NLTE spectral analysis of the intermediate helium-rich subdwarf B star CPD-20{deg}1123. (arXiv:2006.04876v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Lobling_L/0/1/0/all/0/1">L. Löbling</a>
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{deg}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
$T_mathrm{eff} = 25,500 pm 1,000$ together with a surface gravity of
$log,(g,/,mathrm{cm}/mathrm{s}^2) = 5.3 pm 0.3$ 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 T”ubingen 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.
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{deg}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
$T_mathrm{eff} = 25,500 pm 1,000$ together with a surface gravity of
$log,(g,/,mathrm{cm}/mathrm{s}^2) = 5.3 pm 0.3$ 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 T”ubingen 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.
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