Steve Gottlieb
July 30th, 2017, 04:14 AM
During the July new moon window I observed for 4 nights at Grandview campground (https://www.fs.usda.gov/recarea/inyo/recarea/?recid=20268) (8600 ft elevation), situated in the White Mountains of eastern California, just below the Ancient Bristlecone Pine Forest (https://www.bishopvisitor.com/activities/bristlecone-forest/). I met a group of friends including Paul and Debbie Alsing, Kemer Thomson, John Hoey (all from the San Diego area), Jimi and Connie Lowrey (from west Texas but drove directly from Florida) and Carter Scholz and Rick Linden from the San Francisco east bay. The weather turned out great and the Detwiler fire southwest of Yosemite didn't impact us, though I drove through the heavy smoke in Yosemite to reach the site on the 18th. SQM-L readings were generally in the 21.65-21.80 range, though occasionally below 21.5. The largest scope was Rick's 32" Webster, which nearly dwarfed my 24" Starstructure.
One highlight for me and Jimi was a Sagittarius globular that actually resides in Barnard's Galaxy (NGC 6822), a local group dwarf. A bit of background first -- Edwin Hubble was the first to investigate Barnard's Galaxy in detail in 1925 seminal paper "NGC 6822, a remote stellar system" (http://cdsads.u-strasbg.fr/full/1925ApJ....62..409H). He found 10 nebulous objects (http://cdsads.u-strasbg.fr/cgi-bin/nph-iarticle_query?bibcode=1925ApJ....62..409H&db_key=AST&page_ind=4&data_type=GIF&type=SCREEN_VIEW&classic=YES) (labeled with Roman Numerals) within Barnard's Galaxy. Most of these are HII regions (the best two visually are Hubble X and V), but Hubble VII turned out to be a bonafide ancient globular. 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 back in 2010 with my 18", though it was quite challenging to identify within the mottled glow (barely non stellar and lost in a maze of other dim stars within the galaxy). I figured that was probably the last GC I'd see in Barnard's Galaxy.
The following year, four new Barnard Galaxy globulars were announced in 2011 by Hwang et al (http://iopscience.iop.org/article/10.1088/0004-637X/738/1/58/pdf), though these seemed too faint as visual targets for my 18". Then in 2013 three additional GCs were identified (https://arxiv.org/pdf/1211.3896.pdf) in Barnard's Galaxy by Huxor et al, bringing the current known total to 8. It looked like globulars #6 and #7 (called SC6 and SC7) were reasonable targets for my current 24", though when I added these to my observing list I had no idea what to expect as I haven't run across any amateur observations of these globulars.
SC 7 is in the outskirts of Barnard's Galaxy, 22' NE of the center of the galaxy and well outside the visual extent of the galaxy at low power. But that makes identification much easier as the surrounding star field is not a mess! Once the general field was centered using a 6mm Delos (375x in my scope), 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 fairly faint but clearly non-stellar, roughly 6"-8" diameter and perhaps 15-15.5 magnitude. The globular could be held steadily when we backed the magnification down to 282x and possibly had a brighter stellar nucleus.
A 2015 paper by Veljanoski et al titled "The Globular Cluster System of NGC 6822" (https://arxiv.org/pdf/1506.00951.pdf) shows the relatively positions of the 8 known globulars and provides coordinates, projected radii, GC type (compact or extended), half light radius and interstellar reddening. In addition, it derives the following V magnitudes, along with the following positions --
SC 6 19 45 37.0 -14 41 10.8 15.4V
SC 7 19 46 00.7 -14 32 35.0 14.8V
At a distance of 1.6 million l.y., the globulars in Barnard's Galaxy are 4 or 5 times the distance of the outer halo globulars in our own galaxy. I didn't have a chance to go after SC 6, which I hope to track down next month. I'm guessing an 18" might be close to the minimum aperture to track these down, but who knows if you don't try. If anyone else takes a look, post your observations!
2618
One highlight for me and Jimi was a Sagittarius globular that actually resides in Barnard's Galaxy (NGC 6822), a local group dwarf. A bit of background first -- Edwin Hubble was the first to investigate Barnard's Galaxy in detail in 1925 seminal paper "NGC 6822, a remote stellar system" (http://cdsads.u-strasbg.fr/full/1925ApJ....62..409H). He found 10 nebulous objects (http://cdsads.u-strasbg.fr/cgi-bin/nph-iarticle_query?bibcode=1925ApJ....62..409H&db_key=AST&page_ind=4&data_type=GIF&type=SCREEN_VIEW&classic=YES) (labeled with Roman Numerals) within Barnard's Galaxy. Most of these are HII regions (the best two visually are Hubble X and V), but Hubble VII turned out to be a bonafide ancient globular. 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 back in 2010 with my 18", though it was quite challenging to identify within the mottled glow (barely non stellar and lost in a maze of other dim stars within the galaxy). I figured that was probably the last GC I'd see in Barnard's Galaxy.
The following year, four new Barnard Galaxy globulars were announced in 2011 by Hwang et al (http://iopscience.iop.org/article/10.1088/0004-637X/738/1/58/pdf), though these seemed too faint as visual targets for my 18". Then in 2013 three additional GCs were identified (https://arxiv.org/pdf/1211.3896.pdf) in Barnard's Galaxy by Huxor et al, bringing the current known total to 8. It looked like globulars #6 and #7 (called SC6 and SC7) were reasonable targets for my current 24", though when I added these to my observing list I had no idea what to expect as I haven't run across any amateur observations of these globulars.
SC 7 is in the outskirts of Barnard's Galaxy, 22' NE of the center of the galaxy and well outside the visual extent of the galaxy at low power. But that makes identification much easier as the surrounding star field is not a mess! Once the general field was centered using a 6mm Delos (375x in my scope), 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 fairly faint but clearly non-stellar, roughly 6"-8" diameter and perhaps 15-15.5 magnitude. The globular could be held steadily when we backed the magnification down to 282x and possibly had a brighter stellar nucleus.
A 2015 paper by Veljanoski et al titled "The Globular Cluster System of NGC 6822" (https://arxiv.org/pdf/1506.00951.pdf) shows the relatively positions of the 8 known globulars and provides coordinates, projected radii, GC type (compact or extended), half light radius and interstellar reddening. In addition, it derives the following V magnitudes, along with the following positions --
SC 6 19 45 37.0 -14 41 10.8 15.4V
SC 7 19 46 00.7 -14 32 35.0 14.8V
At a distance of 1.6 million l.y., the globulars in Barnard's Galaxy are 4 or 5 times the distance of the outer halo globulars in our own galaxy. I didn't have a chance to go after SC 6, which I hope to track down next month. I'm guessing an 18" might be close to the minimum aperture to track these down, but who knows if you don't try. If anyone else takes a look, post your observations!
2618