1,721,047 research outputs found
Distances and stellar population properties for 12 elliptical galaxies
No full textAims. We use the surface brightness fluctuation (SBF) technique to derive the distances and analyse the radial behaviour of stellar populations in a sample of 12 elliptical galaxies. The data are I-band images collected with the FORS1 camera at the Very Large Telescope (VLT), drawn from the ESO archive. The main purpose of our analysis is to carry out the study of SBF magnitudes without relying on additional colour information that is normally required in SBF studies.
Methods. We measure I-band SBF magnitudes and SBF variations with galaxy radii, which is useful for stellar population studies. Unlike typical applications of the SBF technique, the absolute SBF magnitudes needed to evaluate the distance moduli are derived using the fluctuation star count, \hbox{}.
Results. The distances obtained using the \hbox{} calibration taken from the literature show a good agreement with available estimates. We find a median ~0.2 mag difference between our and literature distance moduli, with the only exception of NGC 5090, which shows the I-band SBF ~ 1 mag brighter than expected. The median statistical and systematic errors are ~0.2 and ~0.1 mag, respectively. On these grounds we consider the test of deriving SBF distances based on the \hbox{} calibration to be successful. Taking into account that some of the previously estimated distances were made as long as 15 years ago, the new measurements provide an updated sketch on distances for a set of galaxies towards the region of the Great Attractor. Furthermore, gauging the SBF of the unresolved stellar systems has returned negative SBF radial gradients in the inner regions of five galaxies: a feature already known and explained by lower metallicity at larger galactic radii. Somehow unexpectedly, though, we detect positive SBF gradients at large radii ( ≳ 20 kpc) in nine targets. This behaviour, if it is not caused by some unaccounted observational bias, could be explained at least partly as a statistical effect on the stellar counts at these radii. Additional (near-IR) observations are necessary to confirm the real existence of this feature and to allow us to reach more robust conclusions
SURFACE BRIGHTNESS FLUCTUATIONS: A POWERFUL TOOL FOR INVESTIGATING UNRESOLVED STELLAR POPULATIONS
No full textSurface Brightness Fluctuations from Archival ACS Images: A Stellar Population and Distance Study
No full textWe derive surface brightness fluctuations (SBF) and integrated magnitudes in the V and I bands using Advanced Camera for Surveys (ACS) archival data. The sample includes 14 galaxies covering a wide range of physical properties: morphology, total absolute magnitude, and integrated color. We take advantage of the latter characteristic of the sample to check existing empirical calibrations of absolute SBF magnitudes both in the I and V passbands. In addition, by comparing our SBF and color data with the Teramo-SPoT simple stellar population models and other recent sets of population synthesis models, we discuss the feasibility of stellar population studies based on fluctuation magnitudes analysis. The main result of this study is that multiband optical SBF data and integrated colors can be used to significantly constrain the chemical composition of the dominant stellar system in the galaxy, but not the age in the case of systems older than 3 Gyr. SBF color gradients are also detected and analyzed. These SBF gradient data, together with other available data, point to the existence of mass dependent metallicity gradients in galaxies, with the more massive objects showing a nonnegligible SBF versus color gradient. The comparison with models suggests that such gradients imply more metal rich stellar populations in the galaxies' inner regions with respect to the outer ones
Effects of dexamethasone on the bovine immune system: cellular and humoral immune responses
No full textDetection of Surface Brightness Fluctuations in Elliptical Galaxies Imaged with the Advanced Camera for Surveys: B- and I-Band Measurements
No full textEffects of the repeated oral administration of cimaterol and clenbuterol upon the liver drug metabolizing enzymes activities (DMEs) in the male chick
No full text
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
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