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Old 16-09-2012, 07:51 PM
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Paddy (Patrick)
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Observations 13/9/12 - GCs (mostly)

Thursday night presented the first observing in quite some time. Although the sky was clear and seeing good, the transparency was quite awful, so it was only a night for clusters.

Thanks for reading.

Telescope 400mm f4.9 tri-dob reflector
Eyepieces 28mm UWAN, 17,13,9 mm Naglers, Paracorr
Navigation: Uranometria

Seeing good, transparency poor.

2030

NGC 5946 GC Norma

175x 3.5’ soft round GC with marked 2’ central concentration. Halfway between the W edge of the core and the edge of the halo is a foreground star. I agree with suggestions that this gives the impression of a dark lane to the W of the core. No cluster stars are resolved.

NGC 6656/Messier 22 GC Sagittarius

135x Always a stunning sight. 15’ blaze of stars and haze with myriad bright members discerned. The chevron-shaped dark lane points NW. No words are adequate. No marked core, several tracts of stars and haze are distracted from the main halo and trail off into the very busy starfield with background stippled by countless faint stars.

NGC 6717 GC Sagittarius

175x 2’ soft glow in the glare of bright foreground star (Nu 2 Sag). Looks quite concentrated and 2 points of light are quite distinct, one of which may be a stellar core.

NGC 6712 GC Scutum

175x 5’ halo of faintly resolved stars with no core. A dark V-shape can be seen on the W edge and there are some small dark lanes on the E side. A wedge of haze trails off to the NE. 5’ to the S is a small squarish 2’ patch of haze not designated on my charts.

NGC 6694/Messier 26 OC in Scutum

175x Beautiful 12’ OC, roughly triangular with apex to the E. Fifty+ moderately bright stars within the triangle form numerous graceful curves, combining to suggest the outline of some elegant winged insect. The cluster stands out well from the surrounding field and is easily seen in the finderscope. The lucida looks more yellow than most of the stars of the cluster, which seem whitish.

NGC 6705/Messier 11 OC in Scutum

135x Stunning 15’ cluster with hundreds of stars of fairly similar magnitude (apart from the lucida which is considerably brighter) and numerous dark lanes. A 6’ square of stars in the centre is delineated by dark lanes and itself contains a number of asterisms and dark lanes. These patterns suggest the square ideograph stamps used by Chinese artists to sign their work. Near the lucida are several faint red stars. Numerous interesting and pleasing asterisms are scattered throughout.


NGC 6934 GC in Delphinus


175x 4’ dia. concentrated and grainy glow 4’ to the E of a foreground star. Very round and with a distinct core.


NGC 7006 GC in Delphinus


175x Faint, but still obvious round, smooth halo. Quite concentrated and with a distinct core. According to the Night Sky Observer’s Guide, this is a very distant halo GC, about 135,000 ly distant.
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Old 19-09-2012, 08:04 PM
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orestis
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Hi Patrick,

Thanks for posting, some great targets observed.
It has been ages since I have done any serious observing because of hectic final yr 11 exams , will hopefully get in a couple of hours in the upcoming holidays.

Great to hear you enjoying the view
Orestis
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Old 19-09-2012, 09:49 PM
Rob_K
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Great report Patrick, some nice globular clusters there. As a matter of interest checked my observing logs for NGC 7006 and found this - "Very remote GC. Easy to see in 4.5-inch. Dim, very small, centrally brightened glow. Seen 5 September 2007." That was at 43x.

Cheers -
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Old 20-09-2012, 09:54 PM
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Paddy (Patrick)
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Thanks guys. Impressive obs in 4.5" Rob, as usual. Hope you get some clear skies for your break Orestis!
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Old 10-12-2012, 01:54 PM
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madbadgalaxyman (Robert)
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Hi Paddy,

As I remarked in previous posts, M11 is arguably a globular cluster.
The radial falloff of the (2-Dimensional) star density and the overall mass of this cluster resemble what is found in a low-mass globular star cluster.

