1,721,119 research outputs found
The Chemical Composition of NGC 5824, a Globular Cluster without Iron Spread but with an Extreme Mg-Al Anticorrelation
Full text linkNGC 5824 is a massive Galactic globular cluster suspected to have an intrinsic spread in its iron content, according to the strength of the calcium triplet lines. We present chemical abundances of 117 cluster giant stars using high-resolution spectra acquired with the multi-object spectrograph FLAMES. The metallicity distribution of 87 red giant branch stars is peaked at [Fe/H] =-2.11 ±0.01 dex, while that derived from 30 asymptotic giant branch stars is peaked at [Fe/H] =-2.20 ±0.01 dex. Both the distributions are compatible with a null spread, indicating that this cluster did not retain the ejecta of supernovae. The small iron abundance offset between the two groups of stars is similar to the abundances already observed among red and asymptotic giant branch stars in other clusters. The lack of intrinsic iron spread rules out the possibility that NGC 5824 is the remnant of a disrupted dwarf galaxy, as previously suggested. We also find evidence of the chemical anomalies usually observed in globular clusters, namely the Na-O and the Mg-Al anticorrelations. In particular, NGC 5824 exhibits a huge range of [Mg/Fe] abundance, observed in only a few metal-poor and/or massive clusters. We conclude that NGC 5824 is a normal globular cluster, without spread in [Fe/H] but with an unusually large spread in [Mg/Fe], possibly due to an efficient self-enrichment driven by massive asymptotic giant branch stars
The chemical composition of the oldest nearby open cluster Ruprecht 147
Full text linkContext. Ruprecht 147 (NGC 6774) is the closest old open cluster, with a distance of less than 300 pc and an age of about 2.5 Gyr. It is therefore well suited for testing stellar evolution models and for obtaining precise and detailed chemical abundance information. Aims. We combined photometric and astrometric information coming from literature and the Gaia mission with very high-resolution optical spectra of stars in different evolutionary stages to derive the cluster distance, age, and detailed chemical composition. Methods. We obtained spectra of six red giants using HARPS-N at the Telescopio Nazionale Galileo (TNG). We also used European Southern Observatory (ESO) archive spectra of 22 main sequence (MS) stars, observed with HARPS at the 3.6 m telescope. The very high resolution (115 000) and the large wavelength coverage (about 380-680 nm) of the twin instruments permitted us to derive atmospheric parameters, metallicity, and detailed chemical abundances of 23 species from all nucleosynthetic channels. We employed both equivalent widths and spectrum synthesis. We also re-derived the cluster distance and age using Gaia parallaxes, proper motions, and photometry in conjunction with the PARSEC stellar evolutionary models. Results. We fully analysed those stars with radial velocity and proper motion/parallax in agreement with the cluster mean values. We also discarded one binary not previously recognised, and six stars near the MS turn-off because of their high rotation velocity. Our final sample consists of 21 stars (six giants and 15 MS stars). We measured metallicity (the cluster average [Fe/H] is +0.08, rms = 0.07) and abundances of light, α, Fe-peak, and neutron-capture elements. The Li abundance follows the expectations, showing a tight relation between temperature and abundance on the MS, at variance with M 67, and we did not detect any Li-rich giant. Conclusions. We confirm that Rup 147 is the oldest nearby open cluster. This makes it very valuable to test detailed features of stellar evolutionary models
ANOTHER BRICK IN UNDERSTANDING CHEMICAL AND KINEMATICAL PROPERTIES OF BSSs: NGC 6752
Full text linkWe used high-resolution spectra acquired with the multifiber facility FLAMES at the Very Large Telescope of the European Southern Observatory to investigate the chemical and kinematical properties of a sample of 22 blue straggler stars (BSSs) and 26 red giant branch stars in the nearby globular cluster NGC 6752. We measured radial and rotational velocities and Fe, O, and C abundances. According to radial velocities, metallicity, and proper motions, we identified 18 BSSs as likely cluster members. We found that all the BSSs rotate slowly (less than 40 km s-1), similar to the findings in 47 Tucanae, NGC 6397, and M30. The Fe abundance analysis reveals the presence of three BSSs affected by radiative levitation (showing [Fe/H] significantly higher than that measured in "normal" cluster stars), confirming that element transport mechanisms occur in the photosphere of BSSs hotter than ≃8000 K. Finally, BSS C and O abundances are consistent with those measured in dwarf stars. No C and O depletion ascribable to mass transfer processes has been found on the atmospheres of the studied BSSs (at odds with previous results for 47 Tucanae and M30), suggesting the collisional origin for BSSs in NGC 6752 or that the CO depletion is a transient phenomenon
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
Magellanic Clouds: a chemical roadmap
No full textIn this talk I will review the main results available so far concerning the chemical composition of the stellar populations in the Large and Small Magellanic Clouds. The derived chemical patterns (from field and stellar cluster stars) for the main elemental families (i.e. alpha, iron-peak, neutron-capture elements) will be discussed in light of the chemical evolution history of these two galaxies and in the perspective of the future spectroscopic surveys
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
Blue Straggler Stars in Globular Clusters: A Powerful Tool to Probe the Internal Dynamical Evolution of Stellar Systems
Full text linkThis chapter presents an overview of the main observational results obtained to date about Blue Straggler Stars (BSSs) in Galactic Globular Clusters (GCs). The BSS specific frequency, radial distribution, chemical composition and rotational properties are presented and discussed in the framework of using this stellar population as probe of GC internal dynamics. In particular, the shape of the BSS radial distribution has been found to be a powerful tracer of the dynamical age of stellar systems, thus allowing the definition of the first empirical "dynamical clock"
The updated BaSTI stellar evolution models and isochrones. IV. α-depleted calculations
No full textThis is the fourth paper of our new release of the BaSTI (a Bag of Stellar Tracks and Isochrones) stellar model and isochrone library. Following the updated solar-scaled, α-enhanced, and white dwarf model libraries, we present here α-depleted ([α/Fe] = -0.2) evolutionary tracks and isochrones, suitable to study the α-depleted stars discovered in Local Group dwarf galaxies and in the Milky Way. These calculations include all improvements and updates of the solar-scaled and α-enhanced models, and span a mass range between 0.1 and 15 MȮ, and 21 metallicities between [Fe/H] = -3.20 and +0.45 with a helium-to-metal enrichment ratio ΔY/ΔZ = 1.31, homogeneous with the solar-scaled and α-enhanced models. The isochrones - available in several photometric filters - cover an age range between ∼20 Myr and 14.5 Gyr, including the pre-main-sequence phase. We have compared our isochrones with independent calculations of α-depleted stellar models, available for the same α-element depletion adopted in the present investigation. We have also discussed the effect of an α-depleted heavy element distribution on the bolometric corrections in different wavelength regimes. Our α-depleted evolutionary tracks and isochrones are publicly available at our BaSTI website
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