Oxygen-neon Novae Research Articles

A Photoionization Model for the Infrared Coronal Line Emission in the Classical Nova V1716 Scorpii

A near-infrared spectrum of nova V1716 Scorpii (PNV J17224490-4137160), a recent bright ( Vmax=7.3 mag), Fermi-LAT detected γ-ray source, was modeled using the photoionization code CLOUDY. Abundances were estimated for He, C, N, O, Si, Al, Mg, Fe, Ne, S, Ca, and P. Notably, P (a factor of 120) and N (a factor of 248) are highly overabundant. It was necessary to assume the ejecta consist of two components (with a cylindrical geometry): a dense component from which the bulk of the H, He, and neutral O i and N emission arises and a more diffuse component from which most of the coronal lines arise. Some of the coronal lines are found to originate from both the dense and diffuse components. The mass of the ejecta, including neutral and ionized gas, is ≃4.19 × 10−4 M ⊙. Our analysis indicates that in the case of V1716 Sco (which has a carbon–oxygen white dwarf), a fraction of 25% white dwarf matter rather than 50% is favored for the mixing between a white dwarf and the accreted envelope before the outburst. This mixing ratio is like that found for oxygen–neon novae where a 25% mixing fraction is also indicated. Helium hydride—the first molecule to form after the Big Bang—may have formed in the ejecta of V1716 Sco based on photoionization modeling. This prediction suggests that novae may be potential formation sites of this important molecular ion.

Phosphorus Enrichment by ONe Novae in the Galaxy

Recent observations have shown that [P/Fe] in the Galactic stars decreases with increasing [Fe/H] for [Fe/H] ≳ − 1 whereas it is almost subsolar for [Fe/H] ≲ −2. These [P/Fe] trends with [Fe/H] have not been well reproduced by previous theoretical models incorporating phosphorus (P) enrichment only by core collapse supernoave. We here show, for the first time, that the trends can be naturally explained by our new models incorporating P enrichment by oxygen–neon (ONe) novae, which occur at the surface of massive white dwarfs whose masses are larger than 1.25M ⊙ with a metallicity-dependence rate. We also show that the observations can be better reproduced by the models by assuming that (i) the total mass of gaseous ejecta per ONe nova (M ej) is as high as 4 × 10−5 M ⊙ and (ii) the number of such novae per unit mass (N ONe) is as large as 0.01 at [Fe/H] ≈ −3. The assumed M ej is consistent with observations, and the high N ONe is expected from recent theoretical models for ONe nova fractions. We predict that (i) [P/Fe] increases with increasing [Fe/H] for −2 ≲ [Fe/H] ≲ −1 and (ii) [P/Fe] and [Cl/Fe] trends with [Fe/H] are very similar to each other due to very large yields of P and Cl from ONe novae. It is thus worthwhile for future observations to assess the validity of the proposed P enrichment by ONe novae by confirming or ruling out these two predictions.

Proton capture onP30in novae: On the existence of states at 6.40 MeV and 6.65 MeV inS31

We use a high-resolution $^{32}\mathrm{S}(d,t)$ measurement to investigate the claimed existence of a 6401(3) keV state in $^{31}\mathrm{S}$ that may affect the $^{30}\mathrm{P}(p,\ensuremath{\gamma})$ nuclear reaction rate in oxygen-neon (ONe) novae. Our data are shown to exclude the null hypothesis---that the state does not exist---with high significance. Additionally, the data also suggest the existence of a hitherto unreported state at 6648(4) keV. This state corresponds to a $^{30}\mathrm{P}(p,\ensuremath{\gamma})$ resonance at 517(4) keV, located below the higher edge of the Gamow window for peak nova temperatures of about 0.4 GK.

Constraining the ^{30}P(p, γ)^{31}S Reaction Rate in ONe Novae via the Weak, Low-Energy, β-Delayed Proton Decay of ^{31}Cl.

