The Hipparcos satellite's photometric observations accurate set of reference directions for dynamical Another goal of astrometry is the establishment of an Tocentric motion to be decoupled from the e ect of per- various levels of accuracy and sensitivity. Identi cation and understanding of multiple systems, andįurthermore allow the e ects of non-linear (orbital) pho- phenomena that can be studied by optical astrometry at Would greatly enhance kinematical studies, improve the The sixth astrometric parameter, the radial velocity. In addition,Ĭonsideration is being given to the parallel determination of (Lindegren & Perryman 1994a, b Lindegren et al. Respect to Hipparcos, in terms of accuracy, number of Recommended that such an interferometric mission beĪ future astrometry mission could be enhanced, with Missions: one of these will be an interferometric observatoryĪccuracy can be demonstrated, the Survey Committee has The period 2005−16, it contains three `cornerstone' Scienti c programme is now being formulated. The European Space Agency's `Horizon 2000 Plus' Results expected to be available during 1996Īl. Motions, has been fully demonstrated, with the nal Providing absolute trigonometric parallaxes and proper Space, resulting in a rigid positional reference frame, and With accuracies in the range 1−2 milliarcsec, and theĬoncept of carrying out a global astrometric survey from Positions,Īnnual proper motions, and parallaxes have been determined The Hipparcos project represented the rst step in theĪcquisition of astrometric data from space. Mission in Japan, and the proposal for an astrometric Recent commencement of studies of an astrometric space Of proposed space programmes in the United States, the (wideangle) ground-based astrometric facilities and a variety Missions within the former Soviet Union, elaborate The future, has inspired the proposal of three astrometric The appreciation of the continuingįundamental importance of astrometry, and its potential for Space Agency (ESA) developed and launched a satelliteĮntirely dedicated to high-accuracy stellar positional Ically illustrated by the fact that, in 1989, the European The resurgence of interest in astrometry today is dramat Perhaps the most dramatic of these subsidiary goals would be the possibility of screening some 100 000 stars within 100 pc for periodic photocentric motions, which would provide the most powerful and systematic method of detecting possible planetary companions proposed to date.Īstrometry | space vehicles | planetary systems | relativity | instrumentation interferometers | Galaxy general As `by-products', the global measurements would yield unprecedented information on the space-time metric (γ to a precision of about 1 part in 106 or better, close to values which might distinguish currently competing theories of gravity), angular diameters of hundreds of stars, and a vast body of information on double and multiple systems. ![]() The scienti c case for such a mission is dramatic: distances and kinematical motions for tens of millions of objects, throughout our Galaxy, would be obtained|the expected accuracy is such that direct (trigonometric) distance estimates to the galactic centre would be accurate to 10%, with transverse motions accurate to about 1 km s−1 at 20 kpc. In its present form, the experiment is estimated to lead to positions, proper motions, and parallaxes of some 50 million objects, down to about V = 15 mag, with an accuracy better than 10 microarcsec, along with multi-colour multi-epoch photometry of each object. | GAIA is a preliminary concept for an astrometric mission, recently recommended within the context of ESA's `Horizon 2000 Plus' long-term scienti c programme. GAIA: Global astrometric interferometer for astrophysicsĠ Sterrewacht Leiden, Postbus 9513, 2300RA Leiden, The Netherlandsġ Astrophysics Division, European Space Agency, ESTEC, Noordwijk 2200AG, The NetherlandsĢ Lund Observatory, Box 43, S-22100 Lund, Sweden
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