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Southern Cross - May 2003

• COTM: Chamaeleon by Steve Crouch
• Double Stars in Chamaeleon by Ross Gould
• The Missing Star Clusters of Vela by Jenni Kay

COTM: Chamaeleon

Steve Crouch

Chamaeleon is a small constellation very near the pole between Carina and Octans. It was proposed by Bayer in 1604 and, like many of the constellations introduced in this era, has little to offer the amateur. The proximity to the pole also makes it difficult to observe – particularly if you have a fork-mounted telescope like me. I would recommend making a precautionary appointment with your chiropractor before attempting this constellation.

As usual, I used the C14 for these observations. The eyepieces used were a 27mm Panoptic and a 9mm Siebert for perusing one of the double stars. Observing conditions were pretty ordinary (fairly typical these days). The seeing varied between fair and poor and the transparency wasn’t any better with intermittent patches of thin cirrus.

Given that I only observed five objects (that’s about all there are), I won’t follow my usual practice of splitting the objects up into categories but just treat each one in turn.

NGC 3195 (10 09.5 –80 52) is a bright and prominent planetary nebula that is well worth searching out. The colour is white and all I could see was a uniform fuzzy patch although photographs do show some structure reminiscent of the dumbbell nebula. An O III filter increased the contrast but did not reveal any further structure.

About 30' to the NNW of NGC 3195 is the galaxy NGC 3149 (10 03.8 –80 25). This one is not particularly bright at 13th magnitude but I found it reasonably easily. It is a small blob showing hints of central condensation.

IC 2631 (11 09.8 –76 37) is a fairly bright patch of reflection nebulosity about 2' across. It was quite easy in the C14 even though conditions weren’t the best and surrounds a 9th magnitude star.

About 20' to the NW of IC 2631 is the spiral galaxy NGC 3620 (11 16.1, -76 13). I found this one a bit more difficult than NGC 3620. It showed definite elongation.

Finally, I had a go at one of the double stars even though it wasn’t a good night for doubles. Hartung lists δ1 Cha (10 45.3 –80 28) as clearly resolved with 20 cm (the separation in 1990 was 0”.78 with the components being almost equal at 6.1 and 6.4). I felt that overstated the case somewhat as all I could do was elongate it with the 9mm eyepiece (413x). Seeing conditions were pretty poor at the time though.

Well that about does it for Chamaeleon. If you want to observe just one object in it, I would pick NGC 3195 as being the best.

Double Stars in Chamaeleon

Ross Gould

Although just off the main band of the Milky Way, Chamaeleon is not a rich area for double stars, with only a couple of dozen within reach of moderate (15-20cm) telescopes. Many of these have primaries of mag 8 or 9. Hartung lists only two doubles here.

Delta-1 Cha (10 45.3, -80 28) is the second-brightest star (deep yellow) in an irregular line of four stars. Delta-2, nearby and brighter, is pale yellow in contrast. The 7" showed Delta-1 as an extremely close, near-even pair at 180x, just separated.

Hartung's other listing was Epsilon Cha ( 11 59.6, -78 13). This pair has been closing over time, and the 1997 measure was 0.4" in PA 211. The 7" showed a bright white star with three field stars NE; at 360x still probably single. Given the separation, it would be a test for a 12-14-inch scope these days.

Two pairs in the same field: HJ 4468 (11 41.0, -83 06) is a 6th mag orange star with an easy wide faintish companion (11th mag). There is another pair 8' W - this is HJ 4462, mags 9.3 and 10.7 at 4.3", rather nice. Both pairs were visible with 100x on the 7-inch but 4462 looked better at 180x.

Older measures of I 212 (10 59.2, -81 33) might suggest it's accessible to an 8-inch scope, but in recent decades this pair of mag 6.7 stars has moved rapidly in PA while the separation diminished. In 1947 the separation was 0.7" in PA 183; by 1991 the Hipparcos measure gave a PA of 248 and a separation of only 0.2". When it will widen again to be within reach of amateur 'scopes is uncertain.

The Missing Star Clusters of Vela

Jenni Kay FRAS

Continuing on from last month where we looked at a handful of missing star clusters of Monoceros, this month will include a few in Vela. To recap on the situation here, these missing star clusters were classed as "nonexistent" star clusters in the Revised New General Catalogue (RNGC) of 1973. They were so named when the RNGC authors could not find star clusters at the positions given in the original New General Catalogue (NGC) by Dreyer of 1888. However, since the RNGC was published, it has been found that many of these star clusters really do exist. Some offer outstanding views and are certainly worthy of note, where others appear little more than a slight grouping of a few stars. But nonetheless, the adventure is in searching for these lost objects and maybe resurrecting their status to "existing" and bringing them back onto the lists for star cluster observers.

In the previous article, I gave details of four clusters for you to conduct your own search for them, and now I shall present my own findings. But first, the following observations were made with either an 8" f/6 Newtonian, or 12.5" f/5 Newtonian, from my semi-rural home site in Lobethal, SA. The skies here typically have a limiting naked eye magnitude of 6.1 with the seeing rated at ANT II-III.

NGC 2932 : 09 35 18 -46 57 (RNGC) - Vela

JH: "This is about the middle of an enormous cluster of a degree and half in diameter, very rich in stars of all magnitude, from 8 mag. downwards, which merits registry as a sort of telescope Praesepe. It may perhaps be regarded as a detached portions of the Milky Way, which is here very much broken up."

