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Old 20-03-2020, 01:25 PM
Placidus (Mike and Trish)
Narrowing the band

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Gabriela Mistral SHO 22 hrs

We are thrilled with this. The completely rebuilt set-up is now working smoothly, and we seem to be getting slightly sharper images than before. The seeing has been very good - say 1.8 sec arc - for a long time now, most likely due to the drought, but perhaps tracking is also a little bit better now.

Big one here

The field is 40 min arc wide, North up.

20 inch PlaneWave CDK. FLI PL 16803 camera at -30C. 2" square Astrodon 3nM filters. Otherwise, all observatory control robotics firmware and software designed and built by us. Processing with our own GoodLook.

We were especially pleased to see that there was a great deal of SII, not just the tight arc all along the rim of Gabriela's face, suggesting "deeply dredged star-guts" and therefore recent supernova activity, but also in the huge yellowish arc occupying much of the left hand 25% of the image. That strongly suggests much ancient supernova activity in the region, accounting for all the the braided shock-fronts that look like Gabriela's hair and perhaps steam.

Another area of great interest is the fan of blue lightning bolts coming out toward 6 to 9 o'clock from the bright star under the chin. Is this a WR star, and this is material ejected in a semi-collimated fashion by who knows what - magnetic field, dust ring? The increased clarity in this image makes the lightning bolts much more obvious than we've seen them before.

Oh, a moment's cosmetic weakness: the NB stars have been artificially removed, whitened, and replaced, with the exception of half a dozen of the brightest stars, which were replaced with RGB stars. The exception is the bright one under the chin, which we didn't want to mess with.

Some of the improved tracking came from adding an alarming 4 Kgs or so of brass weights here and there so that the motors always had to fight against the weights instead of getting lost in the backlash and static friction. Joe Cauchi lent much needed moral support while we were doing that, pointing out that 4 Kg out of balance is nothing compared with the 70 Kgs of scope, 50 Kgs of forks, and about 20 Kgs of cameras and filters. It worked.

Cheers,
Mike and Trish
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Last edited by Placidus; 20-03-2020 at 03:38 PM.
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Old 20-03-2020, 02:45 PM
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multiweb (Marc)
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That's subzero cool. Amazing sharp details. Love the stars colors too. One for the extension room.
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Old 20-03-2020, 02:51 PM
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That's a hot image. Stars are tiny.

Are you referring to that purply plume of gas next to the bright purply star as a SNR? Sharp detail.

Greg.
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Old 20-03-2020, 03:06 PM
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Old 20-03-2020, 03:12 PM
Placidus (Mike and Trish)
Narrowing the band

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Quote:
Originally Posted by multiweb View Post
That's subzero cool. Amazing sharp details. Love the stars colors too. One for the extension room.
Thanks Marc. It will go well with the orchids.

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Originally Posted by gregbradley View Post
That's a hot image. Stars are tiny.
Thanks Greg!

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Originally Posted by gregbradley View Post
Are you referring to that purply plume of gas next to the bright purply star as a SNR? Sharp detail.

Greg.
Not the purply plume. Don't know what that is, but I thought it could be being expelled by the bright purply star.

The thing I thought might be an old falling-apart SNR is the huge arc or half-circle of variously yellowish shocked material occupying more or less the whole of the left hand 25% of the image. Apologies for being unclear. I've edited the original post.

Last edited by Placidus; 20-03-2020 at 03:39 PM.
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Old 20-03-2020, 05:10 PM
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codemonkey (Lee)
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Very nice, M&T! Looks very sharp.

As a software developer, I'm super impressed by the fact that you guys have written all your own software. That's awesome.

I did notice that some stars seemed to be RGB, others NB and was a bit confused before I read your description.

I saw a method of creating synthetic RGB stars from NB data... if I recall correctly it's just using:

R = H
G = H * 0.65 + O * 0.35
B = O

I used it on this image and think it worked really well there. Then again, sounds like you guys have RGB data anyway, so I suppose it's a moot point here!

I'm sure many will be philosophically opposed to such practices, but I'm a heathen, what can I say?

Am I right that you're imaging at about 0.4"/px? Is the image downsampled, or cropped (or both?)?


I certainly feel your pain regarding backlash / static friction. Even the Mach 1 has a small amount of backlash (I've seen Roland say 250-500ms) which can make Declination guiding challenging at times. I'm imaging at 0.5"/px so small amounts of backlash that wouldn't bother lots of people become problematic for me. High res encoders and/or backlash-free designs sound more attractive every day... unfortunately the current economic situation makes such things decidedly less attractive.
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Old 20-03-2020, 05:31 PM
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It has come up really well MnT, from the soft waves on the left to the stark contrasty shock front on the right.
I do find that purple squiggle/lightning fascinating, I've seen it in other images (remember it from your last one too) but it looks more defined here than in other renditions so I imagine that the good seeing helps
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Old 20-03-2020, 05:56 PM
Placidus (Mike and Trish)
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Quote:
Originally Posted by DavidU View Post
Nice to see you over here David.

Quote:
Originally Posted by codemonkey View Post
Very nice, M&T! Looks very sharp.

As a software developer, I'm super impressed by the fact that you guys have written all your own software. That's awesome.

I did notice that some stars seemed to be RGB, others NB and was a bit confused before I read your description.

I saw a method of creating synthetic RGB stars from NB data... if I recall correctly it's just using:

R = H
G = H * 0.65 + O * 0.35
B = O

I used it on this image and think it worked really well there. Then again, sounds like you guys have RGB data anyway, so I suppose it's a moot point here!

I'm sure many will be philosophically opposed to such practices, but I'm a heathen, what can I say?
Thanks muchly Lee. We'll try your SHO to RGB method. Easy!

