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Active Correction of Aperture Discontinuities-Optimized Stroke Minimization. I. A New Adaptive Interaction Matrix Algorithm
No full textInternational audienceFuture searches for bio-markers on habitable exoplanets will rely on telescope instruments that achieve extremely high contrast at small planet-to-star angular separations. Coronagraphy is a promising starlight suppression technique, providing excellent contrast and throughput for off-axis sources on clear apertures. However, the complexity of space- and ground-based telescope apertures goes on increasing over time, owing to the combination of primary mirror segmentation, the secondary mirror, and its support structures. These discontinuities in the telescope aperture limit the coronagraph performance. In this paper, we present ACAD-OSM, a novel active method to correct for the diffractive effects of aperture discontinuities in the final image plane of a coronagraph. Active methods use one or several deformable mirrors that are controlled with an interaction matrix to correct for the aberrations in the pupil. However, they are often limited by the amount of aberrations introduced by aperture discontinuities. This algorithm relies on the recalibration of the interaction matrix during the correction process to overcome this limitation. We first describe the ACAD-OSM technique and compare it to the previous active methods for the correction of aperture discontinuities. We then show its performance in terms of contrast and off-axis throughput for static aperture discontinuities (segmentation, struts) and for some aberrations evolving over the life of the instrument (residual phase aberrations, artifacts in the aperture, misalignments in the coronagraph design). This technique can now obtain the Earth-like planet detection threshold of 10^10 contrast on any given aperture over at least a 10% spectral bandwidth, with several coronagraph designs
Morpho-molecular diversity and evolutionary analyses suggest hidden life styles in Spumellaria (Radiolaria)
No full textAbstract Spumellaria (Radiolaria, Rhizaria) are holoplanktonic amoeboid protists, ubiquitous and abundant in the global ocean. Their silicified skeleton preserves very well in sediments displaying an excellent fossil record, from the early middle Cambrian (ca. 509-521 Ma), extremely valuable for paleo-environmental reconstruction studies. Spumellaria are tedious to maintain in laboratory conditions preventing an accurate perception of their extant diversity and ecology in today’s oceans, most of which being inferred from sediment records. This study represents an integrated and comprehensive classification of Spumellaria based on the combination of ribosomal taxonomic marker genes (rDNA) and morphological characteristics. In contrast to established taxonomic knowledge, we demonstrate that symmetry of the skeleton takes more importance than internal structures at high taxonomic rank classification. Such reconsideration allows gathering different morphologies with concentric structure and a spherical or radial symmetry believed to belong to other Radiolaria orders from the fossil record, as for some Entactinaria families. Results obtained in this study suggest the existence of new Spumellaria diversity at early diverging positions, in which a non-bearing skeleton organism lives within shelled ones. Using fossil calibrated molecular clock we estimated the origin of Spumellaria in the middle Cambrian (ca. 515 Ma), in agreement with the appearance of the first radiolarian representatives in the fossil record. The morpho-molecular and evolutionary framework established herein allows a direct connection between living specimens and fossil morphologies from the Cambrian, bringing both a standpoint for future molecular environmental surveys and a better understanding for paleo-environmental reconstruction studies
Peeling at extreme black hole horizons
No full text33 pages, 3 figuresInternational audienceThe starting point of this work was an intriguing similarity between the behaviour of fields near a degenerate horizon and near the infinity of an asymptotically flat spacetime, as revealed by the scattering theory for Dirac fields in the ``exterior'' region of the extreme Kerr - de Sitter black hole, developed by one of the authors (JB). However, in that situation, the comparison was somewhat clouded by some of the analytical techniques used in intermediate steps of the proof. The aim of the present work is to clarify the comparison further by studying instead the peeling behaviour of solutions to the wave equation at an extremal horizon. We focus first on the extreme Reissner-Nordstr\"om black hole, for which the Couch-Torrence inversion (a global conformal isometry that exchanges the horizon and infinity) makes the analogy explicit. Then, we explore more general spherically symmetric situations using the Couch-Torrence inversion outside of its natural context
Impact of dust and temperature on primary productivity in Late Miocene oceans