The ^{30}P(p,γ)^{31}S reaction plays an important role in understanding the nucleosynthesis of A≥30 nuclides in oxygen-neon novae. The Gaseous Detector with Germanium Tagging was used to measure ^{31}Cl β-delayed proton decay through the key J^{π}=3/2^{+}, 260-keV resonance. The intensity I_{βp}^{260}=8.3_{-0.9}^{+1.2}×10^{-6} represents the weakest β-delayed, charged-particle emission ever measured below 400keV, resulting in a proton branching ratio of Γ_{p}/Γ=2.5_{-0.3}^{+0.4}×10^{-4}. By combining this measurement with shell-model calculations for Γ_{γ} and past work on other resonances, the total ^{30}P(p,γ)^{31}S rate has been determined with reduced uncertainty. The new rate has been used in hydrodynamic simulations to model the composition of nova ejecta, leading to a concrete prediction of ^{30}Si:^{28}Si excesses in presolar nova grains and the calibration of nuclear thermometers.

Spectroscopy of P30 and the abundance of Si29 in presolar grains

The astrophysical $^{29}\mathrm{Si}(p,\ensuremath{\gamma}$) reaction is expected to play a key role in determining the final $^{29}\mathrm{Si}$ yields ejected in nova explosions. Such yields are used to accurately identify the stellar origins of meteoritic stardust and recently, distinctive silicon isotopic ratios have been extracted from a number of presolar grains. Here, the light-ion $^{28}\mathrm{Si}(^{3}\mathrm{He},p$) fusion-evaporation reaction was used to populate low-spin proton-unbound excited states in the nucleus $^{30}\mathrm{P}$ that govern the rate of the astrophysical $^{29}\mathrm{Si}(p,\ensuremath{\gamma}$) reaction. In particular, $\ensuremath{\gamma}$ decays were observed from resonances up to ${E}_{r}=500\phantom{\rule{0.28em}{0ex}}\mathrm{keV}$, and key resonances at 217 and 315 keV have now been identified as ${2}^{+}$ and ${2}^{\ensuremath{-}}$ levels, respectively. The present paper provides the first estimate of the 217-keV resonance strength and indicates that the strength of the 315-keV resonance, which dominates the rate of the $^{29}\mathrm{Si}(p,\ensuremath{\gamma}$) reaction over the entire peak temperature range of oxygen-neon novae, is higher than previously expected. As such, the abundance of $^{29}\mathrm{Si}$ ejected during nova explosions is likely to be less than that predicted by the most recent theoretical models.

Experimental study of Cl35 excited states via S32(α,p)

Presolar grains originating in oxygen-neon novae may be identified by their sulfur isotopic ratios compared with theoretical estimates. These ratios depend on reliable $^{33}$S($p, \gamma$)$^{34}$Cl and $^{34}$S($p, \gamma$)$^{35}$Cl reaction rates. The latter rate has recently been computed based on experimental input, and many new excited states in $^{35}$Cl were discovered above the proton threshold. The experimental $^{34}$S($p, \gamma$)$^{35}$Cl rate was found to be 2 - 5 times smaller than the theoretical one, and the simulated $^{34}$S/$^{32}$S isotopic ratio for nova presolar grains was thus predicted to be smaller than that of type II supernova grains by up to a factor of 3.7. The present study was performed to confirm the existence of these new resonances, and to improve the remaining uncertainties in the $^{34}$S($p, \gamma$)$^{35}$Cl reaction rate. Energies and spin-parities of the $^{35}$Cl excited levels were investigated with an Enge split-pole spectrograph using the $^{32}$S($\alpha, p$)$^{35}$Cl reaction. Differential cross sections of the outgoing protons were measured at $E_{\alpha}$ = 21 MeV. The existence of the newly discovered states are largely confirmed, although a few states were not observed in this study. The spins and parities of several $^{35}$Cl states were assigned tentatively for the first time. The present $^{34}$S($p, \gamma$)$^{35}$Cl experimental thermonuclear reaction rate is consistent within 1$\sigma$ with the previous evaluation. However, our rate uncertainty is larger due to a more realistic treatment of the experimental uncertainties. The uncertainty in the present rate is up to a factor of 3.5 at nova temperatures. We recommend future work to focus on the unknown properties of four excited states of $^{35}$Cl at 6643 keV, 6761 keV, 6780 keV, and 6800 keV.

