Canberra
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Southern Cross - November 2001

• Sculptor by Peter Ogilvie
• A Problem Double: I 1467 in Grus by Ross Gould
• The Galaxies of Sculptor by Jenni Kay

Sculptor

Peter Ogilvie

Sculptor (the sculptor) is a fairly large but obscure southern constellation whose brightest stars are of only about 4th magnitude. It contains the South Galactic Pole - the point in the sky which is 90 degrees from the Galactic plane (the plane of the Milky Way) and so contains almost nothing in the way of prominent star clusters or nebulae. It does however contain a large number of galaxies, including some relatively close ones which form part of the "Sculptor Group". My telescopic descriptions of the galaxies are from views through the CAS's 14 inch (35cm) or otherwise a 10 inch (25cm) Schmidt-Cassegrain.

Variable star

R Sculptoris (01 27.0, -32 33) is a red giant semi-regular variable varying between mag. 5.8 and 7.7 with a period of 370 days.

Double stars

Epsilon Sculptoris (01 45.6, -25 03) is a fairly easy one for small telescopes at high powers, with stars of magnitude 5.4 and 8.6 separated by 4.7 arcsec. It is a binary with a period of nearly 1200 yrs.

Kappa-1 Sculptoris (00 09.3, -27 59) is a very close (1.4 sec) pair. The stars are of equal brightness, mag 6.1 and 6.2. An aperture of at least 100mm at 200x or more will be needed to separate them.

Howe 93 (23 37.1, -31 52) Not too difficult, mags 6.6 and 10.1 separated by 5.4 sec. The primary is orange.

Globular cluster

NGC 288 (00 52.8, -26 35) at mag 8 appears as a small fuzzy ball without much central condensation. A magnification of 100x reveals some of its stars.

Galaxies

NGC 253 (00 47.6, -25 17). Discovered by Caroline Herschel in 1793, NGC253 is one of the best galaxies in the entire sky, and is the brightest member of the relatively close "Sculptor Group". It is visible in 50mm binoculars or finderscope. Sometimes called the "Silver Coin galaxy", this spiral system is tilted only a few degrees from edge-on to our view and in the telescope appears as a huge cigar shape stretching nearly ½ a degree (a full moon diameter) in length. My 10 inch scope reveals some faint mottled structure in the central regions.

NGC 55 (00 14.9, -39 11) is another close member of the Sculptor Group. It too appears as a very large, fairly bright edge-on system, slightly dimmer than 253 but still easily visible in small telescopes, and somewhat asymmetric and uneven in brightness along its length.

NGC 7793 (23 57.8, -32 35) This galaxy presents a moderately sized conspicuous oval, 6 arcmin. across, with a bright, broad nucleus.

NGC 300 (00 54.9, -37 41) Another member of the Sculptor Group. Although quite large in apparent size and listed at mag 8½, this spiral is harder to see because it is face-on, therefore its luminosity is spread over a large area. In the 10 inch it is a large, dim oval haze but is more obvious in the 14 inch.

NGC 613 (01 34.3, -29 25) A more distant galaxy, this one appears as a smaller, dim elongated oval rising to a brighter nucleus.

NGC 7713 (23 36.5, -37 56) Through the 14 inch, a small faint oval with a broad, dim nucleus.

NGC 134 (00 30.4, -33 15) Moderately sized (6 arcmin.) elongated and with a prominent nucleus. A few arcmin. west is NGC 131, another edge-on spiral, smaller and much fainter.

IC 5332 (23 34.5, -36 06) Through the 14 inch it is a faint, medium sized circular haze with a faint, small nucleus.

NGC 7507 (23 12.1, -28 32) Small and circular but fairly conspicuous, with a bright, small nucleus. Very close to the north is NGC 7513, a faint small oval with a dim, broad nucleus.

NGC 7713 (23 36.5, -37 59) A dim, small oval without a nucleus.

The Sculptor Dwarf - ESO 351-G30 (00 60, -33 42) First discovered photographically in 1938, this galaxy is a dwarf system belonging to the "Local Group" of galaxies which includes the Milky Way, the Andromeda galaxy, the Magellanic Clouds and a number of other dwarf systems. It is supposedly just detectable in a large wide-field telescope as an extremely faint soft glow approximately 15 arcminutes across (1/2 a moon diameter). I've tried a few times to detect it with the 14 inch, without success.

