1. Clube, S.V.M., and Nicholson, W.: 1974, New Problems in Astrometry, IAU Symp. 61, p. 97.
2. de Vegt, Ch.: 1974, New Problems in Astrometry, IAU Symp. 61, p. 209.
3. Dieckvoss, W.: 1963, Basic Astronomical Data, (Ed. K.Aa. Strand), Univ. of Chicago Press, Chicago and London, p. 40.
4. Fricke, W.: 1973, Mitt. Astron. Rechen-Inst. Heidelberg, Ser. A, No. 68.
5. Høg, E.: 1972, Astron. Astroph., 19, p. 27.