LL-124 - Gaia
Summary: The second release of Gaia data (Gaia DR2) contains several statistical indicators that can be used to assess the quality and reliability of the astrometric data. One such indicator is the astrometric chi-square, or equivalently the unit weight error (UWE) being the square root of the reduced chi-square. The usefulness of the UWE is however severely hampered by its distribution having strong dependences on magnitude and colour. These dependences can be eliminated by a re-normalisation process, using tables provided with this TN. The re-normalised UWE (or RUWE) is a more reliable and informative goodness-of-fit statistic than for example the astrometric excess noise.
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