Multiple shell planetary nebulae: Evolutionary paths and observed configurations

Recent observations of multiple shell planetary nebulae confirm the existing subdivision into two morphological types: attached halo and detached halo. The multiple shell phenomenon appears in about twentyfive percent of round and elliptical planetary nebulae of theInstituto de Astrofisica de Canarias morphological survey. The analysis of these nebulae together with that of their central stars lead to the interpretation that detached halo nebulae are formed through discontinuous mass loss at the Asymptotic Giant Branch tip. The attached halo nebulae, instead, are probably produced via dynamical nebular shaping.     

The boundary layer of VW Hydri in quiescence

In this short paper, we suggest that the missing boundary layer luminosity of dwarf novae in quiescence is released mainly in the ultraviolet (UV) as the second component commonly identified in the far-UV as the 'accretion belt'. We present the well-studied SU UMa-type system VW Hyi in detail as a prototype for such a scenario. We consider detailed multiwavelength observations and in particular the recent Far Ultraviolet Spectroscopic Explorer ( FUSE ) observations of VW Hyi in quiescence, which confirm the presence of a second component (the 'accretion belt') in the far-UV spectrum. The temperature  (≈ 50 000 K)  and rotational velocity  (≈ 3000 km s ⁻¹)  of this second component are entirely consistent with the optically thick region  (τ≈ 1)  located just at the outer edge of optically thin boundary layer in the simulations of Popham. This second component contributes about 20 per cent of the far-UV flux. Using geometrical assumptions and taking into account the X-ray luminosity, we find that the total boundary layer luminosity sums up to   L _BL= (0.53 ± 0.25) L _disc  , while the theory (Kluźniak) predicts, for the rotation rate of VW Hyi's white dwarf,   L _BL≈ (0.76 ± 0.03) L _disc  . About one-fifth of the boundary layer energy is emitted in the X-ray and the remaining is emitted in the UV. This scenario is consistent with the recent simultaneous X-ray and UV observations of VW Hyi by Pandel, Córdova & Howell, from which we deduce here that the viscosity in the boundary layer region must be of the order of  ν≈ 10¹³–10¹⁴ cm² s ⁻¹  , depending on the white dwarf mass and the size of the boundary layer.     

A multi-disciplinary study of the 2002–03 Etna eruption: insights into a complex plumbing system

The 2002–03 Mt Etna flank eruption began on 26 October 2002 and finished on 28 January 2003, after three months of continuous explosive activity and discontinuous lava flow output. The eruption involved the opening of eruptive fissures on the NE and S flanks of the volcano, with lava flow output and fire fountaining until 5 November. After this date, the eruption continued exclusively on the S flank, with continuous explosive activity and lava flows active between 13 November and 28 January 2003. Multi-disciplinary data collected during the eruption (petrology, analyses of ash components, gas geochemistry, field surveys, thermal mapping and structural surveys) allowed us to analyse the dynamics of the eruption. The eruption was triggered either by (i) accumulation and eventual ascent of magma from depth or (ii) depressurisation of the edifice due to spreading of the eastern flank of the volcano. The extraordinary explosivity makes the 2002–03 eruption a unique event in the last 300 years, comparable only with La Montagnola 1763 and the 2001 Lower Vents eruptions. A notable feature of the eruption was also the simultaneous effusion of lavas with different composition and emplacement features. Magma erupted from the NE fissure represented the partially degassed magma fraction normally residing within the central conduits and the shallow plumbing system. The magma that erupted from the S fissure was the relatively undegassed, volatile-rich, buoyant fraction which drained the deep feeding system, bypassing the central conduits. This is typical of most Etnean eccentric eruptions. We believe that there is a high probability that Mount Etna has entered a new eruptive phase, with magma being supplied to a deep reservoir independent from the central conduit, that could periodically produce sufficient overpressure to propagate a dyke to the surface and generate further flank eruptions.Editorial responsibility: J. Donnelly-Nolan     

