A 0535 + 26/HDE 245770: A typical X-ray/Be system

Among the X-ray/Be systems, A 0535 + 26/HDE 245770 has been noted, since its discovery, for its peculiar features in several respects, in a wide energy range. For this reason and for a series of concomitant favorable causes, this system has been one of the most studied among the massive X-ray binary systems. The most remarkable incident was that its optical identification with an early-type-emission-line star (O9.7IIIe) has led to a deep studies on Be stars and their interactions with neutron stars, which have allowed to discover, without unbiguity, the presence of optical indicators of consequent X-ray flares, as well as that Be stars in X-ray/Be systems behave just as normal Be stars. Overmore, thanks to the multifrequency coordinated observations of this system, the X-ray emissions from binary companion of the Be stars are best explained by assuming the presence of a thick equatorial disk with low expansion velocity and a thin polar region with high expansion velocity. This picture reconciled the strong discrepancy in mass loss rate evaluations coming from IR and from UV measurements, assuming that the observed regions are enterely distinct from each other, one being a high-density, low-velocity region, and the other being a low-density, very hot, rapidly-expanding disk-like zone.Since, this picture seems to be the best up-to-date frame to cuckold all the experimental panorama available on X-ray/Be systems, we would like to paint in this paper the multifrequency behaviour of A 0535 + 26/HDE 245770, which is the best studied among such systems, in order to stimulate future coordinated experimental-theoretical works on this very interesting class of objects.     

A high order method for orbital conjunctions analysis: Sensitivity to initial uncertainties

A high order method to quickly assess the effect that uncertainties produce on orbital conjunctions through a numerical high-fidelity propagator is presented. In particular, the dependency of time and distance of closest approach to initial uncertainties on position and velocity of both objects involved in a conjunction is studied. The approach relies on a numerical integration based on differential algebraic techniques and a high-order algorithm that expands the time and distance of closest approach in Taylor series with respect to relevant uncertainties. The modeled perturbations are atmospheric drag, using NRLMSISE-00 air density model, solar radiation pressure with shadow, third body perturbation using JPL’s DE405 ephemeris, and EGM2008 gravity model. The polynomial approximation of the final position is used as an input to compute analytically the expansion of time and distance of closest approach. As a result, the analysis of a close encounter can be performed through fast, multiple evaluations of Taylor polynomials. Test cases with objects ranging from LEO to GEO regimes are considered to assess the performances and the accuracy of the proposed method.     

The Pre-Main-Sequence Star RU Lupi: An Extreme T Tauri star

In this work I will try to give the most general complete view, comparatively with the conciseness, on RU Lupi, which is an Extreme Classical T Tauri star.T Tauri stars (TTSs) form a class of low luminosity stars which are going to the Main Sequence. They are young contracting objects that are in a particular Pre-Main-Sequence (PMS) evolutionary phase. The study of the Pre-Main-Sequence Stars (PMSSs) can provide crucial information on stellar evolution and formation of planetary systems, and therefore also indirect information on the processes occurred in the primeval solar system.For this reason, firstly I will briefly comment a sort of classification of stars in PMS phases (Section 2); then I will emphasize the main characteristics of TTSs and the current theories (Section 3). The up-to-date observational properties of RU Lupi (Section 4) and a discussion on their explanation within the framework of theories (Section 5) will allow me to draw the conclusions (Section 6) and to argue the most convenient line of investigation (Section 7) both experimental and theoretical for a better understanding of the underlying physics of these systems. Finally (Section 8), I will comment in general on the methodology of investigation of highly variable cosmic sources.An original result has been obtained in this work: the flare-like events (FLEs) of RU Lupi, occurring in all wavelength regions, are periodic with aP _FLE=27.686±0.002 days. This periodicity could be the rotational period of the star.     

ESA research and development activity on SSA-NEO preliminary definition

The paper gives an account of goals, prospects, and planning of the first ESA research associated with definition of the SSA-NEO segment and puts it in the context of ESA system engineering practices of ESA (as defined in ESA’s ECSS standards).     

Structure and fragmentation of meteoroids

This paper is a review of the present knowledge on the structure of meteoroids.A summary of the evidence concerning the common occurrence of fragmentation among both photographic and radio meteors is given first. Then, an attempt is made to examine all the present observational, theoretical and laboratory data on the luminous and ionizing efficiencies of meteors, with the aim of establishing a mass scale. This allows the computation of the bulk density of meteoroids, which, on the average, turns out to be about 0.3 g/cm³.The paramount importance of progressive fragmentation, the behavior of abrupt-beginning meteors and the low density of nearly all meteoroids (even of those of relatively large sizes) support a porous and fragile structure for most of these particles. In turn, the crumbly structure and the cometary origin confirm Whipple's theory of comets and meteor production. A critical analysis of recent papers proposing different conclusions shows that the new theories always arrive at results which do not agree with well-established observational data.     

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.     

PROBA-3 mission and the Shadow Position Sensors: Metrology measurement concept and budget

PROBA-3 is a space mission of the European Space Agency that will test, and validate metrology and control systems for autonomous formation flying of two independent satellites. PROBA-3 will operate in a High Elliptic Orbit and when approaching the apogee at 6·10⁴ Km, the two spacecraft will align to realize a giant externally occulted coronagraph named ASPIICS, with the telescope on one satellite and the external occulter on the other one, at inter-satellite distance of 144.3 m. The formation will be maintained over 6 hrs across the apogee transit and during this time different validation operations will be performed to confirm the effectiveness of the formation flying metrology concept, the metrology control systems and algorithms, and the spacecraft manoeuvring. The observation of the Sun’s Corona in the field of view [1.08;3.0]R_Sun will represent the scientific tool to confirm the formation flying alignment. In this paper, we review the mission concept and we describe the Shadow Position Sensors (SPS), one of the metrological systems designed to provide high accuracy (sub-millimetre level) absolute and relative alignment measurement of the formation flying. The metrology algorithm developed to convert the SPS measurements in lateral and longitudinal movement estimation is also described and the measurement budget summarized.     

Characteristics of nighttime E-region over Arecibo: Dependence on solar flux and geomagnetic variations

Electron concentration (Ne) inferred from Incoherent Scatter Radar (ISR) measurements has been used to determine the influence of solar flux and geomagnetic activity in the ionospheric E-region over Arecibo Observatory (AO). The approach is based on the determination of column integrated Ne, referred to as E-region total electron content (ErTEC) between 80 and 150 km altitude regions. The results discussed in this work are for the AO nighttime period. The study reveals higher ErTEC values during the low solar flux periods for all the seasons except for summer period. It is found that the E-region column abundance is higher in equinox periods than in the winter for low solar activity conditions. The column integrated Ne during the post-sunset/pre-sunrise periods always exceeds the midnight minima, independent of season or solar activity. This behavior has been attributed to the variations in the coupling processes from the F-region. The response of ErTEC to the geomagnetic variability is also examined for different solar flux conditions and seasons. During high solar flux periods, changes in Kp cause an ErTEC increase in summer and equinox, while producing a negative storm-like effect during the winter. Variations in ErTEC due to geomagnetic activity during low solar flux periods produce maximum variability in the E-region during equinox periods, while resulting in an increase/decrease in ErTEC before local midnight during the winter/summer periods, respectively.