Example of radio thermal jet (VLA–2) near a HCH II region (VLA–1): H₂O maser site G240.32+0.07 (Sect. 4.3). Labels and symbols as in Fig. 1. The SED of source VLA–1 was fitted with a model of homogeneous H II region (panelb) with Strömgren radius of 870 au and number of Lyman photons of 3 × 10⁴⁶ s⁻¹. This model accurately reproduces the observed fluxes at each band. Thanks to the high S/N, in panels d and e we can determine the spectral index maps of the C and Ku bands separately with an uncertainty better than ±0.2. The average brightness map (contours) is that of the Ku band in both panels d and e, for comparison. The spectral index maps trace the turnover of the continuum spectrum for source VLA–1 from α = 1.0–6.0 between 4 and 8 GHz (paneld) to α = –0.1 above 15 GHz (panele).