THE APPROACH TO NUCLEAR STATISTICAL EQUILIBRIUM

1966 ◽  
Vol 44 (3) ◽  
pp. 563-592 ◽  
Author(s):  
J. W. Truran ◽  
A. G. W. Cameron ◽  
A. Gilbert
Keyword(s):  
Stellar Evolution ◽  
Reaction Network ◽  
Mass Range ◽  
Reaction Rates ◽  
Thermonuclear Reaction ◽  
Abundant Isotope ◽  
Method Of Solution ◽  
Nuclear Burning ◽  
Beta Decays ◽  
Late Stages

The transformation of a region composed initially of 28Si to nuclei in the vicinity of the iron peak, which is thought to take place in the late stages of evolution of some stars, is considered in detail. In order to follow these nuclear transformations, a nuclear reaction network is established providing suitable reaction links connecting neighboring nuclei. A method of solution of the network equations is outlined. Thermonuclear reaction rates for all neutron, proton, and alpha-particle reactions involving the nuclei in this network have been determined from a consideration of the statistical properties of nuclei. The evolution of this silicon region has been followed in time for two cases: T = 3 × 109 °K, ρ = 106 g cm−3 and T = 5 × 109 °K, ρ = 107 g cm−3. While both the observed solar and meteoritic abundances display a broad peak in the vicinity of iron, centered on 56Fe, in these calculations 54Fe is found to be the most abundant isotope in this mass range. Beta decays required to change the peak to 56Fe are very slow. As the transformation 2 28Si → 54Fe + 2p is endothermic by ~1.3 MeV, these results suggest that the silicon-to-iron conversion may not comprise an exothermic nuclear burning stage of stellar evolution.

scholarly journals Screening effects on resonant thermonuclear reaction rates

2019 ◽  
Vol 11 ◽  
Author(s):  
T. Liolios ◽  
K. Langanke ◽  
W. Wiescher
Keyword(s):  
Reaction Rate ◽  
Nuclear Reactions ◽  
Reaction Network ◽  
Reaction Rates ◽  
Partial Width ◽  
Entrance Channel ◽  
Correction Factors ◽  
Thermonuclear Reaction ◽  
Hydrogen Burning ◽  
Stellar Reaction Rate

The reaction rate of several astrophysically important nuclear reactions is dominated by the contribution of narrow resonances at the astrophysically most effective energies. In the stellar plasma the partial width of the resonances in the entrance channel is modified due to screening corrections. This effect, so far ignored in stellar reaction network calculations, reduces the conventional Salpeterscreening enhancement of the reaction rate. We derive analytical screening correction factors for the contributions of narrow resonances to the stellar reaction rate and discuss the effects for UC (a, j)lsO, 150(a,7)19 Ne and other reactions of relevance to explosive hydrogen burning

scholarly journals A study of AGB stars in LMC clusters

2008 ◽  
Vol 4 (S256) ◽  
pp. 397-402
Author(s):  
Thomas Lebzelter ◽  
Michael T. Lederer ◽  
Sergio Cristallo ◽  
Oscar Straniero ◽  
Kenneth H. Hinkle
Keyword(s):  
High Resolution ◽  
Stellar Evolution ◽  
Near Infrared ◽  
Mass Range ◽  
Asymptotic Giant Branch ◽  
Agb Stars ◽  
Near Infrared Spectra ◽  
Model Predictions ◽  
First Time ◽  
Late Stages

AbstractLMC clusters offer an outstanding opportunity to investigate the late stages of stellar evolution of stars in the mass range between 1.5 and 2 M⊙. In this presentation we will focus on our results on mixing events during the evolution along the Asymptotic Giant Branch (AGB). Surface abundances have been determined for a number of cluster AGB stars from high resolution near infrared spectra. We show for the first time the evolution of C/O and 12C/13C ratios along a cluster AGB. The change of both quantities due to dredge up events is compared with model predictions. Our results indicate the late occurrence of a moderate extra-mixing in some cases.

scholarly journals Nuclear burning in collapsar accretion discs

2020 ◽  
Vol 499 (3) ◽  
pp. 4097-4113 ◽  
Author(s):  
Yossef Zenati ◽  
Daniel M Siegel ◽  
Brian D Metzger ◽  
Hagai B Perets
Keyword(s):  
Angular Momentum ◽  
Gamma Ray ◽  
Nuclear Reactions ◽  
Reaction Network ◽  
Accretion Discs ◽  
Late Time ◽  
Rotating Stars ◽  
Stellar Envelope ◽  
Nuclear Burning ◽  
R Process

