1,720,986 research outputs found
Optical follow-up of 4C+21.35
No full textThe blazar 4C+21.35 (PKS 1222+21) was reported by AGILE (ATel #2686) and FermiGST (ATel #2687) to have a Gamma-ray flare; SWIFT X-ray and UV-optical follow-up was reported in Atel #2698; polarimetry in ATel #2693. We observed the source with the 31cm telescope of Greve in Chianti equipped with a back-illuminated SITe SIA502A CCD chip and Johnson-Cousins BVR filters. The comparison stars by Raiteri et al
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
The present status of four luminous variables in M 33
No full textContext. Understanding the origin of the instabilities of LBVs is important for shedding light on the late evolutionary stages of massive stars and on the chemical evolution of galaxies. Aims. To investigate the physical nature of variable stars in the upper H - R diagram, we performed a spectrophotometric study of the Romano's star GR 290 and the Hubble- Sandage variables A, B, and C in the close galaxy M 33. Methods. New spectroscopic and photometric data were employed in conjunction with already published data of these stars in order to derive spectral types, energy distribution and bolometric luminosities. Results. The yellow hypergiant Var A is still at minimum, with a similar to G-type spectrum and strong H alpha emission (W-eq similar or equal to -35 angstrom). Var B is in a low luminosity hot state (V = 17.5, B - V = -0.15) with very strong Ha emission (W-eq = -310 angstrom). Its absolute bolometric luminosity is 0.6 x 10(6) L-circle dot. Var C, at V = 16.4, is fainter than in the mid 1980s, but its spectrum shows the typical features of LBVs at maximum, a spectrum that is very rich in Fe II emission lines. Its L-bol is about 0.7 x 10(6) L-circle dot. The Romano's star GR 290 has a rich hot emission-line spectrum and is very bright with L-bol = 3 x 10(6) L-circle dot. During 2004 the star brightened by similar to half magnitude in each of the BVR filters. Conclusions. Our observations confirm that Var A probably is an intermediate type hypergiant star surrounded by an expanding envelope with a collisionally excited hydrogen emission, largely obscured by dusty disk and nebula. In recent years, Var B has undergone a blueward transition in the H - R diagram, probably at constant bolometric luminosity, while Var C is in a post- maximum phase with an eta Car-type spectrum. GR 290 is notable for its spectrum and luminosity, and it is likely to develop ample spectral variations in the near future, similar to those observed in AG Car
Intraday variability of BL Lacertae in the great 1997 outburst
No full textWe report intranight observations performed during the Summer 1997
outburst of BL Lac, in the B, V, R_c and I_c bands. The source was never
found to be stable, but always showed a variability of at least 0.04
mag/hour, often with superimposed fast fluctuations on time scales of
about an hour and with amplitudes of about 0.1 mag. The amplitude of the
flux variations was always larger at shorter wavelengths. No time lag
between different bands could be unambiguously detected
The long-term optical variability of the BL Lacertae object S5 0716+714: Evidence for a precessing jet
No full textWe present the historical light curve of the BL Lac object S5 0716+714, spanning the time interval from 1953 to 2003, built using Asiago archive plates and our recent CCD observations, together with literature data. The source shows an evident long-term variability, over which well-known short-term variations are superposed. In particular, in the period from 1961 to 1983 the mean brightness of S5 0716+714 remained significantly fainter than that observed after 1994. Assuming a constant variation rate of the mean magnitude, we can estimate a value of about 0.11 mag yr(-1). The simultaneous occurrence of decreasing ejection velocities of superluminal moving components in the jet reported by Bach and coworkers suggests that both phenomena are related to the change of the direction of the jet to the line of sight from about 5 degrees to 0.degrees 7 for an approximately constant bulk Lorentz factor of about 12. A simple explanation is a precessing relativistic jet, which should at present be close to the smallest orientation angle. One can therefore in the next 10 years expect a decrease of the mean brightness of about 1 magnitude
THE NON-STANDARD MULTIFREQUENCY BEHAVIOUR OF AG DRACONIS
No full textWe summarize the behavior of AG Dra during the last 25 years, characterized by a sequence of 5 active phases (with 14 light maxima). Cool and hot outbursts are discussed. In general, during bursts the X-ray flux weakens or vanishes, which should be mostly due to an increase of the high energy opacity of the envelope, rather than to a decrease of the source temperature. An explanation is suggested for the different behavior of the He II Zanstra temperature during the two burst types, and the possibility is considered that during all the burst events AG Dra first passes through a hot phase, and that only in the strongest bursts it evolves towards the cool burst phase
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