1,721,153 research outputs found
The influence of the C+N+O abundances on the determination of the relative ages of globular clusters: the case of NGC1851 and NGC6121 (M4)
No full textThe colour-magnitude diagram (CMD) of NGC1851 presents two subgiant branches (SGBs), probably due to the presence of two populations differing in total C+N+O (carbon+nitrogen+oxygen) content. We test the idea that a difference in total C+N+O may simulate an age difference when comparing the CMD of clusters to derive relative ages. We compare NGC1851 with NGC6121 (M4), a cluster of very similar [Fe/H]. We find that, with a suitable shift of the CMDs that brings the two red horizontal branches at the same magnitude level, the unevolved main sequence and red giant branch match, but the SGB of NGC6121 and its red giant branch `bump' are fainter than in NGC1851. In particular, the SGB of NGC6121 is even slightly fainter than the faint SGB in NGC1851. Both these features can be explained if the total C+N+O in NGC6121 is larger than that in NGC1851, even if the two clusters are coeval. We conclude by warning that different initial C+N+O abundances between two clusters, otherwise similar in metallicity and age, may lead to differences in the turnoff morphology that can be easily attributed to an age difference.
Based in part on observations made with the European Southern Observatory (ESO) telescopes obtained from the ESO/ST-ECF Science Archive Facility.
This paper makes use of data obtained from the Isaac Newton Group Archive which is maintained as part of the CASU Astronomical Data Centre at the Institute of Astronomy, Cambridge. ‡
E-mail: [email protected] (FD); [email protected] (PBS); [email protected] (PV); [email protected] (APM); [email protected] (GP); [email protected] (VC
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
The Anomalous Horizontal Branch of NGC 2808 - Is it the Result of Environmental Effects?
No full textLuminosity and mass function of galactic open clusters I. NGC 4815
Get PDFWe present deep V and I photometry for the open
cluster NGC 4815 and four surrounding Galactic fields down to a
limiting magnitude . These data are used to study cluster
spatial extension by means of star counts, and to derive the luminosity
(LF) and mass function (MF). The radius
turns out to be arcmin at , whereas the mass
is down to .
From the color-magnitude
diagram, we obtain the LFs in the V and I bands, using
both the standard histogram and an adaptive kernel. After correction
for incompleteness and field star contamination, the LFs were
transformed into the present day mass functions (PDMF). The PDMFs from
the V and I photometry can be
represented as a power-law with a slope and
(the (Salpeter [CITE]) MF in this
notation has a slope ) respectively, in the mass range . Below this mass, the MF cannot be
considered as representative of the cluster IMF,
as it is the result of the combined effect of
strong irregularities in the stellar background,
probable internal dynamical evolution of the cluster and/or
interaction of the cluster with the dense Galactic field.
Unresolved binaries and mass segregation can only flatten the apparent
derived IMF, so we expect that the real IMF must be steeper
than the quoted slope by an unknown amount
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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