Hen 2-169 and PCG 11 – Planetary Nebula and Wolf-Rayet Ring in Norma
At the eastern edge of the constellation Norma, two small but remarkably different nebulae can be found in close proximity on the sky: the bipolar planetary nebula Hen 2-169 and the ring nebula PCG 11.
Hen 2-169 belongs to the class of bipolar planetary nebulae. These show a pronounced bilobed structure, which is generally attributed to a companion star or strong magnetic fields in the progenitor star. The expelled gas is shaped along the polar axis into characteristic, oppositely directed lobes, giving the object its typical butterfly-like appearance. In the image, Hen 2-169 displays a compact central region alongside faint crab-like extensions that hint at its bipolar nature. The distance is approximately 8,700 light-years (±1,700 light-years), with a total extent of around 2.5 light-years. The brighter central part is already visible in the pure RGB image, while the extensions only emerge in the Hα-filtered exposure.
PCG 11 is an emission ring surrounding a central Wolf-Rayet star. Wolf-Rayet stars are massive stars in a late stage of evolution, characterised by exceptionally powerful stellar winds of several thousand kilometres per second. This intense stellar wind sweeps up the surrounding interstellar medium and previously ejected stellar material into an expanding bubble. In the case of PCG 11, this results in an oval shape of approximately 105 × 80 arcseconds, corresponding to a physical extent of about 8 × 6 light-years. The thickness of the ring wall is approximately 0.8 light-years. At a distance of around 16,000 light-years (±1,400 light-years, derived from Gaia measurements of the central star), PCG 11 lies nearly twice as far away as Hen 2-169. The most striking feature is the prominent scalloping along the inner rim of the ring, which reminds me of the open jaws of a shark with protruding teeth. This structure is attributed to Rayleigh-Taylor instabilities, which arise when a denser gas layer meets a less dense one, forming characteristic finger-like intrusions (Cohen et al., Mon. Not. Roy. Astron. Soc. 360, 1439-1447, 2005).
Both nebulae emit predominantly in the Hα and [NII] lines, which are captured together by the Hα filter used. As no significant [OIII] emission from either nebula has been reported in the literature, I did not include additional [OIII] exposures for this image. The field is further crossed by diffuse Hα emission belonging to the outer reaches of the emission nebula NGC 6188.
The animation on the left shows the blend between the pure RGB image and the Hα-enhanced version, which brings PCG 11 and the extensions of Hen 2-169 into full visibility for the first time.
| Date: | 14.07.-23.07.2025 |
| Optics: | Planewave CDK 14 with Televue 0.8x reducer |
| Aperture: | 350 mm |
| Focal Length: | 2050 mm |
| Camera: | QHY268M |
| Exposure: | R:G:B 18:18:18 x 600 s Hα 116 x 600s |
| Location: | Gemsbock Observatory, Rooisand Desert Ranch, Namibia |
| Processing: | PixInsight, Photoshop |
| Diameter: | Hen 2-169: 2.5 light years PCG 11: 8 light years |
| Distance: | Hen 2-169: 8,700 light years PCG 11: 16,000 light years |
