Object of the Week June 28, 2015 - NGC 6712 The Weird Globular

Object of the Week June 28, 2015 - NGC 6712 The Weird Globular

NGC 6712
Type: Globular Cluster
Constellation: Scutum
RA: 18h 53m 4.9s
Dec: -08° 42’ 20”
Size: 9.8’
Mag: 8.1

IC 1295 PK025-4.2
Type: Planetary Nebula
Constellation: Scutum
RA: 18h 54m 37s
Dec: -08° 49’ 39”
Size: 1.7’
Mag: 12.7
Mag of Central Star: 15.0

NGC 6712 was discovered by William Herschel on June 16th, 1784. Designated as H I-47 Herschel described it as “Bright, very large, irregularly faint, easily resolvable stars visible.” The later NGC description is similar, “Globular cluster, pretty bright, very large, irregular, very gradually, then a little brighter in the middle, well resolved, clearly consisting of stars, 15 stars.”

Attachment 1693

NGC 6712 is a relatively small (64 light-years across) and sparse (~1 million stars) globular cluster, which lies 22,500 light years away from us. The easiest way to find this globular is to first locate M26, a well-known compact rich open cluster; from there 6712 is a short 2-degree hop to the northeast.

A study by the European Southern Observatory concludes that NGC 6712 is only a pale remnant of a once much more massive cluster. It notes that none of NGC 6712’s stars are less massive than our Sun, making it totally unlike any globular cluster. Most likely, NGC 6712 is unique only because no other globular cluster comes as close to the Milky Way’s center as does NGC 6712; it penetrates very deeply into the galactic bulge, venturing to within 1,000 light-years of the galactic center. The tidal force of the galaxy not only strips low-mass stars from the cluster but also stretches out the cluster like a comet’s tail.

The ESO study labels NGC 6712 a peculiar globular cluster – and rightfully so based on the study’s findings. The recently published Interstellarum Deep Sky Atlas labels 6712 as The Weird Globular. A Google search failed to turn up any background on the derivation of this name. Perhaps a reader of this OOTW will be able to provide more info.

Attachment 1694
Copyright by Jim Thommes

Under a good dark sky, the globular should be readily detectable as a faint glow in 10x50 binoculars. Moving to a 6-inch scope some stellar resolution is possible, with the brightest stars in the globular cluster being at magnitude 13.3. NGC 6712 becomes resolvable with a 15-inch scope at 172x. Though it is brighter towards the core, the core itself is granular in appearance and surprisingly seems to be less dense then some of the outer regions. It gives the appearance that the core is somewhat off center. The globular is not symmetrical, with one side appearing flattened to an obtuse inverted-vee.

While observing NGC 6712 you can’t avoid coming across IC 1295, a planetary nebula that is only 25’ to the southeast of 6712. Though not the subject of this OOTW this planetary nebula is well worthy of a visit. It responds strongly to both OIII and UHC filters. With either of these filters it appears as bright, if not brighter, than its neighboring globular cluster. Together in a rich field these two objects provide a pleasing, yet interesting contrast.

Attachment 1695
Copyright C.Q.Kimball

Attachment 1696
Copyright ManualJ

"Give it a go and let us know!
Good luck and great viewing!"

My notes from 9/20/14 (NELM 5.7; seeing 7 [Pick.]; transparency 6; 12.5" Discovery Dob, 14mm ES 82* eyepiece [112x]):

large and diffuse, v. granular, number of halo stars—almost has two cores
or figure 8 w/averted—cluster quite bright (8th mag)—core elongated P-F—7’
diam?—to NF side is bright field star (8-9th mag) about 7’ from edge of halo—
brightest star in vicinity 15’ to due N—CC 9-10?—two brighter cluster members on
F side, one on N edge of halo, other more embedded in cluster, pop more w/
averted—surrounded by cloud of field stars to SF and P sides near edge of cluster

My notes with my 6" newt from Southern France:

NGC 6712 appears to have a blue hue, which is funny because it is a faint fuzz. It is surrounded by a very rich star field. That makes it a very pretty sight. The core appears elongated northeast-southwest. It is surrounded by an equally lit sphere that slowly disappears in the sky background.

