Properties of our FSR 1758 targets. Panel a: spatial position. Color-coded symbols represent the S/N of stars with APOGEE spectra whose sizes are proportional to their G mag. Open black squares and gray triangles indicate stars analyzed in Simpson (2019) and Villanova et al. (2019), respectively. Field stars represent black crosses. A circle with 15′ radius is overplotted. Panel b: proper motion density distribution of stars located within 15′ from the cluster center; the color contours refer to the kernel density estimation of this sample. FSR 1758 is clearly distinguishable from the field population. The inner plot on the top right shows a zoom-in of the cluster; concentric ellipses show the 1, 2, and 3σ levels of our best-fit proper motions (PMs) of FSR 1758 based on Gaia EDR3 data, whose mean values are highlighted. The symbols are the same as in panel a. Panel c: color-magnitude diagram corrected by differential reddening and extinction-corrected in the Gaia bands of our sample and stars within 15′. Our targets all lie along the RGB. Panel d: radial velocity vs. metallicity of our members compared to field stars. The [Fe/H] of our targets have been determined with BACCHUS and photometric atmospheric parameters (see Table 2), while the [Fe/H] of field stars are from the ASPCAP pipeline. The red box limited by ±0.15 dex and ±10 km s⁻¹ and centered on [Fe/H]  =   − 1.36 and RV = 225.73 km s⁻¹ encloses our potential cluster members.