References for the numbering systems

Col	Reference

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

R1	Becker W. 1965, Contr. Oss. Astr. Univ. Padova no 180

R2	Hoag A.A., et al. 1961, Publ. US Nav. Obs. 17, 347  (pe)

R3	Hoag A.A., et al. 1961, Publ. US Nav. Obs. 17, 347  (pg)

R4	Hassan S.M. 1973, Astron. Astrophys. Suppl. 9, 261

R5	Yadav R.K.S., Sagar R. 2004, Mon. Not. R. Astron. Soc. 349, 1481

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