The influence of standard relativistic effects on Gaia-like astrometric catalogs

Abstract

With the observational accuracy of astrometric space telescopes such as Gaia, the Newtonian theoretical framework for positional astronomy is no longer appropriate. To model all effects relevant at the corresponding levels of accuracy, a more sophisticated description in the framework of General Relativity is required. It is generally known how various relativistic effects affect a given astrometric observation. In particular, the maximal light deflection of a given Solar System body can be easily estimated for a given observer. However, astrometric parameters for a given source are computed from a series of observations of that source. Depending on the relativistic effect, the fraction of observations affected, at some given level of accuracy, by that relativistic effect can vary and also be very small. Our goal is to investigate the impact of unaccounted relativistic effects on the astrometric parameters of a source observed by a Gaia-like astrometric telescope. The standard relativistic framework for Gaia is used to highlight such effects in some cases where they are most significant. Then, using the simulation tool AGISLab, we fit a set of Gaia-like observations of a given number of sources to the standard Gaia-like astrometric model for astrometric source parameters, but using different incomplete relativistic models. In this way we obtain the errors of the astrometric parameters if one were to drop different elements of the relativity model. A simplified analytical description of the errors is also provided and discussed. We demonstrate that, due to averaging over many observations per source, the errors in the astrometric parameters are drastically smaller than the corresponding relativistic effects in individual observations. This opens a way to potentially simplify the relativistic model for future astrometric projects aiming for higher accuracy than Gaia.