Measurements of H I and O VI velocity distributions in the extended solar corona with UVCS/SOHO and UVCS/Spartan 201

Abstract

The Ultraviolet Coronagraph Spectrometer on the Solar and Heliospheric Observatory, UVCS/SOHO, and the Ultraviolet Coronal Spectrometer on the Spartan 201 satellite, UVCS/Spartan, have been used to measure H I 1215.67 Å line profiles in polar coronal holes of the Sun at projected heliocentric heights between 1.5 and 3.0 R ⊙. UVCS/SOHO also measured line profiles for H I 1025.72 Å, O VI 1032/1037 Å, and Mg X 625 Å. The reported UVCS/SOHO observations were made between 5 April and 21 June 1996 and the UVCS/Spartan observations were made between 11 and 12 April 1993. Both sets of measurements indicate that a significant fraction of the protons along the line of sight in coronal holes have velocities larger than those for a Maxwellian velocity distribution at the expected electron temperature. Most probable speeds for O 5+ velocity distributions along the lines of sight are smaller than those of H 0 at 1.5 R ⊙, are comparable at about 1.7 R ⊙ and become significantly larger than the H 0 velocities above 2 R ⊙. There is a tendency for the O 5+ line of sight velocity distribution in concentrations of polar plumes to be more narrow than those in regions away from such concentrations. UVCS/SOHO has identified 31 spectral lines in the extended solar corona.