Continuum emission in contours overlaid on the optical HST image (Hubble Legacy Archive 2013) in M 2–9. Contours are shown at 4, 8, and 12σ and from then on with a spacing of 12σ (where the root-mean-square noise is 0.1 mJy beam^-1) as a solid line and at −4σ as a dashed line. The synthesized beam is 0.̋27 × 0.̋23 with the major axis PA = 122° and is drawn in the bottom right corner of the last panel. The ellipses delimiting the rims of the inner ring in Fig. 3 are also plotted here, centered at [+0.̋03, −0.̋03] according to the analysis in Sect. 6.