Line profiles of SiO in the L1157-B1 shock. The line intensity in main-beam temperature (T_mb) from ²⁹SiO (red), and ³⁰SiO (blue) is over-plotted on the main isotopologue, ²⁸SiO (grey), by multiplying for their solar isotopic ratios ([²⁸Si/²⁹Si]_⊙ = 19.7, [²⁸Si/³⁰Si]_⊙ = 29.8, Anders & Grevesse 1989). The transitions are labelled. The baseline and the systemic velocity (+2.6 km s⁻¹, Bachiller et al. 2001) are indicated by the horizontal and vertical dotted lines, respectively. The vertical dashed lines indicate the three velocity intervals where the integrated intensity has been calculated: [−23, −13], [−13, −3], and [−3, +5] km s⁻¹, see Table 1. The red-shifted component that appears to be associated with ²⁹SiO 2− 1 is due to blending with the ¹³CH₃OH 4_1,3 –3_−2,2 line.