Integrated spectra of SO 7₆−6₅ (red), SO 6₆−5₅ (blue), and ³⁴SO 5₆−4₅ (green). The integration area for each source is listed in Table B.1 and the ³⁴SO 5₆−4₅ spectra have been multiplied by three, for a better comparison. Black arrows in the panels that correspond to Per-emb 12 B, Per-emb 13, Per-emb 27, Per-emb 29, and Per-emb 44 indicate an offset emission, likely related with a transition from an unidentified COM.