ABSTRACT The core collapse of massive, rapidly-rotating stars are thought to be the progenitors of long-duration gamma-ray bursts (GRB) and their associated hyperenergetic supernovae (SNe). At early times after the collapse, relatively low angular momentum material from the infalling stellar envelope will circularize into an accretion disc located just outside the black hole horizon, resulting in high accretion rates necessary to power a GRB jet. Temperatures in the disc mid-plane at these small radii are sufficiently high to dissociate nuclei, while outflows from the disc can be neutron-rich and may synthesize r-process nuclei. However, at later times, and for high progenitor angular momentum, the outer layers of the stellar envelope can circularize at larger radii ≳ 107 cm, where nuclear reactions can take place in the disc mid-plane (e.g. 4He + 16O → 20Ne + γ). Here we explore the effects of nuclear burning on collapsar accretion discs and their outflows by means of hydrodynamical α-viscosity torus simulations coupled to a 19-isotope nuclear reaction network, which are designed to mimic the late infall epochs in collapsar evolution when the viscous time of the torus has become comparable to the envelope fall-back time. Our results address several key questions, such as the conditions for quiescent burning and accretion versus detonation and the generation of 56Ni in disc outflows, which we show could contribute significantly to powering GRB SNe. Being located in the slowest, innermost layers of the ejecta, the latter could provide the radioactive heating source necessary to make the spectral signatures of r-process elements visible in late-time GRB-SNe spectra.

scholarly journals Effects of bound diprotons and enhanced nuclear reaction rates on stellar evolution

2021 ◽  
Vol 130 ◽  
pp. 102584
Author(s):  
Fred C. Adams ◽  
Alex R. Howe ◽  
Evan Grohs ◽  
George M. Fuller
Keyword(s):  
Nuclear Reaction ◽  
Stellar Evolution ◽  
Reaction Rates

Cross-section measurements and thermonuclear reaction rates for 49Ti(p, γ)50V and 49Ti(p, n)49V

1980 ◽  
Vol 344 (2) ◽  
pp. 351-360 ◽  
Author(s):  
S.R. Kennett ◽  
M.R. Anderson ◽  
Z.E. Switkowski ◽  
D.G. Sargood
Keyword(s):  
Cross Section ◽  
Reaction Rates ◽  
Thermonuclear Reaction

scholarly journals Radio Supernovae as Direct Evidence of Stellar Evolution in Real Time

1998 ◽  
Vol 11 (1) ◽  
pp. 367-367
Author(s):  
S.D. Van Dyk ◽  
M.J. Montes ◽  
K.W. Weiler ◽  
R.A. Sramek ◽  
N. Panagia
Keyword(s):  
Mass Loss ◽  
Stellar Evolution ◽  
Loss Rate ◽  
Direct Evidence ◽  
Mass Loss Rate ◽  
X Ray ◽  
Stringent Constraint ◽  
Clear Change ◽  
Late Stages ◽  
Circumstellar Environment

The radio emission from supernovae provides a direct probe of a supernova’s circumstellar environment, which presumably was established by mass-loss episodes in the late stages of the progenitor’s presupernova evolution. The observed synchrotron emission is generated by the SN shock interacting with the relatively high-density circumstellar medium which has been fully ionized and heated by the initial UV/X-ray flash. The study of radio supernovae therefore provides many clues to and constraints on stellar evolution. We will present the recent results on several cases, including SN 1980K, whose recent abrupt decline provides us with a stringent constraint on the progenitor’s initial mass; SN 1993J, for which the profile of the wind matter supports the picture of the progenitor’s evolution in an interacting binary system; and SN 1979C, where a clear change in presupernova mass-loss rate occurred about 104 years before explosion. Other examples, such as SNe 19941 and 1996cb, will also be discussed.

scholarly journals Global predictions for astrophysics applications

2020 ◽  
Vol 13 ◽  
pp. 18
Author(s):  
P. Demetriou
Keyword(s):  
Nuclear Reaction ◽  
Cross Sections ◽  
Nuclear Reactions ◽  
Nuclear Astrophysics ◽  
Reaction Network ◽  
Reaction Rates ◽  
Reaction Cross ◽  
Hartree Fock ◽  
Microscopic Models ◽  
The Stability

Nuclear reaction rates play a crucial role in nuclear astrophysics. In the last decades there has been an enormous effort to measure reaction cross sections and extensive experimental databases have been compiled as a result. In spite of these efforts, most nuclear reaction network calculations still have to rely on theoretical predic- tions of experimentally unknown rates. In particular, in astrophysics applications such as the s-, r- and p-process nucleosynthesis involving a large number of nuclei and nuclear reactions (thousands). Moreover, most of the ingredients of the cal- culations of reaction rates have to be extrapolated to energy and/or mass regions that cannot be explored experimentally. For this reason it is important to develop global microscopic or semi-microscopic models of nuclear properties that give an accurate description of existing data and are reliable for predictions far away from the stability line. The need for more microscopic input parameters has led to new devel- opments within the Hartree-Fock-Bogoliubov method, some of which are presented in this paper.

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