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| Reconstruction of the solar spectral UV irradiance for nowcasting of the middle atmosphere state on the basis of LYRA measurements |
| The LYRA instrument onboard ESA PROBA2 satellite will provide 6-hourly solar irradiance at the Lyman-alpha (121.6 nm) and the Herzberg continuum (~200220 nm wavelength range). Because the nowcasting of the neutral and ionic state of the middle atmosphere requires the solar irradiance for the wide spectral area (120680 nm) we have developed the statistical tool for the reconstruction of the full spectrum from the LYRA measurements. The accuracy of the reconstructed irradiance has been evaluated with 1-D transient radiative-convective model with neutral and ion chemistry using the daily solar spectral irradiance measured with SUSIM and SOLSTICE instruments onboard UARS satellite. We compared the results of transient 1-yr long model simulations for 2000 driven by the observed and reconstructed solar irradiance and showed that the reconstruction of the full spectrum using linear regression equation based on the solar irradiance in two LYRA channels can be successfully used for nowcasting of the middle atmosphere. We have also defined some conditions when the proposed approach does not provide reasonable accuracy. |
| Publication date: 30 Jun 2008 |
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| Occurrence of reconnection jets at the dayside magnetopause: Double Star observations |
| We present a statistical study on reconnection occurrence at the dayside magnetopause performed using the Double Star TC1 plasma and magnetic field data. We examined the magnetopause crossings that occurred during the first year of the mission in the 0600-1800 LT interval and we identified plasma flows, at the magnetopause or in the boundary layer, with a different velocity with respect to the adjacent magnetosheath. We used the Walén relation to test which of these flows could be generated by magnetic reconnection. For some event we observed opposite-directed reconnection jets, which could be associated with the passage of the X-line near the satellite. We analyzed the occurrence of the reconnection jets and reconnection jet reversals in relation to the magnetosheath parameters, in particular the local Alfvèn Mach number, the plasma beta, and the magnetic shear angle. We also studied the positions and velocities of the reconnection jets and jet reversals in relation to the magnetosheath magnetic field clock angle. We found that the observations indicate the presence of a reconnection line hinged near the subsolar point and tilted according to the observed magnetosheath clock angle, consistently with the component merging model. |
| Publication date: 27 Jun 2008 |
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| Cluster multispacecraft determination of AKR angular beaming |
| Simultaneous observations of AKR emission using the four-spacecraft Cluster array were used to make the first direct measurements of the angular beaming patterns of individual bursts. By comparing the spacecraft locations and AKR burst locations, the angular beaming pattern was found to be narrowly confined to a plane containing the magnetic field vector at the source and tangent to a circle of constant latitude. Most rays paths are confined within 15° of this tangent plane, consistent with numerical simulations of AKR k-vector orientation at maximum growth rate. The emission is also strongly directed upward in the tangent plane, which we interpret as refraction of the rays as they leave the auroral cavity. The narrow beaming pattern implies that an observer located above the polar cap can detect AKR emission only from a small fraction of the auroral oval at a given location. This has important consequences for interpreting AKR visibility at a given location. It also helps re-interpret previously published Cluster VLBI studies of AKR source locations, which are now seen to be only a subset of all possible source locations. The observations are inconsistent with either filled or hollow cone beaming models. |
| Publication date: 24 Jun 2008 |
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| The wave surveyor technique for fast plasma wave detection in multi-spacecraft data |
| Multi-satellite missions like Cluster allow to study the full spatio-temporal variability of plasma processes in near-Earth space, and both the frequency and the wave vector dependence of dispersion relations can be reconstructed. Existing wave analysis methods include high-resolution beamformers like the wave telescope or k-filtering technique, and the phase differencing approach that combines the correlations measured at pairs of sensors of the spacecraft array. In this paper, we make use of the eigendecomposition of the cross spectral density matrix to construct a direct wave identification method that we choose to call the wave surveyor technique. The analysis scheme extracts only the dominant wave mode but is much faster to apply than existing techniques, hence it is expected to ease survey-type detection of waves in large data sets. The wave surveyor technique is demonstrated by means of synthetic data, and is also applied to Cluster magnetometer measurements. |
| Publication date: 18 Jun 2008 |
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| ST-ECF Newsletter 44 |
Contents: - Hubble Legacy Archive - Data Release One
- The WFC3 Slitless Spectroscopy Simulator aXeSIMweb
- Why Should We Bother to Communicate Astronomy?
