An astrophysical oscillator strength for the S ii 94.7-nm resonance line and S abundances in DLAs

Abstract

By using UV spectra for the O star HD 93521 taken with the ORFEUS II echelle spectrograph, we determine an `astrophysical' f value for the Siiλ94.7-nm line: f=0.00498-0.00138+0.00172, error at 1σ level. This is almost a factor of 30 smaller than the guessed value found in the Kurucz data base (f=0.1472), which was until now the only one available for this transition. We use our `astrophysical' f to investigate the S abundance in two damped Lyα absorption systems (DLAs) observed with the UV-Visual Echelle Spectrograph (UVES)Q3 at the European Southern Observatory's 8.2-m Kueyen telescope. In the case of the absorber at z_abs=3.02486 towards QSO 0347-3819, we find a sulphur column density which is consistent, within errors, with that determined by Centurión et al. by means of the λ125.9-nm line, thus providing an external check on the accuracy of our f value. For the damped absorber at z_abs=4.4680 towards BR J0307-4945, we determine a high value of the S abundance, which, however, is probably the result of blending with Lyα forest lines.