its active phase. Our results can be summarized in two points: first, our work suggests that starspots for time series with and without differential rotation have distinct dynamics, and second, the magnetic fields of active stars are apparently governed by two mechanisms with different levels of complexity for fluctuations. Throughout the course of the study, we identified an overall trend whereby the differential rotation is distributed in two $H$ regimes segregated by the degree of asymmetry $A$, where $H$-index denotes the global Hurst exponent which is used as a measure of long-term memory of time series. As a result, we show that the degree of asymmetry can be considered a segregation factor that distinguishes the differential rotation behaviour when related to the effect of the rotational modulation on the time series. In summary, the multifractality signals in our sample are the result of magnetic activity control mechanisms leading to activity-related long-term persistent signatures., Comment: 27 pages, 1 table., 20 figures, accepted to MNRAS

In the present study, high-precision time series photometry for the active \emph{Kepler} stars is described in the language of multifractals. We explore the potential of using the rescaled range analysis ($R/S$) and multifractal detrended moving average analysis (MFDMA) methods to characterize the multiscale structure of the observed time series from a sample of $\sim$40 000 active stars. Among these stars, 6486 have surface differential rotation measurement, whereas 1846 have no signature of differential rotation. As a result, the Hurst exponent ($H$) derived from both methods shows a strong correlation with the period derived from rotational modulation. In addition, the variability range $R_{var}$ reveals how this correlation follows a high activity ``line''. We also verify that the $H$-index is an able parameter for distinguishing the different signs of stellar rotation that can exist between the stars with and without differential rotation. In summary, the results indicate that the Hurst exponent is a promising index for estimating photometric magnetic activity., Comment: 15 pages, 9 figures, 2 tables, accepted to ApJ

Detecting exoplanets in clusters of different ages is a powerful tool for understanding a number of open questions, such as how the occurrence rate of planets depends on stellar metallicity, on mass, or on stellar environment. We present the first results of our HARPS long-term radial velocity (RV) survey which aims to discover exoplanets around intermediate-mass (between ~ 2 and 6 Msun) evolved stars in open clusters. We selected 826 bona fide HARPS observations of 114 giants from an initial list of 29 open clusters and computed the half peak-to-peak variability of the HARPS RV measurements, namely DeltaRV/2, for each target, to search for the best planet-host candidates. We also performed time series analysis for a few targets with enough observations to search for orbital solutions. Although we attempted to rule out the presence of binaries on the basis of previous surveys, we detected 14 new binary candidates in our sample, most of them identified from a comparison between HARPS and CORAVEL data. We also suggest 11 new planet-host candidates based on a relation between the stellar surface gravity and DeltaRV/2. Ten of the candidates have less than 3 Msun, showing evidence of a low planet occurrence rate for massive stars. One of the planet-host candidates and one of the binary candidates show very clear RV periodic variations, allowing us to confirm the discovery of a new planet and to compute the orbital solution for the binary. The planet is IC 4651 9122b, with a minimum mass of msini = 6.3 MJ and a semi-major axis a = 2.0 AU. The binary companion is NGC 5822 201B, with a very low minimum mass of msini = 0.11 Msun and a semi-major axis a = 6.5 AU, which is comparable to the Jupiter distance to the Sun., Accepted to Astronomy and Astrophysics. 14 pages, 11 figures

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.

Observations of circumstellar disks provide a powerful tool for our understanding of planetary systems 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 disk 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 (WISE). 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 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., Comment: 21 pages, and 3 figures, Accepted for publication on ApJL

In the present study, we investigate the multifractal nature of a long-cadence time series observed by the \textit{Kepler} mission for a sample of 34 M dwarf stars and the Sun in its active phase. Using the Multifractal Detrending Moving Average algorithm (MFDMA), 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 ($A$,$\Delta \alpha$,$C$,$H$)-quartet, where $A$, $\Delta \alpha$ 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 Poincar\'e plot method and find a strong correlation between the $\left\langle S_{ph}\right\rangle$ 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 $\left\langle S_{ph}\right\rangle$ 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., Comment: 8 figures and 3 tables (Accepted to ApJ)

