CO and HCN line profiles for IRAS 4A, IRAS 4B, and IRAS 4C (bottom to top). Note the absorption toward all positions. IRAS 4A shows a broad wing component, followed by IRAS 4B, but IRAS 4C shows a steep line profile and only a very narrow red wing in both CO and HCN. The heavy absorption toward IRAS 4C makes it difficult to fit accurate Gaussians. The vertical line at +6.7 km s^-1 indicates the ambient velocity of IRAS 4A and 4B.