Classical novae are the result of thermonuclear flashes of hydrogen accreted by CO or ONe white dwarfs, leading eventually to the dynamic ejection of the surface layers. These are observationally ...known to be enriched in heavy elements, such as C, O and Ne, that must originate in layers below the H-flash convection zone. Building on our previous work, we now present stellar evolution simulations of ONe novae and provide a comprehensive comparison of our models with published ones. Some of our models include exponential convective boundary mixing to account for the observed enrichment of the nova ejecta even when accreted material has a solar abundance distribution. Our models produce maximum temperature evolution profiles and nucleosynthesis yields in good agreement with models that generate enriched ejecta by assuming that the accreted material was pre-mixed. We confirm for ONe novae the result we reported previously, i.e. we found that 3He could be produced in situ in solar-composition envelopes accreted with slow rates (
$\dot{M} < 10^{-10}\,\mathrm{M}_{\odot }\,\mbox{yr}^{-1}$
) by cold (T
WD < 107 K) CO WDs, and that convection was triggered by 3He burning before the nova outburst in that case. In addition, we now find that the interplay between the 3He production and destruction in the solar-composition envelope accreted with an intermediate rate, e.g.
$\dot{M} = 10^{-10}\,\mathrm{M}_{\odot }\,\mbox{yr}^{-1}$
, by the 1.15 M⊙ ONe WD with a relatively high initial central temperature, e.g. T
WD = 15 × 106 K, leads to the formation of a thick radiative buffer zone that separates the bottom of the convective envelope from the WD surface. We present detailed nucleosynthesis calculations based on the post-processing technique, and demonstrate in which way much simpler single-zone T and ρ trajectories extracted from the multi-zone stellar evolution simulations can be used, in lieu of full multi-zone simulations, to analyse the sensitivity of nova abundance predictions on nuclear reaction rate uncertainties. Trajectories for both CO and ONe nova models for different central temperatures and accretion rates are provided. We compare our nova simulations with observations of novae and pre-solar grains believed to originate in novae.
ABSTRACT
Massive stars are crucial to galactic chemical evolution for elements heavier than iron. Their contribution at early times in the evolution of the Universe, however, is unclear due to poorly ...constrained nuclear reaction rates. The competing 17O(α, γ)21Ne and 17O(α, n)20Ne reactions strongly impact weak s-process yields from rotating massive stars at low metallicities. Abundant 16O absorbs neutrons, removing flux from the s-process, and producing 17O. The 17O(α, n)20Ne reaction releases neutrons, allowing continued s-process nucleosynthesis, if the 17O(α, γ)21Ne reaction is sufficiently weak. While published rates are available, they are based on limited indirect experimental data for the relevant temperatures and, more importantly, no uncertainties are provided. The available nuclear physics has been evaluated, and combined with data from a new study of astrophysically relevant 21Ne states using the 20Ne(d, p)21Ne reaction. Constraints are placed on the ratio of the (α, n)/(α, γ) reaction rates with uncertainties on the rates provided for the first time. The new rates favour the (α, n) reaction and suggest that the weak s-process in rotating low-metallicity stars is likely to continue up to barium and, within the computed uncertainties, even to lead.
The rate of the
25
Al(
p
,
γ
)
26
Si reaction is one of the few key remaining nuclear uncertainties required for predicting the production of the cosmic
γ
-ray emitter
26
Al in explosive burning in ...novae. This reaction rate is dominated by three key resonances (
J
π
=
0
+
,
1
+
and
3
+
) in
26
Si. Only the
3
+
resonance strength has been directly constrained by experiment. A high resolution measurement of the
25
Mg(
d
,
p
) reaction was used to determine spectroscopic factors for analog states in the mirror nucleus,
26
Mg. A first spectroscopic factor value is reported for the
0
+
state at 6.256 MeV, and a strict upper limit is set on the value for the
1
+
state at 5.691 MeV, that is incompatible with an earlier (
4
He,
3
He) study. These results are used to estimate proton partial widths, and resonance strengths of analog states in
26
Si contributing to the
25
Al(
p
,
γ
)
26
Si reaction rate in nova burning conditions.
