References for the numbering systems

Col	Reference

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

R1	Sanduleak N., Philip A.G.D. 1968, Astron. J. 73, 566

R2	Pavani D.B., et al. 2001,  Astron. Astrophys. 374, 554

R3	Carraro G., et al. 2007, Astron. Astrophys. 466, 931

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