Celestial fundamental catalogues are a prerequisite for the determination of absolute positions and motions in space. Presently, positional astrometry is at the watershed between classical fundamental catalogues, based on moving reference stars, and modern catalogues, based on extragalactic reference objects with non-measurable motion. This book addresses the concepts and methods of the respective construction techniques leading to the stellar frame of the FK5 (Fifth Fundamental Catalogue) and to the newly adopted extragalactic radio reference frame, ICRF (International Celestial Reference Frame), with its extension to optical wavelengths by the Hipparcos Catalogue. While principal outlines of meridian circle observations are given, emphasis is put in some detail on the VLBI technique as applied to astrometry, and to the observational techniques used in the Hipparcos mission, including the tie of the originally non-anchored rigid Hipparcos sphere into the ICRF.

Inhalt

1. Fundamental Catalogues.- 1.1 Introductory Remarks.- 1.2 Objectives of Fundamental Catalogues.- 1.2.1 Optical Catalogues.- 1.2.2 Radio Source Catalogues.- 1.2.3 Unification of Optical and Radio Catalogues.- 1.3 Background of Conventional Fundamental Catalogues.- 1.3.1 Various Aspects of Catalogue Compilation.- 1.3.2 Terminology and Definitions.- 1.4 Inertial Reference Systems and Frames.- 1.5 Precession and Nutation.- 1.6 Determination of the Luni-solar Precession.- 1.6.1 Luni-solar Precession from Lunar and Solar Torques.- 1.6.2 Dynamical Determination of the Luni-solar Precession.- 1.6.3 Luni-solar Precession Derived from Stellar Proper Motions.- 1.6.4 Luni-solar Precession Derived from Positions of Extragalactic Objects.- 1.7 Conventional Stellar Celestial Reference Systems.- 1.8 Conventional Extragalactic Celestial Reference Systems.- 2. The Conventional Fundamental Catalogue FK5.- 2.1 Historical Review.- 2.2 The FK5 Celestial Reference System.- 2.2.1 Definition of the FK5 System.- 2.2.2 Link Between FK5 and the Solar System.- 2.2.3 Time and Time Scales.- 2.3 First Principles of Compiling the FK5.- 2.3.1 Installation and Operation of Meridian Circles.- 2.3.2 Generation of Absolute Observations by Meridian Circles.- 2.4 Scope of the FK5 Work.- 2.4.1 Systematic Catalogue Differences.- 2.4.2 System Improvement.- 2.5 Transition to the Standard Epoch J2000.0.- 2.6 Organization of the FK5.- 3. Contributions of Space Astrometry to Fundamental Catalogues.- 3.1 Astrometric Space Missions.- 3.2 The Astrometry Satellite Hipparcos.- 3.2.1 Overview of the Instrument Payload.- 3.2.2 Attitude Control.- 3.3 Observing Principle.- 3.4 Organization of the Data Reduction.- 3.5 From Photons to Grid Coordinates.- 3.6 Reduction to Reference Great Circles.- 3.6.1 The Model of Abscissa Estimation.- 3.6.2 The Procedure of Abscissa Estimation.- 3.6.3 The Astrometric Information Content of the Abscissae.- 3.7 Sphere Solution.- 3.7.1 Conceptual Background.- 3.7.2 Observation Equations and Estimation of Unknowns.- 3.8 Construction of the Hipparcos Catalogue.- 3.8.1 Rank Deficiency.- 3.8.2 Iterative Data Reduction.- 3.8.3 Merging of the Provisional Hipparcos Catalogues.- 3.8.4 Differences of Principle Between the Construction of the FK5 and Hipparcos Catalogues.- 4. Astrometry with Radio Interferometers.- 4.1 Radio Astronomy.- 4.1.1 Historical Review.- 4.1.2 Quasars.- 4.1.3 Some Basic Terms and Definitions.- 4.2 Techniques of Radio Interferometry.- 4.2.1 Radio Interferometers for Astrometry.- 4.2.2 Signal Acquisition by Radio Interferometry.- 4.3 The Observables.- 4.3.1 The Phase Observable Derived from VLBI.- 4.3.2 Derivative Observables.- 4.3.3 Fringe Frequency and Time Delay.- 4.3.4 Uncertainties in the Interferometer Observables.- 4.4 Requirements for Astrometry.- 4.4.1 Geometric Delay Models.- 4.4.2 Time Information.- 4.4.3 Retarded Baseline.- 4.4.4 Gravitational Delay.- 4.4.5 Aberration and Parallactic Effects.- 4.4.6 Sensitivity of the Observables.- 5. Fundamental Catalogues of Extragalactic Radio Sources.- 5.1 System Definition.- 5.2 Some Specific Features of the ICRS Definition.- 5.2.1 Origin of Coordinates.- 5.2.2 Principal Plane - Equator.- 5.2.3 Right Ascension Origin.- 5.3 The Extragalactic System Versus the FK5 System.- 5.4 Building Blocks for Catalogue Establishment.- 5.4.1 Absolute Astrometry.- 5.4.2 The Group Delay Observable.- 5.4.3 The Fringe Frequency Observable.- 5.4.4 Accumulation of Source Observations.- 5.4.5 The Right Ascension Zero Point.- 5.4.6 Observation Catalogues of Extragalactic Radio Sources.- 5.4.7 The Physical Models Used for Parameter Adjustment.- 5.5 Methods of Fundamental Catalogue Construction.- 5.5.1 The Classical Method.- 5.5.2 The Observable Method.- 5.5.3 The IERS Catalogue Combination Method.- 5.5.4 Observable Method Versus Combination Method.- 6. The International Celestial Reference Frame: ICRF.- 6.1 The Principles of ICRF Construction.- 6.2 Appraisal of the Origins, Context, and Role of the ICRF.- 6.3 Accuracy Assessment of the ICRF.- 6.3.1 Internal Consistency Tests.- 6.3.2 External Comparisons.- 6.3.3 Remaining Model Deficiencies and an Error Budget.- 6.4 Future Maintenance of the ICRF.- 7. Hipparcos Catalogue Tie with Conventional Celestial Reference Frames.- 7.1 Link with the Extragalactic Reference Frame.- 7.2 Link with the FK5 Reference Frame.- 7.3 Testing the Rigidity of the FK5 Frame.- 7.3.1 Vectorial Harmonics Used for Catalogue Comparison.- 7.3.2 Catalogue Comparison Using Classical Methods.- 7.4 Refinement of the Hipparcos Link with the Extragalactic Reference Frame.- 8. Future Prospects.- 8.1 Interdependence of Astrometry and Fundamental Catalogues.- 8.1.1 New Topics Inspired by Improved Astrometric Accuracy.- 8.1.2 A Sketch of the FK6.- 8.2 Prospective Observational Techniques.- 8.2.1 SIM - The Scientific Basis of the Mission.- 8.2.2 FAME - Mission Profile and Science Summary.- 8.2.3 GAIA - Goals of the Mission.- 8.3 Prospects for the Celestial Reference Frame.- Epilogue.- References.