Magellanic Cloud Globular Clusters

[Allan]

I'm looking for help to compile a list of known globs in both the LMC and SMC. A lot of reliable sources such as Uranometria and Sky Safari are incorrectly listing targets as open clusters, however with deeper research they are actually globular clusters.

This is proving to be a difficult and slow process trying to sift through the mis-information, so I'm wondering if anyone has an available data base they could share.

Days worth of Internet searching just on the Magellanic Clouds is wearing me down, as there isn't a readily available repository of information on this specific subject as far as I can see.

[mental4astro]

Hi Allan,

The LMC and SMC are a true enigma. So close, and yet so poorly mapped.

I too have encountered the same problem of incorrect categorising of most of the clusters within both. Dare I say this could extend to ALL the objects within them...

Most sources are contradictory. Making matters more difficult is that there a many, many objects still not noted. I found this out with a sketch I did of a tiny area within the LMC. I've uploaded the sketch below, and you'll see that there are some curiously labelled objects that really challenge their categorisation. I had to go with the sources I had available, but I am only too happy to revise these. Also, the best sources I had listed 13 objects, yet my sketch has some 17, and photos of this area showed these too, so I wasn't seeing things, :rolleyes::nerd::lol:

I'll have a look myself at a few sources and let you know how I go.

Alex.

[Atmos]

Been a while since I read this paper but it may contain some information.

https://arxiv.org/abs/1001.4289

[el_draco]

Can you access the charts by Morel?

[Rob_K]

Try Patrick's (Paddy's) site, some excellent charts:
http://www.cloudsofmagellan.net.au/

Cheers -

[Allan]

Thanks for the reference, I will check those out.

[Allan]

That's a good link Rob, I haven't seen that before. However it does indicate the problem I'm having gathering the correct information, because I could see straight away the errors in these charts. I just looked in the SMC charts and there are several confirmed globular clusters that are listed as open clusters in the charts. But as an observing guide to show the location of objects they seem like a nice resource.

[mental4astro]

I've got the Morel set of charts on CD. Good, but I feel out of date 12 years down the track from their earliest date. Not fault of Morel. He did a blooming good job. Resolution of the charts is a little lacking compared to what more current charts can offer, which makes these charts very cramped and hard to follow as there is so much going on in just a tiny space. Paddy's charts are better in terms of resolution, but I haven't compared Morel's charts to Paddy's as yet in terms of how complete they are to each other. I don't know of Paddy's sources either, and Morel's charts may well be one of them.

[Robh]

Hi Allan,

You need to careful that you don't get into a mindset that the classification of all these clusters is definitive. There are many clusters in the Milky Way Galaxy that have yet to be ratified as globs and others that have been de-classified from globs back to perhaps open clusters.

http://spider.seds.org/spider/MWGC/mwgc.html

Any research on these clusters has to be supported by follow up research from someone else to support their viewpoint. With many researchers in agreement, the information becomes widespread, accepted and available to all. Previously held ideas about what makes a cluster a glob is not all that clear cut e.g. that they should all have one population of older stars. Some of these clusters might have properties the make them look like globs but others that don't. And that's where the issue is.

When you say there are several confirmed globs, who is confirming it? I think you might find that many of these clusters are not going to be that easy to classify and may even defy classification (at least according to current thinking). That is perhaps why the information is not so easily available.

Regards, Rob

[mental4astro]

Rob, you make a very good point.

Looking over the set of Morel's charts, even in the object catalogue there are several clusters that were as then uncategorized, meaning either OC or GC. But adding to the layer of confusion that I have to agree with Allan about, different catalogues have the same cluster classified differently in each... Some others they don't exist.

[Robh]

Hi Alex,

Where a cluster may be transitioning from one classification to another (e.g. open cluster to glob) there will be conflicting designations by various sources.

For some of these clusters, it is not always clear-cut as to what they are and there will be on-going debate. And a previously classified glob may have it's status reversed by some other defined set of conditions.

One study on the cluster(s) may not be sufficient for the scientific community to generally accept the results as definitive. It may take time before other researchers tie in results that can confirm the proposed status. That is why I asked the question about who is confirming the glob status.

Regards, Rob

[pixelsaurus]

List of bits in the SMC. I don't know whether Ian has extended the list to cover the LMC.

http://www.horoastronomy.org.nz/stargazing/small-magellanic-cloud

[Stonius]

I thought stars in globs were markedly older with a different chemical composition, and different orbits. Do OCs really turn into globs over time? Hadnt heard this before...

-Markus

[Robh]

Hi Markus,

I was talking about the classification changing. Historically, there are many so-called globs that were re-classified as open clusters.
Read NGC 2158, AM 2, UKS 2, FSR 1755 and FSR 0089 in the bottom list of Former Milky Way globular candidates here ...
http://spider.seds.org/spider/MWGC/mwgc.html

In the Magellanic Clouds, there are OCs that may in fact be globs and are called globs by some but not by others. Halton Arp (1958) thought NGC 361 and NGC 419 were "globular-like" clusters. However, he also concluded that a large proportion of stars in the SMC were very much like globular cluster stars. SIMBAD still lists both clusters as OCs. SkySafari calls them both OCs. The NGC/IC Project calls NGC 361 an OC but NGC 416 and NGC 419 globs and SkyAtlas 2000 shows the latter two as globs. SIMBAD calls NGC 416 an OC.

