Flare in Oxygen? O I 7772, on 2026-02-03 Csillagtúra

2026.02.04. 10:56:47

O I 7772 divided by a nearby continuum, stretched. Showing prominences, excess light on sunspots, darkening on active regions, and a dark shadow where the flare occurred at around 2026-02-03 07:49Z

Active region 4366 shows quite the flares. I observed the Sun at around local noon, at the infrared oxygen triplet at 777nm, focusing on the O I 7772 line. Below I present data from two scans, UT 2026-02-03-0727 with little indication of flaring, and UT 2026-02-03-0749 with clear signs of something going on.

I see what seems to be a clear indication of flaring: regions in oxygen go darker when other wavelengths shine, somewhat like He I D3 does — albeit I’ve seen bright helium flares in both D3 and even in He I 5016 before. Instrument: the modified Sol’Ex spectroheliograph, with the 1800 ln/mm grating, and a front mounted full aperture Edmund Optics filter, CWL 775nm FWHM 25nm OD4. With the refractor thus stopped down to about 46/400, I recorded a time series. General observing conditions were poor, with passing clouds and bad seeing.

Processing: reconstructing the disks of the wavelength and a chosen continuum, dividing and stretching the two, and various other scripts for other kinds of output.