Reaction Rate Uncertainties and the Production of 19F in Asymptotic Giant Branch Stars

By M. Lugaro, C. Ugalde, A. Karakas, J. Görres, Michael Wiescher, J. Lattanzio, R. Cannon. 2004

169 citations recorded by the source corpus.

We present nucleosynthesis calculations and the resulting 19F stellar yields for a large set of models with different masses and metallicity. During the asymptotic giant branch (AGB) phase, 19F is produced as a consequence of nucleosynthesis occurring during the convective thermal pulses and also during the interpulse periods if protons from the envelope are partially mixed in the top layers of the He intershell (partial mixing zone). We find that the production of fluorine depends on the temperature of the convective pulses, the amount of primary 12C mixed into the envelope by third dredge-up, and the extent of the partial mixing zone. Then we perform a detailed analysis of the reaction rates involved in the production of 19F and the effects of their uncertainties. We find that the major uncertainties are associated with the 14C(α, γ)18O and 19F(α, p)22Ne reaction rates. For these two reactions we present new estimates of the rates and their uncertainties. In both cases the revised rates are lower than previous estimates. The effect of the inclusion of the partial mixing zone on the production of fluorine strongly depends on the very uncertain 14C(α, γ)18O reaction rate. The importance of the partial mixing zone is reduced when using our estimate for this rate. Overall, rate uncertainties result in uncertainties in the fluorine production of about 50% in stellar models with mass ≃3 M☉ and of about a factor of 7 in stellar models of mass ≃5 M☉. This larger effect at high masses is due to the high uncertainties of the 19F(α, p)22Ne reaction rate. Taking into account both the uncertainties related to the partial mixing zone and those related to nuclear reactions, the highest values of 19F enhancements observed in AGB stars are not matched by the models. This is a problem that will have to be revised by providing a better understanding of the formation and nucleosynthesis in the partial mixing zone, as well as in relation to reducing the uncertainties of the 14C(α, γ)18O reaction rate. At the same time, the possible effect of cool bottom processing at the base of the convective envelope should be included in the computation of AGB nucleosynthesis. This process could, in principle, help to match the highest 19F abundances observed by decreasing the C/O ratio at the surface of the star, while leaving the 19F abundance unchanged.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/1ec098e262e5f05b0eeafa988d1c0fdaf28d47e2

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In Astronomy and Astrophysics

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

In Nuclear and High Energy Physics

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

Citations in the corpus

• Updated stellar yields from asymptotic giant branch models (2009, methodology): “The positive yield indicates that some 15N is produced during TPs by the 18O(p,α)15N reaction rate, which is part of the fluorine production chain (see Lugaro et al. 2004).”
• Evolution and nucleosynthesis of extremely metal-poor and metal-free low- and intermediate-mass stars - I. Stellar yield tables and the CEMPs (2008, methodology): “Cannon 1993; Lattanzio et al. 1996; Lugaro et al. 2004).”
• EVOLUTION, NUCLEOSYNTHESIS, AND YIELDS OF LOW-MASS ASYMPTOTIC GIANT BRANCH STARS AT DIFFERENT METALLICITIES (2009, background): “…of fluorine basically depends on the availability of 13C in the He-intershell (see Paper I for a detailed description of the nuclear chain leading to 19F nucleosynthesis; see also Jorissen et al. 1992; Forestini et al. 1992; Mowlavi et al. 1996; Lugaro et al. 2004; Abia et al. 2010, 2011).”
• Stellar Models and Yields of Asymptotic Giant Branch Stars (2007, methodology): “These later studies used the structure models presented here and changed the reaction rates and/or initial abundances to study particular problems e.g. the effect of reaction rate uncertainties on the production of 19F in AGB stars (Lugaro et al. 2004).”
• s‐Process in low‐metallicity stars – I. Theoretical predictions (2010, background): “15 (top panel), shows a huge amount of fluorine produced in AGB stars via the chain 18O(p, α)15N(α, γ )19F, where protons are produced via 14N(n, p)14C, neutrons via 13C(α, n)16O reaction and 18O via the chain 14N(α, γ )18F(β+)18O (Lugaro et al. 2004, 2008; Abia et al. 2009).”
• Evolution of Asymptotic Giant Branch Stars (2005, methodology): “However, according to the nucleosynthesis and mixing analysis based on stellar-evolution models by Lugaro et al. (2004), the intershell abundance of F is diluted too much when dredged up into the envelope A nn u.”
• The Dawes Review 2: Nucleosynthesis and Stellar Yields of Low- and Intermediate-Mass Single Stars (2014, methodology): “For further details on our method for introducing 13C pockets we refer to Lugaro et al. (2004), Karakas (2010), Karakas et al. (2007), and Kamath et al. (2012).”
• NUGRID STELLAR DATA SET. I. STELLAR YIELDS FROM H TO BI FOR STARS WITH METALLICITIES Z = 0.02 and Z = 0.01 (2013, background): “…stars during CCSN, mostly via neutrino spallation on 20Ne (e.g., Woosley & Haxton 1988), the Wolf-Rayet (WR) wind phase (Meynet & Maeder 2000), and low- – 16 – mass AGB stars (e.g., Jorissen et al. 1992; Lugaro et al. 2004; Cristallo et al. 2007; Stancliffe et al. 2007; Karakas et al. 2008).”
• STELLAR YIELDS FROM METAL-RICH ASYMPTOTIC GIANT BRANCH MODELS (2016, background): “The complex reaction pathway that produces 19F (Lugaro et al. 2004) first produces 15N as an intermediate step.”
• The evolution of isotope ratios in the Milky Way Galaxy (2011, background): “F production peaks at ∼ 3M⊙ at solar metallicity (Lugaro et al. 2004); in higher mass models F is destroyed by α-captures by the higher temperatures reached during He-burning.”
• THE s-PROCESS IN ASYMPTOTIC GIANT BRANCH STARS OF LOW METALLICITY AND THE COMPOSITION OF CARBON-ENHANCED METAL-POOR STARS (2011, methodology): “This method is described in some more detail in Lugaro et al. (2004) and is very similar to that used by Goriely & Mowlavi (2000).”