Direct detection and characterization of Earth-like planets from the ground is a very challenging issue. Among the projects, the Extremely Large Telescopes are very promising to improve the angular resolution and to increase the total number of collected photons. We studied this type of instruments in a very optimistic case to evaluate what level of aberrations limits fundamentally the detection. For that purpose, we considered a perfect coronagraph coupled with an extreme adaptive optics device. Even with a Strehl ratio of more than 96%, it only provides a contrast of $10^{-6}-10^{-7}$ at $30\lambda/D$. A calibration system downstream the coronagraph is therefore mandatory to reach the contrast of $10^{-10}$ between a terrestrial planet and its star in the near infra-red. We modelized a very general system taking into account dynamic aberrations left uncorrected by the adaptive optics system, static aberrations of the system and differential static aberrations due to the calibration channel. Numerical simulations demonstrate that the static aberrations are becoming very limitative and must not be neglected. Indeed, to achieve a contrast of $10^{-10}$, with common aberrations of 5 nm on a 100 meter telescope, the differential aberrations must be controlled at the level of 200 picometers. We also compare this speckle noise to the limitation due to the photon noise.

We are about to embark on a project to directly image low-mass companions orbiting within 1.5″ of their host stars. Our long-term aim is to reach down into the planetary-mass regime. In order to start this project we have time on the VLT NAOS/CONICA (NACO) facility and in the near future we plan to make use of the Near-Infrared Coronographic Imager (NICI) instrument mounted on Gemini-South. Our targets are F-M type dwarfs, and have been selected from the Anglo-Australian Planet Search (AAPS), Keck and Lick search lists. These surveys have been periodically monitoring over 1200 stars between them for the past $\sim$8 years with precisions typically around 3ms$^{-1}$. Our target list comprises objects which show significant evidence for companions on long-period orbits. Having a priori knowledge of companion characteristics allows us the advantage of prioritising our target list. Given the relatively high incidence of multiple planet systems found so far our search may also serve to provide useful constraints on any large separation, massive companions in our target systems.

We study the application of a predictive control law based on a Kalman filter for an extreme adaptive optics system. In particular, we discuss the minimization of temporal error and show the evolution of prediction errors with the order of the model. We also discuss the choice of the optimal temporal frequency as a function of the control law and the level of noise. Finally, the gain expected with respect to a non-predictive law is presented.

Adaptive optics (AO) systems have significantly improved astronomical imaging capabilities over the last decade, and are revolutionizing the kinds of science possible with 4-5 m class ground-based telescopes. A thorough understanding of AO system performance at the telescope can enable new frontiers of science as observations push AO systems to their performance limits. We look at the understanding we have gained from recent Lyot Project images at the Advanced Electro-Optical System (AEOS) 3.6 m telescope to show how progress made in improving WFR can be measured directly in improved science images. We describe how wave front errors affect the AO point-spread function (PSF), and model details of AEOS AO to simulate a PSF which matches the actual AO PSF in the astronomical H-band. Finally, we estimate the impact of improvements to wave front reconstruction techniques on diffraction-limited coronagraphy with the Lyot Project near-infrared coronagraph.

We present experimental results of a new procedure of measurement and pre-compensation of the non-common path aberrations in Adaptive Optics. A significant Strehl ratio increase (from 70 to 95.5 % in R band) is demonstrated.

The Lyot Project near-infrared JHK coronagraph achieved first light on the Advanced Electro-Optical System (AEOS) in March 2004. Optical pupil plane imaging at video rates from this coronagraph provides data on atmospheric scintillation and quasi-static pupil intensity variations. We examine the effect of these variations on coronagraphic performance. Early simulations suggested Strehl ratio reductions of the order of 2–3% due to residual uncorrected phase aberrations in H-band. We find that static or quasi-static pupil illumination non-uniformity in I-band reduces Strehl by $\sim$2%. A lower bound on the effects of dynamic illumination variation over the pupil is also $\sim$2% in I-band. Some of the static intensity variations in the pupil are due to pinned deformable mirror (DM) actuators. We simulate the effects a pinned actuator has on the coronagraph. The resultant speckles in simulated coronagraphic images show similarities to some Lyot Project PSFs. This highlights the importance of knowledge of the pupil in next-generation extreme AO coronagraphs in order to realize the predicted photometric dynamic range of their images.

In principle, band-limited coronagraphic image masks are capable of removing all on-axis starlight providing infinite dynamic range for the direct imaging of exoplanets. In practice, optical aberrations left uncorrected by the adaptive optics system and practical limitations on mask alignment prevent band-limited masks from reaching contrast levels necessary for exoplanet imaging. So-called, “high-order” band-limited masks reduce the coronagraph's sensitivity to low order aberrations, and have been measured to reach contrast levels of $10^{-7}$ at $4\, \lambda/D$ without the aid of a deformable mirror. In this work, we simulate the performance of high-order band-limited coronagraphic image masks in a variety of adaptive optics systems. We compare their performance with that of hard-edge stops, soft-edge Gaussian masks, and traditional (4th-order) band-limited coronagraphs.

TPF-I capability for planetary signal extraction, including both detection and spectral characterization, can be optimized by taking proper account of instrumental characteristics and astrophysical prior information. We have developed the Point Process Algorithm (PPA), a Bayesian technique for extracting planetary signals using the sine/cosine chopped outputs of a dual nulling interferometer. It is so-called because it represents the system being observed as a set of points in a suitably defined state space, thus providing a natural way of incorporating our prior knowledge of the compact nature of the targets of interest. It can also incorporate the spatial covariance of the exozodi as prior information which could help mitigate against false detections. Data at multiple wavelengths are used simultaneously, taking into account possible spectral variations of the planetary signals. Input parameters include the sigma of measurement noise and the a priori probability of the presence of a planet. The output can be represented as an image of the intensity distribution on the sky, optimized for the detection of point sources. Previous approaches by others to the problem of planet detection for TPF-I have relied on the potentially non-robust identification of peaks in a “dirty” image, usually a correlation map. Tests with synthetic data suggest that the PPA provides greater sensitivity to fainter sources than does the standard approach (correlation map + CLEAN), and will be a useful tool for optimizing the design of TPF-I.

This has been a wonderful conference, in a beautiful setting, with many of the world's planet-seekers on hand to present their ideas, at a time when we stand technically almost ready to embark on designing space missions to search for Earth-like planets and signs of life on them. In these remarks, I wish to simply list the ‘big questions’ that face us today, and offer some personal comments on how we might address these questions.

For a bit of inspiration from the past, I will close with a parallel that might be drawn between the journey that we all wish to embark upon, to search for extrasolar planets and to characterize them, and the one described by John Bunyan in his 1678 allegory, Pilgrim's Progress.

A remarkable aspect of this conference has been the agreement on our common goal, to detect and characterize extrasolar planets. While it is true that various of us suscribe to different theories of how planetary systems are formed, or how to best build the telescopes that can investigate these planetary systems, nevertheless we do all believe that the next great frontier in astrophysics is the study of extrasolar planets, and in particular Earth-like planets.

The topic of this conference can be phrased in terms of the following ‘big questions’. Are there Earth-like planets around nearby stars? Are these planets habitable? Do they show signs of life?

These questions generate many sub-questions that we need to answer. In the following I list the questions as I see them today. I will phrase them in terms that can be easily understood by most of the public. Doubtless you will have other questions, but this is a start.