Context. The evolution and structure of the Magellanic Clouds is currently under debate. The classical scenario in which both the Large and Small Magellanic Clouds (LMC, SMC) are orbiting the Milky ...Way has been challenged by an alternative in which the LMC and SMC are in their first close passage to our Galaxy. The clouds are close enough to us to allow spatially resolved observation of their stars, and detailed studies of stellar populations in the galaxies are expected to be able to constrain the proposed scenarios. In particular, the west halo (WH) of the SMC was recently characterized with radial trends in age and metallicity that indicate tidal disruption. Aims. We intend to increase the sample of star clusters in the west halo of the SMC with homogeneous age, metallicity, and distance derivations to allow a better determination of age and metallicity gradients in this region. Positions are compared with the orbital plane of the SMC from models. Methods. Comparisons of observed and synthetic V(B-V) colour-magnitude diagrams were used to derive age, metallicity, distance, and reddening for star clusters in the SMC west halo. Observations were carried out using the 4.1 m SOAR telescope. Photometric completeness was determined through artificial star tests, and the members were selected by statistical comparison with a control field. Results. We derived an age of 1.23 + or - 0.07 Gyr and Fe/H = -0.87 + or - 0.07 for the reference cluster NGC 152, compatible with literature parameters. Age and metallicity gradients are confirmed in the WH: 2.6 + or - 0.6 Gyr/degrees and -0.19 + or - 0.09 dex/degrees, respectively. The age-metallicity relation for the WH has a low dispersion in metallicity and is compatible with a burst model of chemical enrichment. All WH clusters seem to follow the same stellar distribution predicted by dynamical models, with the exception of AM-3, which should belong to the counter-bridge. Bruck 6 is the youngest cluster in our sample. It is only 130 + or - 40 Myr old and may have been formed during the tidal interaction of SMC-LMC that created the WH and the Magellanic bridge. Conclusions. We suggest that it is crucial to split the SMC cluster population into groups: main body, wing and bridge, counter-bridge, and WH. This is the way to analyse the complex star formation and dynamical history of our neighbour. In particular, we show that the WH has clear age and metallicity gradients and an age-metallicity relation that is also compatible with the dynamical model that claims a tidal influence of the LMC on the SMC.
Context.
Observations at millimeter wavelengths of bright protoplanetary disks have shown the ubiquitous presence of structures such as rings and spirals in the continuum emission. The derivation of ...the underlying properties of the emitting material is nontrivial because of the complex radiative processes involved.
Aims.
In this paper we analyze new observations from the Atacama Large Millimeter/submillimeter Array (ALMA) and the
Karl G. Jansky
Very Large Array (VLA) at high angular resolution corresponding to 5 – 8 au to determine the dust spatial distribution and grain properties in the ringed disk of HD 163296.
Methods.
We fit the spectral energy distribution as a function of the radius at five wavelengths from 0.9 to 9 mm, using a simple power law and a physical model based on an analytic description of radiative transfer that includes isothermal scattering. We considered eight dust populations and compared the models' performance using Bayesian evidence.
Results.
Our analysis shows that the moderately high optical depth (
τ
>1) at
λ ≤
1.3 mm in the dust rings artificially lower the millimeter spectral index, which should therefore not be considered as a reliable direct proxy of the dust properties and especially the grain size. We find that the outer disk is composed of small grains on the order of 200 µm with no significant difference between rings at 66 and 100 au and the adjacent gaps, while in the innermost ~30 au, larger grains (≥mm) could be present. We show that the assumptions on the dust composition have a strong impact on the derived surface densities and grain size. In particular, increasing the porosity of the grains to 80% results in a total dust mass about five times higher with respect to grains with 25% porosity. Finally, we find that the derived opacities as a function of frequency deviate from a simple power law and that grains with a lower porosity seem to better reproduce the observations of HD 163296.
Conclusions.
While we do not find evidence of differential trapping in the rings of HD 163296, our overall results are consistent with the postulated presence of giant planets affecting the dust temperature structure and surface density, and possibly originating a second-generation dust population of small grains.
Aim
To evaluate the biocompatibility of three calcium silicate‐based endodontic sealers, Bioroot BC Sealer (Septodont, Saint‐Maur‐des‐Fosses, France), Endoseal MTA (EndoSeal, Maruchi, Seoul, Korea) ...and Nano‐ceramic Sealer (B&L Biotech, Fairfax, VA, USA) (NCS), on human periodontal ligament stem cells (hPDLSCs).
