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Old 20-12-2009, 02:56 PM
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Paddy (Patrick)
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SMC objects and some Arp galaxies

Dear all,

Below is an observation report from three nights' viewing 10,11,12/12/09.

Observation report 10,11,12-12-2009

Telescope 400mm f4.9 tri-dob reflector
Eyepieces 28mm UWAN, 17,13,9 mm Naglers, Paracorr
Guiding: Night Sky Observer’s Guide, Arp Atlas of Peculiar Galaxies, Mati Morel’s Visual Atlas of the Small Magellanic Cloud

10/12/2009

Seeing 2/5 Transparency 6/7

The plan: to observe in and around the SMC and then move to Arp galaxies in Eastern Cetus and Eridanus (chart I of the Arp Atlas)

NGC 362 GC in Tucana, 132x I estimate a radius of 10’, quite a few resolvable stars very concentrated in a tight core with a small arc of resolvable stars stretching from the core to the East and a matching arc to the West reminiscent of a pair of pincers. Behind this core is a bright haze in the centre which seems to dim in an annulus around the core, then brightening again further out, creating a doughnut appearance. A few darker patches on the Western and Northeastern side of the core 175x seeing at this magnification is not aided but heat rising from the roof of my house, but a few more stars can be resolved. The doughnut is less obvious and the dark patches around the core appear more segment or lobular

NGC 361 OC in SMC 132x appears almost as a faint elliptical galaxy with distinct central brightness. A small Y shaped asterism to the SW points to the bottom of the cluster

NGC 330 OC in SMC 175x 4’ across. Elongated in SE-NW direction, lots of faint stars in patchy nebulosity with strands coming out to South and North and a few stars scattered to the East. Strong central concentration of stars with surrounding faint haze of nebulosity

NGC 346 OC in SMC 175x Covers 7’ Bright clump in middle of cluster with many resolvable stars. To the South the haze drops into a dark bay with edge of stars in a line that continues well beyond the boundary of the haze to the East. To the North of the central cluster is a dark patch like an inlet.
NGC 371 GC in SMC 175x much less haze and more stars than in NGC346, 10’ across. The main body of the cluster shows no central core, a more diffuse haze with many scattered resolvable stars. There appears to be a right angled triangular shape to the cluster with a bright circular haze at the right angle which is at the NE corner and points towards NGC 395 & IC1624

NGC 395 OC in SMC 175x A triangular patch of haze with a line of small discernible stars to the North. 2’ across. IC 1624 is about half that size and is a small oval shaped smudge of haze.

NGC 411 and 422 from a nearby equilateral triangle with a bright foreground star

NGC 411 GC? In SMC (my Night sky Obs Guide lists this one as an open cluster as do Archinal and Hynes in “Star Clusters, Morel lists it as a GC and there is one research paper on it as a GC, so I assume that this is correct). 175x A small faint circular smudge, with a few stars at the western edge. In the same FOV NGC 422 OC in SMC 175x is an even smaller and fainter circle of haze.

Treating the triangle formed by NGCs 411,422 and the star as an arrow, it points to Lindsay 84

Lindsay 84 OC in SMC 175x A haze 5’ across with several resolvable stars in its centre

NGC 416 GC in SMC 175x Round haze, very faint with no resolvable stars 2’ dia

NGC 419 GC in SMC 175x Significantly brighter than NGC 416, looks more clearly like a GC dia 3’ again no resolvable stars. Seems very compact but no discernible core.

IC 1644 Nebula in SMC 175x At first glance, this appears almost star like, but fuzzy – a small, bright area of fuzz. Several stars either side of the nebula, with faint s-shaped extension of nebulosity running NE-SW. UHC filter does not diminish the luminosity of the object confirming it as a nebula and enhances the clarity of the s-shaped extension, looking a tad like an open spiral GX.

NGC 456, 460 &465 OCs in SMC. 175x All three in FOV. NGC 456 is the one closest to NGC 419/IC1644. It is roughly roundish, slightly triangular haze with quite a few discernible stars with a bright knot to the South. NGC 460 looks to me to be in 2 parts. To the North, a bright clump with no resolvable stars and a larger, fainter area of haze to the South with several discernible stars. NGC 465 is quite close to 460 and appears Y shaped with a Y-shaped asterism points to the cluster from the north, to the south is a darker patch in the middle of an oval shaped haze. The string of OCs spans 20’ and is about 5’ across. Each element about 5’ dia. UHC filter brightens the knot in the north of NGC 460 and doesn’t change much else in the field suggesting much of the haze is nebulosity rather than stars.

