WIP/DRAFT
The first light of my spectroheliograph was in the summer of 2024. It was a stock Sol’Ex, with a modified setup, using full aperture bandpass filters as an energy rejection method, instead of the recommended full spectrum ND filter or Herschel prism, flooding the instrument with the right kind of wavelength, while also managing the thermal load and keeping the zero order and any internal spectral fog at bay. I quickly left the comfort of the Fraunhofer lines, and stumbled into prominences in „unknown” wavelengths[1], a frustrating experience that lead me towards literature, and also propelled me to create the atlas of spectroheliograms[2].
In the meanwhile, almost as a side project, dedicating telescope time to this in an on and off manner, I started to hunt down prominences in various spectral regions and lines, some known and expected, some not so much. Thus today I know that the ultraviolet „unknown” wavelengths showing prominences were most likely the magnesium triplet around 383nm, that Paschen hydrogens are dwarfed by not just Balmer hydrogens but also by the helium at 1083nm, which shows coronal holes, just like the yellow and the deep red helium do. I’ve seen the hydrogen ladder almost up till the Balmer break, and seen that neutral calcium is something worthy to at least check for prominences, that the infrared oxygen triplet can do very funny stuff, with obvious prominences, and that ionized metals show dark plages and often times prominences that are easier to see than some helium lines.
| Wavelength [Å] | id | prominences | filaments | plages | flares | corona | notes, comments |
| 3706 | Ti II | n/o | n/o | darker | n/o | link darkened plages, a typical image of ionized metals |
|
| 3797.9 | H I | harder | very weak, some are visible if extracted against a continuum |
some mottling, when extracted | n/po | link
H 10 (theta) very anemic, even compared to H 9 |
|
| 3829.37 | Mg I | weaker in the triplet, but there | n/o | bright | n/o | link | |
| 3832.31 | Mg I | medium | n/o | bright | n/o | link
extracting against a continuum can easily reveal the prominences |
|
| 3835.4 | H I | medium | n/o | darken the continuum’s bright plages, mottled like delta, when extracted |
bright | H 9 (eta)
even more anemic than the lower H lines |
|
| 3838 | Mg I | medium | hard but there | bright | bright, flaring prom | part of a triplet
fainter prom than the H 9, but still obvious far enough from H 9 (eta) to not blend |
|
| 3888.65 | He I | n/o | n/o | n/o | in the Sol’Ex, more or less blends with the H 8 line | ||
| 3889 | H I | medium | hard but probably there | darken the continuum’s bright plages, mottled like delta, when extracted |
bright | H 8 (dzeta)
when extracted against a continuum, looks like epsilon, which in turn looks like an anemic delta |
|
| 3914 | Ti II | n/o | n/o | darker | n/o | link darkened plages, a typical image of ionized metals |
|
| 3933.7 | Ca II | trivial | easy | very bright | bright | the Ca II K line | |
| 3968.5 | Ca II | trivial much brighter than Hε |
easy | very bright | bright | the Ca II H line | |
| 3970 | H I | medium, dwarfed by Ca II H |
sometimes | darken the continuum’s bright plages,mottled like delta, when extracted |
bright | Hydrogen epsilon
extracting against a continuum can easily reveal a disk |
|
| Wavelength [Å] | id | prominences | filaments | plages | flares | corona | notes, comments |
| 4077.7 | Sr II | medium | n/o | somewhat darker | n/o | link
extracting against a continuum can easily reveal the prominences |
|
| 4102 | H I | less easily | sometimes | as darker mottled areas | n/o | Hydrogen delta.
