Publication archive

Publication archive

Magnetic reconnection is a favored mechanism for understanding charged-particle acceleration phenomena in space and laboratory plasmas. A change in magnetic field line topology is envisioned in magnetic reconnection to release the stored magnetic field energy. In order for this to take place, some form of dissipation to break the frozen-in condition is required. Since the classical resistivity is often inadequate for collisionless plasmas, anomalous resistivity via charged particles interacting with fluctuating electromagnetic fields is customarily invoked. However, anomalous resistivity is often modeled rather than computed from theory. In this article, we formulate the theory of anomalous transport from first principles. It is found that the effect of fluctuations can be defined through three anomalous transport terms governing momentum and energy transport and the resistivity. To illustrate the utility of these derived equations, examples that bear relevance to the consideration of breakdown in the frozen-in condition in magnetic reconnection are discussed.
Published: 17 February 2006
We present infrared spectra of Mercury and the Moon in the wavelength range 0.7-5.3 mum obtained with the SpeX spectrograph at the NASA Infrared Telescope Facility. The spectra were acquired from pole and terminator locations of Mercury's surface and of Mersenius C and the Copernicus central peak on the Moon. Spectra of both bodies were measured in close temporal succession and were reduced in the same manner with identical calibration stars to minimize differences in the reduction process. The Copernicus spectra display the expected absorption features due to mafic minerals in the near infrared and show spectral features in the SiO combination/overtone vibrational band region above 4 mum. The spectra of Mercury from longitude 170° and north and south mid-latitudes display a 1-mum absorption band indicative of high-Ca clinopyroxene, while a spectrum from longitude 260° and northern mid-latitudes does not. The Mercury spectra show a broad feature of low emittance over the full 3 5 mum thermal infrared region, but no narrow features in this spectral range. The longitude 260° spectrum shows excess thermal emission around 5 mum attributable to the existence of a thermal gradient in the insolated dayside regolith. The thermal-IR spectra suggest a significant difference in the compositional and/or structural properties of Mercury and the Moon that may be due to grain size, absorption coefficient, or the magnitude of near-surface thermal gradients. The results indicate that the composition of Mercury's surface is heterogeneous on regional scales, and that the near infrared wavelength range provides more discriminative information on the surface composition than the 2 4 mum region, where the solar reflected and thermally emitted radiation contribute approximately equally to the observed flux of these bodies.
Published: 15 February 2006
The space weather event of August/September 1859 is now famous because of the observation by Carrington and Hodgson of a solar flare. However, at the time, the associated magnetic disturbances produced widespread auroral displays and disruption to telegraph transmissions which attracted much public attention and were widely reported in the newspapers and scientific articles. In this paper, I review all the available literature to assess the characteristics of the magnetic disturbances and the locations and times of the telegraph effects. This information is used to construct a timeline for the whole of the disturbed interval comprising the magnetic storms of August 28/29 and September 2/3. The first magnetic disturbance started in the evening of August 28 and telegraph operations were disrupted in North America and Europe through till the next morning. The second disturbance started with a sudden commencement at 04.40 UT on September 2 and a major disturbance followed immediately. Between 06.00 and 06.30 UT reports of a negative H variation of ~3000 nT at Rome and a large swing in Z at Greenwich indicate the expansion of the auroral oval to mid latitudes. This coincides with the time of the large disturbance at Bombay but there is no evidence that the auroral currents contributed to the Bombay disturbance. This initial disturbance subsided but magnetic activity increased again in the latter half of September 2 with lesser activity occurring on subsequent days. - Remainder of abstract truncated -
Published: 15 February 2006
