Plots for the identification of the Horo II members for targets with FLAMES spectroscopic observations. Stars consistent with a distant halo origin in Gaia parallax, proper motions, and color magnitude space are plotted in blue, and the non-halo stars are plotted in gray. Stars without Gaia proper motion information, but with a location on the CMD consistent with being an RGB or a BHB star at the distance of the object are plotted in red. The very likely members of the satellite are enclosed within a cyan square and the additional potential members within an orange square. Top left panel: spatial distribution of the targets. The semimajor axes of the ellipses are equal to 1.5 and 3 projected (elliptical) half-light radii and use ellipticity and PA from Kim et al. (2015). Top right panel: location in the proper motion plane; the proper motion selection box of halo stars given by the escape speed criterion is shown in gray. Bottom left panel: extinction-corrected CMD; the Parsec isochrones with [Fe/H] = −2.0 and −1.0 dex and age = 12 Gyr are overlaid. The isocrones have solar-scaled [α/Fe]; this might be a potential source for the discrepancy in the location of stars of a given spectroscopically determined metallicity with the isochrones of similar [Fe/H] because stars in such ancient systems are typically α-enhanced (e.g., Mashonkina et al. 2017, and references therein). Bottom right panel: distribution on the l.o.s. v_helio vs. distance from the satellite center in units of projected elliptical half-light radius. The velocity distribution of disk stars in the mock catalog (z <  |1| kpc) is shown in gray; the horizontal lines indicate the central 1σ interval.