Ultraviolet and Optical Observations of a Coronal Transient with SOHO
Thompson, B. J.; Raymond, J. C.; Modigliani, A.; Ciaravella, A.; Gardner, L.; Antonucci, E.; Kohl, J.; Noci, G.; Strachan, L.; Cyr, O. C. St.
United States, Italy
Abstract
A coronal transient was observed on 1997 March 6 at 1.6 Rsolar over an active region on the east limb. We observed both the edge of horizontally compressed gas and the diffuse curtain of coronal material. The region was monitored for 4 hr, and the H I Lyα, O VI λλ1031.91, 1037.61, N V λλ1242.80, 1238.80, and O V] λ1218.35 lines were detected during the ejection evolution. The density, velocity, temperature, and oxygen abundance of the ejected plasma have been obtained from the observed spectra. Intermediate temperature lines of N V, O VI, and O V show a large enhancement, suggesting a quite narrow range of plasma temperature around 4×105 K. Doppler shifts of the ejected material evolve from an initial blueshift of 100 km s-1 to a redshift of 145 km s-1. The outflow velocity, as determined by Doppler dimming analysis of the O VI doublet, is only about 20 km s-1.