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Paper: Exploring Stellar Evolution Models of sdB Stars Using MESA With Convective Overshoot
Volume: 481, 6th Meeting on Hot Subdwarf Stars and Related Objects
Page: 197
Authors: Schindler, J.; Green, E.; Arnett, D.
Abstract: We have used MESA (Modules for Experiments in Stellar Astrophysics) to explore how well stellar evolutionary theory reproduces observational data on sdB stars. We investigate two problems. First, asteroseismological analyses of g-mode pulsators suggest He-CO cores of the order of 0.25 M, i.e. 40-50% of the total stellar mass. Conventional stellar evolution, using MLT theory without convective overshoot, produces significantly smaller cores (∼0.1 M). We have produced evolutionary sequences with varying amounts of overshoot. A sufficiently high value of convective overshoot does produce He-CO core masses comparable to those suggested by the asteroseismological analyses. The large amount of overshooting required gives rise to a second stage of helium-core burning for some of our models. This may not be physically realistic, since evolution following initial core helium exhaustion with large convective overshoot appears to strain some of the current modules in MESA (with regard to convective boundary layers and composition gradients, for example). The second problem is that surface gravities and effective temperatures determined from optical spectra and asteroseismology do not match very well the evolutionary paths calculated by MESA (or other stellar evolutionary codes). The more extreme overshooting needed to produce more massive He-CO cores has little effect on the effective temperatures and surface gravities.
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