The population of massive stars in R136 from HST/FOC UV observations

New ultraviolet (1300 A, 3400 A),HST FOC observations have been used to derive the UV color-magnitude diagram (CMD) of R136, with the main scientific goal of studying the upper end of the stellar mass function at ultraviolet wavelengths where the color degeneracy encountered in visual CMDs is less severe. The CMD has been compared to a set of theoretical isochrones, which have been computed using the latest generation of evolutionary models and model atmospheres for early type stars. Wolf-Rayet stars are included. Comparison of theTheoretical andobserved CMD suggests that there are no stars brighter than M₁₃₀–11. We use the observed main sequence turn-off and the known spectroscopic properties of the stellar population to derive constraints on the most probable age of R136. The presence of WNL stars and the lack of red supergiants suggests a most likely age of 3±1 Myr. A theoretical isochrone of 3±1 Myr is consistent with the observed stellar content of R136 if the most massive stars have initial masses around 50 M.Bases on Observations with the NASA/ESA Hubble Space Telescope, obtained at the STScI, which is operated by AURA, Inc., under NASA contract NAS5-26555.Astrophysics Division, Space Science Department, ESA     

Elemental Abundances in Coronal Structures

A great deal of evidence for elemental abundance variations among different structures in the solar corona has accumulated over the years. Many of the observations show changes in the relative abundances of high- and low-First Ionization Potential elements, but relatively few show the absolute elemental abundances. Recent observations from the SOHO satellite give absolute abundances in coronal streamers. Along the streamer edges, and at low heights in the streamer, they show roughly photospheric abundances for the low-FIP elements, and a factor of 3 depletion of high-FIP elements. In the streamer core at 1.5 R·, both high- and low-FIP elements are depleted by an additional factor of 3, which appears to result from gravitational settling. This revised version was published online in June 2006 with corrections to the Cover Date.     

The Crab pulsar seen with AquEYE at Asiago Cima Ekar observatory

We are developing fast photon-counter instruments to study the rapid variability of astrophysical sources by time tagging photon arrival times with unprecedented accuracy, making use of a Rubidium clock and GPS receiver. The first realization of such optical photon-counters, dubbed AquEYE (the Asiago Quantum Eye), was mounted in 2008 at the 182 cm Copernicus Observatory in Asiago. AquEYE observed the Crab pulsar several times and collected data of extraordinary quality that allowed us to perform accurate optical timing of the Crab pulsar and to study the pulse shape stability on a timescale from days to years with an excellent definition. Our results reinforce the evidence for decadal stability of the inclination angle between the spin and magnetic axis of the Crab pulsar. Future realizations of our instrument will make use of the Galileo Global Navigation Satellite System (GNSS) time signal.     

Soybean cultivar selection for Bioregenerative Life Support Systems (BLSSs) – Hydroponic cultivation

Four soybean cultivars (‘Atlantic’, ‘Cresir’, ‘Pr91m10’ and ‘Regir’), selected through a theoretical procedure as suitable for cultivation in BLSS, were evaluated in terms of growth and production. Germination percentage and Mean Germination Time (MGT) were measured. Plants were cultivated in a growth chamber equipped with a recirculating hydroponic system (Nutrient Film Technique). Cultivation was performed under controlled environmental conditions (12 h photoperiod, light intensity 350 μmol m⁻² s⁻¹, temperature regime 26/20 °C light/dark, relative humidity 65–75%). Fertigation was performed with a standard Hoagland solution, modified for soybean specific requirements, and EC and pH were kept at 2.0 dS m⁻¹ and 5.5 respectively.     

Potential fossil endoliths in vesicular pillow basalt, Coral Patch Seamount, eastern North Atlantic Ocean

The chilled rinds of pillow basalt from the Ampère-Coral Patch Seamounts in the eastern North Atlantic were studied as a potential habitat of microbial life. A variety of putative biogenic structures, which include filamentous and spherical microfossil-like structures, were detected in K-phillipsite-filled amygdules within the chilled rinds. The filamentous structures (～2.5 μm in diameter) occur as K-phillipsite tubules surrounded by an Fe-oxyhydroxide (lepidocrocite) rich membranous structure, whereas the spherical structures (from 4 to 2 μm in diameter) are associated with Ti oxide (anatase) and carbonaceous matter. Several lines of evidence indicate that the microfossil-like structures in the pillow basalt are the fossilized remains of microorganisms. Possible biosignatures include the carbonaceous nature of the spherical structures, their size distributions and morphology, the presence and distribution of native fluorescence, mineralogical and chemical composition, and environmental context. When taken together, the suite of possible biosignatures supports the hypothesis that the fossil-like structures are of biological origin. The vesicular microhabitat of the rock matrix is likely to have hosted a cryptoendolithic microbial community. This study documents a variety of evidence for past microbial life in a hitherto poorly investigated and underestimated microenvironment, as represented by the amygdules in the chilled pillow basalt rinds. This kind of endolithic volcanic habitat would have been common on the early rocky planets in our Solar System, such as Earth and Mars. This study provides a framework for evaluating traces of past life in vesicular pillow basalts, regardless of whether they occur on early Earth or Mars.     

