ESA Science & Technology - Publication Archive

Water is a crucial molecule in molecular astrophysics as it controls much of the gas/grain chemistry, including the formation and evolution of more complex organic molecules in ices. Pre-stellar cores provide the original reservoir of material from which future planetary systems are built, but few observational constraints exist on the formation of water and its partitioning between gas and ice in the densest cores. Thanks to the high sensitivity of the Herschel Space Observatory, we report on the first detection of water vapor at high spectral resolution toward a dense cloud on the verge of star formation, the pre-stellar core L1544. The line shows an inverse P-Cygni profile, characteristic of gravitational contraction. To reproduce the observations, water vapor has to be present in the cold and dense central few thousand AU of L1544, where species heavier than helium are expected to freeze out onto dust grains, and the ortho:para H₂ ratio has to be around 1:1 or larger. The observed amount of water vapor within the core (about 1.5 × 10^-6 M) can be maintained by far-UV photons locally produced by the impact of galactic cosmic rays with H₂ molecules. Such FUV photons irradiate the icy mantles, liberating water vapor in the core center. Our Herschel data, combined with radiative transfer and chemical/dynamical models, shed light on the interplay between gas and solids in dense interstellar clouds and provide the first measurement of the water vapor abundance profile across the parent cloud of a future solar-type star and its potential planetary system.

Context. A population of obscured supergiant high mass X-ray binaries has been discovered by INTEGRAL. X-ray wind tomography of IGR J17252-3616 inferred a slow wind velocity to account for the enhanced obscuration.
Aims. The main goal of this study is to understand under which conditions high obscuration could occur.
Methods. We have used an hydrodynamical code to simulate the flow of the stellar wind around the neutron star. A grid of simulations was used to study the dependency of the absorbing column density and of the X-ray light-curves on the model parameters. A comparison between the simulation results and the observations of IGR J17252-3616 provides an estimate on these parameters.
Results. We have constrained the wind terminal velocity to 500-600 km/s and the neutron star mass to 1.75-2.15 M_Sun.
Conclusions. We have confirmed that the initial hypothesis of a slow wind velocity with a moderate mass loss rate is valid. The mass of the neutron star can be constrained by studying its impact on the accretion flow.

It is assumed that the radioactive decay of ⁴⁴Ti powers the infrared, optical and UV emission of a supernova remnant since the complete decay of ⁵⁶Co and ⁵⁷Co (3-4 years after the explosion) until the beginning of active interaction of the ejecta with the surrounding matter. Simulations show that ⁴⁴Ti is synthesized in an amount of M₄₄ ~ (0.02-2.5)×10^-4 M_Sun in core-collapse supernovae. Hard X/gamma-rays from this decay have been unambiguously observed from Cassiopeia A only, leading to the suggestion that the high values of M₄₄ occur in exceptional cases. For the Supernova 1987A remnant, an upper limit M₄₄ <= 10^-3 M_Sun was obtained from direct X-ray observations12, and an estimation M₄₄ ~ (1-2)×10^-4 M_Sun - from infrared light-curves and UV spectra by complex model dependent computations. Here we report observations of hard X-rays from SNR 1987A in the narrow band containing two direct-escape lines of ⁴⁴Ti at 67.9 and 78.4 keV. The measured line fluxes imply sufficient energy to power the remnant at late times. An initial mass of ⁴⁴Ti was estimated to be (3.1 +/- 0.8)×10^-4 M_Sun, which is near the upper bound of theoretical predictions.

The history of astrometry, the branch of astronomy dealing with the positions of celestial objects, is a lengthy and complex chronicle, having its origins in the earliest records of astronomical observations more than two thousand years ago, and extending to the high accuracy observations being made from space today. Improved star positions progressively opened up and advanced fundamental fields of scientific enquiry, including our understanding of the scale of the solar system, the details of the Earth's motion through space, and the comprehension and acceptance of Newtonianism. They also proved crucial to the practical task of maritime navigation. Over the past 400 years, during which positional accuracy has improved roughly logarithmically with time, the distances to the nearest stars were triangulated, making use of the extended measurement baseline given by the Earth's orbit around the Sun. This led to quantifying the extravagantly vast scale of the Universe, to a determination of the physical properties of stars, and to the resulting characterisation of the structure, dynamics and origin of our Galaxy. After a period in the middle years of the twentieth century in which accuracy improvements were greatly hampered by the perturbing effects of the Earth's atmosphere, ultra-high accuracies of star positions from space platforms have led to a renewed advance in this fundamental science over the past few years.

