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Astron. Astrophys. 359, 1195-1200 (2000)

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10. Results and conclusions

Table 3 shows our results for the rotation parameters for several selected values of [FORMULA], averaged over the ten groups. The stated [FORMULA] errors reflect the dispersion between the different star groups. The corresponding results for the glide parameters are shown in Table 4. Table 5 shows the corresponding adjusted parameters for the proper motions. These latter parameters are much better behaved and an adjustment with [FORMULA] without outliers elimination was enough to represent the differences. Fig. 4 shows the coefficients of the adjusted series, averaged on the ten star groups. These are the main results of our analysis.

[FIGURE] Fig. 4. Coefficients of the series representation of the positional differences, averaged over 10 groups for the final adjustment with [FORMULA]. The ordering indicates the position of the coefficients into the least squares equations, the first 440 represent the toroidals and the followings the spheroidals ones


Table 3. Rotation parameters for several [FORMULA]. MP are the values obtained with the soft used for check ours results


Table 4. Glide parameters for severals [FORMULA] and for MP


Table 5. Rotation and glide parameters for the proper motion difference field

Our analysis of the statistical properties of the series shows that [FORMULA] and [FORMULA] are enough to represent correctly the difference fields for position and proper motions. As a check, we compared the results with a vectorial analysis program by F. Mignard (Mignard 1999), named MP for us, which gives results similar to ours, with differences of about 10%. These differences are due to the different weighting schemes. The differences in proper motion are much smaller and do not show the presence of outliers.

Our results reveal the existence of several large distortions in the SAO reference system positions, evidenced by large Fourier coefficients of large order. The most important effects are in declination, associated with a large displacement field towards the South Pole (Fig. 3). Taking into account that the HIPPARCOS reference frame, being a materialization of the ICRS, is essentially free of these distortions, these zonal effects are due to the SAO catalogue errors. The present series may correct the main systematic effects.

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© European Southern Observatory (ESO) 2000

Online publication: July 13, 2000