The Hipparcos and Tycho Catalogues were published in 1997. In the intervening 10 years, several thousand papers making more-or-less direct use of the data have been published. I summarise a number of scientific applications which illustrate the variety of problems to which the data have been applied. This includes the re-reduction of old and contemporary astrometric observations, investigations of Galactic structure and dynamics, investigations of stellar structure and evolution, investigations of the Solar System and our Earth's environment, and various uses of the binary star and photometric data.

Precision closure phase measurements obtained with ground-based long baselineoptical interferometers is a promising way to directly detect light from nearbyhot Jupiters. Here we present our closure phase simulations for the CHARA arrayfor several bright hot Jupiters, υ And b, 51 Peg b, and τBoo b. The maximum possible closure phase signals from these hot Jupiters arevery small, for example, only ∼0.17 degrees for υ And b,requiring very high precision and stable closure phase measurements. We presentpreliminary results of a closure phase study on test object β Tau andhot Jupiter system υ And, both obtained with the MIRC instrument atthe CHARA array. We demonstrate that directly detecting the light from hotJupiters is feasible using high precision closure phase measurements obtained byCHARA-MIRC along with its sub-milli-arcsecond resolution, although challengesremain.

As part of an astrometric program (see Loinard et al. in this volume), we have obtained an unprecedented sample of high-resolution (~ 1 mas) VLBA images of several nearby young stellar systems. As was to be expected, these images revealed interesting new characteristics of these objects. Perhaps the most interesting of these characteristics is the detection of a high rate of very tight binary stars (separations of a few mas) in our sample: of the 9 objects observed to date, 5 are binaries of this type.

The present system of astrometric education in the Saint-Petersburg State University is presented. The general courses, specific programs, seminars and observations that a student takes during a 5-year educational program are described.

The European Space Agency decision to include the Hipparcos satellite into its Science Programme is placed in the context of the years 1965-1980 and in the historical perspective of the progress of astrometry. The motivation and ideas which lead to the Hipparcos design are reviewed as well as its characteristics and performance. The amount and variety of applications represent an impressive evolution from the original science case and opened the way to much more ambitious further space missions, especially Gaia, based on the same basic principles. A giant step in technology led to a giant step in science. Next steps are presented at this Symposium.

Microlensing has proven to be a valuable tool to search for extrasolar planets of Jovian- to Super-Earth-mass planets at orbits of a few AU. Since planetary signals are of very short duration, an intense and continuous monitoring is required. This is achieved by ground-based networks of telescopes (PLANET/RoboNET, μFUN) following up targets, which are identified as microlensing events by single dedicated telescopes (OGLE, MOA). Microlensing has led to four already published detections of extrasolar planets, one of them being OGLE 2005-BLG-390Lb, a planet of only ∼5.5 M⊕ orbiting its M-dwarf host star at ∼2.6 AU. Very recent observations (May–September 2007) provided four more planetary candidates, still under study, that will double the number of detections. For non-planetary microlensing events observed from 1995 to 2006 we compute detection efficiency diagrams, which can then be used to derive an estimate of the Galactic abundance of cool planets in the mass regime from Jupiters to Sub-Neptunes.

We present the adaptive optics assisted, near-infrared VLTI instrument GRAVITY for precision narrow-angle astrometry and interferometric phase referenced imaging of faint objects. With its two fibers per telescope beam, its internal wavefront sensors and fringe tracker, and a novel metrology concept, GRAVITY will not only push the sensitivity far beyond what is offered today, but will also advance the astrometric accuracy for UTs to 10 μas. GRAVITY is designed to work with four telescopes, thus providing phase referenced imaging and astrometry for 6 baselines simultaneously. Its unique capabilities and sensitivity will open a new window for the observation of a wide range of objects, and — amongst others — will allow the study of motion within a few times the event horizon size of the Galactic Center black hole.

We present the results of a wide-field, high-precision UBVIc CCD photometric survey of the Galactic open cluster Blanco 1. Standardized photometry was acquired using the Y4Kcam on the SMARTS 1m telescope at CTIO. We have also determined new high-precision proper motions (σμ = 0.3 mas yr−1) over an eight square degree area down to V = 16.5. Combined with 1D kinematic data, our survey yields a complete list of cluster members down to ~ 0.5 M⊙ and new high-fidelity color-magnitude diagrams are presented for Blanco 1. Having established a bona fide membership catalog, astrophysical characteristics of solar-type cluster members such as X-ray activity and lithium abundance have been studied to gain more insights in the process of internal mixing and convection. Our new results should also help to better understand its peculiar location in the Milky Way and to unravel its dynamical history.

