Panel a: distribution of the circularly averaged specific intensity normalized to the peak value as a function of radius toward B1b-S and B1b-N. The gray lines show the analytical fits and the dotted lines the beam profiles. The upper scale presents the baseline in meters corresponding to the angular scale. Data for B1b-N are displayed in blue and data for B1b-S in red. Panel b: dust temperature (T_d) radial distribution, assuming that the 350 GHz emission is optically thick, with a minimum value set to 12 K. Panel c: molecular hydrogen density, using the derived T_d and assuming optically thin emission. This represents a lower limit to the real density. The dashed lines show the densities, assuming a constant value of the dust temperature. Panel d: cumulative mass distribution obtained by combining the information at 350 and 32 GHz.