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Numerical algorithms for the searching of extrasolar planets from photometric data
Full text linkThe aim of this research project was twofold: on one hand, we have developed an automatic photometric pipeline with a real time images reduction, which directly provide lightcurves of objects observed in the field. The lightcurves themselves are analyzed in order to catch light diming due to a transit.
On the other hand, we contribute to investigate the dynamical and physical structure of the planetary systems hosted in multiple stellar systems and to compare the results with the current knowledge both of the planetary and stellar formation in order to gain a new insight on the evolution of extrasolar systems.
Even if this PhD Thesis is made up of these two different but complementary aspects, however the final aim of both converges: it contributes to the comprehension of the planetary formation mechanism in order to identify both the environment conditions where these objects could form and some clues on their physical properties. Moreover, the results may be applied to the future space missions: the reduction pipeline could be exploited in whatever surveys of transit search thanks to its automatic nature while the theoretical results could be the
starting point for the future investigations from space.
Part I: Photometric reduction and analysis software.
An exoplanetary transit occurs when it crosses the line of sight between the observer and the star around which it is orbiting. The flux decrease that it provokes allows us to find out certain orbital parameters and some physical characteristics of the planet that are inaccessible through other techniques. The diversity of the performed studies and the acquired knowledge after the detection of HD 209458b 's transits motivated the use of this technique as a tool for exoplanet discoveries.
In this thesis, we describe the reduction algorithm developed in the RATS (RAdial velocities and Transit Search) project context in order to automatically achieve the lightcurves of photometric stars devoted to the search for exoplanets using the transit method. The main aim of the RATS project is twofold. The detection of extra solar planets that transit the disk of their parent star is the main scientific drive of the whole project. We have planned to observe simultaneously thousands of stars (magnitude range between 9th to 14th) in selected star fields for five years since the beginning of 2005. In this manner we are confident to find new transiting planets.
The second aim of the project is to use its observing strategy and the scientific data management as a bench work for future planetary transits search mission in order to value it effectiveness.
In particular, RATS projects seeks high precision photometric results performed with stellar images which have been purposely defocused in order to avoid saturation of brighter stars because of the size of Schmidt FoV. Moreover, to maximize the transit probability, each RATS field has been partitioned in seven adjacent sub-fields sequentially pointed.
Up to now, two missions already plan to exploit this untypical strategy: the French CoRoT mission devoted to extrasolar planets search and asteroseismology is planning to collect CCD images which are slightly de-focused; the same observational approach has also been proposed for the Kepler extrasolar space mission as well.
Originally, this research project foresaw many observations from the Cima Ekar Schmidt telescope equipped with a frame transfer CCD lended from INAF-OACT (Istituto Nazionale
di AstroFisica-Osservatorio Astronomico di Catania) in concomitance to the very beginning of RATS project. For reasons out of my hands, some months ago INAF-OACT unexpectedly demand it back and the observations were stopped for a considerable amount of time. This aspect, added to the bad weather conditions of the most of 2006, has lessened images acquisition relative to initial expectations. However, in order to automatically reduce the images obtained so far, we have developed an automatic reduction algorithm RATS{ARP (Automatic Reduction Pipeline) which directly provides light curves of objects in the pre-selected RATS fields. The light curves themselves are analyzed in order to catch light diming due to a planetary transit.
This software is based on different modules all called from a main program shell script, each being deputy to an individual step for photometric reduction of images.
The described procedure has been applied both to the images in focus and to defocused ones, in particular two stellar fields have been analyzed among those chosen for the project.
RATS{ARP has shown its robustness in managing both kind of images, performing all its tasks till lightcurve files creation with satisfactory time consuming: it has taken 90 seconds for each
image in focus and 180 seconds for each defocused frame, depending on the crowding of the field.
Therefore, the pipeline can manage different kind of images and it fulfills all its task. Thereby, we can say that RATS-ARP can be exported to projects different from RATS thanks to its pliability.
In particular, thanks to its automatic development approach, it could be easily applicable to future space missions which intend to search exoplanets with the transit method with small
adjustments.
A detailed analysis for the future implementation of RATS database has been, finally, performed. Requirements and structure of this archive have been identified in order to help in developing a database that can be offered both to scientific community and to non-specialists.
Part II: Dynamical simulations
The present dynamical configuration of planets in binary star systems may not reflect their formation process since the binary orbit may have changed in the past after the planet formation
process was completed. An observed binary system may have been part of a former hierarchical triple that became unstable after the planets completed their growth around the primary star.
