179 research outputs found
Interpolating sequences of 3D-data with C2 quintic PH B-spline curves
The goal of this paper is to present an effective method for interpolating sequences of 3D-data by means of C2 quintic Pythagorean-Hodograph (PH) B-spline curves. The strategy we propose works successfully with both open and closed sequences of 3D-points. It relies on calculations that are mostly explicit thanks to the fact that the interpolation conditions can explicitly be solved in dependence of the coefficients of the pre-image PH B-spline curve. In order to select a more suitable interpolant a functional is minimized in two remaining free coefficients of the pre-image PH B-spline curve and some angular parameters
Lithium abundances in globular cluster giants: NGC 1904, NGC 2808, and NGC 362
The presence of multiple populations in globular clusters has been well
established thanks to high-resolution spectroscopy. It is widely accepted that
distinct populations are a consequence of different stellar generations:
intra-cluster pollution episodes are required to produce the peculiar chemistry
observed in almost all clusters. Unfortunately, the progenitors responsible
have left an ambiguous signature and their nature remains unresolved. To
constrain the candidate polluters, we have measured lithium and aluminium
abundances in more than 180 giants across three systems: NGC~1904, NGC~2808,
and NGC~362. The present investigation along with our previous analysis of M12
and M5 affords us the largest database of simultaneous determinations of Li and
Al abundances. Our results indicate that Li production has occurred in each of
the three clusters. In NGC~362 we detected an M12-like behaviour, with first
and second-generation stars sharing very similar Li abundances favouring a
progenitor that is able to produce Li, such as AGB stars. Multiple progenitor
types are possible in NGC~1904 and NGC~2808, as they possess both an
intermediate population comparable in lithium to the first generation stars and
also an extreme population, that is enriched in Al but depleted in Li. A simple
dilution model fails in reproducing this complex pattern. Finally, the internal
Li variation seems to suggest that the production efficiency of this element is
a function of the cluster's mass and metallicity - low-mass or relatively
metal-rich clusters are more adept at producing Li.Comment: Accepted for publication in MNRAS. 10 pages, 8 figure
VLT observations of Compact Central Objects
We present the first results of our VLT observation campaign of the Central
Compact Objects (CCOs) in SNRs RX J085201.4-461753 (Vela Jr), 1E 1648-5051 (RCW
103) and RX J171328.4-394955 (G347.3-0.5). For Vela Jr., we found that the
source is embedded in a compact optical nebulosity, possibly a bow-shock or a
photo-ionization nebula, and we identified a candidate IR counterpart to the
CCO. For RCW 103, we found no convincing evidence neither for 6 hrs IR
modulation nor for variability on any time scale from the proposed counterpart,
as well as for the other candidates close to the revised Chandra position. For
G347.3-0.5, we identified few possible IR counterparts but none of them is
apparently associated with the CCO.Comment: 4 pages, in Proc. of ``40 Years of Pulsars: Millisecond Pulsars,
Magnetars and More'', AIP, in pres
The Blue Straggler population in the globular cluster M53 (NGC5024): a combined HST, LBT, CFHT study
We used a proper combination of multiband high-resolution and wide field
multi-wavelength observations collected at three different telescopes (HST, LBT
and CFHT) to probe Blue Straggler Star (BSS) populations in the globular
cluster M53. Almost 200 BSS have been identified over the entire cluster
extension. The radial distribution of these stars has been found to be bimodal
(similarly to that of several other clusters) with a prominent dip at ~60'' (~2
r_c) from the cluster center. This value turns out to be a factor of two
smaller than the radius of avoidance (r_avoid, the radius within which all the
stars of ~1.2 M_sun have sunk to the core because of dynamical friction effects
in an Hubble time). While in most of the clusters with a bimodal BSS radial
distribution, r_avoid has been found to be located in the region of the
observed minimum, this is the second case (after NGC6388) where this
discrepancy is noted. This evidence suggests that in a few clusters the
dynamical friction seems to be somehow less efficient than expected.
