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In stars that lie on the main sequence in the Hertzsprung Russel diagram, like our sun, hydrogen is fused to helium in a number of nuclear reaction chains and series, such as the proton-proton chain and the carbon-nitrogen-oxygen cycles. Precisely determined thermonuclear rates of these reactions lie at the foundation of the standard solar model. This review, the third decadal evaluation of the nuclear physics of hydrogen-burning stars, is motivated by the great advances made in recent years by solar neutrino observatories, putting experimental knowledge of the proton-proton chain neutrino fluxes in the few-percent precision range. The basis of the review is a one-week community meeting held in July 2022 in Berkeley, California, and many subsequent digital meetings and exchanges. Each of the relevant reactions of solar and quiescent stellar hydrogen burning is reviewed here, from both theoretical and experimental perspectives. Recommendations for the state of the art of the astrophysical S-factor and its uncertainty are formulated for each of them. Several other topics of paramount importance for the solar model are reviewed, as well: recent and future neutrino experiments, electron screening, radiative opacities, and current and upcoming experimental facilities. In addition to reaction-specific recommendations, also general recommendations are formed., Comment: 85 pages, 15 figures. To be submitted to Reviews of Modern Physics

We report on the measurement of $^{11}$B and $^{40}$Ca levels between excitation energies of 8 and 9 MeV using nuclear resonance fluorescence (NRF). The experiment was carried out with nearly-monoenergetic and linearly polarized photon beams provided by the High-Intensity $\gamma$-ray Source (HI$\gamma$S) facility at the Triangle Universities Nuclear Laboratory (TUNL). States in $^{11}$B are important for calibrations of NRF measurements, while the properties of $^{40}$Ca levels impact potassium nucleosynthesis in globular clusters. For $^{40}$Ca, we report on improved excitation energies and an unambiguous $2^-$ assignment for the state at 8425 keV. For $^{11}$B, we obtained improved values for $\gamma$-ray multipolarity mixing ratios and branching ratios of the 8920 keV level., Comment: 14 pages, 9 figures, to be published in Physical Review C

Cataclysmic Variables (CVs) and Symbiotic Binaries are close (or not so close) binary star systems which contain both a white dwarf (WD) primary and a larger cooler secondary star that typically fills its Roche Lobe. The cooler star is losing mass through the inner Lagrangian point of the binary and a fraction of this material is accreted by the WD. Here we report on our hydrodynamic studies of the thermonuclear runaway (TNR) in the accreted material that ends in a Classical Nova explosion. We have followed the evolution of the TNRs on both carbon-oxygen (CO) and oxygen-neon (ONe) WDs. We report on 3 studies in this paper. First, simulations in which we accrete only solar matter using NOVA (our 1-D, fully implicit, hydro code). Second, we use MESA for similar studies in which we accrete only Solar matter and compare the results. Third, we accrete solar matter until the TNR is ongoing and then switch the composition in the accreted layers to a mixed composition: either 25% WD and 75% solar or 50% WD and 50% Solar matter. We find that the amount of accreted material is inversely proportional to the initial 12C abundance (as expected). Thus, accreting solar matter results in a larger amount of accreted material to fuel the outburst; much larger than in earlier studies where a mixed composition was assumed from the beginning of the simulation. Our most important result is that all these simulations eject significantly less mass than accreted and, therefore, the WD is growing in mass toward the Chandrasekhar Limit., Comment: To appear in "The Golden Age of Cataclysmic Variables and Related Objects V (GOLDEN2019)" 2-7 September 2019, Palermo, Italy. Proceedings of Science, in press

