Top panel: integrated CO J = 2–1 emission of the L1157 bipolar outflow (Bachiller et al. 2001). Offsets are with respect to the driving source L1157-mm (black star), at coordinates: α_J2000 = 20^h39^m062, δ_J2000 = + 68°02′160. The black triangles and labels indicate the main blue- and red-shifted knots as defined by Bachiller et al. (2001). Circle is for the largest HPBW of the present dataset (40″), centred on the L1157-B1 bow shock. Bottom panel: the L1157-B1 bow shock as traced by the CH₃CN J = 8–7 K = 0,1,2 emission at 3 mm, observed with the IRAM PdB interferometer (Codella et al. 2009).