Showpiece regions in the LMC (9)

[Steve Gottlieb]

9) LMC-N79 and LMC–N83 region

NGC 1712 (18"): first of three clusters with nebulosity including NGC 1722 + IC 2111 4' NE and NGC 1727 8' NE. At 128x it appeared as an irregularly shaped, 4' nebulous haze just north of an attractive mag 10.7/11.5 double star (17"). A half dozen faint stars are embedded in the haze (part of LMC-N79) besides the two brighter stars at the south edge. This is a young LMC cluster and forms the western portion of association LH 1.

NGC 1722 (18"): in a small group of LMC clusters with nebulosity including NGC 1727 and NGC 1712. At 128x appears as a fairly faint, irregular hazy region with a few stars resolved and a small, bright knot (IC 1211). Good response to the UHC filter. Located 4' SW of NGC 1727. This is a very young open cluster with an unevolved main sequence and forms the eastern component of association LH 2.

IC 2111(18"): this LMC emission nebula/cluster appeared as a very small, high surface brightness knot, ~12" diameter, embedded within NGC 1722. A mag 12 star lies close SW.

NGC 1727 (18"): fairly bright, fairly large, irregular patch, ~2.5'x1.5', with at least a half-dozen stars mag 13 stars resolved. This LMC cluster with nebulosity responds well to a UHC filter at 128x. A small extension is visible to the southeast (KMHK 187 = LMC-N79D) increasing the size to ~3.5'x1.5'. In a group with NGC 1722 4' SW and NGC 1712 7.5' SW. Located 4' N of mag 8.5 HD 31722. This is a very young cluster or association (LH 2) with an unevolved main sequence similar to nearby NGC 1722.

LMC-N79D (18"): this is a small extension or barely detached piece off the SE end of NGC 1727 in the LMC. SIMBAD identiifies this nebula as KMHK 187 (from Kontizas et al, "The cluster system of the Large Magellanic Cloud" in Astron. Astrophys. Suppl. Ser., 84, 527), though it was catalogued earlier by Henize (79D) as an emission object.

NGC 1737 (24"): at 200x appears as fairly faint nebulous patch centered ~1.8' NNW of the core of NGC 1743 and appears nearly connected. The outline is irregular and roughly 45" diameter with a couple of mag 14 stars involved on the south side. In an impressive complex of nebulosity (within LMC-N83 and association LH 5) with NGC 1745 and NGC 1748 as well as cluster NGC 1756.

NGC 1743 (24"): brightest section of an excellent HII/cluster complex including NGC 1737, 1745, 1748 and 1756. At 200x NGC 1743 appeared very bright, moderately large, ~50" diameter. Contains a very high surface brightness "core" with a fairly bright star involved. A larger "halo" extending mostly north roughly doubles the size to ~1.7'. NGC 1737, a faint extension with a couple of stars involved, is 1.8' NNW. NGC 1743 and NGC 1748 (a bright high surface brightness knot 2' NE) are embedded within a very large, irregular, low surface brightness haze extending ~3' (stellar association LH 5 and emission nebula LMC-N83), oriented roughly from NGC 1743 on the SW side to NGC 1745 on the NE end.

NGC 1745 (24"): fairly faint, fairly large nebulosity with a half dozen mag 13.5-14.5 stars involved, ~1' diameter. Located on the NE side of the NGC 1743 complex (association LH 5 and emission nebula LMC-N83), ~1.5' N of NGC 1748 and 3' NE of NGC 1743, the two main sections of the complex.

NGC 1748 (24"): this HII region (LMC-N83B) appeared as a bright, small, high surface bright knot in a striking group of nebulae, 20" diameter. A couple of stars are involved in the bright glow. A mag 10.3 star is 1.9' SW. NGC 1743 lies 2' SW.

NGC 1756 (24"): moderately bright cluster, relatively large, round, 1.0' diameter, broad concentration with no nucleus or resolution. Located ~5' SE of the NGC 1743 HII complex (LMC-N83) and stellar association LH 5, which includes NGC 1737, 1743, 1745 and 1748.

[Ivan Maly]

This is indeed a fascinating region in the LMC. I studied it last year with my travel telescope of 5.5" aperture. Here I include the original field sketch and notes, followed by a paragraph of additional notes that I made upon my return from Australia. It was a rather superficial observation compared with yours, Steve!

796

To get to NGC 1743 (Dunlop 114) I start again from Mu Mensae and this time go to the last (third) star of the said chain leading N to the W of the bar. Near that star are two more, and mimicking their arc and relative brightness somewhat, there is a chain of NGC 1712, -22, and -27. Their fanning arc points at a Uranometria variable, next to which NGC 1743 is obvious at low power with hints of complexity. Higher power resolves the object into 4 as shown on prev. page [sketch above], and reveals the nearby NGC 1756. While 1743 is undoubtedly the brightest, identifying the other three of the tight group requires a photographic chart, and it seems likely that Dunlop 114 is all 4 together (Dunlop notes?).

[Thus Uranometria was no help in this case also (cf. the NGC 1953 case). Back at home, I consulted Archinal and Hynes, who have an extensive note about the area. They cite Dunlop’s original description and identify Dunlop 114 with NGC 1743 alone. The group of 4 together is the association LH 5. NGC 1756 (see sketch) is not part of it. Note that the sketch is mirror-reversed, and note the direction of the west (arrow). The patch E of NGC 1743 is NGC 1748. The two patches to the N, west to east, are NGC 1737 and 1745. All four are nebulous clusters. Some of the respective clusters and nebulae have their own designations. These are outside NGC or IC, with the exception of IC 2114, which is most likely the nebula in NGC 1748.]