The chromosphere as imaged in O I 777.2 nm

We have observed the strongest line in the IR triplet of neutral oxygen 777.2 nm using SST/CRISP. The aim is to better understand the formation of this line and its possible use for chromospheric diagnostics. We investigate the emission outside the solar limb. The observations are compared with synthetic spectra computed for different FAL atmospheric models using the RH code. So far, our results suggest that the off-limb emission follows the variations of the line opacity which is very temperature sensitive. Regions with low emission, like a dark gap often seen close to the limb, thus indicate cooler temperatures.