Single-dish data analysis. Top: spectral index map of the bow shock of BD+43°3654, as seen with the Effelsberg telescope. As can be seen, the data are dominated by free-free emission. Bottom: posterior probability distributions of the fitted T_B and β towards the position indicated by the cross in the middle panel. The maximum posterior possibility point in the parameter space is shown as an orange line. Contours denote the 0.5, 1.0, 1.5, and 2.0σ confidence intervals.