The physical bases of the detection and characterisation of extrasolar are reviewed and the first findings are presented.A special attention is paid to the imaging method inthe reflected light and thermal emissionregimes. They both have their advantages and disadvantages,including artefacts, in the determination of planet physical parameters (mass, size, albedo, surface and atmospheric conditions etc.). New perspectives forthese different aspects are presented. Finally a brief account of theground based programmes and space-based projects and their potentialities forEarth-like planets is made and discussed.

Spectroscopic observations of the Earthshine allowed us to make arelative measurement of the integrated Earth reflectance spectrumin which the terrestrial vegetation signature around λ = 700 nm has been detected. Therefore we conclude that the terrestrialvegetation, and thus terrestrial life, can be detected remotelywhen the Earth is seen as a single dot. We also conclude thatvegetation can be detected on an extrasolar Earth-like planet, ifa spectral resolution around 50 is available.

We discuss the properties of extrasolar planets inferred fromobservations and theoretical models. We show that COROT should be ableto usefully constrain the albedos of extrasolar planets with shortorbital periods, given levels of stellar variability close to that ofthe Sun. We sketch possible strategies for observational astrophysicalprograms using high contrast imaging.

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.

Hot massive stars constitute an important class of objects amongstellar populations. Diffraction limited high dynamic imaging(HDI) with 8-10 m class telescopes of fine structures which oftencharacterize their extended nebulosities can trace back thehistory of their mass-loss, therefore the evolution of the centralstar across the HRD. Since these stars are among the most luminousstars and display unique emission spectral features in galaxies athigh redshift, they can serve as natural candles to estimatecosmological distances through the Wind-momentum LuminosityRelation (WLR, Kudritzki et al. 2000). In thispaper I develop the context of massive stars HDI and derive somegeneral instrumental specifications for coronagraphic adaptiveoptics.

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.

Very High Dynamics Imaging rounds up various techniques that can be used to study the close environmentof a source which flux, comparatively very large, prevents to see the morphological featuresimmediately neighbouring the source.Several instrumental approaches have been devised in this purpose, among which apodisation, mask coronagraphy and nulling techniques. In view of applying them to various scientific programs, both shared constraints andspecific features of the approaches have to be identified. This is the subject of this paper,which also recalls basics principles. A new concept (EvWaCo) achieving coronagraphy by usingevanescent waves is briefly outlined.

The general formalism for Lyot and Roddier & Roddier coronagraphy is detailed. The influence of the masksize, chromatism and central obscuration are discussed. The necessity of entrance pupil apodization forcoronagraphy is introduced from the fundamental limitation that appears in the classical technique. Prolatespheroidal functions are presented as the natural apodizations for coronagraphy.

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.

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.

We describe an alternative design for the 4-quadrant phase maskcoronagraph described recently by Rouan et al. (2000). Based onthe same principle, i.e. producing a very efficient nulling bymutually destructive interferences of the coherent light from themain source, our mask realises the π phase shift using someproperties of ZOGs (Zeroth Order Gratings) and according to anoriginal scheme respecting the 4-quadrant symmetry. When theperiod of the one-dimension grating structure is smaller than thewavelength of the incident light, the structure becomesbirefringent. The effective refractive indices depend on thewavelength. Using this feature, we can design a mask whose nullingefficiency is maintained within a wide wavelength range. Numericalsimulations were made according to the RCWA (Rigorous Coupled WaveAnalyses).

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.

MIRI is the mid infrared instrument planned for the NGST. Workingin the 5 μm - 28 μm band, it includes 3 units: aspectrograph, an imager and a calibration facility. We describehere briefly MIRIM, the MIRI imager channel as it is at the end ofthe phase A study. MIRIM provides 3 observing modes: an imagingmode, with a Field Of View of 1.3 arcmin × 1.7 arcmin and a PixelField Of View of 0.1 arcsec/pixel, a coronagraphic mode and a lowresolution mode for point sources, between 5 μm and 10 μm,with a spectral resolution R = λ/Δλ around 100.

Numerical simulations have been carried out to assess theopportunity to detect extrasolar planets with MIRI: the mid-IRinstrument of NGST. Several coronagraphs and telescope designshave been investigated. As a result, we found that very youngplanets (50 Myr) as well as old planets (5 Gyr) can be imaged in thethermal-IR (5 μm to 20 μm) down to a few Jupiter masses ifan appropriate high-contrast coronagraph is in used. Promisingresults of numerical simulations are presented.

The color-differential astrometry method consists in measuring the variations of thephotocenter position with wavelength. This yields spectral information on the spatial structure of an unresolved source, and could allow, among other applications, the direct detection and spectroscopy of extrasolar planets. We give some estimates of signal-to-noise ratio for CDA using the the NGST mid-infrared instrument (MIRI) spectrograph, assuming for the planetary luminosity either black-body models or recent synthetic spectra. Giant Planets around nearby Sun-like stars are potentially observable over a wide-range of orbital distances, if the precision on the measurement is limited by the fundamental noises. Space-based CDA would then be complementary, in terms of star-planet separation, to ground based interferometry and to coronography. This assumes, though, a proper chromatic stability of the instrument. This note introduces some possible methods for instrumental internal calibration, and presents a possible spatial design for a calibration by spatial modulation.

We report experimental results from the Phase Knife Coronagaph (monochromatic case) which validate our previous theoretical andnumerical simulations, prove the physical principle of it and setrealistic limitations to the nulling properties of thecoronagraph. The optical set-up, phase knives manufacturingtechnique and different aspects of the instrumental limitationsare given. The first results attain easily a 3000 nulling effect.These results are successfully confronted to numericalsimulations, proving the good agreement to theory.

ESO offers the opportunity to install a new (second generation)instrumentation on 8-m telescopes before 2010, for a wide community.We, as a consortium, argue that it is possible to develop a high contrastimager that will improve significantly or will complement current andforthcoming instruments. This project would benefit a interesting numberof astrophysical issues; it will also prepare later more ambitiousground-based imagers or space-based high contrast instruments.The limitations of the turbulence are severe and demand very performantadaptive optics. This critical question is addressed specifically.

High angular resolution provided by adaptive optics on ground-based telescopes allows detailed study of bright starsenvironment. The limitation of dectability of faint companions isthe diffracted light from the star. The 4Q coronagraph(Rouan et al. 2000; Riaud et al. 2001; Abe et al. 2001) decreases this diffracted haloand provides high contrast imaging. The residual speckle patternbecomes the final limitation for the coronagraphic observations.We present here, a complete study of the 4Q coronagraph in usewith an high order adaptive optics on the VLT telescope, withinthe context of "Planet Finder" ESO project. Practically, a simplesolution making use of commercial half waveplates seems wellsuited for a ground-based coronagraphic device.

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.