Observation with an 8" f/6 Newtonian

80X: At the indicated position, the view is rich and interesting with numerous star groupings. There are bunches of stars, stars in short chains, rows, and a great mix of bright and faint stars. The view is splendid! However, nothing here resembles anything like a "telescope Praesepe." 120X: Again, the view is remarkable, with the variety of star patterns offering a magnificent view. But still no "Praesepe". In a sweep of the general area, about 42.0' SW of this position, there is in fact a prominent grouping of bright stars which catch the eye, even in the 8x50mm finderscope, and truly does remind me of Praesepe. 80X: The whole view is a scatter of bright 9/10 mag. stars, thirty in number, mixed with fainter stars, and continues over into adjoining fields. This is a very extensive, rich star region. I can easily move from one field to another, and find plenty to see and enjoy here. In my opinion, I would say that JH was taken by this very large, rich area, that extends and includes the bright star grouping I mentioned which resembles Praesepe.

Conclusion: NGC 2932 seems to refer to a very large, rich star region, and not a cluster per se. It is certainly worth the effort to see.

NGC 2995 : 09 44 06 -54 47 (RNGC) - Vela

Observation with an 8" f/6 Newtonian

80X: Nothing obvious at the given position. Here there is a very extensive scatter of bright and faint stars, with no star patterns or groupings, only an even scatter throughout. 120X: The whole field is full of a spread of bright 10/11 mag. stars, with many fainter in between. However, it does seem that these brighter stars form a foreground group, or a cluster of a sort, over the fainter background stars. The stars in this cluster group appear associated being all similar in brightness, with twenty-five stars in number, well detached, and an overall size of about 15.0'. In a wide sweep looking for another possible candidate for this cluster, I find no other star grouping within this very rich and extensive star region.

Conclusion: NGC 2995 may exist as the star group described above, matching quite well with JH's position and description.

NGC 2999 : 09 45 12 -50 26 (RNGC) - Vela

JH: "A small irregular cluster of a long triangular diverging figure, contains perhaps 50 stars 12...15 magnitude...place only rough...possibly the same object with h 3183 [NGC 2972]." It is possible that NGC 2999 = NGC 2972, however, observations of the area would be useful for final confirmation.

Observation with 8" f/6 Newtonian

80X: At the given position, there is no star grouping here of any sort, in fact, there are few stars at all at this position. Nothing here remotely fits JH's description, or any single part of it. To the WNW lies NGC 2972, a very prominent cluster. There are three strands of stars converging to form a triangle, 4.0' in size, with twenty-five stars involved, all similar in brightness at 12/13 mag. This would appear to be a good match for Herschel's description of N2999.

In a wide sweep of the general area, and carefully looking for a star group of any sort, the eye is caught by a slight grouping of stars 30.0' SW of the N2999 position. This group has a very rough triangular overall shape, very open in the centre, with twelve 12 mag. stars, and one 10 mag. star on the western edge (GSC 8180:1769). It is 4.0' in size. While neither cluster/ star group contains JH's "50 stars" I would think his cluster must be one of these two, especially since there is no other star cluster/ group in the wider, general area.

Observation with a 12.5" f/5 Newtonian

Similar views and impressions as above.

Conclusion: I would tend to think that NGC 2999 is a duplicate of NGC 2972. This cluster fits more closely with JH's descriptions, despite the lack of star numbers. The first group described is hardly a good match, but worth noting here for some consideration.

NGC 3446 : 10 52 06 -45 09 (RNGC) - Vela

JH: "The chief star 9 magnitude of a cluster class VIII [coarse] 7.0' diameter; not rich or compressed, stars 10...13 magnitude."

Brian Skiff (of the Lowell Observatory) has already identified this cluster, describing it as being 15.0' in diameter, comprised of 10-15 stars, positioned at 10 52 07 -45 08 24.

Observation with an 8" f/6 Newtonian

80X: Obvious, loose group of a few stars, with a very irregular overall shape. Thirteen stars were counted here, ranging in brightness from 10 - 11 magnitude. The cluster has a size of 18.0' in diameter. 120X: More obvious as a cluster where the surrounding stars appear fainter, therefore giving more emphasis to the group appearing truly related (visually).

Conclusion: I would concur with Skiff's findings that this cluster is the same cluster JH was referring to.

Here now are a few more clusters for you to hunt for, and see what you think about the JH descriptions compared to the latest conclusions below.

NGC 3036 : 09 49.3 -62 41 (RNGC) - Carina

JH: "The chief star 10 mag. of a cluster class VIII [coarse] of scattered stars 10.0' diameter. It is on the borders of the Milky Way."

Dr. Corwin (of Caltech)/ Brain Skiff : asterism of stars, 20-25 in number.

NGC 3519 : 11 04.0 -61 22 (RNGC) - Carina

JH: "Chief star of a pretty rich cluster, class VII [pretty much compressed clusters of bright and faint stars].

JH: "Cluster VIII.; oblong; 10.0' by 7.0', of loose scattered stars 11 magnitude."

Skiff: asterism.

NGC 5045 : 13 17.0 -63 25 (RNGC) - Cen

JH: "A great cluster, or a surprising rich portion of the milky way. It contains 34 stars 11 magnitude, and perhaps 150 or 200 more or less magnitudes in the field."

Skiff: Star Cloud.