Publication archive

Publication archive

The Analyzer of Space Plasma and Energetic Atoms (ASPERA) on board the Mars Express spacecraft found that solar wind plasma and accelerated ionospheric ions may be observed all the way down to the Mars Express pericenter of 270 kilometers above the dayside planetary surface. This is very deep in the ionosphere, implying direct exposure of the martian topside atmosphere to solar wind plasma forcing. The low-altitude penetration of solar wind plasma and the energization of ionospheric plasma may be due to solar wind irregularities or perturbations, to magnetic anomalies at Mars, or both.
Published: 16 September 2004
On 14 January 2005, after a marathon seven-year journey through the Solar System aboard the Cassini spacecraft, ESA's Huygens probe successfully descended through the atmosphere of Titan, Saturn's largest moon, and landed safely on its surface. It was mankind's first successful attempt to land a probe on another world in the outer Solar System. Following its release from the Cassini mothership on 25 December, Huygens reached Titan's outer atmosphere after 20 days and a 4 million kilometre cruise. The probe started its descent through Titan's hazy cloud layers from an altitude of about 1270 km at 09:06 UTC. During the following three minutes, Huygens had to decelerate from 18 000 to 1400 km per hour.
Published: 15 February 2005
Contents
  • 3rd Announcement of Opportunity
  • Mission Status
  • INTEGRAL science workshop
  • Science Operations - Highlights
  • ISOC at ESAC - latest news
  • List of approved open time AO-3 observations
Published: 01 February 2005
Published: 02 November 2004
We present Chandra and XMM-Newton observations of a small sample (11 objects) of optically-selected Seyfert 2 galaxies, for which ASCA and BeppoSAX had suggested Compton-thick obscuration of the Active Nucleus (AGN). The main goal of this study is to estimate the rate of transitions between "transmission-" and "reprocessing-dominated" states. We discover one new transition in NGC4939, with a possible additional candidate in NGC5643. This indicates a typical occurrence rate of at least 0.02/year. These transitions could be due to large changes of the obscuring gas column density, or to a transient dimming of the AGN activity, the latter scenario being supported by detailed analysis of the best studied events. Independently of the ultimate mechanism, comparison of the observed spectral dynamics with Monte-Carlo simulations demonstrates that the obscuring gas is largely inhomogeneous, with multiple absorbing components possibly spread through the whole range of distances from the nucleus between a fraction of parsecs up to several hundreds parsecs. As a by-product of this study, we report the first measurement ever of the column density covering the AGN in NGC3393, and the discovery of soft X-ray extended emission, apparently aligned along the host galaxy main axis in NGC5005. The latter object hosts most likely an historically misclassified low-luminosity Compton-thin AGN.
Published: 07 January 2005
In the last decade star clusters have been found in the centers of spiral galaxies across all Hubble types. We here present a spectroscopic study of the exceptionally bright (106108 LSun) but compact (re ~ 5 pc) nuclear star clusters in very late type spirals with the Ultraviolet and Visual Echelle Spectrograph at the VLT. We find that the velocity dispersions of the nine clusters in our sample range from 13 to 34 km s-1. Using photometric data from the Hubble Space Telescope WFPC2 and spherically symmetric dynamical models, we determine masses between 8 x 105 and 6 x 107 MSun. The mass-to-light ratios range from 0.2 to 1.5 in the I band. This indicates a young mean age for most clusters, in agreement with previous studies.
Published: 05 January 2005
We report the XMM-Newton discovery of a X-ray bright AGN pair in the interacting galaxy system ESO509-IG066. Both galaxies host an X-ray luminous (LX ~ 1043 erg/s) obscured nucleus with column densities NH ~ 7x1022 and NH ~ 5 x 1021 atoms.cm-2. The optical morphology is only mildly disturbed, suggesting a merging system in the early stage of its evolution. Still, the pair is probably gravitationally bound, and might eventually evolve into a compact, fully gas embedded systems such as NGC6240.
Published: 03 January 2005
Temporal and spatial characteristics of intense quasi-static electric fields and associated electric potential structures in the return current region are discussed using Cluster observations at geocentric distances of about 5 Earth radii. Results are presented from four Cluster encounters with such acceleration structures to illustrate common as well as different features of such structures. The electric field structures are characterized by (all values are projected to 100 km altitude) peak amplitudes of ~1V/m, bipolar or unipolar profiles, perpendicular scale sizes of ~10km, occurrence at auroral plasma boundaries associated with plasma density gradients, downward field-aligned currents of ~10 microA/m², and upward electron beams with characteristic energies of a few hundred eV to a few keV. Two events illustrate the temporal evolution of bipolar, diverging electric field structures, indicative of positive U-shaped potentials increasing in magnitude from less than 1kV to a few kV on a few 100s time scale. This is also the typical formation time for ionospheric plasma cavities, which are connected to the potential structure and suggested to evolve hand-in-hand with these. In one of these events an energy decay of inverted-V ions was observed in the upward field-aligned current region prior to the acceleration potential increase in the adjacent downward current region, possibly suggesting that a potential redistribution took place between the two current branches. The other two events were characterized by intense unipolar electric fields, indicative of S-shaped potential contours and were encountered at the polar cap boundary. -- abstract truncated --
Published: 21 December 2004
Using the Fourier Transform Spectrometer at the Canada France Hawaii Telescope, we observed a spectrum of Mars at the P-branch of the strongest CH4 band at 3.3 Œm with resolving power of 180,000 for the apodized spectrum. Summing up the spectral intervals at the expected positions of the 15 strongest Doppler-shifted martian lines, we detected the absorption by martian methane at a 3.7 sigma level which is exactly centered in the summed spectrum. The observed CH4 mixing ratio is 10+/-3 ppb. Total photochemical loss of CH4 in the martian atmosphere is equal to 2.2x10 cms, the CH4 lifetime is 340 years and methane should be uniformly mixed in the atmosphere. Heterogeneous loss of atmospheric methane is probably negligible, while the sink of CH4 during its diffusion through the regolith may be significant. There are no processes of CH4 formation in the atmosphere, so the photochemical loss must therefore be balanced by abiogenic and biogenic sources. - Remainder of abstract truncated -
Published: 15 December 2004
Data obtained with the NICMOS instrument on board the Hubble Space Telescope (HST) have been used to determine the H-band luminosity function (LF) and mass function (MF) of three stellar fields in the globular cluster M15, located ~7' from the cluster centre. The data confirm that the cluster MF has a characteristic mass of ~0.3 Msolar, as obtained by Paresce & De Marchi (2000) for a stellar field at 4.6' from the centre. By combining the present data with those published by other authors for various radial distances (near the centre, at 20" and at 4.6'), we have studied the radial variation of the LF due to the effects of mass segregation and derived the global mass function (GMF) using the Michie-King approach.
Published: 14 December 2004
Both amateur and professional meteor groups more and more use Low-Light level TV (LLTV) systems to record meteors. Double-station observations can yield orbit data. However, data analysis normally is still done by hand and thus time consuming. This paper addresses the question whether available automated tools can be used to determine reasonably accurate orbits with minimum human intervention.

