APOD: Inside the Flame Nebula (2021 Apr 17)

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APOD: Inside the Flame Nebula (2021 Apr 17)

Post by APOD Robot » Sat Apr 17, 2021 4:06 am

Image Inside the Flame Nebula

Explanation: The Flame Nebula is a stand out in optical images of the dusty, crowded star forming regions toward Orion's belt and the easternmost belt star Alnitak, a mere 1,400 light-years away. Alnitak is the bright star at the right edge of this infrared image from the Spitzer Space Telescope. About 15 light-years across, the infrared view takes you inside the nebula's glowing gas and obscuring dust clouds though. It reveals many stars of the recently formed, embedded cluster NGC 2024 concentrated near the center. The stars of NGC 2024 range in age from 200,000 years to 1.5 million years young. In fact, data indicate that the youngest stars are concentrated near the middle of the Flame Nebula cluster. That's the opposite of the simplest models of star formation for a stellar nursery that predict star formation begins in the denser center of a molecular cloud core. The result requires a more complex model for star formation inside the Flame Nebula.

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Chris Peterson
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Re: APOD: Inside the Flame Nebula (2021 Apr 17)

Post by Chris Peterson » Sat Apr 17, 2021 4:36 am

This certainly demonstrates why telescopes operating in the IR are so useful. So much more information here than we can get in visible bands alone.
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Re: APOD: Inside the Flame Nebula (2021 Apr 17)

Post by Ann » Sat Apr 17, 2021 6:35 am

Chris Peterson wrote:
Sat Apr 17, 2021 4:36 am
This certainly demonstrates why telescopes operating in the IR are so useful. So much more information here than we can get in visible bands alone.
Indeed. IR can provide us with "a deeper look" that optical images can ever achieve.

Speaking of the devil, though. I recently posted a smaller version of today's APOD in a discussion thread, and I'm sure you can guess which one: http://asterisk.apod.com/viewtopic.php?p=312401#p312401


I have been looking at a lot of optical Flame Nebula and Horsehead Nebula region images, and I can this: The color of the Flame Nebula varies in these images. In a few of them, the Flame nebula is almost lemon yellow, while in others, it is as red as the background of the Horsehead Nebula. In most of them, however, the Flame Nebula is yellower than the background of the Horsehead Nebula.

I think there are interesting similarities between the Flame Nebula and the starforming region inside the well-known "Cone Nebula and Christmas Tree Cluster", or NGC 2264 . The similarity is that there is an embedded region of star formation in NGC 2264 too, which can only be seen in infrared light. This region of star formation in NGC 2264 has been named after the distinctive shape of the newborn cluster inside, the Snowflake Cluster (after the stars radiating out from the center like a snowflake).

176216main_image_feature_822_ys_full[1].jpg
Infrared image of NGC 2264 with young
infrared "Snowflake Cluster" at center. Photo: Spitzer.
NGC 2264 Bach Zoltan.png
Optical image of NGC 2264. The position of the Snowflake Cluster
is visible as a yellowish smudge at left. Photo: Bach Zoltan.


Let's begin by looking at the Flame Nebula and the Snowflake Cluster in infrared light.




As you can see, the Flame Nebula looks a lot more "energetic" than the region immediately surrounding the Snowflake Cluster. There seems to be a mighty outflow from the center of the Flame Nebula, which gives the Flame Nebula a bit of a butterfly (or bug) shape. Please note that the outflow in the Flame Nebula seems to be originating from the center of the nebula where the youngest star formation has been taking place. In other words, it looks to me as if most of the infrared energy of the nebula comes from within (the embedded cluster), not from without (hot star Alnitak).

When it comes to the Snowflake Cluster region, there are fewer signs of the background nebulosity being strongly disturbed by the presence of the cluster. Yes, there is a lot of infrared energy in NGC 2264, but not so much around the Snowflake Cluster itself. Yes, we can see what looks like two ridges below the Snowflake Cluster that may have been violently "forced apart" by stellar winds and jets from the cluster. But there are no signs of the mighty outflow of energy that we can see in the Flame Nebula.

Now let's look at the optical images of the Flame Nebula and NGC 2264. The Flame Nebula is yellow, or at least more yellow than the red background of the Horsehead Nebula. If you look at the optical image of NGC 2264 by Bach Zoltan, you can spot some yellowish flecks whose location correspond to the Snowflake cluster (and a few other infrared-bright spots).

So, in short: The embedded star formation in NGC 2264 creates yellowish flecks in an optical image. That's because the mostly blue-white light from newly formed young stars gets reddened to a deep yellow hue by the time it penetrates its dusty cocoon.

I think the same thing is happening in the Flame Nebula. The very young stars inside the Flame Nebula produce a lot of blue-white light, but only the yellow, orange and red light can penetrate the dust.

At the same time, both the Flame Nebula and the Snowflake Cluster region in NGC 2264 are (more or less strongly) affected by bright ultraviolet light from an O-type star: Alnitak when it comes to the Flame Nebula, and 15 Mon when it comes to the Snowflake Cluster. There is definitely hydrogen alpha light in these nebulas.

The combination of hydrogen alpha light due to irradiation by a nearby hot star, and visible and ultraviolet but highly dust-reddened light from within, creates the yellowish color of both the Flame Nebula and the Snow Flake cluster region in NGC 2264.

Ann
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Re: APOD: Inside the Flame Nebula (2021 Apr 17)

Post by Knight of Clear Skies » Sat Apr 17, 2021 9:07 am

I think that's plausible Ann. To see if the ionizing source is the same as the source of the reflection nebulosity I'd have a go at comparing the morphology of an Ha image with the green channel. (I have the data sitting on a disc so I'll take a look if I can get around to it.) Also, is there much OIII signal from the Flame?
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Re: APOD: Inside the Flame Nebula (2021 Apr 17)

Post by Ann » Sat Apr 17, 2021 9:42 am

Knight of Clear Skies wrote:
Sat Apr 17, 2021 9:07 am
I think that's plausible Ann. To see if the ionizing source is the same as the source of the reflection nebulosity I'd have a go at comparing the morphology of an Ha image with the green channel. (I have the data sitting on a disc so I'll take a look if I can get around to it.) Also, is there much OIII signal from the Flame?
If there is any OIII in the Flame Nebula, I'd say it is in the center of the embedded cluster. But I have no idea how much there might be.

I think the presence of OIII requires a very hot star and a "rarefied medium" around the hot star.

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Re: APOD: Inside the Flame Nebula (2021 Apr 17)

Post by orin stepanek » Sat Apr 17, 2021 1:00 pm

FlamenebulaIR1024.jpg

I like this view; really nice! A lot of new stars at the bottom! :D
Looks like a doggie face in the right side of center; another to the
right side in the brown area! 🐶
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Re: APOD: Inside the Flame Nebula (2021 Apr 17)

Post by Knight of Clear Skies » Sat Apr 17, 2021 4:38 pm

Ann wrote:
Sat Apr 17, 2021 9:42 am
If there is any OIII in the Flame Nebula, I'd say it is in the center of the embedded cluster. But I have no idea how much there might be.

I think the presence of OIII requires a very hot star and a "rarefied medium" around the hot star.

Ann
Yes, that's what I'm getting at, looking for OIII may help reveal the ionizing source. If it's Alnitak I'd expect to see little OIII signal and for it to be stronger on the Western side of the nebula.

It might be similar to the California nebula, where the ionizing source is the runaway star Xi Persei. Despite it being a very hot star the OIII signal is much weaker than many nebulae that are ionized by embedded star clusters, I guess because the distance is greater and possibly the concentration of oxygen is lower.
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