1,723,398 research outputs found
Study of the interacting system NGC 6845
Get PDFWe present optical spectroscopy, B, V , R, and I CCD photometry, and VLA neutral hydrogen observations of the interacting quartet NGC 6845, also know as Klemola 30. NGC 6845 A, the dominant component, sports a broad and bright tidal bridge and a faint tidal tail, which bifurcates. The tidal bridge has a B[I color bluer than that of the inner disk of NGC 6845 A. Five strong condensations, identified as H II regions brighter than the brightest one known in our Galaxy, are found along the tidal bridge, with the two most luminous located at the bridge tip. Two giant H II regions, comparable to 30 Dor, are located where the tidal bridge and the tidal tail join the disk of NGC 6845 A
Study of the interacting system NGC 6845
Get PDFWe present optical spectroscopy, B, V , R, and I CCD photometry, and VLA neutral hydrogen observations of the interacting quartet NGC 6845, also know as Klemola 30. NGC 6845 A, the dominant component, sports a broad and bright tidal bridge and a faint tidal tail, which bifurcates. The tidal bridge has a B-I color bluer than that of the inner disk of NGC 6845 A. Five strong condensations, identified as H II regions brighter than the brightest one known in our Galaxy, are found along the tidal bridge, with the two most luminous located at the bridge tip. Two giant H II regions, comparable to 30 Dor, are located where the tidal bridge and the tidal tail join the disk of NGC 6845 A. Since the age of the H II regions is 3-8 Myr, star formation continued to occur along the tidal bridge and in the tidal arm well after they began to be torn apart (≥100 Myr). Satoh model fitting to the optical rotation curve of the A component reveals a kinematical mass of (4.4±1.2)]x1011 M๏ inside the central 12 kpc (H0=75 km s-ˡ Mpc-ˡ). The H I emission consist of two components, a more massive one that belongs to NGC 6845 A and a second one associated with NGC 6845 B. We do not detect gas associated with galaxies C and D. The total amount of H I is 1.4x1010 M๏, 5 time higher than the H I content of the Milky Way. The H I kinematics indicates an amount of dark matter associated with the A component 2 times higher than the mass inside its central 12 kpc. The group kinematics indicates M/L≈43(±2)(M/L)๏ or M/L≈66(±2)(M/L)๏ according to two dierent prescriptions for the internal absorption correction. In spite of this large dierence, both values furnish a similar group mass (≈1x1013 M๏). Although preliminary results on N-body simulations indicate that either B or C might well create a tidal feature like the bridge of the A component, the collision with B appears to be more favorable
NGC 6845 Revisited: Stellar Kinematics on the Early Type Member Galaxies
No full textWe observed the compact group of galaxies NGC 6845 with GMOS-S imaging and long-slit spectroscopy. The group itself is comprised of two spiral galaxies and two S0 galaxies, and shows signs of gravitational interaction among them. While the spiral galaxies have been already well studied, the two S0 galaxies have received little attention. We investigate the morphology and stellar kinematics of the two S0 galaxies in detail in order to derive the value for their mass and subsequently incorporate them into the mass model for the group. It was found that the internal kinematics of the largest S0 (NGC 6845 C) is mostly regular, while the smallest S0 (NGC 6845 D) shows some hint of interaction, most likely with NGC 6845 C and NGC 6845 A. The new determination of the dynamical mass of the group implies that the group mass has to be 10 times the combined mass of the individual members according to their internal kinematics. The results point to an early stage of the group interaction and also to the possibility that it has still not reached virial equilibrium. From the galaxy evolution viewpoint, this group represents an example of the case of the transformation of Spirals into S0 galaxies in dense environments.Fil: Gimeno, German Nicolas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; Argentina. Gemini Observatory; Estados UnidosFil: Díaz, Carlos Ruben. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; Argentina. Gemini Observatory; Estados Unidos. Universidad Nacional de Córdoba; ArgentinaFil: Dottori, Horacio Alberto. Universidade Federal do Rio Grande do Sul; BrasilFil: Rodrigues, Irapuan. Universidade do Vale do Paraíba; BrasilFil: Mast, Damian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; Argentina. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba; Argentin
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
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