Calibration of quasi-static aberrations in exoplanet direct-imaging instruments with a Zernike phase-mask sensor

Context. Several exoplanet direct imaging instruments will soon be in operation. They use an extreme adaptive optics (XAO) system to correct the atmospheric turbulence and provide a highly-corrected beam to a near-infrared (NIR) coronagraph for starlight suppression. The performance of the coronagraph is however limited by the non-common path aberrations (NCPA) due to the differential wavefront errors existing between the visible XAO sensing path and the NIR science path, leading to residual speckles in the coronagraphic image. Aims. Several approaches have been developed in the past few years to accurately calibrate the NCPA, correct the quasi-static speckles and allow the observation of exoplanets at least 1e6 fainter than their host star. We propose an approach based on the Zernike phase-contrast method for the measurements of the NCPA between the optical path seen by the visible XAO wavefront sensor and that seen by the near-IR coronagraph. Methods. This approach uses a focal plane phase mask of size {\lambda}/D, where {\lambda} and D denote the wavelength and the telescope aperture diameter, respectively, to measure the quasi-static aberrations in the upstream pupil plane by encoding them into intensity variations in the downstream pupil image. We develop a rigorous formalism, leading to highly accurate measurement of the NCPA, in a quasi-linear way during the observation. Results. For a static phase map of standard deviation 44 nm rms at {\lambda} = 1.625 {\mu}m (0.026 {\lambda}), we estimate a possible reduction of the chromatic NCPA by a factor ranging from 3 to 10 in the presence of AO residuals compared with the expected performance of a typical current-generation system. This would allow a reduction of the level of quasi-static speckles in the detected images by a factor 10 to 100 hence, correspondingly improving the capacity to observe exoplanets.Comment: 11 pages, 14 figures, A&A accepted, 2nd version after language-editor correction

Strategies D’adaptation Des Agropasteurs Aux Changementsclimatiques Dans La Commune Rurale De Diema (Mali)

La désertification et la dégradation des ressources naturelles induites par les changements climatiques pourraient exacerber l’insécurité alimentaire au Mali, en particulier dans les zones fragiles qui sont en déficit pluviométrique. C’est dans le but de contribuer à la résilience des agropasteurs face aux effets néfastes des changements climatiques que cette étude a été réalisée. Pour atteindre cet objectif, des enquêtes ménages ont été conduites au niveau de huit (8) villages de la commune rurale de Diéma par l’intermédiaire des fiches d’enquêtes individuelles auprès de 188 agropasteurs, des focus group dans chaque village et des entretiens avec les personnes ressources opérant dans la zone d’étude. Les données d’enquêtes ont été traitées à l’aide du logiciel SPSS (Statistical Package on Social Science) et du tableur Excel. Les résultats ont montré que les risques climatiques majeurs identifiés sont : la sécheresse, l’inondation, le déficit pluviométrique, les vents violents, la hausse des températures et la vague de chaleur avec respectivement les indice d’impact de 39, 35, 34, 24, 22, 21. Différentes stratégies ont été développées aussi bien par le passé que de nos jours pour faire face à ces risques climatiques. Ces stratégies comprennent le déstockage stratégique et la mobilité selon 40,4 % des enquêtés ; la conservation des fourrages selon 21.3 % des enquêtés et l’organisation de la pâture nocturne et la diversification des activités (le maraîchage, le petit commerce) selon 36,7 % des enquêtés. Mais elles demeurent moins efficaces. Pour aider les agropasteurs à se prémunir davantage des effets néfastes des changements climatiques, des options d’adaptation sont envisageables notamment la sécurisation de la mobilité pastorale, l’adoption des races résistantes à la sécheresse et la promotion des cultures fourragères.   Desertification and the degradation of natural resources induced by climate change could exacerbate food insecurity in Mali, particularly in fragile areas which are in deficit in rainfall. It is with the aim of contributing to the resilience of agro-pastoralists in the face of the adverse effects of climate change that this study was carried out. To achieve this objective, household surveys were conducted in eight (8) villages of the rural municipality of Diéma through individual survey sheets with 188 agro-pastoralists, focus groups in each village and interviews with resource persons operating in the study area. Survey data were processed using Statistical Package on Social Science (SPSS) software and an Excel spreadsheet. The results showed that the major climatic risks identified are: drought, flooding, rainfall deficit, strong winds, temperature rise and heat wave with respectively impact indexes of 39, 35, 34, 24, 22, 21. Different strategies have been developed both in the past and nowadays to deal with these climatic risks. These strategies include strategic destocking and mobility according to 40.4% of respondents; conservation of fodder according to 21.3% of respondents and organization of night grazing and diversification of activities (market gardening, petty trading) according to 36.7% of respondents. But they remain less effective. To help agro-pastoralists to protect themselves more from the harmful effects of climate change, adaptation options can be envisaged, in particular securing pastoral mobility, the adoption of drought-resistant breeds and the promotion of fodder crops

