Discerning internal conditions of pulsating hot subdwarf B stars. Modelling multiple trapped modes in KIC 10001893

Abstract

The frequencies of gravity mode oscillations are determined by the chemical, thermal, and structural properties of stellar interiors, facilitating the study of internal mixing mechanisms in stars. We investigate the impact of discontinuities in the chemical composition induced by the formation of an adiabatic semiconvection region during the core helium (He)-burning phase of evolution of hot subdwarf B-type (sdB) stars. We scrutinize the asteroseismic attributes of the evolutionary stages and assess the core He-burning phase by evaluating the parameter linked to the average interval between the deep trapped modes in both sdB evolutionary models and the observations of KIC 10001893. We perform evolutionary and asteroseismic analyses of sdB stars using MESA and GYRE to examine the properties of the semiconvection region. We address the challenges of relying solely on average interval between oscillation mode periods with consecutive radial orders to identify the core He-burning stage. To enhance identification, we propose a new parameter representing the average interval between deep trapped modes during some of the stages of sdB evolutionary models. Additionally, our results show that integrating convective penetration with convective premixing improves our models and yields comparable outcomes without the need for additional model parameters. Our results can advance the development of detailed evolutionary models for sdB stars by refining internal mixing schemes, enhancing the accuracy of pulsation predictions, and improving alignment with observational data.