The European Space Agency performed several observing campaigns to observe the Leonid meteor stream. In November 1999, the ESA meteor group was stationed at two locations in Southern Spain, in November 2001 at two stations close to Broome in North-Western Australia. Double-station observations with LLTV systems were conducted. The data was recorded on S-VHS video tapes. The tapes were digitized using automatic detection software. Meteor heights, velocities and radiants were computed. This paper shows the results for the two maximum nights. The radiants determined in 1999 show a very large scatter due to unfortunate observing geometry and inaccurate position determination since one of the cameras was moving because of the wind. The 2001 data is excellent and the radiant was determined to be at RA = 153.96°±0.3° and Dec = 21.09°±0.2°. The error bars for individual meteor radiants are about 0.2° to 0.4°. This demonstrates that is indeed possible to determine good radiant positions using totally automated tools. Orbits, on the other hand, are not well defined due to the fact that the velocity of individual meteors shows large errors. Reasons for this are described.

Published: 01 December 2004
Cassini-Huygens, named after the two celebrated scientists, is the joint NASA/ESA/ASI mission to Saturn and its giant moon Titan. It is designed to shed light on many of the unsolved mysteries arising from previous observations and to pursue the detailed exploration of the gas giants after Galileo's successful mission at Jupiter. The exploration of the Saturnian planetary system, the most complex in our Solar System, will help us to make significant progress in our understanding of planetary system formation and evolution, which is also a key step in our search for extra-solar planets.
Published: 15 November 2004
The change of year is the opportunity to look back over the events of the previous twelve months, and to consolidate one's plans for the year that lies ahead. 2003 was certainly a year of great contrasts for ESA, with unfortunate failures, even dramatic catastrophes, but also some very welcome successes paving the way to the future.
Published: 09 November 2004

