Object of the Week - July 1st, 2018 NGC6818 The Little Gem

[Dragan]

NGC 6818 – The Little Gem


Sagittarius


NGC6818
Sanduleak 2-392
PK 25-17.1

RA 19 43 57.8
DEC -14 09 10


Type: Planetary Nebula

Mag: 9.3
Size: 48”
Central Star Mag: 16.9

First observed by Sir William Herschel in 1787, NGC6818 is small planetary nebula 6000 light years distant towards the norther border of the constellation Sagittarius. Also known as the “The Little Gem”, NGC6818 is very reminiscent of M57 in Lyra, albeit smaller.


A note I discovered while researching this object is that the central star is one of a binary pair. Its companion is much fainter and lies approximately 150 AU, or 5 times the Sun-Neptune distance, from the main central star. Needless to say, this is a double we are just not going to split!
Finding NGC6818 isn’t as easy to find as say M57 since this area of Sagittarius is void of any bright stars. Deep sky hounds should be familiar with the rather faint NGC 6822 or Barnards Galaxy. NGC6818 lies a little less than a degree, and depending on your instrument, within the same FOV N-NW of NGC6822.


Observations in instruments as small as binoculars have been made but to have any hope of some detail, scopes of at least 8” need to be utilized. Smaller scopes reveal 6818 to be a stellar glow in a field of view barren of notably bright stars. NGC818 is bright enough that larger instruments and higher power start to reveal structure. This object does take magnification well so don’t be afraid to use power if you have the aperture. Smaller scopes will reveal a blue-green fuzzy star like what Uranus looks like whereas scopes north of 10” will start to show a crisply defined slightly elongated north-south and blue-green glow. Higher power will start to show a darkened central region resembling a smoke ring much like M57. You may notice a fainter outer halo surrounding the inner elongated ring. OIII filters can help emphasize the elongation of the inner portions. Most observers tend to include the noticeable blue-green color in their notes so if color is something you enjoy in the eyepiece, I would definitely add NGC6818 to your observing lists this summer.


So there ya go. A rather dazzling stellar explosion observable in a multitude of instruments fitting for this week’s 4^th of July celebration. If you get out this next new moon period, be sure to add this Little Gem to your observing list.


And as always,
“Give it a go and let us know!”

[wvreeven]

Great choice! I have one observation logged with my 20” telescope back in September 2010 when I had just purchased it. It read “a bright glow without further structure”. Looks like I need to revisit this one

[Dragan]

Attachment 3110
©Mitch and Michael Dye/Adam Block/NOAO/AURA/NSF

[Steve Gottlieb]

Here are my last two observations of NGC 6818. I've run into NGC 6818 a few times while sweeping around for Barnard's Galaxy, but never the other way around.

24" (7/19/17): at 375x, 500x, 750x and 1000x: small, very high surface brightness oval, slightly elongated N-S, with a blue color at 375x, takes up to 1000x! The planetary is encased in a thin outer shell. Occasionally the center seemed to sharpen to a point, but I couldn't confirm the central star with confidence. The rim seemed to sparkle with slightly brighter regions. Located 40' N of Barnard's Galaxy (NGC 6822).

18" (7/23/06): this very high surface brightness blue planetary takes high magnification well and 565x provided an excellent view. Appears slightly elongated N-S, ~20"x15". Most striking is an annular structure with a brighter rim and darker center. The rim has an irregular surface brightness and is brighter along the southeast and east side. Although the contrast of rim and darker center is fairly low, the relative thickness of the rim is comparable to M57. Barnard's Galaxy lies just 40' S.

[Bertrand Laville]

Hi All,

I gave this PN twice a look*: first in Namibian skies, in 2008, secondly three years ago, in my usual french place, in southern Alps.

The main issue of my first observation, with a 20" Obsession, was an extraordinary seeing which made, at altitude 70°, the stars as pinpoint at 1000x*! This seeing allowed me to see the central star, m17,06V (Benedetti and alter), of course with adverted vision and weakly contrasted.

My second observation was made with my 25" Obsession, without any remembrance of the previous one. In spite of the larger aperture but at 30° high, I didn't see the central star, but was able to much more detail the nebulosities. I think the Astrodon filter OIII 5nm I used that time was of a great improvement for this very bright PN,

All detailed reports at*:http://www.deepsky-drawings.com/?sen...s=6818&x=0&y=0


NGC 6818 T508 BL 2008Tivoli Namibie retraitée 2015.jpg


NGC 6818 T635 BL 2015 09 09.jpg

Clear skies
Bertrand
http://www.deepsky-drawings.com/dsdlang/en/

[Raul Leon]

Hello, my observation of ngc 6818 from 2007 is as follows: very bright, but small, bluish-greenish tint, enveloped in what seems to be two shells of nebulosity, one brighter than the other. The brighter shell has at least three bright knots. The center appears to be darker, and at times I thought I was seeing the central star,but did not include it the sketch because I was not sure. This object takes magnification well so I used an 6mm Ethos at 264x magnification, with my 14.5 f/4.3 Starstructure Dob. I used a NPB filter and no filter for the sketch. Does anyone know the magnitude of the central star? RaulScan0689.jpg

[wvreeven]

Raul, see the previous comment of Bertrand: "This seeing allowed me to see the central star, m17,06V (Benedetti and alter)"

[Howard B]

I've only seen 6818 as a perfectly round, blue planetary with a slightly darker center and no central star. But the observations above have inspired me to take another look next week at the GSSP!

[Uwe Glahn]

The discussion around the CS is interesting, so Betrand's comments are very useful to estimate the visibility.

I had no chance and no popping with a 14.5" under good seeing and good transparency from 51°N. With 27" under very good transparency and very good seeing from 47°N I noted "sure detection of the CS with averted vision, can not hold CS steadily"

14.5", 404x, NELM 6m5+, Seeing II
NGC6818_14.jpg

27", 1172x, NELM 7m0+, Seeing II
NGC6818_27.jpg