The origin of the spurious iron spread in the globular cluster NGC 3201

NGC 3201 is a globular cluster suspected to have an intrinsic spread in the iron content. We re-analysed a sample of 21 cluster stars observed with UVES-FLAMES at the Very Large Telescope and for which Simmerer et al. found a 0.4 dex wide [Fe/H] distribution with a metal-poor tail. We confirmed that when spectroscopic gravities are adopted, the derived [Fe/H] distribution spans ~0.4 dex. On the other hand, when photometric gravities are used, the metallicity distribution from Fe I lines remains large, while that derived from Fe II lines is narrow and compatible with no iron spread. We demonstrate that the metal-poor component claimed by Simmerer et al. is composed by asymptotic giant branch stars that could be affected by non local thermodynamical equilibrium effects driven by iron overionization. This leads to a decrease of the Fe I abundance, while leaving the Fe II abundance unaltered. A similar finding has been already found in asymptotic giant branch stars of the globular clusters M5 and 47 Tucanae. We conclude that NGC 3201 is a normal cluster, with no evidence of intrinsic iron spread.Comment: Accepted for publication by ApJ, 7 pages, 4 figure

Multiple populations in the old and massive Small Magellanic Cloud globular cluster NGC121

We used a combination of optical and near-UV Hubble Space Telescope photometry and FLAMES/ESO-VLT high-resolution spectroscopy to characterize the stellar content of the old and massive globular cluster (GC) NGC121 in the Small Magellanic Cloud (SMC). We report on the detection of multiple stellar populations, the first case in the SMC stellar cluster system. This result enforces the emerging scenario in which the presence of multiple stellar populations is a distinctive-feature of old and massive GCs regardless of the environment, as far as the light element distribution is concerned. We find that second population (SG) stars are more centrally concentrated than first (FG) ones. More interestingly, at odds with what typically observed in Galactic GCs, we find that NGC121 is the only cluster so far to be dominated by FG stars that account for more than 65% of the total cluster mass. In the framework where GCs were born with a 90-95% of FG stars, this observational finding would suggest that either NGC121 experienced a milder stellar mass-loss with respect to Galactic GCs or it formed a smaller fraction of SG stars.Comment: 25 pages, 7 figures, 3 tables; accepted for publication in Ap

A chemical trompe-l'\oe{}il: no iron spread in the globular cluster M22

We present the analysis of high-resolution spectra obtained with UVES and UVES-FLAMES at the Very Large Telescope of 17 giants in the globular cluster M22, a stellar system suspected to have an intrinsic spread in the iron abundance. We find that when surface gravities are derived spectroscopically (by imposing to obtain the same iron abundance from FeI and FeII lines) the [Fe/H] distribution spans ~0.5 dex, according to previous analyses. However, the gravities obtained in this way correspond to unrealistic low stellar masses (0.1-0.5 Msun) for most of the surveyed giants. Instead, when photometric gravities are adopted, the [FeII/H] distribution shows no evidence of spread at variance with the [FeI/H] distribution. This difference has been recently observed in other clusters and could be due to non-local thermodynamical equilibrium effects driven by over-ionization mechanisms, that mainly affect the neutral species (thus providing lower [FeI/H]) but leave [FeII/H] unaltered. We confirm that the s-process elements show significant star-to-star variations and their abundances appear to be correlated with the difference between [FeI/H] and [FeII/H]. This puzzling finding suggests that the peculiar chemical composition of some cluster stars may be related to effects able to spuriously decrease [FeI/H]. We conclude that M22 is a globular cluster with no evidence of intrinsic iron spread, ruling out that it has retained the supernovae ejecta in its gravitational potential well.Comment: Accepted for publication to ApJ; 33 pages, 10 figures, 6 table

2D electrical resistivity tomographies for investigating recent activation landslides in Basilicata Region (Southern Italy)

The results of a geoelectrical survey in the study of recent activation landslides in the Lucanian Apennine chain (Southern Italy) are discussed in this paper. During the last two years, after meteorological conditions which affected Southern Italy and in particular Basilicata Region, many landslides occurred in this area as reactivations of old movements. These reactivations seriously damaged buildings and infrastructure and they threatened the safety of the people living in the area. Taking into account the complexity and danger of the phenomena, some evacuation decrees for a few houses were adopted. In a short time and at low cost, by using the Mobile Laboratory of IMAA for geophysical measurements, active geoelectrical investigations were carried out and data processing performed using innovative techniques for data inversion. The results represent a valid cognitive support to choose the most appropriate technical solution for strengthening of the slopes and an example of best practice for the cooperation between the Civil Protection of Basilicata Region and IMAA-CN

Searching in the dark: the dark mass content of the Milky Way globular clusters NGC288 and NGC6218

