References for the numbering systems

Col	Reference

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

R1	Hawarden T.G. 1976, Mon. Not. R. Astr. Soc. 174,225

R2	Kassis M., et al. 1997, Astron. J. 113, 1723 (BVI data)

R3	Kassis M., et al. 1997, Astron. J. 113, 1723 (VI data)

R4	Frogel J.A., Twarog B.A. 1983, Astrophys. J. 274, 270

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