102 research outputs found
Nuclear uncertainties in the NeNa-MgAl cycles and synthesis of 22Na and 26Al in classical novae
Classical novae eject significant amounts of matter into the interstellar
medium, as a result of thermonuclear runaways. Nucleosynthesis associated with
nova outbursts includes products from explosive H burning, such as 17O, 15N and
13C, and also radioactive species like 7Be, 22Na and 26Al. In this paper we
report on new hydrodynamic calculations of nova outbursts, from the onset of
accretion to mass ejection. We stress the role played by the nuclear
uncertainties associated with key reactions of the NeNa-MgAl cycles on the
synthesis of 22Na and 26Al.Comment: 4 pages (to appear in "Nuclei in the Cosmos V" Conference
Proceedings
Big Bang Nucleosynthesis updated with the NACRE Compilation
We update the Big Bang Nucleosynthesis calculations on the basis of the
recent NACRE compilation. The average values of the calculated abundances of
light nuclei do not differ significantly from that obtained using the previous
Fowler's compilation.
is slightly depressed at high baryon to photon ratio .
The main uncertainty concerns the reaction rate affecting
the synthesis of (via the )
at rather high baryonic density. On the left part of the lithium valley the
uncertainty is strongly reduced due to the improvement of the measurement of
the reaction rate.
We use lithium-7 as the main baryometer, since, though much efforts have been
devoted to the determination of Deuterium in absorbing clouds in the line of
sight of remote quasars, the statistics is very poor compared to the long
series of lithium measurements.
Taking into account the lithium constraints, two possible baryonic density
ranges emerge,
and .
The Be and B abundances produced in the big bang are orders of magnitudes
lower, and spallation of fast carbon and oxygen is probably their unique
source, in the early Galaxy.Comment: 8 pages, 5 figures, accepted in Astronomy and Astrophysic
The Impact of the NACRE Compilation on the Big Bang Nucleosynthesis
We update the Big Bang Nucleosynthesis (BBN) calculations on the basis of the
recent NACRE compilation of reaction rates. We estimate the uncertainties
related to the nuclear reaction rates on the abundances of D, 3He, 4He, 6Li,
7Li, 9Be, 10B and 11B of cosmological and astrophysical interest. We use
lithium as the main indicator of the baryon density of the Universe, rather
than deuterium.Comment: 3 pages, 1 figure, contribution to Nuclei in the Cosmos 2000,
proceedings to appear in Nucl. Phy
Standard big bang nucleosynthesis and primordial CNO Abundances after Planck
Primordial or big bang nucleosynthesis (BBN) is one of the three historical
strong evidences for the big bang model. The recent results by the Planck
satellite mission have slightly changed the estimate of the baryonic density
compared to the previous WMAP analysis. This article updates the BBN
predictions for the light elements using the cosmological parameters determined
by Planck, as well as an improvement of the nuclear network and new
spectroscopic observations. There is a slight lowering of the primordial Li/H
abundance, however, this lithium value still remains typically 3 times larger
than its observed spectroscopic abundance in halo stars of the Galaxy.
According to the importance of this "lithium problem", we trace the small
changes in its BBN calculated abundance following updates of the baryonic
density, neutron lifetime and networks. In addition, for the first time, we
provide confidence limits for the production of 6Li, 9Be, 11B and CNO,
resulting from our extensive Monte Carlo calculation with our extended network.