Excited states of Ca39 and their significance in nova nucleosynthesis

Background: Discrepancies exist between the observed abundances of argon and calcium in oxygen-neon nova ejecta and those predicted by nova models. An improved characterization of the $^{38}\mathrm{K}(p,\ensuremath{\gamma})\phantom{\rule{0.16em}{0ex}}^{39}\mathrm{Ca}$ reaction rate over the nova temperature regime ($\ensuremath{\sim}0.1--0.4$ GK), and thus the nuclear structure of $^{39}\mathrm{Ca}$ above the proton threshold [5770.92(63) keV], is necessary to resolve these contradictions.Purpose: The present study was performed to search for low-spin proton resonances in the $^{38}\mathrm{K}+p$ system, and to improve the uncertainties in energies of the known astrophysically significant proton resonances in $^{39}\mathrm{Ca}$.Methods: The level structure of $^{39}\mathrm{Ca}$ was investigated via high-resolution charged-particle spectroscopy with an Enge split-pole spectrograph using the $^{40}\mathrm{Ca}(^{3}\mathrm{He},\ensuremath{\alpha})\phantom{\rule{0.16em}{0ex}}^{39}\mathrm{Ca}$ reaction. Differential cross sections were measured over six laboratory angles at 21 MeV. Distorted-wave Born approximation calculations were performed to constrain the spin-parity assignments of observed levels with special attention to those significant in determination of the $^{38}\mathrm{K}(p,\ensuremath{\gamma})\phantom{\rule{0.16em}{0ex}}^{39}\mathrm{Ca}$ reaction rate over the nova temperature regime.Results: The resonance energies corresponding to two out of three astrophysically important states at 6154(5) and 6472.2(24) keV are measured with better precision than previous charged-particle spectroscopy measurements. A tentatively new state is discovered at 5908(3) keV. The spin-parity assignments of a few of the astrophysically important resonances are determined.Conclusions: The present $^{38}\mathrm{K}(p,\ensuremath{\gamma})\phantom{\rule{0.16em}{0ex}}^{39}\mathrm{Ca}$ upper limit thermonuclear reaction rate at 0.1--0.4 GK is higher than that determined by Christian et al. [Phys. Rev. C 97, 025802 (2018)] by at most a factor of 1.4 at 0.1 GK.

Determination of Ne20(p,γ)Na21 cross sections from Ep=500−2000keV

Background: The reaction $^{20}\mathrm{Ne}(p,\ensuremath{\gamma})^{21}\mathrm{Na}$ influences the nucleosynthesis of Ne, Na, and Mg isotopes while contributing to hydrogen burning in several stellar sites, such as red giants, asymptotic giant branch (AGB) stars, massive stars, and oxygen-neon (ONe) novae. In the relevant temperature range for these environments ($T$ = 0.05--0.5 GK), the main contributions to this reaction rate are from the direct capture process as well as the high-energy tail of a subthreshold resonance in the ground-state transition at ${E}_{x}$ = 2425 keV in the $^{21}\mathrm{Na}$ compound nucleus.Purpose: The previous measurement of this reaction reports cross sections with large uncertainties for the ground-state transition. At higher energies, where the subthreshold resonance makes a smaller contribution to the total cross section, only upper limits are provided. This work aims to reduce the uncertainty in the cross section where direct capture dominates, as well as provide cross-section data in previously unmeasured regions.Method: The $^{20}\mathrm{Ne}(p,\ensuremath{\gamma})^{21}\mathrm{Na}$ reaction was measured over a wide proton energy range (${E}_{p}$ = 0.5--2.0 MeV) at ${\ensuremath{\theta}}_{\text{lab}}$ = ${90}^{\ensuremath{\circ}}$. Transitions to the ground state and to the 332 and 2425 keV excited states were observed. The primary transitions to these three bound states were utilized in an $R$-matrix analysis to determine the contributions of the direct capture and the subthreshold resonance to the total cross section.Results: The cross sections of the present measurements have been found to be in good agreement with the previous data at low energy. Significantly improved cross-section measurements have been obtained over the ${E}_{p}$ = 1300--1900 keV region. The narrow resonance at ${E}_{\text{c.m.}}$ = 1113 $\mathrm{keV}({E}_{x}$ = 3544.3 keV) has also been remeasured and its strength has been found to be in good agreement with previous measurements.Conclusions: An extrapolation of the $S$ factor of $^{20}\mathrm{Ne}(p,\ensuremath{\gamma})^{21}\mathrm{Na}$ has been made to low energies using the $R$-matrix fit. The reaction rate from the subthreshold resonance was found to be the main contributor to the reaction rate at temperatures below about 0.1 GK. The present rate is lower in the temperature range of interest than those presented in current reaction rate libraries by up to 20%.

