Physical Reference Frames and Astrometric Measurements of Star Direction in General Relativity \\I. Stellar Aberration

TL;DR

This paper discusses the importance of relativistic models for precise astrometric measurements in space, focusing on defining accurate stellar directions within General Relativity to improve star coordinate and motion determination.

Contribution

It compares two relativistic models, GREM and RAMOD, to ensure consistent and physically correct definitions of light direction for high-precision astrometry.

Findings

Validated the consistency between GREM and RAMOD models

Established a framework for accurate stellar position measurements

Enhanced the physical interpretation of astrometric observables

Abstract

The high accuracy of modern space astrometry requires the use of General Relativity to model the propagation of stellar light through the gravitational field encountered from a source to a given observer inside the Solar System. In this sense relativistic astrometry is part of fundamental physics. The general relativistic definition of astrometric measurement needs an appropriate use of the concept of reference frame, which should then be linked to the conventions of the IAU Resolutions (2000), which fix the celestial coordinate system. A consistent definition of the astrometric observables in the context of General Relativity is also essential to find uniquely the stellar coordinates and proper motion, this being the main physical task of the inverse ray tracing problem. Aim of this work is to set the level of reciprocal consistency of two relativistic models, GREM and RAMOD (Gaia, ESA mission), in order to garantee a physically correct definition of light direction to a star, an essential item for deducing the star coordinates and proper motion within the same level of measurement accuracy.