A specific focus is cast on CNO primordial production. Considering
uncertainties on the nuclear rates around the CNO formation, we obtain CNO/H
\approx (5-30) x 10^{-15}. We further improve this estimate by analyzing
correlations between yields and reaction rates and identified new influential
reaction rates. These uncertain rates, if simultaneously varied could lead to a
significant increase of CNO production: CNO/H \sim 10^{-13}. This result is
important for the study of population III star formation during the dark ages.Comment: Version to match accepted version in JCAP. Results unchange
Mirror matter can alleviate the cosmological lithium problem
The abundance of lithium-7 confronts cosmology with a long lasting problem
between the predictions of standard big bang nucleosynthesis and the baryonic
density determined from the cosmic microwave background observations. This
article investigates the influence of the existence of a mirror world, focusing
on models in which neutrons can oscillate into mirror neutrons. Such a
mechanism allows for an effective late time neutron injection, which induces an
increase of the destruction of beryllium-7, due to an increase of the neutron
capture, and then a decrease of the final lithium-7 abundance. Big bang
nucleosynthesis sets constraints on the oscillation time between the two types
of neutron and the possibility for such a mechanism to solve, or alleviate, the
lithium problem is emphasized.Comment: 11 pages, 9 figure
Influence of the variation of fundamental constants on the primordial nucleosynthesis
We investigate the effect of a variation of fundamental constants on
primordial element production in Big Bang nucleosynthesis (BBN). We focus on
the effect of a possible change in the nucleon-nucleon interaction on nuclear
reaction rates involving the A=5 (5Li and 5He) and A=8 (8Be) unstable nuclei.
The reaction rates for 3He(d,p)4He and 3H(d,n)4He are dominated by the
properties of broad analog resonances in 5Li and 5He compound nuclei
respectively. While the triple-alpha process 4He(aa,g)12C is normally not
effective in BBN, its rate is very sensitive to the position of the "Hoyle
state" and could in principle be drastically affected if 8Be were stable during
BBN. We found that the effect of the variation of constants on the 3He(d,p)4He,
3H(d,n)4He nd 4He(aa,g)12C reaction rates is not sufficient to induce a
significant effect on BBN, even with a stable 8Be. The main influences come
from the weak rates and the A=2, n(p,g)d, bottleneck reaction.Comment: To appear in proceedings of "XII International Symposium on Nuclei in
the Cosmos" August 5-12, 2012, Cairns, Australia, PoS(NIC XII)07
Influence of new reaction rates on 18F production in novae
Gamma-ray emission from classical novae is dominated, during the first hours,
by positron annihilation resulting from the beta decay of radioactive nuclei.
The main contribution comes from the decay of 18F and hence is directly related
to 18F formation during the outburst. A good knowledge of the nuclear reaction
rates of production and destruction of 18F is required to study 18F synthesis
in novae and the resulting gamma-ray emission. The rates relevant for the main
mode of 18F destruction (i.e, through proton captures) have been the object of
many recent experiments. However, subsequent analyses were focused on providing
rates for X-ray burst nucleosynthesis not valid at nova temperatures (lower
than 3.5 10^8 K). Accordingly, it is crucial to propose and discuss new
reaction rates, incorporating all new experimental results, down to the domain
of nova nucleosynthesis. We show that in this temperature regime, the
18F(p,gamma) and (p,alpha) reaction rates remain uncertain and deserve further
experimental and theoretical efforts. Our hydrodynamic calculations including
the new nuclear rates demonstrate that their impact on 18F synthesis in nova
explosions is quite large and, consequently, the early gamma-ray emission from
classical novae is also affected.Comment: To appear in Astron. Astrophys., 14 pages with 9 figure
On the 21Na(p,gamma)22Mg thermonuclear rate for 22Na production in novae
Classical novae are potential sources of gamma-rays, like the 1.275 MeV gamma
emission following 22Na beta decay, that could be detected by appropriate
instruments on board of future satellites like INTEGRAL. It has been shown that
the production of 22Na by novae is affected by the uncertainty on the
21Na(p,gamma)22Mg rate and in particular by the unknown partial widths of the
Ex = 5.714 MeV, J^pi = 2^+, 22Mg level. To reduce these uncertainties, we
performed shell model calculations with the OXBASH code, compared the results
with available spectroscopic data and calculated the missing partial widths.
Finally, we discuss the influence of these results on the 21Na(p,gamma)22Mg
reaction rate and 22Na synthesis.Comment: To appear in Phys. Rev. C, 6 pages with 3 figure
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