21Jun2014 PZ SHG: 2nd installment: CaH Arch Prom - SolarChat!
Round 2 of my imaging results for the 21June imaging session. Here is an arch prominence captured on the E solar limb. I'm presenting it as an animation - a "spectral sweep" through the Ca H line. Each frame corresponds to a change in wavelength of 0.028 A proceeding from the red wing of the Ca H line to the blue wing. This corresponds to a step of 2.12 km/s in the line of sight velocity. Line centre is at frame 17 / 18 (out of 33), so the velocity range is about -37.1 km/s to +32.9 km/s, sweeping from red (receding) to blue (approaching), with respect to line centre. Bear in mind that the bandpass of the spectrometer is about 5 times the step size, so I'm not really claiming a resolution of 2.12 km/s, although I'm pretty sure I can see differences in prom shape about every 2nd frame. I'm proceeding to develop these images further - colour Dopplergrams, for example. For the time being, I do enjoy this animation, though. Hope you do!
Last edited by p_zetner on Thu Jun 26, 2014 9:50 pm, edited 1 time in total.
So your next step is to colour each frame separately from red to blue and stack them together so that we can see in one image which parts of the prom are moving away from the observer, which parts are neutral and which parts are moving towards the observer . Is that what you're saying?
Stu, you spoiled the surprise!
Here is a relatively lacklustre image of the proms in emission near the Ca H line centre.
Here is a velocity analysis presented as a set of Dopplergrams, with blue showing approaching plasma and red showing receding plasma at the speeds indicated. Each Dopplergram is produced by subtracting an image constructed at a given blue shift (from line centre) from the image constructed at the corresponding red shift and colourizing. For the Ca H line, a wavelength shift of 0.056 A corresponds to a line-of-sight velocity of 4.23 km/s. It's interesting to see that there are regions of receding plasma very close (in line-of-sight) to regions of approaching plasma, possibly indicating a twisting motion?
Presumably you could do the same with full disk images and close views of active regions.
Very nice work and analysis Peter!
Glad to see that you figured the Dopplergram out!
Hi Walter, Mark, Stu and Alex.
Thanks for your interest and your comments! I appreciate it.
I could apply the same procedure to the disk, once I start processing the disk images. In the case of the disk and active regions I think it's less obvious what the Dopplergrams represent. Different wavelength positions within the chromospheric absorption lines basically arise from different depths in the chromosphere (higher in the chromosphere closer to line centre), although there must also be some velocity effect as well. The Ca H and K lines also have the peculiar "double reversal" feature in active region spectra which, I've read, can be modelled by introducing non-standard temperature variations with height in the chromosphere. That further complicates the interpretation. On the other hand, you could apply the Dopplergram technique to analyzing the velocity characteristics of filaments but these are hard to see in Ca light and are only visible over a pretty restricted range of wavelength near line centre.
p_zetner wrote: ....... Tha but these are hard to see in Ca light and are only visible over a pretty restricted range of wavelength near line centre.
thank very much for that iformation. Where are the boundarys?