We present results from three XMM-Newton observations of the M31 low mass X-ray binary (LMXB) XMMU J004314.4+410726.3 (Bo 158), spaced over 3 days in 2004 July. Bo 158 was the first dipping LMXB to be discovered in M31. Periodic intensity dips were previously seen to occur on a 2.78-h period, due to absorption in material that is raised out of the plane of the accretion disc. The report of these observations stated that the dip depth was anticorrelated with source intensity. In light of the 2004 XMM-Newton observations of Bo 158, we suggest that the dip variation is due to precession of the accretion disc. This is to be expected in LMXBs with a mass ratio 0.3 (period 4 h), as the disc reaches the 3:1 resonance with the binary companion, causing elongation and precession of the disc. A smoothed particle hydrodynamics simulation of the disc in this system shows retrograde rotation of a disc warp on a period of 11Porb, and prograde disc precession on a period of 29 ± 1Porb. This is consistent with the observed variation in the depth of the dips. We find that the dipping behaviour is most likely to be modified by the disc precession, hence we predict that the dipping behaviour repeats on an 81 ± 3 h cycle.
Published: 15 February 2006
As reported in the November issue of ESA Bulletin, at their meeting in Berlin on 5 and 6 December the Ministers responsible for space activities in the Agency's 17 Member States and Canada endorsed the continuation of a set of ongoing ESA programmes and agreed to undertake major new initiatives designed to give Europe a clear vision and tangible means to further strengthen its space exploration and exploitation activities. The Ministers also reaffirmed the strategic importance of Europe continuously improving its scientific, technological and industrial capabilities in the space field, to enable it to better respond to the expectations of its citizens concerning the environment, quality of life and security. A major political step was achieved with the approval of an overall European launcher policy ensuring coherence between the launcher and satellite fields.
Published: 15 February 2006
Mars Express, launched in June 2003 and in orbit around Mars since December that year, has been continuing its investigations, painting a new picture of the 'Red Planet'. This includes the first-ever probing below the surface of Mars, new geological clues with implications for the climate, newly-discovered surface and atmospheric features and, above all, the presence of abundant water ice on this world.
Published: 15 February 2006
Almost exactly twenty years ago, on 14 March 1986, ESA's Giotto spacecraft made its historic fly-by of comet Halley at a distance of about 596 km. This close encounter represented a major milestone for planetary science in general, but also gave an important boost to the European planetary-science community that is still having an impact today. Besides its scientific importance, it was also the first big mission-related media event for ESA. The 'Night of the Comet' at ESOC in Darmstadt (D) was relayed by Eurovision, with 56 TV stations from 37 countries reporting the encounter live, attracting a television audience of more than 1.5 billion. The images sent back by Giotto's Halley Multicolour Camera radically transformed everyone's ideas about what the nucleus of a comet really looked like.
Published: 15 February 2006
We present the results of an XMM-Newton observation of the young (~2-4 Myr) cluster around the hot star sigma Orionis. In a previous paper we presented the analysis of the RGS spectrum of the central hot star; here we discuss the results of the analysis of the full EPIC field. We have detected 175 X-ray sources, 88 of which have been identified with cluster members, including very low-mass stars down to the substellar limit. We detected also eleven new possible candidate members from the 2MASS catalogue. We find that late-type stars have a median log L_X/L_bol ~ -3.3, i.e. very close to the saturation limit. We detected significant variability in ~40% of late-type members or candidates, including 10 flaring sources; rotational modulation is detected in one K-type star and possibly in other 3 or 4 stars. Spectral analysis of the brightest sources shows typical quiescent temperatures in the range T_1~ 0.3-0.8 keV and T_2~ 1-3 keV, with subsolar abundances Z~ 0.1-0.3 Z_sol, similarly to what is found in other star-forming regions and associations. We find no significant difference in the spectral properties of classical and weak-lined T Tauri stars, although classical T Tauri stars tend to be less X-ray luminous than weak-lined T~Tauri stars.
Published: 02 February 2006
ESA's Rosetta spacecraft was pointed towards the Deep Impact target comet Tempel 1 from 28 June to 14 July 2005. The OSIRIS cameras, the wide angle camera (WAC) and narrow angle camera (NAC) continuously observed the comet with high time resolution (down to less than a minute) around the impact on 4 July. The filter sets of the WAC were designed to observe the gas coma emissions whereas the NAC made broadband and panchromatic observations. The scale of the NAC at the comet was 1500 km per pixel. A strong increase of intensity (by almost a factor seven) was observed within a radius of one pixel centred on the nucleus position, followed by a short levelling, and a slow decrease back to the value before the impact. The WAC observed an increase in OH and CN. From this unique set of observations the total amount of excavated dust and water ice can be deduced and will be discussed.
Published: 01 February 2006