Contents

  • 3rd Announcement of Opportunity (AO-3)
  • Science Highlights
  • Mission Status
  • INTEGRAL Public Data Archive
Published: 05 November 2004
This article is based on a talk given by Professor Rudolf von Steiger, Director of the International Space Science Institute, Bern.
Published: 01 November 2004
The brightness of type Ia supernovae, and their homogeneity as a class, makes them powerful tools in cosmology, yet little is known about the progenitor systems of these explosions. They are thought to arise when a white dwarf accretes matter from a companion star, is compressed and undergoes a thermonuclear explosion. Unless the companion star is another white dwarf (in which case it should be destroyed by the mass-transfer process itself), it should survive and show distinguishing properties. Tycho's supernova is one of only two type Ia supernovae observed in our Galaxy, and so provides an opportunity to address observationally the identification of the surviving companion. Here we report a survey of the central region of its remnant, around the position of the explosion, which excludes red giants as the mass donor of the exploding white dwarf. We found a type G0-G2 star, similar to our Sun in surface temperature and luminosity (but lower surface gravity), moving at more than three times the mean velocity of the stars at that distance, which appears to be the surviving companion of the supernova.
Published: 29 October 2004
We report the association of the recently discovered hard X-ray source IGR J17475-2822 with the giant molecular cloud Sgr B2 in the Galactic Center region. The broad band (3-200 keV) spectrum of the source constructed from data of different observatories strongly supports the idea that the X-ray emission of Sgr B2 is Compton scattered and reprocessed radiation emitted in the past by the Sgr A* source. We conclude that 300-400 years ago Sgr A* was a low luminosity (L~ 1.5×1039 erg s-1 at 2-200 keV) AGN with a characteristic hard X-ray spectrum (photon index Gamma ~ 1.8). We estimate the mass and iron abundance of the Sgr B2 scattering gas at 2×106 MSun(r/10 pc)² and 1.9 solar, respectively (where r is the radius of the cloud).
Published: 16 October 2004
Space plasmas present intriguing and challenging puzzles to the space community. Energy accessible to excite instabilities exists in a variety of forms, particularly for the magnetospheric environment prior to substorm expansion onsets. A general consensus of the pre-expansion magnetosphere is the development of a thin current sheet in the near-Earth magnetosphere. This review starts with a short account of the two major substorm paradigms. Highlights of some observations pertaining to the consideration of potential plasma instabilities for substorm expansion are given. Since a common thread of these paradigms is the development of a thin current sheet, several efforts to model analytically a thin current sheet configuration are described. This leads to a review on the instability analyses of several prominent candidates for the physical process responsible for substorm expansion onset. The potential instabilities expounded in this review include the cross-field current, lower-hybrid-drift, drift kink/sausage, current driven Alfvénic, Kelvin-Helmholtz, tearing, and entropy anti-diffusion instabilities. Some recent results from plasma simulations relevant to the investigation of these plasma instabilities are shown. Although some of these instabilities are generally conceived to be excited in spatially localized regions in the magnetosphere, their potentials in yielding global consequences are also explored.
Published: 16 October 2004

A paper originally presented by EADS Astrium at the 55th IAC in Vancouver in October 2004.

On October 26th of next year, Venus Express spacecraft will depart from Baikonur on-board the Soyuz/Fregat Launch Vehicle. It will be the very first European mission to the "morning star", two years after the first European trip to Mars. Venus Express will carry 7 science payloads dedicated to global investigation of the Venusian atmosphere.

Published: 05 October 2004
The Solar Wind Anisotropies (SWAN) instrument is a scanning Lyman-alpha imager on board the Solar and Heliospheric Observatory (SOHO) spacecraft. Since becoming operational in January 1996 SWAN has been producing full sky Lyman-alpha maps which are primarily used to study the interaction between solar wind and the interplanetary neutral hydrogen. In addition to that SWAN images can be used to study the hydrogen coma of comets down to about a visual magnitude of 12. After the retargeting decision of the Rosetta mission the SWAN archive was checked for possible occurrences of 67P/Churyumov-Gerasimenko. Five values were obtained for the 1996 apparition but none for the 2002 apparition because of degraded instrument sensitivity and larger observing distance. The observations suggest a perihelion water production rate of about 8x10^27 per second and possible post perihelion increase of activity.
Published: 02 September 2004
31-Oct-2020 08:31 UT

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