Continuum optical depth derived towards L1551 IRS5 at the resolution of $1\stackrel{″}{.}0$. Panels a and b show the values of τ derived at 1.3 and 3.0 mm, respectively. White contours follow those in Fig. 1. Crosses indicate the coordinates of the extraction regions associated with the profiles in Fig. C1 (see text Sect. 4). Maps are masked at 3σ and the beams are shown in the upper corners.