Proton capture on17O and its astrophysical implications

Abstract

Background: The reaction17 O(p, γ) 18 F influences hydrogen-burning nucleosynthesis in several stellar sites, such as red giants, asymptotic giant branch (AGB) stars, massive stars and classical novae. In the relevant temperature range for these environments (T9 = 0.01-0.4), the main contributions to the rate of this reaction are the direct capture process, two low lying narrow resonances (Er = 65.1 and 183 keV) and the low-energy tails of two broad resonances (Er = 557 and 677 keV).Purpose: Previous measurements and calculations give contradictory results for the direct capture contribution which in turn increases the uncertainty of the reaction rate. In addition, very few published cross section data exist for the high energy region that might affect the interpretation of the direct capture and the contributions of the broad resonances in the lower energy range. This work aims to address these issues.Method: The reaction cross section was measured in a wide proton energy range (Ec.m. = 345 -1700 keV) and at several angles (θ lab = 0• , 45The observed primary γ-transitions were used as input in an R-matrix code in order to obtain the contribution of the direct capture and the two broad resonances to the low-energy region.Results: The extrapolated S-factor from the present data is in good agreement with the existing literature data in the low-energy region. A new reaction rate was calculated from the combined results of this work and literature S-factor determinations. Resonance strengths and branchings are reported for several 18 F states. Conclusions:We were able to extrapolate the astrophysical S-factor of the reaction 17 O(p, γ) 18 F at low energies from cross section data taken at higher energies. No significant changes in the nucleosynthesis are expected from the newly calculated reaction rate.

Cross section measurement of the astrophysically important O17(p,γ)F18Gyürky1, Ornelas2, Fülöp3 et al. 2017Phys. Rev. C12060View full textAdd to dashboardCite

“…The following literature data were considered: Hager et al [12] 18 F reaction in the lower part of the studied energy range. Besides the present work, the partial cross sections of Rolfs [5] and Kontos et al [11] are also shown as discussed in the text. The lines through the points are only to guide the eye.…”

“…Figure 5 shows the measured cross section in this energy range. In order to compare at least the energy dependence of the cross section, besides the present data, partial cross sections measured by Rolfs [5] and Kontos et al [11] are also included in the figure. As in Fig.…”

“…The value is taken from Table I of [10]. Kontos et al [11] do not provide total cross section data directly at (E) p = 500 keV. A measured partial cross section around this energy region, however, is available and, based on these data, the authors provide total S-factor values in tabular form in their Table V. An interpolated value for (E) c.m.…”

“…After the turn of the century, several experimental studies were carried out, mostly concentrating on the low energy region below about 500 keV [4,[6][7][8][9][10][11][12][13][14]. (The only exception was the work of Kontos et al [11] which extended up to 1.6 MeV.)…”

Effects of nuclear cross sections on19F nucleosynthesis at low metallicities

“…After the pioneering work of Rolfs (1973) in the seventies, several studies (Fox et al 2005;Chafa et al 2007;Newton et al 2010;Hager et al 2012;Kontos et al 2012;Scott et al 2012) have determined the reaction rate with improving precision in the past decade. Nevertheless, at the temperatures relevant for AGB nucleosynthesis, the reaction rate is dominated by the lowest energy resonance, E cm = 65 keV, which is too weak to be directly measured with the current experiment possibilities.…”