This study presents a search for IR excess in the 3.4, 4.6, 12 and 22 $\mu$m bands in a sample of 216 targets, composed of solar sibling, twin and analog stars observed by the \textit{WISE} mission. In general, an infrared excess suggests the existence of warm dust around a star. We detected 12 $\mu$m and/or 22 $\mu$m excesses at the 3$\sigma$ level of confidence in five solar analog stars, corresponding to a frequency of 4.1 $\%$ of the entire sample of solar analogs analyzed, and in one out of 29 solar sibling candidates, confirming previous studies. The estimation of the dust properties shows that the sources with infrared excesses possess circumstellar material with temperatures that, within the uncertainties, are similar to that of the material found in the asteroid belt in our solar system. No photospheric flux excess was identified at the W1 (3.4 $\mu$m) and W2 (4.6 $\mu$m) \textit{WISE} bands, indicating that, in the majority of stars of the present sample, no detectable dust is generated. Interestingly, among the sixty solar twin stars analyzed in this work, no \textit{WISE} photospheric flux excess was detected. However, a null-detection excess does not necessarily indicate the absence of dust around a star because different causes, including dynamic processes and instrument limitations, can mask its presence., Comment: 50 pages, 9 figures, Accepted for publication on Astrophysical Journal

Uma aproximacao Bayesiana e adotada para analisar a sequencia de eventos sismicos e suas magnitudes proximo a Joao Câmara que ocorreram principalmente de 1983 a 1998 ao longo da Falha de Samambaia. Neste trabalho, nos escolhemos um modelo Bayesiano para o processo de tempo de ocorrencia condicional sobre os valores de magnitudes observadas seguindo o mesmo procedimento proposto por Stavrakakis e Tselentis (1987). Os parâmetros do modelo sao determinados sobre uma base de informacoes fisicas e historicas. Nos geramos uma amostra a posteriori a partir de sua distribuicao atraves de uma variante do algoritmo Metropolis-Hastings. Nos usamos os resultados em uma variedade de aplicacoes, incluindo a construcao de um intervalo de confianca para a intensidade condicional do processo como uma funcao de tempo, como tambem, uma distribuicao a posteriori como uma funcao da ma ocorrencia por unidade de tempo.

Following our own previous work, we reanalyze the nonextensive behavior over the circum-Pacific subduction zones evaluating the impact of using different types of magnitudes in the results. We used the same data source and time interval of our previous work, the NEIC catalog in the years between 2001 and 2010. Even considering different data sets, the correlation between q and the subduction zone asperity is perceptible, but the values found for the nonextensive parameter in the considered data sets presents an expressive variation. The data set with surface magnitude exhibits the best adjustments. Keywords: Nonextensivity, Seismicity, Solid Earth, Earthquake. RESUMO. No mesmo caminho do nosso trabalho anterior, reanalisamos o comportamento nao extensivo sobre as zonas de subduccao do circuo de fogo do Pacifico, avaliando o impacto do uso de diferentes tipos de magnitude nos resultados. Utilizamos o mesmo intervalo de dados e fonte de nosso trabalho anterior, do catalogo NEIC entre os anos 2001 e 2010. Mesmo considerando diferentes conjuntos de dados, a correlacao entre q e a aspereza das zonas de subduccao e perceptivel, mas os valores encontrados para o parâmetro nao extensivo no conjuntos de dados considerados apresentam uma variacao expressiva. O conjunto de dados com magnitude de superficie exibe os melhores ajustes. Palavras-chave: Nao extensividade, Sismicidade, Terra Solida, Terremotos.

We study the distribution of the photometric rotation period (Prot), which is a direct measurement of the surface rotation at active latitudes, for three subsamples of Sun-like stars: one from CoRoT data and two from Kepler data. We identify the main populations of these samples and interpret their main biases specifically for a comparison with the solar Prot. Prot and variability amplitude (A) measurements were obtained from public CoRoT and Kepler catalogs combined with physical parameters. Because these samples are subject to selection effects, we computed synthetic samples with simulated biases to compare with observations, particularly around the location of the Sun in the HR diagram. Theoretical grids and empirical relations were used to combine physical parameters with Prot and A. Biases were simulated by performing cutoffs on the physical and rotational parameters in the same way as in each observed sample. A crucial cutoff is related with the detectability of the rotational modulation, which strongly depends on A. The synthetic samples explain the observed Prot distributions of Sun-like stars as having two main populations: one of young objects (group I, with ages younger than ~1 Gyr) and another of MS and evolved stars (group II, with ages older than ~1 Gyr). The proportions of groups I and II in relation to the total number of stars range within 64-84% and 16-36%, respectively. Hence, young objects abound in the distributions, producing the effect of observing a high number of short periods around the location of the Sun in the HR diagram. Differences in the Prot distributions between the CoRoT and Kepler Sun-like samples may be associated with different Galactic populations. Overall, the synthetic distribution around the solar period agrees with observations, which suggests that the solar rotation is normal with respect to Sun-like stars within the accuracy of current data., Comment: 13 pages, 8 figures, A&A accepted

