New version of the latitude set derived from observations with a prismatic astrolabe in Poltava

Abstract

The latitude set derived from observations with the prismatic astrolabe in Poltava during 37 years (1964.5--2000.9) is revised in order to improve the reliability and validity of the observation results. To this purpose the accurate coordinates of the HIPPARCOS catalogue are used, and the method is applied which takes into account the instrumental effects typical for Danjon astrolabes. It is just the instrumental instability caused by insufficient accuracy with which the astrolabe installation parameters are reproduced after maintenance works. The set was made homogeneous by 1) dividing it into separate fragments for which the instrumental system is stable; 2) treating the data of each fragment with a modified chain method; 3) estimating the instrumental system jumps at the boundaries of adjacent intervals; 4) merging the set, considering the systematic corrections obtained in the previous step. Low-frequency latitude variations are analysed stable 3.2 and 9-years harmonics are found. The trend caused by the secular polar motion is absent. The results show that it is necessary to treat of the data with the FK6 catalogue and supplement it with the latitude variation data derived with other instruments in Poltava.