Helium in the solar spectrum.

[Merlin66]

The emission line of He1 (known as D3) lies at 14.32A towards the blue from the D1 Sodium line (The doublet D1 and D2)
The intensity of the D3 line is only about 3% above the local continuum.
To make a visible image of the Sun in Helium the continuum image must be subtracted from an image acquired at D3.


According to SimSpec_SHG for the MiniSHG optics, the D3 line should be at 207.43 pixel below the D1 line.


The INTI software allows this offset to be entered (as well as a suitable offset to obtain a continuum image)
Initial trials today were washed out due to cloud and the limited SER videos obtained were overexposed. Bumma!

They did however verify the methodology and the "best" D3 seemed to be around 207 pixel offset. A couple of Helium "plumes" were easily visible.
(about 1 O'clock and six O'clock)


[Edit] When the slit is positioned at the extreme edge of the disk it's possible to see the D3 Helium line in the spectrum close by the D1 Sodium.
The D3 is the bright line and the D1 is the dark absorption line below.


Looks like cloud/ rain through to next Tuesday......
Onwards and Upwards.

[JA]

[American cowboy accent] ...... That's some fancy shootin' there Ken to extract info from such a small difference in wavelength. It's a pity there's not an ultranarrow bandwidth optical filter to split the 1.4 odd nanometer difference for us mere mortals. Well done

Best
JA

[Merlin66]

That's the strength of the Spectroheliograph.
Multi wavelength solar imaging without the embarrassing cost of multiple extreme-narrowband filters!!!
For the cost of one filter, you get the lot in one box!

[Merlin66]

Another day, another trial.
An unusually bright day. This allowed further trials with the imaging of the Sun in Helium (D3) light.
Less exposure times than previous, used the -207 pixel offset for the D3 and a -180 pixel offset for the background continuum.
Processed using both Doug and Matt's versions Valerie's INTI software.
I think I may be getting close.;)
Enjoy!

[Derek Klepp]

Interesting work Ken.I’m always amazed that the plumes are visible in much more than just Ha.
Derek

[Merlin66]

The MiniSHG seems to be capable of pulling out proms in H alpha, Helium and in CaK and CaH.
It’s a good option for solar imaging!