HR diagram containing all post-AGB candidates with an SED indicative of a disc of which the final luminosities were computed using the SED (Sect. 4.1). The evolutionary tracks are from Blöcker (1995) and correspond to stars with, from bottom to top, an initial mass of 1, 3, 4, 5 and 7 M_⊙. The 1 M_⊙ model suffers two late thermal pulses. Note that the objects shown here are a subset of the entire sample of disc sources as the objects for which the final luminosity was computed with the BB fit (Sect. 2.3) lack an effective temperature estimate and are hence missing in this plot.