I hope this selection provides you with some enjoyable observing.

A Problem Double: I 1467 in Grus

Ross Gould

In the last issue of Southern Cross I noted that the 1991 measure of the double star I 1467 (2313.3, -4937) in Grus indicated it is unlikely to be split in moderate telescopes now or in the near future. I later realised I should have checked Hartung, and sure enough it was listed there with some details on changes in separation over time.

Hartung mentions separating the pair in 1960, and in 1961 he found it clearly visible with 15 cm, with an estimated PA of 230. To clearly split this quite uneven pair with 15 cm suggests a separation at that time of distinctly more than 1.0 arcsecond - probably around 2 arcseconds. (The brightness difference of the two stars is about 2.5 magnitudes. The primary is magnitude 7.0.)

The Washington Double Star Catalog has had some problems with data on this pair. The 1984 and 1996 editions gave figures of 0.5" in PA 009 for both 1926 and 1936. The current edition (2001 on-line) lists the 1926 figures as 1.4" in PA 042.

The current WDS also gives the 1991 measure as 0.3" in PA 348. The 1926 and 1991 figures could be read in a number of ways. Obviously one needs more measures between these two dates to show the pattern of change.

I now have a complete list of measures for this pair, courtesy of the US Naval Observatory. These are tabulated here:

Date         P.A.     Sep.     
1926.89     41.5      1.37   
1934.18      9.4      0.42    
1936.05      7.3      0.61    
1936.78     11.3      0.41    
1961.77       .       0.20    
1963.84       .        .      
1991.25    348.       0.343   

The numbers make interesting reading. Assuming the 1926 measure was accurate, the pair then closed very rapidly with a fairly quick reduction in PA (about 3 degrees per year). The scatter in the 1930s observations is typical for measures of a very close uneven pair. The measures (except 1991) were with 26" and 24" refractors.

In 1961 the separation was so small (at about the limit of the 26" refractor used to measure it) that the PA could not be accurately measured. The late 1963 observation (also with 26") has the pair too close to be split.

The 1991 measure is by Hipparcos, and suggests the separation is now increasing again with a continuing slow decline in PA.

Several points emerge. First, Hartung's 1960 and 1961 observations are a puzzle - given the 26" measures in 1961 and 1963. Did he observe some other star in error? Or have an experience of spurious resolution? His PA estimate of 230 is consistent with both these possibilities.

From the measures, the pair was closest in the early 1960s. How soon it will be visible again with moderate amateur telescopes (15-30 cm) will depend on the shape of the apparent orbit, as this will in turn affect how quickly the pair appears to separate.

The distance to I 1467 is 200 parsecs - around 650 light years. This is the Hipparcos measure - the earlier spectroscopic parallax was the same. Given the distance of I 1467 the real separation must be large - at 200 parsecs the line of sight separation of the pair in 1991 equates to 66 AU (1.37" equates to some 260 AU). This implies a long period orbit of high eccentricity. However a great deal depends on the 1926 measure, given the difficulty of the pair in all later periods.

It will be interesting to see future measures of I 1467. Checking my double star notes, I find I observed it in 1996, with a C14 on a night of middling seeing, and found it single at 240x. Pairs like this are very seeing-dependent. I now plan to observe it again, preferably on a very steady night.

The Galaxies of Sculptor

Jenni Kay FRAS

Sculptor is a great hunting ground for galaxies that range in brightness from bright and easy to extremely faint. This makes it suitable for both beginners and advanced observers. In the collection of galaxies I have listed below is only a small sample of the sights to be seen. I have deliberately left out the well known galaxy NGC 253, a very impressive object, only to keep it for a future article where I will include it with many others not mentioned here.

The following observations were made from my semi-rural home site at Lobethal, SA. Typically, the skies here have a naked eye magnitude of 6.1, with the seeing rated at Ant II-III. The telescope used was a 12.5" f/5 Newtonian.

NGC 55 : 00 14.9 -39 11 (8.1v; 30.0' x 6.0'; surface brightness 13.6v; position angle 85 degrees.) 8x50mm Finderscope: relatively faint, long, thin, hazy wisp. 50X: Very impressive - bright, long and broad, brighter on the western half of the galaxy glow. This brighter end seems mottled, with three stars superimposed, or three almost stellar hazy knots. The eastern and fainter half also appears mottled. The whole length of the galaxy must be about 25.0' long. 105/150X: The overall size is 25.0' x 2.0', stretching across the field nearly NW-SE. There is one bright, very small, round knot near the centre. There are also two stars or two very small knots in the west. The brighter half seems to bulge, giving the galaxy an uneven shape.