Methodology
Human periodontal ligament stem cells were cultured in the presence of various endodontic sealer eluates for 24 h. Cell viability was determined using the MTT assay. Cell death and changes in phenotype induced by the set endodontic sealer eluates were evaluated through flow cytometry. Also, an in vitro scratch wound‐healing model was used to determine their effects in cell migration. Finally, to assess cell morphology and attachment to the different sealers, hPDLSCs were directly seeded onto the material surfaces and analysed by scanning electron microscopy (SEM). One‐way analysis of variance (anova) followed by a Bonferroni post‐test was performed (P < 0.05).
Results
At 24 h, cell spreading was evident in the presence of Bioroot BC Sealer (BR) and Nano‐ceramic Sealer (NCS), but not Endoseal MTA (ES). At 72 h, BR and NCS exhibited high and moderate cell proliferation, respectively, whereas ES revealed low rates of cell proliferation (P < 0.05). Similar results were obtained in a cell death assay. In addition, hPDLSCs maintained their mesenchymal phenotype in all conditions although their capacity to migrate was higher in the presence of BR. Finally, SEM studies revealed a good degree of proliferation, cell spreading and attachment, especially when using BR and NCS discs.
Conclusions
BR and NCS were associated with better cytocompatibility than ES. Further in vitro and in vivo investigations are required to confirm the suitability of these calcium silicate‐based endodontic sealers for clinical application.
Aims. The aim of this work is the study of abundances of the heavy elements Ba, La, Ce, Nd, and Eu in 56 bulge giants (red giant branch and red clump) with metallicities ranging from -1.3 dex to 0.5 ...dex. Methods. We obtained high-resolution spectra of our giant stars using the FLAMES-UVES spectrograph on the Very Large Telescope. We inspected four bulge fields along the minor axis. Results. We measure the chemical evolution of heavy elements, as a function of metallicity, in the Galactic bulge. Conclusions. The Ba,La,Ce,Nd/Fe vs. Fe/H ratios decrease with increasing metallicity, in which aspect they differ from disc stars. In our metal-poor bulge stars, La and Ba are enhanced relative to their thick disc counterpart, while in our metal-rich bulge stars La and Ba are underabundant relative to their disc counterpart. Therefore, this contrast between bulge and discs trends indicates that bulge and (solar neighbourhood) thick disc stars could behave differently. An increase in La,Nd/Eu with increasing metallicity, for metal-rich stars with Fe/H > 0 dex, may indicate that the s-process from AGB stars starts to operate at a metallicity around solar. Finally, Eu/Fe follows the α/ Fe behaviour, as expected, since these elements are produced by SNe type II.
Abstract
In this article, we describe a new algorithm for short-time satellite-based forecasts for seeing and photometric quality at the European Extremely Large Telescope (E-ELT) site (Armazones) ...and we analyse the correlation between the Paranal and Armazones sites. The algorithm uses data from the polar satellite Aqua's Moderate Resolution Imaging Spectroradiometer (MODIS) and the Geostationary Operational Environmental Satellite (GOES 13). We have analysed 13 years (2003–2015) of cloud coverage data from MODIS in order to obtain the cyclical perturbations through Fourier analysis. Then we have developed the forecast model using GOES 13 d data (2015). Monthly calibration atmospheric-layer temperature thresholds have been achieved through the daily temperature range detected by the satellite. The algorithm works through conditional probability. This allowed us to extrapolate the main frequency of the cloud-coverage perturbations, achieving three results: there are two major seasonal meteorological frequencies at Armazones and a short one of 14 days. This result allows us to improve the rate of the prediction algorithm by introducing a new threshold function. The correlation of 98 per cent found between the pixel above Paranal and the pixel above Armazones allows us to use the Paranal ground data to validate the prediction model. We analysed the 2015 data at Armazones and reached a correlation of 97 per cent for the short-time photometry and seeing quality forecast.
•Long-term trend in measuring the night sky brightness by Sky Quality Meters.•Effect of instrument ageing in evaluating Artificial Light At Night (ALAN)•Analysis of data from the Italian Sky Quality ...Meter network in Veneto.•Effect of the spectral distribution of the night sky and ALAN emission on the night sky brightness.•Slow reduction of air pollution brings to minor sky glow in a light polluted site.
Several networks of Sky Quality Meters show long-term trends in measuring the night sky brightness. Causes of this variation could be ageing of the instruments and variations of the sky emission. The data from Ekar Observatory (Italy) are here considered.
No significant ageing effect was detected on 9-year-old housing windows. A 9-year-old IR blocking filter shows a variation of its spectral transmittance up to 80%.
No trend on the SQM output was found due to only the variation of the spectral distribution of the night sky emission. Together with ageing of the IR blocking filter, it causes a reduction of the SQM output of about 0.01magSQMarcsec-2 per year.
