= Solution
Core-helium-burning <stars> populate the <horizontal branch> and <red clump>; <hot subdwarf> B <stars> provide examples with a helium-burning core of roughly half a <solar mass> and a very small remaining <hydrogen> envelope. Their high <luminosity> relative to <mass>, hot spectra and locations away from an ordinary hydrogen-burning <main sequence> are observational evidence for such evolved configurations.
A plausible history starts with a hydrogen-burning <star>. After central <hydrogen> exhaustion, hydrogen-shell burning builds a compact <helium> core and the envelope expands on the <red giant branch>. Sufficient core <temperature> ignites <helium>, often by a <helium flash> for a low-mass degenerate core. Strong <mass> loss or binary interaction can strip most of the <hydrogen> envelope, exposing a hot helium-burning remnant; retaining a substantial envelope instead gives an ordinary horizontal-branch or red-clump <star>.
The simple radiative Kramers scaling estimates a <luminosity> contrast but does not uniquely identify one evolutionary state or predict a real subdwarf <luminosity> precisely. A similarly low-mass <helium> <white dwarf> would be a cooling, degenerate object rather than the sustained high-temperature helium-burning configuration assumed here.
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