Sh2-174 / PK 120+18.1. I wasn't planning to photograph this one and I wasn't overly enthusiastic about it, but I had to have something to do while waiting for other, long-planned targets.
I was wrong not to look forward to Sh 2-174.
It is stunningly beautiful when given enough time and effort to show itself!Ha:
OIII:
Object descriptionThis beauty is not a typical planetary nebula, despite its presence in the PK catalog. It is an object with a complex origin and structure, resulting from the interaction of the very fast-moving star GD561, the surrounding, although very distorted, sphere of oxygen (the PN) and the interstellar medium (ISM).
GD561, the central star of the planetary nebula and its progenitor (CSPN) is probably a binary star system. There is a white dwarf in this binary, with a mass of approximately 0.3 solar masses and a surface temperature of 65,000 K.
GD561 is located and moves approximately as noted below. It moves at considerable speed and leaves its former planetary nebula behind.
When GD561 became a white dwarf, it shed its outer layers, creating a spherical planetary nebula that moved at high speed along with the star. However, it careened into a region of interstellar hydrogen gas and the resistance of this medium flattened it and slowed it down. Currently, the OIII nebula appears to be moving through and out of the hydrogen cloud, but it is now in the shape of a flattened sphere. You can also see the compressed and glowing bow-shock structure in OIII.
CSPN stellar wind ionized the hydrogen and the collision with the planetary nebula disturbed its structure and created intriguing areas of turbulent gas flow, which are one of the main attractions of the image, in my opinion.
Very dynamic H and O streams are quite clearly visible, ionized and accelerated by the CSPN stellar wind and the collision itself. They are more or less consistent with the direction of movement of GD561.
The hydrogen part of Sh2-174 is therefore not an element of the planetary nebula. Rather, it is a Strömgren sphere, i.e., interstellar H that has been ionized, heated, and shaped into a sphere by the star- GD561 in this case. The most famous example of a Strömgren sphere is NGC 2237 - the Rosette Nebula, which consist of, as in this case, an emission nebula inside a H II region.
In conclusion, those processes explain the appearance of this object. A sphere of oxygen with a central star collided with a cloud of interstellar Hydrogen. GD561 has pierced the hydrogen cloud and its own planetary nebula like a bullet and is moving on while the PN is still pushing through the hydrogen.
Further readinghttps://articles.adsabs.harvard.edu/pdf/1994AJ....108..978Thttps://en.wikipedia.org/wiki/Str%C3%B6mgren_spherehttps://arxiv.org/pdf/1102.1309.pdfhttps://arxiv.org/pdf/2212.13349.pdfLa vie en rose (Remastered) (youtube.com)
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