ESA Science & Technology - Publication Archive
Context. Nonthermal radio emission in massive stars is expected to arise in wind-wind collisions occurring inside a binary system. One such case, the O-type star Cyg OB2 #9, was proven to be a binary only four years ago, but the orbital parameters remained uncertain. The periastron passage of 2011 was the first one to be observable under good conditions since the discovery of binarity.
Aims. In this context, we have organized a large monitoring campaign to refine the orbital solution and to study the wind-wind collision.
Methods. This paper presents the analysis of optical spectroscopic data, as well as of a dedicated X-ray monitoring performed with Swift and XMM-Newton.
Results. In light of our refined orbital solution, Cyg OB2 #9 appears as a massive O+O binary with a long period and high eccentricity; its components (O5-5.5I for the primary and O3-4III for the secondary) have similar masses and similar luminosities. The new data also provide the first evidence that a wind-wind collision is present in the system. In the optical domain, the broad H-alpha line varies, displaying enhanced absorption and emission components at periastron. X-ray observations yield the unambiguous signature of an adiabatic collision, because as the stars approach periastron, the X-ray luminosity closely follows the 1/D variation expected in that case. The X-ray spectrum appears, however, slightly softer at periastron, which is probably related to winds colliding at slightly lower speeds at that time.
Conclusions. It is the first time that such a variation has been detected in O+O systems, and the first case where the wind-wind collision is found to remain adiabatic even at periastron passage.
Made available online before print publication
High-time-resolution X-ray observations of compact objects provide direct access to strong-field gravity, to the equation of state of ultradense matter and to black hole masses and spins. A 10 m²-class instrument in combination with good spectral resolution is required to exploit the relevant diagnostics and answer two of the fundamental questions of the European Space Agency (ESA) Cosmic Vision Theme "Matter under extreme conditions", namely: does matter orbiting close to the event horizon follow the predictions of general relativity? What is the equation of state of matter in neutron stars? The Large Observatory For X-ray Timing (LOFT), selected by ESA as one of the four Cosmic Vision M3 candidate missions to undergo an assessment phase, will revolutionise the study of collapsed objects in our galaxy and of the brightest supermassive black holes in active galactic nuclei. Thanks to an innovative design and the development of large-area monolithic silicon drift detectors, the Large Area Detector (LAD) on board LOFT will achieve an effective area of ~12 m² (more than an order of magnitude larger than any spaceborne predecessor) in the 2-30 keV range (up to 50 keV in expanded mode), yet still fits a conventional platform and small/medium-class launcher. With this large area and a spectral resolution of <260 eV, LOFT will yield unprecedented information on strongly curved spacetimes and matter under extreme conditions of pressure and magnetic field strength.
This document records the scientific requirements for the Large Observatory for X-ray Timing (LOFT). These are the reference requirements through which the Mission Requirements Document will be derived.
The first issue of this document served as a starting point for an ESA-internal study in the Concurrent Design Facility (CDF). It was left unchanged for the industrial studies, but underwent a few updates driven both by the industrial studies and the payload-related studies.
In case of the selection of this mission for implementation, another update of the document may be required to reflect updates in the scientific progress during the time of the study, resulting in an Issue 2.
STE-QUEST is an M-class mission candidate for the M3 slot within the Cosmic Vision programme, for a planned launch between 2022 and 2024. STE-QUEST, with 3 other science missions, was recommended by the Space Science Advisory Committee (SSAC) to enter an assessment study (Phase 0), starting by an ESA internal study followed by parallel industrial study activities. Within the M3 boundary conditions, the readiness for launch by end 2022/2024 is a severe requirement which in practice requires designing the space segment without major technology developments and with minimum developments risks. Therefore, only technologies with estimated Technology Readiness Levels (TRL) of at least 5 by the end of the Phase A (estimated at the end of 2014) may be used.
This document aims at providing a complete and comprehensive list of all high level mission requirements (including spacecraft and payload, launcher, ground segment and operations) necessary to achieve the science goals detailed in [STE-QUEST Science Requirements Document, FPM-SA-Dc-00001]. It is hence an applicable document that shall be complied with for all mission design activities. The MRD will be further reviewed matching the results of future study phases (e.g. definition phase) to finally evolve in the System Requirements Document at the start of the implementation phase.
