Velocity and FWHM comparison for CH₃OH, H₂CO, and HCO. Top panel: velocity difference between H₂CO and CH₃OH versus the difference between HCO and CH₃OH. Middle and bottom panels: comparison between the FWHM measured for HCO and CH₃OH (middle) and that measured from CH₃OH and H₂CO (bottom). The dotted line indicates FWHM[HCO] = FWHM[CH₃OH] or FWHM[H₂CO] = FWHM[CH₃OH]. The HCO data for 19383+2711 is missing from all panels, for which the resulting fit parameters are affected by the unresolved second velocity feature (see Sect. 4.3).