The physical origin and magnetic sensitivity of the scattering polarization observed in the O ! IR triplet at 777 nm

A crucial first step toward its scientific exploitation is understanding the physical origin of the observed spectral line polarization and its magnetic sensitivity via the Hanle and Zeeman effects.

Here, we study the linear polarization signals observed in the IR triplet of O I at 777 nm, describing in detail the multilevel radiative transfer calculations that allowed us to decipher their physical origin. We investigate the sensitivity of the calculated scattering polarization signals to various modeling parameters, finding that the observed fractional linear polarization pattern originates mainly in the solar chromosphere, although the intensity profiles of the O I IR triplet come mainly from the lower photosphere.