First stars VI - Abundances of C, N, O, Li, and mixing in extremely metal-poor giants. Galactic evolution of the light elements

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dc.creatorSpite, M.
dc.creatorCayrel, R.
dc.creatorPlez, B.
dc.creatorHill, V.
dc.creatorSpite, F.
dc.creatorDepagne, E.
dc.creatorFrancois, P.
dc.creatorBonifacio, P.
dc.creatorBarbuy, B.
dc.creatorBeers, T.
dc.creatorAndersen, J.
dc.creatorMolaro, P.
dc.creatorNordstroem, B.
dc.creatorPrimas, F.
dc.date2004-09-22
dc.date2005-01-26
dc.date.accessioned2026-07-07T02:14:43Z
dc.date.available2026-07-07T02:14:43Z
dc.descriptionWe have investigated the poorly-understood origin of nitrogen in the early Galaxy by determining N abundances in 35 extremely metal-poor halo giants (22 stars have [Fe/H]<-3.0) using the C and O abundances determined in Paper V. Because any dredge-up of CNO processed material to the surface may complicate the interpretation of CNO abundances in giants, we have also measured the surface abundance of lithium. Our sample shows a clear dichotomy between two groups of stars. The first group shows evidence of C to N conversion through CN cycling and strong Li dilution, a signature of mixing. The second group shows no evidence for C to N conversion, and Li is only moderately diluted, and we conclude that their C and N abundances are very close to those of the gas from which they formed in the early Galaxy. These "unmixed" stars reflect the abundances in the early Galaxy: the [C/Fe] ratio is constant (about +0.2 dex) and the [C/Mg] ratio is close to solar at low metallicity, favouring a high C production by massive zero-metal supernovae. The [N/Fe] and [N/Mg] ratios scatter widely. The larger values of these ratios define a flat upper plateau ([N/Mg]= 0.0, [N/Fe]= +0.1), which could reflect higher values within a wide range of yields of zero-metal Sne II. Alternatively, by analogy with the DLA's, the lower abundances ([N/Mg]= -1.1, [N/Fe]= -0.7) could reflect generally low yields from the first Sne II, the other stars being N enhanced by winds of massive Asymptotic Giant Branch (AGB) stars. At present it cannot be decided whether primary N is produced primarily in SNe II or in massive AGB stars, or in both. The stellar N abundances and [N/O] ratios are compatible with those found in Damped Lyman-alpha (DLA) systems.
dc.description15 pages,18 figures, difference of N abundance from NH and CN slightly reduced
dc.identifierhttps://arxiv.org/abs/astro-ph/0409536
dc.identifierhttp://arxiv.org/abs/astro-ph/0409536
dc.identifier2005 A&A 430 p. 655
dc.identifierdoi:10.1051/0004-6361:20041274
dc.identifier.urihttp://salesiana.dossiersoluciones.com/handle/123456789/8223
dc.subjectAstrophysics
dc.titleFirst stars VI - Abundances of C, N, O, Li, and mixing in extremely metal-poor giants. Galactic evolution of the light elements
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