Wavelength measurements of heliumlike 1s2s ³S₁-1s2p ³P_0,2 transitions in Ne⁸⁺, Na⁹⁺, Mg¹⁰⁺, and Si¹²⁺ emitted by solar flare plasmas

Abstract

With the Solar Ultraviolet Measurements of Emitted Radiation instrument-a high-resolution normal-incidence telescope and spectrometer on board the Solar and Heliospheric Observatory-heliumlike 1s2s ³S₁-1s2p ³P_0,2 transitions in the highly ionized species Ne⁸⁺, Na⁹⁺, Mg¹⁰⁺, and Si¹²⁺ were observed. The spectral lines were emitted by high-temperature solar flare plasmas. In this paper, we report on wavelength measurements of the He-like lines identified in the recorded spectra. The wavelength uncertainties we obtained from the solar measurements are <=20 mÅ(1σ), and in one case <=30 mÅ. This is comparable to or better than the best determinations so far achieved for these heliumlike 1s2s ³S₁-1s2p ³P_0,2 transitions with instrumentation in the laboratory. For the Na^{9+ 3}S₁-³P₂ transition we report what is to our knowledge the first wavelength measurement. The knowledge of the accurate wavelengths can provide important checks on atomic structure calculations.