John C. Lattanzio

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Three-dimensional stellar modeling has enabled us to identify a deep-mixing mechanism that must operate in all low mass giants. This mixing process is not optional, and is driven by a molecular weight inversion created by the He(He,2p)He reaction. In this paper we characterize the behavior of this mixing, and study its impact on the envelope abundances. It(More)
We continue our study of the core helium flash using the three dimensional hydrodynamics code Djehuty. Continuing from earlier calculations, we now take relaxed 3D configurations and add various amounts of rotation. We find that rotation periods consistent with those observed in white dwarfs produce negligible changes in the structure and evolution of the(More)
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)
Context. The growing body of spectral observations of the extremely metal-poor (EMP) stars in the Galactic Halo provides constraints on theoretical studies of the chemical and stellar evolution of the early Universe. Aims. To calculate yields for EMP stars for use in chemical evolution calculations and to test whether such models can account for some of 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)
We report on an investigation into stellar evolution and nucleosynthesis in the low and extremely low metallicity regime, including models of stars with a pure Big Bang composition (i.e. Z = 0). The metallicity range of the extremely metalpoor (EMP) models we have calculated is −6.5 < [Fe/H] <−3.0, whilst our models are in the mass range 0.85 < M < 3.0M⊙.(More)
Low-mass stars, approximately 1 to 2 solar masses, near the Main Sequence are efficient at producing the helium isotope 3He, which they mix into the convective envelope on the giant branch and should distribute into the Galaxy by way of envelope loss. This process is so efficient that it is difficult to reconcile the low observed cosmic abundance of 3He(More)
We provide an overview of the current theoretical picture of AGB stars, with particular emphasis on the nucleosynthesis occurring in these stars, both in their deep interiors, associated with thermal pulses or flashes, and also during the phase of “hot bottom burning”. These processes are illustrated with some new results from hot bottom burning(More)