van der Tak et al. (2003) argued that the non
of the 25 m line corresponds to an upper limit to the atomic sulphur of
computed by considering line absorption.
Indeed, this is an upper limit on the S abundance in the absorbing
gas, i.e. the
foreground cold gas, rather than the hot gas. The upper limit on the
emitting hot core
gas is much higher, as explained in the text.