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A New Chart of Extended Objects in the Small Magellanic Cloud

posted Jan 3, 2013, 6:03 PM by Mike White   [ updated Jan 3, 2013, 6:32 PM ]
Magellanic Clouds
If you are new to astronomy, you may be surprised to learn that you can actually see two galaxies outside of the Milky Way without the aid of a telescope or binoculars!  If you look towards the south on a clear night (and preferably from a dark site, free from light pollution), you will see a couple of cloud-like structures, one larger than the other, that don't seem to move as a cloud would.  These are what is known as the "Magellanic Clouds" - the larger one being the Large Magellanic Cloud (LMC), and the smaller being the Small Magellanic Cloud (SMC).  They are, in fact, satellite galaxies that have been captured by the immense gravitational pull of our Milky Way galaxy, and are 160,000 light years and 190,000 light years away, respectively.

Looking at these objects through even a modest telescope reveals a multitude of star clusters and nebulae contained within and around them.  Most of the clusters and nebulae in the LMC have been well-catalogued with reasonable accuracy, but this is not quite so for the SMC.  To that end, Ian Cooper began a project several years ago to accurately chart the SMC, and has now released version 4 of his chart for all to use.  You can view the chart and associated object list on our website here.

The following is a blog post from Ian Cooper, explaining how the project came to be.  Ian is currently President of the Palmerston North Astronomical Society, Vice President of the Horowhenua Astronomical Society and Vice President of the Phoenix Astronomical Society.

"Attention all lovers of the Magellanic Clouds. I would like to present a new, all in one extended object chart of the Small Magellanic Cloud for free use to all those interested. The chart is a large Jpeg file and also available is an excel spreadsheet listing all of the individual objects and their most common names and coordinates. The chart was originally started about 12 years ago as a result of what I outline below.

To access the chart and catalogue visit the website of the Horowhenua Astronomical Society;

In late 1999 I was invited to be a contributing author in an astronomical handbook called, “The Night Sky Observer’s Guide Vol III, The Southern Sky,” by the lead author, American George Robert Kepple. A list of non-stellar objects of just 600 individual members that came mainly from the N.G.C. & I.C. catalogues was sent to me to observe with my 18 inch Dobsonian reflector. The 600 proved to be an insufficient list to represent the section of sky that I was asked to examine which runs from my zenith (declination 40 south) to the S.C.P. (South Celestial Pole). From memory I think I observed about 600 objects in the Large Magellanic Cloud alone.

Over the several years it took to review this large chunk of sky I tried to inspect almost everything that my telescope could pick up from my rural location on the Manawatu Plains, New Zealand. I had intended to use smaller telescopes to inspect many of the brighter objects and add impressions from those ‘scopes as well. The task proved too great for one observer and fortunately renowned deep-sky observer Jenni Kay from Adelaide, South Australia, agreed to come onboard and add her considerable skills and efforts to the project.

Even 13 years ago there were considerable resources available to deep sky observers wanting to rummage through the Milky Way and the extra-galactic regions of the southern sky. Numerous atlases and some of the early computer software available were first rate and allied with some internet sources still available today, the process of finding and confirming individual objects was fairly easy. By the way I don’t operate a ‘Go To’ telescope. I am a star hopper from way back so good charts are necessary!

When it came to the Magellanic Clouds however the usual sources were very limited. When an observer runs their telescope through our two little inter-galactic neighbours it isn’t hard to see why. Both Clouds are crammed full of clusters and nebulae. The sight can be quite daunting even to an experienced observer.

The only resources that I had available that came close to making sense of all of this were charts printed from a friend’s Megastar Version 4 software and the Herald-Bobroff Star Atlas. The H-B Star Atlas proved very accurate in the L.M.C. One had to get used to the nebulae all being depicted as squares of varying sizes and intensities. Although tricky it was workable once you got used to it.

