Hertzsprung-Russell diagram. The left panel presents an overview while the red panel focusses on the T2Cs. The symbols are follows: filled squares (SMC), open squares (LMC), open triangles (M31), filled triangles (M33), filled circles (Galactic Bulge), and open circles (MW). Stars located outside the bulk of objects are identified. The blue and red lines indicate the blue and red edge of the IS of CCs. The results from De Somma et al. (2021) are plotted for Z = 0.03 (thick solid lines) and Z = 0.004 models (thinner dashed lines), for their type A mass-luminosity relation. The green lines indicate evolutionary models from Anderson et al. (2016) (see text for details). The blue and pink crosses indicate MIST evolutionary tracks for v/v_crit = 0.4 for 5.0, 10, and 17 M_⊙ (and [Fe/H]= 0.0 dex) and 4.8, 9, and 15 M_⊙ (and [Fe/H]= −0.50 dex), respectively, plotted at 10⁴ year intervals (Dotter 2016; Choi et al. 2016; Paxton et al. 2015, 2013, 2011). The first crossing of the IS is also visible, except for the highest mass tracks. In the right panel the objects in the sample are plotted in blue, without names and the MIST evolutionary tracks are not shown. Instead, the black and red crosses indicate the evolutionary tracks of the 1.0 and 2.5 M_⊙ solar metallicity stars, respectively, including the post-AGB phase, plotted at 10³ year intervals (from Vassiliadis & Wood 1994). For comparison, the black triangles and spades indicate T2C with periods longer than 50 days in the MCs (from Groenewegen & Jurkovic 2017) and the MW (from Bódi & Kiss 2019), respectively. GD-CEP-1505 is located outside both plots at log T_eff ~ 3.48 and log L ~ 2.18.