Top: spectrum of H¹³CN (2–1) obtained with the IRAM 30 m telescope (black histogram) toward L1157-B1, and NOEMA spectrum (red histogram) extracted from a circular region equal to the IRAM 30 m HPBW (). Bottom: same as top panel for DCN (2–1). In this case the IRAM 30 m HPBW is . All spectra have been smoothed to 1.4 km s^-1 velocity resolution. The vertical dotted line depicts the systemic velocity v_LSR = 2.6 km s^-1.