(55) |

Next, the influence of possible errors in the HW95 model
on the corresponding nutation series H96NUT is investigated.
Assuming the numerical analysis procedure missed the correct
tidal frequency in (55) by this yields an error for the nutation amplitude of about

(56) |

In addition, there are some tides with very small tidal
amplitudes which lead to nutation terms only because
the frequency is close enough to the *K _{1}*-tide.
Since those tidal amplitudes are of the order of the
truncation threshold for the tidal potential,
it is doubtful whether these nutation terms
are real or appear only because of numerical reason.
For the tidal potential HW95 and the nutation series H96NUT
this applies again mainly to the long-periodic nutation terms.

There is also another point to be mentioned. In all tidal and nutation models there are terms which differ in argument only by where is the perigee of the Sun with a period of about 20000 years. By comparison with other tidal models it turned out that HW95 shows some differences concerning the tidal amplitudes of the terms whose argument differs by ,especially when one of the tidal amplitudes is rather large. It seems that the numerical procedure used during the computations, and the final least squares fit of the tidal amplitudes is somewhat critical to these terms. In particular, the rather small tide at in HW95 produces a nutation term in H96NUT with a period of 6786 days and an amplitude of about 5200 as in longitude which is too large in comparison with other nutation models by nearly 5 mas.

Finally, let us consider the accuracy of the constants
involved in the computation of the nutation.
Some discussion about that topic can be found in
Souchay & Kinoshita (1996, 1997a).
The scaling factor for the nutation, namely the
dynamical ellipticity , is currently deduced
from the precession constant .Based on the theory of KS90, chapter eight,
and the precession constant of
Simon et al. (1994),
, the value used for H96NUT is .
Comparing this with the value found
by
Williams (1994)
and used also in
RDAN97 and SMART97, one finds that
the relative accuracy is not better than 10^{-5} which therefore
produces an error in the largest nutation term of about 173 as.
The next largest nutation term is smaller
by almost one order of magnitude.
Therefore, one can doubt whether it presently makes sense to compute
nutation amplitudes much smaller than 1 as.

According to the previous discussions, the conclusion is that short-periodic nutation terms with periods shorter than say 18.6 years except for the largest ones can be computed precisely from the tidal potential HW95 while the long-periodic ones have larger uncertainties.

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