Smithsonian/NASA ADS arXiv e-prints Abstract Service


Title:
Nuclear Reaction Rate Uncertainties and Astrophysical Modeling. II. Carbon Yields from Low-mass Giants
Authors:
Herwig, F.; Austin, Sam M.; Lattanzio, John C.
Journal:
eprint arXiv:astro-ph/0511386
Publication Date:
11/2005
Origin:
ARXIV
Comment:
resubmitted to Phys Rev C
Bibliographic Code:
2005astro.ph.11386H

Abstract

Calculations that demonstrate the influence of three key nuclear reaction rates on the evolution of Asymptotic Giant Branch stars have been carried out. We study the case of a star with an initial mass of 2Msun and a metallicity of Z=0.01, somewhat less than the solar metallicity. The dredge-up of nuclear processed material from the interior of the star, and the yield predictions for carbon, are sensitive to the rate of the N14(p,gamma)O15 and triple-alpha reactions. These reactions dominate the H- and He-burning shells of stars in this late evolutionary phase. Published uncertainty estimates for each of these two rates propagated through stellar evolution calculations cause uncertainties in carbon enrichment and yield predictions of about a factor of two. The other important He-burning reaction C12(alpha,gamma)O16, although associated with the largest uncertainty in our study, does not have a significant influence on the abundance evolution compared to other modelling uncertainties. This finding remains valid when the entire evolution from the main-sequence to the tip of the AGB is considered. We discuss the experimental sources of the rate uncertainties addressed here, and give some outlook for future work.


Title:
Nuclear Reaction Rates and Carbon Star Formation
Authors:
Herwig, Falk; Austin, Sam M.
Affiliation:
AA(Los Alamos National Laboratory, Theoretical Astrophysics Group T-6, MS B227, Los Alamos, NM 87545; ), AB(National Superconducting Cyclotron Laboratory and Joint Institute for Nuclear Astrophysics, Michigan State University, East Lansing, MI 48824; )
Journal:
The Astrophysical Journal, Volume 613, Issue 1, pp. L73-L76. (ApJ Homepage)
Publication Date:
09/2004
Origin:
UCP
ApJ Keywords:
Nuclear Reactions, Nucleosynthesis, Abundances, Stars: Abundances, Stars: AGB and Post-AGB, Stars: Carbon
Abstract Copyright:
(c) 2004: The American Astronomical Society
DOI:
10.1086/424872
Bibliographic Code:
2004ApJ...613L..73H

Abstract

We have studied how the third dredge-up and the carbon star formation in low-mass asymptotic giant branch stars depend on certain key nuclear reaction rates. From a set of complete stellar evolution calculations of a 2 Msolar model with Z=0.01 including mass loss, we find that varying either the 14N(p, gamma)15O or the triple-alpha reaction rate within their uncertainties as given in the NACRE compilation results in dredge-up and yields that differ by a factor of 2. Model tracks with a higher rate for the triple-alpha rate and a lower rate for the 14N(p, gamma)15O reaction both show more efficient third dredge-up. New experimental results for the 14N(p, gamma)15O reaction rates are surveyed, yielding a rate that is about 40% lower than the tabulated NACRE rate and smaller than NACRE's lower limit. We discuss the possible implications of the revised nuclear reaction rate for stellar evolution calculations that aim to reproduce the observed carbon star formation at low mass, which requires efficient third dredge-up.


Title:
Oxygen isotopic ratios in first dredge-up red giant stars and nuclear reaction rate uncertainties revisited
Authors:
Stoesz, Jeffrey A.; Herwig, Falk
Affiliation:
AA(Physics and Astronomy Department, University of Victoria, Canada; Herzberg Institute for Astrophysics, National Research Council, Victoria, Canada), AB(Physics and Astronomy Department, University of Victoria, Canada)
Journal:
Monthly Notice of the Royal Astronomical Society, Volume 340, Issue 3, pp. 763-770. (MNRAS Homepage)
Publication Date:
04/2003
Origin:
MNRAS
MNRAS Keywords:
astrochemistry: nuclear reactions, nucleosynthesis, abundances: stars: abundances
Abstract Copyright:
(c) 2003 RAS
DOI:
10.1046/j.1365-8711.2003.06332.x
Bibliographic Code:
2003MNRAS.340..763S

Abstract

We describe a general yet simple method to analyse the propagation of nuclear reaction rate uncertainties in a stellar nucleosynthesis and mixing context. The method combines post-processing nucleosynthesis and mixing calculations with a Monte Carlo scheme. With this approach we reanalyse the dependence of theoretical oxygen isotopic ratio predictions in first dredge-up red giant branch stars in a systematic way. Such predictions are important to the interpretation of pre-solar Al2O3 grains from meteorites. The reaction rates with uncertainties were taken from the NACRE compilation of Angulo et al. We include seven reaction rates in our systematic analysis of stellar models with initial masses from 1 to 3 Msolar. We find that the uncertainty of the 18O(p, alpha)15N reaction rate typically causes an error in the theoretical 16O/18O ratio of ~= +20/ - 5 per cent. The error of the 16O/17O prediction is 10-40 per cent depending on the stellar mass, and is persistently dominated by the comparatively small uncertainty of the 16O(p, gamma)17F reaction. With the new estimates on reaction rate uncertainties by the NACRE compilation, the p-capture reactions 17O(p, alpha)14N and 17O(p, gamma)18F have virtually no impact on theoretical predictions for stellar mass <=1.5 Msolar. However, the uncertainty in 17O(p, alpha)14N has an effect comparable to or greater than that of 16O(p, gamma)17F for masses >1.5 Msolar, where core mixing and subsequent envelope mixing interact. In these cases where core mixing complicates post-dredge-up surface abundances, uncertainty in other reactions have a secondary but noticeable effect on surface abundances.


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