5 Results

We used 269 different stars belonging to ASPHO1 and ASPHO2 catalogues obtained at OCA. Our goal is to determine 185 declination corrections ($\Delta\delta$) taking into account that 84 stars were in the near maxima digression condition.

An analysis of the individual values of $\Delta\delta$ as obtained from global reduction as well as the extension to the non-common stars, was made and the results are based on HIPPARCOS system.

The $\Delta\delta$ are obtained as the addition of the east and west mean residuals that means they may contain instrumental effects such as magnitude and colour equations. In Table 1 we have the magnitude and colour index coefficients (instrumental effects) obtained by the global reduction.

  

Table 1: Colour and magnitude coefficients - (global reduction)

Based on Table 1 we can conclude that the colour-magnitude effects in the photoelectric astrolabe (ASPHO) are very small confirming the quality of the results.

These results are comparable with the best results presented in the literature. The general standard deviation obtained by the global reduction is 0.027$\hbox{$^{\prime\prime}$}$ and the value of $\eta$ is -0.018$\hbox{$^{\prime\prime}$}$ $\pm$ 0.005$\hbox{$^{\prime\prime}$}$.

It is interesting to note that the magnitudes analysed here are not bigger than 8.0. Thus, we can only say that there is not any colour-magnitude effect in this term. It is possible that it is not true to magnitudes bigger than 8.0. There is a project to transform the detection from photoelectric to CCD form.

The obtained equator correction is small confirming that the equator used in the FK5 system in the observed zone as well as that these values are compatible with the dynamical values for the equator correction taking with others techniques (Leister 1989) as showed in Fig. 1.

  

Figure 1: Equator corrections (Martin & Leister 1997, modified)

The comparison of our results with the dynamical ones confirms the astrolabe as a potential instrument for ground-based astrometry.

Thus, the photoelectric astrolabe can be a very important instrument for the definition of the fundamental reference equator. The results confirm also the position adopted by Fricke (1982) in order to maintain the equator of the FK4 system in the FK5 system.

The $\Delta\delta$ and $\sigma_{\Delta\delta}$ are shown in Figs. 2a,b. The $\Delta\delta$ distribution has mean -0.010$\hbox{$^{\prime\prime}$}$ and standard deviation 0.003$\hbox{$^{\prime\prime}$}$ and the $\sigma_{\Delta\delta}$ distribution has mean 0.049$\hbox{$^{\prime\prime}$}$ and standard deviation 0.003$\hbox{$^{\prime\prime}$}$. The dotted line represents the Gaussian fitting.

  

Figure 2: a) $\Delta\delta$ and b) $\sigma_{\Delta\delta}$ distribution