1,720,967 research outputs found
Carbon stars with increased oxygen and nitrogen abundances: Hydrostatic dust-free model atmospheres
No full textWe have computed a grid of hydrostatic spherical COMARCS models for C stars covering metallicities from [Z/H] = 0 to -2 and values of the carbon excess [C-O] from 6.41 to 9.15, plus some temperature sequences, where the amount of oxygen and nitrogen is increased relative to a scaled solar element mixture. Such abundance variations may appear during the late stages of stellar evolution. Our study covers changes of [O/Z] and [N/Z] going up to +0.5. Based on the atmospheric structures we have calculated synthetic spectra and photometry for all of the models in a consistent way. The sequences with changed [O/Z] and [N/Z] can be used to derive correction terms, which are applied to the colours predicted for a certain combination of effective temperature, surface gravity, metallicity, and carbon excess. If one neglects these shifts in case of a variable oxygen amount, taking [C-O] instead of C/O gives much better results, since the first quantity dominates the formation of many important molecular species. For the warmer C giants with weaker pulsation it is in principle possible to determine [C-O], [O/Z], or [N/Z] from high-resolution spectra, when the opacities in the radiative transfer calculations for the models and observable properties are treated consistently. The corresponding changes due to the abundances often become significantly larger than the deviations caused by uncertainties of the stellar parameters or by an optically thin dust shell. Photometric data and low- or medium-resolution spectra are not sufficient to derive the mentioned quantities
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
Herschel imaging photometry of carbon stars
No full textSterne mit geringen bis mittleren Massen (ca. 0.8-8 Sonnenmassen) finden sich früher oder später am Asymptotischen Riesenast (AGB – Asymptotic Giant Branch) im Hertzsprung-Russell Diagramm ein. Charakteristisch für Sterne in diesem Entwicklungsabschnitt sind, bedingt durch die niedrigen Oberflächentemperaturen, die effektive Bildung von Molekülen und makroskopischen Partikeln (Staub), sowie starke, von thermischen Pulsationen unterstützte, staubgetriebene stellare Winde. Mehr als 90% aller Sterne durchleben die AGB-Phase – folglich trägt der Massenverlust dieser Objekte beträchtlich zur Anreicherung des interstellaren Mediums mit schweren Elementen bei. Für ein umfassendes Bild des kosmischen Materiekreislaufs ist daher detailliertes Wissen um die Eigenschaften des Massenverlustes wesentlich.
Im Rahmen des internationalen Projektes MESS (Mass-loss of Evolved StarS) wurden, unter anderem, zahlreiche Sterne im AGB Stadium sowohl photometrisch als auch spektroskopisch mit dem Herschel Infrarotteleskop beobachtet. Aus diesem Sample wurden im Rahmen der vorliegenden Arbeit photometrische Daten der beiden Kohlenstoffsterne TT Cygni und UX Draconis analysiert und interpretiert. Zusätzlich wurden mit dem Fortran-Code DUSTY Modelle aus Strahlungstransportrechnungen erstellt um weitere Parameter des Massenverlustprozesses zu bestimmen.
Rund um TT Cyg wurde eine geometrisch dünne Hülle aus kaltem Staub detektiert, die räumlich gut mit Beobachtungen der Gaskomponente im (Sub)millimeterbereich übereinstimmt. Im Gegensatz dazu enthüllen die Daten von UX Dra eine unregelmäßige, bisher unbekannte Struktur aus Staub, ohne Pendant in anderen Spektralbereichen.Low to intermediate-mass stars (~0.8-8 solar masses) spend a short but eventful time on the asymptotic giant branch (AGB). Due to the low temperatures, molecules and, in the outermost layers, even solid particles (dust) can form, which are eventually injected into the environment by heavy matter outflows. Since more than 90 percent of the stars become AGB objects, their dusty winds contribute significantly to the enrichment of the interstellar medium with processed elements. Thus, it is of great importance for the understanding of the cosmic matter cycle to comprehend the mechanisms of the mass-loss process.
For this work, photometric data of the two carbon stars TT Cygni and UX Draconis, obtained with the Photodetector Array Camera and Spectrometer (PACS) on-board the Herschel satellite in the course of the MESS (Mass-loss of Evolved StarS) program, were studied. The photometric measurements were used to derive basic parameters of the circumstellar structures. Additionally, radiative transfer calculations were carried out using the radiative transfer code DUSTY, in order to estimate properties of the mass-loss process.
For TT Cyg a geometrically thin and remarkably spherically symmetric detached dust shell was detected. A co-spatial gas equivalent was already found in previous sub-mm observations. Around UX Dra a previously unobserved structure was identified
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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