Search

A forthcoming step in the study of extrasolar planetary systems is the direct detection and characterization of Earth-like planets. An asset of the ELTs in that context is their very high angular resolution and their collecting area. The luminosity ratio between a terrestrial planet and its star ( $10^{-10}$ ) is such an ambitious goal that a thorough study needs to be carried out. We started with a simple analysis of the fundamental limitations for the detection of extraterrestrial planets with ELTs. Here, we considered an extreme adaptive optics device upstream of a perfect coronagraph. Even with high Strehl ratios, the coronagraphic halo level is only $10^{-6}$ to $10^{-7}$ at typical exo-Earth angular distances. A calibration device is therefore mandatory to reach the contrast between a terrestrial planet and its star in the near infra-red. We considered a simple but realistic model taking into account dynamic aberrations left uncorrected by the adaptive optics system, static aberrations of optical system and differential static aberrations due to the calibration channel itself. Numerical simulations prove that, after the calibration, the limitations are set by the static aberrations which cannot be neglected anymore.

General arguments for optimized coronagraphy in the search for planets are presented. First, off-axis telescopes provide the best telescopic platforms for use with coronagraphy, and telescope fabrication technology now allows the fabrication of such telescopes with diameters of up to 6.5 m. We show that in certain circumstances a smaller telescope with an off-axis primary has a signal-to-noise advantage compared with larger Cassegrain telescopes. Second, to fully exploit the advantages of the coronagraph for suppressing stray light, it is necessary to use a high Strehl ratio adaptive optics system. This can be best achieved initially with modest aperture telescopes of 3–4 m in diameter. Third, application of simultaneous differential imaging and simultaneous polarimetric techniques are required to reach the photon-limit of coronagraphic imaging. These three developments, if pursued together, will yield significant improvements in the search for planets.

We present numerical results of the science performance of the SPICES mission, which aims to characterize the spectro-polarimetric properties of cold exoplanets and circumstellar disks in the visible. We focus on the instrument ability to retrieve the spectral signatures of molecular species, clouds and surface of super-Earths in the habitable zone of solar-type stars. Considering realistic reflected planet spectra and instrument limitation, we show that SPICES could analyse the atmosphere and surface of a few super-Earths within 5 pc of the Sun.

Here we present the installation and successful commissioning of an L'-band Annular Groove Phase Mask (AGPM) coronagraph on VLT/NACO. The AGPM is a vector vortex coronagraph made from diamond subwavelength gratings tuned to the L' band. The vector vortex coronagraph enables high contrast imaging at very small inner working angle (here 0″.09, the diffraction limit of the VLT at L'), potentially being the key to a new parameter space. During technical and science verification runs, we discovered a late-type companion at two beamwidths from an F0V star (Mawet et al. 2013), and imaged the inner regions of β Pictoris down to the previously unexplored projected radius of 1.75 AU. The circumstellar disk was also resolved from ≃ 1″ to 5″ (see J. Milli et al., these proceedings). These results showcase the potential of the NACO L-band AGPM over a wide range of spatial scales.

The SEE COAST concept is designed with the objective to characterize extrasolar planets and possibly Super Earths via spectro-polarimetric imaging in reflected light. A space mission complementary to ground-based near IR planet finders is a first secure step towards the characterization of planets with mass and atmosphere comparable to that of the Earth. The accessibility to the Visible spectrum is unique and with important scientific returns. 1. Historic and context Radial Velocity technique has been one of the most prolific method to identify extrasolar planets in the past decade (374 objects listed in http://exoplanet.eu). The comparison with our own Solar System already suggests a large diversity (in mass, eccentricity, semimajor axis ...). One of the next step is the study of exoplanet atmospheres and we must be also prepared for diversity. In that context, direct detection is required as we need to collect the planetary photons to perform for instance spectroscopy. But also, a few self-luminous planets have been already detected either from the ground and space using direct imaging (Kalas et al. 2008, Lagrange et al. 2009) and temperature and mass have been estimated from evolutionary models. In addition, direct imaging covers a parameter space that is complementary to Radial Velocity as it is more sensitive to long period. The ever-growing interest for Super Earths (telluric planets that are more massive than the Earth) has led us to propose a space telescope operated in the visible for spectroscopic and polarimetric analysis of these objects. SEE COAST (Super Earth Explorer Coronagraphic Off-Axis Space Telescope) was first proposed to Cosmic Vision at ESA in 2007 but not selected. The science potential and requirements are briefly described 2. Astrophysical requirements and instrumental concept The Core Science program of SEE-COAST is to explore the diversity of planets especially focusing on Super Earths and mature Jovian planets as a goal (young/massive giants, brown dwarfs and debris disks are also part of the program). We anticipated that in the coming years Radial Velocity instruments will provided many targets accessible with SEE-COAST. Several tools are considered for this study : Spectroscopy: a spectral resolution of 40 to 80 in the visible and near IR (0.4-1.2μm) is required to measure the presence of several molecular species like H2O, O2, CH4