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We use methods of differential astrometry to construct a small field inertial reference frame stable at the micro-arcsecond level. Using Gaia measurements of field angles we look at the influence of the number of reference stars and the stars magnitude as well as astrometric systematics on the total error budget with the help of Gaia-like simulations around the Ecliptic Pole in a differential astrometric scenario. We find that the systematic errors are modeled and reliably estimated to the μas level even in fields with a modest number of 37 stars with G <13 mag over a 0.24 sq. degrees field of view for short timescales of the order of a day for a perfect instrument and with high-cadence observations. Accounting for large-scale calibrations by including the geometric instrument model over such short timescales requires fainter stars down to G=14 mag without diminishing the accuracy of the reference frame.
The Doppler detection of the Jupiter-mass planet around the nearby, solar-type star 51 Pegasi (Mayor and Queloz 1995) heralded the new era of discoveries of extrasolar planets orbiting normal stars. Four different techniques have been successfully used for the purpose of exoplanet detection. Decade-long, high-precision (1–5 m/s) radial-velocity surveys of ˜3000 F-G-K-M dwarfs and subgiants (e.g. Butler et al. 2006, Udry and Santos 2007, Eggenberger and Udry 2010) in the solar neighborhood (d ≤ 50 pc) have yielded so far the vast majority of the objects in the present sample (a total of over 760 planets in ˜600 systems, as of June 2012). Ground-based photometric transit surveys (e.g. Char-bonneau et al. 2007, Collier Cameron 2011) are uncovering new transiting systems at a rate of ˜30 per year, while space-borne observatories such as CoRoT and particularly Kepler hold promise of increasing by an order of magnitude the present yield (over 230 transiting systems known to date). Finally, over three dozen sub-stellar companions have also been detected so far by means of gravitational microlensing (e.g. Bond et al. 2004, Beaulieu et al. 2006, Gaudi et al. 2008, Muraki et al. 2011), direct-imaging surveys (e.g. Chauvin et al. 2005, Kalas et al. 2008, Marois et al. 2008, 2010), and timing techniques (Silvotti et al. 2007, Lee et al. 2009, Beuermann et al. 2010).
GAME (Gravitation Astrometric Measurement Experiment) is a mission concept based on astronomical techniques for high precision measurements of interest to Fundamental Physics and cosmology, in particular the γ and β parameters of the Parameterized Post-Newtonian formulation of gravitation theories extending the General Relativity.
High precision astrometry also provides the light deflection induced by the quadrupole moment of Jupiter and Saturn, and, by high precision determination of the orbits of Mercury and high elongation asteroids, the PPN parameter β.
The astrometric and photometric capabilities of GAME may also provide crucial complementary information on a selected set of known exo-planets.
The science of extra-solar planets is one of the most rapidly changing areas of astrophysics and since 1995 the number of planets known has increased by almost two orders of magnitude. A combination of ground-based surveys and dedicated space missions has resulted in 560-plus planets being detected, and over 1200 that await confirmation. NASA's Kepler mission has opened up the possibility of discovering Earth-like planets in the habitable zone around some of the 100,000 stars it is surveying during its 3 to 4-year lifetime. The new ESA's Gaia mission is expected to discover thousands of new planets around stars within 200 parsecs of the Sun. The key challenge now is moving on from discovery, important though that remains, to characterisation: what are these planets actually like, and why are they as they are?
In the past ten years, we have learned how to obtain the first spectra of exoplanets using transit transmission and emission spectroscopy. With the high stability of Spitzer, Hubble, and large ground-based telescopes the spectra of bright close-in massive planets can be obtained and species like water vapour, methane, carbon monoxide and dioxide have been detected. With transit science came the first tangible remote sensing of these planetary bodies and so one can start to extrapolate from what has been learnt from Solar System probes to what one might plan to learn about their faraway siblings. As we learn more about the atmospheres, surfaces and near-surfaces of these remote bodies, we will begin to build up a clearer picture of their construction, history and suitability for life.
The Exoplanet Characterisation Observatory, EChO, will be the first dedicated mission to investigate the physics and chemistry of Exoplanetary Atmospheres. By characterising spectroscopically more bodies in different environments we will take detailed planetology out of the Solar System and into the Galaxy as a whole.
EChO has now been selected by the European Space Agency to be assessed as one of four M3 mission candidates.
Small ground-based telescopes can effectively be used to look for transiting rocky planets around nearby low-mass M stars, as recently demonstrated for example by the MEarth project. Since December 2009 at the Astronomical Observatory of the Autonomous Region of Aosta Valley (OAVdA) we are monitoring photometrically a sample of red dwarfs with accurate parallax measurements. The primary goal of this ‘pilot study’ is the characterization of the photometric microvariability of each target over a typical period of approximately 2 months. This is the preparatory step to long-term survey with an array of identical small telescopes, with kick-off in early 2011. Here we discuss the present status of the study, describing the stellar sample, and presenting the most interesting results obtained so far, including the aggressive data analysis devoted to the characterization of the variability properties of the sample and the search for transit-like signals.
In its all-sky survey, the ESA global astrometry mission Gaia will perform high-precision astrometry and photometry for 1 billion stars down to V = 20 mag. The data collected in the Gaia catalogue, to be published by the end of the next decade, will likely revolutionize our understanding of many aspects of stellar and Galactic astrophysics. One of the relevant areas in which the Gaia observations will have great impact is the astrophysics of planetary systems. This summary focuses on a) the complex technical problems related to and challenges inherent in correctly modelling the signals of planetary systems present in measurements collected with a space-borne observatory poised to carry out precision astrometry at the micro-arcsecond (μas) level, and b) on the potential of Gaia μas astrometry for important contributions to the astrophysics of planetary systems.
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.
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