- Tiny Tim PSF Simulator - with WFC3 Support
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| Publication date: 15 Jun 2008 |
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| Enceladus - Oasis or Ice Ball? |
| Is it possible for life to exist on Enceladus, the tiny (500 km diameter) icy satellite of Saturn? The Cassini mission found giant gaseous plumes erupting from a tectonically active and warm south polar region. One highly publicized interpretation is that liquid water is present, possibly within tens of meters of the surface, or possibly only at depths of tens of kilometers. An antithetical interpretation is that Enceladus is frigid, stiff, thoroughly solid and composed of ice with interstitial gases to great depths. However, liquid water is just one of the three environmental conditions that are generally thought to be prerequisites for life. There must also be access to the elements out of which complex molecular structures can be constructed--mainly C, H, O, N, S, and--as well as an energy source that can drive metabolism. We examine the range of possible environments on Enceladus that are consistent with the observations in terms of their implications for harboring life. |
| Publication date: 13 Jun 2008 |
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| Iterative inversion of global magnetospheric ion distributions using energetic neutral atom (ENA) images recorded by the NUADU/TC2 instrument |
| A method has been developed for extracting magnetospheric ion distributions from Energetic Neutral Atom (ENA) measurements made by the NUADU instrument on the TC-2 spacecraft. Based on a constrained linear inversion, this iterative technique is suitable for use in the case of an ENA image measurement, featuring a sharply peaked spatial distribution. The method allows for magnetospheric ion distributions to be extracted from a low-count ENA image recorded over a short integration time (5 min). The technique is demonstrated through its application to a set of representative ENA images recorded in energy Channel~2 (hydrogen: 50-81 keV, oxygen: 138-185 keV) of the NUADU instrument during a geomagnetic storm. It is demonstrated that this inversion method provides a useful tool for extracting ion distribution information from ENA data that are characterized by high temporal and spatial resolution. The recovered ENA images obtained from inverted ion fluxes match most effectively the measurements made at maximum ENA intensity. |
| Publication date: 11 Jun 2008 |
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| Observation of three distinct ion populations at the Kelvin-Helmholtz-unstable magnetopause |
| We report Double Star spacecraft observations of the dusk-flank magnetopause and its boundary layer under predominantly northward interplanetary magnetic field (IMF). Under such conditions the flank low-latitude boundary layers (LLBL) of the magnetosphere are known to broaden. The primary candidate processes associated with the transport of solar wind plasma into the LLBL are: (1) local diffusive plasma transport associated with the Kelvin-Helmholtz instability (KHI), (2) local plasma penetration owing to magnetic reconnection in the vicinity of the KHI-driven vortices, and (3) via a pre-existing boundary layer formed through double high-latitude reconnection on the dayside. Previous studies have shown that a cold population of solar wind origin is typically mixed with a hot population of magnetospheric origin in the LLBL. The present observations show the coexistence of three distinct ion populations in the dusk LLBL, during an interval when the magnetopause is unstable to the KHI: (1) a typical hot magnetospheric population, (2) a cold population that shows parallel temperature anisotropy, and (3) a distinct third cold population that shows perpendicular temperature anisotropy. Although no unambiguous conclusion may be drawn from this single event, we discuss the possible mechanisms at work and the origin of each population by envisaging three likely sources: hot magnetospheric plasma sheet, cold magnetosheath of solar wind origin, and cold plasma of ionospheric origin. |
| Publication date: 11 Jun 2008 |
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| The (re-)discovery of G350.1-0.3; a young, luminous supernova remnant and its neutron star |
