Amanda I. Karakas

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Abundances of C, N, and O are determined in four bright red giants that span the known abundance range for light (Na and Al) and s-process (Zr and La) elements in the globular cluster NGC 1851. The abundance sum C+N+O exhibits a range of 0.6 dex, a factor of 4, in contrast to other clusters in which no significant C+N+O spread is found. Such an abundance(More)
Asymptotic giant branch (AGB) stars are a main site of production of nuclei heavier than iron via the s process. In massive (>4 M) AGB stars the operation of the 22 Ne neutron source appears to be confirmed by observations of high Rb enhancements, while the lack of Tc in these stars rules out 13 C as a main source of neutrons. The problem is that the Rb(More)
We present detailed models of low and intermediate-mass asymptotic giant branch (AGB) stars with and without the 18 F(α,p) 21 Ne reaction included in the nuclear network, where the rate for this reaction has been recently experimentally evaluated for the first time. The lower and recommended measured rates for this reaction produce negligible changes to the(More)
Among the short-lived radioactive nuclei inferred to be present in the early solar system via meteoritic analyses, there are several heavier than iron whose stellar origin has been poorly understood. In particular, the abundances inferred for (182)Hf (half-life = 8.9 million years) and (129)I (half-life = 15.7 million years) are in disagreement with each(More)
Observations of planetary nebulae (PNe) by Sterling, Dinerstein and Bowers have revealed abundances in the neutron-capture element Germanium (Ge) from solar to factors of 3 – 10 above solar. The enhanced Ge is an indication that the slow-neutron capture process (s process) operated in the parent star during the thermally-pulsing asymptotic giant branch(More)
We study the effect of uncertainties in the proton-capture reaction rates of the NeNa and MgAl chains on nucleosynthesis due to the operation of hot bottom burning (HBB) in intermediate-mass asymptotic giant branch (AGB) stars. HBB nucleosynthesis is associated with the production of sodium, radioactive 26 Al and the heavy magnesium isotopes, and it is(More)
We present nucleosynthesis calculations and the resulting 19 F stellar yields for a large set of models with different masses and metallicity. During the Asymptotic Giant Branch (AGB) phase 19 F is produced as a consequence of nucleosynthesis occurring during the convective thermal pulses and also during the interpulse periods if protons from the envelope(More)
The abundance of the neutron-rich magnesium isotopes observed in metal-poor stars is explained quantitatively with a chemical evolution model of the local Galaxy that considers-for the first time-the metallicity-dependent contribution from intermediate mass stars. Previous models that simulate the variation of Mg isotopic ratios with metallicity in the(More)