The study of d+d reactions is of major interest since their reaction rates affect the predicted abundances of D, 3He, and 7Li. In particular, recent measurements of primordial D/H ratios call for reduced uncertainties in the theoretical abundances predicted by big bang nucleosynthesis (BBN). Different authors have studied reactions involved in BBN by incorporating new experimental data and a careful treatment of systematic and probabilistic uncertainties. To analyze the experimental data, Coc et al. (2015) used results of ab initio models for the theoretical calculation of the energy dependence of S-factors in conjunction with traditional statistical methods based on Chi-2 minimization. Bayesian methods have now spread to many scientific fields and provide numerous advantages in data analysis. Astrophysical S-factors and reaction rates using Bayesian statistics were calculated by Iliadis et al. (2016). Here we present a similar analysis for two d+d reactions, d(d,n)3He and d(d,p)3H, that has been translated into a total decrease of the predicted D/H value by 0.16%., Comment: To appear in the Astrophysical Journal

The measurement of a reaction cross section from a pulse height spectrum is a ubiquitous problem in experimental nuclear physics. In $\gamma$-ray spectroscopy, this is accomplished frequently by measuring the intensity of full-energy primary transition peaks and correcting the intensities for experimental artifacts, such as detection efficiencies and angular correlations. Implicit in this procedure is the assumption that full-energy peaks do not overlap with any secondary peaks, escape peaks, or environmental backgrounds. However, for complex $\gamma$-ray cascades, this is often not the case. Furthermore, this technique is difficult to adapt for coincidence spectroscopy, where intensities depend not only on the detection efficiency, but also the detailed decay scheme. We present a method that incorporates the intensities of the entire spectrum (e.g., primary and secondary transition peaks, escape peaks, Compton continua, etc.) into a statistical model, where the transition intensities and branching ratios can be determined using Bayesian statistical inference. This new method provides an elegant solution to the difficulties associated with analyzing coincidence spectra. We describe it in detail and examine its efficacy in the analysis of $^{18}$O(p,$\gamma$)$^{19}$F and $^{25}$Mg(p,$\gamma$)$^{26}$Al resonance data. For the $^{18}$O(p,$\gamma$)$^{19}$F reaction, the measured branching ratios improve upon the literature values, with a factor of 4 reduction in the uncertainties., Comment: 25 pages, 7 figures, published in NIM A

Motivated by recent reports concerning the observation of limited enrichment in He but excess K in stars of globular clusters, we revisit the H-burning conditions that lead to the chemical properties of multiple stellar populations in these systems. In particular, we are interested in correlations of He and K with other elements, like O, Na, Al, Mg and Si, reported in stars of NGC 2808. We perform calculations of nucleosynthesis at constant temperature and density, exploring the temperature range of 25 to 200 10$^6$ K (25 to 200 MK), using a detailed nuclear reaction network and the most up-to-date nuclear reaction rates. We find that Mg is the most sensitive "thermometer" of hydrostatic H-burning conditions, pointing to a temperature range of 70-80 MK for NGC~2808, while He is a lesser - but not negligible - constraint. K can be produced at the levels reported for NGC 2808 at temperatures $>$180 MK and Si at T$>$80 MK. However, in the former temperature range Al and Na are totally destroyed and no correlation can be obtained, in contrast to the reported observations. None of the putative polluter sources proposed so far seem to satisfy the ensemble of nucleosynthesis constraints., Comment: Accepted for publication in A&A

Nova explosions occur on the white dwarf component of a Cataclysmic Variable binary stellar system that is accreting matter lost by its companion. When sufficient material has been accreted by the white dwarf, a thermonuclear runaway occurs and ejects material in what is observed as a Classical Nova explosion. We describe both the recent advances in our understanding of the progress of the outburst and outline some of the puzzles that are still outstanding. We report on the effects of improving both the nuclear reaction rate library and including a modern nuclear reaction network in our one-dimensional, fully implicit, hydrodynamic computer code. In addition, there has been progress in observational studies of Supernovae Ia with implications about the progenitors and we discuss that in this review., Comment: 18 pages, 7 figures

