Laboratory Studies on Silicates Relevant for the Physics of TNOs

Silicates are one of the principal components present in Solar System objects.Silicates evolve in space modifying their physical properties according to theastronomical environments they go through. To characterise the nature of TNOsin the framework of the formation and evolution of the Solar System, experimentson structural transitions of silicates have been performed in the laboratoryto simulate some of the processing suffered by the dust. The infrared spectralproperties of possible silicate candidates thought to be present in TNOs have beenstudied. The results of thermal annealing of amorphous silicates and amorphisationof crystalline forsterite (pure-Mg olivine) by ion irradiation are presented. Theobservable properties of TNOs surfaces are inferred.     

Discovery of A New Class of Pulsating Stars: Gravity-mode Pulsators among Subdwarf B Stars

During the course of an ongoing CCD monitoring program to investigate low-level light variations in subdwarf B (sdB) stars, weserendipitously discovered a new class of multimode pulsators withperiods of the order of an hour. These periods are a factor of tenlonger than those of previously known multimode sdB pulsators (EC14026 stars), implying the new pulsations are due to gravity modes rather than pressure modes. The iron opacity instability that drives the short period EC 14026 stars is effective in hot sdB's. Thelong period pulsators are found only among cooler sdB stars, wherethey are surprisingly common. The mechanism responsible for excitingthe deeper g-modes in cool sdB's is currently unknown, but thetemperature and gravity range in which these stars occur must be animportant clue. We present the first observational results for thisnew class of pulsating sdB stars, and discuss some possible implications.     

Comparison between Different Models of Galactic Tidal Effects on Cometary Orbits

Different models of the action of the galactic tide are compared. Each model is a substitute for direct numerical integrations allowing a drastic decrease of the computation time. The models are built using two different techniques, (i) averaging of the fast variable (the mean anomaly) over one cometary period and (ii) fixing the comet in its aphelion direction. Moreover, we consider two different formalisms (Lagrangian and Hamiltonian) and also two different sets of variables. As expected, we find that the model results are independent of the formalism and the set of variables considered, and are highly accurate, whereas mathematical technique leads to poor results. In order to further reduce the computation time, mappings are built from the development of the solution of the models. We show that for these mappings, the set of variables giving the most accurate results is strongly dependent on the cometary eccentricity, e, and semimajor axis, a.     

Projected changes in vertical temperature profiles for Australasia

The vertical temperature profile in the atmosphere reflects a balance between radiative and convective processes and interactions with the oceanic and land surfaces. Changes in vertical temperature profiles can affect atmospheric stability, which in turn can impact various aspects of weather systems. In this study, we analyzed recent-past trends of temperature over the Australian region using a homogenized monthly upper-air temperature dataset and four reanalysis datasets (NCEP, ERA-Interim, JRA-55 and MERRA). We also used outputs of 12 historical and future regional climate model (RCM) simulations from the NSW/ACT (New South Wales/Australian Capital Territory) Regional Climate Modelling (NARCliM) project and 6 RCM simulations from the CORDEX (Coordinated Regional Downscaling Experiment) Australasian project to investigate projected changes in vertical temperature profiles. The results show that the currently observed positive trend in the troposphere and negative trend in the lower stratosphere will continue in the future with significant warming over the whole troposphere and largest over the middle to upper troposphere. The increasing temperatures are found to be latitude-dependent with clear seasonal variations, and a strong diurnal variation for the near surface layers and upper levels in tropical regions. Changes in the diurnal variability indicate that near surface layers will be less stable in the afternoon leading to conditions favoring convective systems and more stable in the early morning which is favorable for temperature inversions. The largest differences of future changes in temperature between the simulations are associated with the driving GCMs, suggesting that large-scale circulation plays a dominant role in regional atmospheric temperature change.

     

Optical Counterparts of Undetermined Type <Emphasis Type="Italic">γ</Emphasis>-Ray Active Galactic Nuclei with Blazar-Like Spectral Energy Distributions

During its first four years of scientific observations, the Fermi Large Area Telescope (Fermi-LAT) detected 3033 γ-ray sources above a 4 σ significance level. Although most of the extra-galactic sources are active galactic nuclei (AGN) of the blazar class, other families of AGNs are observed too, while a still high fraction of detections (～30%) remains with uncertain association or classification. According to the currently accepted interpretation, the AGN γ-ray emission arises from inverse Compton (IC) scattering of low energy photons by relativistic particles confined in a jet, which, in the case of blazars, is oriented very close to our line-of-sight. Taking advantage of data from radio and X-ray wavelengths, which we expect to be produced together with γ-rays, providing a much better source localization potential, we focused our attention on a sample of γ-ray Blazar Candidates of Undetermined type (BCUs), starting a campaign of optical spectroscopic observations. The main aims of our investigation include a census of the AGN families that contribute to γ-ray emission and a study of their redshift distribution, with the subsequent implications on the intrinsic source power. We furthermore analyze which γ-ray properties can better constrain the nature of the source, thus helping in the study of objects not yet associated with a reliable low frequency counterpart. Here we report on the instruments and techniques used to identify the optical counterparts of γ-ray sources, we give an overview on the status of our work, and we discuss the implications of a large scale study of γ-ray emitting AGNs.     

