Publication archive

Publication archive

Propagation pattern (distribution of phase velocities) is determined in three dimensions in the terrestrial magnetosheath on a statistical basis using Cluster spacecraft observations. It is found that the anti-sunward propagation dominates and that the propagation direction is toward the magnetosheath flank at smaller zenith angles, while it is toward the magnetopause at larger angles. This pattern is axially symmetric regardless of the interplanetary magnetic field direction and agrees qualitatively with the density gradient directions in a hydromagnetic flow model of the magnetosheath, suggesting that the wave refraction mechanism is more significant than the wave drift effect.
Published: 21 October 2006
The nature of particle precipitations at dayside mid-altitudes can be interpreted in terms of the evolution of reconnected field lines. Due to the difference between electron and ion parallel velocities, two distinct boundary layers should be observed at mid-altitudes between the boundary between open and closed field lines and the injections in the cusp proper. At lowest latitudes, the electron-dominated boundary layer, named the "electron edge" of the Low-Latitude Boundary Layer (LLBL), contains soft-magnetosheath electrons but only high-energy ions of plasma sheet origin. A second layer, the LLBL proper, is a mixture of both ions and electrons with characteristic magnetosheath energies. The Cluster spacecraft frequently observe these two boundary layers. We present an illustrative example of a Cluster mid-altitude cusp crossing with an extended electron edge of the LLBL. This electron edge contains 10-200 eV, low-density, isotropic electrons, presumably originating from the solar wind halo population. These are occasionally observed with bursts of parallel and/or anti-parallel-directed electron beams with higher fluxes, which are possibly accelerated near the magnetopause X-line. We then use 3 years of data from mid-altitude cusp crossings (327 events) to carry out a statistical study of the location and size of the electron edge of the LLBL. We find that the equatorward boundary of the LLBL electron edge is observed at 10:00-17:00 magnetic local time (MLT) and is located typically between 68° and 80° invariant latitude (ILAT). The location of the electron edge shows a weak, but significant, dependence on some of the external parameters (solar wind pressure, and IMF BZ- component), in agreement with expectations from previous studies of the cusp location.
Published: 21 October 2006
The gamma-ray observatory INTEGRAL was launched in October 2002 and produces since then a wealth of discoveries and important new results. I will present a selection of scientific highlights obtained during the first 2.5 years of the mission.
Published: 16 October 2006
CiteID: A10211 The Cluster spacecraft crossed the magnetopause at the duskward flank of the tail while the European Incoherent Scatter (EISCAT) radars and magnetometers observed the ionosphere during a sequence of intense substorm-like geomagnetic activity in October 2003. We attempt to estimate the local and global energy flow from the magnetosheath into the magnetotail and the ionosphere under these extreme conditions. We make for the first time direct observational estimates of the local solar wind power input using Cluster measurements. The global power input based on Cluster observations was found to be between 17 and 40 TW at the onset of the substorm intensification. However, spacecraft observations and global modelling of the magnetotail suggest that it is most probably closer to 17 TW. This is more than two times lower than the predicted parameter value (37 TW). Energy deposition in the ionosphere has been estimated locally with EISCAT and globally with the assimilated mapping of ionospheric electrodynamics (AMIE) technique. The amount of the global solar wind power input (17 TW) that is dissipated via Joule heating in the ionosphere is found to be 30%. The corresponding ratio based on empirical estimates is only 3%. However, empirical proxies seem to underestimate the magnitude of the Joule heating rate as compared to AMIE estimates (~ a factor 4) and the epsilon parameter is more than twice as large as the Cluster estimate. In summary, the observational estimates provide a good balance between the energy input to the magnetosphere and deposition in the ionosphere. Empirical proxies seem to suffer from overestimations (epsilon parameter) and underestimations (Joule heating proxies) when pushed to the extreme circumstances during the early main phase of this storm period.
Published: 13 October 2006
CiteID: L19105 We report on electron phase space distributions (PSDs) observed near the plasma sheet (PS) boundary layer (PSBL) by the Cluster electron spectrometers when the northern lobe was occupied by significant fluxes of polar rain (PR) electrons. These observations reveal the spatial structure of the electron transition layer (TL) between the polar rain electrons and the PSBL electron population accelerated during reconnection. This TL comprises overlapping spatial dispersion signatures in both energy and pitch angle, which are caused by convection of flux tubes across the magnetic separatrix during the electron time-of-flight (TOF) from the X-line combined with acceleration in the reconnection region. Analysis of this structure allows us to estimate the location of the X-line. By assuming the PSBL population arises through acceleration of the PR electrons, comparison of their PSD indicates that the electrons gain energy proportional to their initial energy.
Published: 12 October 2006
We present a deep image of the radio galaxy MRC 1138-262 taken with the Hubble Space Telescope (HST) at a redshift of z = 2.2. The galaxy is known to have properties of a cD galaxy progenitor and be surrounded by a 3 Mpc-sized structure, identified with a protocluster. The morphology shown on the new deep HST ACS image is reminiscent of a spider's web. More than 10 individual clumpy features are observed, apparently star-forming satellite galaxies in the process of merging with the progenitor of a dominant cluster galaxy 11 Gyr ago. There is an extended emission component, implying that star formation was occurring over a 50 × 40 kpc region at a rate of more than 100 Msolar yr-1. A striking feature of the newly named "Spiderweb galaxy" is the presence of several faint linear galaxies within the merging structure. The dense environments and fast galaxy motions at the centers of protoclusters may stimulate the formation of these structures, which dominate the faint resolved galaxy populations in the Hubble Ultra Deep Field. The new image provides a unique testbed for simulations of forming dominant cluster galaxies.
Published: 11 October 2006
Paper IAC-06-A3.1.04, 57th International Astronautical Congress, Valencia, Spain, 2-6 October 2006.

