Subdwarf B ( sdB ) stars are core helium-burning stars with stratified atmospheres .
Their atmospheres are dominated by hydrogen ( H ) while the helium ( He ) and metal abundances are shaped by an interplay of gravitational settling and radiative levitation .
However , a small fraction of these show spectra dominated by He I absorption lines .
In between these groups of He-deficient and extreme He-rich sdBs , some are found to have intermediate surface He abundances .
These objects are proposed to be young ‘ ‘ normal ’ ’ ( He-deficient ) sdBs for which the dynamical stratification of the atmosphere is still ongoing .
We present an analysis of the optical spectrum of such an intermediate He-rich sdB , namely CPD -20 ^ { \circ } 1123 , by means of non-local thermodynamic equilibrium ( NLTE ) stellar atmosphere models .
It has a He-to-H number ratio of \mathrm { He / H } = 0.13 \pm 0.05 and its effective temperature of \mbox { $T _ { \mathrm { eff } } $ } \hskip { -1.422638 pt } = \hskip { -1.422638 pt } 25 500 \pm 1 % 000 \mathrm { K } together with a surface gravity of \log ( g / cm/s ^ { 2 } ) = 5.3 \pm 0.3 places the star close to the high-temperature edge until which it may be justified to use LTE model atmospheres .
This work states a test of the Tübingen NLTE Model Atmosphere Package for this temperature regime .
We present the first application of revised , elaborated model atoms of low ionization stages of light metals usable with this atmosphere code .