RCW 104, a very faint Wolf-Rayet Nebula

[Placidus]

We rather like WR nebulae, like Thor's Helmet, because they tell a part of the story of star birth and death - things that go bump in the night.

We were encouraged by Don Goldman's stunning H-alpha + OIII shot of RCW 104, a magnitude 18 Wolf Rayet nebula in a busy part of Norma. It proved to be extremely difficult.

Don's image (admittedly somewhat longer total exposure) seems to show a very bright ring of OIII. We found almost no OIII, despite 4 hrs of exposure (four x 1-hour 2x2 binned), taken with essentially the same scope, filters, and camera. It is a mystery.

We have added 4 hrs of 2x2 binned SII. There was actually more SII to be found than OIII, especially toward the top of the main H-alpha ring, but still extremely faint.

Red: 4hrs 2x2 binned [SII]. Green: 5hrs 1x1 H-alpha. Blue: 4hrs 2x2 binned [OIII].

Because we've had to very severely stretch the OIII and SII to see anything at all, and we're in the middle of the Milky Way, controlling the resultant magenta stars was a challenge. We found over 32,000 stars, put boxes around them, feathered, and removed about 70% of the excess magenta over green. Similarly, having decided on religious grounds to stick with Hubble Palette, trying to avoid the bright green look with such precious little OIII or SII was impossible. Think of a quiet deciduous forest in the first flush of new spring leaves. Or better yet, think of a giant clam, on the barrier reef, with a lime shell and purple innards.

Notice how the blue OIII ring comprises multiple closely spaced shock fronts, and how the ring is much smaller and far more circular than the outer H-alpha clam-shell.

Apogee Aspen CG16M on 20" PlaneWave CDK on MI-750 fork. Field 36' arc, 0.55"/unbinned pixel. H-alpha 5hrs in 1hr subs. OIII and SII 4hrs in 1hr subs 2x2 binned. 3nM AstroDOn filters.

If anyone is aware of a NB shot of this object other than Don's, we would be delighted to hear from you.

Don't look at the thumbnail; you can't see anything. Real one here. (http://www.mikeberthonjones.smugmug.com/Category/Wolf-Rayet/i-432tF2c/0/O/RCW%20104%20Ha%205%20OIII%204%20SII %204hrs.jpg)

[strongmanmike]

Fascinating object Mike and Trish and you are right, plenty of fine shock fronts there. Has a 3D feel too, nice.

Are you sure you have your filters designated correctly? Your image seems to be showing the Ha and OIII components where they should be but you are saying you used SII not OIII :question:

Your stars are looking good though :thumbsup:

Mike

[Paul Haese]

This object looks incredibly faint. From a cursory search I think Steve Crouch imaged this object a while ago. Though his image is wide field.

Interesting looking shock fronts and with delicate tendrils of OIII. That's what a 20" gives.

Nice detail.

[gregbradley]

A new to me and interesting image.
Nice work on imaging things that are rarely imaged.

Greg.

[Placidus]

Hi, Mike,

Sorry about the ambiguity. We used Green = H-alpha, Blue = OIII, Red = SII. So all three. The thought that our filters were in the wrong holes for 2 years, or that perhaps there was a software error, made me sit up! Had a quick check. I think they're the right way around.

Best,
MBJ

[Bassnut]

Well captured and different, nice to see a difficult one with so much excellent detail.

[Slawomir]

Hi Mike and Trish,

Although Don managed to capture more detail, his interpretation is way too red for me; I like how you balanced the colours. I think this target might be a good candidate for an ongoing project- maybe you could add more data one day/night and see if that helps to bring up the faintest bits even more?

Having said that, I think it is a fabulous image of a very difficult target - I do not even think of imaging objects past magnitude 10 :)

[RickS]

Nice one, M&T! I'll have to have a go at this target one day.

[topheart]

Congratulations!!

I love the road less well traveled. What a faint challenging object -!!

I hope to see more data on RCW 104 . You are correct, there seems to be nothing else of any value done on this.

Excellent!

Tim

[Rex]

Top shot Mike and Trish. Lots of very fine detail showing on a very faint object. Well done guys.

[Placidus]

Thanks, Paul. The challenge for us seems not so much capturing the faint OIII nebulosity as seeing it between the blinding stars. Easier at altitude or in the desert perhaps. Had a look for Steve Crouch's image. Found one on RCW 57 or so.



Thanks, Greg. There's not so much about it. I thought, where did I get the "magnitude 18" from? Did I just make it up? Eventually found it in Imaging the Southern Sky by Chadwick and Cooper.



Thanks, Fred!



Thanks for the encouragement Slawomir. You are right that perhaps four times the exposure would be worth the effort, to get the grit out of the [OIII].



Thanks Rick. We almost wonder with this one if it would be better to show it as two quite separate shots, one monochrome in H-alpha, and another in OIII, because it's so faint and hard to see against the glare.



Thanks muchly Tim, we're delighted. We'll definitely try adding more data.



Cheers, Rex, glad you like it. Really does look like a cosmic giant clam.

[Shiraz]

processing has resulted in a beautiful delicate image - really nice work on what is obviously a hard target

[Geoff45]

Very nice M&T. Just to see what was going on I split your image into R->SII, G->Ha and B->OIII. I find that Ha is the strongest, there is a distinct OIII ring and an amorphous mass of SII, which, at first glance is on a par with the OIII in brightness. However, I took some brightness samples and found that, on a scale of 0->1 some of the silicon was around the 0.5 mark, while none of the OIII made it past 0.4, so the SIII is definitely brighter than the OIII. Some of the Ha got up to 0.7. (Bear in mind that this is for a stretched image).


Geoff

[Placidus]

Thanks, Ray. Glad you like it.



Hi, Geoff,

Thanks for having a good close look and making some useful observations. That's it exactly: a big bright green H-alpha clam-shell, a small round blue OIII inner ring, and diffuse red clouds of SII top and bottom.

I re-read what I originally wrote and realized that although I said "Hubble Palette", and "Blue OIII ring", I didn't actually spell out the mapping, so in light of both your and Mike S's comments, I've edited the original post.

Your measurements would (correctly) suggest that we could stretch the image more, but the trouble is that the stars just blow out and nothing gets any clearer.

We'd like to collect hugely more OIII data, perhaps unbinned, in the hope that it will be less gritty and that will help guide the eye, but of course it will also make the stars even brighter still. Fingers crossed. Again, thanks for looking.

Best,
Mike

[Geoff45]

Yes, that was careless of me. I've edited my post so it's now correct.

[jase]

Obscure and faint, just the way I like it. A very cool image M&T. The WR nebs make for excellent imaging at your focal length. Looking forward to seeing more. :thumbsup:

[Placidus]

Thanks, Jase.

Sparkling clear sky here, minus 3 degrees overnight, but a blindingly full moon to chase us out of the observatory.