The ALADDIN concept is an integrated Antarctic-based L-band experiment whose purpose is to demonstrate nulling interferometry and to prepare the DARWIN mission. Because of their privileged location, the relatively modest collectors (1 m) and baseline (up to 40 m) are sufficient to achieve a sensitivity (in terms of detectable zodi levels) which is about twice better than that of a nulling instrument on a large interferometer (such as GENIE at the VLTI), and to reach the 20-zodi threshold value identified to carry out the DARWIN precursor science. These numbers are based on a preliminary design study by Alcatel Alenia Space and were obtained using the same simulation software as the one employed for GENIE. The integrated design enables top-level optimization and full access to the light collectors for the duration of the experiment, while reducing the complexity of the nulling breadboard.

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.

We use Monte Carlo techniques to estimate the results and character of the early TPF-C mission. Using 108 samples to represent the planets of interest, we compute the completeness of the first search observations of prioritized target stars with optimized exposure times that sum to one year total. Assuming simple observing protocols and decision rules for searching, verifying, and characterizing observations, and taking into account ranges of probabilities for confusion sources ($P_\mathrm{confusion}$) and the occurrence of planets of interest ($\eta$), we compute 105 samples of the TPF-C schedule and observational outcomes for the first year of exposure time. For example, for Earth-like planets on habitable-zone orbits, assuming no observing overheads or pointing restrictions, and for the values $P_\mathrm{confusion}=0.5$ and $\eta=0.1$, we find that a median 2.2 planets are found, verified, and characterized in one year of exposure time, with the 68 highest priority stars searched.

We investigated two-stage combinations from three methods, nulling interferometer, nulling coronagraph, and modified pupil, calculating reduced intensity profile of a resolved central star and transmission for exo-planets. An achievable dynamic range can be derived by dividing the residual halo intensity of the star by the transmitted peak intensity of the planet. For observation parameters, here assumed are the wavelength of 600 nm in optical and the telescope diameter of 3 m. The combination of the nulling interferometer and the four-quadrant phase mask coronagraph showed the best performance reaching to $10^{-10}$ dynamic range at 100mas distance from the central star among five candidates of combination using nulling interferometer, achromatic interfero-coronagraph, four-quadrant phase mask, and shaped pupil method.

The European southern observatory ESO is currently undertaking the ambitious task of building a “Planet Finder” instrument for the VLT. The concept for this instrument includes a 3D spectroscopic imager assisted by a very powerful eXtreme AO system. In one of the two phase-A studies for this project, we have developed a simulation software for this kind of instrument which has now been extended and applied to the case of various ELTs. In this presentation, we give results of simulations and discuss achievable signal to noise ratios and prospects for detection and characterization from young gas giants down to terrestrial type planets. ELTs of various diameters are considered as well as a set of environmental conditions.

SPICA is a cooled, single large-mirror space-telescope, which is under discussion as an succsesor of the ASTRO-F mission. One of the most ambitious challenges of the SPICA mission is the direct observations of exoplanets with a coronagraph instrument. We report cryogenic infrared optics to realize high quality wavefronts for the SPICA coronagraph.

The SPICA satellite will be launched by an H-IIA rocket to Sun-Earth L2 Halo orbit early in the 2010s. The SPICA telescope is a Ritchey-Chretien optics with 3.5m diameter primary mirror, and cooled down to 4.5 K in orbit by radiation cooling and mechanical cryo-coolers. Main working wavelengths are 5–200 micron. Advantages of the SPICA coronagraph are the infrared wavelenths where the contrast between planets and central stars are smaller than the optical wavelengths, and that the cooled space telescope consists of monolithic mirrors.

Development of light-weight cooled telescope is one of the most important tasks to realize SPICA. At the present, sintered SiC and carbon fiber reinforced SiC (C/SiC) composite are candidate materials for the mirrors, truss, and optical bench. For these materials, estimations and improvements of basic property and surface roughness in cryogenic temperatures have been carried out. Deformation of trial product mirrors by cooling is also examined.

We are developing cryogenic deformable mirrors (DMs) because wave front accuracy of the SPICA telescope is 0.35 micron RMS, which is not enough for our coronagraphic instrument. For MEMS (Micro Electro Mechanical System) DM and some others, measurements of thermal deformation by cooling, electrical response, and heat generation are undergoing. Developments of a tip-tilt system for cryogenic usage started to cancel vibration caused by the cryo-coolers and other components and to realize a diffraction limit resolution. The first result of our binary mask coronagraph experiment is also shown.