The vertical structure of the nightside ionosphere of Mars and its dependence on solar zenith angle are currently poorly determined, as is the importance of two key sources of nightside plasma, electron precipitation and transport of dayside plasma. We examined 37 electron density profiles of the ionosphere of Mars at solar zenith angles of 101-123 degrees obtained by the Mars Express Radio Science Experiment MaRS between 18 August and 1 October 2005. In general, solar activity was low during this period, although several solar energetic particle events did occur. The results show: i) trends in peak electron density and altitude with solar zenith angle are consistent with transport of dayside plasma as an important plasma source up to 115 degrees, but not higher; ii) peak altitudes of around 150 km observed at larger (>115 degrees) solar zenith angles are consistent with simulated plasma production by electron precipitation; iii) peak altitudes observed during solar energetic particle events are at 90 km, consistent with accepted models. Solar energetic particle events can be the main source of nightside plasma. These results challenge current models of the nightside ionosphere, including their implications for plasma sources. The total electron content is correlated with peak electron density, requiring explanation. Due to the geographical distribution of this dataset (latitudes poleward of 38N), we do not explore the influence of crustal field strength and direction on the nightside ionosphere.

Reference: SRE-PA/2011.088/

This Payload Definition Document describes the consolidated instrument designs of the Large Area Detector (LAD) and the Wide Field Monitor (WFM) proposed for LOFT. The current issue (2.0) describes the status of the instruments at the time of the Mid-Term Review (MTR) of the LOFT mission study phase.

Published online 02 October 2012

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.

Between July 2005 and July 2011 Mars Express performed 50 Deimos approaches. 136 super resolution channel (SRC) images were acquired and used for astrometric (positional) measurements of the small Martian satellite. For this study, we have developed a new technique, in which the center-of-figure of the odd-shaped Deimos is determined by fitting the predicted to the observed satellite limb. The prediction of the limb was made based on the moon's known shape model. The camera pointing was verified and corrected for by means of background star observations. We obtained a set of spacecraft-centered Deimos coordinates with accuracies between 0.6 and 3.6 km (1Ã). Comparisons with current orbit models indicate that Deimos is ahead of or falling behind its predicted position along its track by as much as +3.4 km or -4.7 km, respectively, depending on the chosen model. Our data may be used to improve the orbit models of the satellite.

Reference: SRE-SA/LOFT/2011-001

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.

This document describes the detailed scientific requirements for the MarcoPolo-R mission. These requirements are derived from discussions by the MarcoPolo-R Science Study Team (SST) and are based on the scientific objectives as described in the MarcoPolo-R Proposal to ESA's Cosmic Vision programme.

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.

Reference: SRE-PA/2011.074/RQ/MG

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.

By examining electron density profiles from the Mars Express Radio Science Experiment MaRS, we show that the vertical structure of the dayside ionosphere of Mars is more variable and more complex than previously thought. The top of the ionosphere can be below 250 km (25% occurrence rate) or above 650 km (1%); the topside ionosphere can be well-described by a single scale height (10%) or two/three regions with distinct scale heights (25% or 10%), where those scale heights range between tens and hundreds of kilometers; the main layer of the ionosphere can have a sharply pointed (5%), flat-topped (6%), or wavy (8%) shape, in contrast to its usual Chapman-like shape; a broad increase in electron density is detected at 160-180 km (10%); a narrow increase in electron density is sometimes found in strongly-magnetized regions; and an additional layer is present between the M1 and M2 layers (3%).

Reference: SRE-PA/2011.076/MarcoPolo-R

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.

