SAC Seminar - May Gade Pedersen: What slowly pulsating B stars can tell us about internal mixing in massive stars

2017.09.06 | Louise Børsen-Koch

Date Thu 07 Sep
Time 14:15 15:00
Location 1522-221

During ~90% of their evolution, massive stars are highly influenced by internal mixing processes occurring in and near their convective cores, such as convective core overshooting. Unfortunately, our understanding of these processes is poor and the number of useful test cases limited, resulting in large uncertainties in stellar structure and evolution models for massive stars. Stars with gravity mode pulsations, which probe the deep stellar interior, provide the best opportunity to constrain near core mixing processes in stars with convective cores. Gravity modes are highly sensitive to the amount of mass in the overshoot layer, as well as the chemical gradient left behind as the convective core retreats during the main-sequence evolution. The period spacings of gravity modes, and the observed deviations from a uniform pattern, provide information on the mixed core and additional mixing processes just above it.

During this talk, we show how Kepler data of SPBs contain the necessary information to test the mixing properties. Furthermore, we demonstrate how the choice of the description of the convective core overshooting influences the shape of theoretically predicted period spacing series of slowly pulsating B-type stars. With this study we focus on three overshooting descriptions (step, exponential, and extended exponential overshooting), which are currently implemented in the state of the art stellar structure and evolution code MESA. Our aim is to answer the question to what extend, if at all, we can distinguish between these three shapes of the convective core overshooting. Finally, we show initial results of including mixing profiles from 2D hydrodynamic simulations in MESA, and explore their influence on the predicted period spacing series. We end with future prospects about the exploitation of the Kepler data of SPBs.

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