The Impact of Sunspots on the Interpretation of Coronal Observations of the O Vi Doublet

Due to their high intensity of emission in the O VI 1031.9 and 1037.6Å lines, even small sunspots on the solar disk can strongly influence the intensity of the radiative scattering component of O VI lines in the corona. Observations of O VI disk spectra show a 1032/1038 line intensity ratio of >2.6 in a sunspot compared to quiet disk values of ∼2. The enhancement of the 1032 line in comparison to the 1038 is likely due to interaction between molecular hydrogen emission from the sunspot and the chromospheric O. Modeling shows that a contribution from sunspots increases the coronal O VI 1032/1038 intensity ratio to values considerably higher than those achieved with a quiet disk or coronal hole spectrum. Therefore a re-examination of flow velocities derived from UVCS/SOHO streamer observations must be made. This modeling demonstrates that the inclusion of sunspots, when present, may lead to non-zero outflow velocities at lower heights in streamer cores in contrast to some existing model results. Subject headings: Sun: UV radiation: Sun: sunspots: Sun: corona