Spectral energy distributions of RRL with 8 μm photometry available. On each panel, the measured fluxes of a star are marked with red dots. The vertical and horizontal bars mark the measurement uncertainties and the effective widths of the photometric bands, respectively. The black and green curves correspond to DUSTY models with circumstellar envelopes made of amorphous carbon and silicate dust, respectively. The solid, dash-dotted, and dotted lines show progressively higher amounts of dust. Above each panel, the OGLE ID, the adopted values of V-band extinction, and distance are given. The locations of these three stars are marked by arrows on the color-magnitude diagram of the final sample (bottom-left panel of Fig. 2).