Title: First detection of sign-reversed linear polarization from the forbidden [O I] 630.03 nm line,
Abstract: We report on the detection of linear polarization of the forbidden [O i]
630.03 nm spectral line. The observations were carried out in the broader
context of the determination of the solar oxygen abundance, an important
problem in astrophysics that still remains unresolved. We obtained
spectro-polarimetric data of the forbidden [O i] line at 630.03 nm as well as
other neighboring permitted lines with the Solar Optical Telescope of the
Hinode satellite. A novel averaging technique was used, yielding very high
signal-to-noise ratios in excess of $10^5$. We confirm that the linear
polarization is sign-reversed compared to permitted lines as a result of the
line being dominated by a magnetic dipole transition. Our observations open a
new window for solar oxygen abundance studies, offering an alternative method
to disentangle the Ni i blend from the [O i] line at 630.03 nm that has the
advantage of simple LTE formation physics.