All Figures

$\begin{figure} \par\includegraphics[angle=90,width=7.5cm,clip]{7424fig1.ps}\end{figure}$ Figure 1: Grotrian diagram of multiplet 42 of Ti I showing the angular momentum values of the levels of the lower term $\rm a \; ^5F$ and of those of the upper term $\rm y ~ ^5F^\circ$ . The wavelengths (in Angstroms units) of the 13 lines of this multiplet are also indicated.
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In the text

$\begin{figure} \par\includegraphics[angle=90,width=8cm,clip]{7424fg2a.ps}\par\hspace*{1mm}\includegraphics[width=7.8cm,clip]{7424fg2b.ps}\end{figure}$ Figure 2: Emergent fractional linear polarization amplitudes, Q/I, for each of the 13 lines of multiplet 42 of Ti I indicated in Fig. 1. $\square$ : 10 levels model. $\times$ : full multilevel model. Collisions are not taken into account. Panel a) shows the emergent fractional polarizations if dichroism is neglected (i.e., using Eq. (13)). Panel b) shows the emergent fractional polarizations if dichroism is taken into account, in addition to the standard contribution of selective emission of polarization components (i.e., using Eq. (12)). Note that in panel b) the polarization amplitudes corresponding to the calculation performed using the full multilevel model agree with those shown by Manso Sainz et al. (2004) in their Fig. 2b.
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In the text

$\begin{figure} \par\includegraphics[angle=90,width=8cm,clip]{7424fig3.ps}\end{figure}$ Figure 3: Emergent fractional linear polarization amplitudes, Q/I, for each of the 13 lines of multiplet 42 of Ti I indicated in Fig. 1. $\square$ : 10 levels model. $\times$ : full atomic model. The atomic polarization of all (long-lived) lower levels is assumed to be zero. The influence of collisions on the population imbalances of the upper levels is not taken into account.
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In the text

$\begin{figure} \par\includegraphics[angle=90,width=8cm,clip]{7424fig4.ps}\end{figure}$ Figure 4: Emergent fractional linear polarization amplitudes, Q/I, for each of the 13 lines of multiplet 42 of Ti I using the 10 levels model atom shown in Fig. 1 without lower-level polarization. $\times$ : Q/I amplitudes taking into account only D⁽²⁾(J). $\square$ : Q/I values using all collisional rates: D⁽²⁾(J), $C^{(0)}(\alpha J', \alpha J)$ and $C^{(2)}(\alpha J, \alpha J')$ .
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{7424fig5.ps}\end{figure}$ Figure 5: Grotrian diagram of Ca II showing the upper and lower J-levels of the H and K lines and of the IR triplet.
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In the text

$\begin{figure} \par\includegraphics[angle=90,width=7.4cm,clip]{7424fig6.ps}\end{figure}$ Figure 6: Emergent fractional linear polarization amplitudes, Q/I, for the K line and for the IR triplet of Ca II. The calculations have been performed using the multilevel model of Fig. 5, and following the strategy indicated in the text. $\blacksquare$ : Q/I values in the absence of collisions. $\times$ : Q/I amplitudes taking into account only D⁽²⁾(J). $\square$ : Q/I values calculated using all collisional rates: D⁽²⁾(J), $C^{(0)}(\alpha J', \alpha J)$ and $C^{(2)}(\alpha J, \alpha J')$ .
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In the text

$\begin{figure} \par\includegraphics[width=7.4cm,clip]{7424fig7.ps}\end{figure}$ Figure 7: Emergent fractional linear polarization amplitude of the Ca II K line as a function of the neutral hydrogen density. (a) Dot-dashed line: Q/I values calculated assuming that the metastable levels ²D_3/2 and ²D_5/2 are completely unpolarized. (b) Solid line: Q/I amplitudes calculated using all collisional rates, taking the polarization of such metastable levels into account: D⁽²⁾(J), $C^{(0)}(\alpha J', \alpha J)$ , and $C^{(2)}(\alpha J, \alpha J')$ . (c) Dotted line: same as in (b) but taking only D⁽²⁾ (J) into account. The dashed vertical lines, between $n_{\rm H} \simeq 2 \times 10^{12}$ cm^-3 and $n_{\rm H} \simeq 2 \times 10^{14}$ cm^-3, represent the collisional regime where the scattering polarization in the K line increases with the hydrogen number density.
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In the text

$\begin{figure} \par\includegraphics[angle=90,width=7.5cm,clip]{7424fig1.ps}\end{figure}$	Figure 1: Grotrian diagram of multiplet 42 of Ti I showing the angular momentum values of the levels of the lower term $\rm a \; ^5F$ and of those of the upper term $\rm y ~ ^5F^\circ$ . The wavelengths (in Angstroms units) of the 13 lines of this multiplet are also indicated.
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$\begin{figure} \par\includegraphics[angle=90,width=8cm,clip]{7424fig3.ps}\end{figure}$	Figure 3: Emergent fractional linear polarization amplitudes, Q/I, for each of the 13 lines of multiplet 42 of Ti I indicated in Fig. 1. $\square$ : 10 levels model. $\times$ : full atomic model. The atomic polarization of all (long-lived) lower levels is assumed to be zero. The influence of collisions on the population imbalances of the upper levels is not taken into account.
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$\begin{figure} \par\includegraphics[angle=90,width=8cm,clip]{7424fig4.ps}\end{figure}$	Figure 4: Emergent fractional linear polarization amplitudes, Q/I, for each of the 13 lines of multiplet 42 of Ti I using the 10 levels model atom shown in Fig. 1 without lower-level polarization. $\times$ : Q/I amplitudes taking into account only D⁽²⁾(J). $\square$ : Q/I values using all collisional rates: D⁽²⁾(J), $C^{(0)}(\alpha J', \alpha J)$ and $C^{(2)}(\alpha J, \alpha J')$ .
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$\begin{figure} \par\includegraphics[width=8cm,clip]{7424fig5.ps}\end{figure}$	Figure 5: Grotrian diagram of Ca II showing the upper and lower J-levels of the H and K lines and of the IR triplet.
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