## Hipparcos, the New Reduction of the Raw DataThepublication oftheHipparcos andTycho Catalogues in 1997 transformed astrometry, and as a consequence astronomers’ perception of astrometry. What had before often been regarded as a somewhat quaint specialty of limited re- vance to modern astrophysics, was suddenly seen to produce a wealth of data of immediate practical use. The ready availability of many thousand precise trigonometric stellar distances and the access to an accurate and dense - tical reference frame have changed the way astronomers think about certain problems and plan their experiments. Inevitably, the exploitation of so much new data not only solved some old problems, tidied up several confused areas and sharpened many observational constraints, but it also generated new qu- tions about established theory – and about the data themselves. The author of this book has taken a radical approach to answer some of these questions: a complete re-examination of the satellite data and the models used to represent them, in particular the attitude modelling. Eventually this resulted in the new and very signi?cantly improved Hipparcos reduction described in this book. This remarkable achievement was made possible by a combination of many factors, including time and the exponential growth of computing power, but mainly an incredible amount of detailed, tedious and ingenious work by the author and the resulting insight into what really went on with the satellite in its unhappy orbit. Dr. |

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### Contents

THE HIPPARCOS MISSION | 3 |

12 The mission | 17 |

13 The published data | 25 |

14 Concepts of the new reduction | 31 |

HIPPARCOS ASTROMETRY | 39 |

22 The Hipparcos astrometric data | 46 |

23 Reconstruction of the alongscan rotation phase | 56 |

24 Grid distortions | 58 |

93 Magnetic torques and the remaining torque variations | 249 |

94 Predictability of the environmental torques | 251 |

FULLYDYNAMIC ATTITUDE FITTING | 254 |

102 The integration engines | 257 |

103 Implementing the gyro data | 260 |

104 Implementing the star mapper data | 263 |

105 Implementing the IDT transit data | 269 |

106 Conclusions | 282 |

25 Astrometricparameter solutions | 63 |

EXPLORING THE HIPPARCOS ASTROMETRIC DATA | 71 |

INDIVIDUAL SINGLE STARS | 72 |

32 Correlations | 80 |

33 Parallaxes | 85 |

34 Proper motions | 95 |

35 Disturbed solutions | 100 |

36 Comparison with the ICRS | 109 |

THE ASTROMETRIC DATA FOR COMPOSITE IMAGES AND ORBITAL BINARIES | 113 |

41 The modulated signal for smallseparation double stars | 114 |

42 Astrometric parameters for double stars | 126 |

43 Double stars with two catalogue entries | 131 |

44 Variablebrightness of one component | 132 |

45 Multiple systems | 135 |

46 Orbital motions | 137 |

GROUPS OF SINGLE STARS | 143 |

52 Application to star clusters | 145 |

53 Calibrating luminosities | 163 |

54 Conclusions | 176 |

KINEMATICS OF THE SOLAR NEIGHBOURHOOD | 177 |

62 The distribution of nearby stars | 186 |

A DESCRIPTION OF THE CONTENTS AND PECULIARITIES OF THE HIPPARCOS PHOTOMETRIC DATA | 196 |

THE PHOTOMETRIC DATA | 197 |

72 Formal errors and variability indicators | 204 |

73 Variability analysis | 208 |

74 Newly discovered variables | 214 |

HIPPARCOS ATTITUDE MODELLING | 216 |

A FREEFLOATING RIGID BODY IN SPACE | 217 |

82 The internal torques and inertia tensor | 223 |

83 External torques acting on the satellite | 226 |

84 Nonrigidity | 236 |

THE TORQUES ON HIPPARCOS AS OBSERVED OVER THE MISSION | 239 |

92 Solar radiation torques | 241 |

SUMMARY OF SELECTED SPACECRAFT AND PAYLOAD CALIBRATION RESULTS | 284 |

THE MISSION TIMELINE | 285 |

112 Data coverage and detector response | 298 |

PAYLOAD CALIBRATIONS | 299 |

121 The optical transfer function | 301 |

122 Largescale geometricdistortion calibration | 304 |

123 Photometric calibrations | 311 |

SPACECRAFTPARAMETER CALIBRATIONS | 329 |

132 Gyro characteristics | 335 |

133 Thruster ﬁrings and the Centre of Gravity | 340 |

THE NEXT GENERATION | 346 |

GAIA | 349 |

143 The mission plan | 352 |

144 The astrometric data reduction | 354 |

145 The photometric data reduction | 355 |

146 The spectroscopic data reduction | 360 |

147 Dataanalysis challenges | 363 |

148 Organization of the data processing and analysis | 365 |

Transformations for heliotropic and TaitBryant angles | 369 |

Spline functions | 373 |

Linear Least Squares and Householder Orthogonal Transformations | 377 |

Chain solutions running solutions and common parameters | 381 |

Orbit parameters for binary stars | 385 |

Reference orbital parameters | 393 |

The data disk | 403 |

G2 The science data | 406 |

G3 Payload calibration data | 410 |

G4 Spacecraft calibration data | 416 |

419 | |

439 | |

443 | |

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### Common terms and phrases

abscissa residuals absolute magnitude accuracy along-scan attitude amplitude arcsec astrometric data astrometric parameters attitude modelling attitude reconstruction basic angle binaries centre clock drift cluster coefﬁcients components coordinates corrections correlations curve deﬁned derived determined dispersion distance distribution double star drift eclipses effects ﬁeld of view ﬁeld transits Figure ﬁles ﬁnal ﬁrst ﬁt ﬁtted ﬁtting ﬁxed formal errors function Gaia Gaia mission galactic graph gyro harmonic Hipparcos catalogue Hipparcos data HR diagram Hyades identiﬁed instrument parameters interval iterations Leeuwen main sequence matrix measurements modulation NDAC noise observed obtained on-board clock open cluster orbit parallax pass band payload perigee position proper motions published data radial velocity reduction reference frame reﬂect relation relative satellite scan scan-phase shown in Fig shows signal signiﬁcant slits solution spacecraft spin axis spline star mapper stellar Table telescope thruster ﬁrings tion torques values variable variations vector