Wavelength measurements of heliumlike 1s2s 3S1-1s2p 3P0,2 transitions in Ne8+, Na9+, Mg10+, and Si12+ emitted by solar flare plasmas -: art. no. 022502

With the Solar Ultraviolet Measurements of Emitted Radiation instrument-a high-resolution normal-incidence telescope and spectrometer on beard the Solar and Heliospheric Observatory-heliumlike 1s2s S-3(1) -1s2p P-3(0,2) transitions in the highly ionized species Ne8+, Na9+, Mg10+, and Si12+ were observed. The spectral lines were emitted by high-temperature solar hare 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 less than or equal to 20 m Angstrom(1 sigma), and in one case less than or equal to 30 m Angstrom. This is comparable to or better than the best determinations so far achieved for these heliumlike 1s2s S-3(1) -1s2p P-3(0,2) transitions with instrumentation in the laboratory. For the Na9+ S-3(1)-P-3(2) 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.