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Up: Systematic differences Astrolabe-FK5

2. Observations and reductions

According to the latitude of the astrolabe tex2html_wrap_inline839), a zone comprised between tex2html_wrap_inline841 and tex2html_wrap_inline843 in declination can be observed at tex2html_wrap_inline845 zenith distance from Santiago. A zone around the southern celestial pole of about tex2html_wrap_inline847 wide in declination is not observable since in this zone the small declination circles of the stars do not intercept the tex2html_wrap_inline849 almucantar. The observational program at tex2html_wrap_inline851 zenith distance consists of eleven groups of 28 stars each one. The star distribution in azimuth in each group is as uniform as possible. The eleven groups comprise 166 FK5 and 103 FK5 Extension stars. Of these 269 stars, 39 are observed in double transit. The observations were reduced following the IAU76/82 resolutions on fundamental constant and apparent places computation (Kaplan 1981; Chollet 1984). At tex2html_wrap_inline853 zenith distance the stars images as observed with the astrolabe, show permanently a rather strong agitation due to atmospheric effects. The effect of the image agitation on the results is clearly reflected in the precision of the mean zenith distance residuals of the stars. They were obtained with an average mean error of tex2html_wrap_inline855, which is more or less twice the average mean error obtained at Santiago from observations at tex2html_wrap_inline857 zenith distance (Noël & Débarbat 1990).

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