Hg. Walter et C. Ma, CORRECTION TO THE LUNI-SOLAR PRECESSION FROM VERY LONG-BASE-LINE INTERFEROMETRY, Astronomy and astrophysics, 284(3), 1994, pp. 1000-1006
The redetermination of the luni-solar precession is performed by using
VLBI catalogues of extragalactic radio sources containing positions a
t observation epochs which cover 9 years. The positions of the sources
have been determined by the VLBI network of the Crustal Dynamics Proj
ect of NASA from measurements covering consecutive half year and one y
ear intervals between 1981 and 1989. In the course of their reduction
the IAU recommended precession terms were applied. On the assumption o
f an imperfection of the luni-solar precession it is expected that the
positions of each source obtained at different epochs but uniformly r
educed to the reference system J2000.0 exhibit an apparent proper moti
on. - We attributed this motion tentatively to precession and solved f
or a correction of the luni-solar precession by making a least squares
fit to the position differences between homonymous sources in the set
of catalogues. The 18.6 yr terms of nutation entered the process as p
arameters the values of which were set by choice from the reservoir of
recent determinations. Twenty-five sources contributed to the analysi
s with the effect that the annual and semi-annual catalogues contain 1
6 sources on the average. The analysis confirmed the slightly overesti
mated IAU value of the luni-solar precession yielding a mean correctio
n of -3.59 +/- 1.14 mas yr-1 from the annual and -3.84 +/- 1.16 mas yr
-1 from the semi-annual catalogues. We discuss these secular terms and
their dependence on the adopted nutation terms.