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

By M. Spite, R. Cayrel, B. Plez, V. Hill, F. Spite, É. Depagne, P. François, P. Bonifacio, B. Barbuy, Timothy C. Beers and 4 more. 2004

334 citations recorded by the source corpus.

We have investigated the poorly-understood origin of nitrogen in the early Galaxy by determining N abundances from the NH band at 336 nm in 35 extremely metal-poor halo giants, with carbon and oxygen abundances from Cayrel et al. (\cite{CDS04}, AA these stars are generally more evolved and located on the upper Red Giant Branch (RGB) or Horizontal Branch (HB). The second group has [N/Fe] < 0.5, shows no evidence for C to N conversion, and Li is only moderately diluted; these stars belong to the lower RGB 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, they are called ``unmixed stars''. The [O/Fe] and [(C+N)/Fe] ratios are the same in the two groups, confirming that the differences between them are caused by dredge-up of CN-processed material in the first group, with negligible contributions from the O-N cycle. The ``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. Their mean values in each metallicity bin decrease with increasing metallicity, but this trend could be a statistical effect. 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 DLAs, 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. Since all the stars show clear [?/Fe] enhancements, they were formed before any significant enrichment of the Galactic gas by SNe Ia, and their composition should reflect the yields of the first SNe II. However, if massive AGB stars or AGB supernovae evolved more rapidly than SNe Ia and contaminated the ISM, our stars would also reflect the yields of these 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-? (DLA) systems. They extend the well-known DLA ``plateau'' at [N/O] ? -0.8 to lower metallicities, albeit with more scatter; no star is found below the putative ``low [N/?] plateau'' at [N/O] ? -1.55 in DLAs. Based on observations obtained with the ESO VLT under ESO programme ID 165.N-0276(A). This work has made use of the SIMBAD database.

Subfields: Astronomy and Astrophysics, Instrumentation

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In Astronomy and Astrophysics

1. Timothy C. Beers
2. J. Norris
3. R. Hirschi
4. A. Frebel
5. Martin Asplund
6. A. Karakas
7. G. Meynet
8. A. Chieffi

In Instrumentation

1. A. Frebel
2. R. Hirschi
3. Timothy C. Beers
4. M. Pettini
5. J. Norris
6. C. Steidel
7. C. Sneden
8. A. Chieffi

Citations in the corpus

• THE CHEMICAL EVOLUTION OF THE DRACO DWARF SPHEROIDAL GALAXY (2009, background): “…ratios vary enormously from star to star among very metal-poor stars, perhaps as a function of Galactocentric radius, or perhaps as a result of deep mixing, symptoms of which have been found among very metal-poor halo giants by Spite et al (2005), or contamination from a former AGB companion.”
• C, N, O abundances in the most metal-poor damped Lyman alpha systems★ (2007, background): “One of the aims of the present work is to investigate the behaviour of the C/O ratio at low metallicities, motivated by the results of Akerman et al. (2004) and Spite et al. (2005) which we now summarise.”
• Very low-metallicity massive stars: - Pre-SN evolution models and primary nitrogen production (2006, background): “14 in Spite et al. 2005).”
• On the self-enrichment scenario of galactic globular clusters: constraints on the IMF (2006, background): “Since the value of [O/Fe]=0.5 is typical of field halo stars (e.g. Spite et al. 2005), it is usually assumed that stars displaying that ratio (and correspondingly low [Na/Fe]) are those that maintain their original composition, the one of the proto-cluster gas.”
• Carbon-enhanced Metal-poor Stars. I. Chemical Compositions of 26 Stars (2006, background): “…al. (2006), where their new chemical evolution models require the large yields of carbon and nitrogen from the models discussed byHirschi et al. (2007) in order to account for the upturn of the observed [N/O] and [C/O] ratios in the ‘‘unmixed’’ carbon-normal stars described by Spite et al. (2005).”
• Effects of rotation on the evolution of primordial stars (2008, background): “This means that the timescale for the chemical enrichment in the halo is well constrained. with the surface ratios determined for the metal-poor stars observed by Israelian et al. (2004) and Spite et al. (2005).”
• THE MASS SPECTRUM OF THE FIRST STARS (2014, methodology): “We adopt only normal metal-poor stars without an enhancement of C or N because C-enhanced and N-enhanced metal-poor stars might require a specific type of CCSNe (faint SNe; e.g., Umeda & Nomoto 2002) and self enrichment in the low-mass, metal-poor stars (e.g., Spite et al. 2005), respectively.”
• Near-Field Cosmology with Extremely Metal-Poor Stars (2015, background): “Spite et al. (2005) have convincingly argued that this effect is driven by mixing, on the RGB, of material that has been processed by the CNcycle, from interior regions into the outer layers of the observed stars.”
• Quantifying the uncertainties of chemical evolution studies II. Stellar yields (2010, result): “Model predictions are compared to data from Spite et al. (2005), Lai etl.”
• The most metal-poor damped Lyα systems: insights into chemical evolution in the very metal-poor regime★ (2011, methodology): “…by Akerman et al. (2004) who reported a rather surprising evolution of [C/O] with decreasing O abun- 1 We adopt the standard notation: [A/B] ≡ log(NA/NB) − log(NA/NB)⊙, where NA,B refers to the number of atoms in element A and B. dance in their sample of 34 halo stars (see also Spite et al. 2005).”
• A SEARCH FOR STARS OF VERY LOW METAL ABUNDANCE. VI. DETAILED ABUNDANCES OF 313 METAL-POOR STARS (2014, background): “…represents the mean difference, standard deviation, and number of stars: 〈∆〉 (σ, N). a Includes [Ba/Fe] from McWilliam (1998) b Includes [C/Fe] and [N/Fe] from Spite et al. (2005) and [Sr/Fe] and [Ba/Fe] from François et al. (2007) lines of each species were employed in each star by each analysis.”
• THE MOST METAL-POOR STARS. IV. THE TWO POPULATIONS WITH [Fe/H] ≲ −3.0 (2012, background): “The C-normal giants in Figure 2, represented by small open and filled black circles, are described by Spite et al. (2005) as “mixed” and “unmixed”, respectively.”
• Supernova Nucleosynthesis in Population III 13-50 M☉ Stars and Abundance Patterns of Extremely Metal-poor Stars (2007, background): “On the other hand, the EMP and VMP stars with no evidence of the NUCLEOSYNTHESIS IN POP III SNe AND EMP STARS 523 deep mixing show relatively small [N/Fe] ( 1; Spite et al. 2005).”