IC 1295 is visible at 26x and with OIII as a large circular haze. Tere is a faint star on the west side and another a bit further away to the north. Northwest of that star I see another one that could be PK 25-4.1 (but I didn't check that). Nice to see such a large planetairy nebula at such a low magnification. It is about 2/3 of the size of NGC 6712.


Clear skies, Wouter

Mark wrote;

"While observing NGC 6712 you can’t avoid coming across IC 1295, a planetary nebula that is only 25’ to the southeast of 6712. Though not the subject of this OOTW this planetary nebula is well worthy of a visit. It responds strongly to both OIII and UHC filters. With either of these filters it appears as bright, if not brighter, than its neighboring globular cluster. Together in a rich field these two objects provide a pleasing, yet interesting contrast."

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A nice pair of objects, Mark, and yet, by golly, there is a second planetary nebula in the same field of view, this being Kohoutek 4-8, and it is not too difficult if you can manage to blink it with an OIII filter (I never tired the UHC here, so it may work as well). K 4-8 lies almost on a line between NGC 6712 and IC 1295, about 1/5 of the way along from the IC to the NGC...

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... there is a little arc of 4 or 5 mag 14 stars about 4 arcminutes NW of IC 1295 that opens towards the south, and K 4-8 is the middle star of this arc. It responds strongly to the OIII filter. I originally learned of this guy from an Amastro post by Brian Skiff, and Brian states that he has seen it with his Pronto, so no one should pass up the opportunity to go after this little fellow using just about any telescope, but a filter is really needed, IMHO.

All 3 of these objects can been seen at the same time using a low-power eyepiece and this is one of my favorite multiple-object choices, lot of stars here, near the heart of the Scutum star cloud.

Unfortunately I did not find my old notes from K 3-4 and NGC 6712. But I remember that K 3-4 was an easy target for the 16".

I revisited IC 1295 with the 27" and could pick up the double shell nature.

27", 293x, [OIII],
Seeing III, NELM 7m+
Attachment 1707

Here's my sketch from 2001 with my old 20 inch:

Attachment 1711 Attachment 1712

My notes from this observation:

"A very nice pair! Both are obvious at low power (92x) but IC 1295 responds weakly to the UHC filter and barely at all to the OIII. 6712 is fairly large but only moderately bright. The core is not concentrated but there is a dark lane on one side. Best at 170x."

This seems to be my most recent observation of this pair, which inspires me to take another look asap - hopefully next week.

Like Howard, I've also noted an apparent dark lane in NGC 6712 on the southeast side, creating a detached piece. Here are some samples.

18" (7/23/06): situated in a gorgeous low power Milky Way star field at 115x with a dense background mat of faint stars filling the 45' field and planetary IC 1295 24' ESE. At 435x roughly three dozen stars are resolved in a 6' region, mostly on the western half of the cluster. The core is moderately bright but not sharply concentrated. The irregular halo is peppered with faint stars though at the periphery it was impossible to really distinguish from these from the numerous faint field stars that surround the cluster. A dark lane is quite obvious on the south side, appearing to detach the outer section of the halo on the southeast side. The outer halo is poorly resolved on the eastern end.

18" (8/23/03): at 435x, approximately three dozen stars can be counted, although the eastern edge of the halo resists resolution. A dark lane cuts through the cluster on the south side running SW-NE and detaching a small piece of the halo on the SE side and flattening the central blaze which begins just north of the lane. IC 1295 lies 24' ESE and both are nicely framed within the field of the 20mm Nagler.

17.5" (6/29/00): at 220x this is a bright, moderately large cluster, ~6' diameter in a very rich Milky Way field. Contains a relatively large, intense 3' core with a number of very faint stars peppered over the background glow. A small, partially resolved piece is detached at the southeast end by a dark lane. The surrounding halo includes a number of brighter stars, though it is difficult to untangle the maze of stars in the halo from the rich Milky Way background. Roughly 30 stars are resolved at 280x, although it is difficult to accurately count. The core has irregular appearance with a flattened side caused by a sharp light cut off on the south side. PN IC 1295 lies 24' ESE.

I caught this globular by starhopping around M11. It is an easy object with the 8in and 24mm eyepiece at 50X. Really cool this object has some history. I didn't see the planetary nebula, but didn't know to look for it. This globular is listed in the PSA.