Perturbing Effects in Past Optical Astrometric Data. Statistical Modelisation and Separation

Abstract

Past optical astrometric observations are to be re-reduced in order to get a new evaluation of the Earth Orientation Parameters in the more accurate Hipparcos reference frame. Among the selected instruments is the Paris astrolabe, considered here. In this Paper, through multivariate statistical procedures, we deal with the preliminary step of the new evaluation which consists in detection and separation of sources of significant inconsistency and outstanding errors in the Paris reductions so far performed. The analysis is performed over two test periods -one per instrumental setting-that are compared in particular in terms of observer effects,magnitude, colour and sidereal time effects. The Paper also gives a synthetic overview on the statistical methods we used to obtain the main results so that they can be applied to other astrometric data.