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Martin Meredith

Galaxies amongst the Ophiuchus star fields

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When I think of Ophiuchus, I primarily think of the Snake dark nebula (Barnard 72) and Barnard’s Star (quite an influence that guy had). Ophiuchus sits close to the Milky Way, joining it at the enormous Pipe Nebula (Barnard 78), so I don’t tend to think of its star-rich fields as galaxy-hunting ground. But following a wet and cloudy spring I’m still clinging on to as many galaxy sessions as possible in a current run of clear moonless nights, and yesterday spent some time in Ophiuchus and another galactic underdog, Libra, looking for targets.

My main target was NGC 6384, at mag 11.6 the brightest galaxy in Ophiuchus. This is a spiral seen nearly face-on — or at least at an aesthetically-pleasing angle! This galaxy shows lots of structure and would be rewarding wherever it appeared, but having it set amidst a dense star field adds to its appeal. To my eye it conveys the illusion of being supported by the stars; I just can’t see it as 80 MLY more distant. 

NGC.6384_2016.6.8_00.17.59.png

Just half a degree due south I spotted on the charts a lonely galaxy chain consisting of 4 almost equally-bright galaxies (mags 15.5-15.8). Later, I managed to track them down to the Catalogue of Nearby Poor Clusters of Galaxies (also known as the WBL catalogue after the authors of the 1999 article listing 732 such groups). Poor here is to be contrasted with ‘rich’, as in the Abell clusters, and refers to the number of members (the criterion in WBL is 3 or more). The cutoff magnitude for that catalogue is 15.7 so these just slip in under the fence.

WBL642.png

The particular group I found turns out to be WBL 642. The main shot is a single 30s sub, while the labelled inset comes from a 12x30s stack. Some details of the individual galaxies such as spiral arms are apparent. For me the interest in this field comes from seeing the archipelago of galaxies floating adrift against the dense foreground stars.

I found only one specific reference to WBL 642, where it is labelled SSSG2 (small-scale systems of galaxies). The line indicates a mag 17.9 galaxy which doesn’t make it into the group (due to its faintness) but according to the article has a radial velocity consistent with the rest of the group, so we seem to be looking at a chain of 5 co-moving galaxies here. 

These are some of the fainter members of the WBL catalogue, and I've chosen to show a 30s sub to illustrate that the whole WBL catalogue is surely accessible to the EAA style of observing. I have no idea what the other configurations of WBL members are like, but this one is as interesting visually as many of the Hickson groups (indeed, WBL contains 19 Hicksons amongst its entries).

cheers

Martin

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Wonderful stuff, it must have been very satisfying to 'discover' an obscure galaxy group like that. There seems to be no end to the catalogues of galaxies, galaxy clusters/groups, PNs, nebulae, etc. I think there is a lifetime of EAA observing to be had from the galaxy cluster/groups catalogues alone!

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Just love these tours, inspiring stuff, please keep 'em coming.  Are these, like the 'looking south' collection, all around F4 with a Lodestar x2?

Edited by nightvision
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Thanks Rob. I agree, there is enough to see without revisiting the same objects every time (though that is also fun with different kit). I feel I'm just exploring at the moment but have the idea that at some point I'd like to do something more systematic. I'm working through some of the Arp and V-V galaxy/groups at the moment. Nearly all of them have distinctive features even with modest kit and that makes them exciting to see. Later I'll post some of these from the last few days.

Thanks Tony. Yes, these are all with my workhorse scope, the Quattro 8" f/4 + Lodestar X2 mono. That's one combination (with StarlightLive) that I can see myself using for quite a few years yet...

Martin

 

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You have very good eyes Martin. Those star fields are rich and dense. To discover those fuzzy little creatures in that environment requires some selective vision.

Thank you for shring this with us!  --Dom

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Great gx pics Martin ;-)  I applaud your search for unusual targets away the Messier/NGC lists - there are literally thousands of objects that EAA/video reveal that are visually impossible and it's good to see them uniquely 'exposed' on this forum.  Man after my heart !

I've always had a domed obsy which is pretty essential here in London due to LP and one of its [minor] disadvantages is the need to turn the dome frequently - if chasing Messiers.  I learnt my lesson when a mate wanted to view [in the old days] Messiers in numerical order!  But with extremely faint gxs [like your recent targets] there no need to move the dome - just 'nod' the scope up and down as the sky transits the dome slot over an hour or so.

Keep up the good work

Nytecam

 

 

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On 6/8/2016 at 17:09, Martin Meredith said:

When I think of Ophiuchus, I primarily think of the Snake dark nebula (Barnard 72) and Barnard’s Star (quite an influence that guy had). Ophiuchus sits close to the Milky Way, joining it at the enormous Pipe Nebula (Barnard 78), so I don’t tend to think of its star-rich fields as galaxy-hunting ground. But following a wet and cloudy spring I’m still clinging on to as many galaxy sessions as possible in a current run of clear moonless nights, and yesterday spent some time in Ophiuchus and another galactic underdog, Libra, looking for targets.

My main target was NGC 6384, at mag 11.6 the brightest galaxy in Ophiuchus. This is a spiral seen nearly face-on — or at least at an aesthetically-pleasing angle! This galaxy shows lots of structure and would be rewarding wherever it appeared, but having it set amidst a dense star field adds to its appeal. To my eye it conveys the illusion of being supported by the stars; I just can’t see it as 80 MLY more distant. 

NGC.6384_2016.6.8_00.17.59.png

Just half a degree due south I spotted on the charts a lonely galaxy chain consisting of 4 almost equally-bright galaxies (mags 15.5-15.8). Later, I managed to track them down to the Catalogue of Nearby Poor Clusters of Galaxies (also known as the WBL catalogue after the authors of the 1999 article listing 732 such groups). Poor here is to be contrasted with ‘rich’, as in the Abell clusters, and refers to the number of members (the criterion in WBL is 3 or more). The cutoff magnitude for that catalogue is 15.7 so these just slip in under the fence.

WBL642.png

The particular group I found turns out to be WBL 642. The main shot is a single 30s sub, while the labelled inset comes from a 12x30s stack. Some details of the individual galaxies such as spiral arms are apparent. For me the interest in this field comes from seeing the archipelago of galaxies floating adrift against the dense foreground stars.

I found only one specific reference to WBL 642, where it is labelled SSSG2 (small-scale systems of galaxies). The line indicates a mag 17.9 galaxy which doesn’t make it into the group (due to its faintness) but according to the article has a radial velocity consistent with the rest of the group, so we seem to be looking at a chain of 5 co-moving galaxies here. 

These are some of the fainter members of the WBL catalogue, and I've chosen to show a 30s sub to illustrate that the whole WBL catalogue is surely accessible to the EAA style of observing. I have no idea what the other configurations of WBL members are like, but this one is as interesting visually as many of the Hickson groups (indeed, WBL contains 19 Hicksons amongst its entries).

cheers

Martin

Brilliant obs

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Thanks all.

Dom, I only discovered them on the map, then it was a case of finding them for real. I doubt I'd have seen them otherwise. Actually, there's a whole catalogue of galaxies behind the Milky Way to explore. 

Nytecam, I'm still having lots of fun 2.5 years on from obtaining the Lodestar after reading your posts! As you say, there are so many targets out there still to find. Mind you, after spending some time with the faint stuff, the old favourites in the Messier catalogue seem indecently bright and detailed.

Martin

 

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