Main parameters of CSTAR_XPM sample. Panel a: T_eff and log g diagram of CSTAR_XPM. Panel b: Spatial location and density distribution of CSTAR_XPM and random sample in the G_BP − G_RP and log g plane. The random sample (gray) is randomly selected from xp_sampled_mean. CSTAR_XPM stars are located in the giant star branch, with most having 2 < G_BP − G_RP < 5 mag; Panel c shows the distribution of golden sample carbon stars (red) and non-golden sample carbon stars (blue) in CSTAR_XPM.