Stars are born and die in clouds of gas and dust, opaque to most types of radiation, but transparent in the infrared. Requiring complex detectors, space missions and cooled telescopes, infrared astronomy is the last branch of this discipline to come of age. After a very successful sky survey performed in the eighties by the IRAS satellite, the Infrared Space Observatory, in the nineties, brought spectacular advances in the understanding of the processes giving rise to powerful infrared emission by a great variety of celestial sources.

Outstanding results have been obtained on the bright comet Hale-Bopp, and in particular of its water spectrum, as well as on the formation, chemistry and dynamics of planetary objects in the solar system. Ideas on the early stages of stellar formation and on the stellar initial mass function have been clarified.

ISO is the first facility in space able to provide a systematic diagnosis of the physical phenomena and the chemistry in the close environment of pre-main sequence stars, in the interstellar medium, and in the final stages of stellar life, using, among other indicators, molecular hydrogen, ubiquitous crystalline silicates, water and ices.

ISO has dramatically increased our ability to investigate the power production, excitation and fuelling mechanism of galaxies of every type, and has discovered a new very cold dust component in galaxies.

ISO has demonstrated that luminous infrared galaxies were brighter and much more numerous in the past, and that they played a dominant role in shaping present day galaxies and in producing the cosmic infrared background.

Published: 15 November 2005
We report the discovery of two very cold and massive molecular cloud cores in the region ISOSS J18364-0221. The object has been identified by a systematic search for very early evolutionary stages of high-mass stars using the 170 micron ISOPHOT Serendipity Survey (ISOSS). Submillimeter continuum and molecular line measurements reveal two compact cores within this region. The first core has a temperature of 16.5 K, shows signs of ongoing infall and outflows, has no near- or mid-infrared counterpart, and is massive enough (M~75 Msolar) to form at least one O star with an associated cluster. It is therefore considered a candidate for a genuine high-mass protostar and a high-mass analog to the Class 0 objects. The second core has an average gas and dust temperature of only ~12 K and a mass of M~280 Msolar. Its temperature and level of turbulence are below the values found for massive cores so far, and we suggest that this represents the initial conditions from which high-mass star formation occurs.
Published: 20 January 2006
Magnetic field lines are known to reorganize themselves in plasmas, converting magnetic to particle energy. Evidence harvested from the solar wind implies that the scale of the effect is larger than was thought.
Published: 12 January 2006
Magnetic reconnection in a current sheet is a magnetic to particle energy conversion process that is important in many laboratory, space and astrophysical contexts. It is not presently known whether reconnection is fundamentally a process that can occur over an extended region in space or whether it is patchy and unpredictable in nature. Frequent reports of small-scale flux ropes and flow channels in Earth's magnetosphere associated with reconnection raise the possibility that reconnection is intrinsically patchy, each reconnection region extending at most a few Earth radii (RE) even though the associated current sheets span many tens or hundreds of RE. Here we report three spacecraft observations of accelerated flow associated with reconnection in a current sheet embedded in the solar wind flow where the reconnection line extended at least 390 RE (or 2.5 million km). Observations of this and 27 similar events imply that reconnection is fundamentally large scale. Patchy reconnection observed in the magnetosphere is likely to be a geophysical effect associated with fluctuating boundary conditions rather than a fundamental property of reconnection. Our observations also reveal, surprisingly, that reconnection can operate in a quasi-steady-state manner even when undriven by the external flow.
Published: 12 January 2006
Reference: GIPF-TN-730-VHS-0

This document gives a summary of the work performed within ESA Contract No. 16854/03/NL/HB "Development of a compact Geochemistry Instrument Package Facility (GIPF)". Main objective of this study was the development and assembly of a compact instrument facility for in-situ geochemistry sample analysis in planetary research. Several work packages listed in chapter 2 below have been performed, from the assessment of different geochemistry methods to final testing of the hardware and steps described to achieve a flight model for a given mission. The design was driven by the proposed BepiColombo mission to be used on a lander on planet Mercury. In other words BepiColombo was the "reference mission" for the presented study. The study was lead by von Hoerner & Sulger GmbH, Schwetzingen. Subcontracts to built the spectrometers and the camera have been placed at University of Mainz, Max-Planck-Institut für Chemie, Mainz and DLR, Deutsches Zentrum für Luft- und Raumfahrt e.V., Berlin.

