#NEAT ASTROMETRY FULL#

Light propagation in the gravitational ﬁeld of N arbitrarily moving bodies in 1PN approximation for high-precision astrometry, Physical Review D 92 (2015) 063015.The results of the project represent a basis for subsequent investigations, aiming at the sub-micro-arcsecond and nano-arcsecond level of astrometric measurements. In order to go beyond the monopole approximation, the 2PN metric for one body at rest having arbitrary shape and inner structure has been determined.įinally, it has been found that in 3PN approximation only the monopole term needs to be taken into account for astrometry on the nano-arcsecond level, while the 4PN monopole term is irrelevant for astrometry missions observing in the exterior of some solar-aspect angle of a few degree between the Sun and the instrument spin axis of the space-based observer.

In reality, the bodies are not spherically symmetric but are of arbitrary shape. In this project, the initial and boundary value problem of light propagation in the ﬁeld of one arbitrarily moving monopole has been solved and the 2PN light trajectories are expressed in terms of the retarded position of the moving body, which simpliﬁes the expressions and makes the retardation of gravitational action evident. Thus far, however, the 2PN terms were only known for light propagation in the ﬁeld of one monopole at rest. Regarding the 1PN and 1.5PN terms, it has been found that only the ﬁrst ten mass-multipoles and the ﬁrst two spin-multipoles need to be taken into account for astrometry on the nano-arcsecond level.Īstrometry on sub-micro-arcsecond level requires also to consider some 2PN terms. Furthermore, expressions for timedelay and light-deﬂection have been given. The intrinsic multipoles are deﬁned in the local reference system of each individual massive body, in line with the requirements of the theory of relativistic reference systems and in accordance with the resolutions of the International Astronomical Union.

#NEAT ASTROMETRY FULL#

In the approach, the gravitational ﬁeld of the Solar system is described in terms of the full set of intrinsic mass-multipoles and spin-multipoles of each individual massive body, hence allowing for arbitrary shape, inner structure, oscillations and rotational motions of these bodies. Within the project, the 1PN and 1.5PN terms of the trajectory of a light signal, which propagates in the gravitational ﬁeld of N extended bodies moving along arbitrary world lines, have been determined. Thus far, the 1PN and 1.5PN terms have only been determined either for light propagation in the ﬁeld of N point-like bodies in motion or for N extended bodies at rest. Such unprecedented accuracies necessitate corresponding advancements in the theory of light propagation in the Solar system, that means the determination of trajectories of light signals, emitted by some celestial object and which propagate through the curved space-time of the Solar system towards the observer.įor high-precision astrometry on the sub-micro-arcsecond level of accuracy it is of fundamental importance to determine and to investigate the ﬁrst terms of the post-Newtonian (PN) expansion of the light trajectory.

Gaia-NIR, Theia, NEAT) aiming at the micro-arcsecond, sub-micro-arcsecond and nano-arcsecond level of precision.

Several astrometry missions have been proposed to ESA (e.g. The impressive progress has encouraged the astrometric science to proceed further in near future. In particular, the Hipparcos ﬁnal catalogue provides accuracies of stellar positions up to 1 milli-arcsecond, while the Gaia mission has arrived at precisions up to a few micro-arcseconds in angular observations of stellar objects. The ESA astrometry missions Hipparcos (nominal mission: 1989-1993) and Gaia (nominal mission: 2013-2018) have established a new era in astrometric science. Final Report Year 2021 Final Report Abstract

Neat astrometry