The universal rotation curve of spiral galaxies – II. The dark matter distribution out to the virial radius

In the current ΛCDM cosmological scenario, N -body simulations provide us with a universal mass profile, and consequently a universal equilibrium circular velocity of the virialized objects, as galaxies. In this paper we obtain, by combining kinematical data of their inner regions with global observational properties, the universal rotation curve of disc galaxies and the corresponding mass distribution out to their virial radius. This curve extends the results of Paper I, concerning the inner luminous regions of Sb–Im spirals, out to the edge of the galaxy haloes.     

Adaptive optics at short wavelengths

The First Light Adaptive Optics (FLAO) system has been successfully commissioned at the Large Binocular Telescope. It delivers extreme adaptive optics performance using bright natural guide stars reaching 90 % Strehl Ratios in H-band. Observations with current adaptive optics systems are limited to the near infrared wavelengths, in these bands the diffraction limited resolution of the largest ground-based telescopes (8–10 meter class) is comparable to the one of the much smaller Hubble Space Telescope that observes in the visible bands. This study aims to demonstrate the feasibility of an adaptive optics system designed to achieve very high order correction at visible wavelengths (0.5 to 0.8 μ m) with significant sky coverage. Upgrading the FLAO design with a low noise CCD relaxes the reference magnitude limit needed to achieve greater performance. In particular, we demonstrate that a gain of 1–2 magnitudes is possible by upgrading the wavefront sensor with a very low read out noise CCD. For future AO systems, in addition to low noise CCDs, deformable (secondary) mirrors with a higher actuator density will be able to move the high order correction capability from the near infrared to the visible wavelengths (Strehl Ratio of 80 % in R (0.7 μ m), 60 % in V (0.5 μ m)). We investigate, by means of numerical simulation, the gain in imaging performance obtained at Near Infrared, Visible, and UV wavelengths. The results of these simulations have been used to derive the empirical relation between Strehl Ratio and magnitude of the reference star and we then use this relationship to perform a detailed sky coverage analysis based on astronomical catalog data. The detailed simulations of the Point Spread Functions allow us to compute Ensquared Energy and Strehl Ratio for the magnitude working range of such an Adaptive Optics system. We present the results of the instrumental isoplanatic angle determination. We then used these values to compute the relationship between correction level and the off-axis angle from the reference star. The Strehl Ratio relationship with the reference magnitude and the angular distance provides the information needed to perform the sky-coverage analysis, which demonstrates that the designed system is able to provide V and R bands correction on a not negligible few percent of the sky.     

Composition and geochemistry of clay sediments offshore the northeastern Sicilian coast (Southeastern Tyrrhenian Sea,Italy)

Grain-size, mineralogical and chemical analyses were carried out on fine fraction of sediments collected in the Gulfs of Patti and Milazzo, two borderland basins in the Southern Tyrrhenian extending offshore the northeastern Sicilian coast.     

Relationship between the flank sliding of the South East Crater (Mt. Etna, Italy) and the paroxysmal event of November 16, 2006

Over the last 2 years, the south east crater (SEC) at Mt. Etna (Italy) has been characterised by the intermittent emission of lava flows, often accompanied by paroxysmal episodes with violent strombolian activity and/or lava fountains. One of the most intense and intriguing episodes occurred on November 16, 2006 during strombolian and effusive activity from the very top of the SEC. At the eastern base of the crater, a violent and short-lasting outburst generated a 300-m-high eruptive curtain of finely fragmented magma and steam, which collapsed in a few seconds giving rise to a small but significant pyroclastic flow. The paroxysm was preceded by progressive sliding of the eastern flank of the SEC edifice, which led to the formation of a large niche. Previously published models explain the outburst as due to rapid vaporisation of water contained in sediments on contact with hot lava flowing along the flank of the SEC or, alternatively, to gravitational collapse of a destabilised portion of the eastern flank of the crater. However, several lines of evidence suggest that these models do not adequately explain the paroxysm, which we propose was associated with the explosive emission of magma during the rapid opening of an ESE-WNW-oriented fracture at the eastern base of the SEC. Moreover, geochemical data of the products associated with this episode show that they are the most primitive and gas-rich among those erupted during the entire 2006 period. We suggest that the paroxysm of November 16, 2006, which occurred at base of the SEC, was a magma outburst due to rapid ground fracturing related to a drop in confining pressure upon the underlying dyke consequent to the sliding of the eastern flank of the SEC cone. Specifically, the unloaded shallow portion of the feeding dyke did not restrain the arrival of a new batch of gas-rich magma, which worked its way out by fracturing the base of the niche at its weakest point. This paroxysm appears significant because it reveals the potential development of syn-eruptive dynamics acting directly on the uppermost portion of the plumbing system which is able to generate pyroclastic flows even on basaltic volcanoes such as Mount Etna.     

