References for the numbering systems

Col	Reference

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

R1	Phelps R.L., Janes K.A. 1994, Astrophys. J. Suppl. 90, 31

R2	Oja T. 1966, Ark. Astr. 4, 15

R3	McCuskey S.W., Houk N. 1964, Astron. J. 69, 412

R4	Steppe H. 1974, Astron. Astrophys. Suppl. 15, 91

R5	Yadav R.K.S., Sagar R. 2002, Mon. Not. R. Astron. Soc. 337, 133

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