All Figures

$\begin{figure} \par\includegraphics[width=10.7cm,clip]{Hg223_f1.eps} \end{figure}$ Figure 1: Comparison of the normalised spectra of V652 Her ( lower) and the metal-poor hydrogen-deficient star HD 144941 ( upper histogram) with our non-LTE spectrum synthesis for helium and hydrogen (full red line): excellent agreement for the entire line profiles - wings and line cores - is found. The He and H features have been labelled. Forbidden components of He I lines missing in our modelling are indicated by short vertical marks. The red wing of He I 4922 Å in HD 144941 may be affected by an artifact in the data reduction.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{Hg223_f2.eps} \end{figure}$ Figure 2: Departure coefficients b_i for He I in the model of V652 Her as a function of Rosseland optical depth $\tau _{\rm ross}$ for the n = 1 and 2 and selected n = 3 and 4 levels from computations using the P05 and the HBHD89 model atoms (upper panel, full and dotted lines, respectively). The He II ground state is also indicated (dashed line). In the lower panel ratios of line source function S_l to Planck function $B_{\nu }$ for several He I lines are displayed. Line formation depths are indicated. The considerable differences in the populations of the $2\rm s$ $^3\rm S$ state in the two model atoms translate to a discrepant $S_l/B_{\nu }$ ratio for the He I 1.083 $\mu$ m transition, giving a substantially weakened line for the modern model atom, while computations based on the old model deviate only little from detailed balance.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{Hg223_f3.eps} \end{figure}$ Figure 3: Same as Fig. 2, but for H I. The b_i are labelled by the principal quantum number. Non-LTE (full line) and LTE profiles (dashed line) of H $\beta$ are compared in the inset. Line source-functions are displayed for Balmer lines and Paschen and Brackett lines in the J- and K-band.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{Hg223_f4.eps} \end{figure}$ Figure 4: Comparison of the J-band spectrum of V652 Her (histogram) with three model predictions: LTE (dashed line) and two non-LTE computations using the model atom of HBHD89 (dotted line) and the improved model atom of P05 (full red line). In contrast to the other transitions, He I $\lambda$ 1.083 $\mu$ m experiences strong non-LTE weakening. An unbroadened synthetic spectrum is displayed at the bottom in order to illustrate what can be expected from high-resolution observation.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{Hg223_f5.eps} \end{figure}$ Figure 5: Fits of theoretical energy distributions (full red lines) to IUE, visual and IR spectrophotometry for V652 Her (near maximum radius, lower jagged curve and dots) and HD 144941 ( upper curve). The observed fluxes are dereddened by the amounts indicated and the HD 144941 data are shifted vertically by +0.3 units. The models are normalised to the observed Johnson V magnitudes. Locations for the bound-free edges of the n = 2 levels of He I are indicated.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{Hg223_f3.eps} \end{figure}$	Figure 3: Same as Fig. 2, but for H I. The b_i are labelled by the principal quantum number. Non-LTE (full line) and LTE profiles (dashed line) of H $\beta$ are compared in the inset. Line source-functions are displayed for Balmer lines and Paschen and Brackett lines in the J- and K-band.
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