A comparative study of rigid Earth, non-rigid Earth nutation theories, and observational data

Abstract

Context. The past decade has shown strong development of non-rigid Earth nutation theories at the microarcsecond level, now able to match the VLBI observations with differences of about 200 μas in rms, leading the IAU to adopt the conventional analytical model MHB 2000 (Mathews et al. 2002, J. Geophys. Res., 107, B4). This model has been established starting from the REN 2000 rigid Earth nutation theory (Souchay et al. 1999, A&AS, 135, 111). Aims. Users generally do not know the differences between each coefficient of the Fourier series in MHB 2000 and the corresponding one in REN 2000. The aim of this paper is to clarify these differences. Methods. After recalling how the nutation coefficients were obtained in the two above theories, we catch the coefficients that are particularly affected by the non-rigidity. Beside, we develop statistics on the coefficients that are not influenced. Results. At the same time we show some anomalies concerning some coefficients present in REN 2000, but not in MHB 2000 and inversely. The influence of those lacking coefficients is evaluated. Then we simutaneously calculate the REN 2000 and MHB 2000 nutations, thus showing the global contribution of the non-rigidity of the Earth on the nutation. We compare this difference against the differences between observational data and MHB 2000. © ESO 2007.