EVOLUTION, NUCLEOSYNTHESIS, AND YIELDS OF LOW-MASS ASYMPTOTIC GIANT BRANCH STARS AT DIFFERENT METALLICITIES

By S. Cristallo, L. Piersanti, O. Straniero, Roberto Gallino, I. Domínguez, C. Abia, Gianluca DiRico, M. Quintini, S. Bisterzo. 2009

438 citations recorded by the source corpus.

The envelope of thermally pulsing asymptotic giant branch (TP-AGB) stars undergoing periodic third dredge-up (TDU) episodes is enriched in both light and heavy elements, the ashes of a complex internal nucleosynthesis involving p, α, and n captures over hundreds of stable and unstable isotopes. In this paper, new models of low-mass AGB stars (2 M☉), with metallicity ranging between Z = 0.0138 (the solar one) and Z = 0.0001, are presented. Main features are (1) a full nuclear network (from H to Bi) coupled to the stellar evolution code, (2) a mass loss–period–luminosity relation, based on available data for long-period variables, and (3) molecular and atomic opacities for C- and/or N-enhanced mixtures, appropriate for the chemical modifications of the envelope caused by the TDU. For each model, a detailed description of the physical and chemical evolutions is presented; moreover, we present a uniform set of yields, comprehensive of all chemical species (from hydrogen to bismuth). The main nucleosynthesis site is the thin 13C pocket, which forms in the core–envelope transition region after each TDU episode. The formation of this 13C pocket is the principal by-product of the introduction of a new algorithm, which shapes the velocity profile of convective elements at the inner border of the convective envelope: both the physical grounds and the calibration of the algorithm are discussed in detail. We find that the pockets shrink (in mass) as the star climbs the AGB, so that the first pockets, the largest ones, leave the major imprint on the overall nucleosynthesis. Neutrons are released by the 13C(α, n)16O reaction during the interpulse phase in radiative conditions, when temperatures within the pockets attain T ∼ 1.0 × 108 K, with typical densities of (106–107) neutrons cm−3. Exceptions are found, as in the case of the first pocket of the metal-rich models (Z = 0.0138, Z = 0.006 and Z = 0.003), where the 13C is only partially burned during the interpulse: the surviving part is ingested in the convective zone generated by the subsequent thermal pulse (TP) and then burned at T ∼ 1.5 × 108 K, thus producing larger neutron densities (up to 1011 neutrons cm−3). An additional neutron exposure, caused by the 22Ne(α, n)25Mg during the TPs, is marginally activated at large Z, but becomes an important nucleosynthesis source at low Z, when most of the 22Ne is primary. The final surface compositions of the various models reflect the differences in the initial iron-seed content and in the physical structure of AGB stars belonging to different stellar populations. Thus, at large metallicities the nucleosynthesis of light s-elements (Sr, Y, Zr) is favored, whilst, decreasing the iron content, the overproduction of heavy s-elements (Ba, La, Ce, Nd, Sm) and lead becomes progressively more important. At low metallicities (Z = 0.0001) the main product is lead. The agreement with the observed [hs/ls] index observed in intrinsic C stars at different [Fe/H] is generally good. For the solar metallicity model, we found an interesting overproduction of some radioactive isotopes, like 60Fe, as a consequence of the anomalous first 13C pocket. Finally, light elements (C, F, Ne, and Na) are enhanced at any metallicity.

Subfields: Astronomy and Astrophysics, Education, Instrumentation

View Paper: https://www.semanticscholar.org/paper/8a7dc71377786fafc1b366b64fed14494aff54f0

