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We present stellar yields calculated from detailed models of low and intermediate-mass asymptotic giant branch (AGB) stars. We evolve models with a range of mass from 1 to 6Msun, and initial metallicities from solar to 1/200th of the solar metallicity. Each model was evolved from the zero age main sequence to near the end of the thermally-pulsing AGB phase, and through all intermediate phases including the core He-flash for stars initially less massive than 2.5Msun. For each mass and metallicity, we provide tables containing structural details of the stellar models during the TP-AGB phase, and tables of the stellar yields for 74 species from hydrogen through to sulphur, and for a small number of iron-group nuclei. All tables are available for download. Our results have many applications including use in population synthesis studies and the chemical evolution of galaxies and stellar systems, and for comparison to the composition of AGB and post-AGB stars and planetary nebulae., Comment: 26 pages; to appear in Publications of the Astronomical Society of Australia (PASA); typos fixed in the text and in Tables 4 and 6

We investigate the production of aluminium and magnesium in asymptotic giant branch models covering a wide range in mass and composition. We evolve models from the pre-main sequence, through all intermediate stages, to near the end of the thermally-pulsing asymptotic giant branch phase. We then perform detailed nucleosynthesis calculations from which we determine the production of the magnesium and aluminium isotopes as a function of the stellar mass and composition. We present the stellar yields of sodium and the magnesium and aluminium isotopes. We discuss the abundance predictions from the stellar models in reference to abundance anomalies observed in globular cluster stars.

Asymptotic giant branch stars are expected to produce 22Ne through the combined H and He burning that operates during their thermally pulsing evolution. However, observationally there is a fairly tight correlation between the O and Ne abundances as measured in planetary nebulae in various populations. In this paper we use recent detailed stellar evolutionary calculations for compositions appropriate to the Galaxy and the Large Magellanic Cloud, in an attempt to determine if the models are consistent with the observed abundances. We show that there is only a narrow range in stellar mass, about 2 to 4 M⊙ (lower for lower [Fe/H]) where 22Ne is produced in sufficient quantities to affect the total observed elemental neon abundance, which is mostly 20Ne. The models appear to be consistent with the observations, but a more thorough analysis is required.

In this article I review our understanding of s-process nucleosynthesis in Asymptotic Giant Branch (AGB) stars. The discussion begins with the nuclear back~ ground and then shows how the required conditions are found in thermally pulsing AGB stars. The two competing neutron sources (Ne22 and C13) are discussed, as is the observational and theoretical evidence for and against each of them. We conclude by discussing the recent evidence for hot bottom burning, including the observed enhancements of Li7 and Al26 in some AGB stars.

The astrophysical literature contains many discussions on exactly which changes in a star’s structure are responsible for the extremely large radii found after core hydrogen exhaustion. Different authors favour different mechanisms. Unfortunately none of the proposals are easily verified nor are they easily disproven. In this paper we examine the suggestion that it is the increased central mass concentration (i.e., the growth of the hydrogen exhausted core) which is the primary agent responsible for envelope growth.

Although stars can be approximated very satisfactorily by spherical models, it is clear from observations of star forming regions that the break-up of molecular gas to form proto-stars is a highly complex process that cannot be approximated simply. As a consequence, the theoretical picture of fragmentation, which is based on assuming that fragmentation occurs in uniform, static, isothermal clouds, is too crude to provide a guide to the star formation process. The alternative is to simulate the fragmentation process numerically with the ultimate aim of evolving the gas to proto-stars. The difficulties involved with this procedure are discussed in this paper. We also discuss our proposed solution to this problem, together with a very preliminary calculation.

The origin of the elements is one of the major questions of the 21st century. Our current knowledge dates back to the seminal papers of Hoyle (1954), Burbidge, Burbidge, Fowler and Hoyle (1957) and Cameron (1957). These papers defined the new field of nuclear astrophysics and put stellar nucleosynthesis on solid ground. They successfully identified, broadly, the sites and physics of the main processes producing the various elements. It is well known that iron is the most stable element (as measured by the binding energy per nucleon). The process acting here is neutron capture, which has two idealised extremes: the rapid (r) and slow (s) neutron capture processes, where the rapid and slow refers to the relative speeds of neutron captures compared to β-decays. With the development of modern fast computers, it has become possible to produce detailed models of stellar interiors, which provide the conditions for the expected nucleosynthesis. It has become clear that Asymptotic Giant Branch stars, the final stage in the evolution of most of stars, are producers of most of the s-process species. It is the study of these stars and their associated nucleosynthesis that is the principal topic of this special issue. One of the main names associated with this field is Roberto Gallino, the author of over 350 papers on the subject. In the last 20 or so years, the contributions of Gallino and his co-workers have set the agenda and stimulated the research of the entire community. Further, Roberto has been an inspiration to multiple generations of younger astrophysicists, to whom he has always been extremely generous with his time, ideas and enthusiasm. He (and Maurizio Busso) began the series of Torino Workshops, which have stimulated and fertilised the multi-disciplinary nature of this work. For these reasons, a group of Roberto’s collaborators and friends met to celebrate his work and review the current problems in the area of the origin of the elements heavier than iron. The meeting took place in Roberto’s home city of Torino, in the hills where he

In 2007 the field of nuclear astrophysics celebrated its 50th birthday.

