Object of the Week August 12th, 2018 - The hidden treasure NGC 6857 (Sh 2-100)

[Uwe Glahn]

NGC 6857 [PK 70+1.2] in Sh 2-100

Emission Nebula

Constellation: Cygnus

(position of the "pseudo CS" of the brightest part of Sh 2-100)
RA: 20h01m48s
DEC: +33°31'38"

Size brightest part: ~0.8'
Size whole Sh complex: ~4'

The story of the hidden treasure in the centre of Cygnus began in 1784 when William Herschel discovers a "faint [glow], among Milky Way stars".
This bright part ~0.8' across misclassified as the planetary PK 70+1.2, also because of its round, ring shape with its pseudo CS of around 12.8gmag (12.5pmag).
For real this part is not a planetary but a part of the larger (~4') and much fainter emission nebula Sharpless 2-100 which centre is shifted a few minutes to the southwest.

The picture from Martin Germano shows this nebula situation plus some surrounding nebula.
First the bright part NGC 6857 in the centre of the picture. Sh 2-100 shows as the faint glow around the NGC. Sh 2-99 is found 11' to the west. The third nebula, GN 19.59.6 can be found 5' northwest of NGC 6857.

In the telescope the nebula has a bright appearance and it is surprising why the nebula is relative unknown. It shows a triangle shape with darker centre and hard defined straight edges. Some observers noted a very good response with [OIII] filter. I cannot confirm this. For me the increase of contrast was only marginal with filter and the finest view was always without filter, also because of the rich and nice star field around. What did you see?

picture from Martin Germano (14.5", red filter)
N6857lredsg_1024.jpg

sketch: 27", 419x, no filter, NELM 6m5+, seeing III
NGC6857.jpg

"Give it a go and let us know!"

[Bertrand Laville]

Hi All,

Hereunder is my drawing of NGC 6857, and you could observe that it is very similar to Uwe's one.
Detailed report here, in the language you want, due to a recent improvement of my website, under the pressure of Peter Kiss
http://www.deepsky-drawings.com/ngc-6857/dsdlang/en

Bertrand
http://www.deepsky-drawings.com/


NGC 6857 T635 BL 2013 08 06.jpg

[Ivan Maly]

Big favorite. I have this from 2012:

16" F/4.5, 13 mm (thought to approximate the discovery view). No filter. SQM 21.6, variable to low transparency.

"NGC 6857. Small (~1’) compact nebula. 3 stars in a row NE-SW, SW one brighter, the other two equal. The middle star is surrounded by nebulosity. Resembles the Blinking Planetary NGC 6826 by its apparent annularity around the star and by its eccentricity: S side wider and brighter."

[Raul Leon]

Hi Everyone, here is my sketch and observations from 10/24/2008 : ngc 6857 emission nebula in Cygnus; fan-shaped nebulosity with bright notch or star in center; UHC filter helps with contrast but filter-less view preferred. ngc+6857.jpg10mm Radian at 158x with my 14.5 Starstructure Dob

[Norman]

Interesting object Uwe - thx for the presentation.

Last night this object was the very single one before the fog came around and onto my secondary...
Undefined nebulosity already visible in my 26mm eyepiece at 50x - without filter.
Interestingly, the nebula admits high power/ small exit pupil. So my best view was at 270x in my 12". I saw a triangular shape - even with a curvature/bay very similar you draw - but at the opposite site. Strange. Very difficult to catch the real structure at any magnification. No darker interior visible for me although at one time something alike appeared in a fleeting moment - very uncertain yet.
Without OIII-filter best view. With filter (Astronomik) the "central star" disappears / seems to flash now and then. Contrast much better with filter but no real benefit for me since view is not nice anymore.

Conditions: humidity around 90%, milky way visible but far away from brilliant. Seeing 2-3.
I cannot exclude by 100% that my secondary was already affected by fog during the observation but i think it was free.
All in all for me no treasure at all - sorry mate
I´ll give it another try in the mountains yet.

CS
Norman

[wvreeven]

I observed this nebula with my 6" Newtonian telescope back in 2005: This is a tiny nebula. Using the 20 mm eye piece (51x) it only stands out a little bit. Using the 9.7 mm (105x) I see it a little better. Using the 6 mm (170x) it all but disappears. On the west side of the nebula lies a star. I have the feeling that another star lies in the nebula. The nebula is elongated, perhaps a little V-shaped towards the south-east.

I also observed it with my 20" in 2012 but I didn't note down the magnification used: Two small blobs separated by a dark lane.

And again with my 20" in 2015: It took a little while to find this one. At 83x I see a small smudge of light. It responds well to OIII and a little less to H-Beta. At 320x I see a nice round nebula around a star. The stars around it nearly disappear with OIII.

Interesting that I didn't notice the dark lane nor the V-shape during that last observation.