1,721,304 research outputs found
The mass function of Omega Centauri down to 0.15 Msolar
No full textBy means of deep FORS1/VLT and ACS/Hubble Space Telescope observations of a wide area in the stellar system ? Cen we measured the luminosity function of main-sequence stars down to R = 22.6 and IF814W = 24.5. The luminosity functions obtained have been converted into mass functions and compared with analytical initial mass functions (IMFs) available in the literature. The mass function obtained, reaching M ~ 0.15Msolar, can be well reproduced by a broken power law with indices ? = -2.3 for M > 0.5Msolar and ? = -0.8 for M < 0.5Msolar. Since the stellar populations of ? Cen have been proved to be actually unaffected by dynamical evolution processes, the mass function measured in this stellar system should represent the best approximation of the IMF of a star cluster. The comparison with the MF measured in other Galactic globular clusters suggests that possible primordial differences in the slope of the low-mass end of their MF could exist
The red giant branch tip and bump of the Leo II dwarf spheroidal galaxy
No full textWe present V and I photometry of a 9.4 × 9.4 arcmin2 field centred on the dwarf spheroidal galaxy Leo II. The tip of the red giant branch (TRGB) is identified at ITRGB= 17.83 +/- 0.03 and adopting =-1.53 +/- 0.2 from the comparison of RGB stars with Galactic templates, we obtain a distance modulus (m-M)0= 21.84 +/- 0.13, corresponding to a distance D= 233 +/- 15 kpc. Two significant bumps have been detected in the luminosity function of the RGB. The fainter bump (B1, at V= 21.76 +/- 0.05) is the RGB bump of the dominant stellar population while the actual nature of the brightest one (B2, at V= 21.35 +/- 0.05) cannot be firmly assessed on the basis of the available data; it may be due to the asymptotic giant branch clump of the main population or it may be a secondary RGB bump. The luminosity of the main RGB bump (B1) suggests that the majority of RGB stars in Leo II belong to a population that is >~4 Gyr younger than the classical Galactic globular clusters. The stars belonging to the He-burning red clump are shown to be significantly more centrally concentrated than RR Lyrae and blue horizontal branch stars, probing the existence of an age/metallicity radial gradient in this remote dwarf spheroida
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
A comparative high-resolution spectroscopic analysis of in situ and accreted globular clusters
No full textGlobular clusters (GCs) are extremely intriguing systems that help in reconstructing the assembly of the Milky Way via the characterisation of their chemo-chrono-dynamical properties. In this study, we use high-resolution spectroscopic archival data from UVES and UVES-FLAMES at the VLT to compare the chemistry of GCs dynamically tagged as either Galactic (NGC 6218, NGC 6522, and NGC 6626) or accreted from distinct merger events (NGC 362 and NGC 1261 from Gaia-Sausage-Enceladus, and Ruprecht 106 from the Helmi Streams) in the metallicity regime where abundance patterns of field stars with different origin effectively separate (-1.3 ≤ [Fe/H] ≤ -1.0 dex). We find remarkable similarities in the abundances of the two Gaia-Sausage-Enceladus GCs across all chemical elements. They both display depletion in the α-elements (Mg, Si and Ca) and statistically significant differences in Zn and Eu compared to in situ GCs. Additionally, we confirm that Ruprecht 106 exhibits a completely different chemical makeup from the other target clusters, being underabundant in all chemical elements. This demonstrates that when high precision is achieved, the abundances of certain chemical elements can not only efficiently separate in situ from accreted GCs, but can also distinguish among GCs born in different progenitor galaxies. In the end, we investigate the possible origin of the chemical peculiarity of Ruprecht 106. Given that its abundances do not match the chemical patterns of the field stars associated with its most likely parent galaxy (i.e. the Helmi Streams), being depleted in the abundances of α-elements in particular, we believe Ruprecht 106 to originate from a less massive galaxy compared to the progenitor of the Helmi Streams
Wide-field photometry of the Galactic globular cluster M22
No full textWe present wide-field photometry of the Galactic globular cluster M22 in the B, V and I passbands for more than 186 000 stars. The study is complemented by the photometry in two narrow-band filters centred on Halpha and the adjacent continuum, and by infrared J, H and K magnitudes derived from the Two-Micron All-Sky Survey for ~2000 stars. Profiting from this huge data base, we completely characterized the evolved stellar sequences of the cluster by determining a variety of photometric parameters, including new photometric estimates of the mean metallicity, reddening and distance to the cluster. In particular, from our multiwavelength analysis, we re-examined the long-standing metallicity spread problem in M22. According to our data set, we conclude that most of the observed width of the red giant branch must be due to differential reddening, which amounts to a maximum of DeltaE(B-V) ~= 0.06, although the presence of a small metallicity spread cannot be completely ruled out. More specifically, the maximum metallicity spread allowed by our data is of the order of Delta[Fe/H]~= 0.1-0.2 dex, i.e. not much more than that allowed by the photometric errors. Finally, we identified most of the known variable stars and peculiar objects in our field of view. In particular, we have found additional evidence supporting previous optical identifications of the central star of the planetary nebula IRAS 18333-2357, which is associated with M22
On the discrete nature of the red giant branch of omega Centauri
No full textWe report on the results of an extensive Very Large Telescope high-resolution imaging campaign of the central region of the giant globular cluster omega Centauri. More than 100000 stars have been measured in the inner 9 × 9 arcmin2 region of the cluster. On the basis of multiband colour-magnitude diagrams, we confirm the existence of multiple stellar populations along the red giant branch (RGB). Moreover, thanks to the high precision of this data set, we conclude that the RGB does not present a smooth and continuous distribution, but shows a discrete structure: besides the metal-poor and the extreme metal-rich population (anomalous RGB), the existence of three metal intermediate populations is shown
The Rotation of Subpopulations in ? Centauri
No full textWe present the first result of the Ital-FLAMES survey of red giant branch (RGB) stars in ? Cen. Radial velocities with a precision of ~0.5 km s-1 are presented for 650 members of ? Cen observed with FLAMES-GIRAFFE at the Very Large Telescope. We found that stars belonging to the metal-poor (RGB-MP), metal-intermediate (RGB-MInt), and metal-rich (RGB-a) subpopulations of ? Cen are all compatible with having the same rotational pattern. Our results appear to contradict past findings by Norris et al., who could not detect any rotational signature for metal-rich stars. The slightly higher precision of the present measurements and the much larger sample size, especially for the stars richer in metals, appear as the most likely explanations for this discrepancy. The result presented here weakens the body of evidence in favor of a merger event in the past history of ? Cen
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
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