Direct measurement of astrophysically important resonances in K38(p,γ)Ca39

According to sensitivity studies, the $^{38}\mathrm{K}\left( p, \gamma \right){}^{39}\mathrm{Ca}$ reaction has a significant influence on $\mathrm{Ar}$, $\mathrm{K}$, and $\mathrm{Ca}$ production in classical novae. In order to constrain the rate of this reaction, we have performed a direct measurement of the strengths of three candidate $\ell = 0$ resonances within the Gamow window, at $386 \pm 10~\mathrm{keV}$, $515 \pm 10~\mathrm{keV}$, and $689 \pm 10~\mathrm{keV}$. The experiment was performed in inverse kinematics using a beam of unstable $^{38}\mathrm{K}$ impinged on a windowless $\mathrm{H}_2$ target. The $^{39}\mathrm{Ca}$ recoils and prompt $\gamma$ rays from $^{38}\mathrm{K}\left( p, \gamma \right){}^{39}\mathrm{Ca}$ reactions were detected in coincidence using a recoil mass separator and a BGO array, respectively. For the $689$ keV resonance, we observed a clear recoil-$\gamma$ coincidence signal and extracted resonance strength and energy values of $120^{+50}_{-30}~\mathrm{(stat.)}^{+20}_{-60}~\mathrm{(sys.)}~\mathrm{meV}$ and $679^{+2}_{-1}~\mathrm{(stat.)} \pm 1~\mathrm{(sys.)}~\mathrm{keV}$, respectively. We also performed a singles analysis, extracting a resonance strength of $120 \pm 20~\mathrm{(stat.)} \pm 15~\mathrm{(sys.)}~\mathrm{meV}$, consistent with the coincidence result. For the $386$ keV and $515$ keV resonances, we extract $90\%$ confidence level upper limits of $2.54$ meV and $18.4$ meV, respectively. We have established a new recommended $^{38}\mathrm{K}(p, \gamma){}^{39}\mathrm{Ca}$ rate based on experimental information, which reduces overall uncertainties near the peak temperatures of nova burning by a factor of ${\sim} 250$. Using the rate obtained in this work in model calculations of the hottest oxygen-neon novae reduces overall uncertainties on $\mathrm{Ar}$, $\mathrm{K}$, and $\mathrm{Ca}$ synthesis to factors of $15$ or less in all cases.

Direct Measurement of the Key E_{c.m.}=456 keV Resonance in the Astrophysical ^{19}Ne(p,γ)^{20}Na Reaction and Its Relevance for Explosive Binary Systems.

We have performed a direct measurement of the ^{19}Ne(p,γ)^{20}Na reaction in inverse kinematics using a beam of radioactive ^{19}Ne. The key astrophysical resonance in the ^{19}Ne+p system has been definitely measured for the first time at E_{c.m.}=456_{-2}^{+5} keV with an associated strength of 17_{-5}^{+7} meV. The present results are in agreement with resonance strength upper limits set by previous direct measurements, as well as resonance energies inferred from precision (^{3}He, t) charge exchange reactions. However, both the energy and strength of the 456keV resonance disagree with a recent indirect study of the ^{19}Ne(d, n)^{20}Na reaction. In particular, the new ^{19}Ne(p,γ)^{20}Na reaction rate is found to be factors of ∼8 and ∼5 lower than the most recent evaluation over the temperature range of oxygen-neon novae and astrophysical x-ray bursts, respectively. Nevertheless, we find that the ^{19}Ne(p,γ)^{20}Na reaction is likely to proceed fast enough to significantly reduce the flux of ^{19}F in nova ejecta and does not create a bottleneck in the breakout from the hot CNO cycles into the rp process.

