Scheme of the effect of a hot spot that rotates with the star affects the photospheric absorption lines. In A) we show the different parts of the stellar photosphere that produce the photospheric absorption lines. B) shows how the line is affected when a hot spot is included. When the absorption deficit associated with the spot appears blueshifted, the centre of the photospheric lines seems to move towards the red. When the spot appears redshifted, the centre of the absorption line appears shifted towards the blue. Small emission lines are visible within some of the photospheric absorption lines, tracking the local rotational velocity of the part of the stellar surface where the line originates. Non-photospheric lines or lines that are particularly strong on the spot could appear simply as emission lines over the continuum, without any underlying absorption.