Les accidents de cyclomoteurs: mécanismes lésionnels et aspects anatomo-cliniques

Le but de notre étude est de décrire les mécanismes lésionnels et les aspects anatomo-cliniques des  traumatismes par accident de cyclomoteur. C'est une étude transversale menée au niveau du Centre  Hospitalier Régional de Kaffrine sur une période de 12 mois. Elle portait sur les patients admis au service d'accueil pour accident de la voie publique impliquant un cyclomoteur. Il s'agissait de 129 patients (112  hommes et de 17 femmes). L'âge moyen était de 30,5 ans. Soixante-treize patients étaient conducteurs de cyclomoteur, 31 piétons et 25 passagers arrière. Le mécanisme le plus fréquent était une chute de moto. Les lésions prédominaient au niveau des membres. Les accidents de cyclomoteur sont un problème de santé publique.Key words: Cyclomoteur, lésion, mécanisme, cliniqu

Biological control of the millet head miner Heliocheilus albipunctella in the Sahelian region by augmentative releases of the parasitoid wasp Habrobracon hebetor: effectiveness and farmers’ perceptions

On-farm augmentative releases of the parasitoid Habrobracon hebetor (Say) for controlling the millet head miner (MHM) Heliocheilus albipunctella (de Joannis) were tested in Burkina Faso, Mali and Niger from 2007 to 2009. In addition, a survey of farmers’ perceptions of insect pests, with particular focus on MHM, and the biological control program (BCP) was carried out. There was a significant increase of MHM parasitization rate after the releases, with up to 97% mortality. The survey on farmers’ perceptions revealed a fair knowledge of the MHM and the ability of farmers to describe the pest and the damage it caused. Farmers claimed that the biocontrol agent H. hebetor is effective and perceived a significant gain in grain yield due to this control strategy. Implications of these findings for a large extension of the MHM biocontrol program are discussed

Impacts environnementaux de la mise en valeur d’une zone inondable par irrigation

Les zones inondables sont un lieu privilégié d’intensification des systèmes de culture en relation avec un contrôle accru de la ressource en eau. Dans le delta intérieur du Niger, le potentiel hydraulique est considérable et représente une opportunité d’accroissement de la production agricole du Mali. Ce potentiel est estimé à un million d’hectares. Cependant, l’Office du Niger (Bonneval et al., 2002) n’exploite actuellement que 56 675 ha de casiers aménagés (fig. 1), dont 5 000 ha de canne à..

Redundant apodization for direct imaging of exoplanets: I. Robustness to primary mirror segmentation-induced errors outside the segment diffraction limit

International audienceContext. Direct imaging and spectroscopy of Earth-like planets and young Jupiters require contrast values up to 106−1010 at angular separations of a few dozen milliarcseconds. To achieve this goal, one of the most promising approaches consists of using large segmented primary mirror telescopes with coronagraphic instruments. While they are able to reach high contrast at small angular separations, coronagraphs are highly sensitive to wavefront errors, however. The segmentation itself is responsible for phasing errors and segment-level vibrations that have to be controlled at a subnanometric accuracy.Aims. We propose an innovative method for a coronagraph design that allows a consequent relaxation of the segment phasing and stability constraints for low segment-count mirrors and generates an instrument that is more robust to segment-level wavefront errors.Methods. This method is based on an optimization of the coronagraph design that includes a segment-level apodization. This is repeated over the pupil to match the segmentation redundancy and improves the contrast stability beyond the minimum separation set by the single-segment diffraction limit.Results. We validate this method on a Giant Magellan Telescope (GMT)-like pupil (seven circular segments) for two coronagraph types: apodized pupil Lyot coronagraphs, and apodizing phase plate coronagraphs. For the apodized pupil Lyot coronagraphs, redundant apodization enables releasing the piston phasing constraints by a factor of 5-20 compared to classical designs. For the apodizing phase plate coronagraphs, the contrast remains almost constant up to 1 radian RMS of the phasing errors. We also show that redundant apodizations increase the robustness of the coronagraph to segment tip-tilt errors, as well as to missing segment errors.Conclusions. Redundant apodization enables reducing or even removing any constraints on the primary mirror segment phasing at the price of larger angular separations and lower throughputs. This method cannot be applied to higher-segment count mirrors such as the ELT or the TMT, but it is particularly suitable for low segment-count mirrors (fewer than ~20 segments) such as the GMT aperture. These mirrors aim for high-contrast imaging of debris disks or exoplanets down to 100 mas

Apodization in high-contrast long-slit spectroscopy

International audienc