1,721,065 research outputs found
Stelle blue straggler in ammassi aperti galattici
No full textMore than 60 years ago, in the optical color-magnitude diagram of the Galactic Globular Cluster M3 a new type of star was discovered: the blue straggler stars. Since then, these objects have been found in all types of stellar systems and environments, from the dense core of globular clusters to the low-density environment of the Galactic field. Understanding their formation has fascinated both observers and theorists, and today it is widely accepted that they have formed through the interaction with other stars. Among the multiple formation mechanisms proposed, two are the main scenarios: collision-induced stellar mergers and mass transfer in binary systems. Both scenarios, however, can be easily modified by the presence of a third (or more) star. What is still partially unclear is how much each mechanism contributes to the straggler population currently observed. With many authors proposing different pathways that dominate in different environments, it is not easy to identify the exact pathway without information about their BSS properties. To do so we require first having large and homogeneous compilations of these stars, suitable to find pathological cases on which these formation scenarios can be further tested.
This thesis presents an observational effort made to contribute to a better understanding of the properties of blue straggler stars in open clusters (OCs), improve membership-driven BS statistics, and shed light on which formation mechanism is the most predominant from a macro scale point of view.
Two are the sides that define this thesis. From one side, this work presents the most comprehensive and homogeneous catalog of the BSS population in a sample of more than 400 OCs. After having compiled the catalog, we have revisited the most famous relations between the straggler numbers and the cluster environment (age, mass, integrated magnitude, binary fraction) ruling out previous claims and providing invaluable information about the BSS environments, which is crucial to building realistic models of their evolution.
Yellow straggler stars (YSS) are much less sampled and studied than BSS. Their importance, however, relies on the suggestion of these stars as possible evolved-BSS. As part of this thesis, we present the first and largest systematic search of YSS in OCs, where nearly 80 have been found in 45 OCs. This is the first time these systems are reported as part of a catalog, their properties are important to have a complete picture of the formation and evolution of BSS stars.
After our internally consistent and accurate straggler selection, we have ranked the host clusters in terms of their internal dynamical evolution by using the so-called Ar+ parameter, which measures the central concentration of BSS within the cluster. This thesis has extrapolated the calculation of Ar+ from 10 Ocs (previously reported in the literature) to ~40. Moreover, by estimating the parameter Nrelax (indicative of the dynamical state of the cluster) we showed the OCs distribution is completely different from that of the globular clusters.
From the other side and going more into detail, we tried to assess the binary nature of a few blue stragglers to investigate their origin. We managed to identify both, long and short-period binary stars, and we also obtained their rotational velocities. We showed most of them are fast-rotators stars with Vsini > 30 km/s and some of them up to 150 km/s. One unexpected finding is the large short-period binary fractions we found for a sample of 10 OCs. For all of them, we derived their periods between 5 hours and 3 days. Among them, we found more than 50 eclipsing-BSS binaries, where nearly 90 % are new discoveries.More than 60 years ago, in the optical color-magnitude diagram of the Galactic Globular Cluster M3 a new type of star was discovered: the blue straggler stars. Since then, these objects have been found in all types of stellar systems and environments, from the dense core of globular clusters to the low-density environment of the Galactic field. Understanding their formation has fascinated both observers and theorists, and today it is widely accepted that they have formed through the interaction with other stars. Among the multiple formation mechanisms proposed, two are the main scenarios: collision-induced stellar mergers and mass transfer in binary systems. Both scenarios, however, can be easily modified by the presence of a third (or more) star. What is still partially unclear is how much each mechanism contributes to the straggler population currently observed. With many authors proposing different pathways that dominate in different environments, it is not easy to identify the exact pathway without information about their BSS properties. To do so we require first having large and homogeneous compilations of these stars, suitable to find pathological cases on which these formation scenarios can be further tested.
This thesis presents an observational effort made to contribute to a better understanding of the properties of blue straggler stars in open clusters (OCs), improve membership-driven BS statistics, and shed light on which formation mechanism is the most predominant from a macro scale point of view.
Two are the sides that define this thesis. From one side, this work presents the most comprehensive and homogeneous catalog of the BSS population in a sample of more than 400 OCs. After having compiled the catalog, we have revisited the most famous relations between the straggler numbers and the cluster environment (age, mass, integrated magnitude, binary fraction) ruling out previous claims and providing invaluable information about the BSS environments, which is crucial to building realistic models of their evolution.
Yellow straggler stars (YSS) are much less sampled and studied than BSS. Their importance, however, relies on the suggestion of these stars as possible evolved-BSS. As part of this thesis, we present the first and largest systematic search of YSS in OCs, where nearly 80 have been found in 45 OCs. This is the first time these systems are reported as part of a catalog, their properties are important to have a complete picture of the formation and evolution of BSS stars.
After our internally consistent and accurate straggler selection, we have ranked the host clusters in terms of their internal dynamical evolution by using the so-called Ar+ parameter, which measures the central concentration of BSS within the cluster. This thesis has extrapolated the calculation of Ar+ from 10 Ocs (previously reported in the literature) to ~40. Moreover, by estimating the parameter Nrelax (indicative of the dynamical state of the cluster) we showed the OCs distribution is completely different from that of the globular clusters.
From the other side and going more into detail, we tried to assess the binary nature of a few blue stragglers to investigate their origin. We managed to identify both, long and short-period binary stars, and we also obtained their rotational velocities. We showed most of them are fast-rotators stars with Vsini > 30 km/s and some of them up to 150 km/s. One unexpected finding is the large short-period binary fractions we found for a sample of 10 OCs. For all of them, we derived their periods between 5 hours and 3 days. Among them, we found more than 50 eclipsing-BSS binaries, where nearly 90 % are new discoveries
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Biological cycle of Argas (Persicargas) keiransi fed on hen´s blood under laboratory conditions
No full textA. keiransi Estrada-Peria, Venzal & Gonzalez-Acufia (Acari: Argasidae) be-long to the subgenus Persicargas, which includes soft bodied ticks distributed worldwide and commonly found parasitizing birds (Klompen, 1992). Argas (Persicargas) keiransi was described from engorged larvae of the Chimango Caracara (Milvago chimango chimango Vieillot (Ayes: Falconiformes: Falconi-dae: Caracarinae)) from Chillan (Bio Bio Region), Chile (Estrada-Pena et al. 2003). Females of A. keiransi were later described by Estrada-Pefla et al. (2006), also based on specimens from Chillan. The objective of this study was to describe the biological cycle of A. keiransi under laboratory conditions and compare it with related species.Fil: Ardiles, Karen. Universidad de Concepcion del Uruguay; ArgentinaFil: González Acuña, D.. Universidad de Concepcion del Uruguay; ArgentinaFil: Sepulveda, Maria Soledad. Purdue University; Estados UnidosFil: Vargas, Pamela. Universidad de Concepción; ChileFil: Guglielmone, Alberto Alejandro. Instituto Nacional de Tecnologia Agropecuaria. Centro Regional Santa Fe. Estacion Experimental Agropecuaria Rafaela; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Santa Fe; Argentin
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
- …
