On 2025-01-12, I imaged the Sun in He I D3. Using my scripts to extract the weak signal, I got able to show features otherwise characteristic of the corona. I stacked a total of 72 scans, spanning between 2025-01-12-0741Z and 2025-01-12-0933Z. Basically, I imaged the fingerprint of the giant coronal hole.
The Helium I D3 line, unless one knows exactly what to look for, is elusive to put it mildly. Hence the secret. And the poet, Attila JÓZSEF warned us: a titkokat ne lesd meg. So let’s take the spectroheliograph and image the Sun ostinatamente. 78 scans went into this image on 2024-11-02.
Using the spectroheliograph and the ~30nm wide sodium ERF filter, I imaged the Sun in the He I D3 spectral line. Recordings processed with JSol’Ex, and details enhanced by the script below. For the final images, about forty individual frames (reconstructed scans) were stacked.
Fun fact, the light triangle in the lower half of the image corresponds to a dark feature in the corona, as seen on the SDO AIA 211 image.
One day after the X1.8 flare, business as usual on the Sun. I collected 40 scans in the Helium I D3 line, spanning about 40 minutes — so if there were any small scale details to begin with, they are probably lost.
He I D3 enhanced, heavy wizardry
The Sun on 2024-09-13, around the CaH line, also touching Hydrogen epsilon. Pixel shifts range from -36 pixels (blue wing) to +40 pixels (red wing), meaning somewhere around -2..+2 Å in total, give or take.
I combined some spectroheliograph data with the etalon, Sol’Ex at 62/400 with Lunt CaK B1800 at 102/1100.
Solar disk in Altair Astro’s 3nm CaK Ultra filter, enhanced contrast
I got a new filter to pudding-test: Altair Astro’s 3nm Calcium K Ultra, stated to have 3nm FWHM and a very high transmission. Let’s see how it performs.
Before we jump in, let me also present some information I compiled along the way, and some theory and links fellow amateur astronomers may find useful.
Important note: this article is not sponsored by the vendor, and the vendor has not influenced the conclusions presented below in any way.
With a front ERF, Altair Astro’s Triband, 115mm, Tecnosky 102/1100 refractor, Lunt’s CaK B1800 and the ASI 533MM camera, I obtained the following:
CaK, 2.4Å
CaK 2.4Å, colorized
With a Tecnosky 102/1100 refractor, Herschel prism, ND 0.96, a filterwheel and the ASI 533MM camera, I obtained the following:
Antlia 3nm hydrogen alpha. The disk is clearly continuum, but the prominences were obvious even on the live view
Altair Astro’s G-band filter, 2nm fwhm at around 430nm cwl
Using a fairly new setup, as they were in the light train: Altair Astro Triband D-ERF 115mm, Tecnosky 102/1100 ED refractor, Lunt CaK B1800, ASI 533MM, along with my EQ3 with the home built controller, I captured the following frames.
full disk, linear light
full disk, paraboloid gamma curve
detail from the full disk
same, colorized
