Physics
Scientific paper
May 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994apj...426..612s&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 426, no. 2, p. 612-620
Physics
17
Asymptotic Giant Branch Stars, Globular Clusters, Helium, Red Giant Stars, Stellar Cores, Stellar Evolution, Stellar Flares, Stellar Mass, Chemical Composition, Estimates, Hydrogen, Mixing, Stellar Physics
Scientific paper
Evolutionary sequences for the red giant branch (RGB) phase of a representative globular cluster star have been computed in order to investigate the reliability of the current canonical values of the core mass Mc at the helium flash. These computations were motivated by recent suggestions that the canonical values of Mc may be systematically too small due to the numerical algorithms for shifting the hydrogen shell and advancing the chemical composition during the RGB phase. Our results show that these algorithms do not, in fact, introduce a significant error in the values of Mc. Moreover, we demonstrate that a procedure for advancing the chemical composition which is implicit only in the hydrogen abundance will systematically underestimate the amount of hydrogen fuel consumption between RGB models and therefore should not be used in RGB computations. Overall we estimate the uncertainty in the core masses of Sweigart & Gross (1978) due to numerical effects to be approximately equals 0.003 solar mass. From a consideration of the available canonical models we conclude that a change in the canonical values of Mc by a few 10-2 solar mass would require either a substantial change in the canonical input physics or some noncanonical effect such as rotation. Finally our models show that the use of short time steps can significantly increase the extent of the inner tail of the hydrogen shell. This effect may enhance the likelihood of hydrogen mixing following a helium shell flash in an asymptotic giant branch star.
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