| We present an XMM-Newton observation of the long-overlooked radio source G350.1-0.3. The X-ray spectrum of G350.1-0.3 can be fit by a shocked plasma with two components: a high-temperature (1.5 keV) region with a low ionization timescale and enhanced abundances, plus a cooler (0.36 keV) component in ionization equilibrium and with solar abundances. The X-ray spectrum and the presence of nonthermal, polarized, radio emission together demonstrate that G350.1-0.3 is a young, luminous supernova remnant (SNR), for which archival H I and 12CO data indicate a distance of 4.5 kpc. The diameter of the source then implies an age of only ~900 years. The SNR's distorted appearance and small size and the presence of 12CO emission along the SNR's eastern edge all indicate that the source is interacting with a complicated distribution of dense ambient material. An unresolved X-ray source, XMMU J172054.5-372652, is detected a few arcminutes west of the brightest SNR emission. The thermal X-ray spectrum and lack of any multiwavelength counterpart suggest that this source is a neutron star associated with G350.1-0.3, most likely a 'central compact object', as seen coincident with other young SNRs such as Cassiopeia A. |
| Publication date: 09 Jun 2008 |
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| LISA Pathfinder (Invited paper - 7th Edoardo Amaldi Conference) |
| LISA Pathfinder (formerly known as SMART-2) is an ESA mission designed to pave the way for the joint ESA/NASA Laser Interferometer Space Antenna (LISA) mission by testing in-flight the critical technologies required for spaceborne
gravitational wave detection; it will put two test masses in a nearperfect gravitational free fall, and control and measure their motion with an unprecedented accuracy. This is achieved through technology comprising inertial sensors, high-precision laser metrology, drag-free control and an ultraprecise micro-Newton propulsion system. The LISA Pathfinder mission is now in Phase C/Dthe Implementation Phase, and is due to be launched in 2010, with results on the performance of the system being available within 6 months thereafter. |
| Publication date: 07 Jun 2008 |
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| Marco Polo Workshop Presentations - June 2008 |
The first open Workshop on the Marco Polo mission, jointly organized by the Côte d'Azur Observatory and ESA, was held on 5 and 6 June 2008.
More than 80 participants attended the two-day workshop in Cannes, France, which included the following sessions:
| I. | Missions: general studies and programmatics |
| II. | Physical properties of NEOs from laboratory experiments, simulations and observations |
| III. | Instrumentation for global and local characterization |
| IV. | Sampling mechanisms and analysis |
| V. | Japanese-European Collaboration |
The 25+ presentations given at the workshop are available in PDF format via the following link:
Presentations
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| Publication date: 06 Jun 2008 |
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| The Next Decade with XMM-Newton - Its Scientific Impact and Challenges for the Next 10 Years |
| XMM-Newton is one of ESA's most
successful science missions. Launched in
December 1999, the spacecraft is
technically able to continue this scientific
success story and now, encouraged by its
impressive scientific output, ESA has already
extended XMM-Newton's operations well
beyond its original 10-year design lifetime.
This article looks at the impact of XMM-Newton since its launch in December 1999. |
| Publication date: 06 Jun 2008 |
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Multi-wavelength observations of Galactic hard X-ray sources discovered by INTEGRAL
I. The nature of the companion star |
Context. The INTEGRAL hard X-ray observatory has revealed an emerging population of highly obscured X-ray binary systems through multi-wavelength observations. Previous studies have shown that many of these sources are high-mass X-ray binaries hosting neutron stars orbiting around luminous and evolved companion stars.
Aims. To better understand this newly-discovered population, we have selected a sample of sources for which an accurate localisation is available to identify the stellar counterpart and reveal the nature of the companion star and of the binary system.
Methods. We performed an intensive study of a sample of thirteen INTEGRAL sources, through multi-wavelength optical to NIR photometric and spectroscopic observations, using EMMI and SofI instruments at the ESO NTT telescope. We performed accurate astrometry and identified candidate counterparts for which we give the optical and NIR magnitudes. We detected many spectral lines allowing us to determine the spectral type of the companion star. We fitted with stellar black bodies the mid-infrared to optical spectral energy distributions of these sources. From the spectral analysis and SED fitting we identified the nature of the companion stars and of the binary systems.
