Object of the Week June 8, 2014 - NGC 6723 & Its Surrounding Area

[Paul Alsing]

Object of the Week June 8, 2014 - NGC 6723 & Its Surrounding Area

NGC 6723
Globular Cluster
R.A.: 18h59m33.0s Dec.: -36°37'54"
Size: 13.0'
Mag: 6.80

NGC 6726/27 - Reflection Nebulae
NGC 6729 - Bright Nebula
IC 4812 - Reflection Nebula
BSO 14 - Double Star
DN Bernes 157 - Dark Nebula
... and there are other objects here, too, including HH 100 and a couple of dim galaxies... :>)

This week's OOTW is not actually a single object, but rather a collection of objects located in (2) adjacent constellations. The 'anchor' object is a nice globular cluster, NGC 6723, located at the southern edge of Sagittarius, and everything else is about 30 arc-minutes to the southeast in Corona Australis. It is a little early in the year for this area, but in the wee hours of the morning it is available… but culmination is in August, so it not so long to wait.

NGC is a fabulous globular cluster and would be more popular to observers in the northern hemisphere were it to be higher in our sky. It is has an impressive uniform halo and bright core, but from my regular observing site in southern California it never gets any higher in the sky than about 25 degrees, so conditions need to be very good to get a good look. Imagine what M 13 looks like when it is at a similar altitude and you will get a pretty good idea of what NGC 6723 looks like from my place.

NGC 6723 provides a great jumping-off point for locating the other goodies in the area, and you can see many of them, along with the globular, if you have an eyepiece that provides more that a ½ degree field. My best view of this area was achieved using my trusty 13mm Ethos, and the object that initially attracted my attention was the double star BSO 14, appearing as a closely matched blazing pair of 6.5 magnitude headlights, with an easy separation of about 12”, surrounded by the reflection nebula IC 4812, and after that you can wander around to identify the other wonders in the area. One exceptional night allowed me to see the huge cashew-shaped dark nebula, Bernes 157, best seen with whatever combination of telescope and eyepiece that will give you a large field of view. I have identified all of the NGC and IC objects in the area despite the fact that it is low in the sky for me.

The internet is full of wonderful pictures and articles written about this little chunk of sky, and I have listed some of them here. The first in the list is specially informative. I urge you to visit these links and marvel at the photos of this area, but there is nothing like perusing it for yourselves, if it gets high enough in your sky on a night of good seeing and transparency.

http://www.surastronomico.com/sec-58-shedding-light-on-bernes-157.html

http://my.hwy.com.au/sjquirk/ngc6726.html

http://astronomia-para-amadores.blogspot.com/2012/04/coroa-austral-corona-australis.html

If only there was a planetary nebula in the area it would be perfect!

"GIVE IT A GO AND LET US KNOW"

[Ivan Maly]

This is a great field, and I envy you your observation of Bernes 157 (first described by Dunlop). The latitude and humidity here made me observe this field from Australia. Observing with my travel Mak (~140 mm working aperture) and an Orion 9x50 RACI finder (a surprisingly fine wide-field scope in its own right) from a bush location two hours to the NE of Alice Springs in March 2012, I made the following notes.


From Dunlop 100 observations

COLD. Failed to detect [the dark nebula] Bernes 157 in Corona Australis. [Tried with the Canon IS 18x50 as well.]

NGC 6723. GC. [Although technically in Sagittarius, it lies] in the “head” of [the] Corona Australis [asterism]. See the observation with the CrA Caldwells. [It is O'Meara's Hidden Treasure #96.]


From Caldwell list observations

C68 is the R Coronae Australis Nebula, NGC 6729. It is a variable cometary reflection nebula. It seemed that the variability played its trick on this traveler. There was no cometary extension to speak of. The star was definitely nebulous - in fact, I saw no star but only a very compact nebula. Perhaps it did extend a little toward T CrA, but I could not be sure this was not an illusion. T CrA itself was nebulous in the same manner, but much less so. O’Meara credits Marth with the discovery of the R Coronae Australis Nebula. Steinicke (whose Observing and Cataloguing Nebulae and Star Clusters I continued reading on the plane) assigns priority to Julius Schmidt.

The nearby NGC 6726-7 (also discovered by Schmidt from Athens) was a comparatively large nebulous patch. The nicely matched close pair of white stars, which was supposed to be in the center of IC 4812, anchored the field. Only a little farther away burned a nice Dunlop globular, NGC 6723. Although it is unlikely that the variable C68 should change visibly before my departure, I am planning to reobserve it. [Regretfully, I didn’t.]

[Smith]

I had the chance to observe NGC 6723 two years ago, from french Pyrenees mountain (1600 m alt. ; +42° lat.). I was very impressed by the globular seen with my 12". It made me think about M92 cluster, whose mag and size are almost identical. It was my best surprise of the session. :)

Sky conditions were not optimal (poor transparency), and i did not see nearby objects.

French report for the session can be read here : http://www.webastro.net/forum/showthread.php?t=98020

[RolandosCY]

A superb object, or rather collection of objects. I have observed them in the past from southfacing seaside locations with both my 4" Takahashi and my old 12' reflector, after having read about them in the O'Meara Caldwell book. It is an impressive area that I haven't visited for more than four years now. I hope to be able to have a quick look at them with my 18" since their declination allows only a rather small visibility window from my backyard observatory....

[Uwe Glahn]

Unfortunately to low for mid European observers but from Namibia indeed a fascinating area.

NGC 6723
8x30, NELM 7m+, Namibia
sits on the S end of the CrA, small, not much concentrated

Be 157
8x30, NELM 7m+, Namibia
SE of NGC 6723, easy to see with small bino, big

NGC 6726/6727
24", 141x, NELM 7m+, Namibia
conspicuous RN around 7,3mag HD176386 and 9,5mag TY CrA; glow around both stars; separated trough a dark zone from the E; faint and narrow filament from NGC 6727 to the W

NGC 6729
24", 300x, NELM 7m+, Namibia
rhombic nebula between T CrA und R CrA; R CrA seems to be not stellar but a little bit laminar

[Howard B]

Here's my observation from 2002 with my old 20 inch f5 Obsession:

"A most excellent field of view, and only about 8 degrees above the southern horizon too. 6723 has a curved row of stars across its center but they're only a little brighter than the rest of the glob. 6726/27 are bright and obvious reflection nebula centered on two bright stars - they both have surprisingly distinct edges. NGC 6729 is a comet-like streak but much fainter than 6726/27. BE157 is seen only by a lack of stars between 6723 and 6726/27. Very cool area, I'd love to see it at the zenith! 83x, 169x and 261x."

1270 1271

The was an exceptionally dark, transparent and steady OSP sky to see all this so well so close to the horizon. It's about time I go back for another look, but I'll need another really night to compare to this view. My sketch is pretty rough but conveys a little of what a wonderful slice of the southern sky this is.