Harold Corwin

IC 4681 is the star, immersed in some faint blue nebulosity, that ESO and I have chosen. Barnard says (in AN 4239 = AN 177, 232, 1908) that "There is a conspicuous small nebula or nebulous star in position 1860.0 18h 00m 35s +- -23d 26m +- [this is IC 4684 which is a double star with brighter nebulosity around it] and another in 1860.0 17h 59m 46s +- -23d 25m +-." This second star has no nebulosity around it on the red DSS images, but the star does appear to be fuzzy in Barnard's photograph of the region published as Plate 52 in the Lick Publications, Vol. 11 -- I can see why he mentioned it.

There is a faint sheen of nebulosity around the star -- brightest to the north -- on the DSS1 blue plate. It is nowhere as bright as IC 4684, and is defined mostly by relatively dense absorption patches most noticeable to the north of the star and nebula. Following Barnard's lead, the position I give is for the star.

The star that Wolfgang chose is closer to Barnard's nominal position, but is not nearly as bright, and it is superposed on an absorption patch that helps define the nebulosity on the blue plate.

ESO also suggests that IC 4681 might be identical to IC 4684, but this is not possible as Barnard found the two nebulae on the same plate. However, for a case of confusion from his same paper in AN 4239, see IC 4690.

― IC Notes by Harold Corwin

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