Some interesting Ca H Spectra

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Some interesting Ca H Spectra

Post by p_zetner » Sat Jul 12, 2014 9:29 pm

Hello Everyone.

When observing with my spectroheliograph, I enjoy looking at the spectra as much as the final image.
For example, here are some spectra which really caught my attention. They were recorded on July 3rd near the Sun's E limb where AR12109 was just appearing.
100132-0005_prom-spec_final_label_crop.jpg
The Prominence / AR spectrum shows a tremendous "zig-zag". I call it a lightning bolt! The zig-zag is indicative of regions of rapidly receding and approaching plasma closely spaced to each other. The red and blue shifts are associated with of speeds of 90 km/s and the "spiky" nature of the spectrum tells me that there are well-defined streams of gas heading towards and away from us - likely surges. Further out in the prominences (two are mainly visible) the lower spectrum shows gas which seems to be largely blue shifted.

Hope you enjoy these.

Cheers.
Peter.



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Re: Some interesting Ca H Spectra

Post by DSobserver » Sat Jul 12, 2014 11:18 pm

really nice! :hamster:



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Re: Some interesting Ca H Spectra

Post by marktownley » Sun Jul 13, 2014 12:29 am

Yes, I do enjoy! Great science here Peter!


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Re: Some interesting Ca H Spectra

Post by swisswalter » Sun Jul 13, 2014 6:35 am

Hi Peter

most interesting stuff


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Re: Some interesting Ca H Spectra

Post by Carbon60 » Sun Jul 13, 2014 7:14 am

Fascinating detail, Peter.

Again, it illustrates the underlying dynamics which make the Sun such and interesting study.

It would also be interesting to see in detail what's happening in the umbra and penumbral regions, if you can do this with your kit.

Stu.


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Re: Some interesting Ca H Spectra

Post by p_zetner » Sun Jul 13, 2014 6:34 pm

Thanks for the feedback, everyone.

Okay, Stu. You asked for it!

Here is a Ca H spectrum of two active regions taken on June 13.
103546-0000_12frames-AVG_proc_final_crop.jpg
One of the reasons I found this fascinating is the presence of the flare in AR112082 (lower AR). The corresponding flare spectral feature is a bright "smear" extending throughout and beyond the Ca H absorption line. I assume this is an indication of tremendous heating associated with the flare and the correspondingly wide, thermally broadened, emission line.

Stu, you asked about umbral and penumbral features. The spectral feature associated with the upper AR (112080) has a, more or less, typical hourglass shape where the H2 bright regions merge together at the umbra. You can see this in the lower AR as well. Typically, I've found the umbra itself to be dark (in the H3 line core) but the AR112080 spectral feature has a bright patch which looks like it's associated with a light bridge. Cool, eh?

I'm definitely giving thought to re-configuring my SHG to give a better image scale for active region closeups. It seems to require scaling up the size of the entire instrument but, at some point, I'll give it a shot.

Cheers.
Peter.



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Re: Some interesting Ca H Spectra

Post by swisswalter » Mon Jul 14, 2014 3:54 am

Hi Peter

fantastic details , thanks for the explanation


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Re: Some interesting Ca H Spectra

Post by Carbon60 » Mon Jul 14, 2014 6:23 am

Very interesting, Peter.

Is the observed broadening/shape likely also to be associated with the strength of the local magnetic field (Zeeman)?

Stu.


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Re: Some interesting Ca H Spectra

Post by Derek Klepp » Mon Jul 14, 2014 6:41 am

Very well described Peter much easier going than the Zirin text.This really is interesting stuff.
Thanks Derek



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Re: Some interesting Ca H Spectra

Post by alex » Mon Jul 14, 2014 8:17 am

That's truly amazing Peter!



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Re: Some interesting Ca H Spectra

Post by Montana » Mon Jul 14, 2014 11:05 am

Absolutely fascinating Peter :bow :bow :bow

Alexandra



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Re: Some interesting Ca H Spectra

Post by highfnum » Tue Jul 15, 2014 11:38 pm

very interesting




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Re: Some interesting Ca H Spectra

Post by p_zetner » Fri Jul 18, 2014 12:27 am

Thanks for your comments, everyone.

Stu: I haven't done the calculation, but my guess would be that the thermal broadening associated with the flare overwhelms the Zeeman splitting / broadening. I think it would be hard to observe magnetic phenomena with the CaH or CaK lines since they are intrinsically very broad. Zeeman broadening of the CaH or CaK line might, possibly, show up in the line core (H3 or K3, the narrowest part of the line) but at the scale of spectrum in the photo, I don't think anything will be noticeable. People who map out the magnetic fields in active regions usually choose very narrow (photospheric) lines to observe.

