The effect of herbicide rates on weed control and crop yield is the subject of countless and ongoing research projects. Weed seed banks receive very little attention in comparison. The seed bank resulting from 3 yr (2006 to 2008) of single herbicide rates in a cropping system where glyphosate/glufosinate and corn/soybean were rotated or not was evaluated in a field located in St-Augustin-de-Desmaures, Québec, Canada. Field plots under conventional tillage were seeded in corn every year, or corn and soybean (1 yr). These plots received the same herbicide every year or various glyphosate/glufosinate 3-yr sequences. Subplots were sprayed with a single POST application of the recommended rate of glyphosate (900 g ae ha−1) or glufosinate (500 g ai ha−1) or lower rates. Subplots received the same full (1.0×, recommended) or reduced (0.5×, 0.75×) rate every year. After crop harvest in 2008, soil cores were extracted and the weed seed bank was evaluated. Including soybean in the cropping system resulted in lower seed banks compared to those under continuous corn cropping. Including glufosinate in a glyphosate herbicide sequence increased weed seed banks due to the lower efficacy of the glufosinate rates tested at reducing the seed bank of annual grasses. Higher herbicide rates translated into lower seed banks, up to a certain rate. After 3 yr, the lowest seed bank (full glyphosate rates every year) still had 4,339 ± 836 seeds m−2 and was higher than the initial seed bank (2,826 ± 724 seeds m−2).

The cool gas in the central parsec of the Galaxy is organized in the surrounding circumnuclear disk, made of neutral gas, and the internal minispiral, composed of dust and ionized gas. In order to study the transition between them we have investigated the presence of H2 neutral gas in this area, through NIR spectro-imaging data observed with SPIFFI. To preserve the spatial resolution we implemented a new method consisting of a regularized 3D fit. We concentrated on the supposedly fully ionized central cavity and the very inner edge of the CND. H2 is detected everywhere: at the boundary of the CND and in the central cavity, where it seems to split in two components, one in the background of the minispiral and one inside the Northern arm.

We present the adaptive optics assisted, near-infrared VLTI instrument GRAVITY for precision narrow-angle astrometry and interferometric phase referenced imaging of faint objects. With its two fibers per telescope beam, its internal wavefront sensors and fringe tracker, and a novel metrology concept, GRAVITY will not only push the sensitivity far beyond what is offered today, but will also advance the astrometric accuracy for UTs to 10 μas. GRAVITY is designed to work with four telescopes, thus providing phase referenced imaging and astrometry for 6 baselines simultaneously. Its unique capabilities and sensitivity will open a new window for the observation of a wide range of objects, and — amongst others — will allow the study of motion within a few times the event horizon size of the Galactic Center black hole.

Direct detection of Earth-like planets is one of the major objectives for the next generation of ground based telescopes (Extremely Large Telescopes, ELT). ELT instruments will be conditionned by such scientific programs. Here, we consider here a system made with an adaptive optics device, a coronagraph and a simultaneous calibration system. We refined this simple model by including static aberrations upstream the coronagraph and differential aberrations downstream. Using numerical simulations, we evaluate how these static aberrations limit the detectability of telluric planets.

The extreme contrast in mass and luminosity between the extra-solar planets and their host stars make detailed studies of these planets very challenging. In particular, direct observations of extra-solar planets is still beyond the capabilities of the currently available instrumentation, save for perhaps a few extreme cases of very young and massive planets at large distances from the central star. While progress in instrumentation might allow significant progress in detection capabilities either with the 8 and 10-m ground-based telescopes (Planet Finder instruments on the VLT and Gemini) or with the next generation space telescope (JWST), imaging of extra-solar planets over a wide range of parameters, and possibly down to terrestrial planets, will require extremely large ground-based telescopes like OWL or dedicated space instrumentation (TPF or Darwin for instance). We outline here the scientific objectives of EPICS, the OWL Earth-like Planet Imager and Spectrograph, summarize the corresponding high level requirements, present the foreseen observing modes and give a first estimate of its performance.

The performance of high contrast imaging systems is very often limited by the presence of static speckles in the point-spread function of the central source. Several techniques have already been proposed to discriminate a faint companion from these residual speckles. These techniques used different criteria to separate a speckle from a companion: polarization, spectral information or coherence. Here, we propose a new imaging device, the Self-Coherent Camera (SCC), that is based on the lack of coherence between the stellar light and the planet that is searched for. This SCC is a simple instrument that allows us to reach the fundamental limitation of the photon noise by calibrating the speckles in the recorded images. After the description of the general problem of discriminating speckles from planets, we will explain the principle of the SCC. Then, we will analyze the different limitations of this technique as well as the performance that can be reached with current telescopes.

Direct detection and spectral characterization of extrasolar planets is one of the most exciting but also one of the most challenging area in modern astronomy. For its second generation instrumentation on the VLT, ESO has supported two phase A studies for a so-called “Planet Finder” dedicated instrument. Based on the results of these two studies, a unique instrument is now considered for first light in early 2010, including a powerful extreme adaptive optics system, various coronagraphs, an infrared differential imaging camera, an infrared integral field spectrograph and a visible differential polarimeter. We will briefly summarize the science objectives and requirements, describe the proposed conceptual design and discuss the main limitations and corresponding instrumental issues of such a system. We will also derive the expected performance of the proposed Planet Finder and present the project organization.

