References for the numbering systems

Col	Reference

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

R1	Tifft W.G., et al. 1972, Mon. Not. R. Astron. Soc. 158, 47

R2	Pedreros M. 1989, Astron. J. 98, 2146

R3	Surendiranath R. et al. 1990, J. Astrophys. Astr. 11, 151

R4	Stetson P.B. 2000, Publ. astron. Soc.Pacific 112, 925

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