Identification of Three Weak Lines and Their Influences onDiagnostics of Electron Temperature and Density in Astrophysical Plasmas

Abstract

By comparing of the spectra from the Chandra LETGs observation with thesynthetic spectra of argon, we identify two weak emission lines, thatis, the Ar XV 27.470 A line with transition2s3p 1P1−2s2 1S0 and the Ar XVI 27.872 A line withtransition 3d 2D3/2−2p 2P1/2, which blend with the NVII Lyα emission line. Severalsecond-order spectral lines are also identified, one of which isthe second-order Fe XVIII 14.534 A line withtransition 2p4(3P)3d 2F5/2−2p5 2P3/2, whichblends with theinter-combination line of He-like N VI. In order to study the effects ofthese new identified weak lines on the electron temperature anddensity, we diagnose the two parameters using the intensity ratioof triplets of the He-like N VI and that of resonance lines of H-and He-like N. In the literature, there is a discrepancy of thetemperatures deduced from N VI from other He-like ions, suchas C V and O VII. The discrepancy disappears after thecontribution of these weak lines is taken into account.