Andrew Cooper
May 27, 2006    Gila, NM (map)
46cm f/4.5 Deep Violet

Embedded in the rich star field of Trumpler24 is a faint glow, no visible definition or edges, large, faint, requires a very dark sky to see at all

Harold Corwin

IC 4628 is a large diffuse nebula centered about 30 seconds of time following Frost's position (adopted by Dreyer for the 2nd IC). Dreyer also lists Barnard as having observed this, but as with so many other of Barnard's new nebulae in IC2, this one was not published. In any event, Frost's description from an Arequipa Bruce plate is appropriate: "F, L, dif., ext. half a degree in RA and a fourth a degree in dec." I actually make it a little closer to 20 arcmin in Dec, but it's clear that Frost was looking at the same object.

Steve Waldee wrote recently about this nebula, asking about Barnard's work on it. We dug the following description by Barnard out of Lick Publications, Vol. 11, 1913, Plate 37:

The coarse cluster in 16h 48m, -40°.3 does not seem to be in Dreyer's lists. It is a very interesting object and appears to be connected by a scattering chain of stars, with the cluster Dreyer 6231 south of it. In its northern part is the nebula Dreyer *2d Index Catalog* [Barnard's italics] 4628. This was originally discovered on a plate with the Willard lens, but no announcement was made of it. It is a large nebula one half degree in diameter and of irregular form and brightness. A photograph with the 10-inch Bruce telescope at Mount Wilson in 1905 (June 21) shows the irregular group of stars and the nebula very beautifully. There are still fainter portions that extend half a degree to the northeast. The nebulosity, apparently, does not condense about any one of the stars and is probably not actually connected with the cluster.

The nebula and cluster is shown clearly in the plate. In the accompanying
table, Barnard simply gives the same position that appears in the Harvard list
and in the IC.

Finally, in his Milky Way Atlas of 1927, Barnard has this to say about IC 4628:

A little below the center of the plate is a mixture of nebulosity and stars. It is listed as N.G.C. II [sic] 4628. The nebulosity, about 30 [arcmin] in diameter, is placed in the northeastern part of a group of stars about 1 [degree] in diameter. The extreme diameter of the nebulosity toward the northeast is about 50 [arcmin].

Here, he gives the same position precessed to 1875.

Also see NGC 6227 for more about John Herschel's observation of a Milky Way star cloud in the area.

― IC Notes by Harold Corwin

Drawings, descriptions, and CCD photos are copyright Andrew Cooper unless otherwise noted, no usage without permission.

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