New data on the Vrancea Nappe (Moldavidian Basin, Outer Carpathian Domain, Romania): paleogeographic and geodynamic reconstructions

A study has been performed on the Cretaceous to Early Miocene succession of the Vrancea Nappe (Outer Carpathians, Romania), based on field reconstruction of the stratigraphic record, mineralogical-petrographic and geochemical analyses. Extra-basinal clastic supply and intra-basinal autochthonous deposits have been differentiated, appearing laterally inter-fingered and/or interbedded. The main clastic petrofacies consist of calcarenites, sub-litharenites, quartzarenites, sub-arkoses, and polygenic conglomerates derived from extra-basinal margins. An alternate internal and external provenance of the different supplies is the result of the paleogeographic re-organization of the basin/margins system due to tectonic activation and exhumation of rising areas. The intra-basinal deposits consist of black shales and siliceous sediments (silexites and cherty beds), evidencing major environmental changes in the Moldavidian Basin. Organic-matter-rich black shales were deposited during anoxic episodes related to sediment starvation and high nutrient influx due to paleogeographic isolation of the basin caused by plate drifting. The black shales display relatively high contents in sub-mature to mature, Type II lipidic organic matter (good oil and gas-prone source rocks) constituting a potentially active petroleum system. The intra-basinal siliceous sediments are related to oxic pelagic or hemipelagic environments under tectonic quiescence conditions although its increase in the Oligocene part of the succession can be correlated with volcanic supplies. The integration of all the data in the “progressive reorientation of convergence direction” Carpathian model, and their consideration in the framework of a foreland basin, led to propose some constrains on the paleogeographic-geodynamic evolutionary model of the Moldavidian Basin from the Late Cretaceous to the Burdigalian.     

Geochemical Responses to a Major Transgression in Giant African Lakes

Bulk organic matter (OM) in sediments that accumulated in Lakes Victoria, Albert and Tanganyika during the major transgression that transformed these basins from a desiccated or lowstand condition at the time of the Last Glacial Maximum to highstand with overflow in the terminal Pleistocene and early Holocene, show some striking compositional trends. Sediment OM content (TOC) and Rock-Eval Hydrogen Index (HI) both rise markedly, reflecting increasing primary productivity during the transgression and enhanced conditions for the preservation of labile OM, In Lake Victoria rising sedimentary sulphur content tracks the change in HI. Over the same time interval in all three lakes, δ¹³C_OM shows a falling trend of 5–8‰ . Nitrogen isotopic and C/N trends are, in contrast, more variable. Relatively high δ¹⁵N values at an early stage in the transgression may reflect isotopic effects associated with ammonia loss from an alkaline waterbody, while high δ¹⁵N later in the transgression was probably due to periods when stratification-related denitrification had a particularly strong impact upon the lakes' N cycle. The observed changes are attributed to the influence of the landscape drowned during the transgression upon the nutrient budget of the lake, a rise in river-supplied nutrients as the climate became wetter, and an increasing tendency to stable chemical stratification as the water column deepened. In the case of δ¹³C, additional contributory factors were changes in the amount and isotopic composition of river-supplied dissolved inorganic carbon (DIC) as runoff and soil–moisture turnover rates increased, and the replacement of a C4-grassland dominated flora by mixed woodland-grassland and forest with a significant presence of C3 plants. Distinct geochemical changes are also apparent in Lakes Victoria and Albert sediments at the end of the transgression which are consistent with a reduction in nutrient loading. In the case of N this resulted in biological N fixation becoming a major part of the lakes' N cycle, Some of the observed geochemical variations may be generally applicable as proxy indicators of major transgressions in large lakes. IDEAL Contribution No. 152.     

