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Chromospheric layer in CaK?

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#1 BYoesle

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Posted 27 April 2013 - 11:30 AM

I have picked up on this before, but had perhaps erroneously thought it might be a processing artifact.

However, yesterdays (April 26 http://www.cloudynig...5825611/page... ) images seem to show it more clearly than I ever recall seeing. With some additional enhancement (below), the chromosphere in CaK (@ ~ 2.2 A FWHM) appears to be visible as a layer, very much like the “double limb” seen in H alpha with wider bandpass filters. It appears to have details of its own, and that is why I suspect it might not be a processing artifact.

Has anyone else ever noticed this with their CaK images? It would be nice to explore further, and to know if the phenomena disappears with a narrower bandpass in CaK as it does in H alpha... double stacking anyone?

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#2 Aquarist

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Posted 27 April 2013 - 01:35 PM

Interesting. Does anyone double stack CaK? If so, do you have images to share?

#3 BYoesle

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Posted 27 April 2013 - 09:38 PM

Harald Paleske has double stacked two Lunt CaK modules: http://www.cloudynig.../Number/5171136. Features do not seem to change as much as they do with H alpha DSing.

I received this PM from bob71741:

Bob - I got this from John Varsik at BBSO [Big Bear Solar Observatory] some time ago, and hopefully may provide some insight on what you observed.

“You can download the CaK absorption line spectra online to see the K1, K2, and K3 parts of the line. I have one, but cannot attach it.

The line at 3933 angstroms is called K because that's what Fraunhofer called it. The K1, K2 and K3 refer to specific parts of the line. The K line is very dark and wide, but at the center of it is an unusual "brightness reversal" -- the center of the line gets brighter. The very core of the line reverses again -- there is a dip in brightness again. The line arises from a transition between the 4p 2P 5/2 state to the 4s 2S 1/2 state (really need sub- and superscripts to write these correctly) of singly ionized calcium (Ca II). The Ca II K line is one of the most useful lines in the solar spectrum, but it is one of the most complicated lines in terms of its formation.

K1 = the point in the line wings where the reversal starts. There are two
points, called K1R and K1V on each side of the center of the line.

K2 = the point of maximum brightness in the reversal. There are two points, K2R
and K2V again on each side of the center of the line.

K3 = the dip at the very center of the line.

Note that in high resolution spectra the whole line (or parts of it) can be
Doppler shifted and thus vary in appearance depending on what's happening at that location on
the Sun.

These portions of the line arise at different heights in the upper photosphere
and chromosphere. K1 comes from near the temperature minimum, K2 from around1000
km above that, and K3 from higher in the chromosphere. See Mihalas' book _Stellar Atmospheres_ pg. 380 for the gory details.

John Varsik
BBSO”


Therefore the CaK line is actually composed of three differing layer heights. I believe that the layer imaged above is that of the higher K2 and possibly K3 portions of the CaK emission line, which while apparently faint, can be brought out with the right processing. Per the information above and the diagram below, the K2 portion of the CaK emission extends to the height of the H alpha core emission above the photosphere - thus the similarity to the "double limb" seen in H alpha filters with bandpasses over 0.5 Angstroms:

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#4 highfnum

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Posted 27 April 2013 - 10:59 PM

great shot - I've seen proms in caK but never took notice on that thin line

#5 BYoesle

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Posted 28 April 2013 - 01:15 AM

Thanks Jon.

I noticed something in the image of a CaK surge prom last July 26, which was very active in H alpha. Most of the time contrast boosting is used to bring out features of the CaK disk. But with this Cak prom/AR, I kept it minimal and noticed some additional brightness in the area - which I attributed to possibly poor atmospherics and/or processing artifacts.

A closer look now reveals the band extends around the disk, and indeed is the CaK K2/K3 chromosphere layer. To my knowledge these are the first images of this feature I have ever seen as well:

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#6 HPaleske

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Posted 28 April 2013 - 03:36 AM

Hi Bob,

beautiful pictures - congratulation.

The CaK-layer around the Sun is definitely real. The most overview Sun pictures in calcium light be edited very hard. Here, the weak contrast of CaK totally lost chromosphere. This is accepted, however, because you want to make visible the chromospheric faculae. Today, I will add the pictures of the 26.04. with the CaK observations.
Thus we can compare the CaK images well.

cs Harald
www.unigraph.de

#7 BYoesle

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Posted 28 April 2013 - 07:53 AM

Thanks Harald - looking forward to what you captured, and to be humbled ;)

#8 George9

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Posted 28 April 2013 - 10:31 AM

Very nice. Congratulations, in fact. George

#9 BYoesle

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Posted 28 April 2013 - 12:33 PM

Thanks George ;)

A little less compressed version leaves little doubt:

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#10 HPaleske

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Posted 28 April 2013 - 12:52 PM

Hi Bob,

here the link of the Cak pictures from 26.04.. Unfortunately, the CaK - conditions was poor. Nevertheless, you can see very much detail.

http://www.unigraph....11-13-16ana.jpg

cs Harald
www.unigraph.de

#11 marktownley

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Posted 29 April 2013 - 04:32 AM

Great pictures Bob and Harald!

