Complement to VII/239A

NGC 6456

, 6463, 6470, 6471, 6472, and 6477. Here is another mess from Lewis Swift's 4th and 5th lists of nebulae. NGC 6463 and NGC 6470 were found on 9 June 1886, the remainder on 25 September 1886. All of Swift's positions fall within a group of (at least) eight galaxies. It's possible that Swift could have seen most of the objects, but only after seeing the DSS image from the POSS-II plate could I assign his numbers with any confidence to the galaxies. I also have to thank Brian Skiff for asking about the field; his questions forced a re-evaluation that I otherwise would not have made.

The descriptions don't help much. All the galaxies are "eeeF, eS, R" or a close variation, and all are noted "v dif[ficult]" to "eee dif". Swift does mention that the preceding of the group is "bet[ween] 2 sts" – but since the Galactic latitude is so low, there are enough stars around for that description to apply to virtually any of the galaxies in the group. Dreyer added the note "* nr" to N6471 and N6477; this is not in Swift's original paper, so it must be from a letter from Swift to Dreyer.

In any event, there is not much to go on here that will help us assign the NGC numbers to the correct objects. If we make some reasonable assumptions – 1) Swift saw the two brightest galaxies on his first sweep through the area, 2) he did in fact see all six 3.5 months later, and 3) his relative positions for the remaining four galaxies seen only the second night are more or less accurate – then we can make a stab at some identifications. These are not certain by any means, and they do not agree with some previous identifications.

However, they do make sense of Swift's data. On the first night, he saw the two brightest objects in the core of the group, N6463 and N6470. N6456 is reasonably isolated to the west of the core, and N6471 and N6472 flank N6470 in declination. They are also the brightest galaxies in the core after N6463 and N6470. It also is reasonable to suppose that both components of UGC 10973 contributed to the visual appearance of N6471, so I've listed both in the main table. I'm least certain about N6477, but Swift's observation places it following N6470/1/2, and between N6472 and N6470 in declination. The galaxy I've chosen matches these constraints – but its position is still well off Swift's place.

For reference, here is a table of B1950.0 positions, Swift's on the first line, and accurate positions on the second, of my suggested identifications.

Object RA (Swift) Dec Discovered Other names and comments (Precise) Pos source V 76 17 42 29 +67 37.7 25 Sept 1886 CGCG 321-034 N6456 17 42 39.60 +67 36 48.6 GSC

IV 55 17 43 44 +67 36.5 9 June 1886 CGCG 321-037 = MCG +11-21-022 N6463 17 43 42.27 +67 37 24.2 GSC

IV 56 17 44 19 +67 37.8 9 June 1886 CGCG 321-039 = MCG +11-21-025 N6470 17 44 22.98 +67 38 18.3 GSC

V 78 17 44 19 +67 36.4 25 Sept 1886 UGC 10973a = CGCG 321-038w = N6471w 17 44 20.89 +67 36 44.0 GSC = MCG +11-21-023 N6471e 17 44 26.06 +67 36 36.6 GSC UGC 10973b = CGCG 321-038e = = MCG +11-21-024

V 79 17 44 19 +67 39.9 25 Sept 1886 N6472 17 44 11.31 +67 38 58.5 NPM1 = NPM1G +67.0154

V 80 17 44 54 +67 39.2 25 Sept 1886 N6477: 17 44 38.38 +67 37 44.3 HCds

Other possibilities: 17 43 16.26 +67 33 43.7 GSC Star superposed. 17 43 33.48 +67 40 17.4 GSC Extremely compact w vF arms; star superposed on nucleus? 17 44 51.37 +67 33 33.3 HCds



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