The nature of recurrent novae

The observational properties and outburst histories of each member of the small class of recurrent novae are reviewed, with the objective of identifying the outburst mechanisms for these systems. Examples are found of both accretion-powered outbursts (T CrB and RS Oph) and thermonuclear-powered outbursts (T Pyx and U Sco). Outburst properties which might be used in future to distinguish between these mechanisms are identified. Many erstwhile recurrent novae (VY Aqr, RZ Leo, V616 Mon, V1195 Oph, V529 Ori, WZ Sge, and V1017 Sgr) appear to be misclassified examples of other types of cataclysmic variables.Paper presented at the IAU Colloquium No. 93 on Cataclysmic Variables. Recent Multi-Frequency Observations and Theoretical Developments, held at Dr. Remeis-Sternwarte Bamberg, F.R.G. 16–19 June, 1986.     

Long-term radial velocity variations in some Be stars

All the radial velocities (RV) available in the literature since the beginning of the century for the Be stars EW Lac, 28 Tau, Tau, KX And, KY And, CX Dra and 88 Her, are assembled. When possible, a periodogram analysis has been performed to search for eventual periodic phenomena.The following conclusions have been drawn: EW Lac could be a spectroscopic binary with a period of about 40 years; 28 Tau shows some indications of regular long-term RV variations on the time scale of decades; a probable recurrent shell activity of Tau could be hypothesized. Some useful indications for KX and KY And are given, whereas it is not possible to draw any conclusion for CX Dra and 88 Her owing to the lack of data.     

Spectrographic observations of omicron andromedae from 1967 to 1976

The results of qualitative analysis and radial velocity (RV) determinations from 1967 to 1976 are given. These analyses show sometimes the presence of a thin variable shell also in the years 1967–1974, before the appearance of the envelope. Intensity variations of the metallic lines seem to indicate that in the same period changes of temperature and/or electron pressure may occur in the photospheric layers. In the period 1975–76, the considerable range ofRV and the variability of the shell features show that the shell is rather active. Some conspicuousRV variations seem to be correlated to brightness changes. TheRV do not confirm the periods suggested by the photometric observations. A periodogram analysis givesRV curves with a poor evidence of periodicity. However, the periodP=1^d.5845 obtained from this analysis, close to that of Schmidt, seems to confirm Schmidt's hypothesis of a contact binary system. The periodogram analysis of theRV during the years 1900–1976 and some physical arguments, suggest a probable photospheric activity or an invisible companion with the observed shell period of 30 yr. The duplicity, suggested by Kí and Harmanec (1975) for all the Be stars, could be yet questioned foro And.Thesis for the degree of Applied Physics.     

Preliminary Investigation of the Molise (Italy) Earthquakes of 31 October and 1 November 2002

On 31 October and 1 November 2002, two earthquakes took place in the Italian region of Molise. 29 deaths were reported, while many buildings collapsed or suffered major damage. The tectonics of the earthquakes and historic seismicity of the area are briefly described. The distribution of damage and macroseismic intensity are confronted with the current seismic zonation of the region. In particular, the paper deals with the damage suffered by different types of structures, namely masonry and RC buildings and historical churches. The observed damage is mainly attributed to the poor quality of the materials and execution of construction, lack of maintenance and protective devices (e.g., steel ties), as well as to structural interventions. Reference is made to the management of the post-earthquake emergency. This revised version was published online in July 2006 with corrections to the Cover Date.     

Fog measurements at the site “Falda Verde” north of Chañaral compared with other fog stations of Chile

Fog collection data registered through a Standard Fog Collector (SFC) installed by a local fishermen's association at a height of 600 m at the “Falda Verde” site, north of the Chilean harbor Chañaral (26°17′S/70°36′W), from November 1998 to November 2000, are analyzed. Trying to give new lights on the dynamics of fog along the Chilean northern coast, this article compares, for the first time, the data obtained at Falda Verde with those obtained at five other Chilean fog stations. The total time period runs from 1987 to 2001. A mean of 1.46 l/m²/day was registered at the Falda Verde site after 2 years of measurements, one of the lowest yields along the north Chilean coast. After a brief historical recapitulation of fog researches in the study area, geographical explanations of the water yields obtained in different sites are discussed. The annual mean collection from Cerro Moreno and Paposo shows a clearly different behavior from all other sites, showing a greater stability throughout the year. Other stations have a marked difference between extreme seasons. Alto Patache yields, if not the best in Chile, are very high and offer unexpected possibilities for future applications in the coast. Stations located away from the seashore (Cerro Guatalaya) are clearly less productive. Ocean proximity, altitude, south and southwest orientations of the coastal ranges and local relief explain some of the differences noted.     