We have also used this data base to construct the radial star density profile
of the cluster: this is the most extended and accurate radial profile ever
published for this cluster, including detailed star counts in the very inner
region. The star density profile is reproduced by a standard King Model with an
extended core (~25'') and a modest value of the concentration parameter
(c=1.58). A deviation from the model is noted in the most external region of
the cluster (at r>6.5' from the center). This feature needs to be further
investigated in order to address the possible presence of a tidal tail in this
cluster.Comment: 25 pages, 9 figures, accepted for publication on Ap
The local adsorption geometry of benzenethiolate on Cu(1 0 0)
The local adsorption geometry of benzenethiolate in the ordered c(2 × 6) phase on Cu(1 0 0) has been investigated by a combination of S K-edge near-edge X-ray absorption fine structure (NEXAFS), normal incidence X-ray standing waves (NIXSW) and S 1s scanned-energy mode photoelectron diffraction (PhD). NEXAFS and PhD show that the molecular plane is tilted from the surface normal by 20 ± 15°, while NIXSW clearly identifies the S head-group as occupying the four-fold coordinated hollow sites. PhD shows the S atoms lies 1.34 ± 0.04 Å above the outermost Cu atomic layer, leading to a Cu–S bondlength of 2.25 ± 0.02 Å. The combination of the PhD and NIXSW results shows the Cu surface layer has an outward relaxation of 0.15 ± 0.06 Å. Possible origins for this large adsorbate-induced relaxation are discussed
The Blue Straggler Population in Dwarf Galaxies
In this chapter I review the recent developments regarding the study of Blue
Stragglers (BSS) in dwarf galaxies. The loose density environment of dwarf
galaxies resembles that of the Galactic Halo, hence it is natural to compare
their common BSS properties. At the same time, it is unescapable to compare
with the BSS properties in Galactic Globular clusters, which constitute the
reference point for BSS studies. Admittedly, the literature on BSS in dwarf
galaxies is not plentiful. The limitation is mostly due to the large distance
to even the closest dwarf galaxies. Nevertheless, recent studies have allowed a
deeper insight on the BSS photometric properties that are worth examining.Comment: Chapter 6, in Ecology of Blue Straggler Stars, H.M.J. Boffin, G.
Carraro & G. Beccari (Eds), Astrophysics and Space Science Library, Springe
Omics sciences and precision medicine in melanoma
Background: This article provides an overview of the application of omics sciences in melanoma research. The name omics sciences refers to the large-scale analysis of biological molecules like DNA, RNA, proteins, and metabolites. Methods: In the course of this review, we have adopted a focu-sed research strategy, meticulously selecting the most pertinent and emblematic articles related to the topic. Our methodology included a systematic examination of the scientific literature to guarantee a thorough and precise synthesis of the existing sources. Results: With the advent of high-throughput technologies, omics have become an essential tool for understanding the complexity of melanoma. In this article, we discuss the different omics approaches used in melanoma research, including genomics, transcriptomics, proteomics, and metabolomics. We also highlight the major findings and insights gained from these studies, including the identification of new therapeutic targets and the development of biomarkers for diagnosis and prognosis. Finally, we discuss the challenges and future directions in omics-based melanoma research, including the integration of multiple omics data and the development of personalized medicine approaches. Conclusions: Overall, this article emphasizes the importance of omics science in advancing our understanding of melanoma and its potential for improving patient outcomes
A Tale of Three Cities : OmegaCAM discovers multiple sequences in the color-magnitude diagram of the Orion Nebula Cluster
Reproduced with permission from Astronomy & Astrophysics, © 2017 ESO. Published by EDP Sciences.As part of the Accretion Discs in H with OmegaCAM (ADHOC) survey, we imaged in r, i and H-alpha a region of 12x8 square degrees around the Orion Nebula Cluster. Thanks to the high-quality photometry obtained, we discovered three well-separated pre-main sequences in the color-magnitude diagram. The populations are all concentrated towards the cluster's center. Although several explanations can be invoked to explain these sequences we are left with two competitive, but intriguing, scenarios: a population of unresolved binaries with an exotic mass ratio distribution or three populations with different ages. Independent high-resolution spectroscopy supports the presence of discrete episodes of star formation, each separated by about a million years. The stars from the two putative youngest populations rotate faster than the older ones, in agreement with the evolution of stellar rotation observed in pre-main sequence stars younger than 4 Myr in several star forming regions. Whatever the final explanation, our results prompt for a revised look at the formation mode and early evolution of stars in clusters.Peer reviewedFinal Published versio
The performance of the blue prime focus Large Binocular Camera at the Large Binocular Telescope
We present the characteristics and some early scientific results of the first
instrument at the Large Binocular Telescope (LBT), the Large Binocular Camera
(LBC). Each LBT telescope unit will be equipped with similar prime focus
cameras. The blue channel is optimized for imaging in the UV-B bands and the
red channel for imaging in the VRIz bands. The corrected field-of-view of each
camera is approximately 30 arcminutes in diameter, and the chip area is
equivalent to a 23x23 arcmin2 field. In this paper we also present the
commissioning results of the blue channel. The scientific and technical
performance of the blue channel was assessed by measurement of the astrometric
distortion, flat fielding, ghosts, and photometric calibrations. These
measurements were then used as input to a data reduction pipeline applied to
science commissioning data. The measurements completed during commissioning
show that the technical performance of the blue channel is in agreement with
original expectations. Since the red camera is very similar to the blue one we
expect similar performance from the commissioning that will be performed in the
following months in binocular configuration. Using deep UV image, acquired
during the commissioning of the blue camera, we derived faint UV galaxy-counts
in a ~500 sq. arcmin. sky area to U(Vega)=26.5. These galaxy counts imply that
the blue camera is the most powerful UV imager presently available and in the
near future in terms of depth and extent of the field-of-view. We emphasize the
potential of the blue camera to increase the robustness of the UGR multicolour
selection of Lyman break galaxies at redshift z~3.Comment: Accepted for publication in A&A. Uses aa.cls, 10 pages, 10 figures.
Zero points changed in Table
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