Author Topic: Globular Cluster hunting -- in Barnard's Galaxy!  (Read 1798 times)

sgottlieb

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Globular Cluster hunting -- in Barnard's Galaxy!
« on: July 28, 2017, 06:01:55 PM »
For the July new moon I observed for 4 nights in the White Mountains above Bishop (Grandview Campground at 8500 ft), just below the Ancient Bristlecone Pine Forest.  Our group included Paul and Debbie Alsing, Kemer Thomson, John Hoey (all from the San Diego area), Jimi and Connie Lowrey (from west Texas but drove from Florida) and bay area locals Carter Scholz and Rick Linden.  The weather turned out great and the Detwiler fire southwest of Yosemite didn't impact us, though I drove through the smoke in Yosemite to reach the site.  SQM readings were generally in the 21.6-21.8 range, though occasionally below 21.5.  The largest scope was Rick's 32", which nearly dwarfed my 24" Starstructure.

Instead of posting a long list of observations (I logged 125 objects), I'll mention just one -- a Sagittarius globular that actually resides in Barnard's Galaxy (NGC 6822).  Edwin Hubble was the first to investigate Barnard's Galaxy in detail in 1925 (http://cdsads.u-strasbg.fr/full/1925ApJ....62..409H).  His study included a table of 10 nebulous objects within Barnard's Galaxy.  Most of these turned out to be HII regions (including 2 great visual targets), but Hubble VII turned out to be the first confirmed ancient globular in this galaxy.  The location, though, creates a problem -- its a tiny 16th magnitude speck superimposed on the glow of the galaxy and a very nasty visual target.  I was successful observing it twice from GSSP back in 2010 with my 18", though it was quite challenging (barely non stellar and lost in a maze of other dim stars within the galaxy).  I figured that was the last GC I'd see in Barnard's Galaxy

Four new globular discoveries in this dwarf galaxy were announced in 2011 but these seemed too faint for visual targets.  Then in 2013 three more were identified (so the current total is 8 ) and globular #7 (coincidentally the same number as Hubble's object) seemed a reasonable target for my 24".  When I added it to my observing list, I had no idea what to expect as I've never read of amateur observations of these globulars. You can read the discovery paper at http://adsabs.harvard.edu/abs/2013MNRAS.429.1039H, where it's called SC 7 (Star Cluster 7)

SC 7 is in the outskirts of Barnard's Galaxy, 22' NE of the center of the galaxy and well outside the visual extent -- that makes identification much easier!  Once the general field was centered using the 6mm Delos (375x), both Jimi Lowrey and I were surprised to quickly notice a non-stellar glow without first examining an image of the galaxy.  SC 7 was faint in my 24-inch, but clearly non-stellar, roughly 6"-8" diameter and 15-16th magnitude.  The globular could be held steadily when we backed the magnification down to 282x and possibly had a brighter stellar nucleus.

If you're curious about the distance, Barnard's Galaxy is ~1.6 million light years away.  For comparison, the most distant Milky Way globulars are 300 to 400,000 l.y. away, so this one is at least 4 times that distance!  I believe an 18" scope should catch this object from a dark site, if you know the precise location.

-- Steve 



Prana

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Re: Globular Cluster hunting -- in Barnard's Galaxy!
« Reply #1 on: July 28, 2017, 10:27:56 PM »
Great observation Steve.  Reminds me of how surprisingly easy it was seeing that new glob near B86 a few years ago.  Interesting what can be seen.  With I'd been there!

Marko

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Re: Globular Cluster hunting -- in Barnard's Galaxy!
« Reply #2 on: July 29, 2017, 01:57:58 PM »
From the paper i take it Sc6 and Sc7 are around mag 15 and thus doable with very steady skies and 18" scope.

Nice tip for a mini-project.  I enjoy poking about for extra galactic globs in nearby galaxies.

Another link that I found more accessable to that paper was seen at https://www.researchgate.net/profile/Avon_Huxor/publication/233427060_Three_newly_discovered_globular_clusters_in_NGC_6822/links/541032590cf2df04e75b897b/Three-newly-discovered-globular-clusters-in-NGC-6822.pdf

I also attach a quick finder 1-page summary just made for my usage at a later date.
Both Sc6 and Sc7 seem to show up nicely in MegaStar with DSS so other DSS sources should show them fine.

Thanks,
Marko
Let me roam the deep skies and I'll be content.

sgottlieb

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Re: Globular Cluster hunting -- in Barnard's Galaxy!
« Reply #3 on: July 29, 2017, 02:37:12 PM »
Thanks Mark and Marko for the comments and posting the finder chart.  SC 6 is already on my observing list as it's only a 1/2 magnitude fainter than SC 7, but I didn't take a look at Grandview.  Maybe next month.  For the record, here are the coordinates of these two exotic objects.

SC 6   19 45 37.0 -14 41 10.8
SC 7   19 46 00.7 -14 32 35.0

A 2005 study titled "The Globular Cluster System of NGC 6822" (https://arxiv.org/pdf/1506.00951.pdf) gives the following magnitudes (rounded to nearest tenth):

SC 6  15.4V
SC 7  14.8V

Let us know if anyone gives these a try.


sgottlieb

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Re: Globular Cluster hunting -- in Barnard's Galaxy!
« Reply #4 on: August 05, 2017, 09:49:00 PM »
For next fall, I was just approved for an observing article in Sky & Tel on Local Group globular clusters, so I certainly hope to get a look at SC 6!

Marko

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Re: Globular Cluster hunting -- in Barnard's Galaxy!
« Reply #5 on: August 05, 2017, 10:54:00 PM »
What is your count for Fornex Globs?   I seem to have 2,3,4,5  but called out 6 as 'iffy' and decided I would not count it but spent 20 minutes before saying 'no claim'.

I cannot say I recall noting any globs in M33 and this after a great deal of time was spent on assorted objects within it (mostly suggested by yourself I think, thanks).  is it too far away for globs?
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sgottlieb

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Re: Globular Cluster hunting -- in Barnard's Galaxy!
« Reply #6 on: August 06, 2017, 03:36:48 PM »
NGC 1049 = Fornax 3 is the brightest globular, then Fornax 4 and 5 a bit smaller and fainter.  Fornax 2 is the faintest of the main 4, which are all visible in a 10-inch or 12-inch.

I would be surprised if you could pick up Fornax 6 as I called it "extremely faint" in the 48-inch, but Uwe Glahn writes that he glimpsed it a 18" from Namibia.  My full description was "extremely faint, small, very low surface brightness spot, ~0.3' diameter.  Located 7' due north of globular Fornax 4.  Pinpointing the location, a mag 15.8 star is 1.6' W and a mag 16.5 star is 2.1' WNW."   But Fornax 6 isn't a globular anyways -- it's either a group of extremely faint stars (~21st mag) or even distant galaxies!

There is a 5th globular, though -- Fornax 1, which is much fainter than the other 4 (perhaps close to 16th mag).  Perhaps this is the one you looked for?

Marko

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Re: Globular Cluster hunting -- in Barnard's Galaxy!
« Reply #7 on: August 06, 2017, 04:05:58 PM »
No, did not even try for #1.  Of course I knew it existed due to how whole numbers dominate lists but because it does not show on MegaStar or I had not enough options on I did not go for #1.   I attach my finder chart used Oct 10, 2010 in very dark skies (you were not present but often were at this site).
Let me roam the deep skies and I'll be content.