We investigate properties of carbon-oxygen white dwarfs with respect to the composite uncertainties in the reaction rates using the stellar evolution toolkit, Modules for Experiments in Stellar Astrophysics (MESA) and the probability density functions in the reaction rate library STARLIB. These are the first Monte Carlo stellar evolution studies that use complete stellar models. Focusing on 3 M$_{\odot}$ models evolved from the pre main-sequence to the first thermal pulse, we survey the remnant core mass, composition, and structure properties as a function of 26 STARLIB reaction rates covering hydrogen and helium burning using a Principal Component Analysis and Spearman Rank-Order Correlation. Relative to the arithmetic mean value, we find the width of the 95\% confidence interval to be $\Delta M_{{\rm 1TP}}$ $\approx$ 0.019 M$_{\odot}$ for the core mass at the first thermal pulse, $\Delta$$t_{\rm{1TP}}$ $\approx$ 12.50 Myr for the age, $\Delta \log(T_{{\rm c}}/{\rm K}) \approx$ 0.013 for the central temperature, $\Delta \log(\rho_{{\rm c}}/{\rm g \ cm}^{-3}) \approx$ 0.060 for the central density, $\Delta Y_{\rm{e,c}} \approx$ 2.6$\times$10$^{-5}$ for the central electron fraction, $\Delta X_{\rm c}(^{22}\rm{Ne}) \approx$ 5.8$\times$10$^{-4}$, $\Delta X_{\rm c}(^{12}\rm{C}) \approx$ 0.392, and $\Delta X_{\rm c}(^{16}\rm{O}) \approx$ 0.392. Uncertainties in the experimental $^{12}$C($\alpha,\gamma)^{16}\rm{O}$, triple-$\alpha$, and $^{14}$N($p,\gamma)^{15}\rm{O}$ reaction rates dominate these variations. We also consider a grid of 1 to 6 M$_{\odot}$ models evolved from the pre main-sequence to the final white dwarf to probe the sensitivity of the initial-final mass relation to experimental uncertainties in the hydrogen and helium reaction rates., Comment: Accepted for publication in The Astrophysical Journal; 19 Pages, 23 Figures, 5 Tables

The $^{18}$Ne($\alpha$,$p$)$^{21}$Na reaction impacts the break-out from the hot CNO-cycles to the $rp$-process in type I X-ray bursts. We present a revised thermonuclear reaction rate, which is based on the latest experimental data. The new rate is derived from Monte-Carlo calculations, taking into account the uncertainties of all nuclear physics input quantities. In addition, we present the reaction rate uncertainty and probability density versus temperature. Our results are also consistent with estimates obtained using different indirect approaches., Comment: 12 pages, 6 figures, 4 tables, Phys. Rev. C, accepted; V2: affiliation of coauthor updated, typos corrected

We have carried out photodisintegration cross-section measurements on 86Kr using monoenergetic photon beams ranging from the neutron separation energy, S_n = 9.86 MeV, to 13 MeV. We combine our experimental 86Kr(g,n)85Kr cross section with results from our recent 86Kr(g,g') measurement below the neutron separation energy to obtain the complete nuclear dipole response of 86Kr. The new experimental information is used to predict the neutron capture cross section of 85Kr, an important branching point nucleus on the abundance flow path during s-process nucleosynthesis. Our new and more precise 85Kr(n,g)86Kr cross section allows to produce more precise predictions of the 86Kr abundance from s-process models. In particular, we find that the models of the s-process in asymptotic giant branch stars of mass < 1.5 Msun, where the 13C neutron source burns convectively rather than radiatively, represent a possible solution for the highest 86Kr/82Kr ratios observed in meteoritic stardust SiC grains., Comment: 5 pages, 5 figure, accepted for publication on Physical Review Letters

