A bright one and then more quiescent prominences in the G-band
In this post I show a bright prominence in the G-band spectrum, and examples that I can routinely show brighter quiescent prominences in both the G-band 4308Å and in the Ca I 4227Å lines.
Various setup configurations are used, Sol’Ex and ML Astro SHG 700 spectroheliographs, 42/400 (62/400 stepped down) and 80/540 refractors, various filters used as ERF to reduce the thermal load on the delicate parts of the optics. Two cameras provided the images, the ZWO 678MM (IMX 678) and Altair Astro 26M (IMX 571).
Just like climbers and mountaineers go for the peaks, because they are there, I went for more eight-thousanders, clearly showing prominences in under-observed, obscure or forgotten wavelengths. This time in the G-band. There is some personal precedence, so this is by far not the first observation, but perhaps the best one to date, that resulted in a data cube with an obvious signal. By now, I can routinely show some brighter, quiescent prominences in the main G-band spectral line, be that the Fe I 4308Å or more likely the Ca I 4308Å, and some adjacent ionized metal lines also.
At 4308, it is probably the Ca I line, although the Ca and Fe just blend together in my setup. On the one hand, Mg I and Na I is one side of the argument, not to mention the same prominences in Ca I 4227. On the other hand, I have seen Fe II, Ti II, Sc II, Sr II etc. prominences, also routinely, but Fe I not really, see here or here. So without claiming, I suspect Ca I to be the culprit here, not the iron, but I will stick with „G-band prominence” here.
This time there was an active prom that showed up directly in the spectrum simply through visual inspection of the raw video – which is unusual in these wavelength. Most prominences in these fainter lines, but also including the Mg b triplet in the green, show up through continuum subtraction, meaning they are likely the least significant bits or so in the data. I got lucky here, so article.
The spectrum confidently shows, just scrolling through the recording, the bright prom at both 4308Å and probably Ti II at 4300Å. With somewhat less confidence, Ti II 4313, Sc II and Fe II at 4314 and Ti II at 4315 also show something. Perhaps below threshold there seem to be some smears in other lines also, like Ti II 4302 marked on in one of the pictures, but maybe not the best example.
More than a year ago, I have already shown prominences in the G-band, just not routinely
a spectroheliograph setup, ML Astro SHG 700
spectroheliograph setup, stock Sol’Ex with a not-recommended camera that performs well: Altair Astro’s IMX 571 model
solex: slow but 16 bits camera, improvisations, motorizations, autoguider
Altair Astro’s G-band etalon, used as a prefilter/ERF
the etalon’s transmission
prefilters in their suitcase
the etalon in its holder inside the suitcase
Ersatz-Obsi, control panel
Ersatz-Obsi, monitoring station
2025-09-18-0729 UT, G-band 4308 prom (a stack of multiple frames)
2025-09-20-0714 UT, Gband prom (a stack of multiple frames)
2025-09-23-0850 UT, Ca I 4227 prom (a stack of multiple frames)
2025-09-23-0850 UT, Ca I 4227 disk (stack of multiple frames)
2025-10-09-1046, single frame sample
2025-10-09-1046, single frame, curves/sharpening
2025-10-09-1046 UT, five frames from a single scan (well under one second of scanning time) added together, and at the proms, an eventless region got subtracted to better show the signal
20251009104622Th gong, for reference
2025-10-09-1046 UT, single frame (ie. one single scan)
2025-10-09-1046 UT, single scan
2025-10-09, G-band proms, stack of multiple frames
And some more Ca I 4227 proms
2025-09-21, Ca I 4227, stack of the core of the line
continuum-subtracted, etc
further processed