I shall pursue this myself too ;)

Bob, are you processing your images in 8bit or 16bit in your post processing software?

#12 George9

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Posted 29 April 2013 - 07:56 AM

Wow, Harald, in CaK, and I just saw the other thread, too. George

#13 highfnum

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Posted 29 April 2013 - 09:11 AM

I tried this weekend
but seeing was not good enough to get thin line
I did pick up proms - will post shot later

#14 BYoesle

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Posted 29 April 2013 - 04:49 PM

Thanks for the awesome images Harald -- got to get me a bigger scope (working on it)...

Bob, are you processing your images in 8bit or 16bit in your post processing software?


To be honest Mark, I am not sure. The images are first recorded as PGR Chameleon 8 bit monochrome avi files with FireCapture, aligned, stacked, and wavelet processed and output as tiff files in RegiStax6 (lower image).

Thereafter, they are post processed in PaintShop Pro 7 (upper colored image) -- this includes histogram adjustments, unsharp masking, colorizing (rarely and usually via RGB adjustment) and finally conversion to JPEG. The image information I have states "Pixel depth/colors: 24/16 Million". So I believe these would be 24 bit images. But I'm again unsure of the actual bit depth due to all the intermediate limitations.

Hope this helps.

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#15 BYoesle

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Posted 29 April 2013 - 07:58 PM

I thought a comparison between the CaK chromosphere and the H alpha chromosphere in psuedo-realistic colors would be interesting. 40 minutes seperate the images taken 26.04.13 -- 2.2 Angstrom FWHM CaK @ 22:09 UTC showing the K1, K2, K3 components, and the 0.45 Angstrom FWHM H alpha @ 22:48 UTC.

The CaK shows the bright purple disk and K1 features at about the photosphere's level, with the faint K2 & K3 layers rising to about 2000 km above the photosphere. The H alpha image shows the H alpha core at ~ 1500 km above the photosphere (due to the narrow bandwidth, there is no evidence of the photosphere).

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#16 George9

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Posted 30 April 2013 - 09:44 AM

Amazing. You know, the dark oval spot under the biggest prom is presumably a sun spot on edge. It looks like on H-alpha it is about as far from the chromospheric limb as it is on CaK from the photospheric limb. I would have expected it to be the same distance from the photospheric limb in both images. (I realize that you cannot see the photospheric limb in H-alpha; I am just estimating where it would be.)

George

#17 George9

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Posted 30 April 2013 - 10:17 AM

(Perhaps the answer is simply that the sunspot looks higher in the H-alpha image because you are seeing the sunspot at the top of the chromosphere, above the photosphere. I.e., you are NOT seeing the sunspot on the photosphere through the chromosphere. George)

#18 BYoesle

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Posted 30 April 2013 - 11:39 AM

Very astute observation George!

In addition to your postulate, two more factors could help account for this discrepancy. First, there is an additional 40 minutes (~ 0.4 degree) of rotation toward the limb that occurred when the H alpha image was taken. Second, according to the above diagram, the CaK K3 emission level is about 300 km higher than the chromosphere that would be visible with a H alpha filter.

Next time a similar situation arises I will try and image the two as near in time as possible to get a better handle on this. Ideally I will use the same scope (e.g. same exact FL and image scale) and be able to layer the two images to get a more exact representation of how the various layers or levels correspond, and use a single vs. double stack H alpha filter to locate the position of the photosphere... will need some excellent seeing as well ;)

In the meantime perhaps Harald or someone else will investigate...

#19 BYoesle

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Posted 07 May 2013 - 01:52 PM

Unfortunately there were not suitable sunspots close to the limb, but I was able yesterday to capture another comparison of the CaK chromosphere @ 2.2 A FWHM (left), and H alpha @ 0.7 (single stacked - right) 33 min. later. In both images the photosphere is seen via the inner brighter “double” limb:

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#20 Andy Devey

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Posted 07 May 2013 - 04:32 PM

Excellent Bob, looks like case proven!

Regards

Andy

#21 George9

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Posted 09 May 2013 - 06:16 AM

That's great, Bob. They look roughly the same height. Perhaps that other effect was just rotation. Another thing I could do is just to see if the position of a sunspot near the edge appears to change as I tune in H-alpha from on band to off band. George

#22 BYoesle

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Posted 10 May 2013 - 02:59 PM

Thanks Andy & George - would love to see what you find out George...

#23 marktownley

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Posted 01 June 2013 - 01:42 AM

Hi Bob, Hi Harald,

Thought you might be interested in this CaK animation i got, fits in very nicely here. Way too large for CN so got to link to it on my website http://brierleyhills...om-lift-off-...

Mark :)

#24 HPaleske

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Posted 01 June 2013 - 02:33 AM

Hi Mark,
this animation is so beautiful. Especially the prominence lift of, I like it. It is very difficult prominences in CaK light so bright and clear scan , as you can see in this animation. Congratulations.

cs Harald
www.unigraph.de

#25 bob71741

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Posted 01 June 2013 - 01:47 PM

Mark - That is an amazing CaK animation!






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