Star formation in the starburst cluster in NGC 3603

We have used new, deep, visible and near infrared observations of the compact starburst cluster in the giant HII region NGC 3603 and its surroundings with the WFC3 on HST and HAWK-I on the VLT to study in detail the physical properties of its intermediate mass (∼1–3 M_⊙) stellar population. We show that after correction for differential extinction and actively accreting stars, and the study of field star contamination, strong evidence remains for a continuous spread in the ages of pre-main sequence stars in the range ∼2 to ∼30 Myr within the temporal resolution available. Existing differences among presently available theoretical models account for the largest possible variation in shape of the measured age histograms within these limits. We also find that this isochronal age spread in the near infrared and visible Colour-Magnitude Diagrams cannot be reproduced by any other presently known source of astrophysical or instrumental scatter that could mimic the luminosity spread seen in our observations except, possibly, episodic accretion. The measured age spread and the stellar spatial distribution in the cluster are consistent with the hypothesis that star formation started at least 20–30 Myrs ago progressing slowly but continuously up to at least a few million years ago. All the stars in the considered mass range are distributed in a flattened oblate spheroidal pattern with the major axis oriented in an approximate South-East–North-West direction, and with the length of the equatorial axis decreasing with increasing age. This asymmetry is most likely due to the fact that star formation occurred along a filament of gas and dust in the natal molecular cloud oriented locally in this direction.     

Microbial pollution indicators and culturable heterotrophic bacteria in a Mediterranean area (Southern Adriatic Sea Italian coasts)

In the present study we evaluated the degree of microbial water pollution along the coast line between Brindisi and Santa Maria di Leuca (Southern Adriatic Sea) as well as the culturable heterotrophic bacteria abundances and biodiversity in relation to the microbiological quality of the water. A total of 3773 colonies were isolated, subcultured and identified by several morphological, cultural and biochemical methods including the standardized API 20 E and API 20 NE tests. Along the examined coastal tract the microbial pollution indicators were always below the tolerance limits for bathing waters defined by the CEE directive, suggesting a good sanitary quality. Concerning culturable heterotrophic bacteria, different temporal density trends were observed in the four sites in relation to their geographical position. A positive relationship between the bacterial abundances and the temperature was observed in S. Cataldo and Otranto. The culturable bacterial community was mainly composed of the genera Aeromonas, Pseudomonas, Photobacterium and Flavobacterium. The Enterobacteriaceae family represented a conspicuous component of the bacterial community too. Bacilli were predominant among the Gram-positive bacteria. Of interest is the isolation of yeasts (2% at the surface and 1% at the bottom) taking into account their capability of biodegradation of various materials. Because of the low level of microbial pollution recorded, our results are indicative of the natural variation and diversity of the culturable bacterial community in such an oligotrophic ecosystem and could represent a good point of comparison with other ecosystems as well as a baseline for long term studies aimed to evaluate the effects of environmental fluctuations and human impacts on this aspect of biodiversity in coastal areas.     

Filter-feeder macroinvertebrates as key players in culturable bacteria biodiversity control: a case of study with Sabella spallanzanii (Polychaeta: Sabellidae)

The present study investigates the effect of the filtering activity of Sabella spallanzanii on the culturable heterotrophic bacterial community through the comparison of the bacterial diversity in transplanted polychaetes and the surrounding seawater. For isolation of culturable heterotrophic bacteria, seawater samples as well as polychaete homogenates were plated in triplicates onto Bacto Marine Agar 2216 (Difco). All the colonies grown were isolated, subcultured and identified by several morphological, biochemical and cultural methods. Some bacterial genera showed higher average abundances in polychaetes than in seawater (i.e. Lucibacterium and Photobacterium). Aeromonas represented a conspicuous component of the bacterial community both in S. spallanzanii and seawater. The presence of Cytophaga and Pseudomonas was also relevant in the examined seawater samples. The selective concentrations of some bacterial genera inside S. spallanzanii either by grazing on bacteria or their capability as bacterial reservoirs, provides evidence for the role of macrobenthic invertebrates as key determinants for microbial diversity.     

