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Improvement of Nonrigid-Earth Nutation Theory by Adding a Model Free Core Nutation Term

Published online by Cambridge University Press:  12 April 2016

Toshimichi Shirai  and
Toshio Fukushima
Toshimichi Shirai
Affiliation:
University of Tokyo, Graduate School of Science, Department of Astronomy, 3-8-1, Hongoh, Bunkyo-ku, Tokyo 113-0033, [email protected]
Toshio Fukushima
Affiliation:
National Astronomical Observatory, 2-21-1, Ohsawa, Mitaka, Tokyo 181-8588, Japan

Abstract

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From the analysis of VLBI observational data compiled by USNO (U.S. Naval Observatory) from MJD 44089.994 to 51618.250 (McCarthy, 2000), we showed that a strong peak around –400 sidereal days in the spectrum of its differences from the IERS96 nutation theory could be explained by adding a model Free Core Nutation (FCN) term in the form of a single damped oscillation. Then we developed a new analytical theory of the nonrigid-Earth nutation including the derived FCN model. We adopted RDAN98 (Roosbeek and Dehant, 1998) as the rigid Earth nutation theory. It was convolved with a transfer function using numerical convolution in the time domain (Shirai and Fukushima, 2000). The form of the transfer function was the same as that of Herring (1995). However, its free parameters such as the complex amplitude and frequency of the FCN were readjusted by fitting to the above VLBI data. Even after truncating the forced nutation series so as to contain only 180 terms, the WRMS (Weighted Root Mean Square) of the complex residuals for the new nutation series is 0.312 mas, which is significantly smaller than 0.325 mas, that of the IERS96 nutation theory. As for the FCN term, we estimated its oscillatory period as –430.8±0.6 sidereal days, and its Q-value as 16200 ± 1600. Also we estimated the correction of the precession constants as −0.29297±0.00047”/cy in longitude and −0.02430±0.00019”/cy in obliquity, respectively.

Type
Section 2. Improved Definitions and Models
Information
International Astronomical Union Colloquium , Volume 180: Towards Models and Constants for Sub-Microarcsecond Astrometry , March 2000 , pp. 223 - 229
Copyright
Copyright © US Naval Observatory 2000

References

Dehant, V., et al., 1999, Celest. Mech. Dyn. Astron., 72, 245.Google Scholar
Fukushima, T., 1991, Astron. Astrophys., 244, L11.Google Scholar
Gegout, P. et al, 1998, Phys. Earth. Planet. Inter., 106, 337 Google Scholar
Herring, T.A., 1995, Hightlights of Astronomy, 10, 222.Google Scholar
Lieske, J.H., Lederle, T., Fricke, W., and Morando, B., 1977, Astron. Astrophys., 58, 1.Google Scholar
McCarthy, D.D., 1996, ‘IERS Conventions’, IERS Technical Note 21.Google Scholar
McCarthy, D.D., 2000, private communication.Google Scholar
Roosbeek, F. and Dehant, V., 1998, Celest. Mech. Dyn. Astron., 70, 215.Google Scholar
Sasao, T. and Wahr, J.M., 1981, Geophys. J. R. Astron. Soc., 64, 729.Google Scholar
Seidelmann, P.K., 1982, Celest. Mech., 27, 79.Google Scholar
Shirai, T. and Fukushima, T., 2000, Astron. J., 119.Google Scholar
Toomre, A., 1974, Geophys. J. R. Astron. Soc., 38, 335. Google Scholar