Hα images of CRL 618 (top) and OH 231.8+4.2 (bottom) from the Hubble Space Telescope with their respective dust continuum emission [(red contours in steps of ∼3σ × (0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9)] from the SMA observations, superimposed. Both PPNe show a clear asymmetry and the submm emission is roughly elongated in the direction of the outflows (see more details in the text). The positional offset of the continuum peak and (0, 0) position is stated in Sections 2 and 3 for both objects. North is up and east is left in all frames.