Quote:
Originally Posted by codemonkey View Post
Am I right that you're imaging at about 0.4"/px? Is the image downsampled, or cropped (or both?)?


I certainly feel your pain regarding backlash / static friction. Even the Mach 1 has a small amount of backlash (I've seen Roland say 250-500ms) which can make Declination guiding challenging at times. I'm imaging at 0.5"/px so small amounts of backlash that wouldn't bother lots of people become problematic for me. High res encoders and/or backlash-free designs sound more attractive every day... unfortunately the current economic situation makes such things decidedly less attractive.
We're at about 0.55 sec arc/pixel. Not cropped, not downsampled. It is a mini-mosaic with about 90% frame overlap, hence the slightly wider field. We do what one might call giga-dithering, big programmed random movements between frames, which helps remove all sorts of artifacts.


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Originally Posted by Atmos View Post
It has come up really well MnT, from the soft waves on the left to the stark contrasty shock front on the right.
I do find that purple squiggle/lightning fascinating, I've seen it in other images (remember it from your last one too) but it looks more defined here than in other renditions so I imagine that the good seeing helps
Thanks heaps Colin. We'd love to hear a professional verdict on that "lightning bolt".

Best,
MnT
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Old 20-03-2020, 08:16 PM
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Atmos (Colin)
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There doesn't seem to be a lot of information one the purple squiggles. Given that they're purple suggests that they're strong in SII and OIII but in RGB they're mostly blue which would make sense anyway given what the happens when you colour balance a SHO image.

That particular star is an A0 supergiant, quite similar to Rigel in luminosity and temperature. There are a few papers discussing whether or not HD 92207 is a variable magnetic field or not. If it isn't a variable then it is inaccuracy in detection and it's all still under research.

Given the presence of SII and OIII surrounding a blue supergiant, it isn't unusual for these kinds of stars to dredge up material from deep within and bring it towards the surface. With the potential of a variable magnetic field strength, that material could actually be an enormous solar flare that erupted at some stage but in that case you would definitely expect to see a lot of hydrogen.... which we don't.

https://academic.oup.com/mnras/artic...2/1779/1031499

In short, I have no idea and I'm struggling to find any papers on it either.
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Old 20-03-2020, 09:49 PM
Placidus (Mike and Trish)
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Quote:
Originally Posted by Atmos View Post
There doesn't seem to be a lot of information one the purple squiggles. Given that they're purple suggests that they're strong in SII and OIII but in RGB they're mostly blue which would make sense anyway given what the happens when you colour balance a SHO image.

That particular star is an A0 supergiant, quite similar to Rigel in luminosity and temperature. There are a few papers discussing whether or not HD 92207 is a variable magnetic field or not. If it isn't a variable then it is inaccuracy in detection and it's all still under research.

Given the presence of SII and OIII surrounding a blue supergiant, it isn't unusual for these kinds of stars to dredge up material from deep within and bring it towards the surface. With the potential of a variable magnetic field strength, that material could actually be an enormous solar flare that erupted at some stage but in that case you would definitely expect to see a lot of hydrogen.... which we don't.

https://academic.oup.com/mnras/artic...2/1779/1031499

In short, I have no idea and I'm struggling to find any papers on it either.
Thanks for the interesting information Colin. After reading it, I wondered about the difference between an A0 supergiant and a Wolf-Rayet star. I guess an A0 is young, still burning hydrogen, and still on the main sequence, whereas a Wolf-Rayet has stopped burning hydrogen, is burning helium, is throwing off a lot of material, and hasn't got long to go.
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Old 20-03-2020, 10:29 PM
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Originally Posted by Placidus View Post
Thanks for the interesting information Colin. After reading it, I wondered about the difference between an A0 supergiant and a Wolf-Rayet star. I guess an A0 is young, still burning hydrogen, and still on the main sequence, whereas a Wolf-Rayet has stopped burning hydrogen, is burning helium, is throwing off a lot of material, and hasn't got long to go.
If you have a look at this link it shows that it has moved above the main sequence and has finished its hydrogen burning phase. It will go through periods of burning hydrogen and the photosphere is still largely hydrogen based (with mixes of other heavier elements that get dredged up) but it's now largely in He/C/O/N burning now.

This paper also talked about it being a variable star but there are some more recent papers that discuss its variability with regards to magnetic fields.

I guess where things ultimately get difficult and confusing is that not all big bright stars become WR stars. A stars metallicity plays quite a large roll in it. The less metals there are the faster and hotter it burns which also means larger stars. If it is a faster rotating star it tends to dredge up more heavier metals up once it leaves the main sequence. Having more heavier metals towards the chromosphere seems to be one factor in heavy mass loss.
This paper suggests that it isn't self enrichment (dredging up) that is a likely cause of what creates a WR star but more likely to be a star with an initially higher Fe/H so it would have to be a fair bit higher than average as WR stars aren't hugely common compared to the amount of A&O type stars out there.
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Old 21-03-2020, 09:40 AM
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Andy01 (Andy)
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Fascinating image guys - certainly prompted some interesting conversations.
Well done, good to see you back imaging and my oh my - RGB stars too!
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Old 27-03-2020, 10:45 AM
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Glorious image! The framing is very good and it really adds to the picture. The face looks realistic, which is often not the case with this object. Colour is nicely balanced.
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Old 28-03-2020, 07:37 PM
Placidus (Mike and Trish)
Narrowing the band

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Fascinating image guys - certainly prompted some interesting conversations.
Well done, good to see you back imaging and my oh my - RGB stars too!
Cheers, Andy. You'll see that in today's new post, we've had a proper go at RGB stars.

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Glorious image! The framing is very good and it really adds to the picture. The face looks realistic, which is often not the case with this object. Colour is nicely balanced.
Thanks so much, Geoff. We're greatly encouraged.
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