Gaia photometric capabilities should distinguish quasars to a high degree of certainty. With this, they should also be able to deliver a clean sample of quasars with a negligible trace of stellar contaminants. However, a purely photometric sample could miss a non negligible percentage of ICRF sources counterparts - and this interface is required to align with the ICRS and de-rotate the GCRF (Gaia Celestial Reference Frame), on grounds of continuity. To prepare a minimum clean sample forming the initial quasar catalogue for the Gaia mission, an all sky ensemble was formed containing 128,257 candidates. Among them there is at least one redshift determination for 98.75%, and at least one magnitude determination for 99.20% of the targets. The sources were collected from different optical and radio lists. We analyze the redshift, magnitude, and color distributions, their relationships, as well as their degree of completeness.

Complementary, the candidate sources enable to form an optical representation of the ICRS from first principles, namely, kinematically non-rotating with respect to the ensemble of distant extragalactic objects, aligned to the mean equator and dynamical equinox of J2000, and realized by a list of adopted coordinates of extragalactic sources.

Gravitational microlensing observations will lead to a census of planets that orbit stars of different populations. From 2008, ARTEMiS will provide an expert system that allows to adopt a three-step strategy of survey, follow-up and anomaly monitoring of gravitational microlensing events that is capable of detecting planets of Earth mass and below. The SIGNALMEN anomaly detector, an integral part, has already demonstrated its performance during a pilot season. Embedded into eSTAR, ARTEMiS serves as an open platform that links with existing microlensing campaigns. Real-time visualization of ongoing events along with an interpretation moreover allows to communicate “Science live to your home” to the general public.

Comparing proper motions of the FK5 and Hipparcos, several authors declared that the two proper-motion systems are inconsistent with the value of the precession correction obtained from VLBI and LLR observations. Based on the proper-motion data from the PPM and ACRS catalogues which are constructed on the FK5 system, the inconsistent values of the precessional correction and of the time-dependent term of equinox correction, derived from the different subsets of stellar samples, have been found. One of the reasons for those discrepancies should be mostly due to the internally biased proper-motion system of the FK5.

GAME (Gamma Astrometric Measurement Experiment) is a concept for an experiment whose goal is to measure from space the γ parameter of the Parameterized Post-Newtonian formalism, by means of a satellite orbiting at 1 AU from the Sun and looking as close as possible to its limb. This technique resembles the one used during the solar eclipse of 1919, when Dyson, Eddington and collaborators measured for the first time the gravitational bending of light. Simple estimations suggest that, possibly within the budget of a small mission, one could reach the 10−6 level of accuracy with ~106 observations of relatively bright stars at about 2° apart from the Sun. Further simulations show that this result could be reached with only 20 days of measurements on stars of V ≤ 17 uniformly distributed. A quick look at real star densities suggests that this result could be greatly improved by observing particularly crowded regions near the galactic center.

Gaia is an ambitious space astrometry mission of ESA with a main objective to map the sky in astrometry and photometry down to a magnitude 20 by the end of the next decade. While the mission is built and operated by ESA and an industrial consortium, the data processing is entrusted to a consortium formed by the scientific community, which was formed in 2006 and formally selected by ESA one year later. The satellite will downlink around 100 TB of raw telemetry data over a mission duration of 5 years from which a very complex iterative processing will lead to the final science output: astrometry with a final accuracy of a few tens of microarcseconds, epoch photometry in wide and narrow bands, radial velocity and spectra for the stars brighter than 17 mag. We discuss the general principles and main difficulties of this very large data processing and present the organization of the European Consortium responsible for its design and implementation.

The formal errors on the astrometric data in the 1997 publication of the Hipparcos catalogue are, for stars brighter than about magnitude 9, largely the result of inaccuracies in the description of the along-scan attitude of the satellite. A detailed study of the dynamics of the Hipparcos satellite has led to a much improved understanding and modelling of the satellite attitude, taking into account peculiarities in the rotation of the payload (scan-phase jumps) as well as the detections of small hits. A new reduction of the Hipparcos data was initiated, in which the attitude modelling is a direct description of the dynamics of the satellite. In this so-called fully-dynamic attitude modelling the underlying torques acting on the satellite are reconstructed, and rates and error angles are obtained through integrations. Both the hits and the scan-phase jumps could be taken into account in the context of this model. The new model, including the provisions for discontinuities, led to a factor five reduction in the attitude noise. A new reduction, based on a global iterative solution like is also planned for Gaia, was started in 2004, and completed, after some 15 iterations, in 2007. In the process of this reduction, also the sensitivity of the solution to optimal connectivity between the data in the two fields of view was exposed and taken care of, as well as a couple of small-scale calibrations. The latter had not been possible to solve for in the original reductions. In the catalogue that resulted from this new reduction, the errors on the astrometric data for all but stars brighter than magnitude 4, are dominated by photon noise. Error-correlation levels in the underlying abscissa data are down by more than an order of magnitude, and play no longer any significant role. This feature very much simplifies the analysis of, for example, wide-binary stars and open cluster data.

