Crabby crab and a question

[Placidus]

Here is the Crab Nebula, taken under dodgy conditions, and nowhere near enough exposure.

We've been off-air due to technical problems with the dome roof opener. The H-bridge limit switch input (an innocent looking 8015 quad AND gate) was possibly fried after a vicious thunderstorm - we've had some impressive jump-out-of-your-skin thunder. Replaced the chip and we're now operational but yet to see how robust everything is, or whether there is other damage.

Apart from Bildan, everyone else on IIS is wisely leaving the far north alone, perhaps because the seeing has been so appalling. Last night we had and FWHM of 10 pixels, and we lost two subs to intermittent cloud, but we've been waiting for ages and ages, so here's half a crab.

Six hrs of H-alpha mapped to R+G, and only 3hrs of OIII mapped to blue, then palette rotated -15 degrees to give a quarter nod to natural colour. (To recover individual channels, rotate palette +15.)

What can we see that nobody else has mentioned? There is a small and very faint slightly streaky tongue of light (about 90 pixels = 50 sec arc high) heading off toward 9 o'clock, almost to the left hand edge of field, seen in both H-alpha and OIII, that isn't obvious in say the Hubble image or any other that we're aware of.

Question: We've read that the blue glow of the Crab is Cerenkov radiation - electrons spiralling in a powerful magnetic field. Presumably only some proportion of that would go through our 3nM OIII filter. Would we in fact do better with a wideband blue filter? Ordinarily we'd just give it a try, and all would be revealed, but what with Christmas, Cloud, and Crispy Electronics, it's been a struggle.

Field is cropped to only 9.3 min arc. Total exposure 9 hrs in 1hr subs. Aspen CGC16M on 20" PlaneWave.

Best
a slightly crabby
M & T

[Atmos]

That's lovely MnT! It was an object that I've wanted to image until I saw just how damned small it is!
It is one of my favourite objects simply because it is one of the few objects in the sky younger than human history :)

[astroron]

Nice image there Mike and Trish,I have never seen that streak before either.
On checking The "images" on google, there are a few pics with the streak on them.
One pic even has two.
Link here.
http://www.cosmotography.com/images/small_new_m1.html
Cheers:thumbsup:

[Placidus]

Thanks hugely, Ron. That's the most beautiful image. It at least in part answers our question - one of the very few emission nebulae seemingly worth a go in natural colour, especially if we can move the observatory a few feet further north.

[strongmanmike]

Great capture guys! Such a cool object, hard to take from 33deg S too, nicely done :thumbsup: Yes that extension is well seen in several other images, I wonder what caused it? Looks like some sort of expanding bubble breakthrough :shrug:...maybe the Millennium Falcon escaping an Imperial Starship :question:

Mike

[RickS]

The Gold Coast Bulletin has a pic of a crab with one white claw and a likeness of Michael Jackson on its carapace, but yours is a lot more impressive M&T! Shame about the weather and technical difficulties, but still a good result.

The extension is very cool too. I must have a dig around for one of those "time lapse" images of the crab and see if there's anything interesting detectable in that region.

Cheers,
Rick.

[billdan]

Well done M&T, I love the gold and silver colour scheme with the blue glow around the edges. Not sure how you got 3 distinct colours from bi-colour data, must something to do with your palette rotation.

Cheers
Bill

[Stevec35]

That's a very good Crab from your location M&T. I've seen the streak in other images too. I think it was first noticed about 20 years ago.

Cheers

Steve

[Placidus]

Thanks Mike! The Starship theory is very attractive, but the burst bubble explanation has the advantage that it's been observed in other SNR's.



Cheers, Rick. Glad we can't see Mr Jackson in our image.



Thanks Bill. Wild guess about the colours: With any two complementary colours (opposites on the colour wheel), say red and cyan, or yellow and blue, or green and magenta, mixing them 50-50 will produce white, and other ratios will produce various pastel shades that we could give names to.

Cheers,
M & T

[cometcatcher]

A very detailed image M&T! I only got a smudge of light last time I shooted it.

Must be deep to get that side appendage.

