References for the numbering systems

Col	Reference

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

R1	Grubissich C. 1965, Z. Astrophys. 60, 256

R2	Fenkart R.P., Schroder A. 1985, Astron. Astrophys. Suppl. 59, 83

R3	Baume G., et al. 2004, Mon. Not. R. Astron. Soc. 355, 475

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