An astrophysical oscillator strength for the S ii 94.7-nm resonance line and S abundances in DLAs |
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Authors: | Piercarlo Bonifacio Elisabetta Caffau Miriam Centurión Paolo Molaro Giovanni Vladilo |
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Institution: | ;1Osservatorio Astronomico di Trieste,Via G.B.Tiepolo 11, I-34131 Trieste, Italy;2Istituto Magistrale S.P.P. e L. annesso al Convitto Nazionale Paolo Diacono, S. Pietro al Natisone Udine, Italy |
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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 S ii λ 94.7-nm line: f =0.00498?0.00138+0.00172 , error at 1 σ 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 Ly α absorption systems (DLAs) observed with the UV–Visual Echelle Spectrograph (UVES) 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 λ 125.9-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 Ly α forest lines. |
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Keywords: | atomic data stars: individual: HD 93521 ISM: abundances quasars: absorption lines quasars: individual: QSO 0347-3819 quasars: individual: BR J0307-4945 |
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