The dyke swarm of Mount Calanna (Etna, Italy): an example of the uppermost portion of a volcanic plumbing system

A new multidisciplinary study, combining geology, petrography, and geochemistry, on the rocks of the isolated hill of Mount Calanna (Mount Etna, Italy) has provided evidence for the existence of a dyke swarm, formed by more than 200 dykes distributed over an area of ~0.7 km², with an intensity of intrusion up to 40%. All bodies are deeply altered, and the geological and mesostructural surveying of 132 dykes revealed that they intruded in E–W direction, with an average dip of 60°. The faults affecting the outcrop have in general an E–W strike and dip of ~55°: these have all normal motion and have been interpreted as coeval with the dykes. This interpretation contrasts with the previous hypothesis that considered Mount Calanna as a thrust resulting from compressive deformation resulting from the gravitational spreading of the volcanic edifice. Mount Calanna is here interpreted as the uppermost portion of a vertically extensive magmatic plexus that fed the eruptive activity of one (or more) eruptive center/s sited in the Valle del Bove area. Measurements of the apparent densities on 23 dykes and host rock samples give an average value of 2,420 kg/m³ for the entire complex, ~15% lower than the density expected for hawaiitic magma, placing an important constraint on the geophysical identification of similar structures. Considering that Mount Etna is not an old eroded edifice but an active and growing volcano, the exposure of this subvolcanic structure can be regarded as exceptional. Its geometry and physical characteristics can be thus regarded as an interesting example of the present-day shallow plumbing system of Mount Etna as well as of other basaltic volcanoes.     

A novel soil moisture‐based drought severity index (DSI) combining water deficit magnitude and frequency

A correct identification of drought events over vegetated lands can be achieved by detecting those soil moisture conditions that are both unusually dry compared with the ‘normal’ state and causing severe water stress to the vegetation. In this paper, we propose a novel drought index that accounts for the mutual occurrence of these two conditions by means of a multiplicative approach of a water deficit factor and a dryness probability factor. The former quantifies the actual level of plant water stress, whereas the latter verifies that the current water deficit condition is unusual for the specific site and period. The methodology was tested over Europe between 1995 and 2012 using soil moisture maps simulated by Lisflood, a distributed hydrological precipitation–runoff model. The proposed drought severity index (DSI) demonstrates to be able to detect the main drought events observed over Europe in the last two decades, as well as to provide a reasonable estimation of both extension and magnitude of these events. It also displays an improved adaptability to the range of possible conditions encountered in the experiment as compared with currently available indices based on the sole magnitude or frequency. The results show that, for the analyzed period, the most extended drought events observed over Europe were the ones in Central Europe in 2003 and in southern Europe in 2011/2012, while the events affecting the Iberian Peninsula in 1995 and 2005 and Eastern Europe in 2000 were among the most severe ones. © 2015 European Commission ‐ Joint Research Centre. Hydrological Processes published by John Wiley & Sons Ltd.     

A subterminal radial fissure eruption on Mt. Etna

The author describes a subterminal radial fissure eruption of Mt. Etna that took place in February 1964. A sketchmap and a chemical analysis of the lava are given.

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Zusammenfassung Der Verfasser beschreibt den subterminalen Radialspaltenausbruch des Ätnas im Februar 1964 und fügt eine chemische Analyse der geförderten Lava bei.

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Résumé L'auteur décrit une éruption subterminale de l'Etna qui a eu lieu sur une fissure radiale en février 1964. Une carte de la région sommitale de l'Etna et une analyse chimique de la lava sont ajoutées.

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Riassunto L'autore descrive l'eruzione radiale verificatasi al cono terminale dell'Etna nel Febbraio del 1964. Dà inoltre un rilevamento schematico della zona del cratere centrale ed il chimismo della roccia.

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, 1964 .

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Dedicated to Professor Dr. A.Rittmann on the occasion of his 75. birthday

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This study is a part of the researches, carried out with the funds of the National Research Council of the Italy under the direction of Prof. A.Ritmann.