Unknown open cluster in Monoceros?
Posted 04 January 2013 - 04:47 AM
Last evening I was leisurely strolling through Monoceros with my 63mm Zeiss Telemator, equipped with a 2" 42mm Kellner eyepiece, giving 20x and a roughly 2.5° field of view. After examining the Rosette Nebula, open cluster NGC 2244, Hubbles Variable Nebula and the Christmas Tree cluster, as well as other objects, I stumbled upon a small, sparse open cluster. It stood out quite well in the 2.5° field, sitting on a rich background of very faint stars, but with almost no equally bright stars in the immediate vicinity. Most stars in the cluster were of roughly equal brightness, about mag 9.5 to 10, I guess, and I could count about 10-15 members within a 15' diameter. I didn't have any means readily available with which to do a more accurate assessment of their brightness. All in all, it seemed like a surprisingly nice little cluster. I didn't immediately recognize it, so I looked it up in Uranometria 2000.0 (first edition). Or rather, tried to look it up. Imagine my surprise, when it was no shown in the atlas, despite being a fair bit more obvious in the eyepiece than many NGC clusters. I mean, it doesn't even need to be a true open cluster to get a NGC number, so why not this little one?
Today I determined the position from a Digitized Sky Survey image, which shows the suspected cluster nicely:
http://archive.stsci...r=06h 45m 15...
(Warning! Big file. The field is 1° x 1°)
The position is roughly 6h45m15s +8°03', which I promptly fed into SIMBAD and got nothing. There is apparently no catalogued cluster anywhere near this position or within a 20' radius.
So, what have I stumbled across? A true cluster or merely an asterism? It would seem quite unlikely for an open cluster to escape notice for so long, especially in this region, but if so, then why haven't another amateur before me come across it? As I said, it really stands out quite nicely in a small rich-field telescope, possibly even binoculars, so why isn't it more well known? It is much brighter and more concentrated than many genuine NGC clusters.
Posted 04 January 2013 - 05:44 AM
Hope, you can see it from this link.
From time to time I run as well on some interesting grouping of stars. Sometimes, these are real and I quickly identify them with the help of Uranometria2000.0, sometimes, there is nothing (but still the group looks interesting). It is a kind of paradox, I "discovered" most of the clusters with small refractors (many of them unknown at NGC times): for example NGC6997, Cr428, and Basel 1 in 120mm, Stock 2 in 100mm, IC2157 and Roslund3 in 80mm or Cr421 in 63mm. There was only one in my former 250mm Newton: IC2156 (this was just when I was examining in larger scope IC2157 which I found previously).
It is definitely fun, and who knows, sometimes you can really run into something new!
Posted 04 January 2013 - 02:21 PM
Thanks for the very useful link. It was, as I suspected, not a true cluster, despite its very cluster-like appearance. Check it out with your Telementor, it really does look nice, if I may say so myself.
It is the first real "unknown" deep-sky object I've found with my 63mm, but it's far from the first obscure open cluster/asterism I've seen with it. A survey through Cassiopeia, Perseus and Cepheus with Uranometria 2000 and the Telemator showed that almost all open clusters shown in U2000.0, first edition, can be seen in a 63mm! I extrapolated the number and found that there should be on the order of some 800 open clusters visible in this aperture.
Posted 04 January 2013 - 02:24 PM
Thanks. I was unaware that there was such a list. I could not access the group database, as I am not a member. The position is nearly identical to the one I estimated and well within the radius of the group, so there is no doubt that it is the same object.
Posted 04 January 2013 - 04:01 PM
In Monoceros, I run last year with my ED100 on two candidates for clusters/asterism. First, I noticed during random walking in Monoceros an open cluster Do24 near 18 Mon. Then I decided to explore this region more thoroughly.
Both were suspicios regions with size of about 10' which stood out well from milky way when using averted vision at magnification of 16x. The first candidate was looking at 36x as a circle and line. It does not show well on DSS image: here. It is a group of few relatively bright stars in the middle of the image (RA=06h50m51s, DE=+01d30m, J2000.0). There is a suspicious grouping of faint stars but it could be just random group. Interestingly, when I tried now the same trick with Aladin, there are at least 4 stars from the group which seems to share the common proper motion: here.
The other candidate looked even more interesting at the eyepiece (36x) than the first one. However, on DSS image, there is not much to be seen: here. In the lower left part. One could even see that this region is surrounded from by dark nebula - may be this was the reason why it stood out so well at low magnification. These is an interesting reflection nebula connected with the dark nebula. Never heard of it: Parsamyan 15. It looks like a challenge target for larger scopes.
I would like to check these regions again but who knows when...
Posted 04 January 2013 - 04:30 PM
The Pocket Sky Atlas is handy, but too small and simple for my needs. My mainstay atlas for more than fifteen years has been my old Uranometria 2000.0, given to me by a dear friend. I am thinking about getting the new single-volume U2000.0. I think you should consider it as well. Even a 60mm can push the limits of this kind of atlas, when used under a dark sky, by an experienced observer, such as yourself. I think you'll find untold wonders with it, just as I have.
This past autumn and early winter has been poor, but not the worst I can remember. There has been a good night now and then. I'll check out the objects you found, when I get some clear sky again, hopefully soon.
Posted 04 January 2013 - 05:17 PM
Posted 04 January 2013 - 05:31 PM
Ah, I see! My advice is to take that Uranometria out under the stars a lot more. You should see mine. Battered and scarred, with stains from mud and hot chocolate... but it still keeps going strong and now holds many memories.
One of my all-time favorite pastimes has been to find a constellation nice and high in the sky, open up a page of Uranometria showing that constellation and then simply hop across it with the Telemator, trying to see as much as possible. I often hopped across multiple pages, discovering untold surprise objects. On a really clear, dark night, after two or three hours of dark adaption, it seems the limits of what is possible with a 63mm are far, far beyond what is normally considered possible. I've had some really magic nights.
If I lived under really dark, clear skies with many, many clear nights each year, I think I would make it a project to check out *every* single page in Uranometria this way with the Telemator.
Posted 05 January 2013 - 05:40 PM
The Saguaro astronomy club website has a downloads section with several hundred of these "Asterisms" listed. It's definitely worth the download.
One of my favorites is Kemble's Cascade. Looks great in a NP101 at 17X, but I can't even tell it's there in my 12.5".
Posted 06 January 2013 - 03:47 AM
I'll check out the list of asterisms. Thanks for the tip.