Spectacular Filament Lift-Off: A Spectroscopic Study

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Spectacular Filament Lift-Off: A Spectroscopic Study

Post by p_zetner »

Greetings Everyone.

On July 15, from about UT 12:00 to 14:00, there was a spectacular filament disappearance event ("disparition brusque") . The event was, of course, covered by the US NSO Integrated Synoptic Program (NISP) GONG network of telescopes and I've generated a time lapse animation from their publicly available data (from the Spanish El Teide Observatory archive).
GONG data 15Jul2022.gif
GONG data 15Jul2022.gif (11.26 MiB) Viewed 1527 times
By a massive stroke of serendipitous fortune, I was just setting up my spectroheliograph at the outset of the event (around 8:00 am local time). Looking at the CaH spectrum, I noticed some peculiar dark blobs which, I thought, were due to fuzz on the camera sensor. Amazingly, on closer inspection, they turned out to be true spectral features associated with the filament event. I ran off as many SHG scans as I could manage and have been working through the analysis of the data.
Solar_Spectral_Scan_080122_oriented_crop.gif
Solar_Spectral_Scan_080122_oriented_crop.gif (34.56 MiB) Viewed 1528 times
Above is a cropped and abridged portion of the video file acquired from the SHG to which I've added a cropped spectroheliogram, allowing "tracking" along the solar E-W direction as the video plays. The yellow vertical line in the spectroheliogram acts as a cursor which displays the "slice" of solar disk sampled by the SHG entrance slit as the disk image traverses the slit. The dispersion direction of the spectrum, on the right side, is horizontal. The nature of the video can be clarified by two excerpts, frames 1 and 2, extracted from it.
2Frames_Montage_crop.jpg
2Frames_Montage_crop.jpg (103.73 KiB) Viewed 1528 times
This image is a montage of two video frames containing spatial information on the left and associated spectra on the right. The numbers below the spectra give the wavelength in angstroms with 3969 angstroms identifying the CaH line centre. In frame 1 you can see, in the spectrum, an absorption feature (identified with the arrow) with huge extension into the red wing of the CaH line, indicating a huge Doppler redshift brought about by Ca plasma receding from us toward the surface of the Sun. In frame 2, there is a fainter absorption feature (identified with the arrow) with large extension into the CaH line blue wing, indicating plasma streaming towards us, away from the Sun. By visually matching the vertical position of these features within the spectrum to vertical position along the yellow cursor lines on the left, you can see that the origin of the features lies in different sections of the filament. Part of the filament is rapidly sinking toward the solar surface while part is streaming away from the surface, the lift-off.
CaH_Spectral_Series_Montage.jpg
CaH_Spectral_Series_Montage.jpg (7.38 MiB) Viewed 1528 times
Another way of appreciating what is occurring in the filament, is to take a look at the spectral series montage of 9 images above. Each image in the montage is a spectroheliogram generated at a specific wavelength. The wavelengths are indicated by the numbers in the upper left corners of the nine individual images, giving the offset in angstroms from the CaH line centre. The centre image is the line centre image with zero offset. After staring at this for a while, it should become clear that the filament takes on quite a different shape / appearance depending on the wavelength offset. This is, again, due to the Doppler effect, in which portions of the filament moving downward toward the solar surface will absorb more light and show more contrast at positive wavelength offsets while portions lifting off the surface will show more contrast at negative offsets.
CaH_Dopplergrams_Montage.jpg
CaH_Dopplergrams_Montage.jpg (1.64 MiB) Viewed 1528 times
Maybe the best and most dramatic way to visualize the velocities of various parts of the filament is by generating dopplergrams. By taking difference images of spectroheliograms generated at symmetric +/- offsets from line centre, the filament motions become clear. Above is a montage of four dopplergrams. By selecting the magnitude of the wavelength offsets used to generate the difference image, you select the velocity you are interested in studying. The numbers in the upper left hand corners of the four individual images above give velocities in km/s. For example, the upper left hand image is associated with a velocity of 79.4 km/s. The nature of the difference image, the dopplergram, is such that plasma streaming toward the solar surface (receding from us) at 79.4 km/s is given by dark intensities while plasma streaming away from the surface at 79.4 km/s is given by bright intensities. Likewise, the same association of dark regions with downward streaming at 318 km/s and bright regions with upward streaming at 318 km/s is shown in the lower right image.

What's intriguing to me is the complex interweaving of bright and dark regions visible at the "lower" velocities of 79.4 and 159 km/s. This is definitely representative of a complex motion and, from what I've come across in the literature, represents the filament unravelling or untwisting itself as it evolves. At the higher velocities, especially 318 km/s, it's clear that, roughly, the middle of the filament is lifting off while the part near the footpoints is rapidly streaming into the solar surface.

