Helical structures around quiescent solar prominences computed from observable magnetic fields

We analyse the magnetic support of solar prominences in two-dimensional linear force-free fields. A line current is added to model a helical configuration, well suited to trap dense plasma in its bottom part. The prominence is modeled as a vertical mass-loaded current sheet in equilibrium between gravity and magnetic forces.We use a finite difference numerical technique which incorporates both vertical photospheric and horizontal prominence magnetic field measurements. The solution of this mixed boundary problem generally presents singularities at both the bottom and top of the model prominence. The removal of the singularities is achieved by superposition of solutions. Together with the line current equilibrium, these three conditions determine the amplitude of the magnetic field in the prominence, the flux below the prominence and the current intensity, for a given height of the line current. A numerical check of accuracy in the removal of singularities, is done by using known analytical solutions in the potential limit.We have investigated both bipolar and quadrupolar photospheric regions. In this mixed boundary problem the polarity of the field component orthogonal to the prominence is mainly fixed by the imposed height of the line current. For bipolar regions above (respectively below) a critical height the configuration is inverse (respectively normal). For quadrupolar regions the polarity is reversed if we refer the prominence polarity to the closest photospheric polarities. We introduce the polarity of the component parallel to the prominence axis with reference to a sheared arcade. Increasing the shear with fixed boundary conditions can increase or decrease the mass supported depending on the configuration.     

Observed interstellar magnetized supershells and stellar-wind theories

Early theories of stellar winds from an association of OB stars predicted the formation of a common superbubble enclosed by athin, dense supershell, through the combined effort of the winds from the stars at the center. These early theories were adequate for explaining the primary observational features (defined as: shell age, outer radius, shell speed, shell mass, shell energy), but they were not adequate to explain the secondary features (defined as: shell thickness, shell magnetic field, shell gas density). A recently published theory for a stellar-wind-bubble and supershell, predicting a range ofthick supershells, can now be compared with the secondary observational features.Using the observed parameters from all large (> 100 pc) interstellar magnetized supershells near the sun (< 1 kpc away), I assemble for comparison with stellar-wind theories: (a) the primary observational features of these shells — I find: large shell age, large outer radius, low shell speed, large shell mass, large shell energy; and (b) some of their secondary observational features — I find: thick shell, low shell magnetic field strengh, low shell gas density.     

Magnetic Energy and Helicity Fluxes at the Photospheric Level

The source of coronal magnetic energy and helicity lies below the surface of the Sun, probably in the convective zone dynamo. Measurements of magnetic and velocity fields can capture the fluxes of both magnetic energy and helicity crossing the photosphere. We point out the ambiguities which can occur when observations are used to compute these fluxes. In particular, we show that these fluxes should be computed only from the horizontal motions deduced by tracking the photospheric cut of magnetic flux tubes. These horizontal motions include the effect of both the emergence and the shearing motions whatever the magnetic configuration complexity is. We finally analyze the observational difficulties involved in deriving such fluxes, in particular the limitations of the correlation tracking methods.     

Statistical Analysis of the Fluctuations Detected in High-Altitude Neutron Monitor,Solar and Interplanetary Parameters

Galactic cosmic ray fluctuations from six mountain altitude neutron monitors around the world are analyzed during the period 1990–1999. The period comprises the maximum and declining phase of solar cycle 22 and the beginning of cycle 23. The evolution of the most significant periodicities and comparisons with solar activity and interplanetary indicators are presented. We found a 38-day variation present in all neutron monitors, solar activity parameters, and IMF fluctuations. The possible origin of this and other stable periodicities of cosmic ray variations in the analyzed period are discussed.     

PRIMA for the VLTI – Science

The four main scientific objectives of PRIMA – the Phase-Referenced Imaging and Micro-arc second Astrometry facility for the VLTI – will be described:– extra-solar system characterization with astrometry, to detect planets and evaluate their mass, and imaging of the dust accretion disk,– galactic center study with astrometry(dynamics of the bulge stars) and imaging at 10μm (piercing the gas and dust clouds surrounding the galactic center),– observations of AGNs and other extra-galactic objects, too faint to be observed without PRIMA, for which partial imaging is needed to constrain their structuremodels,– micro-gravitational lensing event resolution (imaging and astrometry of their photo-center) in the Galactic Bulge and Magellanic Clouds, helping to determine directly the lens mass and distance. This revised version was published online in July 2006 with corrections to the Cover Date.     

Bi-Dimensional Spectrography at HST-Like Spatial Resolution: [OIII] Kinematics and Ionization in the NLR of NGC 1068

We present a study at HST-like spatial resolution of the gas kinematics in the innermost part of NGC 1068. This work is based on observations with the integral field spectrograph TIGER mounted on the CFH Telescope. We first derived the final spatial PSF of our data and checked its photometric integrity by comparison with two independent [OIII] HST images (FOC and WFPC2). We then performed a spatial deconvolution of the data-cube constraining the sum of the deconvolved velocity-slices to be as close as possible to the HST image. The resulting deconvolved data-cube has then a resolution similar to the HST image. It shows that the velocity distribution of the inner clouds detected with the HST differs strongly from a simple NE-SW ejection flow. We thus show that the previous interpretations of the double-peaked lines NE of the nucleus must be revisited. This revised version was published online in July 2006 with corrections to the Cover Date.     

The structure of the interplanetary medium during the first stip interval (September–October 1975) and prerelease of energetic solar particles

An analysis of the interplanetary medium structure is made during STIP 1. (September–October, 1975). Using a simple extrapolation method a reconstruction of the stream lines is made which shows that the interplanetary space during this time period was very quiet. Such a behaviour is expected because this interval is close to the minimum of the solar cycle activity.The evolution of two fast solar wind streams, which dominated the interplanetary medium for very long time periods, is studied.A peculiar solar proton event, with onset time before the optical flare, is explained according to Elliot mechanism — i.e., that energetic particles are stored for a long time and released, sometimes, before the optical flare.These particles can be seen only when the interplanetary medium is very quiet, (without shock waves) and the flare very isolated.     

Catalogue of unambiguous (Faraday-thin,one-component,spectrum-selected) rotation measures for galaxies and quasars

This all-sky catalogue of unambiguous rotation measure (from a Faraday-thin, one-component, spectrum selection) for 674 galaxies or quasars has been compiled, ordered, and edited from the available literature. All the known applications of the RM distribution toward foreground objects in the Galaxy (i.e., magnetic field in 4 nearby spiral arms and in 4 nearby interstellar magnetic bubbles) have also been catalogued.