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tokens: this solution to be unrealistic. Figure 7. T eff –log( g ) diagram of the primary star in EVR-CB-004 (red star). The EHB/BHB evolutionary tracks for different stellar masses (bottom to top: 0.471, 0.473, 0.475, 0.480, 0.490, 0.500, and 0.510 M ⊙ ), that is, increasing hydrogen envelope mass (0.000, 0.002, 0.004, 0.009, 0.019, 0.029, and 0.039 M ⊙ , respectively), and solar metallicity according to Dorman et al. ( 1993 ) are shown with solid lines. In addition, the post-AGB tracks according to 0.524 M ⊙ are displayed with dotted lines (Bloecker 1995 ), and the pre-He WD track calculated with MESA (Paxton et al. 2011 , 2013 , 2015 , 2018 , 2019 ) is shown with dashed lines. The hot subdwarfs are confirmed binaries with WD companions taken from Kupfer et al. ( 2015 ). The BHB stars are taken from Saffer et al. ( 1997 ), Ramspeck et al. ( 2001 ), Vennes et al. ( 2007 ), Naslim et al. ( 2010 ), Copperwheat et al. ( 2011 ), Østensen et al. ( 2012 ), Geier et al. ( 2014 ), and Schneider et al. ( 2018 ). The plotted error bars include 1 σ statistical and systematic uncertainties as presented in the text (see Section 3 for details). If, instead, the progenitor filled its Roche lobe after He burning started, the envelope would get stripped and form a He core–burning hot subdwarf star that is expected to burn He for ≈100–150 Myr. Depending on its hydrogen envelope, it is considered to be an EHB star (for hydrogen envelopes ≲0.01 M ⊙ ) or a BHB star (for hydrogen envelopes of a few hundredths M ⊙ ). Once burning exhausts the He in the core, the star evolves toward hotter temperatures. As the core contracts, residual hydrogen is predicted to burn in a shell, pushing the surface to a larger radius (Østensen 2009 ) and hence lower surface gravities. This is seen in the solid tracks shown for different masses in Figure 7 . This stage of the evolution is expected to last for only ≈10–20 million yr and is commonly referred to as post-EHB or post-BHB evolution. A helpful discussion of EHB/BHB stars and their evolution can be found in Moehler ( 2001 ), Østensen ( 2009 ), and Heber ( 2016 ). Figure 7 shows the position of the primary of EVR-CB-004 in the T eff –log( g ) diagram, which is consistent with a post-BHB sequence with a mass of ≈0.5 M ⊙ . We note here the limitation of using the EHB/BHB evolutionary models in their current form to describe the primary of EVR-CB-004, since their radii exceed the Roche radius of EVR-CB-004 between leaving the BHB and the present. We suggest more involved modeling, beyond the scope of this work, to explore the post-BHB space specific to EVR-CB-004. If the post-BHB interpretation is correct, the primary of EVR-CB-004 is even rarer, as we would have to have caught the object during this transitioning state. The only other reasonably similar system (compact binary with a WD companion, ellipsoidal deformation, Doppler boosting, gravitational limb darkening, similar mass, and an old evolved primary) we found in the