Dust emissivity spectral indexes, β, as a function of the SED temperature for each source. The indexes were derived between 333 GHz and 32.9 GHz (black lines), 333 GHz and 246.2 GHz (green lines), and 246.2 GHz and 32.9 GHz (red lines). The shaded grey area indicates the authorised range of β values (0–2) provided by theoretical works (see Sect. 2). Applying these limits on β constrains the possible range of T_SED values. For each source, the minimum and maximum values of β derived over the full temperature range are indicated at the top right of the plots. For single systems, the bolometric temperature, T_bol, derived fromHerschel (Furlan et al. 2016), and the radiative temperature, T_rad, are indicated by a vertical blue dashed line and red shaded area, respectively.