The primary goal of this study was measurement of trigonometric parallaxes and proper motions of a dozen members of the TW Hydrae Association (TWA) that are not present in the Hipparcos catalogue.

We use Darwin's theory (Darwin, 1880) to derive the main results on the orbital and rotational evolution of a close-in companion (exoplanet or planetary satellite) due to tidal friction. The given results do not depend on any assumption linking the tidal lags to the frequencies of the corresponding tide harmonics (except that equal frequency harmonics are assumed to span equal lags). Emphasis is given to the study of the synchronization of the planetary rotation in the two possible final states for a non-zero eccentricity : (1) the super-synchronous stationary rotation resulting from the vanishing of the average tidal torque; (2) the capture into a 1:1 spin-orbit resonance (true synchronization), which is only possible if an additional torque exists acting in opposition to the tidal torque. Results are given under the assumption that this additional torque is produced by a non-tidal permanent equatorial asymmetry of the planet. The indirect tidal effects and some non-tidal effects due to that asymmetry are considered. For sake of comparison with other works, the results obtained when tidal lags are assumed proportional to the corresponding tidal wave frequencies are also given.

According to a revised schedule of the Russian Space Agency, in October 2008 the 10 m space telescope RadioAstron will be launched in a high eccentric orbit around the Earth. Acting together with ground based radio telescopes, the VLBI interferometer with a ground-space arm will operate. The interferometer will have extraordinary angular resolution of a few microarcsecond (μas) at the shortest wavelength (1.35 cm). Since typical angular scales for gravitational microlensing are at the μas level for cosmological locations of sources and microlenses, in principle there is a chance to resolve microimages and (or) at least, detect astrometrical shift of bright point like images. In particular, gravitationally lensed systems, such as B1600+434, where in radio band a signature of microlensing is found, look suitable for direct observations of microlensing, since microlensing with the RadioAstron interferometer may be detected in the future (considering its high angular resolution and a relatively high sensitivity and assuming a ground support by the advanced radio telescopes).

SIM PlanetQuest is a very high accuracy space astrometric instrument based on a long baseline stellar interferometer. For global astrometry SIM was designed to be accurate to ≈ 4μas (microarcsec) after a 5 year mission. For narrow angle astrometry (≈ 1000 s integration over a 1° radius field) SIM is designed for 1μas precision. The technology program was completed in 2005 and based on laboratory results, the current best estimate of SIM's performance would be 0.6 μas for narrow angle precision and 2.4 μas for global accuracy. This paper describes a variety of science programs that the SIM science team have proposed to conduct from a search for one Earth mass planets in the habitable zone of (≈130) nearby stars to the study of dark matter in the galactic disk, the galactic halo and the local group.

We investigate the secular evolution of non-resonant exoplanetary systems consisting of a central star and two co-planar planets using a semi-numerical averaging method of the first order in planetary masses (in this case equivalent to “averaging by scissors” or simply dropping the fast periodic terms). The resulting Hamiltonian level curves for different exoplanetary systems were compared to those obtained by direct numerical integration. Studying the dependence of the reliability of the averaging method (as well as chaoticity of numerically integrated trajectories) upon the initial conditions, we found that the averaging methods fails even for Hill stable systems. Based on the Hill stability criterion we introduced empirically a more restrictive stability condition, that enabled us to give an estimate for the region of validity of the averaging method in the plane of initial conditions.

The future PRIMA facility at the Very Large Telescope Interferometer (VLTI) in astrometric mode offers the possibility to perform relative narrow-angle astrometry with 10 micro-arcsecond accuracy. This is achieved with a dual-beam interferometer concept, where a reference star and the scientific target, confined in a 60 arcsecond field, are observed simultaneously. The angular separation of the two stellar objects gives rise to an optical delay in the interferometer, which is measured by the Fringe Sensor Unit (FSU) and an internal laser metrology. PRIMA is using two FSU fringe detectors, each observing the interference of stellar beams coming from one of the two objects and measuring the corresponding phase and group delay. The astrometric observable, yielding the angular separation, is deduced from the group delay difference observed between the two objects. In addition, the FSU phase delay estimate is used as error signal for the fringe stabilisation loop of the VLTI. Both functions of the FSU require high precision fringe phase measurements with a goal of 1 nm rms (corresponding to λ/2000). These can only be achieved by applying a calibration procedure prior to the observing run. We discuss the FSU measurement principle and the applied algorithms. The calibration strategy and the methods used to derive the calibration parameters are presented. Special attention is given to the achieved measurement linearity and repeatability. The quality of the FSU calibration is crucial in order to achieve the ultimate accuracy and to fulfill the primary objective of PRIMA astrometry: the detection and characterisation of extrasolar planetary systems.