Average double side band (DSB) spectra of H- and V-polarizations for the three positions O1, O3, and O4 in the ρ   Oph   A cloud core, shown for the range 484.65 GHz to 489.85 GHz. The spectral lines are found exclusively in the lower side band (LSB) and the LSR velocity, υ_LSR, along the abcissa is in km s^-1 and the antenna temperature T_A along the ordinate in mK. a) 5 GHz wide band of the WBS around the 487 O₂ line ( − 1600,    + 1600 km s^-1). b) The WBS spectrum at expanded scale, showing the O₂ line at 487 GHz, which is detected in all three positions. Inspection of the individual on-off pairs suggests that the apparent absorption features next to the lines are not real but simply due to the noise. c) Similar to b) but for the corresponding HRS data.