Messier 46 and NGC 2438

The nebula NGC 2438 as visible here is really just the innermost of 3 concentric "halos" (Corradi et al. 2000).

Whether or not the cluster and nebula are physically associated seems to have been a matter of some debate.

For M46, Wikipedia provides a distance of "4,920 ± 980 ly (1,510 ± 302 pc)".

For NGC 2438, published distance estimates have ranged from 1,100 to 4,300 pc (approx. 3,600 - 14,000 ly).

Pauls and Kohoutek (1996) state that "contrary to earlier statements the nebula is probably associated with the cluster".

Based on its estimated motion, Kiss et al. (2008) indicate that it is not (or at least no longer) a "bound" member of the cluster.

Öttl et al. (2014) provide a distance of 1.9 ± 0.2 kpc (~6,200 ly) and therefore the nebula is "behind the nearby open cluster M46".

Wikipedia states a distance of:

1,370 ± 130 ly
(420 ± 40 pc)[1] ly

which may be a typographical error.

Corradi, R. L. M., D. Schonberner, M. Steffen, and M. Perinotto. 2000. A hydrodynamical study of multiple-shell planetaries I. NGC 2438. Astronomy and Astrophysics 354: 1071–1085. https://adsabs.harva...A&A...354.1071C retrieved 2022 February 19.

Kiss, L. L., Gy. M. Szabo, Z. Balog, Q. A. Parker, D. J. Frew. 2008. AAOmega radial velocities rule out current membership of the planetary nebula NGC 2438 in the open cluster M46. Monthly Notices of the Royal Astronomical Society 391: 399-404. https://academic.oup...1/1/399/1125572 retrieved 2022 February 19.

Öttl, S., S. Kimeswenger, and A. A. Zijlstra. 2014. Ionization structure of multiple-shell planetary nebulae: I. NGC 2438. Astronomy and Astrophysics 565: A87. https://www.aanda.or...aa23205-13.html retrieved 2022 February 20.

Pauls, R. and L. Kohoutek. 1996. Study of the planetary nebula NGC 2438 I. Spectroscopy of the nebula and of some cluster stars. Astronomical Notes 317: 413-416. https://onlinelibrar...asna.2113170606 retrieved 2022 February 20.

Acquisition:

Bortle 7 skies
Nikon D7000 camera
Orion Apex 102mm telescope, 1300mm focal length
Orion AstroView EQ3 with single-axis drive
30s x 49 frames
f/12.7
ISO 800

Processing:

Siril:

Background extraction
Photometric color calibration
Asinh transformation
Manual histogram adjustment
Deconvolution

RawTherapee:

Luminance curve adjustment
Chroma and luminance denoising
Color curve adjustment
Black point and brightness adjustments

GIMP:

Luminance curve adjustment (again)
Slight saturation increase