Precession-nutation estimates
251
is ve days, only the long-periodic terms (between 13.6 days and 18.6 years) are
considered. In order to estimate how robust the solution is, we did the same
analysis with the most precise part of the solution, covering only 1956.0{1992.0
(OA99/2). Both sets are further compared with the values obtained by analyzing
a recent VLBI solution of GSFC (covering only a twenty-year interval, 1979.59{
1999.92), using exactly the same algorithm. The results of all three analyses are
depicted in Table 2. The correlations between individual values (except for the
constant term that is always correlated with the trend because of the choice of
the epoch J2000.0) in the table are rather small for optical astrometry (They do
not exceed 0.13 in case of OA99/1 and 0.29 in case of OA99/2.), thanks to the
length of the series. It is not the case for VLBI where the correlation is as high
as 0.95 between the trend and cosine term of the 18-yr period.
Table 2. Corrections to precession and long-periodic nutation terms,
derived from optical astrometry observations (OA99/1 from 1899.7{
1992.0, OA99/2 from 1956.0{1992.0) and VLBI. In the rst three rows,
sine columns give the trends in milliarcseconds per year, cosine columns
the mean celestial o sets at epoch J2000.0.
Argument /
Longitude mas]
Obliquity mas]
Period days]
sin (`in')
cos (`out')
cos (`in')
sin (`out')
0
OA99/1
;
2.156 0.046
;
31.02 1.71
;
9.17 0.64
;
0.093 0.018
1
OA99/2
;
1.516 0.143
;
16.15 3.52
;
7.12 1.38
0.007 0.056
VLBI
;
2.990 0.013
;
43.00 0.10
;
4.90 0.05
;
0.220 0.007
OA99/1
;
4.31 1.36
;
2.15 1.39
1.83 0.50
2.76 0.50
6798
OA99/2
;
3.84 1.72
;
2.26 1.81
1.71 0.69
2.36 0.66
VLBI
;
6.89 0.03
3.39 0.07
2.89 0.04
1.44 0.01
2
OA99/1
3.12 1.32
2.41 1.33
;
1.10 0.49
1.22 0.49
3399
OA99/2
2.28 1.65
2.97 1.67
;
1.34 0.66
1.51 0.65
VLBI
1.08 0.03
;
0.15 0.02
;
0.29 0.01
0.10 0.01
2
F
-2
D
+2
OA99/1
;
14.50 1.36
;
4.03 1.39
4.68 0.50
;
2.28 0.50
182.6
OA99/2
;
13.16 1.68
;
4.12 1.72
4.45 0.66
;
0.82 0.65
VLBI
1.57 0.02
;
1.36 0.02
;
0.58 0.01
;
0.43 0.01
l
0
OA99/1
;
14.15 1.23
6.58 1.56 10.69 0.48
5.99 0.52
365.3
OA99/2
;
4.82 1.54
8.50 1.90
9.04 0.63
6.19 0.67
VLBI
4.99 0.01
1.24 0.01
2.10 0.01
;
0.27 0.01
l
0
+2
F
-2
D
+2
OA99/1
;
3.82 1.36
;
0.46 1.37
;
1.92 0.49
;
0.08 0.50
121.7
OA99/2
;
2.75 1.69
;
1.93 1.70
;
0.54 0.65
0.82 0.65
VLBI
0.01 0.01
;
0.02 0.01
0.04 0.01
;
0.05 0.01
2
F
-2
D
+
OA99/1
3.31 1.36
2.97 1.37
;
3.69 0.50
2.80 0.50
177.8
OA99/2
3.76 1.70
4.45 1.70
;
3.80 0.65
2.75 0.65
VLBI
;
0.13 0.02
0.01 0.02
0.11 0.01
0.01 0.01
2
F
+2
OA99/1
;
0.18 1.33
1.37 1.32
0.58 0.49
;
072 0.49
13.66
OA99/2
;
0.90 1.66
1.36 1.66
0.68 0.65
;
0.99 0.65
VLBI
;
0.35 0.02
0.29 0.02
0.14 0.01
0.17 0.01
l
OA99/1
;
0.09 1.32
;
0.47 1.32
;
0.73 0.49
1.04 0.49
27.55
OA99/2
;
0.92 1.65
;
0.25 1.65
;
0.69 0.65
1.20 0.65
VLBI
;
0.13 0.01
;
0.06 0.01
0.06 0.01
0.06 0.01
2
F
+
OA99/1
2.23 1.33
;
1.91 1.32
0.46 0.49
;
0.14 0.50
13.63
OA99/2
3.15 1.67
;
1.19 1.65
0.91 0.65
;
0.23 0.65
VLBI
;
0.19 0.02
;
0.02 0.02
0.07 0.01
0.05 0.01