Exponential Gaussian approach for spectral modelling: The EGO algorithm II. Band asymmetry

The present investigation is complementary to a previous paper which introduced the EGO approach to spectral modelling of reflectance measurements acquired in the visible and near-IR range (Pompilio, L., Pedrazzi, G., Sgavetti, M., Cloutis, E.A., Craig, M.A., Roush, T.L. [2009]. Icarus, 201 (2), 781-794). Here, we show the performances of the EGO model in attempting to account for temperature-induced variations in spectra, specifically band asymmetry.Our main goals are: (1) to recognize and model thermal-induced band asymmetry in reflectance spectra; (2) to develop a basic approach for decomposition of remotely acquired spectra from planetary surfaces, where effects due to temperature variations are most prevalent; (3) to reduce the uncertainty related to quantitative estimation of band position and depth when band asymmetry is occurring.In order to accomplish these objectives, we tested the EGO algorithm on a number of measurements acquired on powdered pyroxenes at sample temperature ranging from 80 up to 400 K. The main results arising from this study are: (1) EGO model is able to numerically account for the occurrence of band asymmetry on reflectance spectra; (2) the returned set of EGO parameters can suggest the influence of some additional effect other than the electronic transition responsible for the absorption feature; (3) the returned set of EGO parameters can help in estimating the surface temperature of a planetary body; (4) the occurrence of absorptions which are less affected by temperature variations can be mapped for minerals and thus used for compositional estimates.Further work is still required in order to analyze the behaviour of the EGO algorithm with respect to temperature-induced band asymmetry using powdered pyroxene spanning a range of compositions and grain sizes and more complex band shapes.     

Chemical and structural defensive external strategies in six sabellid worms (Annelida)

In the marine environment, sessile invertebrates have developed an impressive array of mechanisms to avoid predation, bacterial exploitation, and epibiotic overgrowth. In the present study we investigated several defensive strategies adopted by six sabellids: the hard bottom species Sabella spallanzanii (Gmelin, 1791), Branchiomma luctuosum Grube, 1869, Branchiomma bairdi (McIntosh, 1885), and Sabellastarte spectabilis (Grube, 1878), and the soft bottom species Myxicola infundibulum (Renier, 1804), and Megalomma lanigera (Grube, 1846), which have different morphological characteristics and geographical distribution. We examined and compared some defensive features such as branchial crown toughness, tube structure and strength, amount of released mucus, and antibacterial lysozyme‐activity in the mucus. The investigated species utilize a combination of defence and deterrence strategies that seems to be related to the colonized habitat. Tube strength was, higher in the hard bottom species compared with the soft bottom ones, where the tubes are generally buried and protected within the sediment. Branchial crown appeared stronger and resistant in hard bottom species, except for S. spallanzanii, which is the species showing the strongest tube. Sabella spallanzanii, M. infundibulum and S. spectabilis secreted high amount of mucus with high lysozyme‐like activity. By contrast, B. luctuosum, B. bairdi, and M. lanigera produced low amounts of mucus exerting lower antibacterial activity.     

PheniX: a new vision for the hard X-ray sky

We are proposing a mission devoted to high energy X-ray astronomy that is based on a focusing telescope operating in the 1?C200?keV energy range but optimized for the hard X-ray range. The main scientific topics concern: Physics of compact objects: The proximity of compact objects provides a unique laboratory to study matter and radiation in extreme conditions of temperature and density in strong gravitational environment. The emission of high energy photons from these objects is far from being understood. The unprecedented sensitivity in the high energy domain will allow a precise determination of the non-thermal processes at work in the vicinity of compact objects. The full 1?C200?keV energy coverage will be ideal to disentangle the emission processes produced in the spacetime regions most affected by strong-gravity, as well as the physical links: disk?Cthermal emission?Ciron line?Ccomptonisation?Creflection?Cnon-thermal emission?Cjets. Neutron stars?Cmagnetic field?Ccyclotron lines: Time resolved spectroscopy (and polarimetry) at ultra-high sensitivity of AXP, milliseconds pulsars and magnetars will give new tools to study the role of the synchrotron processes at work in these objects. Cyclotron lines?Cdirect measurement of magnetic filed?Cequation of state constraints?Cshort bursts?Cgiant flares could all be studied with great details. AGN: The large sensitivity improvement will provide detailed spectral properties of the high energy emission of AGN??s. This will give a fresh look to the connection between accretion and jet emission and will provide a new understanding of the physical processes at work. Detection of high-redshift active nuclei in this energy range will allow to introduce an evolutionary aspect to high-energy studies of AGN, probing directly the origin of the Cosmic X-ray Background also in the non-thermal range (> 20?keV). Element formation?CSupernovae: The energy resolution achievable for this mission (<0.5?keV) and a large high energy effective area are ideally suited for the 44Ti line study (68 and 78?keV). This radioactive nuclei emission will give an estimate of their quantities and speed in their environment. In addition the study of the spatial structure and spectral emission of SNR will advance our knowledge of the dynamics of supernovae explosions, of particles acceleration mechanisms and how the elements are released in the interstellar medium. Instrumental design: The progress of X-ray focusing optics techniques allows a major step in the instrumental design: the collecting area becomes independent of the detection area. This drastically reduces the instrumental background and will open a new era. The optics will be based on depth-graded multi-layer mirrors in a Wolter I configuration. To obtain a significant effective area in the hundred of keV range a focal length in the 40?C50 meters range (attainable with a deployable mast) is needed. In addition such a mission could benefit from recent progress made on mirror coating. We propose to cover the 1?C200?keV energy range with a single detector, a double-sided Germanium strip detector operating at 80?K. The main features will be: (a) good energy resolution (.150?keV at 5?keV and <.5?keV at 100?keV), (b) 3 dimensional event localization with a low number of electronic chains, (c) background rejection by the 3D localization, (d) polarisation capabilities in the Compton regime.     

