The Determination of the Core Mass at the Helium Flash in Globular-Cluster Stars

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Session 111 -- Stellar Interiors
Display presentation, Saturday, January 15, 9:30-6:45, Salons I/II Room (Crystal Gateway)

[111.06] The Determination of the Core Mass at the Helium Flash in Globular-Cluster Stars

A.V.Sweigart (GSFC)

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 at the helium flash. These computations were motivated by recent suggestions that the canonical core masses 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 the core mass. 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 and Gross (1978) due to numerical effects to be 0.003 $M_{\sun}$. From a consideration of the available canonical models we conclude that a change in the canonical core masses by a few times 0.01 $M_{\sun}$ would require either a substantial change in the canonical input physics or some noncanonical effect such as rotation.

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