Results. Through spectroscopic analysis of the most likely candidates we found the spectral types of IGR J16320-4751, IGR J16358-4726, IGR J16479-4514, IGR J17252-3616, IGR J18027-2016: They all host OB type supergiant companion stars, with IGR J16358-4726 likely hosting an sgB[e]. Our spectra also confirm the supergiant O and B nature of IGR J17391-3021 and IGR J19140+0951. From SED fitting we found that IGR J16418-4532 is a (likely OB supergiant) HMXB, IGR J16393-4643 a (likely BIV-V star) HMXB, and IGR J18483-0311 a likely HMXB system.
-- Remainder of abstract is truncated -- |
| Publication date: 05 Jun 2008 |
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Multi-wavelength observations of Galactic hard X-ray sources discovered by INTEGRAL
II. The environment of the companion star |
Context. The INTEGRAL mission has led to the discovery of a new type of supergiant X-ray binaries (SGXBs), whose physical properties differ from those of previously known SGXBs. Those sources are in the course of being unveiled by means of multi-wavelength X-rays, optical, near- and mid-infrared observations, and two classes are appearing. The first class consists of obscured persistent SGXBs and the second is populated by the so-called supergiant fast X-ray transients (SFXTs).
Aims. We report here mid-infrared (MIR) observations of the companion stars of twelve SGXBs from these two classes in order to assess the contribution of the star and the material enshrouding the system to the total emission.
Methods. We used data from observations we carried out at ESO/VLT with VISIR, as well as archival and published data, to perform broad-band spectral energy distributions of the companion stars and fitted them with a combination of two black bodies representing the star and a MIR excess due to the absorbing material enshrouding the star, if there was any.
Results. We detect a MIR excess in the emission of IGR J16318-4848, IGR J16358-4726, and perhaps IGR J16195-4945. The other sources do not exhibit any MIR excess even when the intrinsic absorption is very high. Indeed, the stellar winds of supergiant stars are not suitable for dust production, and we show that this behaviour is not changed by the presence of the compact object. Concerning IGR J16318-4848 and probably IGR J16358-4726, the MIR excess can be explained by their sgB[e] nature and the presence of an equatorial disk around the supergiant companion in which dust can be produced.
-- Remainder of abstract is truncated --
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| Publication date: 05 Jun 2008 |
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| Study of near-Earth reconnection events with Cluster and Double Star |
| Observations made by a unique constellation of Cluster (at 14-16 RE), TC2, Goes10, and LANL spacecraft (near 6.6 RE) have allowed us to study the details of three reconnection events in the middle of a thick plasma sheet with the reconnection X-line located unusually close to Earth (10-12 RE). We use mapping along field lines with magnetospheric models adapted to magnetic field observations to confirm that the reconnection region mapped onto localized auroral brightenings. Using simultaneous observations in the inflow and outflow regions, we describe an encounter with a localized tailward Alfvénic jet produced by a short isolated reconnection pulse. A good correlation between intense E and ion [BV] indicates that the concurrent strong turbulence could not destroy the frozen-in ion behavior in the reconnection outflow. We find that a steady quadrupole-like distribution of the magnetic By component in the turbulent reconnection outflow extended far beyond the ion diffusion region and existed for several minutes. We demonstrate an apparent Vx flow reversal, formed owing to the reappearance (switch-on) of reconnection at another location, rather than to a continuous motion of the active X-line. Using the Liouville mapping technique, we show that the acceleration of outflow electrons, after the particles passed a potential drop of 180 V, is consistent with Fermi/betatron acceleration. We also suggest another interpretation of the energetic particle bursts at the onsets, to emphasize the role of seed population and explain the sudden burst as a consequence of changing magnetic topology. |
| Publication date: 05 Jun 2008 |
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| Downward current electron beam observed by Cluster and FAST |
| We report observations from a conjunction of FAST and Cluster during an interval of downward current at an MLT of 3-4 h on field lines mapping to the PSBL. Both spacecraft see upgoing electrons with an energy of a few hundred eV, suggesting substantial acceleration has occurred below FAST's altitude of 3200 km. At Cluster, isolated bursts of electrons are seen, and modeling indicates that the current mapped from the ionosphere exists as a collection of current filaments at Cluster (4-5 RE). The current filaments are aligned with the background magnetic field and have a perpendicular scale at Cluster of about 100 km (which maps to 10-20 km in the ionosphere), and is similar to the mapped width observed by FAST. The electron beams are quasi-steady during a Cluster spacecraft transit time of 1 min. The field aligned current densities at FAST and Cluster are of the order of a few microAms-2 and 0.05 microAm-2, respectively, and j/B is conserved along a current filament. |
| Publication date: 03 Jun 2008 |
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| Preliminary Planning for an International Mars Sample Return Mission |
The international Mars Architecture for the Return of Samples (iMARS) Working Group was chartered by the International Mars Exploration Working Group (IMEWG) in mid-2006 to develop a potential plan for an internationally sponsored and executed Mars sample return (MSR) mission. Its purpose is to outline the scientifi c and engineering requirements of such an international mission in the 2018-2023 time frame.
