Measurements of H I and O VI velocity distributions in the extended solar corona with UVCS/SOHO and UVCS/Spartan 201
Romoli, M.; Raymond, J. C.; Naletto, G.; Cranmer, S. R.; Modigliani, A.; Poletto, G.; Ciaravella, A.; Fineschi, S.; Benna, C.; Giordano, S.; Michels, J.; Antonucci, E.; Noci, G.; Nicolosi, P.; Spadaro, D.; Huber, M. C. E.; Strachan, L.; Tondello, G.; Gardner, L. D.; Siegmund, O. H. W.; Karovska, M.; Martin, R.; Pernechele, C.; Smith, P. L.; Panasyuk, A.; Kohl, J. H.
United States, Italy
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 A˚ line profiles in polar coronal holes of the Sun at projected heliocentric heights between 1.5 and 3.0 R_solar. UVCS/SOHO also measured line profiles for H I 1025.72 A˚, O VI 1032/1037 A˚, and Mg X 625 A˚. 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_solar, are comparable at about 1.7 R_solar and become significantly larger than the H^0 velocities above 2 R_solar. 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.