No full textInternational audienceMost of the primary productivity in the ocean comes from phytoplankton, and is impacted, among other things, by the amount of nutrients available, as well as by temperature. The Late Miocene and Pliocene were marked by global aridification, linked to the emergence of the large deserts, likely increasing the input of dust and thus nutrients into the ocean. There was also a global decrease in temperature during this period, linked to a decline in atmospheric CO2 concentration. The objective of this study is to explore the sensitivity to dust and pCO2 levels on primary productivity in the oceans under Late Miocene boundary conditions. Here we used simulations performed with the coupled ocean-atmosphere model IPSL-CM5A2 and its marine biogeochemistry component PISCES and a Late Miocene paleogeography. Our results show that an increase in dust input produces a quasi-generalized increase in primary productivity, associated with a decrease in nutrient limitation. This increase in productivity also leads to nutrient deficits in some areas, such as coastlines and the Eastern Equatorial Pacific. The decrease in pCO2 levels and the associated lower water temperatures lead to a reduction in primary productivity. This decrease is mainly due to a reduction in the supply of nutrients resulting from less intense remineralization. In addition, our results show that change in carbon export resulting from change in dust input and temperature are highly heterogeneous spatially. Simulations combined with sedimentary data suggesting a link between aridification, cooling and the Biogenic Bloom of the Late Miocene and Pliocene
Network-based analysis of seismo-volcanic tremors
No full textInternational audienceVolcanic tremors represent one of the most important class of seismo-volcanic signals due to their abundant presence in seismic records, their wealth of information regarding magmatic systems, their use as a tool for monitoring the state of volcanoes and their potential as precursor signals to eruptions. These signals have been analyzed for several decades with single station approaches, from which empirical inferences can be made regarding their sources, generation mechanism and scaling relations with eruptions parameters. Modernisation and densification of instrumentation networks coupled with sophistication of analysis methods and enhanced computation capacities, allow to switch from single-station to full seismic network based methods. We introduce in this chapter the interstation cross-correlations methods, the estimation of the network covariance matrix and the study of its eigenvalues and eigenvectors. Such advanced methods enable to measure temporal, spatial and spectral tremor properties. They are contained in the CovSeisNet Python package which has been used for characterizing various tremor episodes, including two examples from Kilauea volcano, Hawaii and Klyuchevskoy Volcanic Group, Kamchatka presented in this chapter. These application examples illustrate the complexity of tremors and emphasize the need to continue the development of new algorithms aimed at the exploration of network covariances to better constrain the different tremor generation processes that can be multiple, simultaneous and interacting. In particular, the combination of network-based analysis with polarization and machine learning approaches may represent a new step in our understanding of the underlying phenomena. In turn, this enhanced discernment of the involved processes and the links with the properties of the volcanic system can lead to a more effective monitoring and ultimately a better apprehension of volcanic system destabilizations and anticipation of the associated unrests
Are isolated compact galaxy groups special?
No full textInternational audienceIt is often believed that isolated, compact groups of galaxies (CGs) are special systems. But CGs have rarely been compared to regular groups, which are selected very differently. We study the global properties of a subsample of 80 groups of four members (CG4s), as well as their correlations, within the HMCG Hickson-like sample of compact groups, and compare them with those of the regular groups of Lim et al.. The latter are split into three control samples, complete in redshift and magnitude: one with the four brightest members, one with the four closest members to the brightest group galaxy (BGG) with less than three magnitudes in range (Control4Cs), and one with exactly four members (RG4s). The vast majority of CG4s are located within regular groups, and a large preponderance of the BGGs of these CG4s are the same as those of their host groups. CG4s are smaller than the groups of all other samples and more luminous than RG4s, both results as expected from their selection as high surface brightness systems. However, CG4s have similar luminosities as Control4Cs. CG4s also have higher velocity dispersions, probably because of a too permissive redshift accordance criterion. The BGGs of CG4s are not more dominant in luminosity than those of RG4s, but they are significantly more offset relative to the group size, because the Lim groups are built around their BGGs. In summary, compact groups have similar properties to the regular groups of four galaxies and to the cores of regular groups, once selection criteria of CGs are considered. A large fraction of CGs are the cores of regular groups, isolated on the sky by construction, but rarely isolated in real space (from simulations), indicating that they are often plagued by chance alignments of host groups galaxies along the line of sight
