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| Two-stage oscillatory response of the magnetopause to a tangential discontinuity/vortex sheet followed by northward IMF: Cluster observations |
| We discuss the motion and structure of the magnetopause/boundary layer observed by Cluster in response to a joint tangential discontinuity/vortex sheet (TD/VS) observed by the Advanced Composition Explorer spacecraft on 7 December 2000. The observations are then supplemented by theory. Sharp polarity reversals in the east-west components of the field and flow By and Vy occurred at the discontinuity. These rotations were followed by a period of strongly northward interplanetary magnetic field (IMF). These two factors elicited a two-stage response at the magnetopause, as observed by Cluster situated in the boundary layer at the duskside terminator. First, the magnetopause suffered a large deformation from its equilibrium position, with large-amplitude oscillations of ~3-min period being set up. These are argued to be mainly the result of tangential stresses associated with DeltaVy the contribution of dynamic pressure changes being small in comparison. This strengthens recent evidence of the importance to magnetospheric dynamics of changes in azimuthal solar wind flow. The TD/VS impact caused a global response seen by ground magnetometers in a magnetic local time range spanning at least 12 h. The response monitored on ground magnetometers is similar to that brought about by magnetopause motions driven by dynamic pressure changes. Second, Cluster recorded higher-frequency waves (~79 s). Two clear phases could be distinguished from the spectral power density, which decreased by a factor of ~3 in the second phase. Applying compressible linearized MHD theory, we show that these waves are generated by the Kelvin-Helmholtz (KH) instability. Varying the local magnetic shear at the Cluster locale, as suggested by the temporal profile of the IMF clock angle, we find that locally stability was reinstated, so that the reduced power in the second phase is argued to be due residual KH activity arriving from locations farther to the dayside. |
| Publication date: 19 Mar 2008 |
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| Mid Infrared Instrument (MIRI) cooler subsystem prototype demonstration |
| In "Advances in Cryogenic Engineering: Transactions of the Cryogenic Engineering Conference - CEC, Vol. 53", edited by J. G. Weisend et al., AIP Conf. Proc. Volume 985, pp. 807-814, 2008, doi:10.1063/1.2908674 The Cooler Subsystem for the Mid InfRared Instrument (MIRI) of the James Webb Space Telescope (JWST) features a 6 Kelvin Joule-Thomson (JT) cooler pre-cooled by a three-stage Pulse Tube (PT) cryocooler to provide 65 mW of cooling at the instrument. MIRI's 6 Kelvin cooling load, directly behind the primary mirror of JWST, is remote from the location of the compressors and pre-cooler. This distance, and the parasitic heat load on the refrigerant lines spanning it, is accommodated by the design. The effort during 2006 and the first part of 2007 has focused on the demonstration of a MIRI Cooler prototype in the relevant environment, required to achieve Technology Readiness Level 6 (TRL 6) as defined by NASA. The tests that have been used to successfully demonstrate TRL 6: launch vibration and cooler performance in the relevant thermal-vacuum environment, will be discussed. |
| Publication date: 16 Mar 2008 |
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| Coverage and pointing accuracy of SMART-1/AMIE images |
| Presented at Lunar and Planetary Science XXXIX, 10-14 March 2008 The SMART-1 spacecraft started from 15 March 2005 with a lunar orbit 400-3000 km for a nominal science period of six months, with 1 year science extension. During these 18 months, the AMIE camera aboard the spacecraft acquired about 32.000 images. We report on the coverage at various resolutions and the pointing accuracy. |
| Publication date: 15 Mar 2008 |
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| Determination of reconnected flux via remote sensing |
| Magnetic reconnection is one of the most fundamental processes in the magnetosphere. We present here a simple method to determine the essential parameters of reconnection such as reconnected flux and location of the reconnection site out of single spacecraft data via remote sensing. On the basis of a time-dependent reconnection model, the dependence of the reconnected flux on the magnetic field z-component Bz is shown. The integral of Bz over time is proportional to the reconnected flux and depends on the distance between the reconnection site and the actual position where Bz is measured. This distance can be estimated from analysis of magnetic field Bz data. We apply our method to Cluster measurements in the Earth's magnetotail. |