It is not that clear-cut!

Regards, Rob

[Robh]

Hi Allan,

These two lists from SEDS may be of some value. At least, they highlight the problems in identification of the globs. I suppose you could treat all the possibles as globs until you find out otherwise. The SEDS list indicates those classified as globs by the NGC2000.0 Catalogue but it is hard to track what the actual data source was.

http://messier.seds.org/xtra/ngc/smc_more.html

http://messier.seds.org/xtra/ngc/lmc_more.html


A useful site is the NGC/IC Project. Probably more reliable than a lot of other databases.

http://www.ngcicproject.org

Regards, Rob

[Stonius]

Certainly it seems there is confusion between sources as to their classification, but I'm curious as to why that is. I would have thought a quick glance with a spetrograph would be enough to determine whether the stars are population I or II? Maybe not all globs are Pop II stars (most, but not all)? My understanding is that OC's do not evolve into globs over time. An interesting anomaly, anyway. :-)

-Markus

[Allan]

Rob, I think that pretty much sums up the problem, different sources classifying them differently. The NGC/IC project is typical. There is an NGC they list as an OC, but in Steve Gottliebs notes he calls it a GC because of its appearance. Then I went to the Hubble/NASA site and they call it a GC, and it certainly looks like a GC.

[Allan]

That's what I thought also. I don't understand all the confusion with these classifications, it should be more straight forward.

[Atmos]

USUALLY a globular cluster is reasonably easy to identify by looking at their HR diagram. GC's typically fall within the ages of 8-12.5 billion years old but there are some younger ones.

Take R136, the centre of NGC 2070 as an example. It is currently an open cluster and large nebulise region which from memory is maybe 10 million years old? Would have to double check that when not on my phone :) R136 is an interesting region as it is widely accepted that in time, it will become a GC. On a cosmic scale, new born GCs are a rare event in this time of the universe. For the most part there just isn't enough molecular star clouds around to form a GC, the universe has just changed a lot over the last 5-8 billion years :)

From memory, R136 is currently going through its first of probably two stellar populations; most GCs have at least two and sometimes three populations.

[Stonius]

Fascinating. So, assuming that the gas cloud has some of the heavier elements, it could be a newborn CG of Population I stars. I looked up the wikipedia entry on R136 because you peaked my interest. I particularly found the following passage interesting;

"R136 produces most of the energy that makes the Tarantula Nebula visible. The estimated mass of the cluster is 450,000 solar masses, suggesting it may become a globular cluster in the future. [...] The cluster R136 contains many of the most massive and luminous stars known, including R136a1. Within the central 5 parsecs there are 32 of the hottest type O stars (O2.0–3.5), 40 other O stars, and 12 Wolf-Rayet stars, mostly of the extremely luminous WNh type. Within 150 parsecs there are a further 325 O stars and 19 Wolf-Rayet stars."

Markus

[Atmos]

Maybe it is 2 million years old? Trying to remember back a few years so my globular cluster research :P

The same thing is happening at the centre of M42 where the trapezium is what lights up near all of the Orion Nebula.

[Steve Pattie]

Hi Allan,

There are detailed charts of the LMC and SMC by Paul Hodge and Frances Wright. Both are now unfortunately hard to get hold of and are rarely available second hand.
I've been meaning to scan my copies but haven't gotten around to it due to the large number of charts (SMC has 72 charts, LMC has 81 charts) and that you need an A3 scanner for the chart size.
If you can get hold of them through a library, then you may find that you have too many objects. LOL

Steve

[Allan]

Thanks Steve, I will have a look around for that reference.

I just ordered the book 'Star Clusters'. It is 500 pages dedicated specifically to all the open and globular clusters. The two authors were inspired to write the book due to their frustration at the mis-classification of so many clusters. Sounds familiar.

[jamespierce]

I have the Hodge charts - SMC and LMC - and have digitized the central portion to print on water proof paper for field use. I wonder when copyright issues expire for something out of date like this, or if the authors care (unlikely to get a re-print now)... Their plates and annotations have yet to be bested for detail. Classification of the objects is another issue.

[ausastronomer]

Are you planning on bringing those with you next Friday James?

Cheers
John B

[jamespierce]

I will bring the atlases and the digital versions certainly... waiting to see if the printers have time to run the waterproof paper as a favour before then. It is magalenic cloud season after all.

[ausastronomer]

Sounds good. I haven't used the Hodge & Wright Charts only Mattie Morels. I am sure our American Visitors can get some good use out of them.

Cheers
John B