First measurement of the S34(p,γ)Cl35 reaction rate through indirect methods for presolar nova grains

Sulphur isotopic ratio measurements may help to establish the astrophysical sites in which certain presolar grains were formed. Nova model predictions of the S-34/S-32 ratio are, however, unreliable due to the lack of an experimental S-34(p,gamma)Cl-35 reaction rate. To this end, we have measured the S-34(He-3,d)Cl-35 reaction at 20 MeV using a high resolution quadrupole-dipole-dipole-dipolemagnetic spectrograph. Twenty-two levels over 6.2 MeV < E-x (Cl-35) < 7.4 MeV were identified, ten of which were previously unobserved. Proton-transfer spectroscopic factors have been measured for the first time over the energy range relevant for novae. With this new spectroscopic information a new S-34(p,gamma)Cl-35 reaction rate has been determined using a Monte Carlo method. Hydrodynamic nova model calculations have been performed using this new reaction rate. These models show that remaining uncertainties in the S-34(p,gamma) rate affect nucleosynthesis predictions by less than a factor of 1.4, and predict a S-34/S-32 isotopic ratio of 0.014-0.017. Since recent type II supernova models predict S-34/S-32 = 0.026-0.053, the S-34/S-32 isotopic ratio may be used, in conjunction with other isotopic signatures, to distinguish presolar grains from oxygen-neon nova and type II supernova origin. Our results address a key nuclear physics uncertainty on which recent considerations discounting the nova origin of several grains depend.

Direct Measurement of the Astrophysical ^{38}K(p,γ)^{39}Ca Reaction and Its Influence on the Production of Nuclides toward the End Point of Nova Nucleosynthesis.

We have performed the first direct measurement of the ^{38}K(p,γ)^{39}Ca reaction using a beam of radioactive ^{38}K. A proposed ℓ=0 resonance in the ^{38}K+p system has been identified at 679(2)keV with an associated strength of 120_{-30}^{+50} meV. Upper limits of 1.16 (3.5) and 8.6 (26)meV at the 68% (95%) confidence level were also established for two further expected ℓ=0 resonances at 386 and 515keV, respectively. The present results have reduced uncertainties in the ^{38}K(p,γ)^{39}Ca reaction rate at temperatures of 0.4 GK by more than 2 orders of magnitude and indicate that Ar and Ca may be ejected in observable quantities by oxygen-neon novae. However, based on the newly evaluated rate, the ^{38}K(p,γ)^{39}Ca path is unlikely to be responsible for the production of Ar and Ca in significantly enhanced quantities relative to solar abundances.

Constraining nova observables: Direct measurements of resonance strengths in33S(p,γ)34Cl

The 33S(p,\gamma)34Cl reaction is important for constraining predictions of certain isotopic abundances in oxygen-neon novae. Models currently predict as much as 150 times the solar abundance of 33S in oxygen-neon nova ejecta. This overproduction factor may, however, vary by orders of magnitude due to uncertainties in the 33S(p,\gamma)34Cl reaction rate at nova peak temperatures. Depending on this rate, 33S could potentially be used as a diagnostic tool for classifying certain types of presolar grains. Better knowledge of the 33S(p,\gamma)34Cl rate would also aid in interpreting nova observations over the S-Ca mass region and contribute to the firm establishment of the maximum endpoint of nova nucleosynthesis. Additionally, the total S elemental abundance which is affected by this reaction has been proposed as a thermometer to study the peak temperatures of novae. Previously, the 33S(p,\gamma)34Cl reaction rate had only been studied directly down to resonance energies of 432 keV. However, for nova peak temperatures of 0.2-0.4 GK there are 7 known states in 34Cl both below the 432 keV resonance and within the Gamow window that could play a dominant role. Direct measurements of the resonance strengths of these states were performed using the DRAGON recoil separator at TRIUMF. Additionally two new states within this energy region are reported. Several hydrodynamic simulations have been performed, using all available experimental information for the 33S(p,\gamma)34Cl rate, to explore the impact of the remaining uncertainty in this rate on nucleosynthesis in nova explosions. These calculations give a range of ~ 20-150 for the expected 33S overproduction factor, and a range of ~ 100-450 for the 32S/33S ratio expected in ONe novae.

