Subdwarf B and O Stars: Second Generation Ignition Through Accretion

Subdwarf B (sdB) and subdwarf O (sdO) stars are conventionally interpreted as evolved stellar cores burning helium after hydrogen envelope stripping. This interpretation requires these objects to be old —post-main-sequence remnants. However, their blue spectral signatures indicate new stellar activity. This study proposes an alternative interpretation: sdB/sdO stars are second generation objects that achieved fusion through accretion from dead companions. They are not old stars burning helium; they are new stars burning contaminated hydrogen. Ultra-tight binary configurations with white dwarf companions provide observational evidence of this succession mechanism.