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Southern Cross - July 1999

• Constellation of the Month - Norma by Albert Brakel
• LUPUS: A mix of deep sky splendours by Jenni Kay

Constellation of the Month - Norma

Albert Brakel

Norma can be translated as the set square or carpenter's square. It was originally formed from the stars that now constitute Triangulum Australe, and called Norma et Regula (the square and level), but after the Triangle was invented by Theodor and Bayer, Lacaille altered Norma et Regula to its present site north of the Southern Triangle, and associated it with adjacent Circinus (the draftsman's compass). It was sometimes given the name Quadra Euclidis (Euclid's square). The name later became shortened to the present Norma. Border readjustments resulted in Alpha and Beta Normae being lost from Norma, so the brightest star in the constellation is now the 4th magnitude Gamma Normae.

The area is in a rich part of the Milky Way, and includes the Norma Star Cloud that is the most conspicuous feature to the unaided eye. Also present is a "rift" caused by dark intervening dust, and part of the well-known "Emu" of Aboriginal lore. While you are waiting to become dark-adapted, it is worth perusing the region with binoculars. Norma's location makes it open cluster territory, and several of them are accessible to binoculars; in fact, the brightest cluster, NGC 6067, is visible to the unaided eye in a non-light-polluted sky.

I checked out the main features of Norma using a medium-sized telescope (a C8) from an inner-city suburb.

Open Clusters

The open clusters in Norma are 2600-6500 light years away, in the Sagittarius Arm of the galaxy. The apparent sizes and brightnesses are no guide to distance, however.

NGC 6087 (RA 16h 18.9m, Dec. -57º 54') is a fairly loose but bright and attractive group of white, yellow and orange stars that become more densely packed towards the northern side. The brightest member is a brilliant yellow one at the northern end of a flattened upside-down "?" pattern. Altogether there are about 40 stars of up to 8th mag. in an area about 15' across.

NGC 6067 (16h 13.3m, -54º 13') is a dense cluster of at least a hundred stars, about 20' across, consisting of 8th mag. and innumerable fainter stars closely spaced. Among the population are some binaries, including an obvious brighter one towards the centre. Some of the stars form curved lines. The best cluster in Norma, it shows up well in binoculars.

NGC 6134 (16h 27.7m, -49º 09') was seen a cluster some 7' across, of mag. 9 and fainter members, set in a Milky Way star field. Not visible in bright moonlight.

NGC 6152 (16h 32.7m, -52º 37'): On the eastern border with Ara, some 70 loosely-spaced faint stars, down to mag. 11 and dimmer, are spread over a diameter of about 30'.

NGC 6167 (16h 34.4m, -49º 36'), with an integrated magnitude of 7.0, is not the brightest cluster in Norma, and its stars are fairly scattered except at the centre. A mag. 7.8 yellow star dominates on the preceding (western) edge, and a bright white star keeps vigil on the south side. Trails of stars extend to the east and NE.

Globular Cluster

NGC 5946 (15h 35.5m, -50º 40') is a small globular only a bit over 1' across, set behind a busy star foreground. In the seeing I had, it appeared as a small hazy spot that was not resolved into stars, but that is not all that surprising given the fact that it lies almost 36,000 light years away. Having to view it through the dust of the galactic disk does not enhance it either. A faint foreground star is located on its western edge. It should not be confused with the somewhat brighter globular NGC 5927 only about 1 degree to the west, just across the border in Lupus.

Double Stars

Four binaries in Norma are worth your attention. h4813 (15h 55.5, -60º 11') lies on the southern border with Triangulum Australe, and contains a 5.9 mag. yellow primary and an 8.5 mag. white companion following it. The pair, however, has a sufficiently wide separation of 3.9" to enable resolution with 77x in spite of the magnitude difference, and is very easy with 117x.

Iota-1 Normae (16h 03.5m, -57º 47') has white 5th mag. and "reddish" mag. 8.1 components a wide 11.0" apart, that were clearly separated with 50x, with the fainter star preceding. The latter had an orangeish, even brownish, color with 50x and 77x powers, but with 117x appeared a dull yellow. Have a look and see what you think. The brighter member is actually a close pair, making this an interesting triple system. The inner pair of equal components (mag. 5.3 and 5.5) are in a tight 27-year orbit and last reached periastron in 1991, when they were only 0.2" apart. They are now widening once again, are currently at about 0.5" (beyond the resolution of the C8 at any magnification), and will reach 0.8" around 2004-2005. This will still be quite close, but resolvable with a 20 cm aperture on nights of excellent seeing. Keep an eye on this one over the next few years.

Holden 124 (15h 45.0m, -50º 47'), with a separation of 2.3", was not resolved with 235x in conditions of poor transparency. When the transparency improved, it took at least 235x to split them. Both stars are white. The mag. 8.4 secondary lies to the south of the mag. 6.8 primary.

