UV TRANSIENT BRIGHTENINGS ASSOCIATED WITH A CORONAL MASS EJECTION

Abstract

In this paper, we analyze transient UV brightenings in spectra acquired by SOHO/UltraViolet Coronagraph Spectrometer (UVCS) on 2003 June 2 in association with a coronal mass ejection (CME) that occurred at the West limb of the Sun at 08:54 UT. Brightenings have been observed in lines from cool (C III, O VI), intermediate (Si VIII, Si XII), and high ([Fe XVIII]) temperature ions over about 7 hr from the CME. Brightenings in cool lines are interpreted in terms of mini-ejections that appear at the time of, and after, the passage of the CME front through the UVCS slit. We give here their temperature and density and we point out that, assuming a spherical shape, a few of these mini-CMEs can provide a mass comparable to that quoted for typical CMEs. Hot lines, like the [Fe XVIII] line at 974.9 A which shows up in the CME associated current sheet (CS), undergo transient brightness as well, but hot lines brightenings are more difficult to interpret. We propose here a scenario where they are signatures of the passage through the UVCS slit of plasmoids similar to those observed in the filamentary CS of the magnetotail that form as a consequence of the tearing-mode instability or of a time-dependent Petschek-type reconnection.