Doppler Shifts and Nonthermal Broadening in the Quiet Solar Transition Region: O VI

Abstract

Using observations from the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) experiment flown on the Solar and Heliospheric Observatory (SOHO) spacecraft, we have measured Doppler wavelength shifts and nonthermal broadening in the 1032 and 1038 Å emission lines of O VI and the 1036 and 1037 Å emission lines of C II. Near Sun center the C II lines exhibit an average redshift of 2 +/- 3 km s^-1, consistent with earlier observations in this temperature range. The O VI emission lines exhibit average Doppler velocities of 5 +/- 3 km s^-1, suggesting the presence of redshifted material at 2.9 × 10⁵ K. For the O VI lines, the average nonthermal component of the observed line width is 34 +/- 3 km s^-1.