STARLIB is a next-generation, all-purpose nuclear reaction-rate library. For the first time, this library provides the rate probability density at all temperature grid points for convenient implementation in models of stellar phenomena. The recommended rate and its associated uncertainties are also included. Currently, uncertainties are absent from all other rate libraries, and, although estimates have been attempted in previous evaluations and compilations, these are generally not based on rigorous statistical definitions. A common standard for deriving uncertainties is clearly warranted. STARLIB represents a first step in addressing this deficiency by providing a tabular, up-to-date database that supplies not only the rate and its uncertainty but also its distribution. Because a majority of rates are lognormally distributed, this allows the construction of rate probability densities from the columns of STARLIB. This structure is based on a recently suggested Monte Carlo method to calculate reaction rates, where uncertainties are rigorously defined. In STARLIB, experimental rates are supplemented with: (i) theoretical TALYS rates for reactions for which no experimental input is available, and (ii) laboratory and theoretical weak rates. STARLIB includes all types of reactions of astrophysical interest to Z = 83, such as (p,g), (p,a), (a,n), and corresponding reverse rates. Strong rates account for thermal target excitations. Here, we summarize our Monte Carlo formalism, introduce the library, compare methods of correcting rates for stellar environments, and discuss how to implement our library in Monte Carlo nucleosynthesis studies. We also present a method for accessing STARLIB on the Internet and outline updated Monte Carlo-based rates., Comment: Accepted for publication in the Astrophysical Journal Supplement Series; 96 pages, 22 figures

For stars between 0.8-8.0 solar masses, nucleosynthesis enters its final phase during the asymptotic giant branch (AGB) stage. During this evolutionary period, grain condensation occurs in the stellar atmosphere, and the star experiences significant mass loss. The production of presolar grains can often be attributed to this unique stellar environment. A subset of presolar oxide grains features dramatic 18O depletion that cannot be explained by the standard AGB star burning stages and dredge-up models. An extra mixing process, referred to as "cool bottom processing" (CBP), was proposed for low-mass AGB stars. The 18O depletion observed within certain stellar environments and within presolar grain samples may result from the 18O+p processes during CBP. We report here on a study of the 18O(p,gamma)19F reaction at low energies. Based on our new results, we found that the resonance at Er = 95 keV (lab) has a negligible affect on the reaction rate at the temperatures associated with CBP. We also determined that the direct capture S-factor is almost a factor of 2 lower than the previously recommended value at low energies. An improved thermonuclear reaction rate for 18O(p,gamma)19F is presented., Comment: 11 pages, 8 figures, 2 tables; to be published in Phys. Rev. C

Type I X-ray bursts are thermonuclear explosions that occur in the envelopes of accreting neutron stars. Detailed observations of these phenomena have prompted numerous studies in theoretical astrophysics and experimental nuclear physics since their discovery over 35 years ago. In this review, we begin by discussing key observational features of these phenomena that may be sensitive to the particular patterns of nucleosynthesis from the associated thermonuclear burning. We then summarize efforts to model type I X-ray bursts, with emphasis on determining the nuclear physics processes involved throughout these bursts. We discuss and evaluate limitations in the models, particularly with regard to key uncertainties in the nuclear physics input. Finally, we examine recent, relevant experimental measurements and outline future prospects to improve our understanding of these unique environments from observational, theoretical and experimental perspectives., Comment: Accepted by Prog. Part. Nucl. Phys., 45 pages, 14 figures

We present a brief summary of the Single Degenerate Scenario for the progenitors of Type Ia Supernovae in which it is assumed that a low mass carbon-oxygen white dwarf is growing in mass as a result of accretion from a secondary star in a close binary system. Recent hydrodynamic simulations of accretion of solar material onto white dwarfs without mixing always produce a thermonuclear runaway and steady burning does not occur. For a broad range in WD mass (0.4 Solar masses to 1.35 Solar Masses), the maximum ejected material occurs for the 1.25 Solar Mass sequences and then decreases as the white dwarf mass decreases. Therefore, the white dwarfs are growing in mass as a consequence of the accretion of solar material and as long as there is no mixing of accreted material with core material. In contrast, a thermonuclear runaway in the accreted hydrogen-rich layers on the low luminosity WDs in close binary systems where mixing of core matter with accreted material has occurred is the outburst mechanism for Classical, Recurrent, and Symbiotic novae. The differences in characteristics of these systems is likely the WD mass and mass accretion rate. The high levels of enrichment of CN ejecta in elements ranging from carbon to sulfur confirm that there is dredge-up of matter from the core of the WD and enable them to contribute to the chemical enrichment of the interstellar medium. Therefore, studies of CNe can lead to an improved understanding of Galactic nucleosynthesis, some sources of pre-solar grains, and the Extragalactic distance scale. The characteristics of the outburst depend on the white dwarf mass, luminosity, mass accretion rate, and the chemical composition of both the accreting material and WD material. The properties of the outburst also depends on when, how, and if the accreted layers are mixed with the WD core and the mixing mechanism is still unknown., Comment: 25 Pages, Bulletin of the Astronomical Society of India (BASI) in press

