SolarChat!

Hello Everyone.

Here is a collection of spectroheliograms taken on June 12. There was a bit of a delay in posting because I'm still experimenting with processing techniques. I set the instrument up for full disk views. It had previously been configured for closeups (using a ~3x barlow on the Celestron 4" SCT) and I actually regret having made the change for this session because it would have been more interesting to view the AR and prominence at higher magnification. Chalk it up to rustiness after a long time since last using the SHG. I also replaced the previous 2400/mm grating with a 1800/mm grating. This sacrifices some spectral resolution for better transmission in the UV.

The first montage shows the solar disk imaged in the four Fraunhofer lines: CaII K, H beta, HeD3 and H alpha.
The second montage shows a series of images in H alpha. The SW limb prominence is evident in the upper frames which are composite images of prominence and disk. A blue wing image shows the expected similarity to H beta shown in the first montage. A dopplergram shows some evidence of complex plasma flow near the AR.
The third montage shows some images in the UV. These are composite images of prom and disk in the CaII K line. A blue wing CaII K line and an image taken in the CN bandhead (3883 angstroms) show strong similarity. The CN molecular band is interesting because magnetic bright points can be observed there (at high spatial resolution) with greater contrast than in the CH molecular G-band (~ 4300 angstroms). The required spatial resolution would be pretty challenging for a spectroheliograph.
The SW limb prominence exhibited some interesting spectral behaviour. If only I had opted for higher magnification! Here is an image taken with an effective spectral resolution of about 2 angstroms. A coronal loop is evident along with a higher lying wispy structure.
These features were captured by a number of observers on this forum:
Eric Roel viewtopic.php?f=4&t=28475
Phil (Astrophil) viewtopic.php?f=4&t=28464
John (highfnum) viewtopic.php?f=4&t=28474
James (DeepSolar64) viewtopic.php?f=4&t=28473.

The spectroheliograph revealed that the prominence consisted of structures that varied significantly with wavelength. In order to demonstrate this, I assembled the following animated spectral sequence of the prominence: a movie showing the shape of the prominence as the wavelength is tuned over a range of about 2.5 angstroms.
Each frame of the video represents a step of 0.058 angstroms, or, in terms of the recessional velocity corresponding to a 0.058 angstrom doppler shift, a velocity step of 2.56 km/s. The frames in the animation are labelled with the recessional velocity with respect to gas at rest on the disk surface. Negative velocities refer to approaching gas while positive numbers refer to receding gas. It looks as if the wispy prom component had a significant recessional velocity component. Was this gas in the process of being ejected?

Anyway, it's good to be making spectroheliograms again! Hope you enjoy.

Cheers.
Peter

Peter, these are exceptionally good spectroheliograms. The quality is amazing.

The prom animation is absolutely fascinating and it would also be interesting to see these images stacked in colour, 'blue to red' to show in one image the entire prom and its velocity field.

Excellent.

Stu.

Absolutely wonderful Peter, a thoroughly enjoyable and informative post, the animation is incredible together with marvellous views of the sun. I do like the He D3 how it is completely inverted to Halpha or CaK view



Alexandra

Fascinating post and excellent images Peter! Love it!

Very interesting to see/read Peter. Nice work.

when it comes to this
you are truly
"Peter The Great"

Thanks for the comments, everyone (and the SPOD!).

Stu: Your idea of stacking these images as individually coloured frames is a good one. I'm not sure how to interpret the colour mixing that would result though. It seems to me the colour associated with some particular frame (and the associated velocity) would be lost in the mixing. I have to give this more thought. I have written a routine to calculate the doppler shift associated with an individual pixel in an image (using the spectrum associated with that pixel) and will experiment with this a bit more. In the meantime, here are some dopplergrams for this particular prominence. Orange (blue) regions correspond to receding (approaching) gas moving at, roughly, the velocities (km/s) indicated by the numeric labels. This gives an idea of which portions of the prominence are moving in what line-of-sight direction and at what speed (with respect to stationary gas at solar disk centre). The high-altitude, wispy portion of the prom and the coronal loop seem to clearly display opposite and fairly substantial line-of-sight velocities.

Cheers.
Peter

I really like that Peter!!

Alexandra

These spectroheliograms are facinating ! Thanks for sharing.
Le CN line is interesting. We don't see a lot of CN images.

very nice spectroheliograms. excellent !
Phil

Thanks Alexandra, Christian and Phil.

Christian: The CN molecular band image looks quite similar to images in the CaK wings. There is professional interest in the CN bandhead because the magnetic bright points, usually studied in the CH molecular G-band, show about a 40% higher contrast in the CN band. Of course, viewing these would require excellent imaging at high spatial resolution, something I'm not capable of with the spectroheliograph.

Prominence analysis:
For the sake of interest, I went a bit further in spectral analysis of the SW limb H alpha prominence. I've chosen a number of points of interest in the image of the prominence (correctly oriented) and present the corresponding spectra.
Position 1 corresponds to the quiescent prom to the north of the large prom and its emission spectrum is peaked at the same location as the disk H alpha absorption so I've used it as a reference for line-of-sight velocity. I did the same with the dopplergrams above so the spectral analysis here is complementary to the dopplergram results. At position 2, I observed a double peaked emission spectrum indicating that light originating from this location in the prominence arises from both receding and approaching clouds of gas. Position 3 locates a fainter region of the prominence at which I observed one of the higher values of the doppler shift, corresponding here to a recessional (red shift) velocity of about 41 km/s. Position 4 is located at the brightest part of the loop prominence and exhibits a slight blue shift corresponding to a velocity of about 7 km/s.

Hope you find this interesting.
Cheers.
Peter

Interesting?.... Absolutely, Peter.

I’m fascinated when I watch prom animations and observe the complex movements of the ionised gases, but these really only provide 2D views of these movement in the plane of our monitors. Your Dopplergrams provide that missing 3rd dimension along the line of sight, providing yet further insight into the dynamics of these formations.

You should collaborate with a University and publish your excellent work.

Stu.

Fascinating work, Peter!

Frank

Hi Frank and Stuart.

Thanks very much for your feedback!

I've expanded my analysis a little and took a look at the large SW limb prominence in the CaK line. The prom looks different (more structured?) in CaK versus H alpha. The CaK data was taken about 45 minutes after the H alpha data so, in addition to any fundamental differences between the H alpha and CaK cases, the prom was evolving in shape during this elapsed time as well.

The first animation is of a spectral sequence through the CaK line. The wavelength offset (from Ca K3 line centre) in angstroms is shown in the upper left corner...positive offsets indicating shifts to longer wavelengths (toward the red). This time I'm presenting corresponding dopplergrams as an animation as well (as opposed to the series of static images I showed for H alpha). The line of sight velocity is shown in the upper left corner. Regions of receding gas are shown in red and approaching gas in blue.

Spectral Sequence: Dopplergram Sequence: The portion of the prominence that is receding looks very curious and persists out to 100 km/s! It's interesting to try and envision how this gas is actually moving.

Cheers.
Peter

Great science Peter!

hi peter

as always your our master!

thanks for sharing your results and giving us some ideas!

Thanks Mark and Vincent.

You can extract a huge amount of data from a typical SHG observing session. Spectra of prominences, filaments and active regions are fascinating and can often reveal surprises.

Thanks again.
Peter