The last hydrogen in the Balmer series visible without extracting against a continuum. When epsilon is extracted, looks like an anemic delta |
|
| 4215.5 | Sr II | medium | n/o | somewhat darker | n/o | link
just like for 4308, an automated script can reveal prominences that are bright and dense enough |
|
| 4227 | Ca I | medium | n/o | bright | n/o | link
just like for 4308, an automated script can reveal prominences that are bright and dense enough |
|
| 4247 | Sc II | n/o | n/o | darker | n/o | link darkened plages, a typical image of ionized metals |
|
| Wavelength [Å] | id | prominences | filaments | plages | flares | corona | notes, comments |
| 4300 | Ti II | easy to hard | n/o | n/o | as below | ||
| 4302 | Ti II | medium to hard | n/o | n/o | as below | ||
| 4307.9 | Fe I,
Ca I, Ti II |
easy, mostly medium, sometimes hard | n/o | brighter | bright | the darkest line of the Fraunhofer G-band,
iron, calcium and titanium blend together at the sol’ex’s resolution. Scripted extraction makes it a routine to reveal prominences at this wavelength |
|
| 4313 | Ti II | easy to hard | n/o | somewhat darker | as above/below | ||
| 4314 | Fe II, Sc II | easy to hard | n/o | as above/below | |||
| 4315 | Ti II | easy to hard | n/o | n/o | Fraunhofer G-band link
bright prominences, without flaring, can show up right in the reconstruction |
||
| Wavelength [Å] | id | prominences | filaments | plages | flares | corona | notes, comments |
| 4340 | H I | medium-easy | dark dense ones are obvious | present as dark mottled areas | bright | Hydrogen gamma | |
| 4471.5 | He I | medium-easy | medium-hard | somewhat darker | n/o | light blanket above active regions at/beyond the limb |
for a novice, hard to even locate the wavelength |
| 4549 | Ti II, Fe II | n/o | n/o | darker | n/o | link | |
| 4554 | Ba II | n/o | n/o | darker, fainter signal | n/o | link | |
| 4861 | H I | easily, but fainter than Hα | easy | some are bright, most are dark-mottled | bright | Hydrogen beta | |
| 5015.7 | He I | very hard | n/o | somewhat darker | a bright one observed | (?)light blanket above active regions at/beyond the limb |
hard to even locate without other lines used as a reference, or having a flare in it |
| 5018.45 | Fe II | medium-hard | n/o | dark | bright | for a novice, an unassuming dark line in the spectrum, but the solar disk reconstructed from this line can be outright shocking | |
| 5167 | Mg I | hard | n/o | brighter | n/o | for a novice, hard to even locate the wavelength | |
| 5169 | Fe II | medium | n/o | dark | n/o | while might blend with the nearby Fe I line, the plages are obviously darker than the quiet disk and the prominences, if flaring, can get brighter than those in Mg |
|
| 5173 | Mg I | medium-hard | some are obvious | brighter | bright | Mg I b2, of the triplet | |
| 5184 | Mg I | medium-hard | some are obvious | brighter | bright | Mg I b1, of the triplet | |
| Wavelength [Å] | id | prominences | filaments | plages | flares | corona | notes, comments |
| 5876 | He I | easily | some obvious on the raw disk reconstructions |
dark | both dark and bright | obvious coronal holes, when extracted against a nearby continuumlight blanket above active regions at/beyond the limb |
He I D3, link
Due to CMOS loosing sensitivity Easy to locate due to the |
| 5890 | Na I | medium-hard | some are obvious | brighter | bright | Na I D2 | |
| 5896 | Na I | medium-hard | some are obvious | brighter | bright | Na I D1 | |
| 6141.7 | Ba II | n/o | n/o | dark | n/o | a typical ionized metal disk with darkened/dark plages | |
| 6563 | H I | trivial | trivial | bright | bright | Hydrogen alpha | |
| 6678 | He I | hard | nothing obvious on the disk |
nothing obvious on the disk |
n/o | some light blanket above active regions at/beyond the limb |
for a novice, hard to even locate the wavelength link |
| 7065 | He I | easily | harder | darker | n/o | coronal holes revealed when extracted against a nearby continuumlight blanket above active regions at/beyond the limb |
a weaker twin of the He I D3 |
| 7772 | O I | easily, some with Doppler |
maybe? | somewhat darker | darkening flares observed, some with obviously red shifted absorption |
light blanket visible above active regions at/beyond the limb(?)dark smudges(?) on the disk, (?)maybe related to hot spots in the corona(?) |
the stronger one of the oxygen triplet
when extracted, shows a mottling |
| 8542 | Ca II | trivial | obvious | much brighter | bright | one of the Ca II triplet in the infrared
looks like an anemic version of the Ca II K/H, these line are somewhat like Hβ is to Hα |
|
| 8806 | Mg I | n/o | n/o | brighter | n/o | A few sessions dedicated to this line revealed no prominences, albeit according to gong, there were no bright ones at the time |
|
| 10830 | He I | obvious | obvious | darker | dark ones observed | a direct line reconstruction yields obvious coronal holes, light blanket visible above active regions at/beyond the limb |
historically „the” helium line, requires special instrumentlink |
| 10940 | H I | dwarfed by the nearby helium |
n/o | somewhat darker | n/o | Paschen gamma, requires special instrumentWhen extracted against a nearby continuum, the result is similar to an anemic H delta or an extracted epsilonlink |
From the above table:
- n/o not observed, not occurred, none while observing (according to helioviewer) etc.
- light blanket: much like in SDO AIA, at and beyond the limb, above active regions, excess light is observed, especially after extracting against a continuum
- extraction against a continuum: subtraction, division, log/log etc.
[1] shortly after my first light, I observed this prominence that I couldn’t solve at the time //csillagtura.ro/wp-content/uploads/2025/03/d9390877-576c-43bf-98bb-c01ff3271a18.jpg
It was maybe the flaring prominence at 8 o’clock on the disk, on UTC 2024-07-12 10:12 … I might have the raw data somewhere.
[2] https://iopscience.iop.org/article/10.3847/2515-5172/adef50 and //csillagtura.ro/atlas
