The goal of the ESA space telescope Gaia is the determination of the spatial positions and velocities as well as the astrophysical characteristics of about 2 billion celestial objects. Gaia is considered as a revolution in astronomy and enjoys the highest international reputation. The team of the Lohrmann Observatory is part of the European Gaia Consortium and primarily responsible for the relativistic aspects of the data processing, the details of the Gaia Celestial Reference Frame as well as the definition, computation and analysis of the astrometric solutions of Gaia.

The ultimate observational accuracy of space astrometry with Gaia requires a thorough relativistic modelling. The usual approach is to require the model that is accurate at a level significantly below the observational accuracy. While this approach was possible for Gaia, it may become prohibitive complex for accuracies just 1-2 orders of magnitude below. A combination of Gaia observations with those of its possible successor GaiaNIR promises to significantly increase the accuracy of the combined astrometric solution reaching a sub-microarcsecond level. The task is to investigate the necessity and the possibility of the corresponding increase of the accuracy of the relativistic models and the parameters required by those models (e.g. orbital data).  The work includes detailed numerical investigations of the influence of various effects on a realistic simulated astrometric solution using a simulation software provided by Gaia Consortium. Certain theoretical investigations of the relativistic effects will also be required. The goal is learn, from the point of view of relativistic modelling, what is actually required to obtain an astrometric solution with a sub-microarcsecond level of accuracy.

This PhD project is part of the MWGaiaDN MSCA Doctoral Network. The network consists of 10 academic partners across Europe at which 12 PhD students will be active in the network researching a range of topics with Gaia and other data. The project includes a number of secondments in the partner universities of the network.