OR: Observing Adventure in Australia (Part II).
by Steve Gottlieb
Over five clear nights at the Spring" OzSky Star Safari (ozsky.org), I logged over 250 objects, but the most astonishing vistas were certainly in the LMC. In one eyepiece field, you can capture a few emission nebulae, possibly a supernova remnant, and several clusters some with resolved LMC stars and others unresolved knots all superimposed on a bright, glowing background of the LMC itself! The following is just of sampler of some of the LMC treats I observed during the week. If this whets your appetite, you can download detailed descriptions and data on my favorite 8 Showpiece Regions of the LMC" on the page of "Catalogs, Lists and Links .
LMC-N59 Complex = Seagull Nebula = Dragon's Head Nebula
(includes NGC 2030, 2032, 2035 and 2040)
Overall the visible structure of this complex using the 25-inch at 202x and 264 with a narrow-band filter, was comparable to the AAO-red image! (without the color, of course).
NGC 2030 is the first section in this remarkable complex (just off the upper right edge in the ESO image), though it was the faintest of three connected patches extending 5.5' from NW to SE with NGC 2032 and 2035. The brightest portion is an elongated "bar" section ~2'x40", oriented WSW-ENE, just west of mag 12.2 HD 269810. Fainter nebulosity spreads to the north in roughly an oval outline and includes a mag 14.5 star, so the total extent of NGC 2030 in the N-S direction is over 2.5'. Very faint nebulosity appears to connect NGC 2030 with brighter NGC 2032 directly SE.
NGC 2032 was extremely bright, elongated SW-NE, ~2'x1', with a scalloped but sharply defined border at the brighter edge along the dust lane. A fairly prominent thin filament extends NE for ~1.5', curling a bit towards the tip. A thin strip on the SE end (just beyond the lane) connects to NGC 2035. The ionizing star was visible unfiltered at the eastern border, in an indentation, though it appeared fainter than the listed mag of 13.5. A second mag 14 star was also involved at 25" to its east. A mag 11.4 star is off the SW side and a mag 12.2 star is at the NE edge.
NGC 2035 was also extremely bright, roughly rectangular but irregular with slightly concave eastern side and lots of complex, internal structure with brighter and darker areas. A fairly thin streamer is attached on the northeast end and extends 2' NNE, similar (though slightly fainter) to a filament attached to NGC 2032! NGC 2035 is attached or merged at the south end by a thin strip of nebulosity to NGC 2032. LMC-N59C is a fairly faint patch that is detached from NGC 2036 to its southeast. It appeared moderately large, roundish, at least 1' diameter. A mag 10.4 star is 2' ESE.
NGC 2040 appeared bright, very large, irregular nebula just east of NGC 2030/2032/2035 (Dragon's Head or Seagull Nebula). The main portion is roughly triangular with one "vertex" on the south side and another on the northeast end. It has a sharp, contrasty edge on the east side to the south tip and some internal, irregular brightness in the interior. Unfiltered a dozen stars mag 14-15 are involved (association LH 88), with several more spreading to the south.
SNR B0536-67.6 is a supernova remnant shell on the south end of NGC 2040 and the objects are merged on the north end of the shell. Sometimes NGC 2040 itself is incorrectly called a SNR in the professional literature. On images the shell extends ~2' in diameter, with a complex interlaced web of delicate filaments. Visually, I could see a very faint, thin curving loop, ~45" in length, which forms the southwest end of the shell. A mag 13.5 star (O5-type) is in the interior of the shell, with the observed strip centered 40" to its WSW. This star was possibly bound to the precursor star of the SNR remnant.
LMC-N83 Complex (includes NGC 1737, 1743, 1745, 1748)
NGC 1743 = N83A is the overall brightest section of another superb HII/cluster complex including NGC 1737, 1743, 1745, 1748 and 1756. Using 244x, along with a narrow-band filter, it appeared extremely bright, fairly large, irregular, extending ~1.5' NW-SE. The most prominent section has a very high surface brightness and contains a mag 12.5 star. This knot is surrounded by a fainter halo to the SE and E, along with an extension towards the NE that ends just south of NGC 1737 (nearly connected). In the same nebulous complex (N83) is NGC 1748 ~2' NE, NGC 1745 3' NE, NGC 1737 2' NW and NGC 1756 5' SE.
NGC 1737 = N83C was fairly faint but moderately large, roughly 0.9' diameter. A mag 14.4 star is at the center of the circular patch. This tract of emission nebulosity is on the northwest side of the complex with NGC 1743 1.8 SE.
NGC 1745 = N83D, on the northeast side of the complex, was also fairly faint, but easily seen as a fairly large, irregular nebulous haze, surrounding a half-dozen stars mag 14 and fainter. Good contrast gain using a narrow-band NPB filter at 244x.
