1,721,416 research outputs found
The discovery of an anomalous RGB in M 2
No full textUsing UV images taken with the Telescopio Nazionale Galileo, we discovered an anomalous sequence in the color-magnitude diagram of M 2. This feature appears as a narrow poor-populated red giant branch, which extends down to the sub giant branch region. We speculate that this new feature could be the extension of the faint component of the split sub giant branch recently discovered by Piotto et al. We identified in our U, V images two CH stars detected in previous studies. These stars, which are both cluster members, fall on this redder sequence, suggesting indeed that the anomalous RGB should have a peculiar chemical pattern. Unfortunately, no additional spectra were obtained for stars in this previously unknown substructure
The distance to the Sagittarius dwarf spheroidal galaxy from the red giant branch tip
No full textWe derived the distance to the central region of the Sagittarius (Sgr) dwarf spheroidal galaxy from the red giant branch tip. The obtained distance modulus is (m-M)0= 17.10 +/- 0.15, corresponding to a heliocentric distance D= 26.30 +/- 1.8Kpc. This estimate is in good agreement with the distance obtained from RR Lyrae (RR Ly) stars of the globular cluster M 54, located in the core of the Sgr galaxy, once the most accurate estimate of the cluster metallicity and the most recent calibration of the MV(RRLy) versus [Fe/H] relation are adopted
Looking Outside the Galaxy: The Discovery of Chemical Anomalies in Three Old Large Magellanic Cloud Clusters
No full textBy using the multifiber spectrograph FLAMES mounted at the ESO-VLT, we have obtained high-resolution spectra for 18 giant stars, belonging to three old globular clusters of the Large Magellanic Cloud (namely NGC 1786, 2210, and 2257). While stars in each cluster showed quite homogeneous iron content, within a few cents of dex (the mean values being [Fe/H]= -1.75 ± 0.01 dex, -1.65 ± 0.02 dex and -1.95 ± 0.02 dex for NGC 1786, 2210, and 2257, respectively), we have detected significant inhomogeneities for the [Na/Fe], [Al/Fe], [O/Fe], and [Mg/Fe] abundance ratios, with evidence of [O/Fe] versus [Na/Fe] and [Mg/Fe] versus [Al/Fe] anticorrelations. The trends detected nicely agree with those observed in Galactic Globular Clusters, suggesting that such abundance anomalies are ubiquitous features of old stellar systems and they do not depend on the parent galaxy environment. In NGC 1786 we also detected two extreme O-poor, Na-rich stars. This is the first time that a firm signature of extreme chemical abundance anomalies has been found in an extragalactic stellar cluster
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
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
Discovery of a stellar system in the background of 47 Tucanae. A new cluster of the Small Magellanic Cloud?
No full textWe report on the discovery of a stellar system in the background of the Galactic globular cluster 47 Tucanae (NGC 104), located 14.8 arcmin North-West of the cluster center. The object, whose apparent diameter is D≃ 30 arcsec, is partially resolved into stars on the available CCD images, reaching a limiting magnitude of V~ 22.5, and is detected as a significant (more than 5 sigma) overdensity of blue stars (B-V<0.7). The color magnitude diagram of the system, its characteristic projected size and its position in the sky suggest that it is an intermediate-old age cluster belonging to the Small Magellanic Cloud, whose outskirts lie in the background of 47 Tuc. Although less likely, the possibility that the object is an unknown dwarf galaxy in the outskirts of the Local Group cannot completely be ruled out by the present data
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
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