Planetary nebula NGC 6058

[iansmith]

NGC 6058 is a small PNe in the constellation of Hercules at a distance of 3.5kpc (11,415.47 lightyears) with a maximum diameter of ~45". I have found one paper that has done a detailed study of this PNe: https://arxiv.org/abs/1304.3248

According to the paper, there are 3 elliptical outflows, more or less in the plane of the sky. These show strong OIII emission (coloured blue in my image) indicating the presence of shocks at these locations. This suggests they are related to collimated outflows from the central star that occurred ~4800 years ago, ~4400 years ago and ~5900 years ago and currently have have polar velocities of ~68kms-1.

The bright central arcs appear to be a ring, but spectroscopic studies show it to be a limb brightened barrel like shell similar to NGC 7354. It does appear to be more difficult to analyse so it’s position angle, relative velocities, etc are less certain than the other outflows. Its inclination to the plane of the sky might be anywhere from 50° to 130°. Its age is estimated to be ~3400 years old making it the youngest of the outflows, but this may be an upper estimate. The bright ring like structure is probably where it is interacting with the earlier outflows particularly their equatorial regions and is protruding through them and this is causing the gasses to slow down which would make it younger than suggested.

These separate outflows suggest that the star underwent 4 different ejection episodes, with the collimation axis precessing between episodes.

There are also two regions of enhance emission and some faint structure within the bright ring. As this is also present in the pro’s image I don’t think it is an artefact of my processing. On a purely speculative note of my own, this reminds me of the filamentary structure that can be seen in HST images of the Eskimo Nebula. In that PNe the filaments are thought to be the edges of bubbles of gas created by shocks as the outflow breaks out from the polar direction. https://www.astro.umd.edu/~jph/eskimo.html shows this for the Eskimo Nebula. Perhaps something similar is going on here?

The image is composed of narrow band data for the PNe and broadband data for the stars:

• NB: 60x300s in Hα, OIII, NII blended as: 0.5* Hα + 0.5*NII, 0.4* Hα + 0.6*OIII and 0.15* Hα + 0.85*OIII for red, green and blue respectively.
• BB: 15x120s in red, green and blue.

The stars were removed from the NB image and the PNe was removed from the RGB image. These two images were processed separately before being combined to create the final picture. 

I hope you like the picture.

Cheers, Ian

[tooth_dr]

Fascinating. Thanks for accompanying writeup which was very interesting. 

Edited August 18, 2019 by tooth_dr

[MarsG76]

Excellent work of a distant object....

[iansmith]

Thank you tooth_dr and MarsG76.

Cheers, Ian