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Two of the most attractive spectral windows for spectropolarimetricinvestigations of the physical properties of the plasma structures in the solarchromosphere and corona are the ones provided by the spectral lines of the He I10830 A and 5876 A (or D3) multiplets, whose polarization signals are sensitiveto the Hanle and Zeeman effects. However, in order to be able to carry outreliable diagnostics, it is crucial to have a good physical understanding ofthe sensitivity of the observed spectral line radiation to the variouscompeting driving mechanisms. Here we report a series of off-the-limb non-LTEcalculations of the He I D3 and 10830 A emission profiles, focusing ourinvestigation on their sensitivity to the EUV coronal irradiation and the modelatmosphere used in the calculations. We show in particular that the intensityratio of the blue to the red components in the emission profiles of the He I10830 A multiplet turns out to be a good candidate as a diagnostic tool for thecoronal irradiance. Measurements of this observable as a function of thedistance to the limb and its confrontation with radiative transfer modelingmight give us valuable information on the physical properties of the solaratmosphere and on the amount of EUV radiation at relevant wavelengthspenetrating the chromosphere from above.

The influence of coronal EUV irradiance on the emission in the He I 10830 A and D3 multiplets