In response to ESA's call for space science themes in the frame of Cosmic Vision 2015-2025, the scientific community identified a Wide-Field Optical and Near Infrared Imager as a potential future science mission for Europe. Such a mission would search for Type Ia supernovae at low redshift in the optical and near infrared part of the spectrum with the aim to measure the changing rate of expansion of the universe and to determine the contributions of decelerating and accelerating energies such as the mass density, the vacuum energy density and other yet to be studied dark energies. To investigate the feasibility of this potential future mission the Science Payload & Advanced Concepts Office (SCI-A) at ESA initiated the Wide Field Imager (WFI) Technology Reference Study (TRS). The WFI would have a 2 m class telescope, a 1 square degree field of view imaging camera and a low-resolution integral field spectrometer. This paper summarizes the results of this ESA internal feasibility study of the WFI. The paper focuses on the spacecraft design and the critical subsystems and provides an overview of required technology development activities for such a mission.

Published: 07 October 2006
The heliosphere is the subject of the present issue of Spatium, the empire of the Sun, or, to be more specific, that part of the universe where the Sun dominates over the surrounding interstellar medium.

This article is based on a lecture by Professor André Balogh to the Pro ISSI Association
Published: 02 September 2006
CiteID: A09221 The use of sensor arrays in space opens up the possibility to investigate the source location of plasma waves. In order to do so, we generalize the wave telescope technique to use spherical waves instead of plane waves. The new tool determines the center of the wavefronts locally measured by the sensor array. This virtual source can be related with the position of the source generating the detected waves provided the wave propagation mode and medium properties are known. Moreover, the motion of the source region can be derived, as well as its basic geometrical characteristics. In this work we give the theoretical background for the new tool and examples of location analysis based on synthetic data. An example based on Cluster magnetic field data in the dayside magnetosheath reveals a virtual source region elongated in the magnetic field direction, moving with the plasma flow in the vicinity of the spacecraft configuration.
Published: 29 September 2006
American Geophysical Union, Fall Meeting 2005, abstract #SM23C-06