This report is a summary of Phase I of iMARS' efforts, which were carried out between September 2007, and May 2008.
Contents
- Executive Summary
- Introduction
- Science Objectives
- High-level Requirements
- Implementation of Mars Sample Return
- Development Timeline
- Management Planning
- Public Outreach and Education
- Conclusions and Next Steps
- Acknowledgements, References, and Appendices
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| Publication date: 01 Jun 2008 |
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| Report of the ESA-ESO working group on Galactic Populations, Chemistry and Dynamics |
| The main task of this Working Group has been to review the state-of-the art knowledge of the Milky Way galaxy, to identify the future challenges, and to propose which tools (in terms of facilities, infrastructures, instruments, science policies) would be needed to successfully tackle and solve the remaining open questions. Considering the leadership position that Europe has reached in the field of Galactic astronomy (thanks to the Hipparcos mission and the Very Large Telescope) and looking at the (near-)future major initiatives it has undertaken (VISTA and VST survey telescopes, Gaia mission), this work clearly has been very timely.
It is of uttermost importance for European astronomy to keep and further consolidate its leading position. This Working Group has made recommendations that would allow dissecting our backyard laboratory, the Galaxy, even further. ESO survey telescopes about to become operational and the upcoming ESA Gaia mission are a guarantee for opening new horizons and making new discoveries. We, the astronomers, with the support of our funding agencies, are ready to fully commit to the best exploitation of the treasure that is ahead of us. The main recommendations this Working Group has made to ESA and ESO are to guarantee the expected tremendous capabilities of these new facilities, to vigourously organise their synergies and to jointly give ways to European astronomers to be leaders in the exploitation of their output data. |
| Publication date: 01 Jun 2008 |
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| SWAP onboard PROBA 2, a new EUV imager for solar monitoring |
| SWAP (Sun Watcher using Active Pixel system detector and image processing) is a solar imager in the extreme ultraviolet (EUV) that has been selected to fly in 2007 on the PROBA 2 technological platform, an ESA program. SWAP will use an off-axis Ritchey Chrétien telescope equipped with an EUV enhanced active pixel sensor detector (coated APS). This type of detector has advantages that promise to be very profitable for solar EUV imaging. SWAP will provide solar coronal images at a 1-min cadence in a bandpass centered on 17.5 nm. Observations with this specific wavelength allow detecting phenomena, such as solar flares or EIT-waves, associated with the early phase of coronal mass ejections. Image processing software will be developed that automatically detects these phenomena and sends out space weather warnings. Together with its sister instrument LYRA, also onboard PROBA 2, SWAP will serve as a high performance solar monitoring tool to be used in operational space weather forecasting. The SWAP data will complement the solar observations provided by instruments like SOHO-EIT, and STEREO-SECCHI. |
| Publication date: 01 Jun 2008 |
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| Secondary anisotropies of the CMB |
| The Cosmic Microwave Background fluctuations provide a powerful probe of the dark ages of the universe through the imprint of the secondary anisotropies associated with the reionization of the universe and the growth of structure. We review the relation between the secondary anisotropies and the primary anisotropies that are directly generated by quantum fluctuations in the very early universe. The physics of secondary fluctuations is described, with emphasis on the ionization history and the evolution of structure. We discuss the different signatures arising from the secondary effects in terms of their induced temperature fluctuations, polarization and statistics. The secondary anisotropies are being actively pursued at present, and we review the future and current observational status. |
| Publication date: 01 Jun 2008 |
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