This is a Mission Requirements Document (MRD) to be used as an Applicable Document in the MarcoPolo-R industrial assessment study. The purpose of the MRD is to provide all high-level mission-level requirements (including spacecraft and payload, launcher, ground segment and operations) necessary to achieve the science goals detailed in [MarcoPolo-R Science Requirements Document (SRD)] for the MarcoPolo-R industrial system design studies running through 2012/2013.
It includes functional and performance requirements down to the sub-system level which can be defined at this stage. Later on in the course of the definition phase, it will result into two self-standing documents, i.e. the Mission Requirements Document and the System Requirements Document.
Recording and tracking of changes as well as giving a brief rationale is very important. The traceability of the requirements is paramount in order to make this document and its associated requirements easy to read and to understand at any stage of the mission assessment and possibly later definition phase, should this mission be selected.
This is issue 3.2 of the MRD. It has been updated after the baseline selection review in the course of the assessment phase. It will be reviewed as part of the assessment phase and will be updated following the Preliminary Requirement Review at the end of 2013.
This document aims at providing the description of the EChO reference payload complement. The payload complement comprises the following elements:
- The telescope
- The common optics, common in the sense that all alternative instrument designs must use this same set of fore-optics
- The instruments:
- The science instrument, defined as a spectrometer covering the complete wavelength range required in [EChO MRD (Mission Requirements Document), SRE-PA/2011.038/]. This wavelength range is split into different science channels.
- The Fine Guidance Sensor (FGS, acting as a non-scientific instrument), also required in [EChO MRD (Mission Requirements Document), SRE-PA/2011.038/] to answer the pointing needs of the spacecraft.
The planet-encircling springtime storm in Saturn's troposphere (December 2010-July 2011) produced dramatic perturbations to stratospheric temperatures, winds and composition at mbar pressures that persisted long after the tropospheric disturbance had abated. Thermal infrared (IR) spectroscopy from the Cassini Composite Infrared Spectrometer (CIRS), supported by ground-based IR imaging from the VISIR instrument on the Very Large Telescope and the MIRSI instrument on NASA's IRTF, is used to track the evolution of a large, hot stratospheric anticyclone between January 2011 and March 2012. The evolutionary sequence can be divided into three phases: (I) the formation and intensification of two distinct warm airmasses near 0.5 mbar between 25 and 35°N (B1 and B2) between January-April 2011, moving westward with different zonal velocities, B1 residing directly above the convective tropospheric storm head; (II) the merging of the warm airmasses to form the large single 'stratospheric beacon' near 40°N (B0) between April and June 2011, disassociated from the storm head and at a higher pressure (2 mbar) than the original beacons, a downward shift of 1.4 scale heights (approximately 85 km) post-merger; and (III) the mature phase characterised by slow cooling (0.11 ± 0.01 K/day) and longitudinal shrinkage of the anticyclone since July 2011. Peak temperatures of 221.6 ± 1.4 K at 2 mbar were measured on May 5th 2011 immediately after the merger, some 80 K warmer than the quiescent surroundings. From July 2011 to the time of writing, B0 remained as a long-lived stable stratospheric phenomenon at 2 mbar, moving west with a near-constant velocity of 2.70 ± 0.04 deg/day (-24.5 ± 0.4 m/s at 40°N relative to System III longitudes). No perturbations to visible clouds and hazes were detected during this period. [Abstract abbreviated due to character limitations.]
Published online on 2 August 2012.
While landing on Titan, several instruments onboard Huygens acquired measurements that indicate the probe did not immediately come to rest. Detailed knowledge of the probe's motion can provide insight into the nature of Titan's surface. Combining accelerometer data from the Huygens Atmospheric Structure Instrument (HASI) and the Surface Science Package (SSP) with photometry data from the Descent Imager/Spectral Radiometer (DISR) we develop a quantitative model to describe motion of the probe, and its interaction with the surface. The most likely scenario is the following. Upon impact, Huygens created a 12 cm deep hole in the surface of Titan. It bounced back, out of the hole onto the flat surface, after which it commenced a 30-40 cm long slide in the southward direction. The slide ended with the probe out of balance, tilted in the direction of DISR by around 10°. The probe then wobbled back and forth five times in the north-south direction, during which it probably encountered a 1-2 cm sized pebble. The SSP provides evidence for movement up to 10 s after impact. This scenario puts the following constraints on the physical properties of the surface ... [Abstract abbreviated due to character limitations.]
Published online on 31 July 2012.