Ion-implanted 32S targets for astrophysics studies Lennard, W.N.; Setoodehnia, K.; Chen, A.A. ...
Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms,
12/2011, Letnik:
269, Številka:
23
Journal Article
Recenzirano
The fabrication of isotopically pure 10.4
μg/cm
2 targets of
32S by the implantation of 60–100
keV negative ions into a 61
μg/cm
2 pure
12C thin foil is described. The process has been accomplished ...in rather shorter times than has been achieved previously by implanting the as-prepared carbon foil while still mounted on the underlying glass slide, thereby allowing for the use of much larger beam current intensities. The target has been assayed for absolute composition as a function of depth using Rutherford backscattering spectrometry and excellent agreement between the measured and nominal
32S fluences was observed. The implanted targets exhibit excellent stability with regard to subsequent 34.5
MeV proton beam irradiation.
The 18F(p,α)15O reaction is key to determining the 18F abundance in classical novae. However, the cross section for this reaction has large uncertainties at low energies largely caused by ...interference effects. In this work, we resolve a longstanding issue with unknown spin-parities of subthreshold states in 19Ne that reduces these uncertainties. The 20Ne(3He,4He)19Ne neutron pick-up reaction was used to populate 19Ne excited states, focusing on the energy region of astrophysical interest (≈ 6 – 7 MeV). The experiment was performed at the Triangle Universities Nuclear Laboratory using the high resolution Enge split-pole magnetic spectrograph. Spins and parities were found for states in the astrophysical energy range. In particular, the state at 6.133 MeV ($E^{cm}_{r}$ = –277 keV) was found to have spin and parity of 3/2+ and we confirm the existence of an unresolved doublet close to 6.288 MeV ($E^{cm}_{r}$ = –120 keV) with Jπ = 1/2+ and a high-spin state. Using these results, we demonstrate a significant factor of two decrease in the reaction rate uncertainties at nova temperatures.
Excited states above the proton threshold in 26Si Komatsubara, T.; Kubono, S.; Hayakawa, T. ...
The European physical journal. A, Hadrons and nuclei,
09/2014, Letnik:
50, Številka:
9
Journal Article
Recenzirano
The level scheme above the proton threshold in
26
Si is crucial for evaluating the
25
Al(
p
,
γ
)
26
Si stellar reaction, which is important for understanding the astrophysical origin of the ...long-lived cosmic radioactivity
26
Al(
T
1/2
= 7.17 × 10
5
y) in the Galaxy. The excited states in
26
Si have been studied using an in-beam
γ
-ray spectroscopy technique with the
24
Mg(
3
He,
nγ
)
26
Si reaction.
γ
-rays with energies up to 4.6 MeV emitted from excited states in
26
Si have been measured using large volume HPGe detectors. The spin-parity of one of the most important states reported recently at 5890.0keV has been assigned as 0
+
by
γ
-
γ
angular correlation measurements in this work.
The star-to-star anticorrelation of sodium and oxygen is a defining feature of globular clusters, but, to date, the astrophysical site responsible for this unique chemical signature remains unknown. ...Sodium enrichment within these clusters depends sensitively on reaction rate of the sodium destroying reactions 23Na(p, γ) and 23Na(p,α). In this paper, we report the results of a 23Na(3He,d)24Mg transfer reaction carried out at Triangle Universities Nuclear Laboratory using a 21 MeV 3He beam. Astrophysically relevant states in 24Mg between 11 < Ex < 12 MeV were studied using high-resolution magnetic spectroscopy, thereby allowing the extraction of excitation energies and spectroscopic factors. Bayesian methods are combined with the distorted wave Born approximation to assign statistically meaningful uncertainties to the extracted spectroscopic factors. For the first time, these uncertainties are propagated through to the estimation of proton partial widths. Our experimental data are used to calculate the reaction rate. The impact of the new rates are investigated using asymptotic giant branch star models. Furthermore, it is found that while the astrophysical conditions still dominate the total uncertainty, intramodel variations on sodium production from the 23Na(p, γ) and 23Na(p,α) reaction channels are a lingering source of uncertainty.
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