A procedure for three-dimensional angular velocity determination using a star sensor in high-rate rotation modes

This paper presents an application for modern star trackers aimed at the estimation of the spacecraft angular velocity vector on the basis of the star field images acquired during fast rotations, when star identification and tracking are not possible. Angular rates in the range 2–8°/s are considered, which strongly affect the characteristics of the acquirable images, in particular for shape and brightness. The procedure consists in the exploitation of the rigid motion equations to identify the rotation that best fits the observed star trajectories in the sensor field of view. Its coverage capability is analysed with reference to the sensitivity of state-of-the-art photodetectors. The probability of an adequate acquisition is shown to be 0.80 with random pointing and rotation axis over the celestial sphere. Firstly, the accuracy of the procedure is discussed in numerical tests. Then, end-to-end tests are reported, which have been operated by implementing the procedure in a hardware sensor model that acquires simulated star field scenes in a laboratory facility. Both the validations point out that the accuracy of 1°/s, suggested by the European Space Agency for this kind of application, has been achieved. Moreover, the rate of rotation about axes perpendicular to the boresight can be computed with accuracy one order of magnitude better.     

Deep and Shallow Solid-Earth Structures Reconstructed with Sequential Integrated Inversion (SII) of Seismic and Gravity Data

In this paper, the possibility of using simultaneously seismic and gravity data, for the reconstruction of solid-Earth structures, has been investigated through the use of an algorithm which allows joint efficient and reliable optimisation of compressional velocity and mass density parameters. We view the measured data as a realisation of a stochastic process generated by the physical parameters to be sought and we construct a “probability density function” which includes three kinds of information: information derived from gravity measurements; information derived from seismic travel time inversion and information on the physical correlation among density and velocity parameters. We show that combining data has a beneficial effect on the inversion since: it makes the problem more stable and as a consequence, providing that the quality of data is sufficiently high, enables more accurate and reliable reconstruction of the unknown parameters. In this context, we look forward the GOCE mission, which promises high spatial resolution (100–200 km) and accurate (1–2 mGals) gravity data. We show results obtained from data sets calculated for a lateral inhomogeneous earth synthetic model and from seismic and gravity field data analysed: — in the framework of TOMOVES (TOMOgraphy of Mt. VESuvius) experiment, an European project aiming at reconstructing the 3-D image of Mt. Vesuvius volcano and the crust underneath. using high resolution seismic tomography techniques and other geophysical methods; — for a profile inserted in a project aiming at reconstructing the crustal structure between Corsica and the Northern Appennines which crosses the Ligurian Sea and cuts the Ligurian Appennines W of La Spezia, extending up to Parma. This revised version was published online in August 2006 with corrections to the Cover Date.     

Solar Weather Event Modelling and Prediction

Key drivers of solar weather and mid-term solar weather are reviewed by considering a selection of relevant physics- and statistics-based scientific models as well as a selection of related prediction models, in order to provide an updated operational scenario for space weather applications. The characteristics and outcomes of the considered scientific and prediction models indicate that they only partially cope with the complex nature of solar activity for the lack of a detailed knowledge of the underlying physics. This is indicated by the fact that, on one hand, scientific models based on chaos theory and non-linear dynamics reproduce better the observed features, and, on the other hand, that prediction models based on statistics and artificial neural networks perform better. To date, the solar weather prediction success at most time and spatial scales is far from being satisfactory, but the forthcoming ground- and space-based high-resolution observations can add fundamental tiles to the modelling and predicting frameworks as well as the application of advanced mathematical approaches in the analysis of diachronic solar observations, that are a must to provide comprehensive and homogeneous data sets.     

K. Koyama, S. Kitamoto and M. Itoh (eds.), The Hot Universe, IAU Symposium

This volume contains the proceedings of the NATO Advanced Study Institute on Polar Cap Boundary Phenomena held at Longyearbyen, Svalbard, Norway on June 4–13, 1997, which was the third NATO Workshop on magnetospheric boundary phenomena observable at high latitudes. Svalbard has a uniquely interesting location from observational point of view in that the dayside aurora can be observed there in the noon local time sector during the midwinter. The Norwegian groups working at Svalbard were the organisers of this third workshop as well as of the two earlier ones, but only this third one was held at Svalbard. It was attended by 86 space physicists from all over the world. The book contains 36 papers, of which the majority were presented as invited papers at the workshop, a few were contributed papers and the last paper in the volume gives a summary of the content of the workshop. As emphasized in both the Foreword and the Summary chapter of the book, the research field of the polar cap and its boundaries to other magnetospheric regions at high latitudes is one that has seen a fast development in the last ten years. This is to a great deal due to the research work done at Svalbard in combination with satellite measurements and theory development. The review in these proceedings provide also the non-specialist reader with good summaries of where different research questions stand at present. This revised version was published online in August 2006 with corrections to the Cover Date.