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Ugalde, C.; Azuma, R.E.; Couture, A.; Lee, Hye Young; Stech, E.; Strandberg, E.; Tan, Wanpeng; Wiescher, M.

doi:10.1103/physrevc.77.035801

Cited by 29 publications

(45 citation statements)

References 22 publications

(69 reference statements)

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“…The only available experiment was done by Ugalde et al (2008). These authors measured this cross section, using an α beam and an F solid target between E cm = 700 and 1600 keV, still far from the relevant astrophysical energy.…”

Section: Reaction Rate Uncertaintiesmentioning

confidence: 99%

Effects of nuclear cross sections on¹⁹F nucleosynthesis at low metallicities

Cristallo

Leva

Imbriani

et al. 2014

A&A

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Context. The origin of fluorine is a longstanding problem in nuclear astrophysics. It is widely recognized that asymptotic giant branch (AGB) stars are among the most important contributors to the Galactic fluorine production. Aims. In general, extant nucleosynthesis models overestimate the fluorine production by AGB stars with respect to observations. Although those differences are rather small at solar metallicity, low metallicity AGB stellar models predict fluorine surface abundances up to one order of magnitude larger than the observed ones. Methods. As part of a project devoted to reducing the uncertainties in the nuclear physics that affect the nucleosynthesis in AGB stellar models, we review the relevant nuclear reaction rates involved in the fluorine production or destruction. We perform this analysis on a model with initial mass M = 2 M and Z = 0.001. Results. We found that the major uncertainties are due to the 13 C(α,n) 16 O, the 19 F(α,p) 22 Ne, and the 14 N(p,γ) 15 O reactions. A change in the corresponding reaction rates within the present experimental uncertainties implies surface 19 F variations at the AGB tip lower than 10%, thus much smaller than observational uncertainties. For some α capture reactions, however, cross sections at astrophysically relevant energies are determined on the basis of nuclear models, in which some low-energy resonance parameters are very poorly known. Thus, larger variations in the rates of those processes cannot be excluded. That being so, we explore the effects of the variation in some α capture rates well beyond the current published uncertainties. The largest 19 F variations are obtained by varying the 15 N(α,γ) 19 F and the 19 F(α,p) 22 Ne reactions. Conclusions. The currently estimated uncertainties of the nuclear reaction rates involved in the production and destruction of fluorine produce minor 19 F variations in the ejecta of AGB stars. Analysis of some α capture processes that assume a wider uncertainty range determines 19 F abundances in better agreement with recent spectroscopic fluorine measurements at low metallicity. In the framework of this scenario, the 15 N(α,γ) 19 F and the 19 F(α,p) 22 Ne reactions show the strongest effects on fluorine nucleosynthesis. The presence of poorly known low-energy resonances make such a scenario possible, even if it is unlikely. We plan to measure these resonances directly.

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Section: Reaction Rate Uncertaintiesmentioning

confidence: 99%

Effects of nuclear cross sections on¹⁹F nucleosynthesis at low metallicities

Cristallo

Leva

Imbriani

et al. 2014

A&A

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“…In Model 3 of Lugaro et al 2004). For the latter, the latest evaluation by Ugalde et al (2008) needs to be tested in AGB models.…”

Section: Uncertainties In Agb Modelsmentioning

confidence: 99%

Fluorine in carbon-enhanced metal-poor stars: a binary scenario

Lugaro

Mink

Izzard

et al. 2008

A&A

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Aims. A super-solar fluorine abundance was observed in the carbon-enhanced metal-poor (CEMP) star HE 1305+0132 ([F/Fe] = +2.90, [Fe/H] = −2.5). We propose that this observation can be explained using a binary model that involve mass transfer from an asymptotic giant branch (AGB) star companion and, based on this model, we predict F abundances in CEMP stars in general. We discuss wether F can be used to discriminate between the formation histories of most CEMP stars: via binary mass transfer or from the ejecta of fast-rotating massive stars. Methods. We compute AGB yields using different stellar evolution and nucleosynthesis codes to evaluate stellar model uncertainties. We use a simple dilution model to determine the factor by which the AGB yields should be diluted to match the abundances observed in HE 1305+0132. We further employ a binary population synthesis tool to estimate the probability of F-rich CEMP stars. Results. The abundances observed in HE 1305+0132 can be explained if this star accreted 3−11% of the mass lost by its former AGB companion. The primary AGB star should have dredged-up at least 0.2 M of material from its He-rich region into the convective envelope via third dredge-up, which corresponds to AGB models of Z 0.0001 and mass 2 M . Many AGB model uncertainties, such as the treatment of convective borders and mass loss, require further investigation. We find that in the binary scenario most CEMP stars should also be FEMP stars, that is, have [F/Fe] > +1, while fast-rotating massive stars do not appear to produce fluorine. We conclude that fluorine is a signature of low-mass AGB pollution in CEMP stars, together with elements associated with the slow neutron-capture process.

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“…Those data were then fitted by means of the Modified R-Matrix procedure [2] and a first evaluation of the widths of the involved resonances has been performed [6,7]. The measured cross-section was then normalized to direct data [9] in the overlap region (0.6÷0.9 MeV in the center-of-mass reference frame), obtaining in the end the absolute units cross-section for the 19 F(α,p) 22 Ne reaction. A comparison between the existing reaction rate [9] and the new one was also attempted, and it resulted in an enhancement -in the temperature window of astrophysical interestup to a factor of four for the destruction rate of 19 F via the (α,p) reaction (Tab.…”

Section: Results and Conclusionmentioning

confidence: 99%

“…Reaction rate and ratio between experimental THM results (R T HM ) and the one parametrized from the results of [9] (R),…”

Section: Results and Conclusionmentioning

confidence: 99%