Until a few years ago, the amplitude variation in the photometric data had been limitedly explored mainly because of time resolution and photometric sensitivity limitations. This investigation is now possible thanks to the Kepler and CoRoT databases which provided a unique set of data for studying of the nature of stellar variability cycles. The present study characterizes the amplitude variation in a sample of main--sequence stars with light curves collected using CoRoT exo--field CCDs. We analyze potential stellar activity cycles by studying the variability amplitude over small boxes. The cycle periods and amplitudes were computed based on the Lomb-Scargle periodogram, harmonic fits, and visual inspection. As a first application of our approach we have considered the photometric data for 16 CoRoT FGK main sequence stars, revisited during the IRa01, LRa01 and LRa06 CoRoT runs. The 16 CoRoT stars appear to follow the empirical relations between activity cycle periods ($P_{cyc}$) and the rotation period ($P_{rot}$) found by previous works. In addition to the so-called A (active) and I (inactive) sequences previously identified, there is a possible third sequence, here named S (short-cycles) sequence. However, recovery fractions estimated from simulations suggest that only a half of our sample has confident cycle measurements. Therefore, more study is needed to verify our results and Kepler data shall be notably useful for such a study. Overall, our procedure provides a key tool for exploring the CoRoT and Kepler databases to identify and characterize stellar cycle variability., 7 pages, 6 figures

http://dx.doi.org/10.5007/2175-7941.2017v34n1p64O presente artigo apresenta uma sequência didática, de perspectiva histórico-filosófica, cujo objetivo é trazer contribuições para o ensino do conceito de pressão atmosférica e a inserção de discussões sobre a natureza do conhecimento científico na educação básica. Busca-se contemplar a compreensão de aspectos da construção histórica do conceito científico em atividades que despertam o pensamento crítico. Propõe-se que os estudantes se engajem em processo “investigativo” sobre determinado fenômeno físico e confrontem suas explicações às que emergem da interpretação diacrônica de excertos de fontes primárias, devidamente contextualizados ao longo das etapas. Sugere-se uma sequência didática mediada, de caráter dialógico, organizada em momentos de discussão a respeito de conteúdos de ciência e sobre a ciência.

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 $q\approx q_{0}(1-\Delta t/q_{K})$, 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 $q_{K}\sim$ 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 $q$., Comment: 6 pages and 2 figures, accepted to EPL on October 17, 2014

The San Andreas fault (SAF) in the USA is one of the most investigated self-organizing systems in nature. In this paper, we studied some geophysical properties of the SAF system in order to analyze the behavior of earthquakes in the context of Tsallis's $q$--Triplet. To that end, we considered 134,573 earthquake events in magnitude interval $2\leq m, 5 pages, 6 figures, EPL accepted

To date, the CoRoT space mission has produced more than 124,471 light curves. Classifying these curves in terms of unambiguous variability behavior is mandatory for obtaining an unbiased statistical view on their controlling root-causes. The present study provides an overview of semi-sinusoidal light curves observed by the CoRoT exo-field CCDs. We selected a sample of 4,206 light curves presenting well-defined semi-sinusoidal signatures. The variability periods were computed based on Lomb-Scargle periodograms, harmonic fits, and visual inspection. Color-period diagrams for the present sample show the trend of an increase of the variability periods as long as the stars evolve. This evolutionary behavior is also noticed when comparing the period distribution in the Galactic center and anti-center directions. These aspects indicate a compatibility with stellar rotation, although more information is needed to confirm their root-causes. Considering this possibility, we identified a subset of three Sun-like candidates by their photometric period. Finally, the variability period versus color diagram behavior was found to be highly dependent on the reddening correction., 12 pages, 16 figures, A&A accepted

