By reprocessing the NICMOS coronagraphic archive using improved PSF subtraction methods, we have obtained new images of 5 debris disks, all previously unseen using classical PSF subtractions. Three of the disks are edge on and two appear to be ring like, one of which is extremely asymmetric.

Their stellar hosts are nearby, young F and G type stars (40-90 pc, 12–30 Myr), including one that is a close analog to the young sun at roughly the age at which terrestrial planets were assembling. This is a 25% increase in the sample of debris disks seen in scattered light. Analysis and modeling of the disk geometries is in process. Given these systems' youth, proximity, and brightness (V = 7.2 to 8.5), these will be superb targets for investigating planet formation, and are perfect targets for studies with GPI, SPHERE and JWST.

The Archival Legacy Investigation of Circumstellar Environments (ALICE) project (AR-12652) is currently conducting a comprehensive and consistent reprocessing of HST-NICMOS coronagraphic survey data to search for point sources and disks using advanced PSF subtraction. The KLIP algorithm (Karhunen-Loève Image Projection) was developed for this project, and has proven very effective at processing the hundreds of selected archival images. This project has already been very successful with numerous detections of previously unseen point sources and several resolved debris disks that we are currently following up by multiple avenues. We give an overview of the project including preliminary scientific results with companion candidates and improved images of known disks

This paper summarizes the general theory and properties for Apodized Pupil Lyot Coronagraphs which consist of a classical hard-edged Lyot coronagraph with an upstream pupil apodization. The ideal apodization function can be determined from an integral eigenvalue problem which solutions are prolate spheroidal functions. Solutions exist for any geometrty, including rectangular, circular, or elliptical. Formal solutions can be extended to the case of arbitrary apertures, using generalized prolate spheroidal functions for centrally obstructed apertures, spiders, or segmented telescopes. The properties of these coronagraphs enable the possibility of multiple stage coronagraphy and achromatization. The new instrument Gemini Planet Imager (GPI) will include such a coronagraph.

In this communication, we study the statistical properties of the light intensity in direct and coronagraphic images, in the context of ground-based Extreme Adaptive Optics observations. The same approach can also be used for space observations with different scales. We show that a coronagraph only affects the perfect part of the wave and leaves the uncorrected part of the wavefront almost unaffected. This statistical model can explain the ‘speckle pinning’ effect (presence of speckles at the position of the diffraction rings), as an amplification of the speckle noise. This statistical approach can be verified on real adaptive optics data.

Deconvolution is a necessary tool for the exploitation of adaptive opticscorrected images, because the correction is partial. The Maximum APosteriori (MAP) framework is used to derive a deconvolution method(MISTRAL) thatcombines the data with our knowledge of the noise statistics as well as ourprior information about the object and the variability of the Point SpreadFunction. The deconvolution of experimental and scientific data illustrates the capabilitiesof this method.

Circumstellar disks from early accretion stages to debris disks motivate anactive theoretical and observational research. Their physics is quite complex and implies thestudy of various domains such as the physics of grains, radiative transfert at variouswavelengths, collisional and radiative destructive processes, dynamics, long term evolution...Such disks provide valuable information on the conditions of exoplanet formation, but alsoon the interaction between disks and already formed planets;they may be in some cases the indicators of the presence of planetsor, on contrary, they may prevent from direct planet detections depending on the observational technique.We review the current most critical issues relative to disk studies, and discuss the needand interest for various observational techniques. We conclude on the importance for highdynamic observations and typical specifications.

The detection of a faint companion to a star with achromatic coronographyand adaptative optics is only limited by the residual speckles.We study a method to increase the detectability of the companion, basedon the difference of two images taken in two different wavelengths, aftersuitable rescaling.

In this work, I show that a wide field nulling imager is a very attractive solution for discovering and characterizing Earth-sized planets around other stars. The concept presented in this paper takes advantage of recent developments in nulling coronagraphy and a number of other techniques (aperture synthesis, pupil densification, pupil dilution) that make it possible to obtain high quality coronagraphic images with an interferometer.

