Helium Disk: 08Aug2018 Spectroheliogram

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p_zetner
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Helium Disk: 08Aug2018 Spectroheliogram

Post by p_zetner » Sun Dec 16, 2018 8:59 pm

Greetings Everyone.

I have been developing my processing workflow for spectroheliograms to create proper images of weak lines, especially my favourite; HeD3. Here's a result from my solitary SHG imaging session on August 8. I've included a H alpha image for comparison (taken on the same date). Aside from some image defects which I have yet to understand, I'm pretty happy with the result.

In my past images, the He absorption was observed to be extremely weak in general but (relatively) strong over the active regions and filaments. However, this is the first time I've noticed He features over the entire disk. The disk is covered with weaker absorbing features having squiggly and curlicue shapes. As yet, I have no reason to doubt that these are real! My new processing also readily reveals the prominences (3:30, 4:00 and 9:00 o'clock) without heavily adjusting exposure levels. I'm pretty sure I can tweak the processing to enhance the proms further. Notice that the bright limb in this picture is a natural feature of the He chromosphere .... no enhancement is done at the limb and this is a single, not composite image.

In my past efforts, there was a lot of trial and error manipulation required to pull out the He features. Image processing is now relegated to an (almost) automatic procedure. All in all, a small leap in my spectroheliography learning curve!

Cheers.
Peter

HeD3
2018-08-08-085412_EQW-proc_AspRat-siz-frame-RGB_AI-enhance-avg_lvl_resiz2.png
2018-08-08-085412_EQW-proc_AspRat-siz-frame-RGB_AI-enhance-avg_lvl_resiz2.png (828.99 KiB) Viewed 891 times
H-alpha Comparison Image.
Finals_Ha-083838.png
Finals_Ha-083838.png (1005.75 KiB) Viewed 1085 times
Last edited by p_zetner on Fri Dec 21, 2018 4:39 pm, edited 1 time in total.

highfnum
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Re: Helium Disk: 08Aug2018 Spectroheliogram

Post by highfnum » Sun Dec 16, 2018 11:35 pm

sheesh !!!
real pro level stuff

you should write document on how to do HeD3

so others can try to do it

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Re: Helium Disk: 08Aug2018 Spectroheliogram

Post by Montana » Mon Dec 17, 2018 12:12 pm

Wow!!! tremendous :bow :hamster:

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Re: Helium Disk: 08Aug2018 Spectroheliogram

Post by marktownley » Mon Dec 17, 2018 12:15 pm

These are stunners Peter!
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Re: Helium Disk: 08Aug2018 Spectroheliogram

Post by LTHB » Mon Dec 17, 2018 5:03 pm

Great and interesting work! A new (at least to me) view of the sun!

Have you researched already which layer(s) of the solar atmosphere is/are depicted in this way (in addition to filaments and proms)?

Thanks for showing!

Frank

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Re: Helium Disk: 08Aug2018 Spectroheliogram

Post by Carbon60 » Mon Dec 17, 2018 8:40 pm

Fascinating work, Peter. I wonder why the limb is so bright.

Stu.
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Re: Helium Disk: 08Aug2018 Spectroheliogram

Post by p_zetner » Tue Dec 18, 2018 8:46 pm

Thanks for your comments, everyone.

Stu:
Maybe I overstated this a little! Zirin (Astrophysics of the Sun 1988 p198) says that "The limb-disk contrast in helium is remarkable. The strong 5876 line (called D3 because of its proximity to the D1 and D2 lines of NaI) is about 0.2 times the disk intensity, nearly as bright as H alpha. Yet on the disk it has a central depth less than 1%." The limb appears so bright in the type of image I'm producing because the intensity scale is set by the weak absorbing features causing the emitting regions to be extremely bright in this scale. My image is similar to an “equivalent width” image used by some astronomers. The intensity underlying the absorbing features is not the continuum (photosphere) intensity but, essentially, zero equivalent width.

Frank:
Here are some of the facts regarding the HeD3 line that I'm familiar with.
The line centre wavelength is 5875.6 Angstroms with a linewidth in absorption features (plage regions) of ~ 0.5 Angstroms fwhm. This line is generally invisible on the solar disk (absorption is too weak) except in regions of plage and filaments where absorption is enhanced. The correlation between He absorption features and H alpha features can be seen in the spectroheliograms presented above. Alexandra has referred to the active regions visible in HeD3 as “black plage” regions.

