1,723,285 research outputs found
Hubble Space Telescope Photometry of the Metal-rich Globular Clusters NGHC 6624 and NGC 6637
No full textWe have observed the metal-rich globular clusters NGC 6624 and NGC 6637 (M69) using the planetary camera of the WFPC2 on the Hubble Space Telescope (HST). Observations of the Ca II triplet lines in giant stars in these clusters show that NGC 6624 and NG
Four pulsar discoveries in NGC 6624 by TRAPUM using MeerKAT
No full textInternational audienceWe report 4 new pulsars discovered in the core-collapsed globular cluster (GC) NGC 6624 by the TRAPUM Large Survey Project with the MeerKAT telescope. All of the new pulsars found are isolated. PSR J1823-3021I and PSR J1823-3021K are millisecond pulsars with period of respectively 4.319 ms and 2.768 ms. PSR J1823-3021J is mildly recycled with a period of 20.899 ms, and PSR J1823-3022 is a long period pulsar with a period of 2.497 s. The pulsars J1823-3021I, J1823-3021J, and J1823-3021K have position and dispersion measure (DM) compatible with being members of the GC and are therefore associated with NGC 6624. Pulsar J1823-3022 is the only pulsar bright enough to be re-detected in archival observations of the cluster. This allowed the determination of a timing solution that spans over two decades. It is not possible at the moment to claim the association of pulsar J1823-3022 with the GC given the long period and large offset in position (~3 arcminutes) and DM (with a fractional difference of 11 percent compared the average of the pulsars in NGC 6624). The discoveries made use of the beamforming capability of the TRAPUM backend to generate multiple beams in the same field of view which allows sensitive searches to be performed over a few half-light radii from the cluster center and can simultaneously localise the discoveries. The discoveries reflect the properties expected for pulsars in core-collapsed GCs
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
No evidence for intermediate-mass black holes in the globular clusters ω Cen and NGC 6624
No full textWe compare the results of a large grid of N-body simulations with the surface brightness and velocity dispersion profiles of the globular clusters omega Cen and NGC 6624. Our models include clusters with varying stellar-mass black hole retention fractions and varying masses of a central intermediate-mass black hole (IMBH). We find that an M-circle dot IMBH, whose presence has been suggested based on the measured velocity dispersion profile of omega Cen, predicts the existence of about 20 fast-moving, m > 0.5M(circle dot), main-sequence stars with a (1D) velocity v > 60kms(-1) in the central 20 arcsec of omega Cen. However, no such star is present in the HST/ACS proper motion catalogue of Bellini etal. (2017), strongly ruling out the presence of a massive IMBH in the core of omega Cen. Instead, we find that all available data can be fitted by a model that contains 4.6percent of the mass of omega Cen in a centrally concentrated cluster of stellar-mass black holes. We show that this mass fraction in stellar-mass BHs is compatible with the predictions of stellar evolution models of massive stars. We also compare our grid of N-body simulations with NGC 6624, a cluster recently claimed to harbour a 20000M(circle dot) black hole based on timing observations of millisecond pulsars. However, we find that models with M-IMBH > 1000M(circle dot) IMBHs are incompatible with the observed velocity dispersion and surface brightness profile of NGC 6624, ruling out the presence of a massive IMBH in this cluster. Models without an IMBH provide again an excellent fit to NGC 6624
No evidence for intermediate-mass black holes in the globular clusters ω Cen and NGC 6624
No full textWe compare the results of a large grid of N-body simulations with the surface brightness and velocity dispersion profiles of the globular clusters ω Cen and NGC 6624. Our models include clusters with varying stellar-mass black hole retention fractions and varying masses of a central intermediate-mass black hole (IMBH). We find that an 45,000M IMBH, whose presence has been suggested based on the measured velocity dispersion profile of Cen, predicts the existence of about 20 fast-moving, m>0.5 M, main-sequence stars with a (1D) velocity v>60 kms/-1 in the central 20 arcsec of ω Cen. However no such star is present in the HST/ACS proper motion catalogue of Bellini et al. (2017), strongly ruling out the presence of a massive IMBH in the core of ω Cen. Instead, we find that all available data can be fitted by a model that contains 4.6% of the mass of ω Cen in a centrally concentrated cluster of stellar-mass black holes. We show that this mass fraction in stellar-mass BHs is compatible with the predictions of stellar evolution models of massive stars. We also compare our grid of N-body simulations with NGC 6624, a cluster recently claimed to harbor a 20,000 M black hole based on timing observations of millisecond pulsars. However, we find that models with M{IMBH}>1,000 M IMBHs are incompatible with the observed velocity dispersion and surface brightness profile of NGC 6624,ruling out the presence of a massive IMBH in this cluster. Models without an IMBH provide again an excellent fit to NGC 6624
Variations on the Author
No full text“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
No full textWe 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
ULTRA-DEEP GEMINI NEAR-INFRARED OBSERVATIONS of the BULGE GLOBULAR CLUSTER NGC 6624
No full textWe used ultra-deep J and Ks images secured with the near-infrared (NIR) GSAOI camera assisted by the multi-conjugate adaptive optics system GeMS at the GEMINI South Telescope in Chile, to obtain a (Ks, J - Ks) color-magnitude diagram (CMD) for the bulge globular cluster NGC 6624. We obtained the deepest and most accurate NIR CMD from the ground for this cluster, by reaching Ks ∼ 21.5, approximately 8 mag below the horizontal branch level. The entire extension of the Main Sequence (MS) is nicely sampled and at Ks ∼ 20 we detected the so-called MS "knee" in a purely NIR CMD. By taking advantage of the exquisite quality of the data, we estimated the absolute age of NGC 6624 (tage = 12.0 ± 0.5 Gyr), which turns out to be in good agreement with previous studies in the literature. We also analyzed the luminosity and mass functions of MS stars down to M ∼ 0.45 M⊙, finding evidence of a significant increase of low-mass stars at increasing distances from the cluster center. This is a clear signature of mass segregation, confirming that NGC 6624 is in an advanced stage of dynamical evolution
A dust bubble within the globular cluster NGC 6624?
No full textA multi-color analysis of CCD frames and polarimetry for both dark patches and stars in the field of the globular cluster NGC 6624 is presented. Several of these patches have a wavelength behavior that is consistent with the existence of intra-cluster dust. The spatial distribution of these patches is not at random, rather, they appear distributed on a circular pattern some 2 parsecs in radius. Remarkably, the center of this structure, that seems to be a "bubble", is not far from the position of the X ray burster 1820-30. A possible connection between these objects might suggest the existence of an explosive event in the past.Asociación Argentina de Astronomí
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