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Data and Methodology

Precession and nutation based on LLR observations from 1969 to 2006 Wassila Zerhouni Observatoire de Paris / SYRTE , 61 Avenue de l’Observatoire 75014 Paris Wassila.zerhouni@obspm.fr. Introduction. Results and conclusion.

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Data and Methodology

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  1. Precession and nutation based on LLR observations from 1969 to 2006 Wassila Zerhouni Observatoire de Paris / SYRTE , 61 Avenue de l’Observatoire 75014 Paris Wassila.zerhouni@obspm.fr Introduction Results and conclusion The Lunar Laser Ranging (LLR) technique measures the round-trip travel times of light pulses between stations on the Earth and four retroreflectors on the surface of the Moon. LLR observations allow to determine the position of the inertial mean ecliptic of J2000.0 with respect to the International Celestial Reference System (ICRS) and with respect to the Mean Celestial Equator (denoted MCEP) of J2000.0. The purpose of this work, based on the paper by Chapront et al.2002, is the determination of the position angles for the systems of reference (ICRS and MCEP) and the correction Δp to the precession . Data and Methodology • Data : • LLR observations used arefrom : • McDonald 1969-2006 • Cerga 1984-2005 • Methodology : • A- LLR residuals • B- Fitted parameters : • First • Lunar parameters • 3*4 reflectors coordinates • Position anglesФ, ε , ψ (cf.figure) • Second • Fixing Ф • Adding stations positions and making a new analysis. • velocities of the stations • fixing all parameters and making a new analysis includingΔp. • This strategy has been applied for two solutions : • Solution 1 (CEP) : P and N are calculated by an analytical model . • MCEP 02 : Solution of Chapront et al .2002 (LLR observations 1969-2001). • MCEP : Based on the same method as Chapront et al.2002 with covering a longer period (1969-2006). • Model : For both MCEP 02 and MCEP : • Precession : Williams 1994 • Nutation : IERS Conventions 1996 (McCarthy 1996) • MCEP 07 : Model • Precession : P03 (Capitaine et al.2003) • Nutation : IAU 2000A (Mathews et al.2002) • Solution 2 (ICRS): P and N are calculated by the conventional matrix and corrected for nutation offsets dψand dε(IERS). For both ICRS 02 and ICRS dψ and dεare with respect to IAU 1980. • ICRS 02 : Solution of Chapront et al .2002 (LLR observations 1969-2001). • ICRS : Based on the same method as Chapront et al. with covering a longer period (1969-2006). • ICRS 07 : dψ and dεare with respect to the conventional model IAU2000. Δ1p (arcsecond/cy) = Δp (MCEP 02) – Δp (ICRS 02) = -0.30488±0.00543 Δ2p (arcsecond/cy) = Δp (MCEP) – Δp (ICRS) = -0.30722±0.00395 Δ3p (arcsecond/cy) = Δp (MCEP 07) – Δp (ICRS 07) = -0.30954±0.00431 Orientation of the axes : Conclusion : The results obtained in this preliminary study are consistent with the previous work of Chapront et al.2002. Based on this longer set of observations and the improved precision, the determination of position angles for different systems of reference and precession is better. We note especially the improvement for the calculation of the residuals Δp in the two solutions. Further work is under development with including the conventional model (precession, nutation and frame bias) for the coordinates X and Y of the CIP (Celestial Intermediate Pole) in the GCRS (Geocentric Celestial Reference System) instead of the classical precession nutation parameters. We will then estimate the observed corrections dX and dY instead of estimating Δp. References : Capitaine et al. 2003, Astron. Astrophys., 412, 567-586. Chapront et al. 2002, Astron. Astrophys., 387, 700-709. Mathews et al.2002, J.Geophys. Res, 107(B4), 10.1029/2001JB00390. McCarthy, D. D. 1996, IERS technical Note 21: IERS Conventions (1996). Williams, J.G.1994,AJ, 108, 2.

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