In the frame of the VLT Planet-Finder project, the phase A system study has demonstrated the feasibility of an extreme adaptive optics system aimed at the direct detection of extrasolar giant planets. The main results of this study are presented in this paper.

The phase or orbital light curves of extrasolar terrestrial planets in reflected or emitted light will contain information about their atmospheres and surfaces complementary to data obtained by other techniques such as spectrosopy. We show calculated light curves at optical and thermal infrared wavelengths for a variety of Earth-like and Earth-unlike planets. We also show that large satellites of Earth-sized planets are detectable, but may cause aliasing effects if the lightcurve is insufficiently sampled.

The interferometry is the most promising way to directly observe exoplanets, their spectra and surfaces at optical or infrared domain. The complex imaging process can be described as the extraction of information from the data gathered by the interferometer. This information can be treated to be independend on any à priori knowledge or the integration process. In this case it is analyzed in a classical way. In fact, the imaging of exoplanets is not the classical way of the data reconstruction. The best extraction of information requires all accessible à priori knowledge. This is the bayesian way. The knowledge gathered during an integration is also contributing as à priori information for futher image reconstruction. We disscuss both approaches supporting the analysis with the estimates of information flow through the interferometer and examples of simulations of imaging.

Nulling Interferometry applied to the search and characterization of earth-like exoplanets requires to eliminate the star's contribution at a rejection level (Rej = collected energy/residual energy)larger than $10^{6}$ over a large bandwidth (6 to 18 $\mu$m). Nulling test-benches are in development in several laboratories so as to master such high a rejection. One approach relies on a Mach-Zehnder set-up with Achromatic Phase Shifters (APS). One APS concept is based on the focus-crossing property, providing an intrinsically achromatic phase shift by $\pi$. Using a confocal configuration for the focus-crossing approach, a Fresnel's diffraction effect degrades the rejection. Usual optical engineering softwares fail in assessing rejection performance and an analytical approach is needed. We describe the bench optical configuration and the Fresnel's diffraction effect as well as a possible way for correction. Then we describe the analytical method, based on Lommel's integrals, to evaluate the expectable rejection.

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.

We present a Japanese “roadmap” on direct extrasolar planet studies spanning from the current ground-based telescope to future IR/Opt space-based telescopes. Several searches for young planets and disks have been conducted with the Subaru 8.2m telescope with adaptive optics (AO) infrared coronagraph, CIAO. The instrument will be soon upgraded to a new AO and a coronagraph with simultaneous spectral and polarimetric differential imaging modes (HiCIAO), which will significantly improve the contrast performance and hence the capability of young planet detection. A sensitive unbiased survey for extrasolar zodiacal emission around nearby stars will be conducted with the ASTRO-F space mission (0.7m telescope, $\sim$2–200 $\mu$m) to be launched around the beginning of 2006. A successor space mission, SPICA (3.5m, 5–200 $\mu$m), is also planned; its high sensitivity will enable the detection and characterization of outer-most planets around nearby stars, if any. For the studies of extrasolar terrestrial planets, a high contrast space telescope (HCST; 3.5m, $\sim$0.3–2 $\mu$m). We are also seeking for collaborations with or are considering to join to foreign missions. We describe an outline, status, and role of each project on the extrasolar planet studies.

The influence of non-isothermal atmosphere on the intensity of details of Raman Scattering is computed for spectra of Uranus and Neptune. It follows that the intensity of this scattering depends on the depth of the level formation in an optically homogeneous non-isothermal atmosphere; neglecting of real temperature profiles during the analysis of observation data leads to large errors in the parameters of the atmosphere upper level.

This paper presents a look at ongoing investigations into the strategies needed to characterize the orbits of observed exoplanets in an optimal manner. Also introduced is an efficient manner of the selection of possible orbits consistent with the observation of an exoplanet. Specifically, this work looks at the ability to conclude that a planet's orbit is resident in the habitable zone (HZ) on the basis of two sequential observations. The role of the range of possible semi-major axes is introduced.