NGC 101 : 00 23.9 -32 34 (12.6v; 1.9' x 1.7'; sb 13.7v; pa 83d.)

105X: Obvious enough, caught in averted vision - extremely faint, relatively large, round, soft dim glow. 150X: Improved view - relatively faint, round, 1.0' in size, with a low surface brightness, and a smooth even glow throughout.

NGC 115 : 00 26.8 -33 41 (12.9v; 1.9' x 0.7'; sb 13.1v; pa 124d.)

105X: Difficult - barely a hint of an extremely faint, hazy glow. 150X: Improved, but still a bit of a struggle - very faint, relatively small, oval, 40" x 30", major axis lies NW - SE, low surface brightness.

NGC 131 : 00 29.6 -33 16 (12.8v; 1.8' x 0.6'; sb 12.7v; pa 63d.)

105X: Obvious enough, especially with averted vision - relatively bright, small, oval in shape. 150X: Improved - relatively bright, oval, 40" x 30", major axis lies ENE - WSW. NGC 134 lies nearby to the east.

NGC 134 : 00 30.4 -33 15 ( 10.4v; 8.5' x 1.9'; sb 13.3v; pa 48d.)

9.0' east of N131. 105X: Very obvious and charming sight - bright, long and broad, with a brighter, central bulge. The halo fades gradually out to the tips. 150X: Improved - overall size is 8.0' x 45", major axis lies NE - SW, and the galaxy has a high surface brightness. In general, the galaxy is bright, with a brighter core, and a stellar nucleus. Impressive at all magnifications!

NGC 148 : 00 34.3 -31 47 (12.1v; 1.9' x 0.8'; sb 12.4'; pa 89d.)

105X: Obvious - relatively bright, very small, little elongated, hazy smudge, Lies SW of a neat little triangle of three 12th mag. field stars. 150X: Improved - bright, 30" x 15" in size, major axis is almost E-W, the galaxy has a high surface brightness and there is a brighter, stellar nucleus.

NGC 150 : 00 34.3 -27 48 (11.3v; 3.4' x 1.6'; sb 13.0v; pa 117d.)

105X: Obvious - relatively bright, relatively large, possibly oval, smooth and even glow. The galaxy lies within a large cruciform of four 11/12 mag. field stars. This adds appeal to the overall visual effect. 150X: Much improved - bright, oval, 1.5' x 50" in size, major axis is NW - SE, high surface brightness, and the glow is smooth from edge to edge.

NGC 174 : 00 36.9 -29 29 (12.8v; 1.6' x 0.7'; sb 12.8v; pa 147d.)

105X: Obvious enough with care - very faint, small, round, hazy glow. 150X: Much improved - faint, oval, 30" x 25"; major axis lies NNW- SSE, with a very smooth and even glow throughout.

NGC 254 : 00 47.5 -31 25 (11.6v; 2.6' x 1.5'; sb 12.9v; pa 131d.)

105X: easy - bright, relatively small, round-oval shape, with a brighter, stellar nucleus. In general, it is the nucleus that catches the eye, appearing as a bright, fuzzy star, and then averted vision notices the softer halo. There is a bright 7th mag. field 5.0' to the NE. 150X: Much improved - bright, 1.5' x 30" in size, major axis is NW - SE, with a high surface brightness.

MCG-5-3-3 (ESO 411-10) : 00 45.9 -31 12 (13.9v; 1.0' x 0.8'; sb 13.5v; pa 70d.)

24.0' NW of N254. 105X: Challenge - glimpses with averted vision of a very faint, small, round, hazy spot. 150X: Improved - very faint, round, 30" in size. Can hold continuously with averted vision.

NGC 289 : 00 52.7 -31 12 (10.6v; 3.3' x 2.9'; sb 12.9v; pa 135d.)

105X: Very obvious - bright, relatively large, round - oval in shape, gradually brightens towards the centre. There are two 10th mag. field stars nearby to the NW. 150X: Much improved - bright, oval, 2.0' x 40" in size, with a bright, small, central core, and a brighter stellar nucleus. Overall, the galaxy has a high surface brightness, and a smooth glow throughout.