Epsilon Nor (16h 27.2m, -47º 33') is a very wide (23") and unequal (4.8 and 7.5 mag.) pair, the B star lying to the north and slightly preceding. The brighter primary is a pale yellow, and the secondary a somewhat deeper yellow (not bluish as Hartung claims).

Planetary Nebulae

NGC 6164-65 (16h 34.0m, -48º 06'), over 1º SE of Epsilon Nor, is a bipolar nebula centred on a hot Wolf-Rayet-type star, that appears in photos with two lobes of gas thrown off in opposite directions. Using 77x and a Lumicon UHC filter, the nebulosity could be detected with averted vision (no doubt it would be easier in a darker sky). Doubling the magnification to 154x made the nebulosity more conspicuous, but the lobate nature of the feature was not obvious. It appeared as an elliptical glow surrounding the central star (an unequal binary) and two field stars to the east. The nebulosity was much brighter with a UHC filter than with an OIII filter, implying that more than OIII emission is involved.

Menzel 2 (16h 14.5m, -54º 57'), also known as VV78 from its number in the Vorontsov-Velyaminov catalog of planetary nebulae, is located just south of Kappa Nor. Glowing at a dim mag. 12, it was a round grey patch 25" across, and not easy to find even with an OIII filter. The filter was essential to pick out the object from the surrounding star field. It looked best with 154x power.

I hope you enjoy this selection from a constellation riding high at culmination this month.

LUPUS: A mix of deep sky splendours

Jenni Kay FRAS

The Lupus constellation appears as a relatively large, loose, scatter of bright stars, lying at the eastern edge of Centaurus. Since Centaurus is also a large scatter of bright stars, it is not easily seen where one constellation ends and the other begins. Nonetheless, within the scatter of the Lupus stars, there is one well-defined shape which can be picked out. Near the centre of the constellation is a long chain of nine bright stars in the form of the letter "S". In general, with only a few moments care, this constellation can be found easily enough.

The following observations were made through a 12.5" Newtonian, from my semi-rural home site at Lobethal, SA. The skies here have a typical limiting naked eye magnitude of 6.1 with the seeing graded at ANT II-III.

IC 4402 (Galaxy - GX): 14 21.2 -46 18

12.0B; 4.1' x 0.8'; Position Angle 127 degrees.

50X: The galaxy is too faint to detect at low power. At 105X, with some care and averted vision, the galaxy can be picked out as a relatively faint, very long, pencil thin wisp, with a 14th mag foreground star at each end. At 151X the view is best! The galaxy does not stretch out to the 14mag stars as seen at 105X, these stars are well detached. The galaxy is much elongated, northwest - southeast, with a size 3.0' x 0.3'. It has an uneven surface brightness, and a much smaller, brighter core towards the centre. In the wider, general field there is a light sprinkle of 10/11 magnitude and fainter stars.

IC 4406 (Planetary - PN) : 14 22.4 -44 09

At low power, the planetary stands out very well in the star field, as a bright, small, round disk. In brightness, this planetary is equal to a 12th mag field star. With an UHC filter in place, there is a very strong response from this planetary. At 105X - 151X the planetary shows a bright and even glow throughout, and has a size of 0.5'. In the wider view, there is a light mix of bright and faint stars ranging from 9-12 mag and then fainter. This planetary is so obvious it would not be overlooked in a general sweep of the area. Furthermore, since the view of this object is bright and easy at all magnifications I would class this as a showpiece to be added to any list of bright and interesting objects.

NGC 5593 (Open Cluster - OC) : 14 25.8 -54 49

In a busy star field, the cluster stands out well appearing as a long, slim, loose group of stars. There are about eleven stars involved with all being similar in brightness at 10/11 mag. The star group is much elongated east to west, with a size of 8.0' x 3.0'. The stars form a long, curving chain, and it reminds me of a strand of beads dangling from a hook. The whole view is most attractive with the prominent star group standing out against a background of numerous field stars of mixed brightness. There is little to be gained at higher powers with the star group appearing the same from 50X - 151X.

NGC 5643 (GX) :14 32.7 -44 10

10.4v; 5.1' x 4.3'; SB 13.6v; PA 89d.

One for the showboat list! At low power, the galaxy can be easily detected appearing as a relatively bright, oval glow, with some superimposed stars in the southwest region. Increasing the magnification shows finer detail. At 105X the galaxy is a bright, oval haze, with a brighter sub-stellar core, and a small chain of four stars in the southwestern region. The major axis of the galaxy is 3.0' long. There are four 13th mag superimposed stars immediately west of the brighter core trailing to the north. In the wider, general view, the field is filled with bright and faint stars, ranging from 10-11 mag, and then fainter. The view is quite splendid, with the obvious galaxy lying in the rich star field.