We present an observational estimate of the fraction and distribution of dark mass in the innermost region of the two Galactic globular clusters NGC 6218 (M12) and NGC 288. Such an assessment has been made by comparing the dynamical and luminous mass profiles derived from an accurate analysis of the most extensive spectroscopic and photometric surveys performed on these stellar systems. We find that non-luminous matter constitutes more than 60% of the total mass in the region probed by our data (R<1.6 arcmin~r_h) in both clusters. We have carefully analyzed the effects of binaries and tidal heating on our estimate and ruled out the possibility that our result is a spurious consequence of these effects. The dark component appears to be more concentrated than the most massive stars suggesting that it is likely composed of dark remnants segregated in the cluster core.Comment: 17 pages, 10 figures, accepted for publication by MNRA

Magnetic and ground penetrating radar for the research of Medieval buried structures in Marche Region

A magnetic and Ground Penetrating Radar joint survey was carried out in the framework of the R.I.M.E.M. project that has the aim of supporting the archaeological prospections and drive the selection of the excavation areas related to the Late Roman Period and Early Middle Ages in the Central and Southern Italy. In particular, this papers deals with the magnetic surveys acquired near “Madonna della Valle” and GPR and magnetic joint surveys carried out in “Monastero”site. Most of magnetic maps carried out in “Madonna della Valle” site shown the absence of structured magnetic anomalies, despite of the presence of archaeological signs. Several hypothesis were given to explain this evidence. Joint interpretation performed in “Monastero” site shown more intense magnetic anomalies related with shallower reflections due to probably to buried pipes. Other reflections are related with magnetic anomalies compatible with archaeological targets, but some significant reflections do not correspond to any magnetic anomaly, indicating magnetic method could be “blind” respect the archaeological target. New field surveys including the electrical resistivity tomography could be carried out in order to overcome these acquisition and interpretation difficulties

An efficient modeling framework for wall heat flux prediction in rocket combustion chambers using non adiabatic flamelets and wall-functions

In this work an efficient numerical framework for the prediction of wall heat loads in Liquid Rocket Engine combustion chambers is presented. The proposed framework is based on a new version of the non-adiabatic flamelet model and on wall functions for turbulent boundary layer modeling. Different wall function models are applied to 2D and 3D wall heat flux simulations of an experimental single-element gaseous oxygen-gaseous methane combustor in an Unsteady Reynolds Averaged Navier Stokes context. A systematic analysis and a comprehensive comparison of the selected wall models is carried out. The role of the constant or variable properties assumption on the near-wall turbulent quantities affecting the wall heat flux is assessed and the resulting friction velocity scaling investigated. When the skin friction velocity based on the local turbulent kinetic energy is defined by considering constant properties across the boundary layer, the equilibrium boundary layer assumption is not fulfilled and a significant overestimation of the wall heat flux is observed. Results obtained with the corrected near-wall turbulence modeling, on the other hand, showed a substantial improvement in terms of wall heat flux when compared with both experimental data and higher fidelity simulations results

Ground Penetrating Radar in Dam Monitoring: The Test Case of Acerenza (Southern Italy)

Nowadays, dam safety management is gaining great importance since it affects in a crucial way the monitoring and improvement of risky reservoirs, but this topic is very challenging since the dam safety requires long-term and time-continuous monitoring. In this framework, the exploitation of conventional geotechnical investigation methods often requires invasive actions in the inner of the structure to be investigated (destructiveness) and only provides punctual information for small volumes. On the contrary, the application of noninvasive sensing techniques makes it possible to investigate higher volumes without affecting the structure. In this paper we describe the application of GPR for the monitoring and diagnostics of one of the largest dams in the Basilicata region (Southern Italy). The investigation aims at detecting and localizing underground sandstone banks that are potential ways of flow of water below the dam. The manageability and the noninvasiveness of GPR have resulted in particularly suitable for this kind of application because the versatility of this geophysical method allows to investigate large areas with a good spatial resolution giving the possibility to detect the presence of inhomogeneities in the subsoil below the dam

Stability analysis of apparent resistivity measurement in the seismically active area of Val d'Agri (southern Italy)

International audienceA magnetotelluric monitoring station has been installed in the Val d'Agri area (southern Italy), to investigate the physics underlying the generation mechanisms of the electrokinetic effect, due to rapid pore pressure changes and fluid flows near the focal area of incoming earthquakes. It is well known that the magnetotelluric method reveals variations in electrical resistivity within the Earth at large depths, reaching within appropriate frequency bands the Earth's mantle. Depth sounding is performed by measuring the ratio between the mutually perpendicular horizontal electric and magnetic fields at the earth's surface, furnishing the apparent resistivity, which describes the electrical properties of subsoil as function of depth. The selected site of Val d'Agri has been struck by strong seismic events in past and recent years, this suggesting the investigation of possible changes in apparent resistivity correlated with the local tectonic activity. We analyzed the stability of the measurement of apparent resistivity and phase of the impedance tensor Z(?) during time. Our findings suggest that the measure of apparent resistivity during night-time is more stable. Therefore, we identified the characteristic apparent resistivity curve of the subsoil of the Val d'Agri site, which could be considered as a reference