LT Hα image (r′-band continuum subtracted and inverted) showing the region around the position of M31N 2008-12a (indicated by the red cross). The white circle, green ×, and magenta box indicate the catalogue positions of the centre of H ii regions, and the blue diamond the position of a star cluster (see text in Sect. 5 for details). The white-dashed ellipse (semi-major axis ) borders the elliptical nebulosity (semi-major axis ) around M31N 2008-12a and is to aid the reader. The position of the south-western knot is also indicated by the green ×. The four black dashed lines indicate the slit position of the four SPRAT spectra that include emission from the SW knot (see Sect. 5.2).