Analysis of Extreme‐Ultraviolet Off‐Limb Spectra Obtained with SUMER/SOHO: Nevi/MgviEmission Lines

Publisher Website
Google Scholar
Abstract
We present results from a study of extreme-ultraviolet (EUV) off-limb spectra. These were obtained on 1996 June 20 with the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) instrument on the Solar and Heliospheric Observatory (SOHO). With the capabilities of SUMER, we rastered the emitting source from 40'' off the limb outward, and secured a unique, high-quality set of high-resolution EUV spectra. The scientific objective of this observing sequence was to record Ne VI and Mg VI intercombination/forbidden lines, which provide good possibilities to study the relative element abundance of Ne (high FIP) and Mg (low FIP) in transition-region emission in the corona, and the electron density in the solar atmosphere. While this observing sequence produced excellent spectra of the Ne VI and Mg VI lines, the occurrence of a dynamic event in the corona is an added bonus of the program. We also observed several other bright, as yet unidentified lines. Among these are lines that have been observed for the first time. Using the new data, we have been able to deduce the plasma density and relative element abundance in the source. In addition, improved values of the wavelengths of the Ne VI and Mg VI intercombination/forbidden lines have been obtained. Possible identifications of the bright lines not previously observed, along with their measured intensities, are discussed.