Here are three views of the Sun showing the hydrogen, calcium and helium chromospheres.
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Posted 12 August 2018 - 05:29 PM
Peter, these are so good! You can see proms in the Calcium capture. Really awesome! Your instrument/imaging is superior to many I've seen that do this. I'm very interested to know more about what instrument you have and how you image if you don't mind taking the time to share more about it.
Man I'm starting to want one of these buggers!
Edited by MalVeauX, 12 August 2018 - 05:36 PM.
Posted 13 August 2018 - 06:37 AM
Most impressive Peter! Image quality approaching optical filter level, with much narrower band-pass.
H3 is quite a change form the ususal...
Do you have a description of your system somewhere?
Posted 13 August 2018 - 10:25 AM
Dear Marty, Mike and Bob;
Thanks for the kind comments!
Marty: There are definitely proms and filaments visible at all three wavelengths (as well as others). Proms were a little weak on the 8th and I lost them in pulling out the disk details. I have brighter exposure versions of the Ca and H with more evident proms and will probably get around to processing them, but I'm slow! I'm also processing images at a couple more wavelengths.
Bob: It's been a learning curve! Spectroheliogram image quality is very dependent on seeing and heavily reliant on image processing. I think I've finally come up with a fairly reliable processing workflow to get the most I can out of the imaging data. I'm fascinated by the HeD3 chromosphere. It's formation by UV photo-ionization from the corona is quite different in comparison to the H and Ca chromospheres. Absorption is very weak at this wavelength and requires some heavy manipulation to extract an image. I’ve had better success in the past and I'm not overly happy with the present result but it shows the correlation of He filaments with H filaments and shows the regions of enhanced He absorption above the (weak) solar active regions.
I have described some details of the instrument in an article written for the online journal "Spektrum" of the Vereinigung der Sternfreunde Fachgruppe Spektroskopie:
Ken Harrison's book ("Imaging Sunlight - using a digital spectroheliograph" - Springer) also gives an overview of the field.
Let me know if you need any more information.
Edited by Peter Z, 13 August 2018 - 10:46 AM.
Posted 14 August 2018 - 09:41 AM
I am quite impressed with your spectroheliograph performance.
Images are amazing in contrast.
What is FWHM in these lines?
Posted 14 August 2018 - 04:44 PM
I haven't bench tested this lately but, if I compare the fwhm of a measured spectral line in my instrument with a spectral linewidth of the same line in the BASS2000 spectrum, I get an instrumental bandpass of ~ 0.21 Angstrom (fwhm) near H alpha for my spectrometer in the present configuration. The BASS2000 spectrum claims a resolution of 0.001 Angstrom and I'm assuming the relation:
BASS2000_fwhm^2 + Instrumental_fwhm^2 = Measured_fwhm^2
which is strict for Gaussian profiles.
Edited by Peter Z, 14 August 2018 - 10:03 PM.
Posted 14 August 2018 - 08:26 PM
Very nice and impressive images. Filaments in Ca? Wow. I don't think I can see then in mine Lunt CaK, FWHM 5 Angstrom? I will try again on Thursday.
Posted 14 August 2018 - 09:19 PM
I don’t believe you’ll be able to see filaments in Ca with 5 Angstrom bandpass. Sub-Angstrom bandpass would be required. Prominences can be seen with the ~2 Angstrom bandpass available in the Lunt. With the spectroheliograph bandpass of ~0.2 Angstroms, filaments are routinely visible.
Posted 15 August 2018 - 02:34 PM
i know peter from solarchat forum
his stuff is as always top notch
process skills hsrd to beat
actually the hed3 shots more impressive than cak filaments
and much harder to do
ive captured cak filaments
but its beyond my skills doing a hed3
Edited by highfnum, 15 August 2018 - 02:40 PM.
Posted 15 August 2018 - 02:52 PM
Thanks for those kind comments, John!
The HeD3 imaging can be hit or miss. I’m not too happy with this latest image but it might just be that there was very little He present for absorption. Keep trying!