[Andy01]

That's cool, looks like a metal brooch - nice colour scheme too :)

[strongmanmike]

Yes, indeed, including in Lionel Murphy (http://www.pbase.com/strongmanmike2002/image/164515288/original)

They are called Supernova Remnant Breakouts, read about our two recently imaged little buggers N11 and N86 that show such breakouts HERE (https://www.researchgate.net/publication/230917510_Supernova_Remnants_in_the _Magellanic_Clouds_II_Supernova_Rem nant_Breakouts_from_N11L_and_N86)

Mike

[Ryderscope]

A tiny but significant object that tracks modern human history and provides for an informative discussion as well. Thanks for posting.

[multiweb]

Very nice Mike. Pity about the seeing and as Mike pointed out pretty low. :thumbsup:

[Placidus]

Thanks, Kevin. Weather might have been even worse for you. There are a few SNR's in the far north that are either low (like the Veil) or that we just can't do at all from here. But we have the Vela SNR.



Aha! Delighted that you like the colour, Andy. We think we might make that "Ha to R+G, OIII to Blue, then rotate -15 deg to add a hint of naturalness" our standard Placidus Palette for bicolour.



Ta. One thinks of an explosion inside a house, and stuff flying out the windows.



Cheers, Rodney.



Thanks, Marc. Last time we had seeing that bad, it was looking over a tiled roof in a suburban summer heat-wave. I actually had to edit our automatic focussing software, because the FWHM was off the graph. That lost half an hour. But as Rodney and Colin mentioned, it's such a juicy target. One has to have a go.

[topheart]

Well done M+T - a difficult capture in difficult conditions, but it came up well.

Cheers,
Tim

[Placidus]

Thanks kindly, Tim.

[Slawomir]

Interesting catch M&T, and it shows that imperfect data is better (more fun) than no data at all! LOL

I think adding some RGB to your NB data would be the way to go with this nebula.

[sjastro]

Hello Mike and Trish,

The correct terminology is synchrotron radiation.

Cherenkov radiation occurs when gamma ray photons from the Crab are converted into high velocity electron/positron showers when interacting with atoms and molecules in our atmosphere.
These showers which carry a charge can further interact with atoms and molecules causing then to be polarized by the shower.
As the shower passes, the atoms and molecules return to their non polarized state and produce Cherenkov radiation in the process.
Our atmosphere is the source for Cherenkov radiation not the Crab.

Since synchrotron radiation is basically a continuous spectrum you will do better with a wideband blue filter.

Synchrotron radiation is highly polarized and using a polarisation filter at different angles combined with luminance data, leads to some very interesting details not ordinarily seen as revealed in the attachment.

There are not too many amateur images of a polarized Crab and it might make an interesting challenge.

Regards

Steven

[Slawomir]

Thank you for clarifying that Steven.

M&T - I hope you do not mind me sharing a link to an interesting read about imaging with polarising filters: http://www.narrowbandimaging.com/images/Crisp_color_astronomical_imaging_us ing_polarizing_filters_release.pdf

[sjastro]

Thanks for the very informative link.
I've been looking at a number of reflection nebulae as potential targets for imaging with a polarization filter none of which are satisfactory.
M78 referenced in the link looks like a good candidate.

Regards

Steven

[Placidus]

Thanks, Steven and Suavi, for a most interesting discussion. Apologies for the late reply as our internet has been down or super-flaky for days.

I'm sure glad I've got my Senior's card to hang on to tightly when I get synchrotron and Cerenkov radiation mixed up. On a less senior day I do know and understand the difference.

What was especially interesting was to learn from the article that Suavi referenced that the "crisp" structures in the Crab are emission line structures, and we would have captured them in our image. The general blue glow, which we've excluded, is the synchrotron radiation.

Mike

[marc4darkskies]

Tipping my hat to you M&T! :thumbsup: I wouldn't even consider imaging anything that doesn't spend a few hours above 30 deg altitude. Certainly a brave attempt and a respectable result for such a low target.

Cheers + Happy New Year!
Marcus

[Placidus]

Thanks muchly, Marcus.

Very best, M&T