30P(p,γ)31S Reaction Rate for Classical Novae: An Indirect Approach

Isotopic abundance ratios of 30Si/28Si found in presolar SiC grains of suspected nova origin agree qualitatively with proposed oxygen-neon (ONe) nova composition but fail to agree quantitatively with ejecta predictions made by hydrodynamic ONe nova models. The Astrophysical 30P(p,γ)31S reaction rate is a key quantity used in nova models that predict isotopic abundances produced during nucleosynthesis leading up to the outburst. Currently, there is a large uncertainty in the rate at nova temperatures (0.1 < T < 0.4 GK) causing the predicted 30Si abundance ratio to vary by a factor of 4. The 30P(p,γ)31S reaction rate can be determined indirectly by measuring triton momenta from 32S(d,t)31S reactions. 31S Resonant states measured up to 600 keV above the proton threshold of 6131 keV and within the Gamow window which contribute most significantly to the rate can then be used to re-evaluate the rate for nova temperatures and reduce the uncertainty.

Improving theP30(p,γ)S31rate in oxygen-neon novae: Constraints onJπvalues for proton-threshold states inS31

Calculation of the thermonuclear $^{30}\mathrm{P}$($p$,\ensuremath{\gamma})$^{31}\mathrm{S}$ rate in oxygen-neon nova explosions depends critically upon nuclear structure information for states within \ensuremath{\sim}600 keV of the ${}^{30}\mathrm{P}+p$ threshold in $^{31}\mathrm{S}$. We have studied the $^{31}\mathrm{P}$(${}^{3}\mathrm{He},t$)$^{31}\mathrm{S}$ reaction at 25 MeV using a high-resolution quadrupole-dipole-dipole-dipole magnetic spectrograph. Tritons corresponding to the states ${E}_{x}$($^{31}\mathrm{S}$) \ensuremath{\sim} 6.1--7.1 MeV were observed at ten angles between ${\ensuremath{\theta}}_{\mathrm{lab}}$ $=$ 10\ifmmode^\circ\else\textdegree\fi{} and 55\ifmmode^\circ\else\textdegree\fi{}. States that were only tentatively identified in past studies have been observed unambiguously. For the first time, we have measured and analyzed angular distributions of the $^{31}\mathrm{P}$(${}^{3}\mathrm{He},t$)$^{31}\mathrm{S}$ reaction. We present, also for the first time, a consistent set of experimental spin constraints for all except one of the critical proton-threshold states in $^{31}\mathrm{S}$. Hydrodynamic nova simulations have been calculated in order to assess the impact on nova nucleosynthesis of remaining uncertainties in ${J}^{\ensuremath{\pi}}$ values of $^{31}\mathrm{S}$ states and the unknown relevant proton spectroscopic factors. We find that these uncertainties may lead to a factor of up to 20 variation in the $^{30}\mathrm{P}$($p$,\ensuremath{\gamma})$^{31}\mathrm{S}$ rate over typical nova peak temperatures, which may then lead to a factor of up to 4 variation in the nova yields of Si-Ar isotopes.

Branches ofS33(p,γ)34Cl at oxygen-neon nova temperatures

Recent simulations of classical novae on oxygen-neon white-dwarf stars indicate that the isotopic ratio 32S/33S has the potential to be a remarkable indicator of presolar grains of nova origin. The 33S(p,\gamma)34Cl reaction influences this ratio directly by destroying 33S in novae. Additionally, \beta-delayed \gamma-rays from the metastable state of 34Cl (t_{1/2} = 32 min) have been suggested to be potential nova observables. We have measured the branches for known 33S(p,\gamma)34Cl resonances that are activated at temperatures relevant to oxygen-neon novae. We provide the first reliable uncertainties on these branches and the first upper limits for several previously unmeasured branches.