Euclid preparation. The Cosmic Dawn Survey (DAWN) of the Euclid Deep and Auxiliary Fields
No full textInternational audienceEuclid will provide deep NIR imaging to 26.5 AB magnitude over 59 deg in its deep and auxiliary fields. The Cosmic DAWN survey complements the deep Euclid data with matched depth multiwavelength imaging and spectroscopy in the UV--IR to provide consistently processed Euclid selected photometric catalogs, accurate photometric redshifts, and measurements of galaxy properties to a redshift of . In this paper, we present an overview of the survey, including the footprints of the survey fields, the existing and planned observations, and the primary science goals for the combined data set
VIGIMONT project: towards landslide Early warning System
No full textInternational audienceThe general objective of VIGIMONT is to develop a new service within two existing early warning platforms, by adding modules dedicated to real-time debris-flow and landslide dynamic vigilance for safety authorities in mountain areas. Indeed, with the deployment of meteorological radars, the occurrence of debris flows and landslides induced by meteorological events will be analysed, based on antecedent precipitations quantification and event rainfalls definition. It will permit to determine critical rainfall thresholds for events occurrences, allowing events detection and mapping. A multi-scale approach is proposed by considering both the regional and the local (municipality) scales, with the development of services for end-users acting at these two scales. Phenomena addressed here are focussed on some typologies of movements: it concerns shallow landslides, deep seated landslides and debris flows
Global climate modelling of Saturn’s atmosphere, Part V: Large-scale vortices
No full textInternational audienceThis paper presents an analysis of large-scale vortices in the atmospheres of gas giants, focusing on a detailed study conducted using the Saturn-DYNAMICO global climate model (GCM). Large-scale vortices, a prominent feature of gas giant atmospheres, play a critical role in their atmospheric dynamics. By employing three distinct methods-manual detection, machine learning via artificial neural networks (ANN), and dynamical detection using the Automated Eddy-Detection Algorithm (AMEDA)-we characterize the spatial, temporal, and dynamical properties of these vortices within the Saturn-DYNAMICO GCM. Our findings reveal a consistent production of vortices due to well-resolved eddy-to-mean flow interactions, exhibiting size and intensity distributions broadly in agreement with observational data. However, notable differences in vortex location, size, and concentration highlight the model's limitations and suggest areas for further refinement. The analysis underscores the</div
Euclid preparation LXI. Cosmic Dawn Survey: ‘Pre-launch’ multiwavelength catalogues for Euclid Deep Field North and Euclid Deep Field Fornax
No full textInternational audienceThe Cosmic Dawn Survey (DAWN survey) provides multiwavelength (UV/optical to mid-IR) data across the combined 59 deg of the Euclid Deep and Auxiliary fields (EDFs and EAFs). Here, the first public data release (DR1) from the DAWN survey is presented. DR1 catalogues are made available for a subset of the full DAWN survey that consists of two Euclid Deep fields: Euclid Deep Field North (EDF-N) and Euclid Deep Field Fornax (EDF-F). The DAWN survey DR1 catalogues do not include data as they are not yet public for these fields. Nonetheless, each field has been covered by the ongoing Hawaii Twenty Square Degree Survey (H20), which includes imaging from CFHT MegaCam in the new filter and from Subaru Hyper Suprime-Cam (HSC) in the filters. Each field is further covered by /IRAC 3.6-4.5m imaging spanning 10 deg and reaching 25 mag AB (5). All present H20 imaging and all publicly available imaging from the aforementioned facilities are combined with the deep /IRAC data to create source catalogues spanning a total area of 16.87 deg in EDF-N and 2.85 deg in EDF-F for this first release. Photometry is measured using The Farmer, a well-validated model-based photometry code. Photometric redshifts and stellar masses are computed using two independent codes for modeling spectral energy distributions: EAZY and LePhare. Photometric redshifts show good agreement with spectroscopic redshifts (\sigma_{\rm NMAD} \sim 0.5, \eta < 8\% at i < 25). Number counts, photometric redshifts, and stellar masses are further validated in comparison to the COSMOS2020 catalogue. The DAWN survey DR1 catalogues are designed to be of immediate use in these two EDFs and will be continuously updated. Future data releases will provide catalogues of all EDFs and EAFs and include data