Luciola hypertelescope space observatory: versatile, upgradable high-resolution imaging, from stars to deep-field cosmology

Luciola is a large (1 km) “multi-aperture densified-pupil imaging interferometer”, or “hypertelescope” employing many small apertures, rather than a few large ones, for obtaining direct snapshot images with a high information content. A diluted collector mirror, deployed in space as a flotilla of small mirrors, focuses a sky image which is exploited by several beam-combiner spaceships. Each contains a “pupil densifier” micro-lens array to avoid the diffractive spread and image attenuation caused by the small sub-apertures. The elucidation of hypertelescope imaging properties during the last decade has shown that many small apertures tend to be far more efficient, regarding the science yield, than a few large ones providing a comparable collecting area. For similar underlying physical reasons, radio-astronomy has also evolved in the direction of many-antenna systems such as the proposed Low Frequency Array having “hundreds of thousands of individual receivers”. With its high limiting magnitude, reaching the m _v?=?30 limit of HST when 100 collectors of 25 cm will match its collecting area, high-resolution direct imaging in multiple channels, broad spectral coverage from the 1,200 Å ultra-violet to the 20 μm infra-red, apodization, coronagraphic and spectroscopic capabilities, the proposed hypertelescope observatory addresses very broad and innovative science covering different areas of ESA’s Cosmic Vision program. In the initial phase, a focal spacecraft covering the UV to near IR spectral range of EMCCD photon-counting cameras (currently 200 to 1,000 nm), will image details on the surface of many stars, as well as their environment, including multiple stars and clusters. Spectra will be obtained for each resel. It will also image neutron star, black-hole and micro-quasar candidates, as well as active galactic nuclei, quasars, gravitational lenses, and other Cosmic Vision targets observable with the initial modest crowding limit. With subsequent upgrade missions, the spectral coverage can be extended from 120 nm to 20 μm, using four detectors carried by two to four focal spacecraft. The number of collector mirrors in the flotilla can also be increased from 12 to 100 and possibly 1,000. The imaging and spectroscopy of habitable exoplanets in the mid infra-red then becomes feasible once the collecting area reaches 6 m², using a specialized mid infra-red focal spacecraft. Calculations (Boccaletti et al., Icarus 145, 628–636, 2000) have shown that hypertelescope coronagraphy has unequalled sensitivity for detecting, at mid infra-red wavelengths, faint exoplanets within the exo-zodiacal glare. Later upgrades will enable the more difficult imaging and spectroscopy of these faint objects at visible wavelengths, using refined techniques of adaptive coronagraphy (Labeyrie and Le Coroller 2004). Together, the infra-red and visible spectral data carry rich information on the possible presence of life. The close environment of the central black-hole in the Milky Way will be imageable with unprecedented detail in the near infra-red. Cosmological imaging of remote galaxies at the limit of the known universe is also expected, from the ultra-violet to the near infra-red, following the first upgrade, and with greatly increasing sensitivity through successive upgrades. These areas will indeed greatly benefit from the upgrades, in terms of dynamic range, limiting complexity of the objects to be imaged, size of the elementary “Direct Imaging Field”, and limiting magnitude, approaching that of an 8-m space telescope when 1,000 apertures of 25 cm are installed. Similar gains will occur for addressing fundamental problems in physics and cosmology, particularly when observing neutron stars and black holes, single or binary, including the giant black holes, with accretion disks and jets, in active galactic nuclei beyond the Milky Way. Gravitational lensing and micro-lensing patterns, including time-variable patterns and perhaps millisecond lensing flashes which may be beamed by diffraction from sub-stellar masses at sub-parsec distances (Labeyrie, Astron Astrophys 284, 689, 1994), will also be observable initially in the favourable cases, and upgrades will greatly improve the number of observable objects. The observability of gravitational waves emitted by binary lensing masses, in the form of modulated lensing patterns, is a debated issue (Ragazzoni et al., MNRAS 345, 100–110, 2003) but will also become addressable observationally. The technology readiness of Luciola approaches levels where low-orbit testing and stepwise implementation will become feasible in the 2015–2025 time frame. For the following decades beyond 2020, once accurate formation flying techniques will be mastered, much larger hypertelescopes such as the proposed 100 km Exo-Earth Imager and the 100,000 km Neutron Star Imager should also become feasible. Luciola is therefore also seen as a precursor toward such very powerful instruments.     

Quark-nova remnants: application to RRATs

This is the third paper of a series of papers where we explore the evolution of iron-rich ejecta from quark-novae. In the first paper, we explored the case where a quark-nova ejecta forms a degenerate shell, supported by the star's magnetic field, with applications to SGRs. In the second paper, we considered the case where the ejecta would have sufficient angular momentum to form a degenerate Keplerian torus and applied such a system to two AXPs, namely 1E2259+586 and 4U0142+615. Here, we explore the late evolution of the degenerate torus and find that it can remain unchanged for  ∼10⁶ yr  before it becomes non-degenerate. This transition from a degenerate torus (accretion-dominated) to a non-degenerate disc (no accretion) occurs about 10⁶ yr following the quark-nova, and exhibits features that are reminiscent of observed properties of Rotation RAdio Transients (RRATs). Using this model, we can account for the duration of both the radio bursts and the quiet phase, as well as the observed radio flux from RRATs. We discuss a connection between XDINs and RRATs and argue that some XDINs may be 'dead RRATs' that have already consumed their non-degenerate disc.     