Nuclear astrophysics is about 50 years old. It grew from nuclear physics and was nurtured by those with an interest in astrophysics. A milestone was the publication of the seminal paper of Geoffrey Burbdige, Margaret Burbidge, Willy Fowler and Fred Hoyle in 1957. Since then, it has become a mainstay of modern astrophysics, and has a natural and especially close link to stellar astrophysics. But there has been a revolution in recent years, which has seen the isolation and analysis of circumstellar dust grains, recovered from meteorites. These ‘pre-solar’grains (indicating that they predate the solar system, and survived the various processes associated with its formation) have provided incomparable and revolutionary data of exceptional quality. It is now common to have access to isotopic abundance ratios for major elements as well as for trace elements, and these can be magnificent indications for processes active in the parent star. Much of the presolar grain analysis has been performed on samples of the Murchison meteorite, which fell around the little town of Murchison, near Melbourne, in 1969. The time was right for a workshop dedicated to the astrophysics learned from this analysis, and we are pleased to present some of the papers in this issue of PASA. This workshop was also the sixth in a series of workshops on nuclear astrophysics, initiated at Torino University. We are proud to continue the name and the tradition of these workshops. This was only the second Torino workshop held outside of Italy. The first was organised by Manuel Forestini, in France. Tragically, Manuel suffered a fatal heart attack on March 11, 2003. Manuel worked in many areas of stellar evolution, and was the author of a textbook on the subject. But his main area was AGB stars, and he has contributed much to our understanding of these complex objects, and especially their nucleosynthesis. Manuel did everything with passion and good humour, and was a very dear friend and a valued collaborator. We wish to dedicate this meeting to his memory, his science and his friendship.

This paper presents recent stellar evolutionary calculations of the Asymptotic Giant Branch evolution of a 5M⊙ model. It is found that temperatures at the base of the convective envelope reach up to almost 100 million degrees, high enough for much nucleo-synthesis to occur. Some implications are discussed briefly.

The classical model of the interstellar medium consists of cool clouds (typical temperature 80 K, number density 20-40 cm-3) moving through a warmer interstellar medium (104 K, 0.15-0.3 cm-3) at a rms velocity of ~ 10 km s-1. More recent models have included the coronal gas (106 K) as part of this medium. We consider the collisions of these clouds in order to determine whether these collisions initiate star formation and/or change the state of the interstellar medium.

Star formation is believed to occur in interstellar clouds consisting of both gas and grains. Under the gravitational influence of such a cloud the constituent dust grains sediment toward the centre, and both calculations and implications of this sedimentation have been published by many authors (McCrea and Williams 1965; Horedt 1973, 1976; Prentice 1976; Krautschneider 1977; Flannery and Krook 1978; and others). Two main results from these calculations warrant our attention. Firstly, the timescale for appreciable sedimentation Ts ≃ 107 -108 years, which is consistent with age estimates of many clouds (Harrison 1978, Blitz and Shu 1980). Secondly, the sedimentation proceeds more rapidly for larger grains. This leads to an increase of mean grain size toward the centre of the cloud.

Duley (1974) has shown that, at the temperatures usually associated with interstellar gas clouds, we would expect CNO grains to be present. During gravitational collapse these grains migrate to the centre of the gas cloud, leading to an enhancement of the heavy-element abundance in the core (Prentice 1976, 1978). It was Krautschneider (1977) who verified such a scenario, by considering the dynamical collapse of gas and grain clouds. If such an initial radial abundance inhomogeneity existed, Prentice (1976a) showed that this configuration may well survive the later convective mixing phase and thus approach the zero-age main-sequence (ZAMS) with a small (-v 3% by mass) metal enhanced core.

The discrepancy between the observed and predicted flux of neutrinos from the Sun is well known. Past attempts at reconciling this difference have been unconvincing (Kuchowicz 1976, Rood 1978), and hence investigations in this area continue.

The evolution of asymptotic giant branch (AGB) stars as a function of mass and composition has been studied by Becker and Iben (1979, 1980) for M≥3 M⊙. The results from calculations like these may be used to provide input data for calculations of synthetic AGB star populations, as has been done by Wood and Cahn (1977), Iben (1981) and Renzini and Voli (1981).

A common test for hydrodynamic calculations is the Boss and Bodenheimer (1979, 1981, hereafter BB) problem in which an isothermal, spherical cloud of 1 M⊙ is given a cos (2Φ) density perturbation and the ensuing evolution studied.