THE EFFECTS OF THERMONUCLEAR REACTION RATE VARIATIONS ON {sup 26}Al PRODUCTION IN MASSIVE STARS: A SENSITIVITY STUDY
- Department of Physics and Astronomy, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3255 (United States)
- Istituto Nazionale di Astrofisica-Istituto di Astrofisica Spaziale e Fisica Cosmica, Via Fosso del Cavaliere, I-00133 Roma (Italy)
- Istituto Nazionale di Astrofisica-Osservatorio Astronomico di Roma, Via Frascati 33, I-00040 Monteporzio Catone (Italy)
We investigate the effects of thermonuclear reaction rate variations on {sup 26}Al production in massive stars. The dominant production sites in such events were recently investigated by using stellar model calculations: explosive neon-carbon burning, convective shell carbon burning, and convective core hydrogen burning. Post-processing nucleosynthesis calculations are performed for each of these sites by adopting temperature-density-time profiles from recent stellar evolution models. For each profile, we individually multiplied the rates of all relevant reactions by factors of 10, 2, 0.5, and 0.1, and analyzed the resulting abundance changes of {sup 26}Al. In total, we performed {approx}900 nuclear reaction network calculations. Our simulations are based on a next-generation nuclear physics library, called STARLIB, which contains a recent evaluation of Monte Carlo reaction rates. Particular attention is paid to quantifying the rate uncertainties of those reactions that most sensitively influence {sup 26}Al production. For stellar modelers our results indicate to what degree predictions of {sup 26}Al nucleosynthesis depend on currently uncertain nuclear physics input, while for nuclear experimentalists our results represent a guide for future measurements. We also investigate equilibration effects of {sup 26}Al. In all previous massive star investigations, either a single species or two species of {sup 26}Al were taken into account, depending on whether thermal equilibrium was achieved or not. These are two extreme assumptions, and in a hot stellar plasma the ground and isomeric states may communicate via {gamma}-ray transitions involving higher-lying {sup 26}Al levels. We tabulate the results of our reaction rate sensitivity study for each of the three distinct massive star sites referred to above. It is found that several current reaction rate uncertainties influence the production of {sup 26}Al. Particularly important reactions are {sup 26}Al(n,p){sup 26}Mg, {sup 25}Mg({alpha},n){sup 28}Si, {sup 24}Mg(n,{gamma}){sup 25}Mg, and {sup 23}Na({alpha},p){sup 26}Mg. These reactions should be prime targets for future measurements. Overall, we estimate that the nuclear physics uncertainty of the {sup 26}Al yield predicted by the massive star models explored here amounts to about a factor of three. We also find that taking the equilibration of {sup 26}Al levels explicitly into account in any of the massive star sites investigated here has only minor effects on the predicted {sup 26}Al yields. Furthermore, we provide for the interested reader detailed comments regarding the current status of certain reactions, including {sup 12}C({sup 12}C,n){sup 23}Mg, {sup 23}Na({alpha},p){sup 26}Mg, {sup 25}Mg({alpha},n){sup 28}Si, {sup 26}Al {sup m}(p,{gamma}){sup 27}Si, {sup 26}Al(n,p){sup 26}Mg, and {sup 26}Al(n,{alpha}){sup 23}Na.
- OSTI ID:
- 21557057
- Journal Information:
- Astrophysical Journal, Supplement Series, Vol. 193, Issue 1; Other Information: DOI: 10.1088/0067-0049/193/1/16; ISSN 0067-0049
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
COSMOLOGY AND ASTRONOMY
ALUMINIUM 26
HYDROGEN BURNING
MONTE CARLO METHOD
SENSITIVITY ANALYSIS
SIMULATION
STAR EVOLUTION
STAR MODELS
SUPERNOVAE
THERMONUCLEAR REACTIONS
VARIATIONS
ALUMINIUM ISOTOPES
BETA DECAY RADIOISOTOPES
BETA-PLUS DECAY RADIOISOTOPES
BINARY STARS
CALCULATION METHODS
ERUPTIVE VARIABLE STARS
EVOLUTION
ISOTOPES
LIGHT NUCLEI
MATHEMATICAL MODELS
NUCLEAR REACTIONS
NUCLEI
NUCLEOSYNTHESIS
ODD-ODD NUCLEI
RADIOISOTOPES
SECONDS LIVING RADIOISOTOPES
STAR BURNING
STARS
SYNTHESIS
VARIABLE STARS
YEARS LIVING RADIOISOTOPES