Appendix A: Comparison of the IUE fluxes of the Pop II A-type stars with the computed fluxes

The figures in this Appendix are only available in electronic form at http://www.edpsciences.org

Figures A.1-A.15 compare the IUE low-resolution spectra with the computed spectra for the sample of stars listed in Table 3. Dashed lines indicate the observed fluxes. Two vertical lines in the plots give the position of the Lyman-$\alpha$ H-H⁺ and H-H quasi-molecular absorptions at 1400 Å and 1600 Å, respectively. For each star there are two plots, plot "OLD'' and plot "NEW''. In the plot "OLD'' the thin line is the old-ODF flux computed with model parameters $T_{\rm eff}$  and $\log\,g$  from KCC (Cols. 9 and 10 in Table 3), while the thick line is the flux computed with parameters derived by fitting the IUE spectra to the grid of fluxes computed with the old-ODFs (Cols. 7 and 8 in Table 3). In the plot "NEW'' the thick line is the flux computed with parameters derived by fitting the observed fluxes to the grid of fluxes computed with the new-ODFs (Cols. 5 and 6 in Table 3).

Observed and computed fluxes are in units erg s^-1 cm^-2 Å^-1and are normalized at 5556 Å.

Thick lines in the plots "OLD'' of Figs. A.1-A.15 show that the fluxes computed from old-ODF models reproduce the IUE spectrum in the whole 1200-3000 Å interval, except around 1400 Å and 1600 Å when the quasi-molecular absorptions H-H⁺ and H-H are observed. Thick lines in the plots "NEW'' of Figs. A.1-A.15 show that the models computed with the new-ODFs improve the agreement at 1400 Å and 1600 Å between the observed and computed fluxes. They usually well reproduce the whole observed energy distribution from 1200 Å to 3000 Å. Only for a few stars, like BD+00 145 (Fig. A.2) and HD 2857 (Fig. A.14) the models with parameters derived from the whole IUE spectra do not reproduce the observed quasi-molecular absorptions. For these two stars, we show in the plot "NEW'' both the computed flux which fits the whole IUE spectrum and the computed flux which fits only the short-wavelength spectrum.

The Figs. A.1-A.15 indicate that the H-H⁺ absorption at 1400 Å is very weak around 10000 K, increases with decreasing temperature up to about 8500 K and then decreases starting from about $T_{\rm eff}$$\,<\,$ 8500 K. Stars with a remarkable depression at 1400 Å are HD 167105 (Fig. A.5) and HD 14829 (Fig. A.5).

The H-H absorption at 1600 Å can be observed starting from about $T_{\rm eff}$=8700 K. It increases with decreasing $T_{\rm eff}$ and with decreasing metallicity. Stars with a remarkable depression at 1600 Å are HD 86986 (Fig. A.10), HD 8376 (Fig. A.11), HD 13780 (Fig. A.11), HD 87047 (Fig. A.12), and HD 202759 (Fig. A.15).