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Constraining the near-core rotation rate in gamma Doradus stars
Timothy Van Reeth (Instituut voor Sterrenkunde, KU Leuven)
Gamma Doradus stars are located in possibly one of the most intriguing regions of the Hertzsprung-Russell diagram. They cover the transition from low-mass stars with a convective envelope to intermediate-mass stars with a convective core. The surrounding physical conditions in these stars can lead to either a growing or a shrinking convective core, but are currently not well understood. The gravity-mode oscillations in gamma Doradus stars predominantly probe the near-core regions, and can help us to constrain the properties of the stellar structure in the deep interior of the stars. Using the traditional approximation, we have developed methodology to derive the near-core rotation rate from observed gravity-mode pulsation periods and identify the mode geometry. We succesfully applied our technique to 40 out of 50 targets in our sample of gamma Doradus stars, allowing us to do ensemble modelling of these stars. For the majority of the observed period spacing patterns we found the corresponding pulsations are prograde dipole modes, while the derived rotation rates cover a large range of possible values. In five of the stars, our analysis has also led to the identification of a solitary pulsation mode, which we suspect to be retrograde dipole modes. Currently, the main limitation of the method is that it cannot be applied directly to retrograde pulsations in moderate to fast rotating stars, due to the neglect of the centrifugal force. This analysis forms the first step towards detailed seismic modelling of observed period spacing patterns in individual gamma Dor stars. We illustrate this for a few well chosen stars from our sample, for which we can determine the shape and size of the convective core.