The present work reports on the discovery of three stars that we have identified to be rotating Sun-like stars, based on rotational modulation signatures inferred from light curves from the CoRoT mission's Public Archives. In our analysis, we performed an initial selection based on rotation period and position in the Period--$T_{\rm eff}$ diagram. This revealed that the stars CoRoT IDs 100746852, 102709980, and 105693572 provide potentially good matches to the Sun with similar rotation period. To refine our analysis, we applied a novel procedure, taking into account the fluctuations of the features associated to photometric modulation at different time intervals and the fractality traces that are present in the light curves of the Sun and of these "New Sun" candidates alike. In this sense, we computed the so-called Hurst exponent for the referred stars, for a sample of fourteen CoRoT stars with sub- and super-solar rotational periods, and for the Sun, itself, in its active and quiet phases. We found that the Hurst exponent can provide a strong discriminant of Sun-like behavior, going beyond what can be achieved with solely the rotation period itself. In particular, we find that CoRoT ID 105693572 is the star that most closely matches the solar rotation properties, as far as the latter's imprints on light curve behavior is concerned. The stars CoRoT IDs 100746852 and 102709980 have significant smaller Hurst exponents than the Sun, notwithstanding their similarity in rotation periods., Comment: 20 pages, 4 figures; ApJLetters accepted

The pioneering study by Skumanich (1972) showed that the rotational velocity of G-type Main-Sequence (MS) stars decreases with stellar age according to $$ $\propto$ $t^{-1/2}$. This relationship is consistent with simple theories of angular momentum loss from rotating stars, where an ionized wind is coupled to the star by a magnetic field. The present study introduces a new approach to the study of stellar rotational braking in unsaturated F and G type stars limited in age and mass, connecting angular momentum loss by magnetic stellar wind with Tsallis nonextensive statistical mechanics. As a result, we show that the rotation-age relationship can be well reproduced using a nonextensive approach from Tsallis nonextensive models. Here, the index $q$, which is related to the degree of nonextensivity, can be associated to the dynamo process and to magnetic field geometry, offering relevant information on the level of stellar magnetic braking for F- and G-type Main-Sequence stars., Comment: 8 pages, 3 figures, MNRAS accepted

In the present study, we analyze the radial velocity distribution as a function of different stellar parameters such as stellar age, mass, rotational velocity and distance to the Sun for a sample of 6781 single low--mass field dwarf stars, located in the solar neighborhood. We show that the radial velocity distributions are best fitted by $q$--Gaussians that arise within the Tsallis nonextensive statistics. The obtained distributions cannot be described by the standard Gaussian that emerges within Boltzmann-Gibbs (B--G) statistical mechanics. The results point to the existence of a hierarchical structure in phase space, in contrast to the uniformly occupied phase space of B--G statistical mechanics, driven by the $q$--Central Limit Theorem, consistent with nonextensive statistical mechanics., Comment: 5 pages, 4 figures: EPL accepted

In this paper we analyze the behavior of the daily Sunspot Number from the Sunspot Index Data Center (SIDC), the mean Magnetic Field strength from the National Solar Observatory/Kitt Peak (NSO/KP) and Total Solar Irradiance means from Virgo/SoHO, in the context of the $q$--Triplet which emerges within nonextensive statistical mechanics. Distributions for the mean solar Magnetic Field show two different behaviors, with a $q$--Gaussian for scales of 1 to 16 days and a Gaussian for scales longer than 32 days. The latter corresponds to an equilibrium state. Distributions for Total Solar Irradiance also show two different behaviors (approximately Gaussian) for scales of 128 days and longer, consistent with statistical equilibrium and $q$--Gaussian for scales $, Comment: 6 pages, 4 figures

The evolution of stars largely driven by rotation, controls a large number of internal and atmospheric stellar phenomena. In the present work we study the evolutionary behavior of stellar rotation along the HR Diagram, taking into account constraint conditions issued from recent observational survey of rotational velocity carried out with high precision procedures and new evolutionary codes. Theoretical predictions are presented for the evolutionary behavior of rotational velocity of solar-type giant and subgiant stars. We show that those simulations taking into account only the stellar evolutionary eects (increasing of moment of inertia) are unable to reproduce the observed rotational velocity of giant and subgiant stars. Dieren t levels of magnetic braking appear to be acting on the rotation of evolved stars.

