In this configuration there is a lot of freedom for the location of the synthetic stellar lines which can artificially enhance the interstellar line or, alternatively, make it disappear almost completely. We thus use several options for the S II absorption profiles defined by an envelope of around the fitted continuum. Each interstellar absorption component is represented by the convolution of a theoretical Voigt profile with the instrumental profile. The software also allows us to fit the lines from several elements simultaneously, which leads directly to a coherent solution for all species in terms of velocity, temperature and turbulent velocity. The histogram-style tracings represent the observations, and the smooth solid lines indicate the fits to the interstellar absorption profiles.
Dotted lines indicate the assumed stellar continua and the individual component contributions.
The spectra have previously been divided out by a stellar absorption profile, as explained in Sect.