1,720,977 research outputs found
Starspot properties and photometric parameters of transiting planets and their host stars
No full textTo begin understanding how the architecture of hot Jupiter planetary systems can be so radically different from that of our own solar system, requires the dynamical evolution of planets to be known. By measuring the sky-projected obliquity � of a system it is possible to determine the dominant process in the dynamical evolution.\ud
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If a transiting exoplanet that crosses the disc of its host star passes over a starspot, then the amount of received intensity from the star will change. By modelling the position of the anomaly in the lightcurve it is possible to precisely determine the position of the starspot on the stellar disc. If the position of the starspot can be found at two distinct times using two closely spaced transits, then it is possible to measure. Before now there was no definitive model capable of accurately modelling both a planetary transit and a starspot.\ud
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This research focuses on the development of prism which is capable of accurately modelling a transit containing a starspot anomaly. Due to the nature of the parameter space a new optimisation algorithm was developed, gemc, which is a hybrid between a genetic algorithm and MCMC
An extremely high photometric precision in ground-based observations of two transits in the WASP-50 planetary system
No full textWe present photometric observations of two transits in the WASP-50 planetary system, obtained using the ESO New Technology Telescope and the defocused-photometry technique. The rms scatters for the two data sets are 258 and 211 ppm with a cadence of 170–200 s, setting a new record for ground-based photometric observations of a point source. The data were modelled and fitted using the PRISM and GEMC codes, and the physical properties of the system calculated. We find the mass and radius of the hot star to be 0.861 ± 0.057 M⊙ and 0.855 ± 0.019 R⊙, respectively. For the planet we find a mass of 1.437 ± 0.068 MJup, a radius of 1.138 ± 0.026 RJup and a density of 0.911 ± 0.033 ρJup. These values are consistent with but more precise than those found in the literature. We also obtain a new orbital ephemeris for the system: T0 = BJD/TDB 245 5558.612 37 (20) + 1.955 0938(13) × E
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Transits and starspots in the WASP-6 planetary system
Full text linkWe present updates to prism, a photometric transit-starspot model, and gemc, a hybrid optimization code combining MCMC and a genetic algorithm. We then present high-precision photometry of four transits in the WASP-6 planetary system, two of which contain a starspot anomaly. All four transits were modelled using prism and gemc, and the physical properties of the system calculated. We find the mass and radius of the host star to be 0.836 ± 0.063 M_⊙ and 0.864 ± 0.024 R_⊙, respectively. For the planet, we find a mass of 0.485 ± 0.027 MJup, a radius of 1.230 ± 0.035 R_(Jup) and a density of 0.244 ± 0.014 ρ_(Jup). These values are consistent with those found in the literature. In the likely hypothesis that the two spot anomalies are caused by the same starspot or starspot complex, we measure the stars rotation period and velocity to be 23.80 ± 0.15 d and 1.78 ± 0.20 km s^(−1), respectively, at a colatitude of 75.8°. We find that the sky-projected angle between the stellar spin axis and the planetary orbital axis is λ = 7.2° ± 3.7°, indicating axial alignment. Our results are consistent with and more precise than published spectroscopic measurements of the Rossiter–McLaughlin effect. These results suggest that WASP-6 b formed at a much greater distance from its host star and suffered orbital decay through tidal interactions with the protoplanetary disc
Transits and starspots in the WASP-19 planetary system
No full textWe have developed a new model for analysing light curves of planetary transits when there are starspots on the stellar disc. Because the parameter space contains a profusion of local minima we developed a new optimization algorithm which combines the global minimization power of a genetic algorithm and the Bayesian statistical analysis of the Markov chain. With these tools we modelled three transit light curves of WASP-19. Two light curves were obtained on consecutive nights and contain anomalies which we confirm as being due to the same spot. Using these data we measure the star’s rotation period and velocity to be 11.76 ± 0.09 d and 3.88 ± 0.15 km s−1, respectively, at a latitude of 65°. We find that the sky-projected angle between the stellar spin axis and the planetary orbital axis is λ = 1| |0 ± 1| |2, indicating axial alignment. Our results are consistent with and more precise than published spectroscopic measurements of the Rossiter–McLaughlin effect
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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