All Figures

	Figure 1: Reduced UVES spectra in the region of the NH band at 336 nm. Crosses represent the observed spectra, while the full lines show synthetic spectra computed for the best-fit N abundance as well as twice that value (thick and thin lines, respectively). The two stars have about the same metallicity, [Fe/H] = -3.06 (BD-18:5550) and [Fe/H] = -3.00 (CS 22186-025).
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In the text

	Figure 2: Observed spectrum of CS 22892-52 near the Li line at 670.7 nm (crosses), and synthetic spectra computed with log N(Li) = 0.15 and 0.45 (thick and thin lines, respectively).
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In the text

	Figure 3: [C/Fe] and [C/Mg] vs. [Fe/H] and [Mg/H]. Both diagrams show far more scatter than seen for other elements in Paper V. The peculiar "carbon-rich'' stars CS 22949-037 and CS 22892-052 are labelled; they cannot be directly compared to the other stars of the sample.
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In the text

	Figure 4: [N/H] values derived from the CN and NH bands. The correlation is good, but shows a systematic shift of about 0.4 dex. The two carbon-rich stars are identified.
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In the text

	Figure 5: [N/Fe] vs. [Fe/H] and [N/Mg] vs. [Mg/H] for our sample. The scatter of the points is even larger than in Fig. 3 (the scale of both figures is the same).
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In the text

	Figure 6: [N/Fe] vs. [C/Fe] for our sample. Two groups are clearly separated: the "mixed'' stars ([N/Fe] > 0.5) shown as open circles, and the "unmixed'' stars ([N/Fe] < 0.5) shown as dots (both with error bars). CS 22892-52 and CS 22949-37 are the two peculiar carbon-rich stars.
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In the text

	Figure 7: [C/N] vs. for the sample; symbols as in Fig. 6. The line [C/N] = -0.4 separates the mixed and unmixed stars. Stars with only upper limits on C and/or N abundance have been omitted. Note that most unmixed stars have   4800 K (cf. also Paper V, Sect. 4.1).
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In the text

	Figure 8: Lithium abundances vs. [N/Fe] and [C/N] (symbols as in Fig. 6). All the mixed stars ([N/Fe] > 0.6 or [C/N] < -0.6; dotted lines) have destroyed their original Li.
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In the text

	Figure 9: log g vs. log diagram for the sample (symbols as in Fig. 6). The RGB and HB are fairly well-defined (dashed lines). At fixed , the unmixed stars on the "low'' RGB have higher log g than the mixed stars.
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In the text

	Figure 10: [O/Fe] vs. [Fe/H] for the sample; symbols as in Fig. 6. The lack of any significant difference between mixed and unmixed stars is strong evidence that deep mixing has not occurred (the O abundances shown here are not corrected for 3D effects; cf. Paper V).
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In the text

	Figure 11: [N/O] vs. [O/H] for the sample; symbols as in Fig. 6 (the carbon stars CS 22892-052 and CS22949-037 are shown as triangles). The [N/O] vs. [O/H] relation in the mixed stars is quite tight, [N/O] decreasing slightly with increasing [O/H] (dashed line). This suggests that the amount of N mixed to the surface does not depend strongly on metallicity.
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In the text

	Figure 12: [(C+N)/Fe] vs. [Fe/H]; symbols as in Fig. 6. The C+N abundance shows much smaller scatter than C or N alone (cf. Figs. 3 and 5). [(C+N)/Fe]  0.25 dex at low [Fe/H]. CS 22949-037 and CS 22892-052 are not shown here.
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In the text

	Figure 13: [C/Fe] and [C/Mg] vs. [Fe/H] and [Mg/H] for the unmixed stars. [C/Mg] may increase slightly towards lower metallicity; for [Mg/H] < -2.9, [C/Mg]  0.0 dex.
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In the text

Figure 14: [C/O] vs. [O/H] for our unmixed stars (dots) and the halo stars from Akerman et al. (2004; squares). The lines show the predictions of their standard model for C and O, using the yields of Meynet & Maeder (2002, dotted), Chieffi & Limongi (2002, dashed), and Chieffi & Limongi with a top-heavy IMF (M > , solid line). The data seem to favour substantial early C production in massive zero-metal supernovae.

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In the text

	Figure 15: [N/Fe] and [N/Mg] vs. [Fe/H] and [Mg/H] for our unmixed stars. With increasing metallicity, [N/Fe] and [N/Mg] decrease (dashed lines) and the dispersion increases, a behaviour unexpected from theoretical expectations.
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In the text

	Figure 16: The same data as in Fig. 15, but interpreted differently. We assume here that the low dispersion at low metallicity is a spurious effect due to the small size of the sample, while [N/Fe] and [N/Mg] in general shows large scatter from star to star, with 0.7 < [N/Fe] < 0.3 and -1.1 < [N/Mg] < 0.2 as seen for [Fe/H] > -3.3.
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In the text

Figure 17: Light-element abundance ratios in metal-poor dwarfs (Israelian et al. 2004, open circles), in our unmixed giants (filled circles), and in DLAs (crosses). [N/O] vs. [O/H] is shown for the stars, for the DLAs, following Centurión et al. (2003), where may denote O, S, or Si in different DLAs. The DLAs with have , while the most metal-poor stars have ; but given the scatter in both samples, this difference may not be significant. The horizontal and sloping dotted lines show the relations for primary and secondary N production, respectively. Neither sample shows any dependence of N abundance on metallicity for [O/H] or  dex; thus, early N production was mainly primary.

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In the text

	Figure 18: Same as Fig. 15, but only for stars included in Fig. 17. The general decrease of [N/Mg] with [Mg/H] and the different behaviors of [N/Mg] and [N/O] remain visible.
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In the text