References for the numbering systems

Col	Reference

---	---------

R1	von Bronkalla W., 1963, Astron. Nach. 287, 249

R2	Stephenson C.B., 1959, Publ. Astron. Soc. Pacific 71, 145

R3	Eggen O.J., 1968, Astrophys. J 152, 77

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