Abstract. We report spectroscopic observations (400−800 nm, R ≈ 100) of Earthshine in June, July and October 2001 from which normalized Earth albedo spectra have been derived. The resulting spectra clearly show the blue colour of the Earth due to Rayleigh diffusion in its atmosphere. They also show the signatures of oxygen, ozone and water vapour. We tried to extract from these spectra the signature of Earth vegetation. A variable signal (4 to 10 ± 3%) around 700 nm has been measured in the Earth albedo. It is interpreted as being due to the vegetation red edge, expected to be between 2 to 10% of the Earth albedo at 700 nm, depending on models. We discuss the primary goal of the present observations: their application to the detection of vegetation-like biosignatures on extrasolar planets.

Abstract. Following the idea developed in Boccaletti et al. (2000), a snapshot imaging interferometer is proposed as an alternative to the nulling interferometer for the NASA Origin project, "Terrestrial Planet Finder". This concept is based on hypertelescope, i.e. densified-pupil, imaging (Labeyrie 1996) and phase-mask coronagraphy (Rouan et al. 2000) to combine a very high angular resolution and a deep attenuation of starlight (10 −8 ) as required to image extra-terrestrial planets. This article aims at presenting thorough estimations of the signal to noise ratio for different classes of stars (from F0V to M5V) and includes several sources of background noise (zodiacal and exozodiacal lights for instance). In addition, numerical simulations have been carried out and are compared to the analytical results. We find that the image of Earth-like planets can be formed with a large hypertelescope (∼80 m) in the thermal infra-red for about 73% of the stars within 25pc.

Abstract. We verify the imaging performance of hypertelescopes on the sky, using a new scheme for pupil densification. To avoid seeing limitations, we used a miniature version with a 10 cm aperture containing 78 sub-apertures of 1 mm size, arrayed periodically as a square grid. The pupil densification is achieved with a pair of micro-lens arrays, where each pair of facing lenses behaves like a tiny demagnifying telescope. We have tested the direct snapshot performance with laboratory-simulated multiple stars and observed the binary star Castor (α Gem). We measured a separation of 3.8 and a magnitude difference of 0.85 which is in agreement with current orbital data. This verified the theoretical expectations for hypertelescopes in terms of field of view and fluxes and qualified the new optical implementation for future arrays at the scale of meters and beyond.

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