Exponential Gaussian approach for spectral modeling: The EGO algorithm I. Band saturation

Curve fitting techniques are a widespread approach to spectral modeling in the VNIR range [Burns, R.G., 1970. Am. Mineral. 55, 1608-1632; Singer, R.B., 1981. J. Geophys. Res. 86, 7967-7982; Roush, T.L., Singer, R.B., 1986. J. Geophys. Res. 91, 10301-10308; Sunshine, J.M., Pieters, C.M., Pratt, S.F., 1990. J. Geophys. Res. 95, 6955-6966]. They have been successfully used to model reflectance spectra of powdered minerals and mixtures, natural rock samples and meteorites, and unknown remote spectra of the Moon, Mars and asteroids. Here, we test a new decomposition algorithm to model VNIR reflectance spectra and call it Exponential Gaussian Optimization (EGO). The EGO algorithm is derived from and complementary to the MGM of Sunshine et al. [Sunshine, J.M., Pieters, C.M., Pratt, S.F., 1990. J. Geophys. Res. 95, 6955-6966]. The general EGO equation has been especially designed to account for absorption bands affected by saturation and asymmetry. Here we present a special case of EGO and address it to model saturated electronic transition bands. Our main goals are: (1) to recognize and model band saturation in reflectance spectra; (2) to develop a basic approach for decomposition of rock spectra, where effects due to saturation are most prevalent; (3) to reduce the uncertainty related to quantitative estimation when band saturation is occurring. In order to accomplish these objectives, we simulate flat bands starting from pure Gaussians and test the EGO algorithm on those simulated spectra first. Then we test the EGO algorithm on a number of measurements acquired on powdered pyroxenes having different compositions and average grain size and binary mixtures of orthopyroxenes with barium sulfate. The main results arising from this study are: (1) EGO model is able to numerically account for the occurrence of saturation effects on reflectance spectra of powdered minerals and mixtures; (2) the systematic dilution of a strong absorber using a bright neutral material is not responsible for band deformation. Further work is still required in order to analyze the behavior of the EGO algorithm with respect to the saturation phenomena using more complex band shapes than pyroxene bands.     

The 1669 eruption at Mount Etna: chronology,petrology and geochemistry,with inferences on the magma sources and ascent mechanisms

 Analysis of the petrochemical characters of the 1669 Etnean lavas shows that they can be grouped into two sets: SET1 lavas were erupted from 11 to 20 March and are more primitive in composition than SET2, erupted later until the end of activity. Both sets may be interpreted as the result of crystallization under different conditions of two primary magmas which are compositionally slightly distinct and which fractionate different volumetric proportions of minerals. To explain why more mafic lavas (SET1) were erupted earlier than more acid ones (SET2), we argue that new deeper magma rose up into a reservoir where residing magma was fractionating. Density calculations demonstrate that new magma is less dense and may originate a plume, rapidly rising through the residing magma which is cooler and more volatile-depleted than the new magma. Calculations of uprise velocity assuming laminar flow are consistent with this hypothesis. Received: 20 November 1995 / Accepted: 2 August 1996