Buoyancy travel time vs. central H fraction for a 1.5 M_⊙ star, for various metallicities, using data from Mombarg et al. (2021). The buoyancy travel time for KIC 4150611 (see Sect. 4), which is an input for the MCMC grid-search component of the modelling, is shown as the horizontal grey band. The grey lines are the solar metallicity, rotating stellar models from Mombarg et al. (2024a) (grid B); the width of the band that they form is indicative of the variation due to stellar rotation.