Astronomy & Astrophysics

All Figures

$\begin{figure} \par\includegraphics[angle=270,width=14cm,clip]{3155f1.ps} \end{figure}$ Figure 1: The horizontal branches of M 13 (Grundahl et al. 1998, left panel) and M 3 (Buonanno et al. 1994, right panel) with the spectroscopic targets marked by open squares.
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In the text

$\begin{figure} \par\includegraphics[width=15.8cm,clip]{3155f2.ps} \end{figure}$ Figure 2: Normalized spectra of the programme stars in M 13 and M 3. The part shortward of 3900 Å was normalized by taking the highest flux point as continuum value.
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In the text

$\begin{figure} \par\includegraphics[width=8.3cm,clip]{3155f3.ps} \end{figure}$ Figure 3: Atmospheric parameters of the programme stars in M 3 and M 13 obtained with $\alpha$ -enhanced metal-poor model atmospheres ([Fe/H] = -1.5, [ $\alpha$ /Fe] +0.4). The solid lines mark the zero-age (ZAHB) and terminal-age (TAHB) loci of canonical HB tracks for [M/H] = -1.54. These loci define the region within which the HB models spend 99% of their HB lifetime. a) Temperatures and gravities from Strömgren $uvby\beta$ photometry (for comparison we also show results for cool field BHB stars obtained with the same method by Kinman et al. 2000). b) Temperatures and gravities for all stars are derived from fits to the Balmer line profiles, using as starting values the photometrically determined parameters. The error bars note the formal 1 $\sigma$ errors from the line profile fits. The model spectra used here do not include metal lines. For comparison we also show the results for blue tail stars in NGC 6752 from Moehler et al. (2000, obtained with metal-poor model spectra without metal lines). c) Temperatures and gravities of the programme stars cooler than 15 000 K from Balmer line profile fits using model spectra that include metal lines for [Fe/H] = -1.5 and [ $\alpha$ /Fe] = +0.4.
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{3155f4.ps} \end{figure}$ Figure 4: Normalized spectra of the programme stars in M 13 and M 3 and theoretical spectra for the atmospheric parameters (from the Balmer line profiles) and iron abundances listed in Table 3. For stars hotter than 12 000 K we show the fits obtained for atmospheric parameters from metal-rich model atmosphere fits. The solid and dotted lines mark the strongest and moderately strong iron lines in the spectra.
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In the text

$\begin{figure} \par\includegraphics[width=8.3cm,clip]{3155f5.ps} \end{figure}$ Figure 5: Abundances of a) helium, b) iron, and c) magnesium for the programme stars in M 3 (open squares) and M 13 (filled squares). Also given are the results of Behr (priv. comm.) for stars in M 3 (open triangles) and M 13 (filled triangles).
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In the text

$\begin{figure} \par\includegraphics[width=7.5cm,clip]{3155f6.ps} \end{figure}$ Figure 6: The u-jump in M 13 with the spectroscopic targets marked: Open triangles mark stars with low iron abundance ([Fe/H] $\approx -1.5$ ), open squares mark stars with high iron abundance ([Fe/H] $\approx +0.5$ ). Stars for which the iron abundance could not be determined due to the limited S/N (hot stars) or uncertainties in the atmospheric parameters (cool stars) are marked by open circles.
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In the text

$\begin{figure} \par\includegraphics[width=8.3cm,clip]{3155f7.ps} \end{figure}$ Figure 7: Temperatures and gravities of the programme stars that show evidence for iron enrichment. The solid lines mark the zero-age (ZAHB) and terminal-age (TAHB) loci of canonical HB tracks for [M/H] = -1.54. These loci define the region within which the HB models spend 99% of their HB lifetime. a) Here we adopted a super-solar metallicity ([M/H] = +0.5) for the model atmospheres (see Sect. 5 for details), but did not include metal lines in the theoretical spectra. For comparison we also show the results for blue tail stars in NGC 6752 from Moehler et al. (2000, obtained with metal-rich model spectra without metal lines). b) These are the results obtained with metal-rich model spectra that include metal lines.
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{3155f8.ps} \end{figure}$ Figure 8: Temperatures and gravities of the programme stars in M 3 and M 13 (from metal-rich model atmospheres for stars hotter than 12 000 K and metal-poor model atmospheres for cooler stars, in both cases including metal lines) compared to non-canonical evolutionary models. The zero-age and terminal-age HB predicted by canonical models for Y = 0.23 and $\rm [M/H] = -1.54$ are plotted as solid lines. a) The zero-age and terminal-age HB for $\rm [M/H] = -1.54$ computed with helium mixing for a Reimers mass-loss parameter $\eta _{\rm R} = 0.45$ (see Sect. 6.1 for details). b) The zero-age and terminal-age HB computed with helium pollution for helium abundances of Y = 0.28 and Y = 0.33 (see Sect. 6.2 for details).
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In the text

$\begin{figure} \par\includegraphics[width=8.3cm,clip]{3155f9.ps} \end{figure}$ Figure 9: Temperatures and masses of the programme stars in M 3 and M 13 (from metal-rich model atmospheres for stars hotter than 12 000 K and metal-poor model atmospheres for cooler stars; in both cases metal lines were included in the theoretical spectra) compared to evolutionary tracks. a) The solid line marks the canonical ZAHB and the mixed ZAHB is given by the short-dashed line (see Sect. 6.1 for details). b) Again the solid line marks the canonical ZAHB and the polluted ZAHBs are given by the dotted (Y=0.28) and long-dashed line (Y=0.33), respectively (see Sect. 6.2 for details).
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In the text

$\begin{figure} \par\includegraphics[angle=270,width=14cm,clip]{3155f1.ps} \end{figure}$	Figure 1: The horizontal branches of M 13 (Grundahl et al. 1998, left panel) and M 3 (Buonanno et al. 1994, right panel) with the spectroscopic targets marked by open squares.
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$\begin{figure} \par\includegraphics[width=15.8cm,clip]{3155f2.ps} \end{figure}$	Figure 2: Normalized spectra of the programme stars in M 13 and M 3. The part shortward of 3900 Å was normalized by taking the highest flux point as continuum value.
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$\begin{figure} \par\includegraphics[width=8.3cm,clip]{3155f5.ps} \end{figure}$	Figure 5: Abundances of a) helium, b) iron, and c) magnesium for the programme stars in M 3 (open squares) and M 13 (filled squares). Also given are the results of Behr (priv. comm.) for stars in M 3 (open triangles) and M 13 (filled triangles).
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