Fig. 1

Left panel: Teff−log g diagram of the full sample of hot, subluminous, RV-variable stars. The size of the symbols scales with ΔRVmax. The black circles mark stars with hydrogen dominated atmospheres (log y< 0), while the red diamonds mark stars with helium dominated atmospheres. The helium main sequence (HeMS) and the HB band are superimposed with HB evolutionary tracks (dashed lines) for subsolar metallicity (log z = −1.48) from Dorman et al. (1993). The three tracks in the high temperature range correspond to helium core masses of 0.488, 0.490 and 0.495 M⊙ (from bottom-left to top-right). Those tracks mark the EHB evolution, since the stars do not reascend the giant branch in the helium shell-burning phase. The two tracks in the upper right correspond to core masses of 0.53 and 0.54 M⊙. Blue horizontal branch stars following those tracks are expected to experience a second giant phase. The solid line marks the relevant part of the zero-age main sequence for solar metallicity taken from Schaller et al. (1992). The two dotted lines are post-AGB tracks for hydrogen-rich stars with masses of 0.546 (lower line) and 0.565 M⊙ (upper line) taken from Schönberner (1983). The two long-dashed lines are post-AGB tracks for helium-rich stars with masses of 0.53 (lower line) and 0.609 M⊙ (upper line) taken from Althaus et al. (2009). Right panel: Teff−log g diagram of RV variable hydrogen-rich sdB and sdOB stars. The two dotted lines mark post-RGB tracks (Driebe et al. 1998) for core masses of 0.234 (left) and 0,259 M⊙ (right).
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