The distinction between high-mass open star clusters and low-mass globular star clusters is increasingly academic;
because of the fact that as the Total Star Cluster Mass progressively increases, the stellar distribution within a cluster increasingly resembles that found in a globular star cluster!
(e.g. the N3603 cluster and the supercompact Star Cluster at the center of the Tarantula Nebula are either high-mass open clusters or low-mass globulars...... 10,000 or more Solar Masses clusters are all very similar to globulars in appearance!)
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Old 30-12-2012, 09:19 PM
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Paddy (Patrick)
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Quote:
Originally Posted by madbadgalaxyman View Post
Hi Paddy,

As I remarked in previous posts, M11 is arguably a globular cluster.
The radial falloff of the (2-Dimensional) star density and the overall mass of this cluster resemble what is found in a low-mass globular star cluster.

The distinction between high-mass open star clusters and low-mass globular star clusters is increasingly academic;
because of the fact that as the Total Star Cluster Mass progressively increases, the stellar distribution within a cluster increasingly resembles that found in a globular star cluster!
(e.g. the N3603 cluster and the supercompact Star Cluster at the center of the Tarantula Nebula are either high-mass open clusters or low-mass globulars...... 10,000 or more Solar Masses clusters are all very similar to globulars in appearance!)
Thanks Rob, that's very interesting. For GCs in the Milky Way isn't there also a distinction based on the age of the constituent stars? I know this doesn't fit in the Magellanic Clouds. Any enlightenment on the nature of GCs would be greatly appreciated.
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Old 11-01-2013, 08:40 AM
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madbadgalaxyman (Robert)
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Quote:
Originally Posted by Paddy View Post
For GCs in the Milky Way isn't there also a distinction based on the age of the constituent stars? I know this doesn't fit in the Magellanic Clouds.
Hello Paddy,

I once looked into the idea of massive and centrally-concentrated clusters of various ages , and whether or not these "various ages" globular star clusters exist in different types of galaxies;
It appears that most non-dwarf spiral galaxies of type Sbc or Sc can form at least modest numbers of new globular clusters, with time........
for instance, in the Milky Way;
NGC 3603, Westerlund 1, and the Arches Cluster, have formed recently.
( NGC 3603 may be a little too small for a globular, especially if it eventually loses some of its stars, as it is currently of the order of 10,000 solar masses.)

There were some initial studies of M83 showing that M83 has recently formed good numbers of 100,000 solar mass, massive & compact, star clusters in the numerous extremely large star-forming complexes that exist in its two main spiral arms; but oddly, these low-resolution observations were never followed up with high-resolution (0.05 arcsec or better) Hubble Space Telescope observations of these clusters ( at least this was the case when I last checked the literature some two years ago!)

Generally, if there exists a Big Enough and Energetic Enough star-forming complex in any galaxy that exists anywhere (or anywhen) in the universe, meaning that there is a sufficent mass of cold molecular gas in the complex and that the amount of energy supplied to begin gas contraction & star formation (energy supplied by gravity, supernovae, stellar winds, violent supersonic turbulence, etc.) is high enough, there is a chance that a massive & compact Young Cluster will form that is essentially indistinguishable from a young globular cluster.
In other cases in the universe, if you give the interstellar medium a big enough "whack" with a shock wave, such as in a collision between two galaxies, new globular clusters can and do form (e.g. in NGC 4038/9 and NGC 3256)

The canonical "old" globulars are a distinct population, or more properly populations (in the plural), of clusters;
these "old" globulars exist in just about every non-dwarf galaxy in the universe.
However, I caution that "old" can mean different things depending on the particular galaxy; usually, astronomers mean between 8 and 12 billion years old when thay talk of "old" objects.
Some galaxies, such as NGC 1316, contain some intermediate-age globulars which are only 3-6 billion years old, but these globular star clusters are already looking a lot like your typical globular, because they have already lost all of their young and luminous stars.

cheers, robert
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