NGC 1748 = N83B is a fairly bright but fairly small round patch with a high surface brightness and a diameter of ~30". At 397x, a 13th mag "star" was resolved at the southeast edge. This star is classified as a high excitation H II Blob" [HEB]. According to Iranian-born astronomer Mohammed Heydari-Malayeri , these unusual objects represent "early stages of massive stars emerging from their embryonic molecular clouds". Unfiltered a second star (mag ~13.5) was seen closer to the center, forming a 7" double with the HEB.
NGC 2029 = LMC-N63 and LMC-N62
I used the 30-inch to examine NGC 2029 at 202x, 264x and 429x, both with and without filters. This is a large, fairly bright cluster (known as Shapley-Lindsay (S-L) 595) with roughly 30 stars resolved in a 3.5 region. It includes at least 4 brighter stars from mag 12.3-13.5 and another mag 12.7 star is at the SW edge. Moderately faint nebulous haze (LMC-N63) encompasses the cluster. Adding a narrow-bandpass NPB filter at 264x increases the contrast with the large nebulous glow, which extended 2.5-3' diameter. Note: this object is identified as NGC 2030 in most sources!
Henize N63A (discovered by Karl Henize in 1956), embedded slightly east of center, is a well-known compact supernova remnant and one of the first 3 extragalactic SNRs to be discovered (1966). The SNR appeared as a small round knot, only ~12"-15" in diameter, and was faintly visible even at 202x. It was easy to distinguish at 264x and stood out fairly prominently at 429x. Surprisingly, I didn't notice any contrast gain adding a NPB filter (similar visibility).
Roughly 14 SSW of NGC 2029 is N62A. I observed this HII region with a 14-inch using a NPB filter. It appeared very bright, very elongated ~E-W, relatively large, ~1.5'x0.4'. The shape is a bit irregular, but has a sharply defined northern edge, while the southern edge weaker and more ill-defined. Visible unfiltered but excellent response to the NPB. A couple of very faint stars are visible with averted. BSDL 2348, an LMC cluster perhaps associated with the nebula, is ~2' W and contains a half-dozen mag 14-15 stars in a 1.5' knot, along with a mag 12.5 star on the west end.
"Lionel Murphy" Supernova = LMC-N86 = SNR
In 1977, Mike Dopita, Don Mathewson & Vince Ford, working at the Mt Stromlo Observatory in Canberra, published a paper titled "Optical emission from shock waves. III. Abundances in supernova remnants. It included a photograph taken at the 150-inch prime focus [of the Anglo-Australian telescope at Siding Spring] that is labeled the "Lionel-Murphy" SNR. Aussie Steve Mencinsky told me he was working as a night assistant at the time on the 74-inch at Mt Stromlo (later destroyed in a bush fire) in early 1976 as a "vacation scholar. One day a few astronomers were taking a break and looking at some of the prints of nebulae in the Magellanic clouds. Steve looked at this SNR image and said "That looks like Lionel Murphy!. Who, you say? Murphy was a politician, former Attorney General turned Judge of Australia's High Court, who is later life got mixed up in a corruption scandal and apparently had a rather distinctive nose. The Wikipedia page on Murphy (https://en.wikipedia.org/wiki/Lionel_Murphy) states ""Murphy normally rejected public honours (such as a knighthood) but accepted this [nickname] because of the symbolic resemblance to his own impact on human rights in Australian law and its lasting significance as a "signpost" to space travelers. Murphy asked for a large mounted photo of SNR N86 from the scientific paper and placed it in his High Court chambers in the place where the other High Court justices usually hung a portrait of the Queen.
With the 25-inch (unfiltered) at 244x, this LMC supernova remnant appeared as a large, low surface brightness hazy region, just south of a mag 11.8 star. A couple of 14th mag stars appear involved with the haze. The mag 11.8 star forms the eastern vertex of an isosceles triangle with a mag 11.5 star 5.6' NW and a mag 10 star 6' SW. There was a weak contrast gain adding a NPB filter, with the most evident section ~1' diameter [centered 1.2' S of the mag 11.8 star] and slightly brighter on the east side.
Images in H-alpha, [O III] and [S II] reveal a relatively well defined shell of over 3' diameter, rich in internal filamentary structure, and a large jetlike stream of filaments extending 2' further north that appear to break out into the interstellar medium.
NGC 2103 = LMC-N214C
This unusual nebulous cluster was observed using the 25-inch at 244x. If found it a fairly bright, very large, roundish glow surrounding a central star (12.7-magnitude O2-type Sk -71°51) with a bright quasi-stellar knot at the north edge (that strange-looking pinkish Pac-Man object on the image above). Increasing the magnification to 397x, at least 8 stars were involved with the nebula (part of OB-association LH 110), which was clearly elongated NNW-SSE (tapering on the SSE end) and brighter along a central spine. The addition of a NPB filter at 244x produced an excellent contrast gain and the nebula appeared very bright with an irregular surface brightness. The small knot at the north edge (a high excitation HII blob or HEB) was prominently visible.
