Harold Corwin

NGC 3645 and five other NGC/IC objects (NGC 3643, NGC 3644, and NGC 3647, which see; and IC 683 and IC 684), lie in a relatively crowded field. There has been considerable confusion about the identifications here because of the crowding -- and because the NGC position of the (presumeably) brightest object, NGC 3645, lies in a blank area of sky a few arcminutes northwest of the group center.

This brightest object was found first by William Herschel on 23 Feb 1784. He placed it 6m 30s preceding and 7' north of 84 (tau) Leo. The NGC position comes from John Herschel's single uncertain observation during Sweep 143; the object is h867 in his 1833 list, though he notes both it and h861 as being II 32. This latter object is considerably brighter than any of the galaxies in the group, and precedes it by 1.3 min. John Herschel saw it during two sweeps (141 and 238), but did not pick it up during Sweep 143. Similarly, h867 was seen only during Sweep 143, but not during sweeps 141 and 238. That, combined with the relative brightness of the object compared to those in the group and John Herschel's uncertain position for h867, strongly suggests that h867 = h861; i.e. NGC 3645 = NGC 3630.

NGC 3645 is also credited to Tempel who has a long discussion of the field in AN 2212 (pp.51-2). I've not translated this yet, but I do not easily see any precise offset from a known object in the text. Is it possible that Tempel was misled by John Herschel's attribution of H II 32 to two different objects? A translation is clearly needed.

― NGC Notes by Harold Corwin

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

A complete list of credits and sources can be found on the about page