Spectro-astrometric analysis of spectral lines of ISO 143 for three different observing times and slit PAs. Top row: photospheric line K I λ7699 as a test for artifacts, middle row: FEL of [S II] λ6716, bottom row: FEL of [S II] λ6731. For each case, we display the line profiles in the top panels, which are the average of 8 pixel rows in the spatial direction centered on the continuum after continuum subtraction, and the spectro-astrometric plots in the bottom panels, which show the spatial offset vs. radial velocity of the continuum (black asterisks) and of the continuum subtracted spectral line (red squares). Velocities are given relative to the stellar rest velocity V₀ of ISO 143.