Occulting focal plane masks for the Terrestrial Planet Finder Coronagraph (TPF-C) could be designed with continuous gray scale profile of the occulting pattern such as $1-{\rm sinc}^2$ on a suitable material or with micron-scale binary transparent and opaque structures of metallic pattern on glass. We have designed, fabricated and tested both kinds of masks. The fundamental characteristics of such masks and initial test results from the High Contrast Imaging Test bed (HCIT) at JPL are presented.

This paper discusses the potential performances of interferometers at the Dome C site in the Antarctic. The work is focussed on the limiting performances for fringe tracking, considering different fringe trackers architectures. The fringe tracking limiting magnitude is combined with estimates of the isopistonic angle at Dome C to evaluate the possibilities of off axis fringe tracking. The first evaluations presented here indicate that the sky coverage with realistic off axis fringe tracking is quite high at Dome C even with modest individual apertures and this could finally the best and decisive advantage of this site for optical interferometry. This might make a Dome C interferometer an unique deep sky very high angular resolution machine.

The next generation of high-contrast imaging instruments will provide the first unresolved image of an extrasolar planet. While the emitted infrared light from the planet in thermal equilibrium should show almost no phase effect, the reflected visible light will vary with the orbital phase angle. We study the photometric variation of the reflected light with orbital phase of a ringed extrasolar planet. We show that a ring around an extrasolar planet, both obviously unresolved, can be detected by its specific photometric signature.

In order to detect directly faint planets around other stars it is important to develop techniques to cancel the central starlight. We report progress in terms of null depth on the visible nulling experiments at JPL, essential for NASAs future space missions as well as for an upcoming sounding rocket based experiment. A level of 1 Million to 1 nulling ratio (1e-6 rejection ratio) has been obtained for the first time for visible laser light, and a level of 100000 to 1 nulling ratio has been obtained for a relatively large (5%) bandpass at 650nm. Using a combination of a fiber array and deformable mirror a null of 1e-6 would correspond to a contrast of 1e-9 at a distance of 2-3$\lambda$ in the airy disk plane, only 10x away from TPFs goal. The configuration used was a fiber fed Mach Zender type interferometer, using 2 or 3 mirrors in each two arm, placed in an enclosed air container. For broadband light we used tilted dispersion glass plates in the nuller arms and an avalanche photon diode module to cover the large dynamic range. We describe a variety of conditions that have to be met and optimized to reach very deep nulls and sub-nanometer optical path difference stability, such as optical alignment, symmetry in the two arms, mechanical stability and vibration isolation.

The limitation to ground based astronomy is the Earth's atmosphere. The atmosphere above the Antarctic plateau is fundamentally different in many regards compared to the atmosphere at temperate sites. The extreme altitude, cold and low humidity offer a uniquely transparent atmosphere at many wavelengths. Studies at the South Pole have shown additionally that the turbulence properties of the night time polar atmosphere are unlike any mid latitude sites. The lack of high altitude turbulence combined with low wind speeds presents favorable conditions for interferometry. More recent site testing at Dome C has revealed the most superb seeing of any site tested. The unique properties of the polar atmosphere can be exploited for Extra-solar Planet studies with differential astrometry, differential phase and nulling interferometers.

Direct detection and spectroscopic characterization of earth-like exoplanets require to eliminate the starlight in the recorded signal at a rejection level (collected flux / residual flux) around 10$^{6}$ in the thermal infrared domain. Another need is to reach angular resolution in the range 0.1 to 0.01 arcsec. In this context, nulling interferometry is recognized as the preferred instrumental approach. In the framework of the ESA-Darwin mission, preliminary studies for nulling systems have been initiated, the prime goal to achieve being mastering nulling process. In this purpose, Alcatel Space has developed a nulling test-bench, operating in near infrared (1.55 $\mu$m), not only to demonstrate capability of obtaining an appropriate rejection level but also to study and characterize the use of emerging techniques. The Darwin system will ultimately benefit from these results. In this paper, we report the most recent configuration of the Alcatel Space nulling breadboard which uses the multi-beam recombination technique, current baseline for Darwin. The results obtained with this version shows rejection performance at nearly 10$^{5}$ (stable level) with a polychromatic source ($\lambda$ = 1.55 $\mu$m, $\Delta\lambda$= 80 nm).