Lewis Swift discovered NGC 3551 = Sw. I-10, along with Sw. I-11 = NGC 3555 on 24 Aug 1883, and noted "eeF; vS; R; diff; s of 2." His position is 50 sec of RA east of CGCG 125-032 (close pair) but similar in declination. His relative separation with NGC 3555 is 10 sec of RA and 0.5' north. This suggests NGC 3555 = UGC 6203 (brightest in the cluster), though the actual RA difference is 3.2 tsec of RA. CGCG 125-032 is not labeled NGC 3551 in UGC (notes) or CGCG. RNGC and PGC identify the brighter western component of this double as NGC 3551.

As an alternative identification, Corwin suggests that NGC 3551 = UGC 6203 and NGC 3555 = CGCG 125-034, but the declination separation of 3' is much larger than Swift's 0.5'. I feel this solution is less likely.

400/500mm - 17.5" (4/15/99): extremely faint, very small, possibly elongated but difficult to confirm, 20" in diameter. Could not resolve this double system with certainty (or only viewed the brighter component). Located 1.4' SSW of NGC 3555.

17.5" (3/12/94): very faint, very small, round, fairly low even surface brightness. Forms a close pair with NGC 3555 1.4' NNE. This is a double system [29" between centers] which was not resolved or only one component visible. Member of AGC 1177.

Notes by Steve Gottlieb