a) Spectra of the C¹⁸O 1  →  0 line toward AB Aur observed with the IRAM 30 m telescope by Fuente et al. (2002). We adopted this profile as a pattern profile for the ambient cloud emission. Vertical lines indicate the velocity interval [5.6, 6.4] km s^-1. b) Interferometric spectra of the ¹²CO 2  →  1 toward the star position (Fig. 2 (bottom) of Piétu et al. 2005). Note that the disk emission occurs at the velocity intervals, [4.2, 5.6] km s^-1 and [6.4, 7.25] km s^-1. These velocities are indicated by vertical dashed lines.