An Extension of the IAU Framework for Reference Systems

IAU 2000 resolutions on the reference frames set up a solid theoretical foundation for implementing general relativity in astronomical data processing algorithms and for unambiguous interpretation of measured relativistic effects. We discuss possible directions for further theoretical development of the IAU resolutions aimed to take into account the decadal progress in observational techniques and computer-based technologies. We address the following subjects: 1) space-time transformations and the structure of the metric tensor; -2) PPN parameters and gauge invariance of equations of motion; -3) astronomical reference frames for cosmological applications.