Mapping soil erodibility from composed data set in Sele River Basin, Italy

Evaluation of soil erodibility is an important task for Mediterranean lands, in which fertility and crop yield are significantly affected by soil erosion. The soil physicochemical parameters affecting soil erodibility are highly variable in space and, as for many other environmental variables, sample measurements are generally not enough for assessing its spatial variability with an acceptable level of uncertainty at the scales of practical interest. This study illustrates the procedure applied for estimating the pattern of soil erodibility across the Sele Basin (Southern Italy), where soil properties have been measured on a limited number of sparse samples. Sampled data were integrated with other sparse data estimated by local regression functions, which relate soil erodibility to auxiliary variables, such as terrain attributes and land system class memberships. Sampled and estimated data were merged in a composed data set to assess the spatial pattern of soil erodibility by ordinary kriging. The proposed approach offers effective spatial predictions, and it is exportable to regions where financial costs for soil sampling are not feasible.     

Sedimentary evolution of the Mesozoic continental redbeds using geochemical and mineralogical tools: the case of Upper Triassic to Lowermost Jurassic Monte di Gioiosa mudrocks (Sicily,southern Italy)

The continental redbeds from the Internal Domains of the central-western Mediterranean Chains have an important role in the palaeogeographic and palaeotectonic reconstructions of the Alpine circum-Mediterranean orogen evolution since these redbeds mark the Triassic-Jurassic rift-valley stage of Tethyan rifting. The composition and the sedimentary evolution of the Middle Triassic to Lowermost Jurassic continental redbeds of the San Marco d’Alunzio Unit (Peloritani Mountains, Southern Italy), based on mineralogical and chemical analyses, suggests that the studied mudrock sediments share common features with continental redbeds that constitute the Internal Domains of the Alpine Mediterranean Chains. Phyllosilicates are the main components in the mudrocks. The 10 Å-minerals (illite and micas), the I–S mixed layers, and kaolinite are the most abundant phyllosilicates. The amount of illitic layers in I–S mixed layers coupled with the illite crystallinity values (IC) are typical of high degree of diagenesis, corresponding to a lithostatic/tectonic loading of about 4–5 km. The mineralogical assemblage coupled with the A-CN-K plot suggest post-depositional K-enrichments. Palaeoweathering proxies (PIA and CIW) record intense weathering at the source area. Further, the studied sediments are affected by reworking and recycling processes and, as consequence, it is likely these proxies monitor cumulative effect of weathering. The climate in the early Jurassic favoured recycling and weathering occurred under hot, episodically humid climate with a prolonged dry season. The source-area is the low-grade Paleozoic metasedimentary basement. Mafic supply is minor but not negligible as suggested by provenance proxies.     

The young open cluster NGC 2129

The first charge-coupled device   UBV ( RI )_C  photometric study in the area of the doubtful open cluster NGC 2129 is presented. Photometry of a field offset 15 arcmin northwards is also provided, to probe the Galactic disc population towards the cluster. Using star counts, proper motions from the UCAC2 catalogue, colour–magnitude and colour–colour diagrams, we demonstrate that NGC 2129 is a young open cluster. The cluster radius is 2.5 arcmin, and across this region we find evidence of significant differential reddening, although the reddening law seems to be normal towards its direction. Updated estimates of the cluster fundamental parameters are provided. The mean reddening is found to be   E ( B − V ) = 0.80 ± 0.08  and the distance modulus is  ( m − M )₀= 11.70 ± 0.30  . Hence, NGC 2129 is located at 2.2 ± 0.2 kpc from the Sun inside the Local spiral arm. The age derived from 37 photometrically selected members is estimated to be approximately 10 Myr. These stars are used to provide new estimates of the cluster absolute proper-motion components.     

Orbit determination with very short arcs: II. Identifications

When the observational data are not enough to compute a meaningful orbit for an asteroid/comet we can represent the data with an attributable, i.e., two angles and their time derivatives. The undetermined variables range and range rate span an admissible region of Solar System orbits, which can be sampled by a set of Virtual Asteroids (VAs) selected by means of an optimal triangulation [Milani, A., Gronchi, G.F., de' Michieli Vitturi, M., Kne?evi?, Z., 2004. Celest. Mech. Dyn. Astron. 90, 59-87]. The attributable 4 coordinates are the result of a fit and they have an uncertainty, represented by a covariance matrix. Two short arcs of observations, represented by two attributables, can be linked by considering for each VA (in the admissible region of the first arc) the covariance matrix for the prediction at the time of the second arc, and by comparing it with the attributable of the second arc with its own covariance. By defining an identification penalty we can select the VAs allowing to fit together both arcs and compute a preliminary orbit. Two attributables may not be enough to compute an orbit with convergent differential corrections. Thus the preliminary orbit is used in a constrained differential correction, providing solutions along the Line Of Variation which can be used as second generation VAs to further predict the observations at the time of a third arc. In general the identification with a third arc will ensure a well determined orbit, to which additional sets of observations can be attributed. To test these algorithms we use a large scale simulation and measure the completeness, the reliability and the efficiency of the overall procedure to build up orbits by accumulating identifications. Under the conditions expected for the next generation asteroid surveys, the methods developed in this and in the preceding papers are efficient enough to be used as primary identification methods, with very good results. One important property is that the completeness in finding the possible identifications is as good for comparatively rare orbits, such as the ones of Near-Earth Objects, as for main belt orbits.