MCG-5-3-12 (ESO 411-28) : 00 53.9 -31 06 (12.9v; 1.3' x 1.0'; sb 13.0v; pa 37d.)

17.0' E of N289. 105X: While sweeping across the field the eye is drawn to a very soft, faint glow. Overall, it is relatively faint, small, round-oval in shape. 150X: Improved - faint, small, round, hazy glow, 30" in size, with a stellar nucleus.

NGC 300 : 00 54.9 -37 41 (8.1v; 20.0' x 13.0'; sb 14.0v; pa 114d.)

105X: Obvious - relatively bright, very large, oval shape, with a smooth even glow. 150X: Improved - Relatively bright, 5.5' x 4.0' in size, major axis lies NW - SE, with a high and even surface brightness. There are a number of bright stars around the galaxy adding to the overall splendour.

NGC 378 : 01 06.2 -30 11 (13.1v; 1.5' x 1.3'; sb 13.7v; pa 74d.)

105X: Bit of a struggle, only suspect as - extremely faint, fuzzy glow, relatively small and round. 150X: Much improved - very faint, round, 35" in size, very gradually brightens towards the centre. The galaxy has a low surface brightness, and averted vision can hold it continuously with confidence.

NGC 418 : 01 10.6 -30 13 (12.5v; 2.2' x 1.7'; sb 13.8v; pa 18d.)

105X: Very obvious, easily caught in averted - very faint, relatively small, round, hazy glow. 150X: Improved - very faint, round, 45" in size, very soft glow, low surface brightness. IC 1637 to the SSE.

IC 1637 : 01 11.0 -30 26 (12.9v; 1.6' x 1.2'; sb 13.5v; pa 84d.)

14.0' SSE of N418. 105X: Suspect only - very faint, small, round, hazy glow. Comes and goes in moments of steady seeing. 150X: Improved - very faint, round, 30" in size, low surface brightness. Can detect with full confidence at this power. Forms a triangle with two 15 mag. field stars.

NGC 423 : 01 11.4 -29 13 (13.4v; 1.1' x 0.4'; sb 12.4v; pa 111d.)

105X: Too faint. 150X: Requires care - extremely faint, small, round, hazy spot, 30" in size. Can hold continuously with averted vision.

NGC 427 : 01 12.5 -32 03 (14.1v; 1.0' x 0.6'; sb 13.4v; pa 13d.)

105X: Too faint. 150X: Requires much care, because on first two attempts to see it, it was too faint. On third and subsequent tries - extremely faint, small, round - little oval in shape, 25" in size. Can detect with full confidence, with perseverance. NGC439 and NGC441 in same, general field to NE.

NGC 439 : 01 13.8 -31 45 (11.4v; 3.2' x 2.1'; sb 13.3v; pa 157d.)

26.0' NE of N427. 105X: Makes a pair with N441 nearby. Very obvious - relatively bright, long and broad, gradually brightens towards the centre. 150X: Improved - bright, much elongated NNW - SSE, 3.0' x 40" in size, with a brighter, small, round, core. In general, there are two obvious patches of light here, N439, N441, with N439 a little brighter than the other.

NGC 441 : 01 14.0 -31 47 (12.7v; 1.5' x 1.2'; sb 13.2v; pa 107d.)

2.0' S of N439. 105X: Very obvious - relatively bright, small, round, hazy spot. 150X: Improved - bright, round, 30" in size, high surface brightness, and gradually brightening towards the middle.

NGC 461 : 01 17.3 -33 50 (13.4v; 1.2' x 0.9'; sb 13.3v; pa 30d.)

105X: Suspect only the most faint stain on the sky. 150X: Much improved - extremely faint, relatively small, round, hazy glow, 35" in size, with a low, smooth, surface brightness. Can be seen with full confidence at this power. N491 nearby.

NGC 491 : 01 21.4 -34 03 (12.5v; 1.3' x 0.9'; sb 12.5v; pa 94d.)

51.0' ESE of N461. 105X: Obvious enough - very faint 14 mag. field star beside a faint, small, fuzzy spot. 150X: Much improved - bright, small, round, hazy spot, 30" in size, high surface brightness and gradually brightening towards the centre.