Séminaires sur les aspects théoriques et expérimentaux de la gravitation

Enhanced terms in the time delay and the direction of light propagation. Discussion for some solar system experiments

by Prof. Pierre TEYSSANDIER (Observatoire de Paris)

Amphithéâtre Léon Motchane (Institut des Hautes Etudes Scientifiques)

Amphithéâtre Léon Motchane

Institut des Hautes Etudes Scientifiques

Bois-Marie 35, route de Chartres 91440 Bures-sur-Yvette
It is generally stated that the determination of the light travel time up to the order G2 is sufficient for modelling space missions in project --- such as LATOR, ASTROD, SAGAS, ODYSSEY or GAME --- designed to reach an accuracy of 10-7 to 5 × 10-9 in measuring the post-Newtonian parameter γ. However, this statement has to be re-examined in light of our recent demonstration that a so-called `enhanced' term of order G3 in the time delay may become comparable to some of the terms of order G2 when the emitter and the receiver are almost on opposite sides of the central body --- a configuration of crucial importance in experimental gravitation.
This talk yields an overview of the new methods enabling us to carry out the calculation of the light travel time as a function of the positions of the emitter and the receiver (time transfer function) at any order of approximation for a large class of static, spherically symmetric metrics generalizing the Schwarzschild solution. The time transfer function is explicitly determined up to order G3. The enhanced terms are inferred from this solution and their significance for some tests of general relativity in the solar system is analyzed.
To finish, the appearance of enhanced terms in the direction of light propagation is discussed.