Synoptic measurements from the DOUBLE STAR and CLUSTER spacecraft offer a unique opportunity to evaluate global models in simulating the complex topology and dynamics of the dayside merging region. We compare observations from the DOUBLE STAR TC-1 and CLUSTER spacecraft on May 8, 2004 with the predictions from a three-dimensional magnetohydrodynamic (MHD) simulation that uses plasma and magnetic field parameters measured upstream of the bow shock by the WIND spacecraft. Results from the global simulation are consistent with the large-scale features observed by CLUSTER and TC-1. We discuss topological changes and plasma flows at the dayside magnetospheric boundary inferred from the simulation results. The simulation shows that the DOUBLE STAR spacecraft passed through the dawn side merging region as the IMF rotated. In particular, the simulation indicates that at times TC-1 was very close to the merging region. In addition, we found that the bifurcation of the merging region in the simulation results is consistent with predictions by the antiparallel merging model. However, because of the draping of the magnetosheath field lines over the magnetopause, the positions and shape of the merging region differ significantly from those predicted by the model.

Published: 15 December 2005
On the 11 August 2004, the UV spectrograph Spectroscopy for Investigation of Characteristics of the Atmosphere of Mars (SPICAM) on board Mars Express made the first observation of auroral-type emission on the Martian nightside. In this paper, we describe the results of a new analysis of the observed emission owing to a better calibration of SPICAM UV channel and the use of all spectral information obtained during this observation. Several possibilities for the origin of this emission are discussed. We discussed, in particular, the possible exact geometry of the observation and the possible origins of the Martian aurorae. The emissions measured by SPICAM ultraviolet spectrometer have most probably been produced by electrons with an energy distribution peaking at few tens of eV rather than by electron distributions peaking above 100 eV.
Published: 23 September 2006
This document provides an overview of the Venus Entry Probe system design study. The Venus Entry Probe is one of ESA's Technology Reference Studies (TRS), which provide a focus for the development of strategically important technologies that are of likely relevance for future scientific missions [Falkner05, Peacock06]. This is accomplished through the study of several technologically demanding and scientifically interesting mission concepts, which are not part of the ESA science programme. The TRSs subsequently act as a reference for possible future technology development activities.
Published: 27 February 2007
We investigate the nonlinear influence of the cross-tail currents carried by beamlets (substructures of PSBL ion beams) on the topology of the magnetic field, and, correspondingly, on the dispersion properties of these substructures self-consistently generated in this field. We found that some of the peculiarities of beamlet shapes found recently in CLUSTER data could be explained by taking into account the nonlinearity of the system. This model explains the steepening of local beamlets dispersion in comparison with the global dispersion of the enveloping VDIS structure. At the same time we found that velocity filter effects operating during beamlets propagation toward the Earth prevent the sign's reversal of this local dispersion.
Published: 21 September 2006

This is the final report of the ESA-ESO working group on Herschel/ALMA synergies, produced by the second joint ESA/ESO working group (Chairman: Tom Wilson, co-chair: David Elbaz).

The Herschel Satellite and the Atacama Large Millimeter Array (ALMA) are two very large sub-mm and far infrared (FIR) astronomy projects that are expected to come into operation in this decade. This report contains descriptions of these instruments, emphasising the overlaps in wavelength range and additional complementarities.

A short rationale for studying sub-mm and far infrared astronomy is given. Following this, brief presentations of Herschel and ALMA are presented, with references to more detailed documents and use cases. Emphasis is placed on the synergies between these facilities, and the challenges of comparing data produced using both. Specific examples of projects are given for a number of areas of astronomical research where these facilities will lead to dramatic improvements.