NGC 5749 (OC) : 14 48.9 -54 31

At low power, the cluster appears as a relatively large, loose group of a few stars. The group stands out somewhat, almost blending into the rich surrounding star field. There are thirty-five stars involved, with the brightest member a 10.5 mag star at the northwestern edge, the rest being about 11/12 th mag. Overall, the cluster is 10.0' in size with an irregular shape. The central region is quite open. The best view is at 151X in the smaller 20' field where the group seems well detached from nearby fainter field stars. In the wider 60' view at low power the entire region is star rich and the group begins to blend into it.

NGC 5764 (OC) : 14 53.6 -52 41

At first, this very small, faint cluster is not easily noticed at low power. The whole view is rich in stars, and the tiny cluster could be easily overlooked. However, once found, the cluster appears as something curious and certainly worthy of note. At 105X, the cluster is more pronounced appearing as a small, faint, almost nebulous knot of stars. At 151X there are only two 12 mag stars resolving well, a few 13 mag stars around the brighter pair, and the glitter from much fainter members. The cluster is about 3.0' x 1.0' in size, and a little elongated east to west. Hogg 16 lies nearby to the northwest.

Hogg 16 (OC) : 14 50.7 -52 16

35.0' northwest of NGC 5764. At 83X, this small, tight cluster is more obvious than the nearby NGC 5764, being a prominent, dainty triangle of three bright stars set among some fainter stars trailing off to the south and east. Overall, there are fifteen stars involved, ranging in brightness from 10 - 13th magnitude, with the cluster being about 5.0' in size. 150X: A similar view! This quaint little cluster is worth seeking out.

NGC 5800 (OC): 15 02.0 -51 55

At low power, the eye is drawn to a neat little strand of three bright stars lying in a small arc. The brightest member of this strand is about 7th magnitude and shows a strong yellow colour. The sight is certainly worthy of note! 150X: A fourth, very faint star can be seen in this group, however, it is still the bright triplet that attracts attention in this busy star field. The strand is 3.0' in length north to south. (The cluster is classed as a nonexistent star cluster of the Revised New General Catalogue - RNGC- however, those authors obviously did not look at the sky searching for the cluster Herschel described.)

NGC 5822 (OC) :15 05.2 -54 21

In an 8x50mm finder scope, this cluster can be picked out as a large, very soft, round haze. At low power, the field is almost filled with stars. There are about one hundred and fifty stars involved, all similar in brightness at 11 mag. The cluster is loose, and well detached, with a size of 40.0'. There is little gain at high power, with only a few very faint stars slightly adding to the star count. The stars form long curving chains that with a little imagination form numerous patterns. Overall, the view is impressive!

NGC 5824 = NGC 5834. (Globular Cluster - GC) : 15 04.0 -33 04

At low power the globular is very easy to pick out in the field appearing as a very bright, small, round hazy glow with softer edges. At 105X - 151X the globular is a brilliant, compact cluster, about 0.5' in diameter, with a softer, grainy halo from the much fainter outliers. The whole size of the cluster is 2.0'. The entire view is most attractive, with the brilliant globular set among a light sprinkle of 12/13 mag field stars.

We are told by Dreyer in the NGC catalogue that NGC 5834 is a duplicate observation of NGC 5824. In the historical records, it was Sir William Herschel who discovered N5834, placing it some 30 arcminutes east of NGC 5824. Since WH did not log any object at the N5824 position it is reasonable to suspect he made an error in measuring the co-ordinates, and he was actually looking at NGC 5824. There is no nonstellar object at WH's co-ordinates. Barnard was the recorded discoverer of NGC 5824.

NGC 5882 [probably = IC 1108] (PN) : 15 16.8 -45 38

At 83X, the planetary is very obvious in the bright star field appearing as a bright, very small, round disc with soft edges. There is a very good response to the UHC where the planetary is much enhanced. 150X: More prominent - very bright, round, 20" in size, with an even glow throughout, and equal to a 9th magnitude star for brightness. [There is no second object nearby as a candidate for IC 1108, therefore, it may well be a duplicate of NGC 5882, or at best, it is still not found.]

NGC 5927 (GC): 15 28.0 -50 40

Set in a very busy star filed lies this bright, round, relatively large, hazy glow. At 105X there are no individual stars resolving, but towards the central region the haze seems quite grainy. Overall, the globular shows a brighter, condensed central area, 2.0' in size, with a softer, hazy envelope out to 6.0' in diameter. At all magnifications, from 50X - 151X, the view is magnificent. The bright hazy glow is eye-catching being set in a very starry field. This object certainly deserves to be included in a glossy hit list.

NGC 5986 (GC) : 15 46.1 -37 47

A real showboat! At low power, the globular is obvious appearing as a large, bright, round haze, which is a little grainy. 105X: A real visual treat - the globular is a bright haze with numerous stars resolving across it, right into the core. There is also a thin, fainter envelope from some unresolved, far-reaching outliers. All the stars seen are equal in brightness at 13 mag, with the diameter of the cluster being 4.0' in size. The view is so superb, the eye is fixed on the cluster.