As midnight arrives, I move to Cetus for some Arp Galaxies

M77/NGC 1068/ Arp 37 GX in Cetus 175X Transparency reduced somewhat with high level haze, bright stars showing slight halo. Bright galaxy, round overall shape with distinct centre and impression of dark ring around centre, which may be dust lanes between tight spiral arms. Bright field star to south. Dia 7’. Arp lists this as a spiral with low surface brightness companion galaxies on the arms, but I can’t make these out.

NGC 1143/4 / Arp 118 GX in Cetus 175x At first appear to be one edge on spiral, but with careful observation 2 galaxies become observable. The pair are about 2’ across.

NGC1253/3a Arp279 GX in Cetus. 175x Appears as a long assembly of 2 edge on spirals, each with a bright field star in front with 2 faint galactic nuclei. Combined length is 9’. Width is about 3’. No features discernible in either galaxy, but a dark area is apparent between the two.

IC 298/298a /Arp 147 GX in Cetus. 250x Very faint, most I can say is that I think I have seen them.

By now weary of the faint galaxies of IC in Cetus, I move to M78

M78/NGC2068 Emission/reflection nebula in Orion. 135x Bright circular nebula 6’ dia with 3 distinct stars, one quite faint. Slight darkening near the centre. Associated areas of nebulosity to north NGC 2071, west NGC 2067 and south NGC 2064

11/12/2009

Seeing 1/5 transparency 7/7
Starting at 47 Tuc 135x, just for a look, I am amazed at the clarity of the sky as shown by the numerous resolvable stars in the “covered wagon” asterism next to the core of the cluster, many more than I have seen through this telescope. In fact the asterism itself is hard to make out due to the many stars where there are normally few. The heat from the roof of my house prevents good seeing at 175x.

NGC 121 GC in Tucanae 135x Very small 3’ dia GC with no resolvable stars, distinct core and averted vision shows a faint halo about twice the dia of the core. Field star to the west.

NGC 152 OC in SMC 135x Faint, diffuse round haze> no resolvable stars, slight concentration in the centre.

NGC 176 OC in SMC 135x Smaller than NGC 152 – a patch of haze, but has a stream of discernible stars stretching to one side and looks a little bit like a tadpole as a result.

Moving further into the SMC, I get confused by the plethora of small nebulae and clusters and even my Morel atlas doesn’t seem to cover all the options. I will have to find a way to navigate through this area.

12/12/2009

Seeing 2/5 transparency 6/7

NGC 1241/2 Arp 304 GX in Eridanus 175x Two galaxies in close proximity – centres about 5’ apart NGC 1241 about twice the size of 1242 and is a partly edge-on spiral with distinct nucleus and impression of spiral structure. NGC 1242 more like a slightly elongated haze close to 2 field stars.

NGC 1232 Arp 41 GX in Eridanus 175x Bright face-on spiral with 3 clear arms and nucleus 6’ across. Small companion galaxy NGC 1232A visible as faint smudge with brightening at its centre about 6’ from the centre of the main galaxy.

The rapid arrival of high cloud ends the session.
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Old 20-12-2009, 08:03 PM
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barx1963 (Malcolm)
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Paddy
Fantastic report. I have had a bit of a crack at the SMC but just got bamboozled trying to figure out what I was looking at! Have to get a better map or some guides. I will print out your report and keep for future reference.

Malcolm
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Old 20-12-2009, 08:35 PM
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Patrick,

Thanks for the intricacy of your report. I also love the Arp catalogue and one day hope to image all of them.

Frank
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Old 21-12-2009, 03:40 PM
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Brilliant report Patrick. As Yoda would say: "Of your dark skies, very jealous I am!!" Well done.