The space mission PEGASE, proposed to the CNES (Centre National d'Etudes Spatiales = French Space Agency) in the framework of its call for scientific proposals : “formation flying missions”, is a 2-aperture interferometer, composed by 3 free flying satellites (2 siderostats and 1 beam combiner), allowing baselines from 50 to 500 m in both nulling and visibility modes. With an angular resolution of a few mas and a spectral resolution of several tens in the spectral range 2.5-5 microns, PEGASE has several goals:

1. science : spectroscopy of hot jupiters (Pegasides) and brown dwarves, exploration of the inner part of protoplanetary disks

2. technology : validation in real space conditions of formation flying, nulling and visibility interferometry concepts.

MIRI, the mid-IR instrument of JWST (James Webb Space Telescope), will include a coronagraphic device for which the ultimate goal is the detection and caracterization of extrasolar planets around nearby stars. In this paper, we describe the optical concept of MIRI and the instrumental choices that were made in phase A and B regarding the coronagraphic system. Finally, we will present numerical simulations that we carried out to evaluate the capability for detecting extrasolar giant gazeous planets.

The difficult goal of directly detecting a planet around a star requires to cancel as much as possible the stellar light. Since the first proposal by Bracewell of a nulling interferometer, where the star is put on a central dark fringe, several interferometric configurations have been presented in order to improve the quality of the rejection, especially to avoid the leaks due to the finite angular dimension of the stellar disk, resolved by the interferometer. In the Bracewell interferometer, the behaviour of the nulling efficiency vs the angular distance θ to the star is as (1-cosθ) ∝ θ2. One goal is to increase the exponent of the term θn which gives the cancellation efficiency. I present one method to define configurations of telescopes positions, sizes and phase-shift that can achieve any given power of θ. The principle is based on a peculiar property found by Prouhet of a partition into two sets of the integers, done according to the Thué-Morse sequence. 2L telescopes regularly spaced on a line, are distributed into two groups, following their rank in the Thué-Morse sequence and, to the telescopes of one of the groups, is applied a π phase shift. The result is a fractal-like distribution of the telescopes where redundancy is minimum and whose interferometric combination produces a very efficient nulling in θ2L. I first examine 1-D patterns of identical telescopes, then extend the method to 2-D configurations, then show that the latter can be used to define 1-D arrays of non identical telescopes, according to some algebra of interferometers. The generalization to arrays where the phase shift between n groups of telescopes is 2kπ/n is finally proposed.

The space mission COROT can be considered as a DARWIN/TPF precursor, since it will contribute to the pre-DARWIN/TPF effort with its dedicated exoplanet program. COROT will survey more than 50 thousands stars, each one during five months, in order to detect transits of planets. Despite of the modest size of the telescope, the photon-noise limited performances may lead to the detection of several tens of “hot jupiters” and, more important, of a few planets of the Earth-Uranus class, i.e. with a size of typically 1.5 to 4 Earth radius. In the basic mode of operation (characterization of a planet by at least 3 detected transits), only planets with a short orbital period, and thus rather “hot” ones (T = 600K), should be discovered. However, one of the COROT's features is its capability to provide a wavelength dependent information, thanks to a prism in the optical path.

We report on the facility we developed at the Observatoire de Meudon to test the Four Quadrant Phase Mask (4QPM) coronagraph in the Infrared (IR) and at low temperature. This facility has been developed in the context of the mid-IR instrument MIRI for the James Webb Space Telescope. Three 4QPM will take place inside MIRI and need to be qualified for space environment. The performance of the coronagraph is in agreement with our expectations from numerical simulations. The peak intensity of the diffraction pattern is reduced by a factor 380, a performance being limited by the chromatic effects and the size of the bench source.

High angular resolution provided by adaptive optics on ground-based telescopes allows detailed study of bright stars environment. The limitation of dectability of faint companions is the diffracted light from the star. The 4Q coronagraph (Rouan et al. 2000; Riaud et al. 2001; Abe et al. 2001) decreases this diffracted halo and provides high contrast imaging. The residual speckle pattern becomes the final limitation for the coronagraphic observations. We present here, a complete study of the 4Q coronagraph in use with an high order adaptive optics on the VLT telescope, within the context of "Planet Finder" ESO project. Practically, a simple solution making use of commercial half waveplates seems well suited for a ground-based coronagraphic device.

Numerical simulations have been carried out to assess the opportunity to detect extrasolar planets with MIRI: the mid-IR instrument of NGST. Several coronagraphs and telescope designs have been investigated. As a result, we found that very young planets (50 Myr) as well as old planets (5 Gyr) can be imaged in the thermal-IR (5 μm to 20 μm) down to a few Jupiter masses if an appropriate high-contrast coronagraph is in used. Promising results of numerical simulations are presented.

We describe an alternative design for the 4-quadrant phase mask coronagraph described recently by Rouan et al. (2000). Based on the same principle, i.e. producing a very efficient nulling by mutually destructive interferences of the coherent light from the main source, our mask realises the π phase shift using some properties of ZOGs (Zeroth Order Gratings) and according to an original scheme respecting the 4-quadrant symmetry. When the period of the one-dimension grating structure is smaller than the wavelength of the incident light, the structure becomes birefringent. The effective refractive indices depend on the wavelength. Using this feature, we can design a mask whose nulling efficiency is maintained within a wide wavelength range. Numerical simulations were made according to the RCWA (Rigorous Coupled Wave Analyses).

A 8x8 InSb CID array, developed in France by SAT (1) (Société Anonyme de Télécommunications) for terrestrial applications, has been tested at Meudon Observatory in order to evaluate if its performances at LHe temperature, meet the requirements of infrared astronomy. Next sections give : 1) Description of the array and the experimental conditions; 2) The test results; 3) Work under development.