First detection of CYP1A1 and CYP2B induction in Mediterranean cetacean skin biopsies and cultured fibroblasts by Western blot analysis

The need to develop powerful tools to detect exposure and effects of POPs and emerging contaminants in Mediterranean cetaceans led us to develop a suite of sensitive non-lethal biomarkers in integument biopsies of free-ranging animals. In order to propose induction of CYP1A1 and CYP2B, detected by Western blot analysis, as biomarkers of exposure to OCs, PAHs and PBDEs, a three-phase experimental protocol (in vitro experiments, calibration experiments and field applications) was followed using fibroblast cell cultures and biopsies of Mediterranean Stenella coeruleoalba and Tursiops truncatus. This methodology was confirmed to be sensitive and stable in comparison to previous methods used to detect CYP1A1 in biopsies, enabling analysis of several inducible proteins in non-lethal samples and analysis of material from stranded animals.     

Data-driven decision management of urban underground infrastructure through groundwater-level time-series cluster analysis: the case of Milan (Italy)

Hydrogeology Journal - The significant increase in urbanization has resulted in greater use of the subsurface in urban planning and, therefore, increased interaction between groundwater and...     

Thermal characterization of the Vulcano fumarole field

Ground-based thermal infrared surveys can contribute to complete heat budget inventories for fumarole fields. However, variations in atmospheric conditions, plume condensation and mixed-pixel effects can complicate vent area and temperature measurements. Analysis of vent temperature frequency distributions can be used, however, to characterise and quantify thermal regions within a field. We examine this using four thermal infrared thermometer and thermal image surveys of the Vulcano Fossa fumarole field (Italy) during June 2004 and July 2005. These surveys show that regions occupied by low temperature vents are characterised by distributions that are tightly clustered around the mean (i.e., the standard deviation is low), highly peaked (positive kurtosis) and skewed in the low temperature direction (negative skewness). This population is associated with wet fumaroles, where boiling controls maximum temperature to cause a narrow distribution with a mode at 90–100°C. In contrast, high temperature vent regions have distributions that are widely spread about the mean (i.e., the standard deviation is high), relatively flat (negative kurtosis) and skewed in the high temperature direction (positive skewness). In this dry case, fumaroles are water-free so that maximum temperatures are not fixed by boiling. As a result greater temperature variation is possible. We use these results to define two vent types at Vulcano on the basis of their thermal characteristics: (1) concentrated (localized) regions of high temperature vents, and (2) dispersed low temperature vents. These occur within a much larger region of diffuse heat emission across which surfaces are heated by steam condensation, the heat from which causes elevated surface temperatures. For Vulcano's lower fumarole zone, high and low temperature vents occupied total areas of 3 and 6 m², respectively, and occurred within a larger (430 m²) vent-free zone of diffuse heat emission. For this lower zone, we estimate that 21–43 × 10³ W of heat was lost by diffuse heat emission. A further 4.5 × 10³ W was lost by radiation from high temperature vents, and 6.5 × 10³ W from low temperature vents. Thus, radiative heat losses from high and low temperature vents within Vulcano's lower fumarole zone respectively account for 10% and 15% of the total heat lost from this zone. This shows that radiation from open vents can account for a non-trivial portion of the total fumarole field heat budget.     

Some results on the global dynamics of the regularized restricted three-body problem with dissipation

We perform an analysis of the dynamics of the circular, restricted, planar three-body problem under the effect of different kinds of dissipation (linear, Stokes and Poynting–Robertson drags). Since the problem is singular, we implement a regularization technique in the style of Levi–Civita. The effect of the dissipation is often to decrease the semi-major axis; as a consequence the minor body collides with one of the primaries. In general, it is quite difficult to find non-collision orbits using random initial conditions. However, by means of the computation of the Fast Lyapunov Indicators (FLI), we obtain a global view of the dynamics. Precisely, we detect the regions of the phase space potentially belonging to basins of attraction. This investigation provides information on the different regions of the phase space, showing both collision and non-collision trajectories. Moreover, we find periodic orbit attractors for the case of linear and Stokes drags, while in the case of the Poynting–Robertson effect no other attractors are found beside the primaries, unless a fourth body is added to counterbalance the dissipative effect.