Behaviour of the SMF method for the numerical integration of satellite orbits

The SMF algorithms were recently developed by the authors as a multistep generalization of the ScheifeleG-functions one-step method. Like the last, the proposed codes integrate harmonic oscillations without truncation error and the perturbing parameter appears as a factor of that error when integrating perturbed oscillations. Therefore they seemed to be convenient for the accurate integration of orbital problems after the application of linearizing transformations, such as KS or BF. In this paper we present several numerical experiments concerning the propagation of Earth satellite orbits, that illustrate the performance of the the SMF method. In general, it provides greater accuracy than the usual standard algorithms for similar computational cost.     

Magnetic Helicity Budget of Solar-Active Regions from the Photosphere to Magnetic Clouds

We have analyzed the long-term evolution of two active regions (ARs) from their emergence through their decay using observations from several instruments on board SoHO (MDI, EIT and LASCO) and Yohkoh/SXT. We have computed the evolution of the relative coronal magnetic helicity combining data from MDI and SXT with a linear force-free model of the coronal magnetic field. Next, we have computed the injection of helicity by surface differential rotation using MDI magnetic maps. To estimate the depletion of helicity we have counted all the CMEs of which these ARs have been the source, and we have evaluated their magnetic helicity assuming a one to one correspondence with magnetic clouds with an average helicity contain. When these three values (variation of coronal magnetic helicity, injection by differential rotation and ejection via CMEs) are compared, we find that surface differential rotation is a minor contributor to the helicity budget since CMEs carry away at least 10 times more helicity than the one differential rotation can provide. Therefore, the magnetic helicity flux needed in the global balance should come from localized photospheric motions that, at least partially, reflect the emergence of twisted flux tubes. We estimate that the total helicity carried away in CMEs can be provided by the end-to-end helicity of the flux tubes forming these ARs. Therefore, we conclude that most of the helicity ejected in CMEs is generated below the photosphere and emerges with the magnetic flux.     

Infrared Observations of High-Mass X-Ray Binaries

We present the first results of our ISO program on High-Mass X-ray Binaries (HMXBs). Infrared photometry, obtained at different aspect angles of the systems, is used to investigate the massive star's disrupted stellar wind and the accretion flow towards the compact X-ray source. Scenarios for massive binary evolution predict that HMXBs receive a large kick velocity during the supernova explosion of the compact star's progenitor. One might, therefore, expect to observe wind bow shocks around these systems such as observed around many OB-runaway stars. Such a wind bow shock has recently been discovered around the system Vela X-1. This revised version was published online in August 2006 with corrections to the Cover Date.     

PDRS and Shocks in S106 IR and CEP a East

We present SWS grating scans of pure H2 rotational lines, as well as several infrared fine-structure lines for two embedded Young Stellar Objects, S106 IR and Cep A East. Excitation temperatures and masses were derived from the low-lying pure rotational levels of H2 and are 490 and 740 K and 0.04 and 0.007 M⊙ for S106 and Cep A, respectively. The observations were compared to theoretical models for PDRs and dissociative and non-dissociative shocks. The infrared spectrum of S106 IR is dominated by PDR emission while that of Cep A East has a large shock component. We suggest that the difference between these two objects could reflect an evolutionary trend. This revised version was published online in August 2006 with corrections to the Cover Date.     

Improved Approximated Solutions to the Nonlinear Debye Potential

The shielding effect of plasma on the electrostatic potential due to a central nucleus is studied. The potential is determined by the Poisson equation with Boltzmann factor for the charge density of ions. The aim of this work is to find approximated analytical solutions, without the usual linearization hypothesis, by means of the technique of quasifractional approximants in two points. In a previous work (Martín and Pérez, 1994) a quasifractional fractional approximation was obtained, but the coefficients were found by means of the numerical solution of the differential equation. Now we find a complete analytical expression. The approximant found is highly precise in the range of validity of the physical model used.     

Orbital Elements of 2004 Perseid Meteoroids Perturbed by Jupiter

Jupiter and Saturn produce important gravitational impulses on meteoroids released by comet 109P/Swift-Tuttle. The meteoroids from this comet once released follow retrograde orbits that during their periodic approaches to these planets (within 1.6 and 0.9 A.U., respectively) are impulsed gaining orbital energy. This perturbation effect is translated into a net inward shift in the node of the perturbed meteoroids. Such geometry with Jupiter occurred in 2004 over a meteoroid trail ejected by this comet during the 1862 A.D. return of the comet to perihelion. In order to study the predicted outburst produced by one-revolution meteoroids, the Spanish Photographic Meteor Network (SPMN) performed an extensive campaign. As a part of this observational effort here are presented 10 accurate meteoroid orbits. We discuss their origin by comparing them with the theoretical orbital elements of the dust trails intercepting the Earth during the 2004 Perseid return.     

Using the Evolution of Coronal Dimming Regions to Probe the Global Magnetic Field Topology

We demonstrate that study of the evolving magnetic nature of coronal dimming regions can be used to probe the large-scale magnetic structure involved in the eruption of a coronal mass ejection (CME). We analyse the intensity evolution of coronal dimming regions using 195 Å data from the Extreme ultraviolet Imaging Telescope (EIT) on board the Solar and Heliospheric Observatory (SOHO). We measure the magnetic flux, using data from the SOHO/Michelson Doppler Imager (MDI), in the regions that seem most likely to be related to plasma removal. Then, we compare these magnetic flux measurements to the flux in the associated magnetic cloud (MC). Here, we present our analysis of the well-studied event on 12 May 1997 that took place just after solar minimum in a simple magnetic configuration. We present a synthesis of results already published and propose that driven “interchange reconnection” between the expanding CME structure with ‘`open’' field lines of the northern coronal hole region led to the asymmetric temporal and spatial evolution of the two main dimming regions, associated with this event. As a result of this reconnection process, we find the southern-most dimming region to be the principal foot-point of the MC. The magnetic flux from this dimming region and that of the MC are found to be in close agreement within the same order of magnitude, 10²¹ Mx.     

Space Charge Potentials in Cylindrical Geometries Including Temperature Effects

The analysis of space-charge in cylindrical geometries has been performed using kinetic theory. The current collected by central electrodes inmersed in plasmas with a discriminant grid has been determined through the Poisson equation and truncated Maxwellian distribution functions for the ions. The electrons are assumed to be repelled by the entrance grid. The non-linear adimensional equations have been solved approximately using linear expansion around the point with zero potential.