Solar Disk at 3883.3 Angstroms (CN Band)

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Solar Disk at 3883.3 Angstroms (CN Band)

Post by p_zetner »

Hello Everyone.

Since I am sidelined by my brutally harsh, but oddly beautiful, winter weather, I'm giving some thought to new projects and re-thinking old projects. I was looking into the subject of G-Band imaging (near 430.5nm). G-Band images are associated with absorptions by the CH molecular radical. These images are used to investigate small scale magnetic field concentrations in the photosphere which show up as "bright spots" (sub-arcsecond size) in G-Band filtergrams. This type of imaging is interesting since it doesn't require excessively narrow bandpass of the optical filters involved. A bandpass of 1nm to several nm is typically used. I realize that sub-arcsecond resolution is basically out of reach but, what the heck, it's something to think about!

Then, in my investigations, I came across a paper which claimed that the contrast of these bright spots could be improved roughly 50% (or more) by imaging in the absorption region of the CN molecule, particularly the bandhead at 388.83nm. This was happy news because some of the spectra taken with my SHG over the summer included this line. Here is a portion of the spectrum captured by my instrument with the CaK3 line and CN bandhead identified. (In the left hand side of the image, you can see, just resolved, the classic "double reversal" of the CaK line where plage is present.)






So, I thought I would generate some full disk shots of the Sun at this wavelength. Once again, there would be no possibility of observing bright spots at this image scale but it would be interesting to see what the photosphere looks like.

Here is a comparison of the 2013Aug25 CaK3 Sun (chromosphere) with the CN Sun (photosphere) taken from the same video and identical processing.





Cheers.
Peter.


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Re: Solar Disk at 3883.3 Angstroms (CN Band)

Post by marktownley »

Way cool Peter! I'm always learning new things on this forum! :)


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Re: Solar Disk at 3883.3 Angstroms (CN Band)

Post by swisswalter »

Hi Peter

wonderful informations. Thank you for sharing them. Are you aware of any filters we can use on refractors around 388 nm. I guess the response of our CCD's to 388 nm light is not that great :?


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Re: Solar Disk at 3883.3 Angstroms (CN Band)

Post by SolarJohn »

Peter - Very interesting work; I too have been looking into improving solar images using phase diversity, and much work has been done in the G-band (430.5nm) region. Here are titles of several papers explaining the technique; sorry about the titles only, but I have misplaced the text file with the download URL.

Phase diversity restoration of sunspot images

Two dual-wavelength sequences of high-resolution solar photospheric images captured over several hours and restored by use of phase diversity

Solar image restoration by use of multi-frame blind deconvolution with multiple objects and phase diversity

Solar Image Restoration by use of Multi-Object Multi-Frame Blind Deconvolution

If you cannot find these papers by Googling the titles, I can upload the papers here-just let me know.

SolarJohn

Walter- G-band (430.5) filters are readily available, but still pricey.


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Re: Solar Disk at 3883.3 Angstroms (CN Band)

Post by Wah »

It's interesting that the CaK bright region has split into 2 lines in the spectrum.
I saw the same thing in my spectrum, but I once thought that it was caused by the poor quality of my spectroscope.


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Re: Solar Disk at 3883.3 Angstroms (CN Band)

Post by p_zetner »

Thanks, Mark!

Walter: The CN image I've shown was taken with a DMK camera - still good response in this spectral region. The image was generated with a pretty narrow bandpass (0.5 Angstroms) - a 3 pixel spectral slice from the SHG video. The contrast looks good at this narrow bandpass but worsens as you increase. Here's a comparison of 3883.3 Angstrom centre wavelength images generated with 14 Angstrom bandpass (still pretty narrow - it would be an expensive filter!) and 0.5 Angstrom bandpass.





John: The phase diversity idea seems like a pretty ambitious undertaking in image processing. Certainly an interesting concept worth more study.

Wah: The plages exhibit the "double reversal" in CaII K (and CaII H as well as some other lines MgII, for example). This double reversal feature divides the CaII K line into the CaII K1v,K1r, K2v, K2r and K3 regions. Here's a map:





Cheers.
Peter.


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Re: Solar Disk at 3883.3 Angstroms (CN Band)

Post by marktownley »

Very informative, thanks Peter :)


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Re: Solar Disk at 3883.3 Angstroms (CN Band)

Post by Wah »

I have been searching for "double reversal" but found no related results in Google.
I'd like to know more about this interesting thing~

BTW, is the CN full name "Cyanide"?
Thanks!


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Re: Solar Disk at 3883.3 Angstroms (CN Band)

Post by Montana »

:hamster: fabulous information and work Peter :bow: :bow: :bow:

I was reading about the G band in a book I got in the summer and I can't quite remember but I think they said that WL flares were best seen in this region. I need to re-read this bit.

Alexandra


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Re: Solar Disk at 3883.3 Angstroms (CN Band)

Post by Derek Klepp »

Yes very interesting Peter the g band also rings a bell in past readings.Now why wasn,t hidh school this interesting.
Cheers Derek


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Re: Solar Disk at 3883.3 Angstroms (CN Band)

Post by p_zetner »

Thanks for your comments, everyone.

Alexandra; I think I also read somewhere that the G-band was good for observing white light flares. I don't believe this has anything to do with the CH absorption itself other than to generally reduce the background photospheric light and enhance the contrast. I would guess that the further into the violet you go the better the WL flare contrast would be simply because of the drop-off in continuum light.

Wah: An absorption line which exhibits reversal is dark in the line wings but brightens somewhat near the line core where it looks like a little emission feature - a "reversal" from absorption to (apparent) emission. This happens quite often in H-alpha and H-beta lines from "Be" stars, for example. The CaK line is called doubly reversed because the little emission feature near the line core reduces in intensity at the line core itself ("reversing" again to apparent absorption).
Also, CN is the "cyanide radical". Sometimes it's called cyanogen but that name is generally used for the gas (CN)2, which you can buy in a bottle. There are highly toxic compounds like HCN (hydrogen cyanide) or KCN (potassium cyanide) which have a bound CN radical.

Derek: High school is all about the ABC's and getting your lunch money stolen. I guess you have to walk before you can run.

Cheers.
Peter.


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Re: Solar Disk at 3883.3 Angstroms (CN Band)

Post by highfnum »

it does look very similar to caK


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