3-D reconnection related to new emerging flux

We present evidences that emergence of new flux in the lower atmosphere leads to magnetic reconnection of field lines. In a first phase the phenomenon is observed in the chromosphere by the formation of dark filaments (arch filament system) which are overlaid by bright loops visible in soft X-rays. Different types of event appear according to the magnetic field configuration and the amount of energy involved. 3-D modelling of the photospheric magnetic field provides a new tool for understanding reconnection in real configurations. The observed chromospheric and coronal loops are good diagnostics for the modelling. We document our statement by examples obtained during coordinated campaigns with the H Multichannel Subtractive Double Pass spectrographs-MSDP (Pic du Midi and Tenerife) and the Yohkoh instruments.     

Stability of spinning satellite under axial thrust and internal mass motion

This paper considers a spinning rigid body and a particle with internal motion under axial thrust. This model is helpful for gaining insights into the nutation anomalies that occurred near the end of orbit injections performed by STAR-48 rocket motors. The stability of this system is investigated by means of linearized equations about a uniform spin reference state. In this model, a double root does not necessarily imply instability. The resulting stability condition defines a manifold in the parameter space. A detailed study of this manifold and the parameter space shows that the envelope of the constant solutions is in fact the stability boundary. Only part of the manifold defines a physical system and the range of frequency values that make the system unstable is restricted. Also it turns out that an increase of the spring stiffness, which restrains the internal motion, does not necessarily increase the stability margin. The application of the model is demonstrated using the orbit injection data of ESA's Ulysses satellite in 1990.     

Introduction to a Further Examination of the Hipparcos Data

We present an introduction to four papers on further analysis of the raw Hipparcos data. This analysis has lead to the recognition of how orbit, radiation and temperature conditions did or didn't affect the scientific results of the Hipparcos mission. It also led the way to a new reduction of the scientific data that shows from its initial results a real potential for a substantial improvement of the astrometric parameters for stars brighter than V=8.5. This short paper serves as an introduction to the four main papers, and provides some general references. This revised version was published online in August 2006 with corrections to the Cover Date.     

Cataractogenesis from high-LET radiation and the Casarett model.

Space radiations, especially heavy ions, constitute significant hazards to astronauts. These hazards will increase as space missions lengthen. Moreover, the dangers to astronauts will be enhanced by the persistence, or even the progression, of biological damage throughout their subsequent life spans. To assist in the assessment of risks to astronauts, we are investigating the long-term effects of heavy ions on specific animal tissues. In one study, the eyes of rabbits of various ages were exposed to a single dose of Bragg plateau 20Ne ions (LET infinity approximately equals 30 keV/micrometer). The development of cataracts has shown a pronounced age-related response during the first year after irradiation, and will be followed for two more years. In other studies, mice were exposed to single or fractionated doses of 12C ions (4-cm spread-out Bragg peak; dose-averaged LET infinity = 70-80 keV/micrometer) or 60Co gamma-photons (LET infinity = 0.3 keV/micrometer). Measurements of the frequency of posterior lens opacification have shown that the tissue sparing observed with dose fractionation of gamma-photons was absent when 12C-ion doses were fractionated. Development of posterior lens cataracts was also followed for long periods (up to 21 months) in mice exposed to single doses of Bragg plateau HZE particles (40Ar, 20Ne and 12C ions: LET infinity approximately equals 100, 30 and 10 keV/micrometer, respectively) or 225 kVp X-rays. Based on average cataract levels at the different observation times, the RBE's (RBE = relative biological effectiveness) for the ions were circa 5, 3 and 1-2, respectively, over the range of doses used (0.05-0.9 Gy). Investigations of cataractogenesis are useful for exploring the model of radiation damage proposed by Casarett and by Rubin and Casarett with a tissue not connected directly to the vasculature.     

Reflections on the quest for international cooperation

Changed political objectives, straitened economic circumstances and an altered balance of capability and expertise in space endeavours have together produced more discussion of the need for international cooperation than ever before, but the meaning of the term has subtly shifted. Insisting on US ‘leadership’ is self-defeating; what is instead firmly desired by the USA's potential partners is a balanced relationship in which each nation makes an identifiable contribution and takes the lead in at least one of a package of projects. If this is going to happen, there must be an international forum or framework in which projects can be discussed and agreed. This in turn requires initiative at governmental level.     

X-ray binaries and stellar evolution

Observational evidence suggests that most — if not all — binary X-ray sources are neutron stars. The evolutionary status and possible formation mechanisms of the type I (massive) and type II (low-mass) X-ray binaries are discussed. The difference between the standard massive X-ray binaries and the Be/X-ray binaries is ascribed to a somewhat different evolutionary history and status, and possible reasons for the existence of short- and long — period X-ray pulsars are discussed. Type II X-ray sources in globular clusters were most probably formed by capture processes; their formation rate inferred from the observations indicates that only a small fraction ( 1 to 10 percent) of the originally formed neutron stars have remained in their clusters. Type II sources in the galactic bulge may also have formed from cataclysmic binaries in which a white dwarf was driven over the Chandrasekhar limit by accretion.