Left: IRS SED of source SSID 141, compared with our interpretation based on synthetic modelling. Right: AGB evolution with time of the luminosity of 1.5, 2, 2.5 M_⊙ stars; the O-rich phase was omitted for readability. The sequence of the 2.5 M_⊙ was artificially shifted by 1 Myr for readability. The grey shaded region indicates the luminosity range of the low-luminosity stars SSID 3, SSID 66, SSID 103, and SSID 141.