The spectra of singly and doubly ionized sulphur in the region λλ 3300-4900 a

Abstract

The atomic spectra of the elements of the oxygen group in various stages of ionization have been of increasing importance to spectroscopic theory in the last few years. Of no less prominence is their astrophysical importance : in the determination of stellar radial velocities, and in the study of stars of spectral types 0, B, and A, an accurate knowledge of wave-lengths in the high excitation spectra of these atoms is indispensable. For these reasons it has been disappointing to find that the published data on sulphur, in particular, are of inadequate accuracy. The early observations of EDER and VALENTA* and of EXNER and HASCHEK are incomplete and hardly reliable to 0.2 A. Wave-lengths listed by BHATTACHARYYA appear to be in error by amounts up to 0.5 A., whilst Ingram’s measurements in S II§ include only the stronger fines, and in S III|| only those which have been classified. Recent work of comprehensive scope is due chiefly to L. and E. BLOCH and to GILLES,** who unfortunately record many fines ascribable to impurities. In addition, the wave-lengths of their fines are sometimes in disagreement by as much as 0 • 1 A. It therefore seemed desirable to investigate the spectra S II and S III, beginning with the region of greatest astrophysical importance, viz., from X 3300 to X 4900 A., and taking particular care not only to obtain accurate wave-lengths, but also to exclude all impurity fines.