# Gravitational wave effects on astrometric observables

## TL;DR

This paper investigates how gravitational waves and planetary quadrupole moments affect astrometric measurements, providing models crucial for high-precision data reduction in space missions like Gaia.

## Contribution

It develops a model for astrometric observables considering gravitational waves and planetary multipole effects, enhancing previous models for Gaia.

## Key findings

- Gravitational waves induce measurable shifts in star positions.
- Planetary quadrupole moments significantly affect light propagation.
- Models improve accuracy of astrometric data analysis.

## Abstract

Observational data from the ESA astrometric mission Gaia determining the positions of celestial objects within an accuracy of few microarcseconds will be soon fully available. Other satellite-based space missions are currently planned to significantly improve such precision in the next years. The data reduction process needs high-precision general relativistic models, allowing one to solve the inverse ray-tracing problem in the gravitational field of the Solar System up to the requested level of accuracy and leading then to the estimate of astrometric parameters. Besides a satisfactory description of the background field due to the planets (which should include their multipolar structure), one should consider also other effects which may induce modifications to the light propagation. For instance, the interaction of the light signal with the superposed gravitational field of a gravitational wave emitted by a distant source would cause a shift in the apparent positions of the stars. We compute here the main astrometric observables needed for data reduction of satellite-based missions in the presence of a passing plane gravitational wave. We also take into account the effect of the mass quadrupole moment of the planets, improving previous results obtained for Gaia.