Left: integrated intensity (from 0 to 14 km s^-1) and velocity field of the H₂CO(2_0,2−1_0,1) line. Purple contours show the continuum emission at 145 GHz. The plus signs indicate the positions of B1b-N and B1b-S. The star shows the position of B1b-W. The black ellipse shows the beam size. The small panels show the centroid velocity towards B1b-N (top) and B1b-S (bottom) in km s^-1. Right: integrated intensity images (from 1.5 to 12.5 km s^-1) of the four CH₃OH lines detected towards B1b: from left to right and top to bottom: 3₀−2₀ A, 3_-1 − 2_-1 E, 3₀−2₀ E and 3₂−2₂ E. The intensity scale in K km s^-1 is given by the color bar on the right. Contours of the 3₀−2₀ A line are superimposed in all plots, ranging from 1 to 20 K km s^-1 with a step of 3 K km s^-1. Offsets are given relative to the pointing center given in Table 1.