Slow trend of the aerosol optical depth suggests the air near the considered site is changing towards less polluted conditions. It reduces scattering of the artificial light and consequently sky glow in the light polluted considered site.
ABSTRACT
The study of artificial light at night (ALAN) by satellite is very important for the analysis of new astronomical sites and for the long-term temporal evolution observation of the emission ...from the ground. The analysis of satellite data presents many advantages but also some critical points because of fluctuations in measurements. The main result of this paper is the discovery of a correlation between these fluctuations and the aerosol concentration combined with cloud cover and lunar cycles. In this work, we also present a mathematical empirical model for the light pollution propagation study in relation to the aerosol concentration detected by satellite. We apply this model to the astronomical site of Asiago (Ekar Observatory) providing a possible explanation for the temporal ALAN fluctuations detected by satellite. Finally, we validate the results with the ground collected data.
Abstract
The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters is providing a major breakthrough in our knowledge of globular clusters (GCs) and their stellar populations. Among ...the main results, we discovered that all the studied GCs host two main discrete groups consisting of first generation (1G) and second generation (2G) stars. We exploit the multiwavelength photometry from this project to investigate, for the first time, the Red Giant Branch Bump (RGBB) of the two generations in a large sample of GCs. We identified, with high statistical significance, the RGBB of 1G and 2G stars in 26 GCs and found that their magnitude separation as a function of the filter wavelength follows comparable trends. The comparison of observations to synthetic spectra reveals that the RGBB luminosity depends on the stellar chemical composition and that the 2G RGBB is consistent with stars enhanced in He and N and depleted in C and O with respect to 1G stars. For metal-poor GCs the 1G and 2G RGBB relative luminosity in optical bands mostly depends on helium content, Y. We used the RGBB observations in F606W and F814W bands to infer the relative helium abundance of 1G and 2G stars in 18 GCs, finding an average helium enhancement ΔY = 0.011 ± 0.002 of 2G stars with respect to 1G stars. This is the first determination of the average difference in helium abundance of multiple populations in a large number of clusters and provides a lower limit to the maximum internal variation of helium in GCs.
Aims.Updated data of the 153 Galactic globular clusters are used to readdress fundamental parameters of the Milky Way, such as the distance of the Sun to the Galactic centre, the bulge and halo ...structural parameters, and cluster destruction rates.Methods.We build a reduced sample that has been decontaminated of all the clusters younger than 10 Gyr and of those with retrograde orbits and/or evidence of relation to dwarf galaxies. The reduced sample contains 116 globular clusters that are tested for whether they were formed in the primordial collapse.Results.The 33 metal-rich globular clusters ($\rm Fe/H\geq-0.75$) of the reduced sample basically extend to the Solar circle and are distributed over a region with the projected axial-ratios typical of an oblate spheroidal, $\Delta x:\Delta y:\Delta z\approx1.0:0.9:0.4$. Those outside this region appear to be related to accretion. The 81 metal-poor globular clusters span a nearly spherical region of axial-ratios ${\approx}1.0:1.0:0.8$ extending from the central parts to the outer halo, although several clusters in the external region still require detailed studies to unravel their origin as accretion or collapse. A new estimate of the Sun's distance to the Galactic centre, based on the symmetries of the spatial distribution of 116 globular clusters, is provided with a considerably smaller uncertainty than in previous determinations using globular clusters, $R_{\rm O}=7.2\pm0.3\,\rm kpc$. The metal-rich and metal-poor radial-density distributions flatten for $R_{\rm GC}\leq2\,\rm kpc$ and are represented well over the full Galactocentric distance range both by a power-law with a core-like term and Sérsic's law; at large distances they fall off as ${\sim} R^{-3.9}$.Conclusions.Both metallicity components appear to have a common origin that is different from that of the dark matter halo. Structural similarities between the metal-rich and metal-poor radial distributions and the stellar halo are consistent with a scenario where part of the reduced sample was formed in the primordial collapse and part was accreted in an early period of merging. This applies to the bulge as well, suggesting an early merger affecting the central parts of the Galaxy. The present decontamination procedure is not sensitive to all accretions (especially prograde) during the first Gyr, since the observed radial density profiles still preserve traces of the earliest merger(s). We estimate that the present globular cluster population corresponds to ${\leq}23\pm6\%$ of the original one. The fact that the volume-density radial distributions of the metal-rich and metal-poor globular clusters of the reduced sample follow both a core-like power-law, and Sérsic's law indicates that we are dealing with spheroidal subsystems at all scales.
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