Rationale
‘To contribute usefully to the scientific progress, one must sometimes not disdain from undertaking simple verifications’ (Foucault, 1847).
Despite the precautions taken when building the Gaia data processing, completely avoiding errors in a one billion source catalogue, with many intricate data for each object, is an impossible task. Before the publication of the Gaia archive, an in-depth validation of its contents should thus be undertaken. This will rely on methods and tools developed in the CU9 Work Package or in the other Wps, and which can also be used, with little or no adaptation, by the scientific community for the analysis of the catalogue.
The definition of what a systematic error is will lead to check for suspect spatial (or epoch, colour, magnitude, ...) variations, if any, which could be due processing artifacts. The validation will thus address the statistical distribution of the astrometric parameters, typically the unbiasedness of the parallaxes and proper motions, as one of the main outcome of the mission, and which may be subject to many perturbations. It will also scrutinize the photometry and spectroscopy data, assisted by the important classification task performed in Gaia, and, when available, external data.
It is planned to have two plenary validation meetings per year. The first meeting in Vienna in July 2014 described the work done in the various Work Packages. This CU9(940) and GENIUS (T5) workshop rather intends to enter more into the details of all the validation procedures, by :
- familiarising with the validation development and runtime environments,
- studying and improving current methods,
- running tests on existing or simulated catalogues,
- and analysing their results.