Unfortunately the same could not be said for the S.M.C. Both the H-B Atlas and Megastar 4 were full of mistakes. Many objects were either misplaced which created confusion, or as was the case with Megastar clusters were shown as stars. Obviously this came about in the process of creating their charts from photographs and perhaps some use of automated procedures which may not have recognized the smaller clusters for what they really were.

To overcome some of these problems I created a mosaic of photographic images of fields downloaded from the Digitized Sky Survey (DSS). I then mosaiced another chart of fields from Megastar 4 that covered an A1 sheet. Between the two I made up a working chart that made it possible to finish my observations in the S.M.C. I left it like that for about ten years before deciding to take it a lot further. The catalyst for this was the arrival of the MCELS (Magellanic Cloud Emission Line Survey) mosaic image of the S.M.C. that came out in 2006, along with an equally brilliant image of the L.M.C. to be found at this web site.

My first step was to reduce my original hand drawn chart to an A3 size so that I could scan it. Only having a basic drawing programme, Microsoft Paint, I set about tidying up the chart and colour coding the objects. I also realized that this was an opportunity to take the chart to a more comprehensive level, one that would be useful to astrophotographers as well. This is where the MCELS image proved invaluable as well. In association with that image I had a hard copy of the Extended Object List of the S.M.C. I used the latter list to create the accompanying catalogue for the objects shown on the chart.

As I worked my way through the upgrade on version 2 I found many mistakes that I was able to correct. Just when I thought I had it nailed I found more resources that added more objects to the chart and highlighted more mistakes to fix. That was mid 2012. I decided to put the chart aside and come back to it when I had more time. 

The Christmas holidays of 2012 have given me that extra time to re-visit this project. Once again whilst looking for something else on the net I came up with more great resources in the form of the Revised and Extended Catalogue of the S.M.C. and accompanying charts provided by the American Astronomical Society and the NASA Astrophysics Data System.

Things to note on the chart; I have avoided the use of grid lines as I feel that the chart is very full of information as it is. As I have found throughout people may find that stars shown on this chart do not exist in reality. I have removed such cases where I have found them but I have not put a great deal of effort into seeking them out. Some may notice that there are several open red circles that have no label to them. These are purely photographic and as yet I have not found a catalogue that lists them so they are there as a reminder to astrophotographers of their presence.

You will notice on the version 1 attached that I used a DSS field at the bottom of the chart to help sort out the field of ‘The Magnificent Seven’ (if you turn the image so that east is at the top then you find that the strongest seven nebulae in the field form the number ‘7’). I also made an attempt at an index chart for the nebula complex around NGC 456 etc. For the latest version of the chart Stephen Chadwick of Himatangi Beach near me has kindly provided these fine colour images of both of those crowded fields as well as a brilliant image of the lucida of the S.M.C., NGC 346, the Barred Spiral Nebula.

The image provided is a big file made that way so that it can be printed on a big format. My local stationary shop produced an A1 sized colour image on plain paper for $6.50 N.Z. for a similar price or a bit more I can have it laminated so that it can be placed on the wall of our observatory. Printing this chart at anything smaller than A3 would require a magnifying glass to read it!

This is a living entity in that if anyone finds a mistake I will correct it and advise anyone accordingly. I put this out now knowing that it is possibly not 100 % correct but that it is as close as I can make it by self checking. If anyone has the resources and inclination to check it thoroughly then feel free to do so.

I would like to thank Alan Gilmore of Mount John University Observatory at Tekapo for his assistance in this work.

Now I know that there is one question all of you Magellanic Cloud lovers want to ask. What about the L.M.C.? As I mentioned earlier I did find the Herald-Bobroff Atlas very good to use for the L.M.C. but it is not an overly easy set of charts to use. In the meantime I did go through and annotate Robert Gendler’s fine image of the Large Cloud, but unfortunately that is not my image to share with you. Suffice it to say that if I give the L.M.C. a go you won’t have to wait another dozen years to see the results."

Ian Cooper