Effect of Galactic aberration on Earth orientation parameters: From the ICRF2 to the ICRF3

Abstract

Aims. At the beginning of 2019 the third realization of the International Celestial Reference Frame (ICRF3) replaced the previous version (ICRF2). In the current International Celestial Reference Frame (ICRF), a major improvement is the inclusion of the Galactic aberration (GA) effect. The Earth orientation parameters (EOP), which link the celestial and terrestrial reference frames, are thus accordingly affected. This paper investigates the influence of the ICRF evolution and the modeling of the GA effect on the determination of the EOP. Methods. The EOP time series derived within the frame of two official ICRF realizations, as well as different ways of handling the GA effect, were estimated based on the very long baseline interferometry (VLBI) observational data obtained over the past 40 yr. The correlation between the station network and the GA contribution to the EOP was then analyzed by comparison of IVS R1 and R4 routine observations, which have a different distribution of antennas. We also studied the effect of GA on nutation and free core nutation amplitudes by least-squares fits. Results. The application of different reference frames (ICRF2 and ICRF3) in VLBI solutions leads to constant offsets of 315 microarcsec in the components of dX, dY, and dUT 1. This difference is mainly the reflection of the orientation offsets between the two realizations of the International Celestial Reference System. In a separate study of the GA effect, an approximate 0.3 ± 0.3 uas yr−1 bias is found in dY, while other components are not significantly affected. This bias results in an increasing offset in precession which is non-negligible after several tens of years. We further found that the bias caused by the GA effect will decrease when using a set of more uniformly distributed sources or stations in the most recent decades.