1,721,093 research outputs found
Thirteen facts that you need to know on multiple populations in globular clusters
No full textI review the methods, mostly developed in the last decade, that are commonly used to identify and characterize multiple populations (MPs) in Globular Clusters (GCs) based on photometry. I summarize the results from the recent surveys of MPs with the Hubble Space Telescope (HST) and ground-based facilities and provide a list of the main properties of MPs as inferred from these studies
When Does the Onset of Multiple Stellar Populations in Star Clusters Occur. II. No Evidence of Multiple Stellar Populations in Lindsay 113
No full textThe presence of multiple populations (MPs) in almost all globular clusters (GCs) older than ∼10 Gyr has drawn lots of attention. Recently, cumulative evidence has indicated that extragalactic GCs that are older than 2 Gyr seem to also harbor MPs; however, those that are younger than 2 Gyr do not. These observations seem to imply that age is a primary property that controls the presence of MPs in star clusters. However, because of the lack of studies of intermediate-age (∼2-6 Gyr old), low-mass clusters, it is unclear if the cluster mass, in addition to age, also plays a role in the occurrence of MPs. In this work, we studied a ∼4 Gyr old, low-mass (∼23,000 M o˙) cluster, Lindsay-113, in the Small Magellanic Cloud. Using Hubble Space Telescope photometry, we found that the width of the red-giant branch in this cluster, when measured in a specific color index that is sensitive to star-to-star chemical variations, can be adequately explained by a "simple" stellar population model with some possible noises contributed from measurement uncertainty, photometric artifact, and differential reddening. The comparison of observations with predictions from synthetic spectra indicates that the internal chemical spread in nitrogen abundance, which is a signature of MPs, would not exceed 0.2 dex. Since Lindsay 113 is significantly older than other GCs with MPs, we suggest that the onset of MPs is likely determined by the combination of cluster age and mass
When Does the Onset of Multiple Stellar Populations in Star Clusters Occur? III. No Evidence of Significant Chemical Variations in Main-sequence Stars of NGC 419
No full textRecent studies have revealed that the onset age for the presence of multiple stellar populations (MPs) in star clusters seems to correspond to the disappearance of the extended main-sequence turnoff in young clusters, a pattern associated with stellar rotations. A speculative suggestion is that MPs might be caused by the magnetic brake, a stellar evolutionary effect linked to rotation. In this work, we use the young massive cluster NGC 419 as a testbed. We examined if its magnetically baked MS stars would exhibit MPs. Using the deep ultraviolet and visible images observed through the Hubble Space Telescope, combined with a specific color index that is sensitive to the nitrogen (N) abundance, we examined if its late G-and K-type MS stars are affected by N variation. Our analysis reports that the morphology of its GK-type MS is most likely a simple stellar population, and only a negligible probability, which indicates a N variation up to 0.4 dex is present. We therefore conclude that there is no significant N variation among its GK-type MS stars. The absence of a significant chemical variation among the late-type MS stars indicates that MPs might not be a specific pattern of magnetically braked stars
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
The Hubble Space Telescope UV legacy survey of galactic globular clusters - X. The radial distribution of stellar populations in NGC2808
No full text
Is helium the key parameter in the extended colour spread of the first generation stars in M3?
No full textThe study of the 'chromosome maps' of Galactic globular clusters has shown that the stars identified as 'first generation' often define an extended sequence in the mF275W. mF814W colour, whose straightforward interpretation, by comparison with synthetic spectra, is that they are inhomogeneous in helium content. The cluster M3 (NGC 5272) is one of the most prominent example of this phenomenon, since its first generation is distributed on an extended colour range, formally corresponding to a large helium enhancement (~0.1). It is necessary to ask whether the bulk of photometric observations available for this cluster supports or falsifies this interpretation. For this purpose, we examine the horizontal branch morphology, the period and magnitude distributions of the RR Lyrae variables, and the main sequence colour distribution. Simulating the first generation stars with such internal variation of helium content we cannot meet all the observational constraints at the same time, concluding that the origin of the first generation colour spread is still without a straightforward explanation
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