Astronomisches Rechen-Institut Heidelberg

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ARI-Heidelberg Veröffentlichungen, No. 27

Author(s): Schwan, H.
Title: Development and Testing of a Method to Derive an Instrumental System of Positions and Proper Motions of Stars
Source: Veröffentlichungen Astronomisches Rechen-Institut Heidelberg, No. 27, Verlag G. Braun, Karlsruhe, 36 pages
Year: 1977
Abstract: A series of computer programs has been developed to determine the systematic differences between different fundamental observations. The simultaneous dependence of the (weighted) differences on the position (alpha,delta) and the magnitude m is taken into account. Following essentially a method proposed by Brosche (1965) the systematic part of the differences is determined in a statistically reliable manner by the F-test and developed in a series of suitable orthogonal functions. The procedure was tested by analysing the absolute obser- vations made with the 6"-transit circle in Washington from 1925 until 1962. In right ascension the circumpolar stars in the catalogue W450 show systematic difference between the observations in upper and lower culmination. It will be shown that they can be explained by lateral refraction. For the declinations no systematic differences between either culmination were found. The systematic deviation of the catalogues W25, W150, W250, W350 and W450 from the FK4 was derived. A magnitude equation was found only in a few catalogues; no magnitude equation in declination was found except in W450. Most of the functions depending significantly on the magnitude are not correlated with alpha or delta. A simultaneous dependence on the position on the sphere and the magnitude was found only in the combination (delta,m). In general the functions which depend on delta alone (DELTAalphadelta- and DELTAdeltadelta-waves respectively) are dominant. For the catalogues W350 and W450 (observation period 1949 until 1962) the systematic deviations from the FK4 agree in many cases. Such deviations can be interpreted as local errors of the FK4 system. The instrumental system of the Washington 6"-transit circle was derived by determining the systematic deviation of the observations from 1925 until 1962 from the FK4. The mean difference |DELTAµalpha cos(delta)|= 0.s022 per century is a measure for the precision in deriving a proper motion system from the observations made with a single instrument during a period of about 40 years.
Preprint issued:
Remarks: With a correction in Nr. 29, p. 21 (1978)

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