Fit parameters of intensity isocontours using ellipses. B1b-N data are shown in blue and B1b-S data in red. The top panel presents the variation of the major and minor axis sizes. The middle panel shows the ellipse position angle, PA, and the bottom panel the ellipticity, e = 1 − R_min/R_maj. The beam profiles are displayed in the top panel. The beam position angles and ellipticities are 1.1° and 0.2 for B1b-N and 16° and 0.21 for B1b-S. The upper scale displays the correspondence between antenna baseline and angular scale.