| Publication date: 15 Mar 2008 |
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| ISOC Newsletter #19 |
Contents:
- Foreword
- AO-6 Announcement
- Key Programmes in AO-6
- Recent Scientific Highlights
- Science Operations
- Long Term Observation Planning
- Changes at ISOC
- Contacting ISOC
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| Publication date: 15 Mar 2008 |
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| James Webb Space Telescope - A Bigger and Better Time Machine |
| Inspired by the success of the Hubble Space Telescope, NASA, ESA and the Canadian Space Agency have collaborated since 1996 on the design and construction of a scientifically worthy successor. Due to be launched from Kourou in 2013 on an Ariane-5 rocket, the James Webb Space Telescope is expected to have as profound and far-reaching an impact on astrophysics as did its famous predecessor. |
| Publication date: 13 Mar 2008 |
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| Statistical properties of tail plasma sheet electrons above 40 keV |
| We use data from four tail seasons (2001-2004) of the Cluster spacecraft to study statistical features of energetic electrons (40-400 keV) in the magnetotail plasma sheet in combination with plasma parameters and indices of geomagnetic activity. We find that the horizontal magnetic field magnitude best orders the energetic electron observations. Using this method we observe a statistical flux gradient toward the neutral sheet. The fluxes also increase with an increase in the vertical magnetic field component (dipolarization). The intensity of supra-thermal electrons is observed to increase strongly as function of plasma temperature. Although the energetic electron fluxes also appear to increase strongly with geomagnetic activity this is found to be mainly due to the increase in plasma temperature with increasing Kp. Investigation of neutral sheet fluxes and phase space densities at fixed first adiabatic invariant (mu) indicates that adiabatic heating can explain observed flux increases during field dipolarization. The spectral slope in the supra-thermal range is observed to be independent of geomagnetic activity (Kp), while there is a significant local time dependence, with harder spectra observed at dawn compared to the dusk side. |
| Publication date: 11 Mar 2008 |
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| XMM-Newton slew survey discovery of the nova XMMSL1 J070542.7-381442 (V598 Puppis) |
Aims. In an attempt to catch new X-ray transients while they are still bright, the data taken by XMM-Newton as it slews between targets are being processed and cross-correlated with other X-ray observations as soon as the slew data appear in the XMM-Newton archive.
Methods. A bright source, XMMSL1 J070542.7-381442, was detected on 9 Oct. 2007 at a position where no previous X-ray source had been seen. The XMM slew data and optical data acquired with the Magellan Clay 6.5 m telescope were used to classify the new object.
Results. No XMM slew X-ray counts are detected above 1 keV and the source is seen to be ~750 times brighter than the ROSAT All-Sky Survey upper limit at that position. The normally mV ~ 16 star, USNO-A2.0 0450-03360039, which lies 3.5' from the X-ray position, was seen in our Magellan data to be very much enhanced in brightness. Our optical spectrum showed emission lines that identified the source as a nova in the auroral phase; hence, this optical source is undoubtedly the progenitor of the X-ray source - a new nova (now also known as V598 Pup). The X-ray spectrum indicates that the nova was in a super-soft state (with kTeff 35 eV). We estimate the distance to the nova to be ~3 kpc. Analysis of archival robotic optical survey data shows a rapid-decline light curve consistent with what is expected for a very fast nova.
Conclusions. The XMM-Newton slew data present a powerful opportunity to find new X-ray transient objects while they are still bright. Here we present the first such source discovered by the analysis of near real-time slew data. |
| Publication date: 11 Mar 2008 |
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| Phobos observations by the OMEGA/Mars Express hyperspectral imager |
Abstract No. 1832 As a complement to Mars observations,
Phobos spectral imaging was implemented in
order to acquired compositional mapping with the
prime objective to answer to the following questions: - Is Phobos a "primitive" (undifferentiated) body, or is its mass sufficient for this small body to have suffered some degree of internal differentiation, so as to
exhibit surface compositional variations reflecting
variation with depth?
