APOD: A Filament in Monoceros (2022 Mar 18)

[APOD Robot]

A Filament in Monoceros

Explanation: Bluish reflection nebulae seem to fill this dusty expanse. The sharp telescopic frame spans over 1 degree on the sky toward the faint but fanciful constellation Monoceros, the Unicorn. Seen within the Monoceros R1 cloud complex some 2,500 light-years away, bluish IC 447 is on the left, joined by a long dark filament of dust to IC 446 at lower right. Embedded in IC 447 are young, massive blue stars much hotter than the Sun, whose light is reflected by the cosmic cloud of star stuff. Observations reveal that IC 446 also contains a young stellar object, a massive star still in an early stage of evolution. The dark filament of dust and molecular gas joining the two star-forming regions is over 15 light-years long.

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[saturno2]

very interesting

[Ann]

APOD Robot wrote:

Seen within the Monoceros R1 cloud complex some 2,500 light-years away, bluish IC 447 is on the left

Sorry to rain on your parade, but the Gaia parallaxes for some of the stars in IC 447 puts this reflection nebula at some 2,000 light-years rather than 2,500.

I can't keep this from you:

IC 447 with the Cone Nebula and the Rosette Nebula.
Photo: Alberto Pisabarro.

IC 447 with the Cone Nebula by Eric Africa.

I love this part of the sky. There's the Rosette Nebula, the Cone Nebula, young blue O-type star 15 Mon, young cluster NGC 2264 (the Christmas Tree Cluster) and rich age-old extra reddened cluster Trumpler 5. And lovely blue reflection nebula IC 447, standing out in its blue glory among all the red emission nebulas.

It's beautiful!

Ann

[AVAO]

What is the reason why IC 447 does not also glow in red like Mon 15?
There are enough young, hot stars ...

[Ann]

What is the reason why IC 447 does not also glow in red like Mon 15?
There are enough young, hot stars ...

No, there aren't. I believe that the hottest star in IC 447 is of spectral class B3. That is not enough to ionize an emission nebula.

By contrast, the Rosette Nebula contains at least three stars of spectral class O, and NGC 2264 contains O7-type star 15 Mon. That is more than enough to ionize a nebula.

Okay, edit. According the the otherwise extremely non-informative Simbad page on IC 447 (IC 2169) this nebula is in fact an HII (ionized) region. That means there is a red Hα component in the nebula. The reason why there is any Hα emission there at all, even though the hottest star is "only" a B3 star, could be that there are several B-type stars in the nebula. The combined amount of ultraviolet light from several B-type stars could be enough to ionize a nebula, even if none of the individual stars are capable of doing it on their own.

However, the red component in IC 447 is weak and completely overwhelmed by the blue reflection nebulosity.

Check out the picture of the Iris Nebula and its central star, B2V-type star HD 200775.

The Iris Nebula. Photo: Göran Nilsson, Hole Observatory.

---

The central star of the Iris Nebula, HD 200775, is of spectral class B2 and is therefore hotter than any star in IC 447. You can see two small and faint pink regions very close to the star in Göran Nilsson's image. These regions glow pink from Hα emission. But as you can see, these pink patches are small and faint, and most pictures of the Iris Nebula do not, in fact, show them.

See the full resolution of Göran Nilsson's image here.

Ann

[XgeoX]

This will be a tasty target for the Webb.

BTW has anybody seen the latest images from the Webb? She is coming along beautifully!

Eric

[orin stepanek]

Oh; the beautiful images we get from APOD!

[johnnydeep]

"The Dark Filament" - sounds like the first book of the next Philip Pullman epic.

[Ann]

What is the reason why IC 447 does not also glow in red like Mon 15?
There are enough young, hot stars ...

15 Mon is a star, not a nebula. I don't know if the red nebulosity around the Cone Nebula and bright star 15 Mon has a name. All right, at least a part of it is called Sharpless 2-273, and other parts are called Lynd's Bright Nebula 911 and Lynd's Bright Nebula 912. Not very memorable.

Ann

[orin stepanek]

Notice that the dark filament also connects to two more objects at
the top right of photo!

[AVAO]

What is the reason why IC 447 does not also glow in red like Mon 15?
There are enough young, hot stars ...

15 Mon is a star, not a nebula. I don't know if the red nebulosity around the Cone Nebula and bright star 15 Mon has a name. All right, at least a part of it is called Sharpless 2-273, and other parts are called Lynd's Bright Nebula 911 and Lynd's Bright Nebula 912. Not very memorable.

Ann

Thanks Ann. Your explanations are - like allways - very helpful!

[AVAO]

IC447_446GiorgioFerrari1024.jpg
Notice that the dark filament also connects to two more objects at
the top right of photo!

I think you are right.
(The picture is a superposition of different wavelengths in the IR (Herschel(white), GLIMPSE(pink)).


Jac Berne (fickr)

[Makiko]

I like IC447 and I've shoot this object several times.
I was surprised that the filaments were connected in this way.

Makiko