2007A&A...470..699C

Unlike silicon and calcium, sulphur is an α-element that does not form dust. Some of the available observations of the evolution of sulphur with metallicity indicate an increased scatter of sulphur-to-iron ratios at low metallicities or even a bimodal distribution, with some stars showing constant S/Fe at all metallicities and others showing an increasing S/Fe ratio with decreasing metallicity. In metal-poor stars Si lines of Multiplet 1 at 920nm are not yet too weak to permit the measurement of the sulphur abundance A(S); however, in ground-based observations they are severely affected by telluric lines. We investigate the possibility of measuring sulphur abundances from Si Mult. 3 at 1045nm lines. These lie in the near infrared and are slightly weaker than those of Mult. 1, but lie in a range not affected by telluric lines. We investigated the lines of Mult. 3 in the Sun (G2V), Procyon (F5V), HD 33256 (F5V), HD 25069 (G9V), and ε Eri (HD 22049, K2V). For the Sun and Procyon the analysis was performed with CO⁵BOLD 3D hydrodynamical model atmospheres, while the three other stars, for which hydrodynamical simulations are not available, were analysed using 1D model atmospheres. For our sample of stars we find a global agreement between A(S) from lines of different multiplets. Our results suggest that the infrared lines of Mult. 3 are a viable indicator of the sulphur abundance that, because of the intrinsic strength of this multiplet, should be suitable for studying the trend of [S/Fe] at low metallicities.