- Can one detect surface material containing either
volatile or organic compounds ?
We will present an overview of the results acquired,
and discuss them in terms of planetary differentiation. |
| Publication date: 10 Mar 2008 |
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| V5116 Sagittarii, an Eclipsing Supersoft Postoutburst Nova? |
| V5116 Sgr (Nova Sgr 2005 No. 2), discovered on 2005 July 4, was observed with XMM-Newton in 2007 March, 20 months after the optical outburst. The X-ray spectrum shows that the nova had evolved to a pure supersoft X-ray source, with no significant emission at energies above 1 keV. The X-ray light curve shows abrupt decreases and increases of the flux by a factor ~8. It is consistent with a periodicity of 2.97 hr, the orbital period suggested by Dobrotka and coworkers, although the observation lasted just a little more than a whole period. We estimate the distance to V5116 Sgr to be 11±3 kpc. A simple blackbody model does not fit correctly the EPIC spectra, with Chi²>4. In contrast, ONe-rich white dwarf atmosphere models provide a good fit, with NH=(1.3±0.1)x1021 cm-2, T=(6.1±0.1)x105 K, and L=(3.9±0.8)x1037 (D/10 kpc)² erg s-1 (during the high-flux periods). This is consistent with residual hydrogen burning in the white dwarf envelope. The white dwarf atmosphere temperature is the same both in the low- and the high-flux periods, ruling out an intrinsic variation of the X-ray source as the origin of the flux changes. We speculate that the X-ray light curve may result from a partial coverage by an asymmetric accretion disk in a high-inclination system. |
| Publication date: 10 Mar 2008 |
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| The Dust Halo of Saturn's Largest Icy Moon, Rhea |
| Saturn's moon Rhea had been considered massive enough to retain a thin, externally generated atmosphere capable of locally affecting Saturn's magnetosphere. The Cassini spacecraft's in situ observations reveal that energetic electrons are depleted in the moon's vicinity. The absence of a substantial exosphere implies that Rhea's magnetospheric interaction region, rather than being exclusively induced by sputtered gas and its products, likely contains solid material that can absorb magnetospheric particles. Combined observations from several instruments suggest that this material is in the form of grains and boulders up to several decimetres in size and orbits Rhea as an equatorial debris disk. Within this disk may reside denser, discrete rings or arcs of material. |
| Publication date: 07 Mar 2008 |
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| Gravitational astronomy: Hearing the heavens |
| LISA is perhaps the most ambitious space mission envisaged for the coming decades. A recent assessment of astrophysics research proposed for NASA's Beyond Einstein programme by America's National Research Council (NRC) gave the "extraordinarily original and technically bold" project its highest scientific ranking. Under joint development by NASA and the European Space Agency (ESA), LISA's goal is to detect gravitational waves - fluctuations in the fabric of space and time - by measuring the relative motions of three spacecraft with great precision. Although that assessment carried out by the NRC saw LISA as the "least scientifically risky" of the proposals for future flagship missions, there is no getting away from the fact that no one has ever tried anything remotely similar before. |
| Publication date: 05 Mar 2008 |
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| James Webb Space Telescope - A bigger and better time machine |
| Inspired by the success of the Hubble Space Telescope, NASA, ESA and the Canadian Space Agency have collaborated since 1996 on the design and construction of a scientifically worthy successor. Due to be launched from Kourou in 2013 on an Ariane-5 rocket, the James Webb Space Telescope is expected to have as profound and far-reaching an impact on astrophysics as did its famous predecessor. |
| Publication date: 01 Mar 2008 |
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| The first XMM-Newton slew survey catalogue: XMMSL1 |
Aims: We report on the production of a large area, shallow, sky survey, from XMM-Newton slews. The great collecting area of the mirrors coupled with the high quantum efficiency of the EPIC detectors have made XMM-Newton the most sensitive X-ray observatory flown to date. We use data taken with the EPIC-pn camera during slewing manoeuvres to perform an X-ray survey of the sky.