This paper is describing the fundamental notions of phase contrastmethod introduced by F. Zernike (Zernike 1934) and how it can beapplied to coronagraphy. These techniques were first designed foroptical surface testing and therefore their use as coronagraphicinstrument is not straightforward. This paper is mainly describingthe Foucault knife edge test, its later improvement by Zernike andBurch and their effects as coronagraphic concepts. A formaldemonstration is given in the case of the Phase Knife Coronagraph.

In this paper we present some preliminary simulations concerning adaptive-optics-aided coronagraphy.The starting point used for this goal is the software system CAOS (Code for Adaptive Optics System),because of the simulation design ease given by its graphical programming environment, and thecompleteness and flexibility of its set of modules dedicated to adaptive optics (AO) simulations.We have so developed the complementary numerical tools necessary to implement the CoronographeInterférentielle Achromatique (CIA) within CAOS, together with differential imaging, andconsidering Fresnel propagation through the turbulent atmosphere. Hence we give an example ofapplication to exoplanet detection with the characteristics of the Very Large Telescope AO systemNAOS and the CIA.Finally, we also discuss on some other recent developments concerning CAOS.

This paper describes our strategy and presents the specific additional calibration tool added to the near-infrared focal instrument AMBER of the Very Large Telescope Interferometer, to achieve the direct detection of extrasolar planets with color-differential interferometry. The measurement of the angular orbits, masses and spectra of hot giant extra solar planets can be achieved for Jupiter size planets up to 0.2 a.u. away from a 10 pc distant star, if it is limited only by photon, detector and background noises. However, this requires an extremely good control and calibration of the atmospheric and instrumental stability.

"Densified-pupil multi-aperture imaging interferometers" also called "hypertelescopes" can provide direct images at their focal plane. Coronagraphic masking is applicable for nulling a star's image and searching associated planets. The scheme is applicable at the infra-red wavelengths where a planet has its best contrast, but also potentially at visible wavelengths where chlorophyll-like spectral features are to be searched. In the infra-red, where zodiacal and exo-zodiacal clouds tend to contaminate the image, the scheme provides a better rejection of this contamination than schemes using a beam-splitter and flat interference. For a typical Earth-like exo-planet the detection time is reduced 10 to 100 times. In the visible, planets are often resolved from their star by an interferometer's sub-aperture. Visible coronagraphy is then achievable in each sub-aperture before combining the beams and producing the high-resolution image. This relaxes the piston tolerances. Whether for sub-apertures or a densified pupil, or even a conventional telescope, multiple stages ofcoronagraphy are of interest, if equipped with as many deformable mirrors or transmissive plates. Located in the successive image planes, such adaptive correctors can phase the residual stellar speckles without affecting the planet peak. This generates a central peak of starlight, which can be masked without much obstructing the planet's wavefront. A design concept studied for an "Exo-Earth Discoverer", a hypertelescope variant proposed to NASA for its Terrestrial Planet Finder, involves 37 mirror elements of 1 m, driven by small solar sails and arranged to form a 40-300 m diluted spherical mirror. One or several focal combiners move along the focal surface. Optical solutions have been explored in preliminary detail.

In this communication, the general properties of AGNs are firstreviewed: history, classification, model and unification. Thecontribution of direct optical imaging is thus discussed. A HSTimage is taken into example showing the observational limitationsnear the center. The interest of high contrast imaging is thendiscussed.

We give in this short communication the principle of the densification of a large classical on-axis aperture,with aperture central obscuration and spider arms into a full circular unobstructed aperture, forapplication to high-contrast coronagraphy. An example is shown using a VLT like aperture. In space, such atechnique would allow to produce a perfect null of the star image using coronagraphic techniques such as the4QC or the PKC, at the expense of a small reduction of the transmitted light. The drawback of the techniqueis that a surprisingly very small ZOF is obtained, if the telescope full resolution is considered. However,if a loss of resolution of a factor 2 is accepted, then the system might behave as a perfect imaging system.The technique is found useless for ground based observations with the Strehl ratios reached at the presenttime.

