2002 (lines of different Z) sdB progenitors >1.8 M¤ can ignite He nondegenerately, with core masses as low as ~0.32 M¤ observationally, we measure <0.4 M¤ sdBs in: • 2M 1533+3759: For et al. 2010 (eclipsing binary) • 2M 1938+4603: Barlow et al. 2012 (Rømer delay) • TIC 278659026: Charpinet et al. 2019 (seismology)
evolve into < 0.4 M¤ CO-core WDs Prada Moroni & Straniero 2009 He vs. CO WD could be distinguished by: • Precise mass/radius observations • Asteroseismology Asymptotic mean period spacing for dipole modes: • 0.3 M¤ He-core: Δπ = 75 s • 0.3 M¤ CO-core: Δπ < 60 s
RGB stars in Kepler: • ~7 are underluminous – smaller cores • ~32 are too low-mass for single-star evolution MESA models with and without mass loss Models >1.8 M¤ end up underluminous after RLOF Yaguang Li et al. 2022
2022 Of the 7000 CHeB RGB stars in Kepler: • ~7 are underluminous – smaller cores • ~32 are too low-mass for single-star evolution None of the three underluminous CHeB giants with multi-epoch APOGEE/LAMOST spectra show large RV variability yet eRV < 0.1 km/s
CO-core white dwarfs likely exist, but eclipses not yet revelatory New analysis of Kepler data shows core He-burning giants with small cores: stripped, sdB analogues 0.09% ± 0.04% of all CHeB are underluminous Heber 2009, ARA&A : where are the companions?!