Handbook of Isotopes in the Cosmos

Clayton, Donald D.

doi:10.1017/cbo9780511550225

Cited by 129 publications

(157 citation statements)

References 0 publications

Supporting

Mentioning

152

Contrasting

Order By: Relevance

“…Sodium is an odd-Z element, synthesised mostly during hydrostatic carbon burning, and partly during hydrogen burning through the NeNa cycle; the s-process produces some Na as well (Clayton 2003). Adopting the LTE approximation in standard abundance analyses of Na can lead to substantial overestimates of the Na abundances.…”

Section: Odd-z Elementsmentioning

confidence: 99%

Quantifying the uncertainties of chemical evolution studies

Romano

Karakas

Tosi

et al. 2010

A&A

391

570

View full text Add to dashboard Cite

Context. Galactic chemical evolution models are useful tools for interpreting the large body of high-quality observational data on the chemical composition of stars and gas in galaxies that have become available in recent years. Aims. This is the second paper of a series that aims at quantifying the uncertainties in chemical evolution model predictions related to the underlying model assumptions. Specifically, it deals with the uncertainties due to the choice of the stellar yields. Methods. We adopted a widely used model for the chemical evolution of the Galaxy to test the effects of changing the stellar nucleosynthesis prescriptions on the predicted evolution of several chemical species. Up-to-date results from stellar evolutionary models were carefully taken into account. Results. We find that, except for a handful of elements whose nucleosynthesis in stars is well understood by now, large uncertainties still affect model predictions. This is especially true for the majority of the iron-peak elements, but also for much more abundant species such as carbon and nitrogen. The main causes of the mismatch we find among the outputs of different models assuming different stellar yields and among model predictions and observations are (i) the adopted location of the mass cut in models of type II supernova explosions; (ii) the adopted strength and extent of hot bottom burning in models of asymptotic giant branch stars; (iii) the neglection of the effects of rotation on the chemical composition of the stellar surfaces; (iv) the adopted rates of mass loss and of (v) nuclear reactions; and (vi) the different treatments of convection. Conclusions. Our results suggest that it is mandatory to include processes such as hot bottom burning in intermediate-mass stars and rotation in stars of all masses in accurate studies of stellar evolution and nucleosynthesis. In spite of their importance, both these processes still have to be better understood and characterized. As for massive stars, presupernova models computed with mass loss and rotation are available in the literature, but they still wait for a self-consistent coupling with the results of explosive nucleosynthesis computations.

show abstract

Section: Odd-z Elementsmentioning

confidence: 99%

Quantifying the uncertainties of chemical evolution studies

Romano

Karakas

Tosi

et al. 2010

A&A

391

570

View full text Add to dashboard Cite

show abstract

“…The constant [Cr/Fe] with metallicity is derived from the LTE analysis of Cr ii lines (Gratton & Sneden 1991;Bonifacio et al 2009) that has a simple interpretation in the theory of nucleosynthesis. The Cr is formed with Fe in explosive Si-burning that occurs in supernova (SN) events, and the production ratio Cr/Fe is roughly solar in both SNe II and SNe Ia (Clayton 2003). Thus, using standard prescriptions for Cr nucleosynthesis, most of the GCE models reproduce the flat [Cr/Fe] trend with [Fe/H] (e.g., Timmes et al 1995;Samland 1998;Goswami & Prantzos 2000).…”

Section: Introductionmentioning

confidence: 99%

Chromium: NLTE abundances in metal-poor stars and nucleosynthesis in the Galaxy

Bergemann

Cescutti

2010

A&A

157

124

View full text Add to dashboard Cite

Aims. We investigate statistical equilibrium of Cr in the atmospheres of late-type stars to ascertain whether the systematic abundance discrepancy between Cr I and Cr II lines, as often found in previous work, is due to deviations from local thermodynamic equilibrium (LTE). Furthermore, we attempt to interpret the Non-LTE (NLTE) trend of [Cr/Fe] with [Fe/H] using chemical evolution models for the solar neighborhood. Methods. NLTE calculations are performed for the model of the Cr atom, comprising 340 levels and 6806 transitions in total. We use the quantum-mechanical photoionization cross-sections of Nahar (2009) and investigate the sensitivity of the model to uncertain crosssections for H I collisions. NLTE line formation is performed for the MAFAGS-ODF model atmospheres of the Sun and 10 metal-poor stars with −3.2 < [Fe/H] < −0.5, and Cr abundances are derived by comparing the synthetic and observed flux spectra. Results. We achieve good ionization equilibrium of Cr for models with different stellar parameters, if inelastic collisions with H I atoms are neglected. The solar NLTE abundance based on Cr I lines is 5.74 dex with σ = 0.05 dex, which is ∼0.1 dex higher than the LTE abundance. For the metal-poor stars, the NLTE abundance corrections to Cr I lines range from +0.3 to +0.5 dex. The resulting [Cr/Fe] ratio is roughly solar for the range of metallicities analyzed here, which is consistent with current views on the production of these iron peak elements in supernovae. Conclusions. The tendency of Cr to become deficient with respect to Fe in metal-poor stars is an artifact caused by the neglect of NLTE effects in the line formation of Cr i, and has no relation to any peculiar physical conditions in the Galactic ISM or deficiencies of nucleosynthesis theory.

show abstract

“…Cr is of particular interest in the fact that besides the neutron rich effects on 54 Cr, 53 Cr is the decay product of 53 Mn, an extinct radionuclide, which has been shown to be present in the early solar system (e.g., Birck & Allègre 1985;Clayton 2003a). The isotopic compositions of 53 Cr and 54 Cr are reported as ε 53,54 Cr values.…”

Section: Introductionmentioning

confidence: 99%

The Chromium Isotopic Composition of the Ungrouped Carbonaceous Chondrite Tagish Lake

Petitat

Birck

Luu

et al. 2011

ApJ

View full text Add to dashboard Cite

Early solar materials bear a variety of isotopic anomalies that reflect compositional differences deriving from distinct stellar nucleosynthetic processes. As shown in previous studies, the stepwise dissolution with increasing acid strengths of bulk rock carbonaceous chondrites liberates Cr with both excesses and deficits in 53 Cr and 54 Cr relative to the terrestrial standard. The magnitude of the 54 Cr variations within a meteorite decreases in the sequence CI1 > CR2 > CM2 > CV3 > CO3 > CK4 and correlates with the degree of metamorphism of each carbonaceous chondrite class. This study shows that the Tagish Lake meteorite presents the highest excesses in 54 Cr ever measured in a bulk silicate phase. According to this study, the Tagish Lake meteorite is composed of the least re-equilibrated material known at this time. The magnitude of 54 Cr variation decreases now in the following sequence: Tagish Lake (ungrouped CI2) > Orgueil (CI1) > Murchison (CM2) > Allende (CV2). Moreover, this study shows that excesses in 53 Cr relative to Earth can be interpreted as representing the extent of aqueous alteration on meteorite parent bodies. Finally, the high 54 Cr anomalies measured in this meteorite make Tagish Lake one of the major targets to decipher the host of these anomalies.

show abstract

Handbook of Isotopes in the Cosmos

Cited by 129 publications

References 0 publications

Quantifying the uncertainties of chemical evolution studies

Quantifying the uncertainties of chemical evolution studies

Chromium: NLTE abundances in metal-poor stars and nucleosynthesis in the Galaxy

The Chromium Isotopic Composition of the Ungrouped Carbonaceous Chondrite Tagish Lake

Contact Info

Product

Resources

About