References for the numbering systems

Col	Reference

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R1 Lindoff U. 1969, Ark. Astr. 5, 221

R2 Grubissich C. 1975, Astron. Astrophys. 21, 99

R3 De Graeve E. 1979, Publ. Obs. Vatican 1 no 16

R4 Maciejewski G. & Niedzielski A. 2007, Astron. Astrophys. 467, 1065


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