Astronomy & Astrophysics

All Figures

$\begin{figure} \par\includegraphics[width=8cm,clip]{3412fig1.eps}\end{figure}$ Figure 1: Comparison of observed equivalent widths for He I 10830 Å (Lennon & Dufton 1989: filled circles; Leone et al. 1995: open circles) with model predictions: Auer & Mihalas (1973, dotted line), Dufton & McKeith (1980, dashed line), and present computations (full lines) for $\xi =0$ ( lower) and 8 km s^-1 ( upper curve). The abscissa is the reddening-free [ c₁ ] index. Measurements of LD89 without error bars have uncertainties >80 mÅ. Uncertainties for the fast rotators of the LLP95 sample can be well above 100 mÅ.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{3412fig2.eps}\end{figure}$ Figure 2: Comparison of departure coefficients b_i as a function of Rosseland optical depth $\tau _{\rm ross}$ for the n = 1 and 2 levels of He I from computations using the standard (dotted lines) and the present (full lines) model atom, and computations for the new model atom with the photoionization cross-section for the 2s ³S state replaced by that used in the old one (dashed lines). Good agreement is found except for the 2s ³S state, the lower level of the He I 10 830 Å transition. Line-formation depths for this feature are indicated. The computations are for a stellar atmospheric model with $T_{\rm eff} = 30~000$ K, $\log g = 4.0$ (cgs), zero microturbulence, solar metallicity, and solar helium abundance.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{3412fig3.eps}\end{figure}$ Figure 3: Ratio of the line source function S_l to Planck function $B_{\nu}~(T)$ at the centre of the 10 830.34 Å fine-structure component of the transition, for the same atmospheric parameters as in Fig. 2. The same line designations as in Fig. 2 apply. In addition, results from a computation using the new model atom, but neglecting line blocking (dashed-dotted lines), are also shown. In the inset the resulting line profiles are compared after convolution with a Gaussian of FWHM of 20 km s^-1. Use of the improved photoionization cross-sections turns the absorption into emission, while neglect of line blocking effects gives excess emission.
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In the text

$\begin{figure} \par\includegraphics[width=7.7cm,clip]{3412fig4.eps}\end{figure}$ Figure 4: Comparison of the photoionization cross-sections for the 2s ³S state of Fernley et al. (1987, full line), as used in the present He I non-LTE model atom and of Gingerich (1964, dotted line), as used in the AM73 and Husfeld et al. (1989) models. The cross sections differ by more than 50% at threshold.
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In the text

$\begin{figure} \par\includegraphics[width=7.7cm,clip]{3412fig4.eps}\end{figure}$	Figure 4: Comparison of the photoionization cross-sections for the 2s ³S state of Fernley et al. (1987, full line), as used in the present He I non-LTE model atom and of Gingerich (1964, dotted line), as used in the AM73 and Husfeld et al. (1989) models. The cross sections differ by more than 50% at threshold.
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