EDP Sciences
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Volume 428, Number 1, December II 2004
Page(s) 255 - 260
Section Celestial mechanics and astrometry
DOI http://dx.doi.org/10.1051/0004-6361:20035952

A&A 428, 255-260 (2004)
DOI: 10.1051/0004-6361:20035952

Effects of zonal deformations and the Earth's rotation rate variations on precession-nutation

S. Lambert1 and N. Capitaine2

1  Department of the Navy, US Naval Observatory, Earth Orientation Department, 3450 Massachusetts Avenue NW, Washington DC 20392, USA
    e-mail: sbl@usno.navy.mil On leave from 2
2  SYRTE - UMR 8630/CNRS - Observatoire de Paris, 61 avenue de l'Observatoire, 75014 Paris, France
    e-mail: capitaine@syrte.obspm.fr

(Received 29 December 2003 / Accepted 9 August 2004)

Because of their importance in the accurate modeling of the Earth's orientation in space, some non-negligible predictable effects on precession-nutation are investigated. This paper considers the coupling effects between the axial and the equatorial components of the Earth's rotation vector in the dynamical equations, and the effects of the second order lunisolar torque due to the Earth's zonal deformations. Firstly, the coupling effects are shown to contribute for less than 0.1  $\mu$as and are therefore negligible. Secondly, we demonstrate that the 0.7 mas contribution of the rotation rate variations due to zonal tides to the nutation in obliquity deduced by Bretagnon et al. (2000, Proc. IAU Coll., 180, 230; 2001, Celest. Mech. Dyn. Astr., 80, 177) is an artefact which comes from an incomplete way of taking into account the effect of the rotation rate variations. The net contribution is shown to be negligibly small. Thirdly, for an Earth model with an elastic mantle and decoupled liquid core, the contribution of the second-order lunisolar torque due to the Earth's zonal deformations is shown to be 207.9  $\mu$as and -9.7  $\mu$as on the 18.6-year nutation respectively in longitude and in obliquity, and a correction of -4925.9  $\mu$as/century on the precession in longitude.

Key words: reference systems -- astrometry -- time

© ESO 2004