Assessing aquifer vulnerability to pollutants by electrical resistivity tomography (ERT) at a nitrate vulnerable zone in NE Spain

There is an increasing demand for groundwater vulnerability maps which illustrate the exposure of aquifers against pollution. These maps show areas of greatest potential for groundwater contamination on the basis of local subsurface conditions. Parameters affecting vulnerability are mainly permeability and thickness of each protective layer. For unconsolidated sediments, the permeability is strongly related to the clay content, which can be deduced from indirect resistivity methods, like electrical-imaging. Such geophysical methods can be of great help in groundwater vulnerability studies because they disturb neither the structure nor the dynamics of the soil. Sensibility analysis was performed of the electrical resistivity tomography method for accurately mapping soil media. Managers and public administrators may effectively use this method for assessing the potential risk of groundwater contamination. In the studied zone, electrical resistivity exhibits a wide range of variability that can be easily correlated to soil parameters, such as clay content and hydraulic conductivity. A numerical index of protection has been assessed from the geophysical information derived from 2D electrical resistivity tomography. This work represents a preliminary approach on the natural vulnerability evaluation of shallow aquifers at the Empordà basin (NE Spain) that is highly affected by diffuse pollution by nitrates.     

Multidimensional scaling visualization of earthquake phenomena

Earthquakes are associated with negative events, such as large number of casualties, destruction of buildings and infrastructures, or emergence of tsunamis. In this paper, we apply the Multidimensional Scaling (MDS) analysis to earthquake data. MDS is a set of techniques that produce spatial or geometric representations of complex objects, such that, objects perceived to be similar/distinct in some sense are placed nearby/distant on the MDS maps. The interpretation of the charts is based on the resulting clusters since MDS produces a different locus for each similarity measure. In this study, over three million seismic occurrences, covering the period from January 1, 1904 up to March 14, 2012 are analyzed. The events, characterized by their magnitude and spatiotemporal distributions, are divided into groups, either according to the Flinn–Engdahl seismic regions of Earth or using a rectangular grid based in latitude and longitude coordinates. Space-time and Space-frequency correlation indices are proposed to quantify the similarities among events. MDS has the advantage of avoiding sensitivity to the non-uniform spatial distribution of seismic data, resulting from poorly instrumented areas, and is well suited for accessing dynamics of complex systems. MDS maps are proven as an intuitive and useful visual representation of the complex relationships that are present among seismic events, which may not be perceived on traditional geographic maps. Therefore, MDS constitutes a valid alternative to classic visualization tools, for understanding the global behavior of earthquakes.     

Water column characterisation on the Azores platform and at the sea mounts south of the archipelago

This study provides data concerning the hydrography and water chemistry of the Atlantic region between 29-38° N and 27-31° W, and establishes background values for dissolved Cu, Cd, Pb and As. Three water masses were identified: the Eastern North Atlantic Central Water (ENACW), the Mediterranean Water (MW) and the North Atlantic Deep Water (NADW). The ENACW exhibits a clear meridional gradient of temperature and salinity, with comparatively high values at the southern sites and lower values on the Azores platform. The ENACW, which includes the euphotic zone, also had comparatively high concentrations of oxygen and lower concentrations of nutrients and metals. The Cu, Cd and Pb results suggest that new background concentrations for OSPAR Region V (the Wider Atlantic) should be established as follows: 0.15-13nM for Cu, 0.05-1.4nM for Cd and 0.03-5nM for Pb. The background concentrations of As for OSPAR Region V should be 7-28nM.     

Principal component analysis (PCA) and mineral associations of litoraneous facies of continental shelf carbonates from northeastern Brazil

The distribution of mineral phases according to the provenance of carbonate and terrigenous facies of carbonate sediments from a large area of the continental shelf of northeast Brazil was investigated using a major element multivariate analysis approach. Heavy minerals such as ilmenite are restricted to the litoraneous facies of the continental shelf of the states of Paraíba and Pernambuco, and clay minerals are found in distal facies of the continental shelf of the State of Ceará. In the carbonate fraction, composed essentially by Mg-calcite and aragonite, there is co-variation between CaO/MgO and bathimetry in part of the studied continental shelf from depths between 15 and 20 m, apparently due to influence of the seawater temperature, degree of oxygenation and luminosity. The terrigenous facies are mainly composed of quartz, clay minerals, K-feldspars and micro-micaceous minerals, having Fe and Ti oxide and hydroxide minerals as major accessory phases. Major element behavior attests to the presence of arenaceous quartz-rich relict sediments in the 35, 60 and 80 m isobaths of the continental shelf of the state of Ceará which is here interpreted as a proxy of ancient coast lines during the Flandrian transgression.     

Quality assessment of benthic macroinvertebrates under the scope of WFD using BAT, the Benthic Assessment Tool

Assessing the health of ecosystems has become a focal point among researchers worldwide. Recently, the European Water Framework Directive intensified the development of approaches to assess ecosystems’ ecological quality. The Benthic Assessment Tool (BAT) is a multimetric approach to evaluate condition of subtidal soft bottom macroinvertebrates of coastal and transitional waters. The effects of anthropogenic disturbances on benthic macroinvertebrate communities, from 1990 to 2006, allowed testing BAT performance in Mondego estuary (Portugal). The method was able to detect decrease on ecological quality, induced essentially by eutrophication and physical disturbances, and follow communities’ subsequent recovery. It evidenced, nevertheless, some limitations associated with the unstable nature of estuaries. The ecological classification of key species in the community and the balance expected between ecological groups of estuarine communities had great influence in the final ecological assessment. Shortcomings of the method were discussed in the light of its suitability for assessing transitional waters’ condition.