Published: 12 January 2006
The eclipsing active binary SV Cam (G0V/K6V, Porb=0.593071 d) was observed with XMM-Newton during two campaigns in 2001 and 2003. No eclipses in the quiescent emission are clearly identified, but a flare was eclipsed during the 2001 campaign, allowing us to strongly constrain, from purely geometrical considerations, the position and size of the event: the flare is compact and it is formed at a latitude below 65deg. The size, temperature and Emission Measure of the flare imply an electron density of log n_e (cm^-3)~10.6-13.3 and a magnetic field of ~65-1400 G in order to confine the plasma, consistently with the measurements that are obtained from density-sensitive line ratios in other similar active stars. Average emission seems to come from either extended or polar regions because of lack of eclipses. The Emission Measure Distribution, coronal abundances, and characteristics of variability are very similar to other active stars such as AB~Dor (K1V).
Published: 11 January 2006
The determination of the metal abundances in the neutral interstellar medium (ISM) of dwarf star-forming galaxies is a key step in understand- ing their physical and chemical evolution. This type of investigation has been possible in the last 5 years thanks to FUSE. We will give a flavor of the issues involved by presenting the work that we are performing in this astrophysical field.
Published: 10 January 2006
In this paper we report the second soft gamma-ray source catalog obtained with the IBIS/ISGRI gamma-ray imager on board the INTEGRAL satellite. The scientific data set is based on more than 10 Ms of high-quality observations performed during the first 2 years of Core Program and public IBIS/ISGRI observations, and covers ~50% of the whole sky. The main aim of the first survey was to scan systematically, for the first time at energies above 20 keV, the whole Galactic plane to achieve a limiting sensitivity of ~1 mcrab in the central radian. The target of the second year of the INTEGRAL mission lifetime was to expand as much as possible our knowledge of the soft gamma-ray sky, with the same limiting sensitivity, to at least 50% of the whole sky, mainly by including a substantial coverage of extragalactic fields. This catalog comprises more than 200 high-energy sources detected in the energy range 20-100 keV, including new transients not active during the first year of operation, faint persistent objects revealed with longer exposure time, and several Galactic and extragalactic sources in sky regions not observed in the first survey. The mean position error for all the sources detected with significance above 10 sigma is ~40", enough to identify most of them with a known X-ray counterpart and to unveil the nature of most of the strongly absorbed ones, even though they are very difficult to detect in X-rays.
Published: 10 January 2006
Gamma-rays from radioactive 26Al (half-life ,7.2 x 105 years) provide a 'snapshot' view of continuing nucleosynthesis in the Galaxy. The Galaxy is relatively transparent to such gamma-rays, and emission has been found concentrated along its plane. This led to the conclusion1 that massive stars throughout the Galaxy dominate the production of 26Al. On the other hand, meteoritic data show evidence for locally produced 26Al, perhaps from spallation reactions in the protosolar disk. Furthermore, prominent gamma-ray emission from the Cygnus region suggests that a substantial fraction of Galactic 26Al could originate in localized star-forming regions. Here we report high spectral resolution measurements of 26Al emission at 1808.65 keV, which demonstrate that the 26Al source regions corotate with the Galaxy, supporting its Galaxy-wide origin. We determine a present-day equilibrium mass of 2.8 (±0.8) solar masses of 26Al. We use this to determine that the frequency of core collapse (that is, type Ib/c and type II) supernovae is 1.9 (±1.1) events per century.
Published: 05 January 2006
Some examples of space-borne applications that require improvements in detector technology compared with conventional Si and Ge designs are described. Properties of compound semiconductors are noted, and a range of different detector developments are briefly reviewed. Material fabrication improvements for several compound semiconductors have resulted in near Fano-limited performance.
Published: 01 January 2005
Very long (172 ks effective exposure time) observations of the BALQSO LBQS 2212-1759 with XMM-Newton yield a stringent upper-limit on its 0.2-10 keV (rest- frame 0.64-32.2 keV) flux, F < 6 E-17 erg/cm2/s, while simultaneous UV and optical observations reveal a rather blue spectrum extending to 650 A in the source rest frame. These results are used to set a tight upper-limit on its optical to X-ray spectral index alpha_{ox} < -2.56. Given the HI-BAL nature of LBQS 212-1759, its X-ray weakness is most likely due to intrinsic absorption. If this is the case, and assuming that the intrinsic alpha_{ox} of LBQS 2212-1759 is -1.63 - a value appropriate for a radio-quiet quasar of this luminosity - one can set a lower limit on the X-ray absorbing column N_{H} > 3.4 E25 cm-2. Such a large column has a Thomson optical depth to electron scattering tau > 23, sufficient to extinguish the optical and UV emission. The problem only gets worse if the gas is neutral since the opacity in the Lyman continuum becomes extremely large, > 2 E8, conflicting with the source detection below 912 A. This apparent contradiction probably means that our lines-of-sight to the X-ray and to the UV emitting regions are different, such that the gas covers completely the compact X-ray source but only partially the more extended source of ultraviolet photons. An extended (~ 1) X-ray source is detected 2 to the south-east of the QSO. Given its thermal spectrum and temperature (1.5 < T < 3.0 keV}, it is probably a foreground (0.29 < z < 0.46) cluster of galaxies.
Published: 04 January 2006
6-Mar-2021 07:46 UT

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