Reference: SRE-PA/2011.039/

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.

It is also important to highlight that not all elements of this payload complement are applicable to all partners: specificities are foreseen with each partner, i.e. industry and instrument team(s) will have different responsibilities.

During the first half of the universe's life, a heyday of star formation must have occurred because many massive galaxies are in place after that epoch in cosmic history. Our observations with the revolutionary Herschel Space Observatory reveal vigorous optically obscured star formation in the ultra-massive hosts of many powerful high-redshift 3C quasars and radio galaxies. This symbiotic occurrence of star formation and black hole driven activity is in marked contrast to recent results dealing with Herschel observations of X-ray-selected active galaxies. Three archetypal radio galaxies at redshifts 1.132, 1.575, and 2.474 are presented here, with inferred star formation rates of hundreds of solar masses per year. A series of spectacular coeval active galactic nucleus/starburst events may have formed these ultra-massive galaxies and their massive central black holes during their relatively short lifetimes.

Available online 31 August 2012

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.]

The Large-Yield Radiometer (LYRA) is a radiometer that has monitored the solar irradiance at high cadence and in four pass bands since January 2010. Both the instrument and its spacecraft, PROBA2 (Project for OnBoard Autonomy), have several innovative features for space instrumentation, which makes the data reduction necessary to retrieve the long-term variations of solar irradiance more complex than for a fully optimized solar physics mission. In this paper, we describe how we compute the long-term time series of the two extreme ultraviolet irradiance channels of LYRA and compare the results with those of SDO/EVE. We find that the solar EUV irradiance has increased by a factor of 2 since the last solar minimum (between solar cycles 23 and 24), which agrees reasonably well with the EVE observations.

We report the first in situ observation of high-latitude magnetopause (near the northern duskward cusp) Kelvin-Helmholtz waves (KHW) by Cluster on January 12, 2003, under strongly dawnward interplanetary magnetic field (IMF) conditions. The fluctuations unstable to Kelvin-Helmholtz instability (KHI) are found to propagate mostly tailward, i.e., along the direction almost 90° to both the magnetosheath and geomagnetic fields, which lowers the threshold of the KHI. The magnetic configuration across the boundary layer near the northern duskward cusp region during dawnward IMF is similar to that in the low-latitude boundary layer under northward IMF, in that (1) both magnetosheath and magnetospheric fields across the local boundary layer constitute the lowest magnetic shear and (2) the tailward propagation of the KHW is perpendicular to both fields. Approximately 3-hour-long periods of the KHW during dawnward IMF are followed by the rapid expansion of the dayside magnetosphere associated with the passage of an IMF discontinuity that characterizes an abrupt change in IMF cone angle, phi = acos B x B , from -90° to -10°. Cluster, which was on its outbound trajectory, continued observing the boundary waves at the northern evening-side magnetopause during sunward IMF conditions following the passage of the IMF discontinuity. By comparing the signatures of boundary fluctuations before and after the IMF discontinuity, we report that the frequencies of the most unstable KH modes increased after the discontinuity passed. This result demonstrates that differences in IMF orientations (especially in phi) are associated with the properties of KHW at the high-latitude magnetopause due to variations in thickness of the boundary layer, and/or width of the KH-unstable band on the surface of the dayside magnetopause.

Supermassive black holes (SMBHs; mass is greater than or approximately 10⁵ times that of the Sun) are known to exist at the center of most galaxies with sufficient stellar mass. In the local universe, it is possible to infer their properties from the surrounding stars or gas. However, at high redshifts we require active, continuous accretion to infer the presence of the SMBHs, which often comes in the form of long-term accretion in active galactic nuclei. SMBHs can also capture and tidally disrupt stars orbiting nearby, resulting in bright flares from otherwise quiescent black holes. Here, we report on a ~200-second x-ray quasi-periodicity around a previously dormant SMBH located in the center of a galaxy at redshift z = 0.3534. This result may open the possibility of probing general relativity beyond our local universe.
Published online on 2 August 2012.