Nova reaction rates and experiments

Oxygen–neon novae form a subset of classical novae events known to freshly synthesize nuclei up to mass number A ≲ 40 . Because several gamma-ray emitters lie in this mass range, these novae are also interesting candidates for gamma-ray astronomy. The properties of excited states within those nuclei in this mass region play a critical role in determining the resonant ( p , γ ) reaction rates, themselves, largely unknown for the unstable nuclei. We describe herein a new Doppler shift lifetime facility at the Maier–Leibnitz tandem laboratory, Technische Universität München, with which we will map out important resonant ( p , γ ) nova reaction rates.

γ-ray spectroscopy study of states inSi27relevant for theAl26m(p,γ)Si27reaction in novae and supernovae

The heavy-ion, fusion-evaporation reaction C12(O16,n) was used to identify γ-decay transitions from excited states in Si27 above the proton threshold. The precise level energy measurements, Jπ assignments, and lifetime measurements of astrophysically important Al26m+p resonances have allowed an evaluation of the Al26m(p,γ)Si27 reaction rate. An lp=0 resonance has been newly identified at a center-of-mass energy in the Al26m+p system of 146.3(3) keV and is expected to dominate the rate for low stellar temperatures. In addition, an lp=1 resonance has been identified at 378.3(30) keV and is likely to dominate the rate at high astrophysical temperatures, such as those found in oxygen-neon novae and core-collapse supernovae. © 2009 The American Physical Society.

γ-ray spectroscopy study of states in Si27 relevant for the Al26m(p,γ)Si27 reaction in novae and supernovae

The heavy-ion, fusion-evaporation reaction 12 C( 16 O,n) was used to identify γ-decay transitions from excited states in 27 Si above the proton threshold. The precise level energy measurements, J π assignments, and lifetime measurements of astrophysically important 26 Al m + p resonances have allowed an evaluation of the 26 Al m (p,γ) 27 Si reaction rate. An l p = 0 resonance has been newly identified at a center-of-mass energy in the 26 Al m + p system of 146.3(3) keV and is expected to dominate the rate for low stellar temperatures. In addition, an lp = 1 resonance has been identified at 378.3(30) keV and is likely to dominate the rate at high astrophysical temperatures, such as those found in oxygen-neon novae and core-collapse supernovae.

NewP30(p,γ)S31resonances and oxygen-neon nova nucleosynthesis

Enriched isotopic abundance ratios of $^{30}\mathrm{Si}$/$^{28}\mathrm{Si}$ in several presolar SiC and graphite grains qualitatively indicate massive oxygen-neon (ONe) nova origins but fall short of hydrodynamic ONe nova model ejecta predictions by as much as an order of magnitude. The astrophysical $^{30}\mathrm{P}$($p,\ensuremath{\gamma}$)$^{31}\mathrm{S}$ reaction rate uncertainty at ONe nova temperatures ($0.10lTl0.35$ GK) spans several orders of magnitude through which the predicted amount of ejected $^{30}\mathrm{Si}$ can vary by a factor of 100. By measuring triton momenta from the $^{31}\mathrm{P}$($^{3}\mathrm{He}$,$t$)$^{31}\mathrm{S}$ reaction at 20 MeV, the energies of $^{30}\mathrm{P}$ $+p$ resonances in the Gamow window for ONe novae have been determined to better than \ifmmode\pm\else\textpm\fi{}3 keV, and two new resonances at ${E}_{\mathrm{c}.\mathrm{m}.}=194.0(25)$ and 266.4(27) keV that likely dominate the $^{30}\mathrm{P}$($p,\ensuremath{\gamma}$)$^{31}\mathrm{S}$ rate for $0.08lTl0.25$ GK have been resolved. A resulting increase in the experimentally determined $^{30}\mathrm{P}$($p,\ensuremath{\gamma}$)$^{31}\mathrm{S}$ reaction rate puts it in accord with Hauser-Feshbach statistical model estimates for $0.08lTl0.40$ GK, supporting conclusions drawn from ONe nova model studies that employed a Hauser-Feshbach rate.