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RA: 12h 35m 50.04s
Dec: +27° 03′ 12.5″
Con: Coma Berenices
Ch: MSA:654, U2:149, SA:7
Ref: Corwin (2004)
Type: stars (three)
Mag: B=?, V=?
NGC 4557 is a triple star. Bigourdan did not provide a precise micrometric offset for this object, but his approximate offset with respect to NGC 4558 (-3 seconds of time, +2.8 arcmin), combined with his description ("Trace of nebulosity which may be accompanied by a star...") clearly identifies the triple as the object which he saw. The MCG and PGC identifications are wrong. Wolf's identification in the Konigstuhl Nebel-List No. 4 is correct, where he calls it stellar and places it between two stars (he obviously resolved the triple while Bigourdan did not). The GSC includes 2 of the three stars, one being the central one measured by Wolf. The position that I've adopted for N4557 is for this central star.
The RNGC (Sulentic and Tifft 1973) notes that this is a 15.5 mag galaxy. Their coded description reads SLEL,BM,HISB,DBOR*NR.
The Messier objects
The Bennett objects
The Caldwell list
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