Models of the r-process are sensitive to the production rate of 9Be because, in explosive environments rich in neutrons, alpha(alpha n,gamma)9Be is the primary mechanism for bridging the stability gaps at A=5 and A=8. The alpha(alpha n,gamma)9Be reaction represents a two-step process, consisting of alpha+alpha -> 8Be followed by 8Be(n,gamma)9Be. We report here on a new absolute cross section measurement for the 9Be(gamma,n)8Be reaction conducted using a highly-efficient, 3He-based neutron detector and nearly-monoenergetic photon beams, covering energies from E_gamma = 1.5 MeV to 5.2 MeV, produced by the High Intensity gamma-ray Source of Triangle Universities Nuclear Laboratory. In the astrophysically important threshold energy region, the present cross sections are 40% larger than those found in most previous measurements and are accurate to +/- 10% (95% confidence). The revised thermonuclear alpha(alpha n,gamma)9Be reaction rate could have implications for the r-process in explosive environments such as Type II supernovae., Comment: 26 pages, 10 figures

Nucleosynthesis in Type I X-ray bursts may involve up to several thousand nuclear processes. The majority of these processes have only been determined theoretically due to the lack of sufficient experimental information. Accurate reaction Q-values are essential for reliable theoretical estimates of reaction-rates. Those reactions with small Q-values (< 1 MeV) are of particular interest in these environments as they may represent waiting points for a continuous abundance flow towards heavier-mass nuclei. To explore the nature of these waiting points, we have performed a comprehensive series of post-processing calculations which examine the sensitivity of nucleosynthesis in Type I X-ray bursts to uncertainties in reaction Q-values. We discuss and list the relatively few critical masses for which measurements could better constrain the results of our studies. In particular, we stress the importance of measuring the mass of 65As to obtain an experimental Q-value for the 64Ge(p,gamma)65As reaction., Comment: accepted for Physical Review C; table and figures added, discussion expanded

We have continued our studies of the Classical Nova outburst by evolving TNRs on 1.25Msun and 1.35Msun WDs (ONeMg composition) under conditions which produce mass ejection and a rapid increase in the emitted light, by examining the effects of changes in the nuclear reaction rates on both the observable features and the nucleosynthesis during the outburst. In order to improve our calculations over previous work, we have incorporated a modern nuclear reaction network into our hydrodynamic computer code. We find that the updates in the nuclear reaction rate libraries change the amount of ejected mass, peak luminosity, and the resulting nucleosynthesis. In addition, as a result of our improvements, we discovered that the pep reaction was not included in our previous studies of CN explosions. Although the energy production from this reaction is not important in the Sun, the densities in WD envelopes can exceed $10^4$ gm cm$^{-3}$ and the presence of this reaction increases the energy generation during the time that the p-p chain is operating. The effect of the increased energy generation is to reduce the evolution time to the peak of the TNR and, thereby, the accreted mass as compared to the evolutionary sequences done without this reaction included. As expected from our previous work, the reduction in accreted mass has important consequences on the characteristics of the resulting TNR and is discussed in this paper., Comment: Accepted to the Astrophysical Journal

