S I emission in EUV spectra of late-type stars.

Abstract

Observations of strong neutral sulfur emission lines in the EUV spectra of late-type giant and supergiant stars are discussed. Low- and high-resolution spectra of Alpha Tauri and Beta Gru are presented which demonstrate the contribution of the S I (UV 9) multiplet to the observed features at approximately 1296 A as well as the strong O I multiplet at 1304 A. S I lines which must be taken into consideration in the analysis of stellar spectra are also found at 1807.34, 1820.36 and 1826.26 A (UV 2) in the vicinity of Si II lines, at 1900.27 and 1914.68 A (UV 1), at 1474.0 and 1474.4 A (UV 3), and possibly near 1640 A (UV 5). Evidence of photoexcitation and high line opacities of neutral S is pointed out, and it is noted that the opacities together with absolute fluxes can provide information on atmospheric structure.