Methods: Data from 218 slews have been subdivided into small images and source searched. This has been done in three distinct energy bands; a soft (0.2-2 keV) band, a hard (2-12 keV) band and a total XMM-Newton band (0.2-12 keV). Detected sources, have been quality controlled to remove artifacts and a catalogue has been drawn from the remaining sources.
Results: A "full" catalogue, containing 4710 detections and a "clean" catalogue containing 2692 sources have been produced, from 14% of the sky. In the hard X-ray band (2-12 keV) 257 sources are detected in the clean catalogue to a flux limit of 4×10-12 ergs s-1 cm-2. The flux limit for the soft (0.2-2 keV) band is 6×10-13 ergs s-1 cm-2 and for the total (0.2-12 keV) band is 1.2×10-12 ergs s-1 cm-2. The source positions are shown to have an uncertainty of 8" (1 sigma confidence). |
| Publication date: 01 Mar 2008 |
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| CDF Summary of PLATO Mission |
A presentation style summary of the ESA Concurrent Design Facility investigation into the PLATO mission.
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| Publication date: 26 Feb 2008 |
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| Cosmic Vision cycle 1, Presentation to Industry |
Contents of presentation:
- Cosmic Vision Cycle 1
- Selected Missions
- Assessment Studies
- National Activities Parallel to Cosmic Vision studies
- Technology Developments
- Schedule
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| Publication date: 26 Feb 2008 |
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| Recent activity of the Rapid Burster (MXB 1730-335) |
| Observations taken as part of the INTEGRAL Galactic bulge monitoring program (see ATel #1385) on 2008, February 23 13:32-17:13 (UT) showed bursting activity from the X-ray transient, the Rapid Burster (MXB 1730-335). During one of the 1800-sec pointings when the source was in the field-of-view of JEM-X a series of 6 X-ray bursts were observed, once every 250-350 sec, with durations of 30-60 sec and peak fluxes of about 0.6-0.9 Crab (3-10 keV). |
| Publication date: 26 Feb 2008 |
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| Small-Scale Energy Cascade of the Solar Wind Turbulence |
| Magnetic fluctuations in the solar wind are distributed according to Kolmogorov's power law f -5/3 below the ion cyclotron frequency fci. Above this frequency, the observed steeper power law is usually interpreted in two different ways, as a dissipative range of the solar wind turbulence, or another turbulent cascade, the nature of which is still an open question. Using the Cluster magnetic data we show that after the spectral break the intermittency increases toward higher frequencies, indicating the presence of nonlinear interactions inherent to a new inertial range and not to the dissipative range. At the same time the level of compressible fluctuations rises. We show that the energy transfer rate and intermittency are sensitive to the level of compressibility of the magnetic fluctuations within the small-scale inertial range. We conjecture that the time needed to establish this inertial range is shorter than the eddy-turnover time, and is related to dispersive effects. A simple phenomenological model, based on the compressible Hall MHD, predicts the magnetic spectrum ~k-7/3 + 2 alpha, which depends on the degree of plasma compression alpha. |
| Publication date: 20 Feb 2008 |
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| 21 February 2007 Eclipse Field Guide |
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| Publication date: 19 Feb 2008 |
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| ESSC Report: Science-Driven Scenario for Space Exploration |
| Report from the European Space Sciences Committee (ESSC), the ESF's strategic board on space research.
The international space exploration programme foresees multiple robotic and human missions in the solar system in the coming decades. A global strategy is being developed jointly by a large number of space-faring nations and organisations. In Europe a major planning effort is ongoing in the framework of the ESA Aurora Programme, Europe's Exploration Programme (EEP) that envisages the launch of ExoMars in 2013 as a first step towards a robust and renewed effort for exploration.
In view of the evolving international context, ESA has initiated further analysis and definition of Europe's potential role in the exploration initiative by identifying scientific, technological and societal priorities. For the science part ESA has asked the ESSC-ESF to conduct a broad consultation in support of the definition of a science-driven European scenario for space exploration. |
| Publication date: 15 Feb 2008 |
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