The line is very bright at the limb and in prominences. There is a bright D3 limb "band" visible in telescopes with very high angular resolution. Measurements show that this band corresponds to He D3 emission from a shell with a sharply defined lower edge about 1400km above the photosphere (Zirin, Astrophysics of the Sun 1988, fig 7.24)

The mechanism of He D3 absorption is interesting. Extreme ultraviolet (EUV) radiation from the corona shines downward, illuminating the He from above. This EUV light is energetic enough to ionize the He. Recombination of the ions and free electrons then produces neutral He in excited states of high excitation energy (~20eV) from which we see absorption at the D3 line as well as the He IR (10830 Angstroms) line. The observed shell in limb emission is consistent with this idea. The bottom of the shell corresponds to the maximum depth that the coronal EUV radiation can penetrate (downwards). Also, because radiation from the corona is required, He D3 absorption features don't appear where coronal holes are present. He IR images are used as "proxy" maps of coronal holes, the only tool to map coronal holes from the ground. I guess He D3 images could serve the same purpose but the D3 absorption is much weaker than the IR absorption.

Here is a relatively recent professional He 10830A IR image taken with the ChroTel telescope run by the Kiepenheuer-Institut für Sonnenphysik http://www.leibniz-kis.de/en/observatories/chrotel/
Unfortunately, I can't make a direct comparison with my 08Aug2018 D3 image because of the difference in dates of observation. Many similar features are evident, though.

ChroTel He1083 12Sep2018.jpg
ChroTel He1083 12Sep2018.jpg (873.48 KiB) Viewed 983 times
As opposed to other chromospheric gases, He is optically thin and can be used (in emission, at the limb) to measure chromospheric magnetic fields by a phenomenon called the Hanle effect. The Hanle effect is responsive to much weaker fields than the Zeeman effect and such measurements have given the first accurate picture of chromospheric magnetic fields. Finally, the D3 line has also been used as a diagnostic of solar flare dynamics. The additional information this line provides for flare studies is of great interest to the experts but beyond my understanding, at the moment.

References.

Zirin (1988) "Astrophysics of the Sun", Cambridge University Press

Zirin (1996) Solar Physics v169, p313
"The Mystery of the Chromosphere"

LaBonte (1977) Solar Physics v53, p369
"A Measurement of the Helium D3 Profile with a Birefringent Filter"

Bray R.J., (1964) Zeitschrift fur Astrophysik v60, p207
"The Helium D3 Absorption Line in the Spectra of Chromospheric Flares"
Last edited by p_zetner on Wed Dec 19, 2018 3:52 pm, edited 1 time in total.

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Re: Helium Disk: 08Aug2018 Spectroheliogram

Post by Carbon60 » Wed Dec 19, 2018 7:24 am

Your answers are always so informative, Peter. Thank you.

I have to say, your SHG images knock the socks off those from ChroTel.

Stu
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Re: Helium Disk: 08Aug2018 Spectroheliogram

Post by Merrill55 » Sat Dec 22, 2018 2:59 am

Very interesting !

Have you tried line spectrum 5303A ?
I did'nt yet.

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Re: Helium Disk: 08Aug2018 Spectroheliogram

Post by p_zetner » Sat Dec 22, 2018 3:58 am

The coronal green line FeXIV 5302.86 Å is extremely weak and, previously, I would not have attempted it. It might be possible although I have not seen any professional results of imaging at this wavelength.

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Re: Helium Disk: 08Aug2018 Spectroheliogram

Post by Merrill55 » Sat Dec 22, 2018 4:13 am

Thank you for the reply.
Very old time,Norikura Coronal Observatory successed to get green emmision line.

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Re: Helium Disk: 08Aug2018 Spectroheliogram

Post by MapleRidge » Sun Dec 23, 2018 9:55 pm

Great results Peter :bow

Brian
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Re: Helium Disk: 08Aug2018 Spectroheliogram

Post by p_zetner » Mon Dec 24, 2018 4:48 am

Thanks for your interest and comments, everyone.

Mark, thanks for the SPOD!

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Re: Helium Disk: 08Aug2018 Spectroheliogram

Post by Merlin66 » Mon Dec 24, 2018 6:26 am

Well done mate!!
It really does go to show that Lunt and Coronado have some serious competition!!!
I’d love to be able to replicate your work but the weather down here has been absolutely terrible, that and the very poor seeing conditions close to the Bay.
I’ve been using ImageJ and Wha’s processing software....what do you do differently???
Again, congratulations on your success.
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