The 16O(p,gamma)17F reaction rate is revisited with special emphasis on the stellar temperature range of T=60-100 MK important for hot bottom burning in asymptotic giant branch (AGB) stars. We evaluate existing cross section data that were obtained since 1958 and, if appropriate, correct published data for systematic errors that were not noticed previously, including the effects of coincidence summing and updated effective stopping powers. The data are interpreted by using two different models of nuclear reactions, that is, a potential model and R-matrix theory. A new astrophysical S-factor and recommended thermonuclear reaction rates are presented. As a result of our work, the 16O(p,gamma)17F reaction has now the most precisely known rate involving any target nucleus in the mass A >= 12 range, with reaction rate errors of about 7% over the entire temperature region of astrophysical interest (T=0.01-2.5 GK). The impact of the present improved reaction rate with its significantly reduced uncertainties on the hot bottom burning in AGB stars is discussed. In contrast to earlier results we find now that there is not clear evidence to date for any stellar grain origin from massive AGB stars., Comment: 14 pages, 9 figures, PRC, accepted

Stardust is a class of presolar grains each of which presents an ideally uncontaminated stellar sample. Mainstream silicon carbide (SiC) stardust formed in the extended envelopes of carbon-rich asymptotic giant branch (AGB) stars and incorporated the radioactive nucleus 26Al as a trace element. The aim of this paper is to analyse in detail the effect of nuclear uncertainties, in particular the large uncertainties of up to four orders of magnitude related to the 26Al_g+(p,gamma)27Si reaction rate, on the production of 26Al in AGB stars and compare model predictions to data obtained from laboratory analysis of SiC stardust grains. Stellar uncertainties are also briefly discussed. We use a detailed nucleosynthesis postprocessing code to calculate the 26Al/27Al ratios at the surface of AGB stars of different masses (M = 1.75, 3, and 5 M_sun) and metallicities (Z = 0.02, 0.012, and 0.008). For the lower limit and recommended value of the 26Al_g(p,gamma)27Si reaction rate, the predicted 26Al/27Al ratios replicate the upper values of the range of the 26Al/27Al ratios measured in SiC grains. For the upper limit of the 26Al_g(p,gamma)27Si reaction rate, instead, the predicted 26Al/27Al ratios are approximately 100 times lower and lie below the range observed in SiC grains. When considering models of different masses and metallicities, the spread of more than an order of magnitude in the 26Al/27Al ratios measured in stellar SiC grains is not reproduced. We propose two scenarios to explain the spread of the 26Al/27Al ratios observed in mainstream SiC, depending on the choice of the 26Al_g+p reaction rate. One involves different times of stardust formation, the other involves extra-mixing processes. Stronger conclusions will be possible after more information is available from future nuclear experiments on the 26Al_g+p reaction., Comment: 6 pages, 5 Postscript figures, accepted for publication in Astronomy and Astrophysics

We have studied natural parity states in $^{26}$Mg via the $^{22}$Ne($^{6}$Li,d)$^{26}$Mg reaction. Our method significantly improves the energy resolution of previous experiments and, as a result, we report the observation of a natural parity state in $^{26}$Mg. Possible spin-parity assignments are suggested on the basis of published $\gamma$-ray decay experiments. The stellar rate of the $^{22}$Ne($\alpha$,$\gamma$)$^{26}$Mg reaction is reduced and may give rise to an increase in the production of s-process neutrons via the $^{22}$Ne($\alpha$,n)$^{25}$Mg reaction., Comment: Published in PRC

Classical novae participate in the cycle of Galactic chemical evolution in which grains and metal enriched gas in their ejecta, supplementing those of supernovae, AGB stars, and Wolf-Rayet stars, are a source of heavy elements for the ISM. Once in the diffuse gas, this material is mixed with the existing gases and then incorporated into young stars and planetary systems during star formation. Infrared observations have confirmed the presence of carbon, SiC, hydrocarbons, and oxygen-rich silicate grains in nova ejecta, suggesting that some fraction of the pre-solar grains identified in meteoritic material come from novae. The mean mass returned by a nova outburst to the ISM probably exceeds ~2 x 10^{-4} Solar Masses. Using the observed nova rate of 35 per year in our Galaxy, it follows that novae introduce more than ~7 x 10^{-3} Solar Masses per year of processed matter into the ISM. Novae are expected to be the major source of 15N and 17O in the Galaxy and to contribute to the abundances of other isotopes in this atomic mass range. Here, we report on how changes in the nuclear reaction rates affect the properties of the outburst and alter the predictions of the contributions of novae to Galactic chemical evolution. We also discuss the necessity of including the pep reaction in studies of thermonuclear runaways in material accreted onto white dwarfs., Comment: 9 pages, 2 figures, as it appeared in the Proceedings of the Tours 2006 Symposium on Nuclear Physics

