Harold Corwin

IC 4613, IC 4614, IC 4615 = NGC 6196, and IC 4616 = NGC 6197. Bigourdan found a group of five "nebulae" here during his several observations beginning in August of 1886 and extending through April of 1897. He was searching for the four previously catalogued objects, NGC 6194, NGC 6196, NGC 6197, and NGC 6199. He managed to "find" NGC 6194, NGC 6196, and NGC 6197, though his entries under those numbers are for stars. He found no trace of NGC 6199, and gave the three galaxies new numbers (B209, B325, and B426, respectively), though later correctly identified B209 with NGC 6194, and found a new galaxy B324 = IC 4614. The entry in the NGC notes for NGC 6196 has further discussion of the NGC objects.

When Dreyer assembled IC2, B325 became IC 4615 and B426 became IC 4616, while the other two objects, B324 and B425 became IC 4614 and IC 4613, respectively. As I explain in the notes for NGC 6196, Marth's positions for N6196 and N6197 are off by equal amounts: 38 seconds of time in RA, and 1.3 arcmin in declination. When these offsets are applied to Marth's positions, it is clear that NGC 6196 = IC 4615 and NGC 6197 = IC 4616.

While Bigourdan measured micrometric positions for the three brightest galaxies (NGC 6194, NGC 6196, and NGC 6197), he gave the two fainter objects only estimated offsets from the comparison stars. There is nothing in the place of B425 = IC 4613, though for B324 = IC 4614, there is a galaxy (CGCG 196-087) about an arcmin preceding the estimated position. I have had two earlier, both incorrect, ideas about this object, making it first a faint galaxy 6 arcmin south of the position, then a star 18 seconds of time following the IC position. Malcolm has correctly pointed out that Bigourdan's RA offset is to be read as -46 seconds, not -0.46 minutes. This pretty well secures the identification with the CGCG galaxy, which additionally has a star superposed on its northern edge. This would have enhanced the visibility of the object.

An earlier identification of mine for IC 4613 as the galaxy at 16 37 16.2, +35 58 45 (J2000) doesn't hold up to the scrutiny of Bigourdan's estimated offsets. There is nothing at all at his position, so this, too, must be another of his "fausse image".

In summary, IC 4613 is "not found," IC 4614 is almost certainly a galaxy, IC 4615 is certainly NGC 6196, and IC 4616 is just as certainly NGC 6197.

― IC Notes by Harold Corwin

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