Although the spectroscopic study may not be quite as dramatic as observing the time evolution of the filament itself, as in the GONG video, there is a lot of interesting information to be had which is not necessarily evident or obtainable from the time lapse video.

Hope you enjoyed the presentation.
Cheers.
Peter


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Re: Spectacular Filament Lift-Off: A Spectroscopic Study

Post by Montana »

Incredible information, incredible presentation and of course incredible timing :bow :bow :bow I thoroughly enjoyed this!

Alexandra


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Re: Spectacular Filament Lift-Off: A Spectroscopic Study

Post by p_zetner »

Thanks very much, Alexandra!
Cheers.
Peter


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Re: Spectacular Filament Lift-Off: A Spectroscopic Study

Post by robertsaintjean »

Very interesting observations. This opens up a new opportunity for me (and for others !) to understand the Sun.

Robert


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Re: Spectacular Filament Lift-Off: A Spectroscopic Study

Post by p_zetner »

Thanks for your interest, Robert.
Do you have a spectroheliograph?
Cheers.
Peter


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Re: Spectacular Filament Lift-Off: A Spectroscopic Study

Post by marktownley »

Fascinating analysis Peter, very insightful!

I reckon come cycle 26 (and myself retired and time on my hands) I would very much like to be able to get into the world of SHGs etc.


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Re: Spectacular Filament Lift-Off: A Spectroscopic Study

Post by fulvio.mete »

Hi,Peter, very interesting work:what soft did you use? and what dispersion did you get with your spectrograph?
Fulvio


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Re: Spectacular Filament Lift-Off: A Spectroscopic Study

Post by p_zetner »

Hi Everyone.
Here are some more results from my spectroheliograph observation of the erupting filament. These results are from data taken approximately 25 minutes later than the results above. The first image is a spectral series taken through the CaH absorption line. Numbers in the upper left hand corners of component images in this montage refer to wavelength offsets (in angstroms) measured with respect to line centre. Positive offsets refer to wavelength shifts to the red while negative offsets refer to wavelength shifts to the blue.
CaH_spectral_sweep_9Montage_proc_labels_siz.png
CaH_spectral_sweep_9Montage_proc_labels_siz.png (5.87 MiB) Viewed 1311 times
There are two striking features of this image. First, the filament is visible out to nearly 5 angstroms to the blue and the red of CaH line centre. Clearly, this involves Doppler shifts caused by extreme velocities (more below). Secondly, the morphology of the filament changes radically as you progress through the spectral series, telling us that different sections of the filament are moving in drastically different ways. Sections of the filament visible with high contrast in images at positive wavelength offsets are receding from us and experiencing Doppler red shifts. Sections of the filament visible with high contrast in images at negative wavelength offsets are approaching us and experiencing Doppler blue shifts. Here is a link to a more comprehensive, animated version of the spectral series.

Image

A more detailed understanding of the velocities can be had with dopplergrams. Here is a montage of four dopplergrams with the velocity in km/s indicated by the number in the upper left hand corner. Bright regions identify blue shifted plasma (moving away from the Sun) while dark regions identify red shifted absorption by plasma moving toward the solar surface at the speeds indicated by the number.
CaH_Dopplergrams_4Montage_labels.png
CaH_Dopplergrams_4Montage_labels.png (2.83 MiB) Viewed 1311 times
Note that the entwined bright and dark regions at lower velocities evolve to more distinct separate filament regions at higher velocities. At lower velocities, the filament is exhibiting very complex motion (twisting ?) while, at higher velocities, separate regions are rising and falling. Here is a link to a more comprehensive, animated look at the dopplergrams.

Image

The other thing that intrigues me about these results is the huge velocities measured. I had to quadruple check my spectrum calibration to make sure that these measured velocities were actually sensible. From my reading, I've also learned that velocities up to 1000 km/s have been observed during eruptions.

Cheers.
Peter


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Re: Spectacular Filament Lift-Off: A Spectroscopic Study

Post by Carbon60 »

Superb work, Peter. Fascinating to see the incredible speeds involved. Edge-view and, in this case, top view animations and Dopplergrams really bring solar dynamics to life. Thank you for taking the time and trouble to pull all of this together so beautifully.

Stu.


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Re: Spectacular Filament Lift-Off: A Spectroscopic Study

Post by Montana »

This work is incredible Peter, you should write it up as a paper and send it in to the Journal of the British Astronomical Association, it is perfect!

:bow :bow

Alexandra


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