Cheers.
Peter.



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Re: Some interesting Ca H Spectra

Post by Carbon60 » Sat Jul 19, 2014 10:04 pm

Hi Peter,

What's the reason behind the dark line down the centre of the bright emissions? The prom spectra don't show this feature (they only display Doppler broadening). The spectra for the ARs feature broadening, but also a dark centre line.


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Re: Some interesting Ca H Spectra

Post by p_zetner » Sun Jul 20, 2014 5:13 pm

Hi Stu.

You're right, the proms basically display emission lineshapes which are Doppler broadened / shifted and relatively easy to interpret. The complicated absorption profile is another story altogether! I don't think I can say it any better, so I'll quote from Foukal's "Solar Astrophysics" (p.289, 3rd ed):

"As seen in Fig. 9-9 (below) the Ca II resonance lines observed in absorption on the disk show broad wings, an increase of intensity toward the line center, and a sharper dip at line center. Since the opacity in such a line increases toward its center, the shape can be broadly interpreted as a map of brightness temperature with depth in the solar atmosphere. In the far wings, where opacity is least, we see to the local H- continuum level (the photospheric surface) ...... Closer to the line center, as the opacity increases, we see higher in the photosphere, where the temperature decreases and the intensity drops. At the point of first minimum, called K1 we are observing the temperature minimum region. The increase of Tb (brightness temperature) with opacity even closer to line center, marked K2 , is caused by the chromospheric temperature rise. Finally, the K3 dip or central reversal arises because near the line core the opacity is so high that we see layers of low density whose emission falls well below that of a plasma of the same temperature in LTE (local thermodynamic equilibrium)."

(I've added the text in parentheses.)

Hopefully, you can make sense of this explanation with the aid of the figures below. The first is an absorption spectrum of Ca K (very similar to the Ca H case) on the quiet Sun and in a plage region.
CaK spectrum.png
The second figure shows the "heights of formation" of Ca K features (same as Ca H) overlayed on the standard (VAL) model of temperature vs. height in the solar atmosphere. I added the blue curve which gives an idea (roughly) of how this temperature variation changes in a plage region. You can see that the K2 (or H2) regions will be brighter in plage regions, where chromospheric heating takes place, while K3 (H3) will remain dark (for the opacity argument given by Foukal) and K1 (H1) will show the photosphere.
Fraunhofer lines VAL model ver3.png
Fraunhofer lines VAL model ver3.png (157.23 KiB) Viewed 2631 times
Cheers.
Peter.



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Re: Some interesting Ca H Spectra

Post by swisswalter » Mon Jul 21, 2014 4:14 am

Hi Peter

thank you very much for the Details and explanation


Only stardust in the wind, some fine and some less fine scopes, filters and adapters as well. Switzerland 47 N, 9 E, in the heart of EUROPE :)

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Re: Some interesting Ca H Spectra

Post by Carbon60 » Mon Jul 21, 2014 6:21 am

Thanks, Peter.

All very interesting stuff.

A complex mix of emission, absorption and optical density occurring in 3 dimensions!

It's fascinating to see the complexity underpinning the images we see in filtered light.

Cheers

Stu.


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Re: Some interesting Ca H Spectra

Post by p_zetner » Tue Jul 22, 2014 1:02 am

Thought I'd add one more measured spectrum. This one illustrates the change in going from the disk to a prominence.
spec1-2_colour.jpg
The top plot is a "quiet disk" reference spectrum near Ca H (line centre at 3968.5 A). The middle and lower plots were taken from the indicated locations on the measured spectrum, looking near the E solar limb. You can see the "doubly reversed" Ca H absorption on the disk (middle plot - yellow peaks plus dip) which makes the transition to the pure emission spectrum in the prominence (bottom spectrum - yellow peak). Notice the H epsilon feature visible as well.

There seems to be a lot of science in the exact nature of the transition from Ca H absorption on the disk to Ca H emission "off limb". In the recent paper "Spectroscopy at the Solar Limb" by C. A. R. Beck and R. Rezaei (Astronomy & Astrophysics, v531, pg.A173 (2011)), the authors claim: "The average off-limb spectra of Ca II H present a good opportunity to test static chromospheric atmosphere models because they lack the photospheric contribution that is present in disk-center spectra."

Cheers.
Peter.



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Re: Some interesting Ca H Spectra

Post by swisswalter » Tue Jul 22, 2014 5:19 am

Thanks Peter, very interesting


Only stardust in the wind, some fine and some less fine scopes, filters and adapters as well. Switzerland 47 N, 9 E, in the heart of EUROPE :)

from 7 am - 7 pm http://www.nanosys.ch

from 7.01 pm - 6.59 am http://www.wastronomiko.com some times vice versa ;)

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