References for the numbering systems

Col	Reference

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R1	Moffat A.F.J., Vogt N. 1975, Astron. Astrophys. Suppl. 20, 85

R2	Hilditch R.W., Dodd R.J. 1977, Mon. Not. R. Astron. Soc. 178, 467

R3	Dodd R.J., Ellery L.A. 1980, Mon. Not. R. Astron. Soc. 193, 895

R4	Orsatti A.M. 1992, Astron. J. 104, 590

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