13Aug SHG: 1st installment. Spectral study of AR12401.

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13Aug SHG: 1st installment. Spectral study of AR12401.

Post by p_zetner » Tue Aug 18, 2015 5:50 am

Hello Everyone.

I had a productive SHG session on 13Aug and am processing a number of images. I did notice something interesting while generating the H-alpha spectroheliogram. As shown below, there was a rapid variation in the spectrum of AR12401 which may be an observation of a loop prominence, in absorption. Here is a (line centre) H-alpha spectroheliogram of the disk:
Ha_092754_AVG_ARL_proc_frm_sz_proc_AR.png
AR12401 appears, in the spectroheliogram, as a region of bright plage with a central absorbing region. In the picture below, I've added, for comparison, a filtergram taken with my Daystar system the next day, on 14Aug. I also present two spectra, taken at different locations in the AR, which show the central absorbing gas to have a region of high outflow velocity next to a region of high inflow velocity.
Ha_SHG13Aug_Filtergram14Aug_spec_mosaicV2.png
My first interpretation is that this corresponds to a "top view" of streaming gas in a loop. Does H plasma actually stream this way in a loop? I'll have to research the idea further.

Cheers.
Peter.

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Re: 13Aug SHG: 1st installment. Spectral study of AR12401.

Post by Merlin66 » Tue Aug 18, 2015 7:12 am

Peter,
very interesting....
Evershed effect??
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Re: 13Aug SHG: 1st installment. Spectral study of AR12401.

Post by Montana » Tue Aug 18, 2015 9:22 am

Wow! superb! :bow :bow :bow

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Re: 13Aug SHG: 1st installment. Spectral study of AR12401.

Post by marktownley » Tue Aug 18, 2015 2:02 pm

Excellent indeed Peter!
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Re: 13Aug SHG: 1st installment. Spectral study of AR12401.

Post by Spectral Joe » Wed Aug 19, 2015 1:49 am

p_zetner wrote: My first interpretation is that this corresponds to a "top view" of streaming gas in a loop. Does H plasma actually stream this way in a loop? I'll have to research the idea further.

Cheers.
Peter.
Short answer, yes. Here is a pair of images from March 8, 2011, when AR1165 blew a bubble. The bubble is actually gas flowing downward, as seen:
AVG_B  sub crop.jpg
AVG_B sub crop.jpg (8.79 KiB) Viewed 996 times
AVG_R  sub crop.jpg
AVG_R sub crop.jpg (8.74 KiB) Viewed 996 times
Stereo Image.jpg
Stereo Image.jpg (8.44 KiB) Viewed 996 times
The two images are +/- 0.03nm from Ha line center. This was a very lucky catch, very late in the day and the Sun was getting close to the horizon. Large air mass and a lot of atmospheric scatter but the best example of counterflow I have.
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Re: 13Aug SHG: 1st installment. Spectral study of AR12401.

Post by p_zetner » Wed Aug 19, 2015 4:50 am

Thanks, Joe. That is a terrific catch!

If I understand your observation, the loop has a receding velocity component (red) and an approaching velocity component (green) with respect to the line of sight. But the overall flow is downwards. This makes sense and is consistent with what I expected of the behaviour of gas flow in loops (prominences in general). The prominence plasma is thought to condense in the corona and stream downwards.

In the present case, though, I'm observing the behaviour of an absorber against a plage region on the solar disk, a "view from the top", with an upwards stream and downwards stream separated by a small (angular) distance. I make the simple-minded interpretation of a flow which originates on the surface (?) flows radially outward and returns to the surface. The attached picture, borrowed from Wikipedia, seems to suggest such flow is possible, but I haven't read anything further about it.

Cheers.
Peter.
800px-Cartoonloops.png
800px-Cartoonloops.png (100.21 KiB) Viewed 986 times

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Re: 13Aug SHG: 1st installment. Spectral study of AR12401.

Post by p_zetner » Wed Aug 19, 2015 4:54 am

Thanks Ken, Alexandra and Mark for your comments!

Ken: My understanding of the Evershed effect is that it describes radial outflow from a sunspot's umbra, across the penumbra, to the surface. I'm pretty sure that, with a bandpass of about 0.02nm near line centre, I'm looking at exclusively chromosphere and sunspot gas dynamics are not really visible.

Cheers.
Peter.

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