We test the effect of proton-capture reaction rate uncertainties on the abundances of the Ne, Na, Mg and Al isotopes processed by the NeNa and MgAl chains during hot bottom burning (HBB) in asymptotic giant branch (AGB) stars of intermediate mass between 4 and 6 solar masses and metallicities between Z=0.0001 and 0.02. We provide uncertainty ranges for the AGB stellar yields, for inclusion in galactic chemical evolution models, and indicate which reaction rates are most important and should be better determined. We use a fast synthetic algorithm based on detailed AGB models. We run a large number of stellar models, varying one reaction per time for a very fine grid of values, as well as all reactions simultaneously. We show that there are uncertainties in the yields of all the Ne, Na, Mg and Al isotopes due to uncertain proton-capture reaction rates. The most uncertain yields are those of 26Al and 23Na (variations of two orders of magnitude), 24Mg and 27Al (variations of more than one order of magnitude), 20Ne and 22Ne (variations between factors 2 and 7). In order to obtain more reliable Ne, Na, Mg and Al yields from IM-AGB stars the rates that require more accurate determination are: 22Ne(p,g)23Na, 23Na(p,g)24Mg, 25Mg(p,g)26Al, 26Mg(p,g)27Al and 26Al(p,g)27Si. Detailed galactic chemical evolution models should be constructed to address the impact of our uncertainty ranges on the observational constraints related to HBB nucleosynthesis, such as globular cluster chemical anomalies., Comment: accepted for publication on Astronomy & Astrophysics

Microscopic presolar grains extracted from primitive meteorites have extremely anomalous isotopic compositions revealing the stellar origin of these grains. The composition of presolar spinel grain OC2 is different from that of all other presolar spinel grains. Large excesses of the heavy Mg isotopes are present and thus an origin from an intermediate-mass (IM) asymptotic giant branch (AGB) star was previously proposed for this grain. We discuss the isotopic compositions of presolar spinel grain OC2 and compare them to theoretical predictions. We show that the isotopic composition of O, Mg and Al in OC2 could be the signature of an AGB star of IM and metallicity close to solar experiencing hot bottom burning, or of an AGB star of low mass (LM) and low metallicity suffering very efficient cool bottom processing. Large measurement uncertainty in the Fe isotopic composition prevents us from discriminating which model better represents the parent star of OC2. However, the Cr isotopic composition of the grain favors an origin in an IM-AGB star of metallicity close to solar. Our IM-AGB models produce a self-consistent solution to match the composition of OC2 within the uncertainties related to reaction rates. Within this solution we predict that the 16O(p,g)17F and the 17O(p,a)14N reaction rates should be close to their lower and upper limits, respectively. By finding more grains like OC2 and by precisely measuring their Fe and Cr isotopic compositions, it may be possible in the future to derive constraints on massive AGB models from the study of presolar grains., Comment: 10 pages, 8 figures, accepted for publication on Astronomy & Astrophysics

We have measured the 14N(p,g)15O excitation function for energies in the range E_p = 155--524 keV. Fits of these data using R-matrix theory yield a value for the S-factor at zero energy of 1.64(17) keV b, which is significantly smaller than the result of a previous direct measurement. The corresponding reduction in the stellar reaction rate for 14N(p,g)15O has a number of interesting consequences, including an impact on estimates for the age of the Galaxy derived from globular clusters., Comment: 5 pages, 3 figures, submitted to Phys. Rev. Lett