The central star (and nearly centered in the ESO image above) is unusually hot and bright and has been resolved by the HST into a compact cluster of at least 6 components in a 4 arc-second region! The HEB at the north edge is typical of small dense regions, usually "only" 4 to 9 light-years wide, that sometimes form adjacent to or inside giant H II regions and represent "early stages of massive stars (O-type) emerging from their embryonic molecular clouds.
LMC-N11 Complex = Bean Nebula
The Bean Nebula complex (LHA 120-N11) is the second largest stellar nursery in the LMC after the Tarantula Nebula. I showed off this tasty piece of eye-candy treat to the other OzSky participants using the 30 at 244x and this inspired Tony Tanner to image the field above. Ive viewed this region several times and the following notes were taken through the same scope a few years ago. The showpiece is certainly NGC 1763, which sits near the center of a stunning field of emission nebulae and clusters including NGC 1760 7' S, NGC 1761 3' S, NGC 1769 6.5' SE, NGC 1773 8' ENE and NGC 1776 11' E. NGC 1763 is a very bright, very large irregular nebula, shaped like a kidney-bean or a fetus. The main body extends 5'x3', elongated SW-NE with a bulbous portion on the northeast side and an indentation (weaker nebulosity) on the south side. Overall the surface brightness is very high, though uneven, and much fainter haze and filaments flow out from the Bean in most directions. Within the main body, the nebula is brightest in a loop on the southwest side and secondly in a section on the northeast side.
Involved with NGC 1763 is a large cluster catalogued as OB-association LH 10 (the youngest cluster in the LMC-N11 complex), with roughly two dozen resolved stars. This cluster includes a number of 12-13 mag stars (several of which are massive O3-type stars), many in an elongated 1' group on the southwestern side. At the northeast edge is mag 11.3 HD 268726 and 45" further east is LMC-N11A = IC 2116, a high surface brightness knot of ~15" diameter. Very faint haze at the NE side of NGC 1763 bulges towards N11A. This compact, discrete object is also classified as an HEB (High Excitation Blob), distinguished by high excitation, small size, high density and tightly linked to early states of massive star formation. The surrounding field is rich in stars between the individual objects with some locally brighter patches of nebulosity.
NGC 1761 is a bright, large cluster sandwiched between the Bean Nebula (NGC 1763) to the north and NGC 1760 to the south. There are roughly 80 stars mag 11 to 16 in a 3.5' irregularly shaped group over some background haze. The stars are fairly even distributed except for a detached 1.3' group of 10-12 stars off the NW side. Including this detached section, the overall size of this star cloud (association LH 9) is 5 x 3.5'. A close bright double star (h3716 = 10.2/10.9 at 5") is on the NW side of the main group.
NGC 1760 appears as a string of a half-dozen stars, nearly 2 in length, over fairly bright nebulosity. The emission haze is brightest just south of the string and extending to the west of the string a couple of arc minutes. Irregular nebulosity also branches out to the south of the string for another 2' and involves a mag 12 star. Another 2' string of N-S stars is on the west side of the haze.
NGC 1769 is a bright, large oval nebula oriented SW-NE, roughly 3 x 2'. At the center is a mag 11.5 star (Sk -66 41), with three mag 14-14.5 companions, the closest 15" SE. A small, bright knot (~10" diameter) is embedded on the south side of the nebula, just 0.9' S of the central star. Sk-66 41 was once thought to be one of the most single massive and luminous stars in the LMC but has been shown to be a very compact cluster with over a dozen components. The companion to the SE (an O3-class star) is actually the ionizing source of the nebula. The bright knot on the south side was also discovered to be a compact cluster of very faint stars in 1987 and is identified as HNT 1 in SIMBAD.
NGC 1773 is a fairly large, bright glow, elongated 3:2 ~N-S, 2.2 x 1.5'. On first glance, two brighter mag 12/13 stars are offset southwest of the geometric center and separated by 17". But on closer inspection the more central star (0-type supergiant SK -66 43), resolved into a very close double. In additional a couple of fainter mag 15/15.5 stars are superimposed on the north side of the glow. The nebulosity is slightly irregular in surface brightness and brighter along the rim, particularly on the southwest side. This emission nebula is located at the northeast end of the Bean Nebula complex.
NGC 1776, located on the east edge of the N11 complex, is a moderately bright cluster, fairly small, well concentrated with a small bright core surrounded by a 50" halo. A couple of extremely faint stars are just visible in the halo.