Initial selection of our sample of mass-transferring candidates, based on a) the Gaia EDR3 StarHorse colour-magnitude diagram, b) the Gaia XP spectra, c) the AllWISE colour-colour diagram, and d) the GaiaG-band variability. In a, c, and d, we show the final sample of 67 candidates as orange stars. The red lines in a show the cuts used to select stars between the MS and the RGB based on MESA Isochrones & Stellar Tracks. In b, we show the Gaia XP spectrum of one of the sources in our sample as an example, and we compare it with our follow-up spectrum taken with CAFOS (see Section 3.2), and the ⊕ symbols represent telluric absorption (absorption by the Earth’s atmosphere). The red dashed lines in panel c indicate the zero levels and divide the plot into four regions: warm dust, hot dust, both hot and warm dust, and no hot or warm dust. The shaded green region in d corresponds to the 90th percentile of the initial HG sample.