Posted 15 August 2018 - 03:13 PM
there must ne additional steps taken than just
scanning hed3 line
you must be subtracting nearby continuum
Posted 21 December 2018 - 11:53 AM
I wanted to resurrect this thread because I was never happy with the way the HeD3 image turned out. Over the last months, I've developed some improved methods to process spectroheliograms, especially for weak lines like this helium line. There are still a few puzzling image artifacts (the "wrinkles" in the north polar region) but I'm much happier with the newly processed image so I'd like to post it here.
The level of detail here is similar to that produced by the KIS ChroTel telescope which images the infrared He 10830 A line. This infrared line is closely related to the HeD3 (5875.6 A) line so images in these two wavelengths show essentially the same features. The latest ChroTel image is available here: http://www.leibniz-k...tories/chrotel/
Edited by Peter Z, 21 December 2018 - 11:54 AM.
Posted 21 December 2018 - 01:38 PM
Really awesome Peter! Even got a helium prom there at 3 o'clock!
Posted 21 July 2020 - 11:27 AM
Posted 22 July 2020 - 09:33 AM
Thanks for your interest. I was a little surprised to find a new reply to this old thread!
The passband of my spectroheliograph for these 2018 images is about 0.2 angstroms in comparison to the native HeD3 linewidth, in absorption features (plage regions), of about 0.5 angstroms fwhm. The spectral selectivity of the Daystar .3A QPE is more than sufficient to isolate this line. The problem with HeD3 is the extremely weak absorption it shows against the disk. According to Zirin, HeD3 absorption on the disk has a central depth less than 1%. It is, for example, completely undetectable on the BASS2000 solar spectrum (http://bass2000.obsp...pect.php?step=1). On the other hand, prominences show up well at the HeD3 wavelength and you should be able to image these relatively easily with the Daystar.
In order to image the solar disk in this line with a spectroheliograph I've had to resort to some intensive processing, the biggest part of which is to subtract the contribution of the photospheric continuum at 5876 angstroms. My processing has now become a little more sophisticated than it was in 2018 but, in the old days, I made a whole spectral series of images around the HeD3 line centre then would (arbitrarily) choose an image from this series to subtract from all the others and hope that HeD3 features become visible. It was largely a guess and check procedure to find the proper continuum subtraction.
Nowadays, I process the entire spectrum (around 50 angstroms span centred around 5876 angstroms) associated with an image pixel by first subtracting from it a spectrum averaged over the entire disk. This is done pixel by pixel over the entire image. It seems to work well and I've attached a recent montage of spectroheliograms where HeD3 was processed this way. Here's the montage of spectroheliograms in four wavelengths taken on July 12, 2020:
Good luck with your Daystar HeD3 filter. I would love to have one of these to experiment with but it's out of my price range!
Posted 22 July 2020 - 02:07 PM
Posted 12 August 2020 - 10:40 PM
These are excellent images, congrats! D3 is difficult... in the old days I worked with 1083nm, which might be easier than D3, but it is on the far end of silicon sensitivity.
Looking forward to seeing any velocity maps that you might produce. I also worked with Doppler maps in the old days, and if there is anything I can do to help, please let me know!
Edited by MattPenn, 12 August 2020 - 10:40 PM.
Posted 17 August 2020 - 10:44 AM
Thanks for the reply and your comments. I have done some studies involving velocity maps (dopplergrams). Here is one where I looked at H alpha and observed inflow and outflow near the penumbral boundary of a sunspot:
I have generated dopplergrams in a number of photospheric and chromospheric lines. It's a bit more difficult in He D3 because of the weak absorption and the problem of ensuring acquisition at symmetric displacements blue and red of line centre. Presently, I'm using an 1800 lines/mm grating versus my previous 2400 lines/mm grating. The decreased spectral resolution makes the dopplergram exercise a little more difficult (for narrow lines) but I get better transmission in the UV and IR with the present grating.
Here is a latest series of spectroheliograms taken on August 3, 2020.
Edited by Peter Z, 17 August 2020 - 10:45 AM.
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