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.     

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.     

Obliquity‐dominated glacio‐eustatic sea level change in the early Oligocene: evidence from the shallow marine siliciclastic Rupelian stratotype (Boom Formation,Belgium)

Our results prove that glacio‐eustatic sea level oscillations in the early Oligocene were dominantly obliquity controlled with additional influence of the ∼100‐ and 405‐kyr eccentricity cycles. This was derived from spectral analysis of resistivity records from an extended downhole section of the Boom Clay succession in Belgium, that reveals a prevailing obliquity control on the laterally persistent metre‐scale alternations of shallow marine silt‐ and claystones in the Rupelian historical stratotype succession. These direct measurements of sea level variations in a shallow marine setting corroborate that variations with similar frequencies in benthonic oxygen isotope records from the open ocean indeed reflect, at least partly, ice volume change. A very tentative astronomical tuning has been established for the Boom Clay succession which awaits future confirmation with the addition of more accurate age calibration points.     

Structure of the 5-minute solar oscillations 1976–1980

The discrete structure in the 5 min velocity oscillations of the solar surface has been confirmed by a re-analysis of data obtained between 1976 and 1979, and in addition a preliminary analysis of 1980 data show excellent consistency of the determined frequencies over the five year period. It is further shown that atmospheric transparency, as measured by the power in the solar intensity fluctuations, shows no correlation with the measured amplitude of the velocity fluctuations, over 2 orders of magnitude.Proceedings of the 14th ESLAB Symposium on Physics of Solar Variations, 16–19 September 1980, Scheveningen, The Netherlands.     

The stability of coronal loops: Finite-length and pressure-profile limits

Solar Physics - Vertically propagating traveling waves have been observed in the solar photosphere. These waves have a period of 278 ± 41 seconds and a vertical phase velocity of about 2 km...