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$\begin{figure} \par\includegraphics[angle=270,width=17cm,clip]{2973fig1.eps} \end{figure}$ Figure 1: VLT H $\alpha$ - R images of Sextans A ( left) and Sextans B ( right). The f.o.v. is 2 $^\prime$ $\times$ 2 $^\prime$ . The H II regions and PNe observed spectroscopically are indicated with their identification numbers as in Table 1 for H II regions and as in Magrini et al. (2002, 2003) for PNe.
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In the text

$\begin{figure} \par\includegraphics[angle=270,width=14.2cm,clip]{2973fig2.eps} \end{figure}$ Figure 2: VLT spectrum of the planetary nebula in Sextans A.
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In the text

$\begin{figure} \par\includegraphics[angle=270,width=14.2cm,clip]{2973fig3.eps} \end{figure}$ Figure 3: VLT spectra of the five planetary nebulae in Sextans B. Identification numbers come from Magrini et al. (2002).
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In the text

$\begin{figure} \par\includegraphics[angle=270,width=14.2cm,clip]{2973fig4.eps} \end{figure}$ Figure 4: VLT spectra of four H II regions in Sextans A.
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In the text

$\begin{figure} \par\includegraphics[angle=270,width=14.2cm,clip]{2973fig5.eps} \end{figure}$ Figure 5: VLT spectra of another five H II regions in Sextans A.
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In the text

$\begin{figure} \par\includegraphics[angle=270,width=14.2cm,clip]{2973fig6.eps} \end{figure}$ Figure 6: VLT spectra of four H II regions in Sextans B.
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In the text

$\begin{figure} \par\includegraphics[angle=270,width=14.2cm,clip]{2973fig7.eps} \end{figure}$ Figure 7: VLT spectra of another four H II regions in Sextans B.
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In the text

$\begin{figure} \par\includegraphics[width=8.2cm,clip]{2973fig8.eps} \end{figure}$ Figure 8: H-burning (dashed lines) and He-burning (continuous line) evolutionary tracks for metallicity Z=0.004 from Vassiliadis & Wood (1994). Final mass of the central star are quoted close to the corresponding track. Large symbols (circles) correspond to Sextans B PNe and the small one (square) indicates the Sextans A PN.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{2973fig9.eps} \end{figure}$ Figure 9: Relationship between He/H and N/O. The solid line is the stellar model for the progenitor by Marigo (2004) for Z=0.001 and the dashed line for Z=0.004. Values of the initial masses are indicated. Full circles correspond to Sextans B PNe and the diamond is the Sextans A PN. PNe with uncertain N/H determination are marked with dot-dashed error bars.
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In the text

$\begin{figure} \par\includegraphics[width=8.6cm,clip]{2973fig10.eps} \end{figure}$ Figure 10: Relationship between N/O and N/H for PNe. The central dot-dashed line is the fit from Henry (1990) using a sample of PNe of the Galaxy, LMC, SMC and M 31. The external dot-dashed lines are placed at a distance of $\pm$ 3 $\sigma$ from the fit, where $\sigma =0.1$ dex. The solid line is the model for LMC by Groenewegen & de Jong (1994) built for the LMC metallicity and several initial masses. The top-right point of the curve corresponds to a model with an initial mass of 8.5 $M_\odot$ , the first change of slope with 2 $M_\odot$ , and the last point ( bottom-left) is for 0.93 $M_\odot$ . The dashed line is the model for Z=0.004 and initial masses from 0.8 ( left) to 5 ( right) $M_\odot$ by Marigo (2001). Observed abundances are from: Galaxy (Perinotto et al. 2004a); LMC and SMC (Leisy et al., in prep.); M 31 (Jacoby & Ciardullo 1999); M 33 (Magrini et al. 2004); Sextans A and Sextans B (this work). PNe of Sextans B with uncertain N/H determination are marked with dot-dashed error bars.
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In the text

$\begin{figure} \par\includegraphics[width=8.5cm,clip]{2973fig11.eps} \end{figure}$ Figure 11: Relationship between Ne/H and O/H. The solid line is the fit built by Henry (1989). The dotted lines are placed at a distance of $\pm$ 1 $\sigma$ from the fit, and the dashed lines at $\pm$ 3 $\sigma$ , where $\sigma =0.1$ dex as indicated by Henry 1989. Only H II regions with $T_{\rm e}$ measured are reported.
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In the text

$\begin{figure} \par\includegraphics[angle=270,width=17cm,clip]{2973fig1.eps} \end{figure}$	Figure 1: VLT H $\alpha$ - R images of Sextans A ( left) and Sextans B ( right). The f.o.v. is 2 $^\prime$ $\times$ 2 $^\prime$ . The H II regions and PNe observed spectroscopically are indicated with their identification numbers as in Table 1 for H II regions and as in Magrini et al. (2002, 2003) for PNe.
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$\begin{figure} \par\includegraphics[angle=270,width=14.2cm,clip]{2973fig2.eps} \end{figure}$	Figure 2: VLT spectrum of the planetary nebula in Sextans A.
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$\begin{figure} \par\includegraphics[angle=270,width=14.2cm,clip]{2973fig3.eps} \end{figure}$	Figure 3: VLT spectra of the five planetary nebulae in Sextans B. Identification numbers come from Magrini et al. (2002).
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$\begin{figure} \par\includegraphics[angle=270,width=14.2cm,clip]{2973fig4.eps} \end{figure}$	Figure 4: VLT spectra of four H II regions in Sextans A.
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$\begin{figure} \par\includegraphics[angle=270,width=14.2cm,clip]{2973fig5.eps} \end{figure}$	Figure 5: VLT spectra of another five H II regions in Sextans A.
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$\begin{figure} \par\includegraphics[angle=270,width=14.2cm,clip]{2973fig6.eps} \end{figure}$	Figure 6: VLT spectra of four H II regions in Sextans B.
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$\begin{figure} \par\includegraphics[angle=270,width=14.2cm,clip]{2973fig7.eps} \end{figure}$	Figure 7: VLT spectra of another four H II regions in Sextans B.
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$\begin{figure} \par\includegraphics[width=8.2cm,clip]{2973fig8.eps} \end{figure}$	Figure 8: H-burning (dashed lines) and He-burning (continuous line) evolutionary tracks for metallicity Z=0.004 from Vassiliadis & Wood (1994). Final mass of the central star are quoted close to the corresponding track. Large symbols (circles) correspond to Sextans B PNe and the small one (square) indicates the Sextans A PN.
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$\begin{figure} \par\includegraphics[width=8cm,clip]{2973fig9.eps} \end{figure}$	Figure 9: Relationship between He/H and N/O. The solid line is the stellar model for the progenitor by Marigo (2004) for Z=0.001 and the dashed line for Z=0.004. Values of the initial masses are indicated. Full circles correspond to Sextans B PNe and the diamond is the Sextans A PN. PNe with uncertain N/H determination are marked with dot-dashed error bars.
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$\begin{figure} \par\includegraphics[width=8.5cm,clip]{2973fig11.eps} \end{figure}$	Figure 11: Relationship between Ne/H and O/H. The solid line is the fit built by Henry (1989). The dotted lines are placed at a distance of $\pm$ 1 $\sigma$ from the fit, and the dashed lines at $\pm$ 3 $\sigma$ , where $\sigma =0.1$ dex as indicated by Henry 1989. Only H II regions with $T_{\rm e}$ measured are reported.
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