A definition study for a Ground-based European NullingInterferometry Experiment (GENIE) has been initiated by theEuropean Space Agency (ESA) and the European SouthernObservatory (ESO). This instrument is planned to be installed in 2006 on the VLTI at Mount Paranal, Chile. The primaryobjective of the GENIE experiment is to gain experience in the design, manufacture and operation ofa nulling interferometer using a Darwin representative technology. Besides its technological goal,GENIE is designed to survey exozodiacal dust clouds around nearby stars and to study the brightestof them by means of low-resolution spectroscopy. GENIE also aims at low-mass companion detection,including hot Jupiters. In this paper, the expected performances of the GENIE interferometer areinvestigated as a function of the observation wavelength and of the performances of criticalsubsystems.

Highly performing adaptive optical systems are required for nextgeneration giant telescopes as well as next generationinstrumentation for 10 m-class telescopes. Different types of AOsystems are currently under study, including Multi-Conjugate AO(MCAO), high dynamic range AO, and low-order AO for distributedpartial correction AO. These systems require a large variety ofdeformable mirrors with very challenging parameters. Thedevelopment of new technologies based onmicro-opto-electro-mechanical systems (MOEMS) is promising forfuture deformable mirrors. We are currently developing a MDM basedon an array of electrostatic actuators with attachments to acontinuous mirror on top. The most challenging building block forthis device is the high optical quality mirror. Our first resultsshow a very efficient planarization of the surface with ourdesign. The integration of this mirror surface on top of anactuator array is under investigation.

Using simplificative assumptions, we show that a redundant configuration of diluted apertures should permitan easier exoplanet detection than a non-redundant one. This result assumes that after coronagraphy theplanet appears over an uniform background whose statistical fluctuation is the unique source of noise. Thedetection is made using a matched filter, cross-correlating the observed image with the telescope array PSF.In that case, the relevant parameter appears to be the integral of the modulus squared of the aperture MTF.

In this paper, some basics concepts in statistical approachesfor detection of signals embedded in noise are brieflyreviewed. Though most material presented in the first part ofthe paper is well documented in the litterature (seereferences), some effort is made to provide a self-containedand concise introduction to the subject. The importance andrelevance of the likelihood ratio is highlighted from aBayesian formulation of the problem; the optimal (in the senseof maximized detection probability for given false alarm rates)Neyman Pearson test and likelihood ratio test are discussed inthe general framework of test performance studies. Therefore,the usefullness of the ROCs (Receiver OperatingCharacteristics) is illustrated on simple examples. When someunknown parameters must be taken into account, extension of theprevious approaches are mentionned, with some emphasis put onthe GLRT (generalized likelihood ratio test). Most resultsintroduced in this tutorial are then applied and discussed inthe framework of the extra-solar planet detection problem. Aobservation model involving Poisson random variables isstudied. A thorough study in performed, and the Gaussianasymptotics are discussed in the case where all parameters ofthe model are assumed. In a more realistic situation where someparameters must be estimated, the GLRT is derived and itsperformances are evaluated by Monte Carlo simulation.

In the frame of ESA's DARWIN mission technological studies, Alcatel Space, supported by ESA, is designing and manufacturing a nulling interferometer whose aim is to demonstrate in laboratory the extinction of a point source with a stable nulling ratio of 10-6. This breadboard is presented with emphasis on the integrated optics beam combiner.

The formalism for the prolate apodized coronagraphs is shortly outlined. A presentation of the numericalcomputation of the circular prolate apodization is given, and a comparison is made between the exact prolateand the solution obtained by Guyon &Roddier (2000), with an iterative algorithm. The agreement is excellentbetween the two solutions, provided a sufficient sampling of the mask. Numerical simulations are presented for circular apertures with prolate apodizations and compared to theclassical unapodized technique: off-axis response, effect of mask size, central obscuration and chromatism.