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High angular resolution imaging of extra-solar planetary systems with the very large Telescope Interferometer

Final Activity Report Summary - HARI-EPS-VLTI (High angular resolution imaging of extrasolar planetary systems with the very large telescope interferometer)

The main purpose of this project was to study the innermost regions of extrasolar planetary systems at the highest possible angular resolution, by combining the light coming from multiple telescopes with typical ground separations of one hundred meters. By performing observations in the near-infrared regime with such interferometers (in particular, the European VLTI located at Cerro Paranal in Chile), it is possible to directly detect light from circumstellar dust and from hot giant planets located within the first astronomical unit (Sun-Earth distance) around nearby solar-type stars.

During our 2-year project, we have surveyed about 30 stars for the presence of hot dust, and found that about one third of them have abundant circumstellar material, with dust densities up to 1000 times larger than the zodiacal dust cloud in our own Solar system. This discovery considerably challenges our current understanding of dust processing and minor body dynamics in mature planetary systems, and has therefore led to a series of follow-up theoretical studies. In particular, we have used radiative transfer simulations to constrain the nature and the mass of circumstellar dust, and state-of-the-art dynamical models in an attempt to explain the presence of copious dust within inner planetary systems. Most of this theoretical work is still in progress in the context of an International Space Science Institute working group. Besides searching for hot dust, we have also been involved in the preparation of an Open Time Key Project ("DUNES") on the Herschel space telescope to search for cold extrasolar Kuiper belts around nearby stars.

More complicated is the direct detection of hot extrasolar giant planets, as their near-infrared flux does not exceed one thousandth of the nearby stellar signal. Our 2-year project has mainly focused on technical and data processing developments to enable the first direct detection with the AMBER near-infrared spectro-imager installed at the VLTI. This ambitious programme has also been prepared by performing observations of a less demanding (yet scientifically interesting) low-contrast binary star. Thanks to our developments, we have been awarded a significant amount of observing time with VLTI/AMBER to perform our first observations of a hot giant planet. These observations will be carried out in January 2009 and, if successful, will provide much-needed constraints on chemical and dynamical atmospheric models. In particular, these observations could lead to the first ground-based detection of carbon monoxide, water vapour and/or methane in the emission spectrum of an exoplanet atmosphere.

Finally, we have also been strongly involved in the design and performance estimate of future interferometric facilities, either ground-based (VSI for VLTI, interferometer for Antarctica) or spatial (Darwin) proposed to or scheduled by European Agencies (ESO and ESA) which will address these particular science cases (among others) in a more comprehensive and sensitive way.