  Aims: In this paper we aim to study the chemical evolution of sulphur in the
galactic disk, using a new optimal abundance indicator: the [SI] line at 10821
A. Similar to the optimal oxygen indicators, the [OI] lines, the [SI] line has
the virtues of being less sensitive to the assumed temperatures of the stars
investigated and of likely being less prone to non-LTE effects than other
tracers. Methods: High-resolution, near-infrared spectra of the [SI] line are
recorded using the Phoenix spectrometer on the Gemini South telescope. The
analysis is based on 1D, LTE model atmospheres using a homogeneous set of
stellar parameters. Results: The 10821 A [SI] line is suitable for an abundance
analysis of disk stars, and the sulphur abundances derived from it are
consistent with abundances derived from other tracers. We corroborate that, for
disk stars, the trend of sulphur-to-iron ratios with metallicity is similar to
that found for other alpha elements, supporting the idea of a common
nucleosynthetic origin.