Alternatively, in a dense stellar environment even a single stellar encounter between the star pair and a singleton may significantly alter the binary orbit. In both cases the planets we observe at present would have formed when the dynamical environment was different from the presently observed one.
We have numerically integrated the trajectories of the stars (binary plus singleton) and of test planets, hosted around the primary star of the inner binary, to investigate the above mentioned mechanisms. Different values of mutual inclination, binary separation and singleton initial semimajor axis are explored in a statistical way.
Our simulations show that the circumstellar environment during planetary formation around the primary was gravitationally less perturbed when the binary was part of a hierarchical triple
because the binary was necessarily wider and, possibly, less eccentric. We find that a significant mutual inclination between the singleton and the binary is a key factor for instability of the
planetary system in terms of orbital spacing, eccentricity, and mass of the individual planets.
Infact, from our integration we have found that when the mutual inclination is larger than 40, the fraction of planets in the binary surviving the chaotic phase of the triple declines dramatically.
and for an inclination around 90, the percentage of surviving planets is lower than 20% for all binaries with a semimajor axis smaller than 200 AU. The combination of eccentricity and inclination oscillations of the binary companion induced by the secular perturbations of the singleton and the sequence of close encounters preceding the ejection of one star fully destabilize
a planetary system extending beyond 1 AU from the star.
Even in the case of a single stellar encounter the present appearance of a planetary system in a binary may significantly differ from what it had while planet formation was ongoing.
However, while in the case of instability of a triple the trend is always towards a tighter and more eccentric binary system, when a single stellar encounter affects the system the orbit of the binary can become wider and be circularized.
We can conclude that the frequency of planets in binaries with low separation may be strongly reduced by the residence of the pair in the past in a temporary inclined hierarchical triple
RATS: the photometric data reduction automatic pipeline
No full textThe automatic photometric pipeline provides a real time images reduction and directly the light curves of object in the field within the RATS project (RAdial Velocities Transit Search). The light curves themselves will be analyzed in order to catch light dimming due to a transit. For this purpose, the algorithm needs as input files a list of fits images taken at Schmidt Telescope of Asiago (INAF, Italy), a reference master list of stars and three files with the optional parameters for the DAOPHOT photometry package (Stetson 1987, PASP, 99, 191). The master list is previously obtained from a photometric characterization of the field (for more details: http://www.rats.it and Claudi et al. 2006, in Observatoire de Haute Provence Colloquium, Tenth Anniversary of 51 Peg-b: Status of and prospects for hot Jupiter studies, 22-25 August 2005, eds. Arnold, L., Bouchy, F. and Moutou, C., 350)
Jumping Jupiters in Binary Star Systems
Full text linkWe investigate the outcomes of the dynamical interaction of Jupiter-mass planets orbiting the central star in a binary system. These systems are unstable and lead to the hyperbolic ejection of one or more planets, while the surviving bodies are inserted in inner eccentric orbits. The gravitational perturbations of the companion star, set at an intermediate distance (50 AU) and typically on an eccentric orbit, influence both the development of instability and the outcome of the subsequent chaotic evolution. We compute the statistical properties of the resulting planetary systems when they reach a stable configuration. The binary eccentricity and the number of initial planets (two or three) are strong predictors of the final configuration of the planetary system. Cases of apsidal resonance between two final planets, Kozai resonance between a single surviving planet and the companion star, and retrograde orbits with respect to the binary orbit are naturally produced
`Jumping Jupiters' in Binary Star Systems
No full textWe study the outcome of a gravitational scattering phase in a system of three giant planets in binary star systems where the companion star is within 50 AU from the primary star and can significantly perturb the orbits of the planets
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
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
VSX J071108.7+695227: a Newly Discovered Short-period Eclipsing Binary
No full textWe report the discovery of an EW variable, VSX J071108.7+695227, with a short orbital period of ~0.238 day. This period is very close to the lower limit of ~0.22 day that has been found for EW systems. Here we present and discuss photometric and spectroscopic data of the variable, collected at the Astronomical Observatory of the Autonomous Region of the Aosta Valley and at the Asiago Astrophysical Observatory. The light curves show some asymmetries and the spectra suggest a dK4 classification for the two components. It could be interesting to carry out further observations of this system at different epochs because such systems frequently show variations in period and in the features of the light curve
A PSF-based approach to Kepler/K2data – III. Search for exoplanets and variable stars within the open cluster M 67 (NGC 2682)
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