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gaia data release 3 documentation

14.1 Introduction

14.1.2 Astrometric accuracy

The astrometry in Gaia DR3 is identical to the one in Gaia EDR3. For the accuracy we note:

  • The deformation detected versus ICRF2 as expected, and correct with respect to ICRF3 (Section 14.4.2).

  • The global parallax zero point has been reduced with respect to Gaia DR2, and now it is estimated to be around -0.02 mas (Section 14.4).

  • Zero-point variations using differential parallaxes of binaries (differential parallaxes of potential common proper motion pairs) and from open cluster (Section 14.7.1) analysis show a systematic difference between Gaia DR2 and Gaia DR3.

  • Tests from Open Clusters show strong variations of the parallax zero point with G magnitude and colour (Section 14.7.1).

  • Tests from Open Clusters show variations of the proper motion zero point with G magnitude and colour. The effect is more evident in right ascension than in declination (Section 14.7.1).

  • Tests with APOGEE binaries confirm the large variations of zero-point with magnitude for bright stars, and tests using QSOs also confirm the variation at faint magnitudes (Section 14.4.2).

  • The large scale regional variations in parallax zero-point are much improved since Gaia DR2 for 5p solutions, both on the average and for fluctuations, but 6p solutions show more pronounced systematics, as shown by the checks using QSO parallaxes and proper motions (Section 14.2).

  • Small scale zero-point fluctuations have also been reduced with respect to Gaia DR2, as shown by checks in several regions with different densities (Section 14.2). The effects of the scanning law have been greatly reduced in Gaia EDR3.

  • In all cases, 6p solutions show a very different behaviour from 5p, and look more prone to systematic effects.

  • Spurious solutions (objects with very negative parallaxes) have been significantly reduced from Gaia DR2. However, the percentage is still large for 6p solutions and the banding effect (over 0.6) is still present.

  • The parallax zero point also shows variations with (pseudo-)colour for dwarf spheroidals that were not present in Gaia DR2. These variations, however, are not showing in the QSOs.