1,720,972 research outputs found
Optical spectral evolution of Nova Cygni 1992 = V 1974 Cygni
No full textWe report the results of the optical spectrophotometric observations of N Cyg 1992 = V 1974 Cyg performed at Asiago between 6 and 670 days after its visual maximum (1992 February 22, m_v approximately 4.4). On 1992 February 28, during the first decline the spectrum of the nova was characterized by the presence over a strong continuum of wide emission lines of HI (Balmer), FeII, NaI, CaII, flanked by two systems of P Cyg absorptions with mean radial velocities of -1250 and -1900 km/s. The transition phase was reached at the beginning of April with a gradual fading of the lines of lower ionization potential and the emerging of the HeI, NII, NIII lines. P Cygni absorption features with radial velocity higher than in February were still perceptible. The nova entered the nebular stage some weeks later, at the end of April. The presence in the spectrum, besides (OIII) λλ 4959, 5007, of strong forbidden lines of (NeIII) at λλ 3869, 3968, left no doubt of its classification as a 'neon nova' similar to QU Vul. The evolution of the spectrum in the next months was characterized by the progressive growth of the ionization degree. Following the forbidden lines of (NeIII) and (OIII), also those of (NeIV), (FeVI), (FeVII) and (NeV) became outstanding. The highest degree of ionization was attained on 1993 July, about 500 days from visual maximum, when the coronal lines of (FeX), (FeXI), (AX) reached their highest strength. The steadily decline of the degree of ionization began about one-hundred days later, with the rapid disappearance of the coronal lines and the progressive fading of the lines of highest ionization potential. The intensities of the emission lines during the nova evolution are reported. The discussion concerns the determination of: color excess, absolute magnitude and distance (2.8 kpc) of the nova; effective temperature of the contracting photosphere; and abundance in the ejecta of He, O, N, and Ne, relative to H
Fifty-two Novae discovered in M31 from 1970 to 1986
No full textThe nova survey of M31, carried out at the Asiago Astrophysical Observatory since 1954, has led to the discovery of 52 other novae on plates taken from 1971 to 1986 with the 1.22 and 1.82 m telescopes, in addition to the 90 novae previously found. Positions, magnitudes, and identification charts of the 52 novae are reported. Light curves have been obtained for 18 of them. They show the same variety of shapes as in previous research
Distances of the Virgo and Coma clusters of galaxies through Novae and Supernovae
No full textA distance modulus equal to 31.30 + or - 0.40 mag for the Virgo Cluster is estimated from a revised calibration of the maximum-magnitude versus rate-of-decline relation applied to the photometry of seven novae discovered by Pritchet and van den Bergh. The distance of the Coma Cluster is then evaluated in units of the Virgo Cluster distance, equal to 3.75 + or - 0.20, by comparing the critically revised maximum-magnitudes for the Type Ia supernovae. From there, a value of 70 + or - 15 km/s Mpc is derived for the Hubble constant as well as a Virgocentric infall velocity of 318 + or - 150 km/s
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
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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