V4334 Sgr spectra of the emission line detected with APEX. The width of the channels is 20 km s^-1 and the dotted vertical line corresponds to the systemic velocity of the source, v_sys = 125 km s^-1 (Duerbeck et al. 1997). The flux density in the right axis was calculated using the corresponding value of Γ shown in Table 1. Top: spectrum of the HCN (J = 4 → 3) emission. Bottom: spectrum of the H¹³CN (J = 4 → 3) emission. The arrows in the upper axis indicate the rest frequencies for the CO (J = 3 → 2) and H¹³CN (J = 4 → 3) lines.