s‐Process in low‐metallicity stars – I. Theoretical predictions

By S. Bisterzo, Roberto Gallino, O. Straniero, S. Cristallo, F. Generale, U. Torino, 1. ViaP.Giuria, Torino, Italy., Inaf Osservatorio Astronomico di Collurania and 13 more. 2010

135 citations recorded by the source corpus.

A large sample of carbon enhanced metal-poor stars enriched in s-process elements (CEMP-s) have been observed in the Galactic halo. These stars of low mass (M � 0.9 M� ) are located on the main-sequence or the red giant phase, and do not undergo third dredge-up (TDU) episodes. The s-process enhancement is most plausibly due to accretion in a binary system from a more massive companion when on the asymptotic giant branch (AGB) phase (now a white dwarf). In order to interpret the spectroscopic observations, updated AGB models are needed to follow in detail the sprocess nucleosynthesis. We present nucleosynthesis calculations based on AGB stellar models obtained with FRANEC (Frascati Raphson-Newton Evolutionary Code) for low initial stellar masses and low metallicities. For a given metallicity, a wide spread in the abundances of the s-process elements is obtained by varying the amount of 13 C and its profile in the pocket, where the 13 C(�, n) 16 O reaction is the major neutron source, releasing neutrons in radiative conditions during the interpulse phase. We account also for the second neutron source 22 Ne(�, n) 25 Mg, partially activated during convective thermal pulses. We discuss the surface abundance of elements from carbon to bismuth, for AGB models of initial masses M = 1.3 – 2 M� , low metallicities ([Fe/H] from 1 down to 3.6) and for different 13 C-pockets efficiencies. In particular we analyse the relative behaviour of the three s-process peaks: light-s (ls at magic neutron number N = 50), heavy-s (hs at N = 82) and lead (N = 126). Two s-process indicators, [hs/ls] and [Pb/hs], are needed in order to characterise the s-process distribution. In the online material, we provide a set of data tables with surface predictions. Our final goal is to provide a full set of theoretical models of low mass low metallicity s-process enhanced stars. In a forthcoming paper, we will test our results through a comparison with observations of CEMP-s stars.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/a6bb444ff935f446d03ebfe732a5f7333c0ab45c

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In Astronomy and Astrophysics

1. A. Karakas
2. M. Lugaro
3. J. Lattanzio
4. Roberto Gallino
5. Falk Herwig
6. S. Bisterzo
7. S. Cristallo
8. O. Straniero

In Nuclear and High Energy Physics

1. A. Karakas
2. Falk Herwig
3. J. Lattanzio
4. M. Lugaro
5. S. Bisterzo
6. Roberto Gallino
7. C. Abia
8. S. Cristallo

Citations in the corpus

• The Dawes Review 2: Nucleosynthesis and Stellar Yields of Low- and Intermediate-Mass Single Stars (2014, methodology): “…in metallicity and mass (e.g., Hollowell & Iben 1988; Gallino et al. 1998; Goriely & Mowlavi 2000; Busso et al. 2001; Lugaro et al. 2003; Karakas et al. 2007, 2009; Cristallo et al. 2009, 2011; Karakas & Lugaro 2010; Bisterzo et al. 2010, 2011, 2012; Lugaro et al. 2012; Pignatari et al. 2013).”
• The s-Process in Low Metallicity Stars. II. Interpretation of High-Resolution Spectroscopic Observations with AGB models (2011, background): “The AGB models with different initial masses (1.3 6 M/M⊙ 6 2), metallicities (−3.6 6 [Fe/H] 6 −1.5) and s-process efficiencies (ST/150 6 13C-pocket 6 ST×2) have been presented by Bisterzo et al. (2010), hereafter Paper I.”
• EVOLUTION, NUCLEOSYNTHESIS, AND YIELDS OF LOW-MASS ASYMPTOTIC GIANT BRANCH STARS AT DIFFERENT METALLICITIES (2009, background): “A full discussion on the behavior of these quantities as a function of the metal content can be found in Bisterzo et al. (2010).”
• NUGRID STELLAR DATA SET. I. STELLAR YIELDS FROM H TO BI FOR STARS WITH METALLICITIES Z = 0.02 and Z = 0.01 (2013, methodology): “Heavy element predictions for elemental compositions based on the parameterized post-processing method are available from Bisterzo et al. (2010). s-process yields from stellar evolution models are available for a wide range of metallicities from the FRUITY database (Cristallo et al. 2011), however…”
• CHEMICAL ABUNDANCES FOR 855 GIANTS IN THE GLOBULAR CLUSTER OMEGA CENTAURI (NGC 5139) (2010, background): “1996; Bisterzo et al. 2010).”
• STELLAR YIELDS FROM METAL-RICH ASYMPTOTIC GIANT BRANCH MODELS (2016, background): “We do not provide [hs/Fe] and [hs/Fe] in the surface abundance data files, owing to the fact that there are a number of different choices of the elements included in the definition in the literature (Bisterzo et al. 2010; Cristallo et al. 2011; Lugaro et al. 2012).”
• THE s-PROCESS IN ASYMPTOTIC GIANT BRANCH STARS OF LOW METALLICITY AND THE COMPOSITION OF CARBON-ENHANCED METAL-POOR STARS (2011, methodology): “In Table 6 we present a comparison of our results with those of Cristallo et al. (2009b) and Bisterzo et al. (2010) for the same element ratios as shown in Tables 3 and 4.”
• GALACTIC CHEMICAL EVOLUTION AND SOLAR s-PROCESS ABUNDANCES: DEPENDENCE ON THE 13C-POCKET STRUCTURE (2014, methodology): “As a minimum 13C pocket, we assume case ST × 0.1 at disk metallicities and case ST × 0.03 in the halo (see discussion by Bisterzo et al. 2010, 2011).”
• The s process: Nuclear physics, stellar models, and observations (2010, methodology): “11 for an AGB star with an initial massM = 1.5M⊙ and for a range of 13C pockets (from case ST down to ST/12) at solar metallicity (top panel) and at [Fe/H] = −0.5 (bottom panel) (see Bisterzo et al. 2010; Husti et al. 2009).”