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Ou4: The Giant Squid Nebula

Explanation: Squids on Earth aren't this big. This mysterious squid-like cosmic cloud spans nearly three full moons on planet Earth's sky. Discovered in 2011 by French astro-imager Nicolas Outters, the Squid Nebula's bipolar shape is distinguished here by the telltale blue emission from doubly ionized oxygen atoms. Though apparently surrounded by the reddish hydrogen emission region Sh2-129, the true distance and nature of the Squid Nebula have been difficult to determine. Still, one investigation suggests Ou4 really does lie within Sh2-129 some 2,300 light-years away. Consistent with that scenario, the cosmic squid would represent a spectacular outflow of material driven by a triple system of hot, massive stars, cataloged as HR8119, seen near the center of the nebula. If so, this truly giant squid nebula would physically be over 50 light-years across.

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I want to believe! I want to believe that the central star of Ou4, the multiple star HR 8119, of spectral class O9.5IV, or B0V, or B0IV, had an outburst and created Ou4, and that this same multiple star is also responsible for ionizing the emission nebula Sharpless 129, or the Flying Bat Nebula!

Wouldn't that be fun? Wouldn't be a lot more fun than if Ou4 is just a boring foreground planetary nebula, whose white dwarf central star is exactly superimposed on the hot main sequence or slightly evolved O-type of B0-type star ionizing the red Flying Bat Nebula?

Then again... I guess I have to admit that Ou4 could be a planetary nebula, because it looks an awful lot like some of those long-winged bipolar planetaries:


Another thing that makes my hypothesis that HR 8119 is responsible for both Ou4 and the Flying Bat nebula stand on shaky ground is that the outlines of these nebulas are not the same at all. I mean, the Flying Bat Nebula looks like a cross between a potato and a groundhog, whereas Ou4 Looks like the collar around the groundhog's neck!


Shouldn't the red Flying Bat Nebula be at least slightly elongated in the direction of the elongation of Ou4, if they were created by the same star? The only saving grace here is that the red nebula appears to be brightest just where the outer edge of Ou4 "touches" it. (As for that fat blob at top of the red nebula, it appears to be a nebula of its own, ionized by B0V-type star HD 239626.)


Sharpless 129, the Flying Bat Nebula, is located right next to the rather famous IC 1396 nebula. But Sharpless 129 is so much fainter:


It makes sense that IC 1396 should be brighter than Sharpless 129, because the ionizing star of IC 1396, HD 206267, is a lot hotter than the ionizing star of Sharpless 129. And as for the fact that Ou4 isn't visible in the picture by J-P Metsävainio that I just posted, this brilliant Finnish photographer has made another version of the same pair of nebulas where he has coaxed out the elongated shape and cyan color of Ou4:


Now you see it, now you don't, the damned elusive Ou4! Like the Scarlet Pimpernel! And we don't know what Ou4 is, either. Like the bird in Disney's 1947 animated short film, Clown of the Jungle. They say the bird is an Aracuan bird. Really? I don't know what or where it is!





Ann

The same mysterious nebula was depicted ten years ago (https://apod.nasa.gov/apod/ap140718.html).

But then, the "telltale blue emission from doubly ionized oxygen" was not blue but very clearly green!

So, which is the correct colour aand why?

The elongated blue (ionized OIII) nebulae have the same configuration with central star and explosion out fore and aft ends. Why would you doubt, if I am reading your post correctly, that they are the same mechanism? Orientation will probably ensure that some nebulae are pointed at, or away from us, and appear spherical. As to what the mechanism is, refer to the cartoon - its the old exploding cigar trick!

Lasse H wrote: ↑Mon Jun 17, 2024 3:22 pm The same mysterious nebula was depicted ten years ago (https://apod.nasa.gov/apod/ap140718.html).

But then, the "telltale blue emission from doubly ionized oxygen" was not blue but very clearly green!

So, which is the correct colour aand why?

Doubly ionized oxygen emits light at 501nm, which given a brighter source would be described by most people as blue-green or cyan. The color that it appears in images depends upon the processing and how the different channels are mixed. Mapping [OIII] to the blue channel is one common approach.

I am not doubting anything. Nor am I talking about mechanisms, orientation, or anything like that.

I am just pointing out that two different hotos of the same nebula have been presented as APOD 2014 and 2024, but with different colours then and now. Why green then, if the correct colour is blue?

Roy wrote: ↑Mon Jun 17, 2024 3:27 pm The elongated blue (ionized OIII) nebulae have the same configuration with central star and explosion out fore and aft ends. Why would you doubt, if I am reading your post correctly, that they are the same mechanism? Orientation will probably ensure that some nebulae are pointed at, or away from us, and appear spherical. As to what the mechanism is, refer to the cartoon - its the old exploding cigar trick!

The doubt comes from not knowing the distance to the nebula, and therefore not being certain it is associated with that star or is a chance alignment.

Lasse H wrote: ↑Mon Jun 17, 2024 3:22 pm The same mysterious nebula was depicted ten years ago (https://apod.nasa.gov/apod/ap140718.html).

But then, the "telltale blue emission from doubly ionized oxygen" was not blue but very clearly green!

So, which is the correct colour aand why?

The blue color is not true. What we see is OIII. The primary wavelength of OIII is 500.7 nm, which is about this, ███ and the secondary line is 495.9 nm, which is about this, ███. As you can see, OIII is pretty green.

There is however a reasonably bright blue star in the center of Ou4, and its blue light may well be scattered in the OIII nebula, turning it more bluish. The color of a B0V star like HR 8119 is light blue, probably something like this, ███. The color is very unsaturated, but the light from the star is very bright.

Ann

Ann wrote: ↑Mon Jun 17, 2024 3:51 pm

Lasse H wrote: ↑Mon Jun 17, 2024 3:22 pm The same mysterious nebula was depicted ten years ago (https://apod.nasa.gov/apod/ap140718.html).

But then, the "telltale blue emission from doubly ionized oxygen" was not blue but very clearly green!

So, which is the correct colour aand why?

The blue color is not true. What we see is OIII. The primary wavelength of OIII is 500.7 nm, which is about this, ███ and the secondary line is 495.9 nm, which is about this, ███. As you can see, OIII is pretty green.

There is however a reasonably bright blue star in the center of Ou4, and its blue light may well be scattered in the OIII nebula, turning it more bluish. The color of a B0V star like HR 8119 is light blue, probably something like this, ███. The color is very unsaturated, but the light from the star is bright.

Ann

I will tell you that when I look through my narrowband [OIII] filter it is less green than the RGB approximation seen here. I'd call it a green-biased cyan. (For vision research purposes, "pure green" is usually taken to be 550 nm.)

Insane