Object of the Week, August 8, 2023 – OC NGC 6846 + PN K 4-41

[Uwe Glahn]

OC NGC 6846
R.A.: 19h56m28s
Dec.: +32°20'56"
Size: 0.8'; Magnitude: 14.2v; Type: (IV1p) II2m

PN K 4-41 (PNG 068.7+01.9, PK 068+01.1)
R.A.: 19h56m34s
Dec.: +32°22'13"
Size: 3"x2"; Magnitude: 15.9v

In the southern part of Cygnus we find a close pair of an Open Cluster and a Planetary Nebula. Both objects are not stunning for their own but their rare near positions (1.8') are the remarkable quality of both.

The small OC was discovered by Edouard Stephan in 1873 with his modern silvered 31-inch glass mirror. Modern scientific paper [JKAS 2011, 44 (1), pgs. 1-11] gives a distance of 1445pc and an age of 0,55 Gyr. This OC suffers from a incorrect position (in the RNGC) that Steve Gottlieb found out. This seems also be the reason of the wrong Trumpler classification. The Archinal/Hynes estimated a more precise II2m. Deep images shows an interesting small and faint clump of around 50 stars.

Only 1.8' NE we find a tiny PN as a faint and stellar object. Even PanSTARRS shows a very small, somewhat elongated object with a very faint central star. It has been suggested that this object is not a true PN, but rather a symbiotic system, or possibly even a supernova remnant [2002MNRAS.336...66R]. The HST pictures a true PN [2016ApJ...830...33S] and shows/suggested, that the large opening angle of the ring segment could be a bow-shock, which would indicate a low velocity interaction through a low density ISM.

With the 16-inch and 360x, the OC shows four stars within a small and unresolved, mottled spot. The PN was barely seen without a filter as a very small, stellar spot. It shows good [OIII] reaction.

picture: Rick J, 14" (cloudynights)
post-40734-0-93405800-1453928726.jpg

sketch: 16", 360x, NELM 6m0+, no filter, Seeing III
K4-41_NGC6846.jpg


As always, give it a go and let us know.

[wvreeven]

I haven't tried the planetary nebula, but my notes for NGC 6846 with my 20" read: At 83x a small fuzzy ball. At 256x a larger fuzzy ball. At 427x resolved in stars. About 2' across.

[Steve Gottlieb]

I've only observed NGC 6846 once, back in 1991 with my 17.5-inch f/4.5.

Appears using 225x as a small, faint clump of stars over unresolved haze. Elongated about 3:2 E-W with dimensions 1.5'x1.0'. A mag 13.5 star is off the NW edge, a mag 14 star is at the west edge and three additional mag 14 stars in a clump are just visible over of the haze, although clean resolution is difficult.

I wasn't able to see K 4-41 without a filter. Using an OIII filter, K 4-41 was seen faintly about 15" S of a mag 14 star. Appeared stellar and about 16th magnitude.