Published: 16 August 2006
In September 2003, the executives of ESO and ESA agreed to establish a number of working groups to explore possible synergies between these two major European astronomical institutions on key scientific issues. The first two working group reports (on Extrasolar Planets and the Herschel-ALMA Synergies) were released in 2005 and 2006, and this third report covers the area of Fundamental Cosmology.
Published: 21 September 2006
We have used HST imaging of the central regions of the globular cluster 47 Tucanae (=NGC 104), taken with the WFPC2 and ACS instruments between 1995 and 2002, to derive proper motions and U- and V-band magnitudes for 14 366 stars within 100" (about 5 core radii) of the cluster center. This represents the largest set of member velocities collected for any globular cluster. The stars involved range in brightness from just fainter than the horizontal branch of the cluster to more than 2.5 mag below the main-sequence turnoff. In the course of obtaining these kinematic data, we also use a recent set of ACS images to define a list of astrometrically calibrated positions (and F475W magnitudes) for nearly 130 000 stars in a larger, ~3'×3' central area. We describe our data reduction procedures in some detail and provide the full position, photometric, and velocity data in the form of downloadable electronic tables. We have used the star counts to obtain a new estimate for the position of the cluster center and to define the density profile of main-sequence turnoff and giant branch stars in to essentially zero radius, thus constraining the global spatial structure of the cluster better than before. A single-mass, isotropic King model fit to it is then used as a rough point of reference against which to compare the gross characteristics of our proper-motion data. We search in particular for any evidence of very fast-moving stars, in significantly greater numbers than expected for the extreme tails of the velocity distribution in a sample of our size. We find that likely fewer than 0.1%, and no more than about 0.3%, of stars with measured proper motions have total speeds above the nominal central escape velocity of the cluster. At lower speeds, the proper-motion velocity distribution very closely matches that of a regular King model (which is itself nearly Gaussian given the high stellar density) at all observed radii.
Published: 16 September 2006
We study the nuclear star clusters in spiral galaxies of various Hubble types using spectra obtained with STIS on-board HST. We observed the nuclear clusters in 40 galaxies, selected from two previous HST/WFPC2 imaging surveys. At a spatial resolution of about 0.2", the spectra provide a better separation of cluster light from underlying galaxy light than is possible with ground-based spectra. Approximately half of the spectra have sufficient signal-to-noise ratio for detailed stellar population analysis. For the other half we only measure the continuum slope, as quantified by the B-V color. To infer the star formation history, metallicity and dust extinction, we fit weighted superpositions of single-age stellar population templates to the high signal-to-noise spectra. We use the results to determine the luminosity-weighted age, mass-to-light ratio, and masses of the clusters. The models provide excellent fits to the data and generally require a mixture of populations of different ages. Approximately half of the sample clusters contain a population younger than 1 Gyr.
Published: 16 September 2006
  • Foreword
  • INTEGRAL AO-4 Results
  • INTEGRAL AO-5 Key Programme
  • INTEGRAL Publication Status
  • Science Highlights
  • Science Operations - Highlights
  • The ISOC Science Data Archive
  • The 6th INTEGRAL Workshop
  • Changes at ISOC
Published: 16 September 2006

Context. In coded mask techniques, reconstructed sky images are pseudo-images: they are maps of the correlation between the image recorded on a detector and an array derived from the coded mask pattern.

Aims. The INTEGRAL/IBIS telescope provides images where the flux of each detected source is given by the height of the local peak in the correlation map. As such, it cannot provide an estimate of the flux of an extended source. What is needed is intensity sky images giving the flux per solide angle as typically done at other wavelengths.

Methods. In this paper, we present the response of the INTEGRAL IBIS/ISGRI coded mask instrument to extended sources. We develop a general method based on analytical calculations in order to measure the intensity and the associated error of any celestial source and validated with Monte-Carlo simulations.

Results. We find that the sensitivity degrades almost linearly with the source extent. Analytical formulae are given as well as an easy-to-use recipe for the INTEGRAL user. We check this method on IBIS/ISGRI data but these results are general and applicable to any coded mask telescope.

Published: 16 September 2006
Spectra from Cassini's Visual and Infrared Mapping Spectrometer reveal the presence of a vast tropospheric cloud on Titan at latitudes 51° to 68° north and all longitudes observed (10° to 190° west). The derived characteristics indicate that this cloud is composed of ethane and forms as a result of stratospheric subsidence and the particularly cool conditions near the moon's north pole. Preferential condensation of ethane, perhaps as ice, at Titan's poles during the winters may partially explain the lack of liquid ethane oceans on Titan's surface at middle and lower latitudes.
Published: 16 September 2006
19-Sep-2020 01:41 UT

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