2020ApJ...899...38W

Asteroseismology is a powerful tool for probing the inner structure and determining the evolutionary status and the fundamental parameters of stars. The oscillation spectra of slowly pulsating B (SPB) stars show almost uniform period spans, whose pattern is sensitive to the structure of the µ-gradient shell beyond the central convective core and hence can be used to efficiently describe their shapes and constrain the convective core. The SPB star KIC 8324482 was observed by Kepler for over 1470 days with a long-cadence pattern. Nearly equidistant period spacing patterns are found for the 14 connective dipolar modes that are extracted from the oscillation spectrum by Zhang et al. In the present work, we analyze them in depth with the χ²-matching method and determine their χ²-minimization models (CMMs). Based on those calculated CMMs, we find that KIC 8324482 is a young (t_age=20.96_–1.28^+3.85 Myr), metal-poor ([Fe/H]=-0.6.9_–0.115^+0.176 dex), and intermediate-mass (M=6.075_–0.2500^+0.1375M_☉) star with a convective core of M_CC=1.338_–0.091^+0.057M_☉ in mass and R_CC=0.5175_–0.0103^+0.0048R_☉ in radius and with a surface rotation velocity V_eq=2.61_–0.11^+0.13kms^–1. The central hydrogen abundance is of X_C=0.5046_–0.0074^+0.0018. Asteroseismic analyses indicate that the "propagation time" of g-mode in KIC 8324482 is of Λ₀=276.85_–0.47^+1.26µHz. To well match with the observed period spacing pattern, an extra diffusion mixing (logD_mix=3.125_–0.250^+0.125) should be considered, but the normal core overshooting f_ov must be fixed as zero in the best-fitting model. Such ultraweak mixing beyond the convective core corresponds to a fast rotation that is about 20-30 times the asteroseismic suggested rotation Ω_rot ≃ 0.2 µHz, if it is thought of as shear mixing induced completely by differential rotation.