Three upper panels: spatial distribution of Hα, [S ii] λλ6716+30, and [O iii] λ5007 emission in a line passing by HD 37061 in the west-east direction (see Fig. 2), obtained from the corresponding WFC-INT images. The dashed red line indicates the position of HD 37061. The vertical dotted line indicate the western limit of M 43. Bottom panel: Hα/Hβ spatial distribution in the same line direction. Some dust features outlined by Smith et al. (1987) and the position and size of the ISIS-WHT slit are indicated. Horizontal dotted lines show the Hα/Hβ value in the M 43 west region.