We have had a trough with rain and cloud up our way. I did have a couple of good nights before that, looking at NGC 2090 Columba and 1904 (M79) Lepus, along with some favourites. Trying to probe the magnitude limits of my suburban site. Can go deeper than mag 12 I think. It depends more on surface brightness than magnitude alone. Cheers, Paul.
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Old 21-12-2009, 04:16 PM
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I enjoyed that report Pat, thanx
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Old 21-12-2009, 09:42 PM
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Paddy (Patrick)
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Thanks for the feedback gentlemen, much appreciated. Malcolm, I started out on the SMC with the firm conviction that I would be able to identify most things, as I'd had quite a bit of success doing so with parts of the LMC using Mati Morel's LMC atlas, but here were so many things in the SMC that just aren't listed in the SMC version. It is truly perplexing. For my next attempt I will take my copy of "Star Clusters" by Archinal and HYnes out with me. It lists all open and globular clusters in the SMC by RA/Dec and I hope using my laptop and Skywatch software to be able to decode it all. Should be fun. And that surprises me - I used to think going out and just looking at things was fun and that recording/sketching was a good thing to do but felt a bit like work. Now I feel like something's missing if I'm not making notes. Also I've now found a way to hang a red light off my finder so I can do some sketching. I really enjoy doing something as I observe and plodding my way systematically through the SMC will be just another enjoyable thing. All quite uncharacteristically methodical for me, but I'm loving it. And the support of this IIS section, with everyone's reports and feedback is just great.
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Old 21-12-2009, 11:06 PM
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Paddy, well you inspired me to have another go at the SMC, Knocked up about a dozen NGC objects in about an hour last night! Haven't had time to set up a proper reprt but will get that done hopefully this week.
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Old 23-12-2009, 06:52 PM
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Quote:
Originally Posted by barx1963 View Post
Paddy, well you inspired me to have another go at the SMC, Knocked up about a dozen NGC objects in about an hour last night! Haven't had time to set up a proper reprt but will get that done hopefully this week.

Very good! I look forward to reading it, Malcolm.
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Old 25-12-2009, 12:39 PM
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Fantastic report. Enjoyed it muchly.

If you think the SMC is "bad"....just you wait till you hit up the LMC
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Old 25-12-2009, 08:11 PM
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Fantastic report. Enjoyed it muchly.

If you think the SMC is "bad"....just you wait till you hit up the LMC
Thanks Sab. The LMC is pretty full on, but I'm fortunate that the Morel atlas I have of the LMC inlcudes just about everything, so I've usually been able to work out what I'm looking at, admittedly after quite a bit of effort. But to work through the whole lot systematically could take years. a worthwhile project though.
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Old 26-12-2009, 04:00 AM
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That is a great write up Patrick, well done.
You said "Moving further into the SMC, I get confused by the plethora of small nebulae and clusters and even my Morel atlas doesn’t seem to cover all the options. I will have to find a way to navigate through this area."
There are some maps here: http://www.iceinspace.com.au/forum/s...&highlight=643
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Old 04-01-2010, 04:19 PM
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That is a great write up Patrick, well done.
You said "Moving further into the SMC, I get confused by the plethora of small nebulae and clusters and even my Morel atlas doesn’t seem to cover all the options. I will have to find a way to navigate through this area."
There are some maps here: http://www.iceinspace.com.au/forum/s...&highlight=643
Thanks for the link, Glen. I think I need something with more detail. I find the 16" scope shows so many of the fainter objects from catalogues other than NGC or IC that it gets hard to tease apart. I'll see how I go using Archinal and Hynes and the lappy.
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Old 07-01-2010, 09:51 AM
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Eeeeexcellent write up

Hi Paddy,

Thanks for taking the time to post you observations -- well done an excellent report.

Re NGC 419, this is an O.C not a G.C -- not your fault at all because most maps get this wrong as well as most cattledogs. The SMC only has one genuine true G.C -- NGC 121. All the others marked on many (most) maps and planetarium software as G.C's are in error. All these other clusters marked as G.C's are simply extremely large, middle-aged, exceptionally rich open clusters. NGC 121 is the only one certainly older than 10gyr in the SMC. Many were designated as G.C's in the old catalogues based on appearance only and this has carried over to a lot of the modern catalogues despite the object's spectra proving it is an O.C.

Both the LMC and SMC have many of these "super-clusters" -- ie clusters of >10,000 stars that look like G.C's but their spectra shows them to be relatively metal rich, middle aged (2-6 gyr) and not to have a "horizontal branch". They came about as a result of star-burst episodes in the relatively recent past. The LMC has about 6-7 genuine G.Cs but I can't remember off-hand which are which at the moment. The LMC is at present building a globular-sized cluster in the centre of the Tarantula Nebula (NGC 2070), but it is decidedly "open" in population.

To be a G.C the object must be very old (>10gyr) and exceptionally metal-poor (ie they are all Population II stars). It's not just "how they look in the ep". They also need RR Lyrae stars which indicates a proper horizontal-branch in their H.R diagram not merely a "red-clump".

But great report -- very much enjoyed mate .


Best,

Les D

Last edited by ngcles; 07-01-2010 at 10:15 PM.
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Old 07-01-2010, 08:07 PM
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Thanks for the feedback and some very interesting information, Les. I was browsing the LMC last night and both my Morel atlas and the Night Sky Observer's Guide listed quite a few GCs - I will now approach this more sceptically. They certainly look like GCs. Do you know of any online resource that would list the actual GCs. I am also curious about why so many OCs in the Magellanic Clouds look so round and compact and so like GCs. Is it just because they are further away than those in the Milky Way which look so much more variable, or is it actually a difference in the structure of them.
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Old 07-01-2010, 10:38 PM
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What is a G.C ??

