All Figures

$\begin{figure} \par\includegraphics[width=7cm]{6074fig1.eps} \end{figure}$ Figure 1: CM diagram of NGC 6441 from the data by Piotto et al. (2002). The crosses (in red) indicate our selection of HB members; also shown is the histogram of their distribution with respect to B-V.
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In the text

$\begin{figure} \par\includegraphics[width=7cm]{6074fig2.eps} \end{figure}$ Figure 2: An enlargement of the HB red clump region: crosses (red) indicate stars with B-V > 0.5 mag, open circles (blue) stars with B-V < 0.5 mag. The histogram of red HB stars with respect to V mag is shown.
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In the text

$\begin{figure} \par\includegraphics[width=7cm]{6074fig3.eps} \end{figure}$ Figure 3: Evolutionary tracks for a few helium-rich HB models: the long loops that they perform cover large portions of the allowed HB region. The tracks end at $Y_{\rm c}=0.10$ .
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In the text

$\begin{figure} \par\includegraphics[width=7cm]{6074fig4.eps} \end{figure}$ Figure 4: Simulations show the effect on the evolutionary tracks of an increasing helium content: open triangles (red) indicate stars with fixed Y=0.25 (red histogram), filled triangles (blue) stars with increasing maximum helium content ( $Y_{\rm max}$ ) (blue histogram), as labeled in the four panels. The black histogram refers to the whole HB. Z =0.006 in all models.
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In the text

$\begin{figure} \par\includegraphics[width=7cm]{6074fig5.eps} \end{figure}$ Figure 5: A synthetic CM diagram of the HB in NGC 6441 for an age of 11 Gyr, mass loss of 0.165 $M_\odot$ with $\sigma =0.02$ , and extra mass loss as in the text. Stars with fixed Y=0.25 (open triangles, red) plus stars with variable Y up to 0.40 (stars, blue). For the helium distribution, see text and the following figures. The standard deviation assumed for both V and B-V in this and in the following figures is 0.05 mag. The histograms give the number of stars as a function of B-V: the total number is represented by the full line histogram, while the dotted one is the Y=0.25 population and the dashed one is the population with variable Y.
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In the text

$\begin{figure} \par\includegraphics[width=12cm]{6074fig6CMJN.eps} \end{figure}$ Figure 6: For the simulation of Fig. 5, we show the synthetic CM of the red clump region in the top panel, with the details of the distribution in luminosity (line-dotted histogram, red). The continuous line gives the observed histogram, as in Fig. 2. Different symbols (and colours) denote different helium contents. Points: stars with Y=0.25 (red); open triangles (black): 0.27<Y<0.32; asterisks (blue): 0.32<Y<0.38; squares (green): 0.38<Y<0.40. The dashed line indicates the approximate position of the RR Lyr variables, derived from Pritzl et al. (2003). The assumed age, the number of RR Lyr (RR), the average period of the RR Lyr (P), and the fraction of HB stars bluer than B-V = 0.5 (R) in the simulation are listed at the top right. The lower panel shows the number distribution of HB stars vs. helium content corresponding to the CM diagram in the upper panel. The total number of the first stellar generation with Y=0.25 is given at the top right and labeled N(0.25).
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In the text

$\begin{figure} \par\includegraphics[width=7.2cm]{6074fig7CMJN.eps} \end{figure}$ Figure 7: As in Fig. 6, but with no gap in the Y distribution (see the lower panel): it is not possible to avoid a substantially larger peak in the luminosity histogram than the one observed.
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In the text

$\begin{figure} \par\includegraphics[width=7.2cm]{6074fig8CMJN.eps} \end{figure}$ Figure 8: As in Fig. 6, but with a gap of 0.035 between the Y of the red clump and the lower limit of the population with varying Y: two well-defined peaks appear in the luminosity histogram.
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In the text

$\begin{figure} \par\includegraphics[width=7.2cm]{6074fig9CMJN.eps} \end{figure}$ Figure 9: As in Fig. 6, except that the standard deviation on V and B-V is reduced from 0.05 to 0.03 mag: the clump appears separated in two groups.
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In the text

$\begin{figure} \par\includegraphics[width=7.2cm]{6074fi10.eps} \end{figure}$ Figure 10: The relation between B-V and helium content Y for the case in Fig. 6, but a quite similar behaviour has been found in all the simulations.
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In the text

$\begin{figure} \par\includegraphics[width=7cm]{6074fig1.eps} \end{figure}$	Figure 1: CM diagram of NGC 6441 from the data by Piotto et al. (2002). The crosses (in red) indicate our selection of HB members; also shown is the histogram of their distribution with respect to B-V.
Open with DEXTER

$\begin{figure} \par\includegraphics[width=7cm]{6074fig2.eps} \end{figure}$	Figure 2: An enlargement of the HB red clump region: crosses (red) indicate stars with B-V > 0.5 mag, open circles (blue) stars with B-V < 0.5 mag. The histogram of red HB stars with respect to V mag is shown.
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$\begin{figure} \par\includegraphics[width=7cm]{6074fig3.eps} \end{figure}$	Figure 3: Evolutionary tracks for a few helium-rich HB models: the long loops that they perform cover large portions of the allowed HB region. The tracks end at $Y_{\rm c}=0.10$ .
Open with DEXTER

$\begin{figure} \par\includegraphics[width=7cm]{6074fig4.eps} \end{figure}$	Figure 4: Simulations show the effect on the evolutionary tracks of an increasing helium content: open triangles (red) indicate stars with fixed Y=0.25 (red histogram), filled triangles (blue) stars with increasing maximum helium content ( $Y_{\rm max}$ ) (blue histogram), as labeled in the four panels. The black histogram refers to the whole HB. Z =0.006 in all models.
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$\begin{figure} \par\includegraphics[width=7.2cm]{6074fig7CMJN.eps} \end{figure}$	Figure 7: As in Fig. 6, but with no gap in the Y distribution (see the lower panel): it is not possible to avoid a substantially larger peak in the luminosity histogram than the one observed.
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$\begin{figure} \par\includegraphics[width=7.2cm]{6074fig8CMJN.eps} \end{figure}$	Figure 8: As in Fig. 6, but with a gap of 0.035 between the Y of the red clump and the lower limit of the population with varying Y: two well-defined peaks appear in the luminosity histogram.
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$\begin{figure} \par\includegraphics[width=7.2cm]{6074fig9CMJN.eps} \end{figure}$	Figure 9: As in Fig. 6, except that the standard deviation on V and B-V is reduced from 0.05 to 0.03 mag: the clump appears separated in two groups.
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$\begin{figure} \par\includegraphics[width=7.2cm]{6074fi10.eps} \end{figure}$	Figure 10: The relation between B-V and helium content Y for the case in Fig. 6, but a quite similar behaviour has been found in all the simulations.
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