The Effects Of Near-Core Convective Shells On The Gravity Modes Of The Subdwarf B Pulsator Kic 10553698A

KIC 10553698A is a hot pulsating subdwarf B (sdB) star observed by the Kepler\nsatellite. It exhibits dipole (l = 1) and quadrupole (l = 2) gravity modes with\na clear period spacing structure. The seismic properties of the KIC 10553698A\nprovide a test of stellar evolution models, and offer a unique opportunity to\ndetermine mixing processes. We consider mixing due to convective overshooting\nbeyond the boundary of the helium burning core. Very small overshooting ( f =\n10^{-6} ) results in a progressive increase in the size of convective core.\nHowever, moderate ( f = 10^{-2} ) and small ( f = 10^{-5} ) overshooting both\nlead to the occurrence of inert outer convective shells in the near-core\nregion. We illustrate that the chemical stratifications induced by convective\nshells are able to change the g-mode period spacing pattern of a sdB star\nappreciably. The mean period spacing and trapping of the gravity modes in the\nmodel with moderate and small core overshooting are fully consistent with the\nperiod spacing trends observed in KIC 10553698A. Atomic diffusion driven by\ngravitational settling as well as thermal and chemical gradients is applied to\nreach a better match with the observed period spacings. Models that include\nsmall or very small overshooting with atomic diffusion have a decreased\nlifetime of the extreme horizontal branch phase and produce chemical\nstratification induced by convective shells during helium burning phase. In\naddition of being consistent with asteroseismology, their calculated values of\nthe R2 parameter are more compatible with the observed R2 values.\n