Hi Paddy & All,

Well the short answer to your question is that I conversed with David Frew over this very topic about 12-15 years ago and he set me straight on it (David was then studying to become a professional astronomer) and gave me a list.

Interestingly as a result of your question, I opened Megastar (V5) tonight to track down the purported G.Cs and found a lot of them have "disappeared". In the older versions of Megastar there were heaps. They are now fewer. One example is NGC 1978. In v3 and 4 (I think) it is marked as a G.C. in v5 is is marked as an O.C.

In fact the ages of so much of the stuff in the LMC and SMC is not particularly well known. I've read a lot of journal reports tonight to discover the state of things and they are now more mixed than they were 15 years ago.

Back then, professionals had a pretty rigid definition of what a G.C was -- ie Population II stars, extreme age, metal poor, horizontal branch etc. But many of the more recent papers I've read tonight seem to be content to call many of these clusters "globular" while at the same time commenting on their relatively young ages 1-3 gyr, lack of RR Lyrae stars and horizontal branch. Some other papers refer to them as "intermediate age" clusters and comment that these LMC objects (in particular the LMC) are in effect a snapshot of what our Milky Way G.C's looked like 6-10 gyr ago.

So it seems the water has been "muddied" from what I believed.

You might find some interesting reading here:

http://nedwww.ipac.caltech.edu/level..._contents.html

This may be interesting too:

http://www.univie.ac.at/webda/smc_cat.html

The oldest cluster in the SMC is NGC 121 just over 10gyr old and has several RR Lyrae variable stars. Kron 3 is the second (measured) oldest about 9.7gyr and has none. Curious ...

if I think of it, I'll keep digging. One thing I have found with some certainty -- NGC 2257 is a classical G.C. NGC 1978 is a young intermediate age cluster and not comparable with a "true" G.C.

Still reading ...

Hector (Andrew Murrell) may well know a quicker and better answer than I ...


Best,

Les D
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Old 08-01-2010, 04:23 AM
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Thanks Les and Patrick for the interesting discussion on GC in the LMC & SMC. I reckon if it looks like a GC it probably is one.
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Old 08-01-2010, 07:58 AM
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Hi guys,

I'm not sure if this is useful or not, but there are some good links here:

http://www.asnsw.com/articles/clouds/

A pdf of objects in the SMC attached. Hope it helps. Cheers, Paul.
Attached Files
File Type: pdf SMC-CLUSTERS.pdf (116.5 KB, 10 views)
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Old 08-01-2010, 10:22 AM
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Hi All,

This paper is recent and pretty helpful on the ages and apparent history of the SMC and its clusters:

http://arxiv.org/PS_cache/astro-ph/p.../9907398v1.pdf

and provides pretty good evidence regarding the ages of a sample of clusters using HST. They conclude that there have been two distinct bursts of star formation about 2 and 8 gyr ago that formed these extremely massive and rich intermediate age clusters. They are without doubt "globular-like" in structure, mass and size but are different to what one might call a classical G.C ie >10gyr-old, high-mass, extremely rich, extremely low metallicity, RR Lyrae stars, horizontal branch, low turn-off point from the main sequence and strong red-giant and AGB branch etc etc.

There are a larger number of similar clusters to these in the LMC. Our galaxy doesn't have clusters of this sort. The closest Milky Way analogues I can think of off-hand is M67, NGC 188 and NGC 2477, NGC 2158 that are all massive, rich (relatively) old open clusters of intermediate metallicity -- but they are an order of magnitude smaller than what we see in the SMC and particularly the LMC where they are truly "globular-scale" ie >10,000 stars up to 50,000 stars and I guess if we all came back in 4-5 gyr and re-analysed many of them that are now 6-9 gyr old, we'd likely happily call them globular clusters because by then their evolution would have produced the features that define a classical GC (except for metallicity perhaps).

By this definition only NGC 121 passes the grade, but in the end I guess it now depends on what your definition of a G.C is.

I'll continue to have a poke around as time allows.


Best,

Les D
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Old 08-01-2010, 08:06 PM
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Thanks Les and everyone for your replies. There is a lot to chew on here and I love the new uncertainty of it all. It will take quite a bit of time to digest these articles. A most rewarding discussion indeed. What a great learning tool this forum is, populated by such generous and knowledgeable people. I'm now off to stick my head into the LMC for a few hours - report to follow.
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