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

1. A. Karakas
2. Timothy C. Beers
3. A. Helmi
4. M. Lugaro
5. A. Frebel
6. Roberto Gallino
7. J. Lattanzio
8. J. Norris

In Education

1. A. Karakas
2. L. Girardi
3. Martin Asplund
4. A. Bressan
5. Timothy C. Beers
6. M. Bessell
7. P. Marigo
8. A. Helmi

In Instrumentation

1. A. Helmi
2. A. Karakas
3. A. Frebel
4. Timothy C. Beers
5. M. Lugaro
6. M. Irwin
7. Roberto Gallino
8. J. Norris

Citations in the corpus

• THE s-PROCESS IN ASYMPTOTIC GIANT BRANCH STARS OF LOW METALLICITY AND THE COMPOSITION OF CARBON-ENHANCED METAL-POOR STARS (2011, methodology): “In low-mass and low-metallicity AGB stars this convective region can extend into the H-rich layer and peculiar nucleosynthesis is expected to occur there (Campbell & Lattanzio 2008), including s-process nucleosynthesis (Cristallo et al. 2009a).”
• Dissecting stellar chemical abundance space with t-SNE (2018, result): “…relations of the thin disc (see also Spina et al. 2018), but are still roughly consistent with the trends set by chemical-evolution models with metallicity-dependent yields from intermediate-and low-mass AGB stars (e.g. Cristallo et al. 2009, 2015; da Silva et al. 2016; Delgado Mena et al. 2017).”
• THE MOST METAL-POOR STARS. II. CHEMICAL ABUNDANCES OF 190 METAL-POOR STARS INCLUDING 10 NEW STARS WITH [Fe/H] ⩽ −3.5,, (2012, background): “…elements from AGB stars are strongly dependent on mass and metallicity, such that they may be good candidates for explaining part, or perhaps most, of the large range of C ands-process element abundances (e.g., Karakas & Lattanzio 2007; Karakas 2010; Cristallo et al. 2011; Lugaro et al. 2012).”
• GALACTIC CHEMICAL EVOLUTION AND SOLAR s-PROCESS ABUNDANCES: DEPENDENCE ON THE 13C-POCKET STRUCTURE (2014, methodology): “…C with M(pocket) = 5.30E−4 M (empty circles) and TEST D with M(pocket) = 2 × 5.30E−4 M (empty squares). a case an outer 14N-rich zone, also called 14N pocket, forms in the outer layers of the He intershell (Goriely & Mowlavi 2000; Cristallo et al. 2009; Karakas et al. 2010; Lugaro et al. 2012).”
• Evolution of thermally pulsing asymptotic giant branch stars - I. The COLIBRI code (2013, background): “…of stellar structure with the aid of classical 1D stellar evolution codes, are becoming increasingly successful thanks to the speeding-up of modern processors, and to the particular care devoted to the nucleosynthesis (e.g. Ventura, D’Antona & Mazzitelli 2002; Cristallo et al. 2009; Karakas 2010).”
• Updated stellar yields from asymptotic giant branch models (2009, methodology): “This is because all the models in Cristallo et al. (2009) have 13C pockets that formed as a consequence of the algorithm used to find the convective border following a TP.”
• Dust formation in the oxygen-rich AGB star IK Tauri (2015, methodology): “Photospheric atomic and molecular abundances are calculated by assuming TE at 1 R? and by taking the initial elemental composition given by the FRUITY database of Cristallo et al. (2011), for a 1.5 M star on the ZAMS with solar metallicity, that has experienced three thermal pulses on the AGB.”
• Astrophysics with Extraterrestrial Materials (2016, background): “For example, s-process nucleosynthesis occurs in AGB stars in the He-rich intershell region between He- and H-burning shells, where seed neutrons arise from the 13C(α,n)16O reaction (Gallino et al. 1998, Cristallo et al. 2011).”
• NUGRID STELLAR DATA SET. I. STELLAR YIELDS FROM H TO BI FOR STARS WITH METALLICITIES Z = 0.02 and Z = 0.01 (2013, methodology): “While for 14N yields are consistent within 20% and for 16O within 60%, for 12C Karakas (2010) show a much weaker production compared to Set 1 and Cristallo et al. (2011).”
• Yields of AGB and SAGB models with chemistry of low- and high-metallicity globular clusters (2013, background): “Some of these investigations were focused on the efficiency of mixing in low–mass AGBs, and on the treatment of the borders at the convective/radiative interface (Cristallo et al. 2009; Stancliffe & Jeffery 2007).”
• ON THE SOURCE OF THE DUST EXTINCTION IN TYPE Ia SUPERNOVAE AND THE DISCOVERY OF ANOMALOUSLY STRONG Na i ABSORPTION (2013, background): “This is because of the formation of a 13C pocket, a necessary ingredient for the production of s-process elements (see e.g., Mowlavi 1999; Cristallo et al. 2009; Karakas 2010).”
• The s process: Nuclear physics, stellar models, and observations (2010, background): “9 illustrates the changes of the structural characteristics of a given AGB model with time (Cristallo et al., 2009a,b), the position in mass coordinates of the inner border of the convective envelope, the maximum energy production of the H-burning shell and the maximum energy production within the…”
• The Dawes Review 2: Nucleosynthesis and Stellar Yields of Low- and Intermediate-Mass Single Stars (2014, methodology): “2M⊙, regardless of Z (see also Cristallo et al. 2009; Lugaro et al. 2012).”
• CONVECTIVE–REACTIVE PROTON–12C COMBUSTION IN SAKURAI'S OBJECT (V4334 SAGITTARII) AND IMPLICATIONS FOR THE EVOLUTION AND YIELDS FROM THE FIRST GENERATIONS OF STARS (2010, background): “…including the He-shell flash of AGB stars of extremely low metal content (e.g. Fujimoto et al. 2000; Suda et al. 2004; Iwamoto et al. 2004; Cristallo et al. 2009), metallicity low-mass stars (e.g. Hollowell et al. 1990; Schlattl et al. 2002; Campbell & Lattanzio 2008), young white dwarfs…”
• s‐Process in low‐metallicity stars – I. Theoretical predictions (2010, methodology): “…developed TP extends till the H-rich zone, bringing protons at high temperature and causing the development of a violent thermonuclear runaway (Hollowell, Iben & Fujimoto 1990; Fujimoto, Ikeda & Iben 2000; Iwamoto et al. 2004; Campbell & Lattanzio 2008; Cristallo et al. 2009b; Lau et al. 2009).”
• A high-resolution VLT/FLAMES study of individual stars in the centre of the Fornax dwarf spheroidal galaxy (2010, background): “20, the new, lower Ba abundances in Fornax reduce the potential s-process content of Eu in Fornax, and furthermore no longer allow us to discriminate between the set of different metallicity AGBs yields (Cristallo et al. 2009) for the production of the s-process in Fornax.”