Em contraste com a tendência positivista de outrora, fontes primárias não são mais consideradas como documentos oficiais que contém “a verdade sobre o passado”. Atualmente, são compreendidas como artefatos culturalmente produzidos que refletem intencionalidades de personagens. São essenciais para o trabalho interpretativo realizado por historiadores e historiadores da ciência. No contexto educacional, na disciplina escolar de História, os estudantes já costumam ser convidados a uma interpretação diacrônica de documentos históricos. De modo distinto, o uso desse tipo de material é ainda raro em iniciativas para a inserção da História e Filosofia da Ciência no ensino de Física. Adicionalmente, há lacunas quanto a refletir sobre o uso didático dessas fontes em aulas de Física numa perspectiva não ilustrativa, mas sim investigativa, a qual estaria em ressonância com pressupostos historiográficos da História da Ciência e objetivos didáticos atualizados. Atividades investigativas, dialógicas, baseadas na interpretação diacrônica de documentos podem incentivar a curiosidade e a imaginação dos alunos acerca do processo de construção do conhecimento científico, evocando elementos usualmente ausentes em livros didáticos. O presente artigo reflete sobre tais questões e discute dois exemplos de possibilidades didáticas de uso de fontes primárias relacionadas à História do Vácuo e da Pressão Atmosférica.

The present work is based on a description for the angular mometum loss rate due to magnetic braking for main-sequence stars on the relationship between stellar rotation and age. In general, this loss rate denoted by $\mathrm dJ/\mathrm dt$ depends on angular velocity $��$ in the form $\mathrm dJ/\mathrm dt\propto��^{q}$, where $q$ is a parameter extracted from nonextensive statistical mechanics. Already, in context of stellar rotation, this parameter is greater than unity and it is directly related to the braking index. For $q$ equal to unity, the scenario of saturation of the magnetic field is recovered, otherwise $q$ indicates an unsaturated field. This new approach have been proposed and investigated by de Freitas \& De Medeiros for unsaturated field stars. In present work, we propose a nonextensive approach for the stellar rotational evolution based on the Reiners \& Mohanthy model. In this sense, we developed a nonextensive version of Reiners \& Mohanthy torque and also compare this generalized version with the model proposed in de Freitas \& De Medeiros based on the spin-down Kawaler torque for the main-sequence stars with F and G spectral types. We use the same sample of $\sim16 000$ field stars with rotational velocity $v \sin i$ limited in age and mass. As a result, we show that the Kawaler and Reiners \& Mohanthy models exhibit strong discrepancies, mainly in relation to the domain of validity of the entropic index $q$. These discrepancies are mainly due to sensitivity on the stellar radius. Finally, our results showed that modified Kawaler prescription is compatible with a wider mass range, while the Reiners \& Mohanty model is restricted to masses less than G6 stars., 5 pages, 1 figure, Accepted for publication in Europhysics Letters. arXiv admin note: text overlap with arXiv:1304.7644

We analyzed the host stars of the present sample of confirmed planets detected by Kepler and Kepler Objects of Interest (KOI) to compute new photometric rotation periods and to study the behavior of their angular momentum. Lomb-Scargle periodograms and wavelet maps were computed for 3,807 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$_{\odot}$) with rotation periods that span a range of 2 to 89 days. These periods exhibit an excellent agreement with 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., Comment: 11 pages, 7 figures, 1 table

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.

Rotation is a fundamental physical parameter in stellar astrophysics, playing an important role on the formation and evolution of stars. This parameter may also offer valuable information on stellar magnetism, mixing in the stellar interior, tidal interactions in close binary, as well as on angular momentum transfer and rotational breaking due to planets. The present work brings the results of an unprecedented study on the behavior of the distribution of the projected rotational velocity (v sin i) as a function of galactic position, on the basis of an unique sample of 14000 main-sequence field stars, along the spectral regions F and G. The vsini measurements used in this analyses were obtained from observations carried out with the CORAVEL spectrometers, with a precision better than about 1 km/s.

The present study demonstrates that behavior of rotational velocity as a function of stellar age is consistent using Tsallis' nonextensive formalism, resulting in a new approach to understanding the stellar rotational scenario.