Late Pleistocene stratigraphy and sedimentary environments of the Severnaya Dvina‐Vychegda region in northwestern Russia

The Late Pleistocene stratigraphy from the Severnaya Dvina‐Vychegda region of northwestern Russia is revised based on investigations of new localities, revisiting earlier localities, introduction of about 110 new OSL dates and burial depth corrections of earlier published OSL dates, in addition to six new radiocarbon dates. Most of the OSL samples studied here are from fluvial and subaquaeous sediments, which we found to be well bleached. Six chronostratigraphical units and their sedimentary environment are described, with the oldest unit consisting of pre‐Eemian glacial beds. For the first time, Early Weichselian sediments are documented from the region and a fluvial environment with some vegetation and permafrost conditions is suggested to have persisted from the end of the Eemian until at least about 92 ka ago. The period in which a Middle Weichselian White Sea Lake could have existed is constrained to 67?62 ka, but as the lake level never reached the thresholds of the drainage basin, the lake probably existed only for a short interval within this time‐span. Blocking and reversal of fluvial drainage started again around 21?20 ka ago when the Fennoscandian Ice Sheet advanced into the area, reaching its maximum 17?15 ka ago. At that time, an ice‐dammed lake reached its maximum water level, which was around 135 m above present sea level. Drainage of the lake started shortly after 15 ka ago, and the lake was emptied within 700 years. Severe periglacial conditions, with permafrost and aeolian activity, prevailed in the area until about 10.7 ka.     

Multiwavelength focusing with the Sun as gravitational lens

The light deviation caused by the gravitational potential in the vicinity of the sun could be used as a means of focussing radiation that cannot be focussed easily otherwise. The gravitational lens formed by the sun is not stigmatic, but does have the advantage of being achromatic and acts identically on all types of mass-less radiations. For a source at infinity, its geometrical characteristics present a “caustic” line starting at 550 astronomical units (UA) downstream from the sun. In a plane perpendicular to that caustic line, images of distant objects are formed.The perturbations by the solar corona plasma will significantly blur electromagnetic radiation for wavelengths longer than those of the IR domain. At shorter wavelengths, for example the γ domain, the focussing process could lead to 10⁸ amplification factors. In order to reach the regions where images are formed, long distance space missions are necessary. Once launched, missions of this type would be dedicated to a single field. Some possible targets are considered, such as Sagitarius A observed in X and γ rays.In this paper we study the point spread function (PSF) of the sun as a gravitational lens. Taking into account perturbations by the planets, the non sphericity of the sun and coronal plasma index, we derive limits within which such observations could be possible.     

Plio-Pleistocene mammals from Mille-Logya,Ethiopia, and the post-Hadar faunal change

We describe the non-primate mammalian fauna from the late Pliocene to earliest Pleistocene deposits of Mille-Logya in the Lower Awash Valley, Ethiopia, dated to c. 2.9–2.4 Ma, and divided into three successive units: Gafura, Seraitu, and Uraitele. We identify 41 mammalian taxa (including rodents), the most diverse group being the Bovidae, with 17 taxa. While the Gafura assemblage still resembles those from the earlier Hadar Formation, the younger Seraitu assemblage documents a major turnover. While there is little change in the species present across this interval, the relative abundances of various taxa change dramatically, with suids being largely replaced by open-country bovids (Alcelaphini and Antilopini). We interpret this faunal change as reflective of an environmental shift, contemporaneous with the replacement of Australopithecus afarensis by Homo in the area.     

Predicting seiche hazard for coastal harbours along the northern and western coasts of France

Natural Hazards - Long-period waves propagating inside harbours can lead to the generation of seiche that can affect and significantly disrupt port operations. This study is based on the analysis...     

Integration of multiple soft data sets in MPS thru multinomial logistic regression: a case study of gas hydrates

A new approach is described to allow conditioning to both hard data (HD) and soft data for a patch- and distance-based multiple-point geostatistical simulation. The multinomial logistic regression is used to quantify the link between HD and soft data. The soft data is converted by the logistic regression classifier into as many probability fields as there are categories. The local category proportions are used and compared to the average category probabilities within the patch. The conditioning to HD is obtained using alternative training images and by imposing large relative weights to HD. The conditioning to soft data is obtained by measuring the probability–proportion patch distance. Both 2D and 3D cases are considered. Synthetic cases show that a stationary TI can generate non-stationary realizations reproducing the HD, keeping the texture indicated by the TI and following the trends identified in probability maps obtained from soft data. A real case study, the Mallik methane-hydrate field, shows perfect reproduction of HD while keeping a good reproduction of the TI texture and probability trends.     

Estimating the phase of the response of the Earth to long-period geomagnetic fluctuations

Samples collected by the deep submersible “Alvin” from four hot spring fields (T = 3–13°C) on the crest of the Galapagos spreading ridge show pronounced and varied compositional anomalies. If it is assumed that these have a general significance, that they are associated with hydrothermal reactions between seawater and basalt wherever new oceanic crust is being produced then global fluxes can be computed. These are large. For Mg and SO₄ they balance the river input. For Li and Rb they exceed it by factors of between five and ten. Calcium is supplied at a rate equivalent to that of non-carbonate Ca from the continents. The additions of K, Ba and Si are between one third and two thirds of the river load. There are large positive and negative anomalies for Cl and Na indicating that substantial amounts of Cl may be taken up by the newly formed crust and transported deep into the subduction zones.Where there are data in common, the field measurements agree with the experimental findings at low (<5) water/rock ratios.     

Noncyclic variation andS q harmonic dials

Summary A method is presented for the determination of noncyclic variation in geomagnetic hourly mean values, which employs only 24 hourly values or 12 bihourly values, etc. The manner in which the method bears on the ellipticity of distributions of points onS _q harmonic dials is discussed. A review of other available methods is also included.